Airmar's Theory of Operations

Theory of Operations

TECHNOLOGYAIRMAR CORPORATION 35 Meadowbrook Drive, Milford, New Hampshire 03055 Tel 603 -673-9570 • Fax 603-673-4624• www.airmar.com

17-256-01 Rev. 01 Theory of Operations

Contents

I. Introduction ...... 1

A. Airmar Technology Corporation ...... 2

B. Echosounder Systems ...... 3

C. Transducers ...... 3

D. Frequencies ...... 5

E. Piezoceramic Elements ...... 7

F. Sound Waves ...... 9

G. The Structure of Transducers ...... 11

H. Performance Testing ...... 13

I. Airmar Products ...... 16

J. Glossary of Terms ...... 19 Theory of Operations

The purpose of this booklet is to inform you about the products that are designed and manufactured by Airmar and give you a basic understanding of how they work and how they are used. Our customers depend upon us for products that meet their requirements. As a member of the Airmar Team, your quality work is a vital part of meeting those requirements and contributes to maintaining Airmar’s leadership position in the transducer industry. The information in this booklet will help you to better understand how significant what you do is, and how it fits into the overall picture. Included is a glossary of frequently used scientific terminology. If you have any questions not answered by this booklet, please submit them to your manager.

1 Theory of Operations

Airmar Technology Corporation What is Airmar? Designers, engineers, and scientists develop the products. Assemblers on the manufacturing floor produce the sen- Airmar Technology Corporation was founded in Amherst, sors and a full line of parts and accessories. All this activity New Hampshire in 1982 by two engineers, Stephen G. is supported by shippers, receivers, maintenance people, Boucher and Robert K. Jeffers. Airmar moved to Milford in and business personnel. 1987 where it continues to grow as a leader in the transducer industry. At Airmar, we pride ourself on our ability to work hand-in- Who are Airmar’s customers? hand with our customers to fulfill their specific require- Airmar has a world-wide customer base of Original ments with the highest quality products. This may be Equipment Manufacturers (OEMs). Our sensors are done with one of our existing products, a slight modifica- bought to be coupled with the OEM’s electronics. Usually, tion to a standard product, or an entirely new design. the OEM sells the system to the public with its name on Airmar’s first product in 1982 was a simple, marine, ultra- the label. sonic transducer. Today, marine transducers remain the While many of our customers are echosounder producers, core of our product line with over 1,000 transducer part we have customers in other industries as mentioned earli- numbers available. We now offer: er. Some of our customers include: • Recreational sensors for echosounders, fishfinders, and • Raytheon personal watercraft • Furuno • Commercial fishing transducers for vessels of all sizes • Yamaha • Large navigation and survey transducers for use on ships • Odom and research vessels • Hycontrol • Aquaculture systems • Lowrance • Air transducers for industrial uses • Standard Communications Airmar holds over twenty-five United States and foreign • Interphase patents. We have won the important Innovation Award • Kawasaki presented by the International Marine Trade Exhibition • Bombardier Conference for the first truly low-cost phased array trans- We also sell to one after-market distributor, Gemeco. This ducer developed for use in marine environments. This company sells replacement transducers as well as marine transducer allows electronic steering of the ultrasonic accessories to the public. beam giving the user the ability to gather more information.

2 Theory of Operations

Echosounder Systems What is an transceiver generates high voltage electrical pulses and sends them to the transducer. The transducer converts echosounder system? these pulses into sound waves that bounce off objects An echosounder system is specialized equipment which underneath the boat, then echo back to the transducer. gives a boater or fisher the ability to see below the sur- The transducer converts the sound energy of the echo to face of the water. It gives information about the depth an electrical pulse which is returned to the echosounder. and shape of the bottom and of any fish present. The echosounder measures the time between the begin- An echosounder system is made up of two major parts. ning of a pulse of sound and the return of the echo. The The first is the echosounder. This includes a display screen microprocessor then “reads” this information, translates it, to present the information, the transceiver to drive the and presents it on a display screen in a way that depicts transducer and receive echo informa- the bottom, any objects, and the location of tion, and a microcomputer to process any fish. the information. Different echosounders display information in The second key part is the transducer. It different ways. A flasher type echosounder generates sound waves and receives the displays illuminated bars of varying intensity echoes of those sound waves. The infor- to depict the depth of the water and any mation is fed from the transducer objects in the water. A digital echosounder through cables to the echosounder displays the bottom depth in numbers or let- which interprets and presents the infor- ters. Echosounders with LCD and CRT screens mation in an understandable form on display the information in a “picture” form. the display screen. What part of the echosounder How does an echosounder system does Airmar produce? system work? Airmar produces the transducer—the under- All echosounder systems work in essen- water sensor for the echosounder system. tially the same way. The echosounder

Transducers What is a transducer? ducer then converts the transmit pulses into sound. The sound travels through the water as pressure waves. When The transducer is the heart of an echosounder system. It is a wave strikes an object like a weed, a rock, a fish, or the the device that changes electrical pulses into sound waves bottom, the wave bounces back. The wave is said to or acoustic energy and back again. In other words, it is the echo—just as your voice will echo off a canyon wall. device that sends out the sound waves and then receives the echoes, so the echosounder can interpret or “read” When the wave of sound bounces back, the transducer what is below the surface of the water. acts as a microphone. It receives the sound wave during the time between each transmit pulse and converts it back How does a transducer work? into electrical energy. A transducer will spend about 1% of The easiest way to understand how a transducer functions its time transmitting and 99% of its time quietly listening is to think of it as a speaker and a microphone built into for echoes. Remember, however, that these periods of time one unit. A transducer receives sequences of high voltage are measured in microseconds, so the time between pulses electrical pulses called transmit pulses from the echo- is very short. sounder. Just like the stereo speakers at home, the trans-

3 Theory of Operations

How does a transducer know what the bottom looks like? As the boat moves through the water, the echoes of some sound waves return more quickly than others. We know that all sound waves travel at the same speed. When a sound wave in one section of the sound field returns more quickly than another, it is because the wave has bounced off something closer to the transducer. These early returning sound waves reveal all the humps and bumps in the underwater surface. Transducers are Transducer transmitting pulses Transducer receiving echoes able to detect whether a bottom is soft or hard and even distinguish between a The echosounder can calculate the time difference clump of weeds and a rock, because the sound waves will between a transmit pulse and the return echo and then echo off of these surfaces in a slightly different manner. display this information on the screen in a way that can be easily understood by the user. How does a transducer see a fish? The transducer can see a fish, because it senses the air How does a transducer bladder. Almost every fish has an organ called an air blad- know how deep the water is? der filled with gas that allows the fish to easily adjust to The echosounder measures the time between transmitting the water pressure at different depths. The amount of gas the sound and receiving its echo. Sound travels through in the air bladder can be increased or decreased to regu- the water at about 4,800 feet per second, just less than a late the buoyancy of the fish. mile per second. To calculate the distance to the object, the echosounder multiplies the time elapsed between the sound transmission and the received echo by the speed of sound through water. The echosounder system interprets the result and displays the depth of the water in feet for the user.

