US3703652A

US3703652A - Electroacoustic transducer

Info

Publication number: US3703652A
Application number: US117619A
Authority: US
Inventors: Masahiro Noda
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1970-02-25
Filing date: 1971-02-22
Publication date: 1972-11-21
Anticipated expiration: 1989-11-21
Also published as: FR2161734A1; DE2109013A1; DE2109013C3; GB1331841A; FR2161734B1; DE2109013B2

Abstract

An electroacoustic transducer includes an electroacoustic transducer element and inner and outer acoustical reflection plates respectively positioned within an exterior to the transducer element. The electroacoustic transducer element emits an acoustic signal, such as an ultrasonic wave, from both the inner and outer surfaces of the element by expansion and contraction oscillations caused by an electrical signal applied thereto. Similarly, the transducer element can generate an electrical signal by applying an acoustical oscillation thereto. The inner and outer acoustical reflection plates will reflect acoustic oscillations emitted from the inner and outer surfaces in an axial direction in such a manner that a variable range of directivity may be realized and a high acoustic output obtained. The acoustic reflection plates are provided at suitable inclined angles so that the phases of acoustic oscillations emitted in the radial direction from both the inner and outer surfaces of the cylindrically shaped element of the electroacoustic transducer will essentially coincide.

Description

D United States Patent [15] 3,703,652 Noda 1 Nov. 21, 1972 1 ELEQIROACOUSTIC Primary Examiner.|. D. Miller TRANSDUCER Assistant Examj'ner-Marlt O. Budd 72 lnventor: Masahlro Noda,Amagasaki,.lapan [73] Assignee: MitsublshiDenki Kabushiki Kaisha, [57] ABSTRACT Tokyo'japan An electroacoustic transducer includes an elec- [22] Filed: Feb. 22,1971 troacoustic transducer element and inner and outer 130] Foreign Application Priority Data Feb. 25, 1970 Japan ..45/l6082 [52] U.S. Cl ..310/8.3, 310/96, 340/8 FT [51] Int. Cl. ..H04r 17/00 [58] Field of Search ..3 l0/8.2-8.7, 9.1, 310/94, 9.6; 340/10, 8, 8 PT [56] Reierences Cited UNITED STATES PATENTS 3,302,163 1/1967 Andrews, Jr. ..340/8 FT 2,855,526 10/1958 Jones ..3l0/8.3 X 2,005,741 6/1935 Hayes ..340/8 FI 3,325,779 6/1967 Supernaw et al ..340/8 FT 3,271,596 9/1966 Brinkerhoff ..3l0/8.3 X

l a. M I

Appl. No.: 117,619

acoustical reflection plates respectively positioned within an exterior to the transducer element. The electroacoustic transducer element emits an acoustic signal, such as an ultrasonic wave, from both the inner and outer surfaces of the element by expansion and contraction oscillations caused by an electrical signal applied thereto. Similarly, the transducer element can generate an electrical signal by applying an acoustical oscillation thereto. The inner and outer acoustical reflection plates will reflect acoustic oscillations emitted from the inner and outer surfaces in an axial direction in such a manner that a variable range of directivity may be realized and a high acoustic output obtained. The acoustic reflection plates are provided at suitable inclined angles so that the phases of acoustic oscillations emitted in the radial direction from both the inner and outer surfaces of the cylindrically shaped element of the electroacoustic transducer will essentially coincide.

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PRIOR ART PRIOR ART PRIOR ART INVENTOR.

MASAH I R0 NO DA m i/1115a: a waE PATENTEBNDVZI m2 mvsmoa MASAHIRO NODA AN ELECTROACOUSTIC TRANSDUCER BACKGROUND OF THE INVENTION 1 Field Of The Invention This invention relates generally to a transducer having a cylindrically shaped electroacoustic transducer element which may be expansion and contraction oscillated in the radial direction of the cylinder, and more particularly, to a transducer having two acoustic reflection plates, one being within the cylindrically shaped transducer element and the other being exterior thereto.

2. Description Of The Prior Art Conventionally, electroacoustic transducers used for ultrasonic impulse proof devices, substance movement detectors, and the like have included a cylindrically shaped electroacoustic transducer element and a single acoustical reflection plate. The electroacoustic transducer element will emit an acoustic oscillation when excited by an electrical signal and will generate an electrical signal when excited by an acoustic or mechanical oscillating signal. In the prior art transducers, the single acoustic reflection plate was provided on either the inside or the outside of the cylindrically shaped electroacoustic transducer element. Thus, with the prior art transducers, the acoustic oscillations emitted from the inner surface of the cylindrically shaped electroaeoustic transducer element would be of an opposite phase to that of the acoustic oscillations emitted from the outer surface of the cylindrically shaped element. In order to eliminate the problem caused with the generation of opposite phase oscillations, in the past, the acoustic oscillations emitted in the radial direction from either the inner surface of the cylinder or the outer surface of the cylinder would be reflected in the axial direction of the cylinder and the remaining portion of acoustical oscillations would be shielded with an acoustic shielding plate.

