US1923619A - Process for electrooptical reg - Google Patents

Description

Aug. 22, 1933. 1,923,619

A. GUERBILSKY PROCESS FOR THE ELECTROOPTICAL REGISTERING OE SOUNDS OR ANY 0TH ELASTIC WAVES led May 1951 QJTWMWAA/V/Z/W Patented Aug. 22,- 1933 PATENT OFFICE ELECTROOPTICAL REG- PROCESS" FOR ISTER OF SOUNDS OR ANY OTHER ELASTIC WARES 7 Alexis Guerbilsky, Paris, France Application May 23,1931, Serial No. 539,606, and

in France May 24, 1930 4 Claims. (Cl. 179-1003) My invention relates to processes for the electro-optical registering of sounds or 'any other elastic waves, which are based on the use of piez'o-electric crystals for modulating luminous waves in accordance with the sounds or other waves to be recorded. 2

These processes involve the use of an oscillatory circuit and of a piezo-electric crystal having both exactly the same frequency, so that the luminous variations which can be recorded by the known methods. Up to this time it has been found impossible for practical 'purposeto obtain a satisfactory result through processes of that kind, due to the acuity 'of resonance of the piezo-electric crystals. Very slight accidental variations 'of the frequency of-the oscillatory circuit or of the frequency of "ther'crystals are sufficient for destroying tuning. Furthermore, said acuity of resonance of the crystals is accompanied bya small logarithmic decrement of their oscillations which renders modulation very difficult unless special'precautions are taken. Thus, for example, some authors have recommended an arti- 330 ficial damping of the oscillations of the crystals.

, 5 these disadvantages by. making use, for the recording of. elastic waves, of fpiezo electric resonators adapted to vibrate in tune not with one single-frequency, but with 'several frequencies,

forinstancewith'a wholerange of frequencies. My invention also includes several particular arrangements making it possible to effect, for practical purposes, in a-simple and efficient manner, theiegistering' of elastic waves in accordance with'theprinciple of my invention.

My: invention m'akesit possible to register elasticwaves, and, in particular, sounds,':as well by the method of inscription=called variable density method which consists in causingthe luminous intensity of a light beam of fixed di-- .50v rection to .vary as by the so .called"variable ordinates method which consists in'va'r'ying the direction of a light beam of fixed intensity.

In the first case (variable density method), I actupon the piezo-electric resonators by means of an alternating electrostatic field having the same frequency as the resonators or a harmonic of said resonators, and I cause that field to be modulated in accordance with the amplitude of the elastic vibration to .be registered. In that case, I obviate the disadvantage result- '60 ing from the acuity of resonance by making use 1 of resonators corresponding to different frequencies.

The method of utilizing the vibrations of the resonators for the production of optical effects may be of any suitable type. J Thus in my U. S. patent application Ser. No. 272,319 filed Apr. 23, 1928, and inmy French patent filed Sept. 21, 1929, I have disclosed several such methods. In particular I may make use of a prism of quartz whose frequencyvaries from one point to another according to its thickness. By suitably choosing the angle. of the prism, it is possible to obtain, according to the case, luminous "spots of. different dimensions. ,75 Besides, .said angle may be chosen very small 1 and the prism may diflFer but by part of the thickness of a fringe from a plate having parallel faces as the one referred to by some authors but whichdid not give satisfactory results. It should be noticed that in this case as in the case of a group of quartz described in'my above mentioned patents, the localized resonances must not necessarily be utilized with polarized light. It is quitepossible to make use of the Giebe and Scheibe'efiect or of any other known phenomenon. 7 'It is also possible, instead of, modulating the intensity of the field to modify its frequency, which has for its result to produce a displace- .9 ment of the luminous spot; It is possible to soadjust said displacements with respect to an opening such as a slot that they cause variations of" the intensity of the light beam issuing from said aperturethat are proportional to the 5 frequency of the field." Nowit is possible to cause said frequency to depend on the elastic condenser from which depends the frequency. of I the field; The displacements of said membrane 1 can cause the capacity of the condenser to vary, 10'5 either as a result of the variation in the dis- 'tance between the armatures, or owning 110413119 variation of pressure of a gas that would constitute the dielectric of the, condenser. It is also possible to useto this effect a microphone 1 10'.

and to cause the microphonic current to act upon the frequency of the above mentioned field through any known method. However it is evidently preferable to avoid the microphone and to use a variable capacity condenser which does not necessitate any amplifying arrangement.

In the second case (variable ordinates meth- 0d) the device for carrying out the process will be the same but the displacements of the luminous spot will be directly utilized.

Inthe case of feeble energies to be registered or of variable condensers that are not very sensitive I may amplify the relative variations of the frequency that act upon the resonators by the following method:

I produce by means of the condenser variations of a very high frequency; said variations are caused to produce beats with a fixed frequency, and c is the difference of the two frequencies which is caused to act on the two resonators. In that way, the absolute variations of the frequency determined directly by the condenser and of the frequency acting on the resonators are the same, but the relative variations are greater for the last mentioned frequency, since it is smaller.