Because the air bladder contains gas, it is a drastically different density than the flesh and bone of the fish as well as the water that surrounds it. This difference in density causes the sound waves from the echosounder to bounce off the fish distinctively. The transducer receives the echoes and the echosounder is able to recognize these differences. The echosounder, then, displays it as a fish.

4 Theory of Operations

Frequencies What is frequency? hear. Humans can hear sound waves from 10 Hz to 20 kHz. Most fish are unable to hear frequencies higher than Frequency is the number of complete cycles or vibrations about 500 Hz to 1 kHz. The ultrasonic sound waves sent that occur within a certain period of time, typically one out by Airmar transducers have frequencies ranging from second. Sound waves can vibrate at any one of a wide 10,000 kHz to 2 Megahertz (200,000,000 Hz), clearly number of frequencies. The easiest way to understand fre- beyond the hearing of fish. However, most people can quency is to think of it in terms of sounds that are familiar. hear the transmit pulses of our 10 kHz transducers; they For example, a kettle drum produces a low-pitched sound sound like a series of clicks. (low frequency). That is, it vibrates relatively few times per second. Whereas, a flute produces a high-pitched sound (high frequency). It vibrates many more times per second How does the frequency of a transducer than a kettle drum. determine what we see? The frequency of sound waves is measured in a unit A higher frequency transducer will put out quicker, short- called a Hertz. A Hertz is one cycle per second. For exam- er, and more frequent sound waves. Like the ripples made ple: a 150 kHz transducer operates at when a small pebble is thrown into 150,000 cycles per second. still water, small waves of sound move evenly out and away from the Is the frequency of all source. Because they are just small transducers the same? waves, they will not travel far and No, transducers can be designed to small obstacles will cause them to operate efficiently at any number of bounce back. Higher frequencies specific frequencies depending upon are more sensitive to small objects the application and performance and will send back detailed informa- requirements of the customer. Airmar tion which will show as crisp, high- transducers are often designed for 50 resolution pictures on the kHz (50,000 cycles per second) or echosounder screen. The range of 200 kHz (200,000 cycles per sec- high frequency sound waves, how- ond). ever, is short. In fact, sound waves emitted by a 200 kHz transducer have a limited range of about 600 Can fish hear the sound feet. waves produced by a Now, think of the large waves creat- transducer? ed by a large boulder thrown into still water. Low frequency sound No, the sound waves are ultrasonic. waves are like these large waves; They are above (ultra) the sound they travel much farther than high (sonic) that human ears are able to

Higher Frequency Lower Frequency Number of waves or cycles per second more fewer Wave length shorter longer Detail more detail, small objects less detail, large objects Depth Capacity shallow to moderate deeper

5 Theory of Operations

The speed of sound in water is 4,800 feet per second. If we have a 200 kHz transducer then our equation would look like this: 4800 ft/sec ÷ 200,000 cyc/sec = 0.024 ft/cyc = 0.29 inches/cyc One sound wave at 200 kHz is slightly longer than 1/4 of an inch, so a 200 kHz sound wave will be able to detect fish as short as a quarter of an inch. Let us compare the 200 kHz Higher frequency waves transducer to the size of a wave length of a 50 kHz transducer: 4800 ft/sec ÷ 50,000 cyc/sec = 0.096 ft/cyc = 1.15 inches/cyc Lower frequency waves One sound wave at 50 kHz is slightly over one inch, so a 50 frequency waves. But because low frequency waves are kHz sound wave will only detect fish if their air bladders so large, they wash right over small obstacles. Low fre- are large, slightly longer than an inch. quency sound waves are not as sensitive in detecting small fish or other small obstacles as are high frequency waves, and although they can see to greater depths, How does a customer decide what they will not send back detailed information or clear frequency is needed? crisp pictures. A higher frequency sound wave will give the user a higher resolution picture of what is present under the water, but the range will be short. Fishers in more shallow lakes Why is it important to know the length who want a crisp clear picture of the bottom need a high- of a sound wave? er frequency transducer. Knowing the length of sound waves is particularly impor- Low frequency sound waves will not give the user as clear tant, because it determines where the sound waves will a picture of the bottom, but they have greater range for bounce. A sound wave will bounce strongly off some- very deep areas where high frequency sound waves can- thing that is larger than itself. If the object is smaller, then not reach. A low frequency unit will work well in the the sound wave will almost wash over the object, and the depths of Lake Michigan or the ocean. You may find the echo will be very weak. chart on page 5 helpful. The length of a sound wave is determined by the frequency of the sound vibrations and the density of the medium that the sound is traveling through. At Airmar, wave length is calculated by dividing the speed of sound in water by the frequency.

6 Theory of Operations

Piezoceramic Elements What are piezoceramic elements? Like a piece of china that has been fired in a kiln, the piezoceramic element is very strong, yet brittle and easily The main component of a depth transducer is the piezo- cracked or broken. Any piezoceramic element that has ceramic element. It is the part that converts electrical puls- been cracked or chipped, even slightly, will not function es into sound waves, and when the echoes return, the properly in a transducer. piezoceramic element converts the sound waves back into electrical energy. Coating—After pressing, the piezoceramic element is coat- ed on two opposite sides Airmar does not manufacture its own piezoceramic ele- with a layer of silver and ments, because their manufacture is a very specialized baked a second time, so process. Instead, we buy piezoce- the silver actually bakes ramics from companies that make onto the element. This sil- them to our specifications. ver functions as the electrode, the material that What does a will conduct electric cur- piezoceramic element rent through the element. look like? Polarizing—Next the piezoceramic element is Piezoceramic elements are most polarized. Piezoceramic often in a disk form, but they may elements are made up of also be in the shape of a bar or a individual crystals that have a positive (+) and negative (–) ring. A transducer may contain electric charge on respective ends. These crystals are nor- one element or a series of ele- mally resting in a haphazard way in the piezoceramic elements linked together called ment. But if a high voltage electric current is applied to an array. the element, the crystals will adjust their alignment until nearly all are positioned in straight columns with their What are piezoceramic positive (+) and negative (–) poles lying in the same elements made of? direction. Most of the piezoceramic elements that we use in our transducers are Note: Since this process is done in an oil bath, it is very made of Barium Titanate (BT) or important that the piezoceramic element has all of the oil Lead Zirconate Titanate (PZT). carefully removed or the potting material will not bond to it. A weak bond will result in poor transducer performance and poor reliability. How are piezoceramic elements made? The BT and PZT elements go through several processes before Airmar receives them. How do piezoceramic elements work? Pressing—Both BT and PZT begin in powdered form. The Remember, transducers work by taking electrical pulses powder is pressed into the desired shape. from the echosounder and changing them into sound waves. This process is reversed when the transducer is Firing—The pressed shapes are baked in a kiln just like we acted upon by the pressure of the returning echoes which might fire a clay pot made in an art class. The tempera- is called transduction. ture of the kiln depends upon the element’s maximum heat tolerance. It is important to fire the piezoceramic at The internal arrangement of the piezoceramic element’s precisely the right temperature. crystals with their positive (+) and negative (–) poles lying 7 Theory of Operations

