US2753543A - Transducers - Google Patents

Description

W. H. RYMES Jul 3, 1 956 TRANSDUCERS 2 Sheets-Sheet 1 Filed Aug. 28, 1952 "Hill 'r ii/ i: ll DJ.

IIIIIIH a El l ji W. H. RYMES TRANSDUCERS July 3, 1956 2 Sheets-Sheet 2 Filed Aug. 28, 1952 l9 7' TOIPIVE Y United States Y atent TRANSDUCERS William H. Rymes, Randolph, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass, a corporation of Delaware Application August 28, 1952, Serial No. 306,875

4 Claims. (Cl. 340-41) This invention relates to a compressional wave transducer and, more particularly, relates to means for increasing the effective driving surface of a transducer to achieve greater directivity of the energy radiated therefrom.

An object of this invention is to provide means for increasing the effective driving surface of a compressional wave transducer.

Another object of this invention is to provide a compressional wave transducer having improved directivity for a given size.

A further object of this invention is to provide means for varying the focal length of the beam of a compressional wave transducer as a function of the shape of a reflector mounted near one face of said transducer.

As is well known in the art, the intensity of compressional wave energy at different points equidistant from a transducer is dependent upon the dimensions of the driving surface compared with the wave length of said energy. The energy is largely confined within a diver ing beam Whose axis is perpendicular to the center of the driving surface. The angle of spread of the beam is proportional to the ratio of the wave length of said energy to the dimensions of the driving surface. The larger this ratio is made, that is, the larger the area of the driving surface for a given frequency, the greater the directivity from the transducer.

Pursuant to this invention, the directivity of a transducer having a first generating surface in contact with the medium through which transmission of energy is required and a second generating surface opposite said first surface is increased with the aid of one or more reflectors so positioned adjacent said second surface of the transducer that the compressional wave energy radiated from said second surface and reflected from said reflector or reflectors is in phase with the energy radiated from said first surface.

By adjusting the angle of the reflector or reflectors and thus the angle of incidence of the energy reaching the reflector after emission from said second surface, the beam of compressional wave energy may be focused at any desired depth in said surrounding medium.

In the drawings:

Fig. l is a central longitudinal section view of a first embodiment of a transducer assembly according to the invention;

Fig. 2 is a view in elevation of the transducer assembly of Fig. 1 illustrating certain principles of operation and omitting the transducer supporting means for the sake of clarity;

Fig. 3 is a plan view, partly in section, of the transducer assembly of Fig. l, the section being taken through line 33 of Fig. 1;

Fig. 4 is a fragmentary detail view of the transducer used in the assembly of Figs. 1 to 3;

Fig. 5 is a sketch illustrating certain operating principles ofthe transducer assembly shown in Figs. 1 to 3;

Patented July 3, 1956 Fig. 6 is a view illustrating the effective driving surface obtained with a conventional transducer;

Fig. 7 is a view showing the effective driving surface obtained with the transducer assembly shown in Figs. 1 to 3;

Fig. 8 is a second form of reflector which may be used in a transducer assembly according to the subject invention;

Fig. 9 is a view in elevation, partly in section, of a second embodiment of a transducer assembly according to the invention utilizing the reflector shown in Fig. 8;

Fig. 10 is a view illustrating the effective driving surface obtained with a conventional transducer having an area equal to the base of the pyramidal re-entrant portion of the reflector of Fig. 9; and

Fig. 11 is a view showing the effective driving surface of the transducer assembly shown in Fig. 9.

Referring to Figs. 1 to 4, a transducer assembly, generally indicated by reference numeral 10, comprises a magnetostrictive transducer 11 molded in a substance 12 having an acoustical impedance substantially equal to that of the medium into which the transducer is to operate. For example, if the medium is sea water, the substance 12 may be a type of rubber whose wave impedance is substantially equal to that of the aforesaid medium.

Although substance 12 is shown as a solid mass, it is possible to use castor oil or other liquids having a suitable acoustical impedance, in which case it is necessary to provide proper supporting means for transducer 11.

