US2443178A - Piezoelectric vibrator - Google Patents

Description

je 15, 194. H. BEN|OFF 2,443,178 l PIEzoBLEcTnIc vmmoa Filed April 3, 1941 2 'sheets-sheet 2 INVENTOR HUGO ENIOFF Y (f t. I?" u ATTORNEY Patented June 15, 1948 PYIEZOELECTRIC VIBRATOR Hugo Benioif, La Canada, Caif., assignor, by

mesne assignments, to Submarine Signal Company, Boston, Mass., a corporation of Delaware Application April 3, 1941, Serial No. 386.583 claims. (ci. 111-386) The present invention relates to a piezoelectric vibrator adapted to be used particularly for producing and receiving compressional waves of a frequency in and above the range of audibility of sound to the human ear. More particularly the present invention is applied to submarine signaling for the purpose of producing a beam of compressional waves at high frequency and for receiving compressional waves.

The device of the'present invention is particularly useful not only for determining the direction of an unknown vessel in the vicinity of the listening craft having the present apparatus, but it also may be used for sending a beam lof sound and picking up the echo reflected from a distant reflecting object, thereby determining by usual methods the distance and direction of the distant vessel.

The present device may also be used for other purposes, for instance, as protecting channels and harbors and serving as directive beacons and signaling elements ln the prevention of collisions in water ways and on the seas and also for vi-v brating and treating liquids.

The present invention will be more fully described in connection with an embodiment of the same which is described in the specification below and illustrated in the drawings in which Fig. 1 shows a section through the device on the line I-I of Fig. 2; Fig. 2 shows a section view on the line II-II of Fig. 1; and Fig. 3 shows a perspective of one of the crystal units used in the apparatus. y

1n the drawings, I is a metallic case of rectangular shape with open faces on both sides, the element I, therefore, forming merely a shell to which the covers for both sides are attached to form the complete housing. On one side the cover is formed with a plate 2 at the back edge of which a peripheral flange 3 extends to which is integrally formed a rearwardly extending flange 4 which comes in contact with a shoulder in the housing I and is rigidly fastened to it by being welded about its whole contact surface, as indicated at 5. The plate 2 has mounted on its rear side within the casing a group of piezoelectric units t which, as indicated in Fig. 2, are nested together in a rectangular fashion. These units, as indicated in Fig. 2, are nested with nine units in a row and nine rows, making eightyone units in all. This number may be increased or decreased, if desired, and they may be arranged in a different manner, as indicated in my prior copending application Serial No. 344,363, led July 8, 1940, Patent No. 2,406,792, dated Cil September 3, 1946. In the arrangement indicated in the present invention these units are tapered slightly from the base towards the top, as indicated. The tapered units comprise a vbase element 'l from which a narrowing taper extends upward to the top member 8 forming two recessed sections on opposite sides of the unit in which the piezoelectric crystals are rmly cemented with the top, bottom and back edges of the crystals cemented to the surface of the recess on the top, back and bottom sides. The bases of the units 8 are aligned on the plate 2 by the ridges 2' and are also cemented to the plate 2 as well as being held in Vplace by means of the machine screw Il which passes through the center of the unit into the .plate 2. The cement t2 between the unit and the base is essentially in this structure in order to provide a continuous acoustic transmitting path from the crystal units to the outer water or propagating medium. The units are separated at their bases only by a very narrow rib or ridge so that practically they cover the entire plate surface. This makes it possible to consider the plate thickness as merely added to the base of thel unit in computing the frequency of the system and provides, therefore, the same effect as if the unit were operating alone with the added thickness of mass at its base.

The crystals, which may be Rochelle salts or other similar types, are provided with two inner electrodes I2 and I3 which contact with the surfaces 9 andv I0 or which have leads which contact the plate 2, thus grounding these electrodes to the plate 2 and the casing of the structure. The external electrodes I4 and I5 are connected to the bus-bar I6 by means of the leads il and I8 which are taken upwards directly from the electrodes I4 and I5 and because of the taper of the units are .spaced away from them. These units are so proportioned with mass members comprising the elements l and 8 at either end so as to provide a node either in the ange 3 or somewhere on a line in the base element 1.

The Rochelle salt or piezoelectric units so formed with the crystals mounted in recesses on the side faces of the polyhedral units constitute reactance members in which the .top and bottom masses bearing upon the crystals at the top and bottom sides of the recesses form compressional bearing surfaces parallel to the radiating surfaces while the electrodes on the surfaces of the crystal parallel to the longitudinal axis of the vibrating unit form the electric potential surfaces from which the generated potential due to the vibration of the crystal will be taken to the receiving system. An opening 22 is provided at one end of the unit through which the electrical connecting cables may be taken, one of which may be grounded to the casing and the other of which is connected to the other electrode terminals through means of the bus-bars I8.

