March 21, 1933. F. REEBER 1,902,184 VIBRATION SENSITIVE SYSTEM Filed June 7, 1927 S N SéNa Na N N N 2e N Š % 2 INVENTOR Aarak Aeber BY 76 HIS AT TORNEY Patented Mar. 21, 1933 1902,184 UNITED STATES PATENT OFFICE EFRANK REBER, OF SAN FRANCIsco, CAFORNA VIBRATION SENSITIVE SYSTEM Application filed June 7, 1927. Serial No. 197,211. kind of work, such as microphones, magneto This invention relates to a system for con phones, and condenser microphones. verting mechanical vibrations into electrical My invention possesses many other advan vibrations. More particularly it relates to tages, and has other objects which may be a system of that character in which a piezo made more easily apparent from a considera 55 electric crystal is utilized. tion of one embodiment of my invention. it is now well-known that certain crystals, For this purpose I have shown a form in the such as rochelle salt crystals or quartz, ex drawing accompanying and forming part of hibit piezo-electric properties; that is, elec the present specification. I shall now pro tric potential differences are created across 60 O certain points of the crystal when it is sub ceed to describe this form in detail, which jected to pressure variations. It is also illustrates the general principles of my in known that each individual crystal exhibits vention; but it is to be understood that this resonant properties; that is, it responds to detailed description is not to be taken in a a greater extent to a definite frequency of limiting sense, since the scope of my inven 65 15 vibration. However, this trait or character tion is best defined by the appended claims. istic is not very well defined, for these crys Referring to the drawing: tals do nevertheless respond substantially to The single figure is a schematic diagram mechanical vibrations of frequencies differ showing one embodiment of my system. ing materially from the resonant frequency. As stated heretofore, it is well-known that 70 20 It is one of the objects of my invention to certain types of crystals produce potential sharpen up the resonance point of such sys differences upon variations of physical pres tems, whereby a crystal device can be ren sure being applied to them. For example, dered exceptionally sensitive to vibrations if the piezo-electric member 3 is exposed to of some particular frequency, but insensitive alongitudinal variable pressure, a potential 75 25 to vibrations of all other frequencies. difference varying in accordance with the In piezoelectric crystals, it has been found pressure, is created between the conductive that the resonance frequency depends on the coatings 6 and 7 placed on opposite sides of physical characteristics of the crystal; and in the crystal 3. general, the larger the crystal, the lower the It is also well-known that if the coatings 30 resonance frequency. It is obvious that be supplied with varying potential differ under most circumstances it may sometimes ences, then the crystal varies in length in ac be impracticable to operate and control a cordance with these potential differences. I crystal beyond definite physical limits. It make use of this phenomenon to increase the response of the crystal 3 to pressure varia 85 ispossible another to object set or of adjust my invention the frequency to make ofit tions, by providing another piezo-electric de resonance of a pieza crystal in a novel and vice 2 having coatings 4 and 5, which is simple manner. caused mechanically to affect the crystal 3 Such vibration sensitive devices have been and in phase with the pressure variations so used in many diverse ways, such as for receiv as to enhance their effect on this crystal. 90 AO ing and recording earth shocks, artificially. In order to explain how this is possible, I roduced for geophysical explorations; or shall first of all describe the mountings of or receiving and recording earth shocks the crystals. A casing 1 serves to enclose both caused by other happenings, such as the fir crystals 2 and 3; it is covered at the bot ing of guns or the like for locating batteries; tom by the rigid plate or foot 11. To this 95 45 or for receiving and recording vibrations plate is rigidly attached a contacting mem from air or from water, whereby objects can be located, or signaling effected to mines or ber 24, arranged to be placed in the medium the like. My invention may be applied to from which vibrations are to be received. any of these uses, and is iniended to replace The bottom of the crystal 3 abuts this mem 00 50 devices that are not so well adapted for this ber 24; and its top is accommodated in a 2 1,902,184, socket 