in the same direction is the key resonant frequencies. The size, factor. Pulses of alternating cur- Piezoceramic expands shape, and thickness of the rent (AC) from the echosounder when + voltage applied piezoceramic element determine activate the piezoceramic ele- the frequency at which it will ment. The AC changes its direc- vibrate best. Engineers very care- tion of flow back and forth. fully control these factors to pro- [Which is why it is said to alter- duce transducers that resonate at nate, and this change in the the correct frequency to meet the direction of the flow is noted as customers’ needs. (+) and (–).] Because the piezoce- Most of the piezoceramic ele- ramic elements are polarized, they ments that Airmar uses are thick- will expand when a positive volt- ness resonant. The thickness age is applied and contract when dimension of the piezoceramic a negative voltage is applied. Piezoceramic contracts element, rather than its diameter The piezoceramic’s expansion and when - voltage applied or shape, determines the contraction changes the electrical resonant frequency. pulse into sound waves that will travel through the water A transducer can be designed with one piezoceramic that until they bounce off an object or weaken and finally operates at two frequencies. Our popular 50/200 kHz dissipate. transducer houses a piezoceramic element that can When an echo returns to the transducer, the pressure of vibrate efficiently at two separate frequencies. It resonates the sound waves act on the piezoceramic element caus- at 200 kHz in the thickness mode and at 50 kHz across its ing it first to contract and then to expand as each cycle in the echo hits it. This alternating pressure on the element creates a small voltage which is then sent back to the transceiver and microprocessor.

The element expands and contracts at Vibrates Vibrates Vibrates the frequency of the electrical pulse. This across the thickness across the diameter across the thickness occurs very rapidly, faster than can be and the diameter seen by the eye. The frequency of the expansion and contraction is controlled by the frequency diameter which is called the radial mode. A transducer of the pulse generator in the echosounder. that can operate at two frequencies will have the characteristics of both frequencies—the ability to “see” well in both shallow and deep water with good bottom How do the engineers know which definition. piezoceramic element to use? When an electrical voltage is applied to a piezoceramic What is capacitance? element, it will vibrate best at a certain frequency. Capacitance comes from the word capacity. It is the ability Piezoceramic materials can be thought of as bells. When a of a material to store an electrical charge. Piezoceramic bell rings, it produces a tone. Each bell has its own natur- elements are first class capacitors, able to hold a large al resonant frequency. Those who cast bells know the size electrical charge. In fact, the larger the piezoceramic the and shape necessary to create a bell that produces a cer- larger the charge that can be stored. tain tone. Knowing that piezoceramic elements store a charge and Like bells, every piezoceramic material has its own natural 8 Theory of Operations

that even slight cooling and heating will build-up an elec- piezoceramics, their ability to store an electrical charge trical charge, means that all piezoceramics must be han- can be used to our advantage. With a simple capacitance dled with great care. Production workers must always meter, we can test the piezoceramic after wires have been short a piezoceramic before handling it. If this is not done, soldered in place and the cable has been attached. If a the piezoceramic may discharge, damaging other compo- wire connection is faulty, only a small capacitance will nents in a multi-sensor transducer or even giving the han- show on the capacitance meter. A much larger capaci- dler a very nasty, albeit harmless, shock. tance will show if the piezoceramic is wired properly. This In spite of the precautions that need to be taken with is an easy check of the manufacturing process. Sound Waves How do the sound waves ic, the wider and less concentrated travel in the water? is the sound Understanding wave motion can help you understand beam. For exam- the way in which transducers work. When you throw a ple, the beam- pebble into still water, you can see small ripples or waves width produced form around the spot where the pebble entered the by the smaller, water. If you watch closely, you will see these circular one inch, piezo- ripples or waves move evenly away from the center. When ceramic will “see” waves move in this manner, they are said to move in fish over a large concentric circles. area, whereas a When sound waves are transmitted, they too begin to larger, two inch, spread out as they make their way deeper into the water. piezoceramic will Because the sound waves have been transmitted under provide a narrow- the boat, they are moving downward and outward in con- er beamwidth centric circles. Since the downward and outward move- giving better bottom definition and detection of small fish ment is happening at the same time, the waves are actual- in shallow water. ly making a cone shape. This is referred to as the radiation pattern. Thinking of the sound waves transmitted from a transducer as an ice cream cone turned up side down will How much underwater area can be seen help visualize the sound field for a typical single- by an echosounder? ceramic transducer. Engineers determine how wide an area will be seen on the water’s bottom by knowing the depth of How wide is the radiation pattern the water and the transducer’s made by a transducer? cone angle. If you have a mathe- We refer to the widest part of the cone-shaped radi- matical calculator or trigonometry ation pattern as the beamwidth. It is the diameter tables, you can calculate of the outer most circle of sound waves. Engineers beamwidth using the following are able to increase or decrease the beamwidth and formula: therefore the area that the transducer can “see”. (2 x depth) x (tangent of 1/2 cone One way to change the beamwidth is to use piezo- angle) = diameter of the beam ceramic elements of different diameters. The larger (beamwidth) the piezoceramic, the smaller and more concentrated is the sound beam; the smaller the piezoceram- 9 Theory of Operations Theory of Operations

