US 2797399 A
Description (OCR text may contain errors)
June 25, 1957 L. W. CAMP ETAL UNDERWATER TRANSDUCER" Filed March a, 1955 l2 IO- I49 15 I49 a -23 17 v IO- INSULATION LEON w. CAMP WILLIAM A. DANIEL INVENTORS ATTORNEY tromechanically UnitedStates Patent G 1 2,797,399 UNDERWATER TRANSDUCER Application March 8, 1955, Serial No. 492,895
9 Claims. (Cl. 340-=8) ,"This invention relates to underwater transducers for convertingelectrical oscillations into traveling pressure waves in liquids, and vice versa, and is particularly adapted to utilize longitudinally vibratile'ceramic elenients which are electromechanically responsive.
object of the invention is to provide a simple, reliable, eflicient and inexpensive transducer employing elecresponsive ceramic bodies as, the active elementse. 1 1
fOther more specific objects and features of the invention ,will appear from the description to follow.
Briefly, a transducer in accordance with the invention consists, in its preferred form, of an array of electromechanically responsive ceramic cylinders in spaced relation, all bonded at one end .to a first common electrode and all bonded at their other ends to a second common electrode. The cylinder and electrode assembly is contained in a fiat rubber case or body adapted (when used for depth sounding) to be secured against the under surface of a boat. The front wall of the case juxtaposed to the active elements is constituted by a thin diaphragm which forms a watertight barrier through which vibrations are readily transmitted between the front ends of the active elements and the exterior water. The portion of the caseback of the active elements is a rubber wall spaced from the rear ends of the elements by soundabsorptive material that constitutes a poor medium for propagation of acoustic energy to and from the rear ends of the elements.
A full understanding of the invention may be had from the following detailed description with reference to the drawing, in which:
Fig. l is a front view of a transducer in accordance with the invention.
Fig. 2 is a sectional view taken along the line IIII of Fig. 1.
Referring to the drawing, the transducer therein disclosed comprises a body 10 molded or otherwise formed from rubber or similar material and having a pair of countersunk faces 10a and 10b, respectively, juxtaposed to each other. Exterior of the countersunk faces 10a and 10b, the front surfaces 100 and 10d, respectively, of the body 10 are flat and parallel. Two mounting holes 11 are provided near the middle of the body for screwing or bolting it against the under surface of a boat with the rear surface 10d lying against the boat and the front surface 100 facing downwardly.
As will be observed from Fig. l, the recessed or countersunk faces 10a and 1011 are located adjacent one end of the body, which is extended in wedge form to a leading edge 10e, which is pointed toward the forward end of the boat so that it divides the water and reduces turbulence at the active face. A cable 12 containing the electrical conductors is preferably extended from the rear end (the end opposite the leading edge 102) of the body 10. The cable extends through an aperture in a neck portion 10 of the body which is compressed tightly about the cable by a clamp 13.
i In the particular model shown, there are seven active elements 14 in the form of solid cylinders of an electromechanically responsive ceramic, such as barium titanate, supported in holes 10g provided in that portion of the body 10 extending from the front face 10a to the rear face 10b, hereinafter referred to as the inner wall. The holes are dimensioned to snugly receive the elements 14 and support them in relatively fixed relative positions. Each element 14 has electrodes 14a and 141) on its front and rear ends, respectively, intimately bonded to the ceramic material. These electrodes are formed by painting the elements with silver paint and baking them to leave a thin film of metallic silver. The front electrodes 14a of all the ceramic elements 14 are bonded by a suitable cement 15 to a lamination 16 of metallic foil which constitutes one electrical terminal. The other electrodes 14b of the elements 14 are similarly cemented to a common terminal consisting of a disk 17 of metallic foil. It is found that by sandblasting the surfaces of the foil terminals that are cemented to the electrodes 14a and 14b, the surfaces are roughened sufficiently to penetrate the cement at numerous points and make electrically conductive contact with the electrodes.