While somewhat satisfactory, one of the problems with using only the acoustic oscillations emitted from one surface of the cylindrically shaped element was that only a small amount of acoustic oscillation could be effectively utilized. Thus, the efficiency of the single reflection plate transducer is rather low. Moreover, with the prior art transducer using a single reflection plate, the range of directivity in the axial direction of the cylinder for changes in the angle of the acoustic reflection plate has been too narrow.

SUMMARY OF THE INVENTION Accordingly, it is one object of the present invention to provide a new and improved unique electroacoustical transducer having a high efficiency when an electrical signal is generated by exciting a transducer element from either an acoustic or mechanical oscillation.

It is another object of the present invention to provide a new and improved unique electroacoustical transducer having a high efficiency and a broad and variable range of directivity in the axial direction of the cylindrically shaped element thereof.

One other object of the present invention is to provide a new and improved unique electroacoustical transducer wherein the acoustical oscillations emitted from both the inner and outer surfaces of the cylindrically shaped element thereof can be effectively utilized.

Briefly, in accordance with the present invention, these and other objects, are in one aspect attained, by the provision of an electroacoustical transducer which utilizes a pair of acoustical reflection plates one mounted within a cylindrically shaped transducer element and the other mounted exterior thereto such that the acoustic oscillations emitted from both the inner and outer surfaces of the cylindrically shaped transducer element will be axially directed when the element is expansion and contraction oscillated by an electrical signal. In a particular embodiment, the inner acoustical reflection plate is of a conical shape and the outer acoustical reflection plate is a conical cylinder having a notched portion on the upper edge thereof. The angles of the two reflection plates are appropriately determined so as to increase the power of acoustical oscillation and to provide a variable sharp to broad range of directivity. Additionally, it is possible to select a sectional shape of directivity by shielding a part of an acoustical reflection plate with an acoustical shielding plate.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete appreciation of the invention will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying Drawings, wherein:

FIG. 1 is a view of a cylindrically shaped electroaeoustical transducer element showing the various modes of oscillation thereof;

FIG. 2 shows a plane view and a longitudinal sectional view of a conventional prior art transducer having a cylindrically shaped electroacoustical transducer element and a single acoustical reflection plate therein,

FIG. 3 shows a plane view and a longitudinal sectional view of another conventional prior art transducer having a cylindrically shaped electroacoustical transducer element and an acoustical reflection plate therein;

FIG. 4 shows a plane view and a sectional side view of one preferred embodiment of an electroacoustical transducer in accordance with the present invention; and,

FIG. 5 shows a plane view, a longitudinal sectional view taken along the line bb of the plane view, and a longitudinal section view taken along the line c--c of the plane view of an electroacoustical transducer in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the Drawings, wherein like reference numerals designate identical, or corresponding parts throughout the several views, and more particularly to FIG. 1 thereof, wherein the modes of mechanical oscillation of a cylindrically shaped electroacoustical transducer element of the present invention is shown and may be made of a porcelain of barium titanate, lead zirco-titanate, or the like. The electroaeoustical transducer element 1 may be expansion oscillated in the direction shown by the arrows 2 and may be contraction oscillated in the direction shown by the arrows 3. It will be apparent that the cylindrically shaped electroacoustic transducer element 1 will emit acoustic oscillations by causing expansion and contraction oscillations when excited with an electrical signal supplied by a proper source, and on the other hand will generate an electrical signal when acoustically or mechanically oscillated from a proper source.

Referring now to FIG. 2, a conventional prior art transducer is shown in a plane view (A) and in a longitudinal sectional view (B). The transducer includes the cylindrically shaped electroacoustic transducer element 1, an acoustic shielding plate 4, and a conical acoustical reflection plate mounted within the transducer element 1. The acoustical reflecting plate 5 is shown as having an angle dz, for reflecting acoustic oscillations. The symbol P shows the direction of transmission of the reflecting acoustic oscillations.

