US2438936A - Electromechanical transducer - Google Patents

Description

P 1948. w. P. MAsoN ELECTROMECHANICAL TRANSDUCER Filed 001;. 6, 1943 zlll/rl v NON-CORROJ'IVE MID/UM IION-CORROJ'IVE mum 1:10AM.

MEDIUM 7 n r/lilllll iiiii INVENTOR W P MASON IVON' C ORROS I V! MEDIUM NON'CORROSIVE MEDIUM ATTORNEY Patented Apr. 6, 1948 ELECTROMECHANICAL TRANSDUCER Warren P. Mason, West Orange. N. J., 'assignor toBell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application October 6, 1943, Serial No. 505,159 .1 Claim. (01. 177-386) This invention relates to compressional wave transmission in the ultrasonic range and has for its object the provision of means to transmit signals of high power over a wide range.

In submarine detection work it is often desirable to get a large amount of power into a wide beam at relatively high frequencies. If a conventional fiat plate radiator is employed these requirements are mutually exclusive, for great power requires a large area and at high frequencies this inherently gives a very sharp pattern of power distribution. 7

In accordance with the present invention means are employed to equalize the intensity of the compressional waves over a wide angle so as to change the characteristic sharp lobe pattern into a very broad lobe pattern. In general this may be accomplished by making the shape of the face of the radiator convex in shape, approximating a spherical section.

In accordance with one form of the invention a crystal array is mounted on a curved plate so that each crystal face is approximately in a spherical surface.

In accordance with another and a preferred form of the invention an array of crystals is mounted on a fiat plate and a lens shaped body having a, high index of refraction to ultrasonic compressional waves is interposed between the crystal array and the sea water.

A feature of the invention is a plurality of transducers arranged to transmit compressional waves from a surface approximately spherical in contour.

Another feature of-the invention is an array of transducer faces formingan approximately spherical surface.

Another feature of the invention is a radiator formed of a plurality of transducers having their faces approximately in a plane surface and a lens-like diaphragm interposed between said surface and the outer, surface of said radiator.

Other features will appear hereinafter.

The drawings consist of a single sheet having four figures, as follows:

Fig. 1 is a vertical section of an electromechanical transducer in which the crystal array is mounted on a plate having a generally spherical contour; 1

Fig. 2 is a similar figure showing the crystal array secured to 'a flat mounting plate and the rubber diaphragm in the form of a lens of generally spherical contour;

Fig. 3 is a similar figure showing the use of a diaphragm formed like a Newtonian lens; and

Fig. 4 is a similar figure showing the use of a plurality of lens-like diaphragms to give greater spread to the transmitted compressional waves.

In the drawings various forms of electromechanical transducers are shown as being immersed in water. In Fig. 1 the transducer consists of a rigid housing I and a sound transparent plastic diaphragm 2, which may be clamped together to provide a watertight casing. Within such casing there is secured a mounting plate 3 having a generally spherical shape. Secured to this mounting plate there are a plurality of crystal mosaics 4, 5 and 6, each having its resonator I, 8 and 9 respectively. The casing is filled with a liquid such as castor oil or a mixture of dimethyl phthalate and xylene hexafluoride which like the rubber of which the diaphragm is generally constructed has substantially the same mechanical impedance as the sea water in which the transducer is immersed.

Since thecompressional waves produced by a crystal mosaic travel in a line normal to the end faces thereof or along the longitudinal axis of the combination of the crystal mosaic and its backing resonator the effect of mounting them on a spherical surface is to produce an aggregate wave spread out as indicated by the curved lines to the right of the device.

A single crystal mosaic will of course produce a compressional wave having a wide spread but where a plurality of crystals must be used, in order to produce a wave of sufiicient intensity to be useful, the effect is usually highly directional and this effect increases with the frequency. Therefore to produce a wide wave front a construction such as shown in Fig. 1 must be employed.