The chart on the bottom of this page shows this concept. the rings of light will The Structure Of Transducers There are several ways to specify beamwidth. The com- be dimmer. These rings mercial fishing and naval industry frequently provide are the sidelobes of the What goes into the making and provides a water-tight seal to minimize any possibility flashlight beam. beamwidth information by measuring the sound beam at of a transducer? of water entering the unit. –3 dB. The marine recreation industry, however, provides When engineers design It is clear that the transducer would not work without the beamwidth information measured at transducers, piezoceramic element, however, other parts are also need- –6 dB, giving the impression that their they calculate What is an acoustic window? ed. A transducer is made up of six separate components: transducers have a wider beam field. what sidelobes The acoustic window is the surface through which the are present. In • Piezoceramic element or an array of elements sound waves travel. It occupies the space between the piezoceramic assembly and the water. Any material used fact, 60% to • Housing What is target masking? 70% of the to create the acoustic window will absorb some of the • Acoustic window There are areas within the transducer’s sound waves sound waves that pass through it. Therefore, engineers range which seem to be invisible to will be concen- • Encapsulating material carefully choose the least absorbent materials. The the echosounder. This is known as tar- acoustic window is sometimes referred to as the trated in the • Sound absorbing material get masking. It can happen if the lake cone area and acoustic face. or sea bottom drops off suddenly or the remaining waves will escape in all directions. • Cable Epoxy, plastic, and urethane are the three materials Airmar contains a large rock. The sound Engineers generally like to minimize sidelobes, uses most often for our acoustic windows. These materials waves will bounce off all of the sea What is the housing although they may actually be desirable in some have sound wave carrying capabilities or acoustic bottom within the sound beam and of a transducer? situations. As with a flashlight, a transducer does properties between those of the piezoceramic element return as strong echoes. The echoes The housing is the container that covers, protects, and not “see” as well in the sidelobes, because fewer and water. from the highest point, the rock or supports the component parts of the transducer. The of the sound wave echoes return to the transduc- drop-off, return to the transducer first, falsely indicating piezoceramic element is very brittle, and the wire connec- er. Fish might be present in this area, but a fisher would the apparent depth of the bottom. Small fish below the tions to the piezoceramic are fragile. Because of this, the Acoustic window materials fall be unaware of them. However, in the case of a narrow highest point will produce relatively small echoes which housing needs to be sturdy as well as resistant to the beam transducer, sidelobes can be useful, since they effec- into two categories. will return after the larger ones. Therefore, fish can be chemical, mechanical, and electrical forces in the environ- tively widen the coverage. Soft, rubbery, elastic materials like urethane carry sound swimming around the sides of a large rock or a drop-off, ment where it will be used. waves in almost the same manner as water. So, water and Sidelobes are typically presented as part of the transduc- be in the sound field, and yet remain invisible to the Our housings are made of a variety of materials and take urethane are said to have similar acoustic properties. er’s radiation pattern. The lower, smaller, and narrower the echosounder. on different shapes depending upon the customer’s need Because of this close match, the thickness of acoustic win- sidelobes, the better the transducer performs, because and intended type of installation. Some of the housing dows made from urethane does not need to be tightly What are sidelobes? more of the sound waves are focused in the main beam. materials are: Our engineers are concerned about a phenomenon called controlled in our product designs. Sidelobes are watched carefully during product develop- • Molded plastic • Stainless steel Hard materials like plastic and epoxy have acoustic proper- sidelobes. You can see sidelobes for yourself by using a ment. Each transducer model creates its own particular • Bronze • Urethane (SEALCAST™) ties somewhere between those of piezoceramic elements flashlight. If you shine a flashlight against a wall, you will sidelobe pattern as the sound waves travel through the The plastic and ure- and water. In other words, see an area at the center where most of light is water. This information is very important to those who thane housings are the plastic or epoxy acts concentrated. Around the edge of the flashlight beam, design the echosounders to be used with our transducers. produced in our own like an intermediate acoustic step between the Diameter of Viewable Area or Beamwidth molding department. Airmar’s custom SEAL- fluid water and the rigid CAST ™ transducers piezoceramic element. Cone Angle feature a seamless A plastic or epoxy acoustic Depth in Feet 9° 16° 18° 20° 32° 45° 53° housing and a com- window is called a match- pression fitting at the ing layer. Layer thicknesses 5 0.8 1.4 1.6 1.7 2.8 3.9 4.6 cable exit. This com- are carefully calculated 10 1.6 2.8 3.1 3.5 5.6 7.9 9.2 pression fitting secures and produced to match 25 3.9 7.0 7.9 8.7 14.0 19.6 23.1 the flexible cable at the sound wavelength at 35 5.5 9.8 11.0 12.3 19.5 27.5 32.4 the point of attach- the operating frequency. 50 7.9 14.0 15.7 17.4 27.9 39.3 46.2 ment to the housing 10 11 Theory of Operations

The Structure Of Transducers What goes into the making and provides a water-tight seal to minimize any possibility of a transducer? of water entering the unit. It is clear that the transducer would not work without the piezoceramic element, however, other parts are also need- What is an acoustic window? ed. A transducer is made up of six separate components: The acoustic window is the surface through which the • Piezoceramic element or an array of elements sound waves travel. It occupies the space between the piezoceramic assembly and the water. Any material used • Housing to create the acoustic window will absorb some of the • Acoustic window sound waves that pass through it. Therefore, engineers • Encapsulating material carefully choose the least absorbent materials. The acoustic window is sometimes referred to as the • Sound absorbing material acoustic face. • Cable Epoxy, plastic, and urethane are the three materials Airmar What is the housing uses most often for our acoustic windows. These materials have sound wave carrying capabilities or acoustic of a transducer? properties between those of the piezoceramic element The housing is the container that covers, protects, and and water. supports the component parts of the transducer. The piezoceramic element is very brittle, and the wire connec- tions to the piezoceramic are fragile. Because of this, the Acoustic window materials fall housing needs to be sturdy as well as resistant to the into two categories. chemical, mechanical, and electrical forces in the environ- Soft, rubbery, elastic materials like urethane carry sound ment where it will be used. waves in almost the same manner as water. So, water and Our housings are made of a variety of materials and take urethane are said to have similar acoustic properties. on different shapes depending upon the customer’s need Because of this close match, the thickness of acoustic win- and intended type of installation. Some of the housing dows made from urethane does not need to be tightly materials are: controlled in our product designs. • Molded plastic • Stainless steel Hard materials like plastic and epoxy have acoustic proper- • Bronze • Urethane (SEALCAST™) ties somewhere between those of piezoceramic elements The plastic and ure- and water. In other words, thane housings are the plastic or epoxy acts produced in our own like an intermediate molding department. acoustic step between the Airmar’s custom SEAL- fluid water and the rigid CAST ™ transducers piezoceramic element. feature a seamless A plastic or epoxy acoustic housing and a com- window is called a match- pression fitting at the ing layer. Layer thicknesses cable exit. This com- are carefully calculated pression fitting secures and produced to match the flexible cable at the sound wavelength at the point of attach- the operating frequency. ment to the housing 11 Theory of Operations

How will air bubbles interfere In what other ways do acoustic with transducer function? windows differ? Because air is much less dense than water, air bubbles Acoustic windows can be “hard” or “soft.” Soft acoustic scatter and reflect sound waves. Any air bubbles in the windows made of urethane provide excellent sensitivity to acoustic window material or in the water will interfere echoing sound waves, therefore soft windows can “read” with the proper working of the transducer, greatly reduc- through deeper water with better clarity of detail. This ing its performance. To minimize the chance for tiny, fleck- material is extremely stable in water, therefore providing like, micro-bubbles in the acoustic window material, it is excellent reliability for years. Because the acoustic proper- placed under a vacuum for a specific amount of time. ties of urethane are similar to water, the acoustic window Air bubbles must, also, be carefully guarded against by can be made in the shape of a dome, wedge, or an arc. the installer and user. If the transducer is glued to the Hard plastic and epoxy acoustic windows are especially inside of the hull of a boat, even the glue cannot have air good for boats that are trailered or often in and out of the bubbles in it. Indeed, a transducer needs to be placed water, because these windows become wet quickly. They away from anything, including the propeller, that will also have characteristics which are good in shallow water cause air bubbles to form while the boat is underway. and in fishfinding.

