US 3019660 A
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Feb. 6, 1962 w. wELKowlTz 3,019,660
ULTRAsoNIc TRANSDUCER Filed April 26, 195e INVENTOR. WALTER WELKOM/wz 8% MMM/1.014,
QTTOPNEY Biiili Patented Feb. 6, i962 3,019,660 ULTRASGNIC TRANSDUCER Walter Welkowitz, Metuchen, NJ., assigner to Gulton gndustries, Inc., Metuchen, NJ., a corporation of New ersey Filed Apr. 26, 1956, Ser. No. 580,881 6 Claims. (Cl. 741) My invention relates to ultrasonic transducers and in particular to those transducers whose active, driving element is a hollow cylinder with -a small radiating surface and wherein a radiator is employed to acoustically transform the small radiating surface to a larger one.
When a hollow cylindrical electromechanical driving element vibrates in length mode (parallel to the axis of the cylinder), it is usually a very inefiicient sound radiator. It is necessary to provide means for acoustically transforming the small radiating area into a much l-arger radiating area. Many other methods and techniques have been employed to obtain these results but up to now, it has been diflicult to obtain good results using hollow cylindrical driving elements. The hollow cylinder is preferred since it -is easy to cast the various ceramics in this shape. It is best to keep the driving element of reasonable size (neither very large nor very small) in order to produce the elements economically with little production shrinkage.
Accordingly, it is a principal object of my invention to provide an ultrasonic transducer wherein it is possible to acoustically transform a small radiating area into a greater radiating area.
It is a further object of my invention to provide an i acoustic radiator whose acoustic resistance is substantially equal to that of the active driving element and which presents -a much greater radiating area to the `transmission medium than the radiating area of the active driving element.
It is a still further object of my invention to provide an ultrasonic transducer whereby it is possible to obtain more than the usual amount of energy from the active driving element.
ther objects and advantages of my invention will be apparent during the course of the following description. In the accompanying drawings, forming a part of this application, and in which like numerals are employed to designate like parts throughout the same,
FIGURE 1 is 'a plan View of a preferred embodiment of my invention in which the driving element is a hollow cylinder formed of polarized electrostrictive material, to one end of which is aixed a solid radiator, and
FIGURE 2 is a cross-sectional View along the line 2-2 of FIGURE l.
In the drawings, wherein for the purpose of illustration is shown a preferred embodiment of my invention, the numeral designates a polarized electrostrictive driving element. I prefer to fashion the driving element 10 of material composed largely of barium titana'te but any other material or type of electromechanically sensitive body, which can be formed in the shape of a hollow cylinder and driven in its length mode, parallel to the axis of the cylinder, may be employed with equally good results. Radiator 11 is joined to 1t? at joint 1S using a high strength thermo-setting plastic adhesive of epoxy resin and having a very low compliance. I prefer to fashion radiator 11 of brass which has an acoustic resistance approximating that of barium titanate but other solid materials such as various aluminum alloys may also be used. If materials other than barium titanate are used for the drivin y element, it is conceivable that a solid other than brass will have an acoustic resistance more closely approximating that of the material of the driving element. The front face of 11 is designated by 12. I
prefer to fashion face 12. as a flat face in a single plane but I have found that those having a slight curvature may also be utilized with equally goed results. Curve 13 generates the outer surface of revolution and is seen to taper outwardly from where radiator 11 is joined to element 10 as shown in FlGURE 2 and curve 14 generates the cylindrical portion of the outer surface of 11. Curve 15 generates the inner surface of revolution which terminates in point 16. Point 16 is substantially in the same plane las the plane of the junction between the surfaces of revolution generated by curves 13 and 14. 17 designates the `air space within element 10 and radiator 11.
Element 10 is driven by the usual power generator 19 which applies excitation voltage to the electrodes (not shown) such that element 10 is driven in its length mode, parallel to the axis of the cylinder. The Vibration of element 10 causes radiator 11 to vibrate and thereby transmit an acoustical wave from the whole area of face 12 into the transmission medium.
ln use, the combination is mounted so that face 12 is in contact with the liquid and .the balance of radiator 11 and all of element 10 are in air. The transducer may be mounted in the hull of a vessel or in the side of a tank so long as the above conditions are maintained.
If it is desirable to submerge the combination in liquid, it is necessary to enclose all of the unit except face 12 in a liquid-tight container (not shown). This container may be of metal or other suitable material and is attached to the unit at the outer surface of revolution generated by curve 14.
Ultrasonic transducers of my invention may be utilized at frequencies from approximately 10 kc. to approximately 200 kc.
By way of example :and without limiting the scope of my invention, I have found the following dimensions to produce excellent results at an excitation frequency of 40 kc.:
Length of 10:2", outside diameter of 10:21AM', thickness of 1tl=%, length of 11:4", diameter of 12:4, length of 14:1/16 and diameter of 11 (at its midlength) =2% These dimensions are for a driving element composed largely of barium titanate and a radiator of brass. For these materials, and for a 2 diameter cylinder, the following formulas will give excellent results:
y for the driving element where f is in kilocycles and l is in inches; for the radiator f where fis in kilocycles and l is in inches.
I have had excellent results: when curve 13 is of the form y=yoeax and 15 Iis its mirror; when curve 13 is of the form y: yo
While I have described my invention by means of spe- 3 cie examples and in a specic embodiment, I do not wish to be limited thereto, for obvious modifications will occur to those skilled in the art without departing from the spirit of my invention or the scope of the subjoined claims. Y
Having thus described my invention, claim:
1. An ultrasonic transducer comprising a hollow, cylindrical, polarized electrostrictive, electromechanicaliy sensitive body; a radiator; and power generating means; said radiator being aixed to one end of said electromechanicallly sensitive body by means of a high strength, thermo-setting adhesive of low compliance, said radiator having a ace opposite said electromechanically sensitive body greater in area than that of the portion of said radiator atlixed to said electromechanically sensitive body so that the outer surface of said radiator tapers outwardly from said electromechanically sensitive body toward the face of said radiator, said outer surface being a surface of revolution which terminates a small distance from said face, where said surface of revolution becomes a cylinder, said radiator having an inner surface of revolution smaller in area than said outer surface, said inner surface being generated by a curve which is the mirror of the curve generating said outer surface, said inner surface terminating in a point which is substantially in the same plane with the points at which said outer surface becomes a cylinder, said radiator having approximately the same -acoustic resistance as said electromechancally sensitive body, said electromechanically sensitive body being vibrated in length Inode by said power generating means.
2. An ultrasonic transducer as described in claim 1 wherein said face of said radiator lies in a plane.
3. An ultrasonic transducer as described in claim 1 wherein the curve generating said tapered outer surface 4 is vof the form yyom, where x is distance along laxis, y is distance away from axis, e is an exponential number, and ais a constant.
4. An ultrasonic transducer asfdescribed in claim 1 wherein the curve generating said tapered outer surface is of the for-m where x is distance along axis, and y is distance away from axis.
5. An ultrasonic transducer as described in claim 1 wherein the curve generating said tapered outer surface is of the form y==yo cosh ax, Where x is distance along axis, y is distance away from axis, and a is a constant. 6. An ultrasonic transducer as described in claim 1 vwherein said electromechanically sensitive body is composed largely of `barium titanate.
'References Cited in the 'tile of this patent VUNITED STATES PATENTS France Jan. 24, 1940 Fay Mar. 26, 1920