The molded mass 12 is encased in a housing 13 which, although shown as rectangular in Fig. 3, may be any convenient shape, such as rectangular, circular or oval. Housing 13 may be made of any material having sufficient rigidity and mechanical strength.

Transducer 11 is illustrated in detail in Fig. 4; the body portion 11 comprises a plurality of laminations 14 having elongated slots 15 through which winding 16 may be inserted. The terminals of winding 16 are adapted to be connected to the usual receiving and transmitting means, as is well known in the art.

The transducer need not be limited to the exact details shown in Fig. 4, and other types of magnetostrictive transducers may be used. Moreover, crystal transducers may be used in lieu of magnetostrictive transducers, if desired.

Transducer 11 has two opposed radiating surfaces 20 and 21; surface 20 is adapted to contact a medium through which the compressional wave energy is to be propagated.

A multi-surface reflector 17, which is opaque to compressional wave energy, is positioned in housing 13 adjacent surface 21 of transducer 11. Reflector 17 may comprise a solid metallic plate, as shown in Figs. 1-3, or may comprise a metallic backing plate to which a coating having good reflecting properties is cemented or otherwise attached. This coating, for example, may consist of a combination of cork and neoprene having several air cells. Since air is a good reflector of compressional wave energy, the reflecting power of reflector 17 may be enhanced.

Energy radiated from surface 21 impinges upon re flector 17 and is reflected therefrom. The path of the compressional waves radiated from surfaces 21 of trans ducer 11 is shown by the broken lines 23 of Fig. 2. An inspection of Fig. 2 indicates that not only the energy from surface 20 but also that from surface 21 is available for propagation into the desired transmission medium in contact with surface 20'.

The radiating surface 20 resulting from the transducer of Figs. 1 to 3 when reflector 17 is omitted is shown in Fig. 6. The effective radiating surface 26, resulting when transducer 11 is provided with a reflector, is shown in Fig. 7. For a reflector whose sides are positioned at an angle of forty-five degrees with surfaces 20 and 21, as shown in Figs. 1 to 3, the area of the driving surface is doubled when a reflector is used.

words, the time required for the compressional waves from the various points on surface 21 of transducer 11 to travel to reflector 17 and be reflected back to surface 20 is dependent upon the degree of spacing between the reflector and the transducer. By moving the entire reflector up and down, an optimum distance d is reached at which the reflected compressional waves emerge from surface 20' in time phase with the compressional waves radiated directly from surface 20 of transducer 11. By adjustment of the angles 6 shown in Fig. 5, a focusing of the beam may be accomplished For example, if angles n at p and are equal to forty-five degrees, and if either of angles 6 or or both are made larger than forty-five degrees, the compressional waves reflected from surfaces 24- and 25 will be bent inward toward the center of the transducer. At some point in the transmitting medium, dependent upon angles 9 or 0 or both and also dependent on the angles p and the beam will be focused. Since the wave length of the compressional waves is of the order of four inches, the amount of change in angle 6 necessary to focus the beam at a distance, say 100 feet, will be only a fraction of a degree. For this reason, therefore, the adjustment of angles 0 and 0' is somewhat critical. It is preferable, therefore, to preset the angle 0 which surfaces 24 and 25 of reflector 17 make with either surfaces 20 and 21 of transducer 11 to correspond to the focal length desired and build this angle into the transducer.

The shape of the beam pattern may also be varied by selection of reflectors. A second possible compound reflector 17' for use with transducer 11 is shown in Figs. 8 and 9. Reflector 17' comprises a metallic sheet in the form of a frustum of a pyramid having a pyramidal reentrant portion whose apex lies in the plane of the base 27 of said frustum. The angles formed by any two adjacent surfaces impinged by the compressional waves from transducer 11 are made substantially equal to forty-five degrees. Reflector 17' is positioned adjacent to and spaced from surface 21 of transducer 11, as in the case of reflector 17 of Figs. 1 to 3 and 5.