What will interfere with an acoustic What is the encapsulant? window’s ability to become wet? The encapsulant is the material that encases the parts of In order for a transducer to work correctly, the surface of the transducer within the housing. It can act as an the acoustic window must be thoroughly wet. How quick- acoustic window material, filler, or sealant. At Airmar the ly the acoustic window becomes wet depends, in part, encapsulant is often called potting material and includes upon the type of material used to make it. epoxies and urethanes. The choice is based upon its ability to meet the performance and application requirements Glossy surfaces, such as our plastic and SEALCAST™ ure- of the particular transducer design. thane acoustic windows, wet almost instantly, because they are smooth. Our sanded ure- What is sound absorbing material? thane acoustic Sound absorbing material is any material that inter- windows take rupts or stops the flow of sound waves. In our much longer to Sanded, urethane, acoustic window (magnified) case, it is the material used to dampen any become thor- unwanted vibrations of the piezoceramic element oughly wet. Although the sanded in a transducer. urethane does not seem rough to the touch, the sanding When AC voltage is applied to a piezoceramic element, process leaves microscopic peaks and valleys which all surfaces of the element vibrate. This means it sends trap air bubbles keeping the water from touching the off or radiates sound waves in all directions. Therefore, urethane. the piezoceramic element could pick-up echoes returning Because of this, transducers with sanded urethane from all directions giving false information to the echo- acoustic windows would have to soak in water for a mini- sounder. This effect is called spurious radiation and must mum of one hour before testing their ability to transmit be avoided. and receive. In order to shorten this process, our testers To reduce spurious radiation as much as possible, the lightly scrub the urethane window with alcohol in order piezoceramic element is surrounded with sound absorb- to hasten the wetting process. Both the scrubbing and ing material, usually a layer of cork or foam. In this way the alcohol help to quickly displace the microscopic air vibrations of the piezoceramic element are dampened on bubbles. all the surfaces except the surface facing the acoustic win- 12 Theory of Operations

dow. As a result, the sound waves are given directionality. snowy—the clarity and sharpness of the image is lost. They are concentrated in one direction only. Directionality Depending upon the application and performance is also effected by the piezoceramic’s shape and frequency. requirements for the transducer, several types of shielding are used such as: How do Airmar cables function? Aluminum foil on Mylar A transducer cable is the vehicle which carries the electri- Tinned braided shield cal current between the echosounder and the transducer. Spiral shield It is usually made of several conductors or wires. Cables The cables outer jacket protects the inner conductors and are carefully engineered to carry a specified voltage and provides strength and flexibility. current from the echosounder to the sensor(s) in the Jackets materials include: transducer. PVC—polyvinyl chloride Inside the jacket of each cable is shielding to protect against electrical pulses from other electrical equipment TPR—thermoplastic rubber that could interfere in the workings of the transducer. This Neoprene interference is called electrical noise. Commonly heard as Polyurethane static, electrical noise could come from a ship-to-shore radio, navigation equipment, ignition impulses, or even another transducer. Interference has the same effect on the echosounder display screen as it does on a televi- sion screen; the picture becomes

Performance Testing What is performance testing? This information is known as performance data which is made Airmar products are designed to a cus- available to customers and used tomer’s specifications or to fill a market as the standard for final testing need. Engineers most often begin with a of the product. The figures are required frequency and cone angle. After extremely important to our OEMs the transducer is designed, a sample is as this data is used to determine built in the lab where it is extensively test- the frequency at which the ed. Data is collected on: echosounder must • Frequency be set. • Beamwidth Airmar products are tested many • Transmitting Voltage Response (TVR) times during their manufacture • Receiving Voltage Response (RVR) and are subjected to a careful • Figure-of-Merit final inspection. A wide variety of test equipment, including our • “Q” (Bandwidth) test tanks, is used. • Ringing • Impedance

13 Theory of Operations

What are the Transmitting As we know from the Receiving Voltage Response, the returning Voltage Response sound wave will be far weaker than and the Receiving Voltage the original sound wave that was Response? sent out. This is because the transmit- Each Airmar transducer model is test- ted sound wave looses energy by the ed to measure the strength of the time it travels through the water, transmitted sound wave and the bounces, and returns. received sound wave (what we have Engineers test each transducer been calling the echo). model and graph the results of the The Transmitting Voltage Response Transmitting Voltage Response, the (TVR) is a measure of the acoustic Receiving Voltage Response, and the pressure of the sound wave at a dis- Figure-of-Merit. The graphed curve of tance of one meter when one volt of the Figure-of-Merit will usually peak electricity is applied to the transducer. somewhere between the peak of the If we could hear the sound waves, Transmitting Voltage Response and we might say the TVR is an indication the peak of the of how loud a sound the transducer Receiving Voltage produces when one volt is applied to it. Response. The Receiving Voltage Response (RVR) is a measure of the voltage produced within the transducer when a 1 mPa (micropascal) of acoustic pressure is received. An What is “Q”? “Q” stands for quali- mPa is a unit for measuring sound pressure. The pres- ty and is a measure sure of the echoing sound waves causes the piezoce- of the sharpness of ramic to produce voltage, the RVR. Think of a lamp that the response of the can be turned on by the clap of hands. It is the loudness piezoceramic ele- of the clap, the pressure of the sound wave, that turns ment to the fre- on the lamp. If we could see the transducer’s response quency that is sup- to the echoing sound waves, we might say the RVR is plied to it. In other an indicator of how brightly the lamp shines. words, “Q” Comparing the TVR and RVR shows that the difference describes how pre- between the actual voltage used for transmitting and cisely the frequency the actual voltage generated by the returning echo is must be output to tremendous. Sound waves are emitted by voltage mea- achieve the best suring in the hundreds (100s) of volts, yet the returning performance from echoes are measured in hundredths (1/100s) of a volt. the transducer. It answers the questions: “What is the piezoceramic element’s best or resonant frequency?”, What is the Figure-of-Merit? “How well does the piezoceramic element work on either side of its resonant frequency?”, and “How long will the The Figure-of-Merit is a measure of how well a transducer transducer continue to ring after a transmit pulse?” works when used for both transmitting and, then, receiving its own echoes. It is the algebraic sum of the Engineers have a standard method for determining “Q”. It Transmitting Voltage Response and the Receiving Voltage is the operating frequency divided by the bandwidth. For Response. The Figure-of-Merit is sometimes referred to as non-engineers, it is helpful to think of frequency and the Insertion Loss. bandwidth in terms of volume and tuning-in your favorite

