United States Patent [191 [11] 4,095,775 Hotham [45] Jun

United States Patent [191 [11] 4,095,775 Hotham [45] Jun. 20, 1978 [54] PARTICLE EVALUATOR Primary Examiner-Conrad J. Clark Attorney, Agent, or Firm—Reed C. Lawlor [76] Inventor: Geoffrey A. Hotham, 1130 Channel Dr., Santa Barbara, Calif. 93108 [57] ABSTRACT [21] App1.No.: 642,915 The invention is employed for evaluating particles, such as droplets of aerosol sprays suspended in a gaseous [22] Filed: Dec. 22, 1975 medium. A stream of the particles to be analyzed is [51] Int. Cl.2 ................... .. G01N 21/00; G01N 21/18; ?owed into a narrow sample zone across the optical axis GOZB 21/34 of a beam of light. Scattered radiation from the particles [52] US. Cl. .................................. .. 356/102; 356/ 181; is focused on the image plane in which a photosensitive ' 250/574; 350/95 surface is located. Images of particles formed there are [58] Field of Search ............. 356/102, 103, 246, 181; reproduced on a ?uorescent or phosphorescent display 250/574; 350/63, 89, 95 screen of a cathode ray tube. A scale on the screen is employed for measuring the dimensions of the particles. [56] References Cited The con?nement of the stream of the mixture to about U.S. PATENT DOCUMENTS the depth of focus of the objective lens of the camera reduces effects of out-of-focus particles and permits 3,609,043 9/1971 Simmons et a1. .................. .. 356/102 evaluation of individual particles. 3,614,231 10/1971 Sham ..................... .. 356/102 3,646,352 2/ 1972 B01 et al. .. 356/ 102 3,720,470 3/ 1973 Berkham ............................ .. 356/ 103 21 Claims, 7 Drawing Figures U. S. Patent June 20,1978 ' Sheet 2 of2 4,095,775 QR.m, QQ ‘ 9 TNKQR6?V“ .. M. k.$/ 4,095,775 1 2 Numerous other methods having a super?cial resem PARTICLE EVALUATOR blance to the present invention, involve transmitting light from a detected particle to a photodetector such as This invention is concerned with an improved system a photoelectric or photomultiplier tube. Such systems for evaluating particles and has particular application to are disclosed in Solkowski et al US. Pat. No. 3,504,183, the measurement of the sizes of such particles, espe Goldberg US. Pat. No. 3,536,898, Shaw US. Pat. No. cially liquid aerosol particles that originate in aerosol 3,614,231, and B01 et al US. Pat. No. 3,646,352. In such sprays. systems, the diminution in'the amount of light reaching While the invention may be employed particularly the photodetector, when a particle enters the light for the measurement of the sizes of droplets, it may also beam, causes the photodetector to produce a pulse of be employed to study solid particles such as asbestos electric current. Such systems suffer from the disadvan particles and coal dust. It may also be employed in the tage that they are incapable of distinguishing between study of impaction, evaporation, agglomeration, and several particles that lie within the ?eld of view of the droplet disintegration. For simplicity of explanation, optical system at any one time and a single large particle the invention will be described particularly with refer that lies in the ?eld of view at another time. ence to'the measurement of the sizes of such liquid aerosol particles suspended in air. Of the prior art now known to me, only the Simmons The importance of this invention resides particularly et al US. Pat. No. 3,609,043 involves the formation of ’ an image of particles on an image recording system as in in the fact that aerosol sprays are developed in many a vidicon system. circumstances where the inhalation of the spray is dan 20 gerous to the user. This applies, for example, to deodor Such a system is also described in my article titled ant sprays, hair sprays, paint sprays, air fresheners, in “Sizing Aerosols in Real Time by Pulsing UV Laser secticides, and the like, where the spray is likely to be Machine” which appears as National Bureau of Stan inhaled by the user. Such a spray is usually dispensed by dards Special Publication 412 under date of May 7, 1974 releasing it through a nozzle from a pressurized con 25 and which was issued in October 1974. I have employed tainer by depressing a simple valve that normally blocks such a system for over a year. Both the Simmons et a1 the passage through the nozzle when the valve is not system and my prior system suffer from the disadvan depressed. tage that out-of-focu's particles that may be present In the design of such spray nozzles, it is important to produce images that interfere with sharp imaging of the design the nozzle in such a