It should be well understood that in the preceding specification, as well as in what follows, the term piezo-electric resonator is intended to designate not only piezo-electric crystals, but also combinations of said crystals with other bodies, and even substances that are rendered, through any suitable process, capable of vibrating in resonance under the action of an alternating electrostatic field. It is further possible to replace the piezo-electric resonators by other resonators, for instance by resonators capable of vibrating under the action of an electro-magnetic field which would replace, in that case, the electro-static field. It is also possible to make use of magneto-striction. In order to utilize, in that latter case the action of the vibrating rods, several processes may be chosen, such as interference fringes, which, of course may be also made use of in the case of piezoelectric crystals.

Preferred embodiments of my invention will be hereinafter described with reference to the appended drawing, given merely by way of ex ample, and in which: 7

Fig. 1 is a diagrammatical view of an oscillatory circuit provided with the piezo-electric resonator;

Fig. 2 is a diagrammatical view of the optical system;

Figs. 3a. and 3b are curves adapted to illustrate the operation of the system; and

Figs. 4 and 5 are detail views.

In Fig. 1, I have shown a standard arrangement of oscillatory circuit whose frequency is determined by coil L and the capacity of variable condenser C as above explained.

I have shown in Q a prism of quartz placed between two armatures 1 and 2, connected to the terminals of a coil L coupled with coil L.

In Fig. 2 I have shown the optical arrangement. The source of light S is placed at the focus of a lens Z. The parallel beam passes through a polarizer P and an analyzer A in the extinction position. Between P and A is placed the prism of quartz Q, and in order to reestablish extinction, a compensator Q. Compensator Q consists, for instance of a plate of quartz having the same thickness as Q, but rotated through an angle of with respect to Q. The system is completed by a lens L forming an image of Q on the sensitized film f disposed behind a slot a.

When condenser C is not subjected to any pressure, prism Q is not energized, the frequency of the current being outside of the range of frequencies for which it resonates. On the contrary, when a pressure, due for instance to acoustic vibrations (human voice, noises to be registered and the like) acts upon condenser C, its capacity varies and together with it the frequency of the electric oscillations. A part of the prisms then breaks into oscillations, and its image, formed on the film, is lighted in such manner that the film is recorded.

If the angle of the prism is very small, the luminous part will extend along a relatively great length and the variations of the frequency will produce displacements of the luminous spot along the spot, the spots corresponding to the various frequencies overlapping each other, so that their succession in time will be recorded on the film by a white side and a black side, 7 the line of separation being a sinuous curve correspondingto the displacements of the spot, and therefore to the frequency of the electric circuit, which itself depends on the pressure exerted on the condenser. M

Figs. 4 and 5 show examples of piezo-electric resonators. In Fig. 4, the resonator comprises a single crystal whose faces 3 and 4 make a small angle. In Fig. 5 the resonator consists of a plurality of crystals of decreasing length,- The planes passing through the angles 5 and no 6 of the crystals also make in this embodiment a very small angle. Said angle should preferably be so small that the breadth of the part of the resonator that is set in vibration for-- a given frequency may be greater than the amplitude of the displacement of said part under the action of the variations of frequency to be registered.

In Fig. 3 I have shown two curves a and b.- Curve 0. shows, for example, the quantity of light as a function of the frequency when the prism is replaced by a plate having parallel faces.

Curve b indicates the same relation for prism s Q. The ordinates are proportional to the quantity of light of the image of any part of the prism.

The essential difference between these two cases will be easily shown by these twofiguressj' It should be well understood that my invention is not limited to the above described embodiments, but that changes may be made therein without departing from the principle of my invention as comprehended within the scope" of the appended claims.

What I claim is:

1.'A device for the electro-optical registering of elastic waves, and in particular of sounds which comprises, an electric circuit, a source of high frequency current in said circuit, means for varying the intensity of the current in said circuit that are sensitive to the action of said elastic waves, a piezo-electric crystal of nonuniform thickness in the direction of its electric axis coupled with said circuit, and optical means adapted to cooperate with said crystal.

'2. A device for the electro-optical registering of elastic waves, and in particular of sounds, which comprises in combination, an electric circuit, a source of high frequency current in said circuit, means, sensitive to the action of said elastic waves, for varying the intensity of the current in said circuit, a piezo-electric crystal having two opposite faces making an angle with each other disposed in said circuit so that said faces of said crystal are those across which extends its electric axis, and optical means adapted to cooperate wtih said crystal. 1

3. A device for the electro-optical registering of elastic waves, and in particular of sounds, which comprises in combination, an electric circuit, a source of high frequency current in said circuit, means sensitive to the action of said elastic waves for varying the intensity of the current in said circuit, a prism of quartz having two opposite faces that make a small angle with each other coupled with said circuit sothat the said faces of the prism of quartz are those across which its electric axis extends, and optical means adapted to cooperate with said prism of quartz.

' 4. A device for the electro-optical registering of elastic waves, and in particular of sounds, which comprises in combination, an electric circuit, a source of high frequency current in said circuit, means sensitive to the action of said elastic waves for varying the intensity of the current in said circuit, a piezo-electric resonator consisting of a series 'of piezo-electric crystals having substantially parallel opposite faces disposed in adjacent relation with one another, the edges of said crystals being substantially located in two planes making a small angle with each other, said piezo-electric resonator being coupled to said electric circuit in such manner that said faces of the crystals are parallel to the field in which the resonator is placed, and optical means adapted to cooperate with said resonator.

ALEXIS GUERBILSKY.

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