14 Theory of Operations

What is Ringing? Ringing is the continued vibration of the piezoceramic element after each transmit pulse. Imagine the ringing of a large church bell. After the church bell is struck by the clapper, it continues to ring for a time if the vibrations are not dampened. radio station. The operating frequency is that spot on the This phenomenon also occurs in piezoceramic elements. radio dial where your favorite station comes in the loudest The vibrations of the element continue after the transmit and clearest. pulse. These vibrations decrease in amplitude (or “loudness” if we could hear them) just as the ring of the church The bandwidth includes the frequencies slightly above bell gets softer over time. The tapering off of the vibra- and below the best spot, but where the station can still tions is called the ring down. be heard. Engineers use the standard of three decibels below the peak Transmitting Voltage Response, shown as In effect, ringing causes a “stretching” of the transmit –3 dB. If we could hear the transducer sound waves, the pulse, because it generates unnecessary sound waves. –3 dB point is where the sound would be half as loud. As These additional sound waves add additional microsec- we turn the dial above and below our station, the signal onds to the dead band, interfering with the reception of begins to fade, so we can’t hear it as well. The points echoes. above and below the radio station on the dial at which If a desired echo arrives during the ring down it will our radio is half the appear on the echosounder screen as a volume of the correct smear or it may even be hidden by the ring radio station frequency down and not appear on the echosounder determines our band- screen at all. Ringing, therefore, reduces the width. clarity of the display on the echosounder The “Q” of a transducer screen. model can be deter- Ringdown also keeps the transducer from mined by analyzing its “seeing” in very shallow water. Transmitting Voltage Ringing can never be totally eliminated. With Response graph. The the proper engineering, however, it can be resonant frequency greatly reduced. A transducer with a high “Q” and peak TVR is at 50 factor is one which will ring for a long time kHz. At 3 dB below after being struck with a transmit pulse. TVR, the frequencies Conversely, a low “Q” transducer exhibits less are 47.6 kHz and 52.8 ringing. kHz, giving us a bandwidth of 5.2 kHz (52.8 kHz – 47.6 kHz = 5.2 How are the deadband and kHz). To determine “Q”, blanking zone related? the resonant frequency is divided by the bandwidth giv- As you have learned, during the transmit pulse the piezo- ing us a “Q” factor of 9.6. (50 kHz ÷ 5.2 kHz = 9.6). ceramic is vibrating, so no echoes can be received—in the “Q” factors range between 1 and 40. At 9.6 this model’s same way that you cannot listen when you are talking. “Q” factor is relatively low. The OEM need not be as pre- The microseconds when the transducer is transmitting is cise in setting the echosounder’s drive frequency when a the deadband for the reception of echoes. transducer has a lower “Q”. When something very close to the transducer (usually between one and three feet), the bouncing echoes will 15 Theory of Operations

return before the piezoceramic has stopped ringing. Since quotient is the impedance. the echo is in the deadband, these echoes cannot be The echosounder must be designed to match the imped- received—the object will be invisible. The minimum dis- ance of the transducer to deliver the correct power to it. If tance between the transducer housing and an object that they do not match, the output from the transducer will be can be “seen” is called the blanking zone. OEMs typically reduced lessening the performance of the entire system. want a small blanking zone, so their echosounders can Airmar chooses materials that are natural conductors of “see” objects close to the transducer. electricity. Silver is used on our piezoceramic elements, because it is an excellent conductor and is easy to apply What is Impedance? and bake onto our piezoceramic elements. Copper is used in all electric wiring, because it is an excellent conductor Impedance stems from the word impede and means and less expensive than silver. something that hinders progress. In the field of electricity, it refers to the limitation of the amount of current that can Some materials will not allow electrons to flow through flow through a material. Impedance is technically the ratio them at all. These materials are called insulators. They are of voltage to current. Airmar measures the amount of used around all electrical wires to keep electricity flowing electrical force applied to the transducer and the amount through the conductor(s) and prevent electricity from of current that actually runs through the transducer. The flowing elsewhere.

Airmar Products How are Airmar products unique? • Depth with Speed and Temperature (TRIDUCER ® multisensor) Airmar’s products incorporate the most advanced technology; often pioneered by Airmar. Our attention to detail • Speed only makes our sensors more accurate and reliable than the • Speed with Temperature competition. Careful design, manufacture, and testing Recreational transducer housings come in several shapes insures that our transducers perform to specifications. We depending upon their intended method of installation. use waterproof connectors, multiple O-rings, seamless —This transducer is installed against the inside of a construction, and strong materials to produce sensors that In-hull boat hull bottom and sends its signal through the hull. can withstand harsh environments. Some people prefer this method, because the unit cannot be damaged when the boat is trailered. Also, drilling What products does Airmar manufacture through the hull is not necessary. In-hull transducers can in each product line? work better than other models at high boat speeds. —Our recreational transducers can Because in-hull units “shoot” through the layers of the Recreational Sensors be manufactured to perform several different functions hull, there is a loss in performance. In addition, this instal- when used with the appropri- lation will not work on a boat made of any ate information display unit. material containing air bubbles, because the air bubbles reflect and scatter the sound before it Airmar sensors can measure: reaches the water. Wooden hulls and fiberglass • Temperature only hulls with foam, balsa wood, or plywood layers • Depth only sandwiched between the inner and outer skins • Depth with Speed are not recommended for in-hull installation. —This transducer style is mount- • Depth with Temperature Transom Mount ed to the back (transom) of a boat hull. Some people prefer this style, because it affords easy

16 Theory of Operations

installation and removal of the unit—especially if a kick-up In our bronze transducer the temperature sensor is placed bracket is used. A kick-up bracket allows the transducer inside the housing cavity because the metal housing itself to be moved out of the way to prevent damage from a is a good thermal conductor. The bronze quickly takes on boat trailer. A transom mount installation gives better per- the temperature of the water and, as a result, the tempera- formance than the in-hull installation at boat speeds up ture sensor doesn’t require direct water contact. to 30 MPH. In a few other types of transducers a semiconductor tem- —This transducer is installed through a hole in perature sensor is also used. Because the electrical voltage Thru-hull the boat and protrudes into the water. It is most often put out by the semiconductor changes slightly with each used on boats 25 feet or longer and usually provides the degree of temperature, the temperature of the water can best performance. The transducer is low enough in the be determined by measuring the electrical voltage put out water to avoid most of the air bubbles caused by the by the semiconductor. motion of waves. Thru-hull units are not recommended in two situations: Speed Sensors • Plastic thru-hull housings should not be used on a Boat speed is measured in nautical miles per hour called wooden boat. Wood swells as it absorbs water, so it knots. A nautical mile is 6,076 feet, approximately 1.15 may crack the housing. land miles. • Bronze thru-hull housings should not be used in alu- The component used to determine boat speed is called a minum boats. The interaction between the aluminum Hall Cell and works like an on/off switch. Within the sen- and the bronze especially in the presence of salt water, sor are magnetic parts that can be turned on and off by a will eat away the aluminum hull and/or bronze housing. passing magnet. The Airmar paddlewheel blades are magnetized. As the boat moves through the water, the paddle- Temperature Sensors wheel turns. Each time a magnetized blade of the paddlewheel passes by the Hall Cell, it is turned on or off, creat- Temperature sensors are desirable for several reasons. ing a pulse of electricity. Electronics in the echosounder Anglers know that fish prefer certain water temperatures, system count the frequency of these pulses, then convert so a temperature sensor can help the fisher determine them into knots. A paddlewheel may create as many as where the fish may be hovering. Boaters may wish to 22,000 electrical pulses per nautical mile. know the water temperature before jumping in for a swim, but more importantly, it can be a navigational aid. For example, the water in the Gulf Stream is much warmer TRIDUCER® Multisensor than the surrounding Atlantic Ocean. Boats traveling north The Airmar TRIDUCER® multisensor is a combination of are wise to locate and ride the current while those travel- three sensing devices built into one housing to measure ing south need to avoid the Gulf Stream entirely. depth, speed, and temperature. Temperature is most commonly read by a temperature sensor called a thermistor. The Airmar thermistor is a 10,000 ohm resistor which varies in value according to its temper- Phased Array Transducer ature. This means that the amount of electricity flowing A phased array transducer can function as both a down- through the resistor is directly related to the temperature ward looking and a forward looking transducer. It does of the resistor. The warmer the resistor the more electricity not point straight down only. Rather, the echosounder can is able to flow through it. Conversely, less current is able to steer the beam about 45 degrees to either side. These flow through the resistor when it is cold. The amount of transducers are able to “see” both the immediate underwa- electrical current flowing through the resistor, therefore, ter depths and what is ahead of the boat. It can see both tells us the temperature of the water. a large schools of fish toward which a boater would like to Most of Airmar’s temperature sensing devices are built right steer and large objects or a shallowing bottom to be into the transducer housing. avoided. 17 Theory of Operations