26 fastened to a flexible diaphragm grounded on the cover 11, and is heated by 12 extending across casing 1. The crystal 2 current from the “A” battery 18. One coat is placed immediately over the crystal 3. Its ing of piezo-electric device 3, such as 6, is ends are accommodated respectively in the connected to filament 28 as by the ground 5 top of socket member 26, and in socket men connection 29; the other coating connects G y ber 27 fastened to another flexible diaphragm to the control electrode or grid 30. In this 13 across the casing 1. A loading weight 14 way potential differences between the coat rests on top of diaphragm 13, and serves to ings 6 and are impressed on the input of provide an opposing pressure to that oc audion 8. The plate electrode 31 is con 10 casioned by vibrations received at foot 24, nected to filament 28 through the output in and to impart a longitudinal stress on the pedance coil 32, the “B” battery 17, and crystals. ground connection 33. The grid 30 can be If foot 24 be placed in contact with the biased to cause the space current character earth or other medium from which vibrations istic to be set at the desired point, by the 15 are received, the crystal 3 being held against aid of the “C” battery 9 and resistance 10, EE said foot by mass 14, which tends to stand which are connected between the grid 30 and still, will be subjected to pressure varia filament 28. As variations in potential dif tions. These are translated, in a manner to ference are produced between coatings 6 and be hereinafter described, into electrica in 7, amplified potential difference variations 20 pulses. These impulses in turn act upon coat exist across the plate 3i and filament 28. 85 ings 4 and 5 of crystal 2 to cause it to vary These potentiai differences can be in in length and in Such sense as to assist crea pressed in succession on the two amplifiers tion of pressure variations in crystal 3. The i5 and 16, each operating as amplifier 8. mechanical characteristics of crystals 2, 3 The control electrode of amplifier 15 is coin 25 and mass 14 are preferably so chosen that the nected, for this purpose, through stopping natural resonant vibratory frequency of the condenser 33 with plate 31; and the filament combined system is much lower than the 34 being in parai ei With filament 28, is of range of frequencies it is desired to receive. course in connection there with. The otit Within the range of operation, the system put circuit includes the impedance 25 and 30 can by appropriate choice of the electrical battery 17. The amplifier 16 is connected to : amplifier devices, be made to respond strong the output circuit of amplifier i5 in the same ly to any frequency; and frequencies beyond manner as described in connection. With the the range are cut off by proper design of the previous ones; and its output circuit, includes amplifying system. In this way, even if leads 22 and 23, which can connect to a re 35, there exist disturbing vibrations at or near corder 35 or other translating device. The the natural resonance of the mechanical sys control electrodes of amplifiers 15 and 16 tem just described, these vibrations will have can be biased by the aid of the “C” battery little or no effect upon the amplifier systems. i8 and resistances 36 and 3. I shall now describe the electric system of In order to affect piezo-electric device 2 40 amplification. This system in the present in the manner hereinbefore specified, the 05 instance utilizes electronic emission devices, coating 4 thereof is connected, as by ground Such as audions. These audions each in connection 38, with the filament system of cludes an evacuated vessel enclosing three the audions. The other coating 5 is connect electrodes. One electrode serves to emit elec ed, as by lead 20, with the plate electrode of 45 trons, as by being heated by an electric cur one of the amplifiers, for example, of ampli rent, the electrode being made in filamentary fier 15. it is thus evident that the ampli form. The electron stream is received at fied electrical impulses produced by device another electrode called the plate or anode, 3 is impressed on the device 2; and of course - which is kept at a potential positive with re this is done in such manner, and the propor 50 spect to the filament. It has been found that tions of element 2 are so chosen, as to cause s a third electrode, interposed between the fila it to assist the device 3. The apparatus thus ment and plate, can control the “space cur becomes somewhat similar to the regenera rent” in the tube; so that even slight varia tive receiver used in radio work.