. An additional hole 10h is provided extending between' central high potential conductor 12a and a concentriclow potential conductor 12!) surrounding it. The central conductor 12a is connected to the rear electrical terminal 17, and the outer conductor 12b is connected to the front. electrical terminal 16 and to a shielding electrode 19. which is positioned back of the rear electrode 17' and electrically and acoustically insulated therefrom by one or more layers 21 of insulating material, such as air cell rubber or Corprene.
To seal the mechanism described from the outside water, the front terminal foil 16 is covered by a flexible impervious diaphragm 22 which fills the recess defined by the front face 10a and is cemented to the body 10 at its edges. The diaphragm 22 may consist of a lamination of acoustically suitable plastic material, such as fiberglass, and the front foil 16 may be bonded to the rear surface of the diaphragm 22 prior to assembly. The rear recess back of the rear face 10b is closed by a rear rubber wall 23 which is dimensioned to fit against a countersunk face 119 in the body 10 and is cemented thereto.
Water pressure against the diaphragm 22 is opposed by the supporting force of the ceramic elements 14 and by the front face 10a of the inner wall of the body, the two being arranged flush in a common plane. The rear ends of the elements 14 may or may not be flush with the rear face 10b. However, they should either be flush with the rear face or projected thereabove, as shown in Fig. 2, to insure that the rear ends of the elements 14 will be supported through the insulating pads 21 and the shield electrode 19 by the rear wall 23, which is subjected to the same hydrostatic pressure as the diaphragm 22.
The front terminal 16 and the diaphragm 22 are relatively flexible, so that the diaphragm does not necessarily vibrate as a complete piston, but rather each portion of the diaphragm juxtaposed to an active unit 14 vibrates with the front face of that unit. The terminals 16 and 17 are preferably made of very thin metal foil so that their mass is inconsequential.
The ceramic elements 14 may be of any well-known material, such as barium titanate, and are pre-polarized in accordance with well-known practice, so that they respond to mechanical vibrations applied thereto through the diaphragm 22 to generate potentials: between their electrodes 14a and 14b and respond to alternating electrical potentials applied to their electrodes to expand and contract longitudinally and thereby vibrate the dia- Patented June 25, 1957 phragm 22-; Itis custornaryto make vibrating devices of this type of length equal to one-halfwavelength ofan inner wall of rubberlike material ofsubstantial thickness having parallel: front and rear faces and defining a hole extendingbetween said faces,- a rear wall of rubberlike material parallel toand: spaced from said rear face, a diaphragm, element covering said front face, and lateral wall means defining with said rear wall and diaphragm element: a watertight enclosure; a longitudinally vibratile electromechanically-responsive ceramic element positioned in and fitting said hole whereby it is supported by said inner wall, saidelement having electrodes on its end surfaces; said diaphragm having a conductive inner surface-layer bonded to and constituting a front electrical terminalfor the front electrode of said ceramic element; and a rear conductive electrical terminalelement overlying and. bondedto the rear electrode of said ceramic element.
2;VA transducer according to claim 1 in which said inner wall has. a plurality of additional holes extending between. said faces and a plurality of additional ceramic elements in said additional holes, each like the mentioned ceramic element and bondedat its ends to said diaphragm element and: said rear electrode element, respectively.
2,797,399 7 a a e 3. A depth sounding transducer according to claim 1,
adapted to be mounted against the under-side of-a boat in which: said body is of substantially uniform thickness except at said front and rear faces, which are countersunk therebelow to such extent that said diaphragm element and said rear wall element are flush with the front and rear surfaces of the body.
4. A transducer according to claim 3 in which the leading portion of said body extends substantially away from said faces and the extended portion of the sides,
ofsound-absorptive material-between said rear electrode":
element andisaid rear wall. I
8. A transducer according to claim 7 including-1 an electrostatic shield consisting of a layer of electrically" conductive material-between said sound-absorptive matef ria-l-and-said rear wall.
9'. A transducer according to claim 1 in which said} front and rear electrical terminals each consist ofa metal" foil overlying and cemented to its associated ,electrode. and the foil surface next to the electrode is rough to provide high pointspenetrating the cement and electrically contacting the electrode;