Commercial Fishing Transducers easy meal. The sound has been likened to the scratching of fingernails on a blackboard. These transducers are available in frequencies from 24 kHz to 200 kHz. Units feature high-efficiency designs produc- The dB PLUS II™ Acoustic Deterrent System has a ing superior fish finding and clear and distinct images of unique “soft-start” feature. The system takes 25 seconds to both the bottom and closely spaced fish. reach full power. This gradual sound increase provides a warning to divers and allows seals and sea lions the option of leaving the area before the sound reaches its Navigation highest volume. and Ocean Survey Transducers This product has been successfully used in waters off of This broad product group features transducers ranging the U.S., Canada, Chile, New Zealand, and Europe. The from 10 kHz to 2 MHz. Airmar offers transducers sized seals are keeping their distance, so the customers are from small portable units for harbor survey to multi-fre- very happy. quency arrays for deep sea sounding. Arrays of more than 100 piezoceramic elements have been designed and manufactured by Airmar. We can produce dual beam and split Air Transducers beam transducers and linear phased, and multi-beam Air transducers work in a way that is very similar to transducer arrays. marine transducers. Air, however, is not as good a conductor of sound waves as water. In fact, sound travels One hydrographic product specifically designed for a cus- only 25% as fast in air as in water. Think of the time delay tomer is the Swath bathymetry transducer. It’s transmitting between seeing lightning and hearing the thunder or transducer uses a fan beam which is very narrow in one between your shout and its echo. Speed is not the deter- directions and very broad in the other direction. Echoes mining factor in the loss of efficiency. Temperature, are received by 30 separate transducer elements which humidity, and wind are the determining factors. form 30 separate beams. This provides 30 sets of data yielding a great amount of detail about the bottom. One Air transducers can be used in a variety of ways in both Swath is used to monitor the ever shifting channels in the commercial and industrial applications: Mississippi River. • Silo or tank level detection of liquids such as oil; or of solids such as grain, coal, flour, or anything stored in bulk dB PLUS II™ • Proximity measurement Acoustic Deterrent System • Process control The dB PLUS II™ Acoustic Deterrent System uses Airmar’s • Object detection skill at producing sound waves, to scare away marine life rather than to find it. Our popular acoustic deterrent sys- • Volume of liquid flow through weirs tem is designed to protect fish farms from seals and other • Sensing through foams marine predators who find the fish an inviting target. • Level detection in waters with sediment such as septic The acoustic deterrent system has a series of four trans- plants or in environments that are dusty ducers positioned around the fish pens which are made • Liquid column measurement of net. The transducers work as projectors only, giving out sound waves for 2.5 seconds in turn. It takes 18 seconds to complete one full four-transducer transmission cycle. What are the characteristics The amplifier for creating the electrical power supplied to of air transducers? the transducers is centrally located among the net pens. Frequencies from 25 kHz to 225 kHz are available in our Research tells us a sound wave frequency of 10 kHz is not air transducers. harmful to seals, but it is definitely irritating. Their desire Airmar’s models are designed to meet criteria set by haz- to get away from the sound overcomes their desire for an ardous environmental certification agencies. Because air 18 Theory of Operations

has relatively low density, air transducers are susceptible water around the transducer, so that drag on the boat is to ringing. The dead band specification is very important minimized. All Airmar fairings are made from a polymer to the OEMs and our engineers strive to design air trans- resin which will not swell or rot. ducers with low “Q” and, therefore, low ringing. Our parts and accessory line includes: • Housings, hull nuts, and cap nuts Parts and Accessories • Switch boxes What is a Fairing? • Mounting kits A fairing is a structure which is added to the transducer at • Cables and connectors the mounting location to improve its performance. If the • Speed sensor parts hull slopes, a fairing orients the transducer so the sound • Fairings beam will aim straight down. The chance of water with • Diplexer air bubbles flowing across the acoustic window is reduced by mounting the transducer deeper in the water. Also, Airmar carefully designs the shape its fairings to direct Glossary of Terms

the abbreviation for Alternating a person who fishes. the measurement of AC Angler Cone Angle Current. Electrical current that reverses beamwidth in degrees. It is an indication the use that direction at regular intervals. Application Requirement of how large an area is covered by a the sensor is designed for. transducer’s sound beam. The larger the used to cause the piezoce- AC voltage a series of piezoceramic elements cone angle the larger the area covered. ramic element to vibrate. Array in a transducer. the measure of the number of relating to sound and sound Current Acoustic the range of frequencies over electrons that flow past a point in a spe- waves. Bandwidth which the transmitting sensitivity (TVR) is cific unit of time. when work can be no less than one half of the peak sensitiv- Acoustic Energy an abbreviation for decibel. A unit for done because energy is provided by the ity at –3dB. dB measuring the power of a sound wave. physical pressure of a sound wave. the diameter of the circle Beamwidth the time during and immedi- see Acoustic Window in which 50% to 70% of the sound Deadband Acoustic Face ately after a transmit pulse when a trans- waves emitted by a transducer are con- the ability of a mate- ducer cannot receive echoing sound Acoustic Property centrated. rial to carry sound waves through it. waves and therefore cannot “see” the the wire that carries power area below the surface of the water. that part of the trans- Cable Acoustic Window between the echosounder and the transducer through which the ultrasonic vibra- the minimum distance ducer. It is usually constructed of several Deadzone tions from the piezoceramic assembly between the transducer housing and an conductors. travel to the water or other transporting object that can be “seen” by an medium. It occupies the space between the ability to store an elec- echosounder. Capacitance the piezoceramic assembly and the water. trical charge. the controlled emission of Directionality an organ in a fish which a commonly used name for the sound waves in the desired direction. Air Bladder Ceramic allows it to adjust easily to changes in piezoceramic element. the part of the water pressure at different depths. It is Display Screen a series of circles of echosounder unit on which an image of the organ that allows the echosounder to Concentric Circles different sizes having a common center. the underwater area is projected. detect the fish. anything that carries electri- the retarding force exerted on a the degree of intensity (pres- Conductor Drag Amplitude cal current. This may be a copper wire or moving object. sure) of a sound wave. If we could hear any other material that readily allows the sound wave, the amplitude would be electrons to pass through it. its “loudness.”