The distance between the base 27 of reflector. 17 and surface 21 determines the phasing between the compressional waves emitted directly from surface 20 of transducer 11 and the reflected compressional waves arriving at surface 20.

As in the embodiment of Figs. 13 and 5, the beam focus may be adjusted by varying slightly the slope of one or more of the surfaces of reflector 17 V V The active surface of transducer assembly of Fig. 9 in the absence of reflector 17' is equal to the area of surface of the transducer 11 and is shown in Fig. 10, while the active surface obtained when reflector 17 is used with the same transducer is shown by Fig. 11. Because of the reflection of energy from the surfaces of the pyramidal reentrant portion, as well as from the surfaces of the frustum of the pyramid, in the reflector 17' of Figs. 8 and 9, the effective driving surface of the transducer assembly of Figs. 8 and 9 is of square configuration, rather than rectangular, and furthermore, is oriented at an angle of forty-five degrees with respect to that obtained without the use of the reflector 17'. For this reason, the effective driving surface shown in Fig. 11 is positioned at an angle of forty-five degrees relative to that shown in Fig. 10. A comparison with Fig. 10 indicates that the surface area and hence the directivity of transducer 10 of Fig. 9 is increased over that for a similar transducer without a reflector.

The reflectors herein shown and described are merely illustrative; other reflectors may be used besides the two types shown and described to accomplish an increase in the efiective driving surface of the transducer.

This invention is not limited to the particular details of construction, materials and processes described, as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

' What is claimed is:

1. A device for transmission of compressional wave energy through a medium comprising'a transducer having a pair of opposed vibrating surfaces, said transducer being mounted within a body of material having a wave impedance substantially equal to that of said medium and having one of said surfaces in physical contact with said medium, a multi-surface reflector secured to said body and positioned adjacent the other of said opposed surfaces, said reflector being in the form of a frustum of a pyramid having a pyramidal reentrant portion whose apex lies in the plane of the base of said frustum, said reflector being adapted to reflect incident energy from said other surface in phase with the energy radiated from said one surface, thereby increasing the effective driving surface of said device to obtain greater directivity therefrom.

2. A device as recited in claim 1 wherein said surfaces of said reflector are disposed at an angle of forty-five degrees with said opposed transducer surfaces.

3. A device for transmission of compressional wave energy through a medium comprising atransducer having a pair of opposed vibrating surfaces, said transducer being mounted within a body of material having a wave im pedance substantially equal to that of said medium and having one of said surfaces in physical contact with said medium, a multi-surface reflector secured to said body and positioned adjacent the other of said opposed surfaces, said reflector being in the form of a frustum of a pyramid having a pyramidal reentrant portion whose apex lies in the plane of the base of said frustum, said reflector being adapted to reflect incident energy from said other surface in phase with the energy radiated from said one surface, thereby increasing the effective driving surface of said device to obtain greater directivity therefrom, said portions of said reflectors forming said frustum being disposed at an angle with respect to said opposed vibrating surfaces differing from forty-five degrees by a slight amount so that said beam is focused.

4. A device for transmission of a beam of compressional wave energy through a medium comprising a transducer having a pair of opposed vibrating surfaces, said transducer being maintained Within a body of material having a wave impedance substantially equal to that of said medium and having one of said surfaces in physical contact with said medium, a reflector secured to said body and positioned adjacent the other of said opposed surfaces, said reflector having a first, pair of adjacent surfaces arranged at an angle of substantially forty-five degrees with said other opposed surface and a second pair of angularly adjustable surfaces, said second pair of surfaces being inclined at an angle with respect to said vibrating surfaces differing slightly from forty-five degrees such that the beam is focused at a point Whose distance from said transducer is dependent upon the deviation of said angle from forty-five degrees.

References Cited in the file of this patent UNITED STATES PATENTS 2,005,741 Hayes June 25, 1935 2,398,117 Rost Apr. 9, 1946 2,491,982 Kincart Dec. 20, 1949 V FOREIGN PATENTS 379,649 Italy Apr. 1, 1940

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