way that the particles or in-focus particles. Sometimes in such systems, pro droplets formed in the spray are neither excessively grammed computers are employed to discriminate be large nor excessively small. If they are too large, such as tween particles to be studied and other particles that in excess of 1000 micrometers in diameter, the spray might interfere with such study. tends to deposit on the skin or other object being In one form of the best mode of practicing this inven sprayed as a ?owable liquid. If they are too small, such 35 tion now contemplated, a vidicon camera is aligned as below about 10 micrometers in diameter, they are with a laser-beam source along a common optical axis, easily inhaled into and retained in the lungs, where they and the optical axis is entirely enclosed within a light may prove to be toxic. tunnel that extends from the light source to the screen When applied to particle size measurement the inven of the vidicon camera except for a narrow sampling gap tion relates particularly to a system in which optical 40 between the ends thereof. In another form of the best images of the particles to be studied are recorded on mode of practicing this invention now contemplated, magnetic tape or on ?lm, or the like, and the recordings the vidicon camera tube is oriented with its axis on a line are then reproduced as optical images and then sized by which is normal to the optical axis of the laser-beam making measurements directly on the optical images of source while the lens of the vidicon camera lies on that the particles. When applied to other methods of evaluat 45 common optical axis, and an apertured mirror is located ing particles the recordings are reproduced as optical on the optical axis in a plane at 45° to the optical axis. images and then studied visually or otherwise. An aperture in the mirror is located at the point where While many systems have been developed for mea the laser beam is focused to provide for spatial suppres suring particle size, this invention is advantageous be sion of the laser beam, but reflection of the radiation cause of the fact that sharp optical images of the parti scattered by the droplets to a focal plane at the face of cles are formed, and fogging of such images is reduced the vidicon camera. In an alternative arrangement for by con?ning the sample of the gas containing the parti separating the rays of the laser beam from the scattered cles to a very short space along the axis of a light beam radiation, the laser beam is de?ected by a small mirror within the con?nes of about the depth of focus of an to the side of the optical axis and the scattered radiation optical system that forms an optical image of particles is transmitted directly to the vidicon camera tube along on an image recording medium. the optical axis. In one prior art system, somewhat similar to the pres In either form the particles to be evaluated or sized ent system, “holographic” images are formed on ?lm are projected into the sample zone along a path that is and then these holographic images are reproduced by a transverse to the optical axis X-—X. holographic reproducing system. Such a system is re 60 IN THE DRAWINGS ferred to in an article by W. W. Zinky appearing in FIG. 1 is the schematic diagram of the invention; Annals NY-ACAD-SCI 158:781-52 (1969) titled “Ho FIG. 2, FIG. 2A, and FIG. 2B are diagrams repre logram Techniques for Particle Size Analysis”. senting arrangements for con?ning the low of a gas In a somewhat similar system such as that disclosed in sample into the focal region of the objective system to a Silverman et al, US. Pat. No. 3,451,755, a record is 65 narrow zone along the optical axis; made of the diffraction patterns produced by the parti FIG. 3 is a cross-sectional view of the particle size cles and measurements are made on the diffraction pat measuring system taken along the optical axis and terns in order to calculate the sizes of the particles. showing some features of construction in more detail; 4,095,775 3 4 FIG. 4 is a diagram employed to explain how the lens ate with a magni?cation of 10X, as described hereinaf of different focal lengths and magni?cation characteris ter, the depth of focus is 333 micrometers. tics are located relative to the crossover point of the By restricting the flow of the sample under study laser beam; and substantially entirely to a narrow region at a sample FIG. 5 is a diagram employed to explain a second plane that is conjugate relative to the photosensitive form of the invention.

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