19 Glossary of Terms

an instrument comprised the limitation of the Echosounder Impedance Original Equipment Manufacturer of a display screen and electronic circuit- amount of flow of electrical current. It is These are the businesses that buy (OEM) ry. It provides necessary power to the commonly used as a comparison our product for use with their manufac- transducer, interprets the information between the amount of voltage needed tured products. received from the transducer, and to get a specific amount of current. the work displays this information in a readable Performance Requirement the method of that a customer needs the transducer to format. In-hull Installation installing a transducer by attaching it to do, e.g. see a narrow but deep area or a system com- the inside of the hull. measure speed and temperatures in salt Echosounder System prised of two major components—an water below 32° F. process of creat- echosounder and a transducer. This sys- Injection Molding the ing parts by forcing melted material a jet-ski tem measures the depth of the water Personal Water Craft (PWC) (usually plastic) into a mold in the type recreational water vehicle. and the distance to any objects in its desired shape. The material is then field of vision, and displays this informa- a series of piezoceramic cooled and released from the mold. Phased Array tion in a readable format. elements in a transducer. The piezoce- the algebraic sum of the ramic elements are wired in a manner when work can be Insertion Loss Electrical Energy Transmitting Voltage Response and the which allows them to fire in time done because energy is provided by an Receiving Voltage Response. This usually delayed sequence, so the echosounder electrical force. indicates a net loss of energy. Often can electronically steer the array. interference in an elec- referred to as the Figure-of-Merit. Electrical Noise a material tronic signal, often called static. Piezoceramic Element any material that will not made of crystals with positive and nega- Insulator a solid material which con- allow electrons to pass through. These tive charges. Frequently referred to as a Electrode ducts electricity and is used at the point materials are used to surround conduc- piezoceramic or ceramic. where electrical current enters or leaves tors to keep the current flowing in the the ability to align electrically an object. desired direction. Polarize charged crystals placing like poles in the the material that acts as a the covering that surrounds a same direction. Encapsulant Jacket filler in and around the transducer parts cable and provides strength. one end of polarized material, i.e. within the housing. It may also function Pole one thousand cycles the positive pole of a piezoceramic ele- as an acoustic window or a sealant. Kilo-Hertz (kHz) or complete vibrations of sound per sec- ment. Encapsulant is often called potting ond. material. see Encapsulant Potting Material nautical miles per hour. A nautical a measure of a system’s ability Knots when the transducer acts as Energy mile is 6,076 feet or roughly 1.15 Projector to do work. a transmitter only. This is the case with statute miles. the dB PLUS™ II Acoustic Deterrent ) the algebraic Figure-of-Merit (FOM an acoustic window System. sum of the Transmitting Voltage Matching Layer material like plastic or epoxy that has Response and the Receiving Voltage “ an abbreviation for quality. A mea- acoustic properties somewhere between Q” Response. The Figure-of-Merit usually sure of how tolerant a transducer is to those of the piezoceramic element and indicates a net loss of energy, and is changes in frequency. the water. It acts as an intermediate sometimes referred to as Insertion Loss. acoustic step and facilitates the travel of outline of sound Radiation Pattern the number of complete sound waves from the piezoceramic ele- waves as they travel outwards from a Frequency cycles or vibrations that occur within a ment to the water. transducer, usually represented as a specific time frame, typically one second. cone shape. 6,076 feet or 1.15 statute It is usually measured in Hertz. Nautical Mile miles. Receiving Voltage Response (RVR) a wafer of silicon altered by the measure of the voltage produced Hall Cell a unit of resistance to an electrical electrical current so that it responds Ohm within the transducer when returning current. Some materials conduct electric- magnetically. echoes are received. ity readily while others are poor conduc- a measure of one cycle or tors. The poorness of the conductivity is an electrical component used Hertz (Hz) Resistor complete vibration per second. the resistance of the molecular structure to limit the amount of an electrical cur- to carrying the electrical current. rent passing through it. The level of this something that covers, sup- Housing limitation is measured in ohms. ports, or protects the mechanical parts.

20 Glossary of Terms

the ability to show fine usually a an Airmar Resolution Sound Isolating Material TRIDUCER® Multisensor detail. Better resolution provides better layer of cork or foam that surrounds the trademarked name for a sensor that can discrimination among individual objects. piezoceramic element except where it measure three functions: depth, speed, comes in contact with the acoustic win- and temperature in one unit. Airmar has the natural tendency of a Resonant dow. This is done to focus the sound been granted a patent for TRIDUCER® material to vibrate at its own favored waves in one direction and prevent spu- multisensors and has sole rights to this rate (frequency). rious radiation. design. the tapering off of the vibra- Ring Down a device that detects the sound waves of high fre- tions from a transmit pulse. The vibra- Speed Sensor Ultrasonic rate of speed of a water craft. quency than cannot be heard by tions may interfere with the reception of humans. Sound waves higher than accurate information by the transducer sound waves that Spurious Radiation 20,000 Hertz. and thereby distort the information dis- escape in non-desired directions. This played by the echosounder screen. produces false readings by the a unit of electrical force. Volt echosounder system. the continued vibration of a a measure of electrical force or Ringing Voltage piezoceramic element beyond the elec- the areas within a the potential for current to flow. Target Masking trical transmit pulse. This causes distort- transducer’s range which seem to be the effect of force acting on a ed information to be displayed on the invisible to the transducer. Work body. It is the relationship between the echosounder screen. a device that application of a force to an object and Temperature Sensor an Airmar trademarked detects the temperature of water. the distance that object moves when SEALCAST™ name for a transducer housed in one the force is applied. It is calculated by a material with the seamless unit. Thermal Conductor multiplying the force times the distance ability to let heat travel through it. A the object is moved. any device that detects and good thermal conductor adjusts quickly Sensor responds to a stimulus such as tempera- to the temperature of its environment. ture, speed, motion, light, various chem- a unit for sensing and mea- icals, etc. Thermistor suring temperature. material used to prevent Shielding a method for interference from other electrical equip- Thru-hull Installation installing a transducer through a hole in ment on the boat or in the area that the hull of a boat. could interfere with the workings of the transducer. a device that changes elec- Transducer trical energy to acoustic energy and those portions of the acoustic Sidelobes back again. This function is performed signal that are located outside the main by a piezoceramic element(s). sound beam. a usually brief sequence distorted informa- Transmit Pulse Smear/Smearing of sound waves sent out by the trans- tion, specifically a running together of ducer. Following the transmit pulse fish images displayed by the there is a longer period of time when echosounder system because of unwant- the transducer stops transmitting and ed sound waves. receives the echoes. derived from the words sound Sonar navigation ranging. An apparatus that Transmitting Voltage Response (TVR) the pressure or “loudness” of a sound uses reflected sound waves to detect wave produced by one volt of electricity. and locate underwater objects. a method the total area where sound Transom Mount Installation Sound Field for installing a transducer on the back waves travel from a transmit pulse. The (transom) of a boat hull. sound field includes the main beam and sidelobes as well as spurious radiation.

Theory of Operations

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