An alternative method of spreading the wave front from a transducer constructed from a plurality of crystal mosaics isto mount them on a hat plate so that'their faces are in one plane and then to interpose a lens-shaped diaphragm in the path of the transmission therefrom. In Fig. 2, the element In represents a steel casing to which a plastic lens-shaped diaphragm H is secured. In the assembly of these two elements there is a mounting plate l2 to which are secured a plurality of crystal mosaics l3, M and I5 and their respective backing resonators i6, I 1 and ill.

The lens-like diaphragm It is constructed of a material having a transmission velocity greater than the transmission velocity oi water, whereby an acoustic lens with a negative focal length is produced. By way of example, there is commercially available an oil resisting type of synthetic rubber which has a density and a transmission velocity Through these figures the quantity corresponding to the index of refraction in a lens is 1.50 5l0 "1, ac-1x10 where Dw is the transmission velocity of water and aiis the transmission velocity of this synthetic rubber. From standard lens formulae, the focal lengths of the lens formed from two segments of a sphere is LXSBIE f where t is the thickness of the lens and 2a is the width. If, for example, we wish to spread out a beam over a 45-degree angle, with the focal length i must be given by Then the thickness t is and the thickness is nearly half the width.

To cut down the total weight of rubber and to cut down the loss due to the acoustic path length through the rubber, a lens of the Newtonian type shown as element IS in Fig. 3 can be constructed. The curvature of any part is the same as that of element Ii in Fig. 2 but the thickness is much less. It appears that with the type of synthetic rubber mentioned above, any spread up to 45 degrees should be obtainable. To get a larger angle, say 90 degrees, would be impossible with a single lens" on account of the thicknessdimensions, but this should be possible by arranging two 45-degree lenses as indicated in Fig. 4. The first lens would have a virtual focus at the same point as the element IQ of Fig. 3, but when the diverging beam is sent through the second lens 21 a further divergence is obtained by the relation 7Ff2 and the position of the second virtual center is at half the focal length of the second lens.

In each of Figures 2, 3 and 4, thespread of the beam is indicated by dot-and-dash lines.

It will be apparent that other arrangements may be made in accordance with the properties of available plastic materials, due consideration being had with regard to other properties necessary in the use of these devices.

What is claimed is:

In ultrasonic compressional wave transmitting means the combination of a plurality of transducers mounted in closely adjacent relationship and having an aggregate comparatively great area of transmitting surface. the individual surfaces of said transducers being substantially in a common surface whereby a wave conforming in shape to said surface is transmitted therefrom, a housing for said transducers, a plurality of lens shaped diaphragms for closing the open end of said housing and directly in the path of a beam transmitted from the surfaces of said transducers for retaining within said housing a liquid transmission medium and for excluding therefrom the sea water in which said device will be immersed, said diaphragms being formed of elastic material having a high index of refraction to ultrasonic compressional waves whereby the waves transmitted therethrough are dispersed in a beam widened successively by each said lens shaped diaphragm, said elastic material having transmission characteristics closely approaching the transmission characteristics of sea water, a liquid transmission medium filling said housing and the space between said diahragms for transmitting waves from the faces oi said transducers to and through said diaphragms, said liquid medium having transmission characteristics closely approaching the transmission characteristics of sea water and apertures in a diaphragm both of whose faces are in contact with said liquid medium for equalizing the ressure in said different bodies of said liquid medium. a

' WARREN P. MASON.

REFERENCES CITED UNITED STATES PATENTS Number Name Date 2,143,175 Waite Jan. 10, 1939 2,122,010 Savage et al June 28, 1938 1,587,107 Edwards June 1, 1926 2,216,949 Kellogg Oct. 8, 1940 1,472,558 Fessenden et al. Oct; 30, 1923 2,147,649 Halnes Feb. 21, 1939 2,169,304 Tournier Aug. 15, 1939 2,283,285 Pohlman May 19, 1942 1,471,547 Chilowsky et al. Oct. 23, 1923 2,399,820 Morgan May 7, 1946 2,384,465 Harrison Sept. 11, 1945 FOREIGN PATENTS Number Country Date 546,202 Great Britain July 2, 1942 279,878

Great Britain Mar. 8, 1928

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