As indicated in Fig. 1, the back of one side of the casing is closed by means of the cover 23 which rests against a flange 24 extending inwardly from the casing I. A watertight gasket 25 may be inserted between the cover 23 and the flange 24 and suitable bolts 2B may hold the cover in place with the rubber gasket 25 in between the two clamped surfaces. r

Fig. 3 shows in perspective a single crystalmounting unit corresponding to the mounting unit indicated in Fig 1. It will be noted from this unit that the recesses at the sides of the units are rectangular in shape and that in the metal of the block there are provided slots I9 and 20 on either side in which are positioned conducting ribbons I7 spaced away from the metal of the unit and extending directly to the electrode le. The electrode ifi is spaced away from the edge of the recess a distance equal to or greater than the thickness of the crystal so that the potential gradient at no point within the crystal is greater than at any point on the line directly through the crystal from electrode to electrode. If desired, the conductor Il may be brought over to a mounting block 28 and held in place between two insulating washers 29 and 30 being joined at the same time to the conducting ring or terminal 37 from Which a connector 32 extends upward to the bus-bar i6 or other connecting element. The back electrodes. which are not shown in Fig. 3. may also be connected by conducting ribbons 33 and 34 to the terminal 35 which is supported by means of the screw 36 against the mounting unit, whereby these electrodes are positively grounded to one side of the system. It will be appreciated that the device as a projector of high frequency compressional waves is directive where the linear dimensions of the projectors radiating surface 2 is large as compared to the wave length in the medium of the wave to be propagated, and that likewise it is directive in the reception of compressional waves at these high frequencies, and for this purpose theunit may be mounted to rotate with the plate or radiating surface 2 in a vertical direction for the purpose of producing a horizontal beam or for directively receiving compressional waves approaching from the direction normal to the surface of the plate or radiating element 2.

Having now described my invention, I claim:

1. A piezoelectric vibrator comprising a casing having a plate at one side whose linear dimensions are large as compared with the Wave length of the compressional wave to be propagated, means joining and supporting said plate to the rest of said casing by a thin peripheral flange, a plurality of piezoelectric crystal units, each comprising a longitudinalvibrating system formed -With rectangular masses at either end and having on opposite sides recesses adapted to hold piezoelectric crystals for longitudinal vibration, means mounting said units in continuous rows closely adjacent one another within said casing on said plate, said piezoelectric elements having electrode surfaces extending substantially in the direction of the longitudinal axis of said vibrating units and compressional surfaces parallel to said plate surface.

2. A piezoelectric vibrator comprising a casing having one side formed with its face as a radiating surface with a thin flange about its periphery joining it to the rest of the casing, a great number of longitudinal vibrating units having rectangular bases, means screwing and cementing said units to the inner surface of said side forming the radiating surface in said bases, said units being arranged to cover substantially the entire surface, and longitudinally vibratable piezoelectric crystals mounted and cemented in recesses in opposite sides of said units, said crystals having electrodes substantially parallel to said longitudinal axis.

3. A piezoelectric vibrator comprising a casing having one side formed with its face as a radiating surface with a thin flange about its periphery joining it to the rest ofthe casing, a great number of longitudinal vibrating units having rectangular bases, means screwing and cementing said units to the inner surface of said side forming the radiating surface in said bases, said units being arranged to cover substantially the entire surface, the units being tapered slightly away from the bases leaving a free space about the back ends of the units, longitudinally vibratable piezoelectric crystals mounted and cemented in recesses 0n opposite sides of said units, and electrodes cemented to said crystals on faces parallel to the sides of said units, and electrode connections extending straight upwards from said electrode faces to common connections.

4. In a piezoelectric vibrator, a piezoelectric vibrating unit comprising a longitudinally vibrating polyhedral metallic member having recessed side faces, piezoelectric crystals mounted and cemented in said recesses having external electrodes on said crystals parallel with said faces, said electrodes being spaced away from said metallic member to maintain an equalization of electric stresses in said crystals.

5. In a piezoelectric vibrator, a piezoelectric vibrating reactance unit consisting of a longitudinal Vibrating element having mass members joined by elastic elements, a plurality of piezoelectric crystals securely mounted in said unit with opposite end faces forming compressional bearing surfaces against the mass members and said crystals having electrodes mounted on said crystals in planes substantially parallel to the longitudinal axes, said element being tapered longitudinally.

HUGO BENIOlF'F.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,495,429 Nicolson May 27, 1924 2,086,891 Bachman July 13, 1937 2,405,186 Benioff Aug. 6, 1946 2,406,792 Benioi Sept. 3, 1946 FOREIGN PATENTS Number Country Date 145,691 Great Britain July 28, 1921 613,799 France Sept. 4, 1926

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