Referring now to FIG. 3, another conventional prior art transducer is shown in a plane view (A) and in a longitudinal sectional view (B). Here, the transducer again includes the cylindrically shaped electroacoustic transducer element 1, and an acoustical shielding plate 6. However, differing from the prior art transducer of FIG. 2, an acoustical reflection plate 7 is herein provided and the same is mounted exterior to the transducer element 1 and has an angle d), for reflecting acoustical oscillations therefrom.

In the conventional embodiments shown in FIGS. 2 and 3, the

reflection plates

5 and 7 may be made of any material having an acoustical impedance such as a metal, for example, of copper, aluminum or the like, or a plastic or the like.

In the conventional transducers described above, it should be understood that since the same have only a single reflection means that the acoustic oscillations emitted from the inner surface of the cylindrically shaped electroacoustic transducer element 1 will be of a phase opposite to that of the acoustic oscillations emitted from the outer surface of the cylinder. Because of the oppositely phased produced acoustic oscillations, only those emitted from either the inner surface of the cylindrically shaped electroacoustic transducer element or those emitted from the outer surface of the cylinder may be effectively utilized with that portion of the acoustic oscillations not utilized being properly shielded. Thus, for example, either the acoustical oscillations emitted from the inner surface or the outer surface of the cylinder 1 in the radial direction will be reflected to the axial direction of the cylinder 1 by utilizing the

acoustic reflection plate

5 or 7, while the remaining acoustic oscillations will be shielded by using either the

acoustic shielding plate

4 or 6. Since the conventional transducers, as described above with reference FIGS. 2 and 3, only include a single reflection means and thereby may effectively utilize the acoustic oscillations emitted from either the inner surface or the outer surface of the cylindrically shaped transducer element, but not both, the efficiency thereof will be extremely low and thereby may not be effectively utilized. Moreover, with the above described conventional transducers, the range of directivity in the axial direction of the cylinder is extremely narrow for changes in either of the angles 4), or (b, of the acoustical reflection plates.

Referring now to FIG. 4, one preferred embodiment of the present invention for overcoming the above described disadvantages of the prior art is illustrated in a plane view (A) and in a longitudinal sectional view (B). The electroacoustic transducer of FIG. 4 includes a pair of

reflection plates

5 and 7, the first plate 5 being mounted within the cylindrically shaped electroacoustic transducer element 1 and the second plate 7 being mounted exterior thereto. The inner acoustical reflection plate 5 has an angle of a, of reflection and the acoustical reflection plate 7 has an angle of o of reflection and the same again may be made of a metal, plastic, or the like. It should be noted that the acoustical reflection plate 5 may be formed in a conical shape, but it should be understood that the same is not so limited and that, for example, the inclined straight lines of the reflection plate 5 may be of a rounded nature. The outside or exterior acoustical reflection plate 7 may be formed of a conical cylindrical shape and again, the inclined straight line portions thereof may be rounded.

In the transducer of the present invention, the cylindrically shaped electroacoustic transducer element 1 may be oscillated by an electrical signal provided from a conventional source such that acoustic oscillations are emitted from both the inner and outer surfaces of the element 1. Again, the phase of the acoustic oscillations emitted from the inner and outer surfaces are initially opposite each other. However, with the present invention, the angle d5, of the inner acoustical reflec tion plate can be adjusted with the angle (1!): of the outer acoustical reflection plate so that a differential is provided between the transmission path of the acoustical oscillations emitted from the inner surface of the cylinder and the transmission path of the acoustical oscillations emitted from the outer surface of the cylinder such that the phase of all of the acoustical oscillations emitted from the transducer will substantially coincide with each other in the axial direction of the cylinder. Accordingly, the magnitude of the usable acoustical oscillations is greatly increased and likewise the efficiency of the electroacoustic transducer. Moreover, with the present invention, the directivity of the transducer can be varied over a wide range by properly selecting the angle d2, of the inner acoustical reflection plate and the angle d), of the outer acoustical reflection plate.

By way of particular examples of the above described embodiment of the present invention, the directivity was 10 of half value angle, when the electroacoustic transducer element 1 had an outer diameter of 25 mm., an inner diameter of 21 mm., and a height of IO mm. The electroacoustic transducer element 1 was excited by a 40 kHz. electrical signal and the angle of the inner acoustical reflection plate 5 was and the angle d), of the outer acoustical reflection plate 7 was 50.

The directivity was also 10 of the half value angle when the electroacoustical transducer element 1 had an outer diameter of 38 mm., an inner diameter of 34 mm., and a height of 10 mm. Again, an electrical signal of 40 kHz. was applied to the electroacoustical transducer element 1; however, here the angle a, of the inner acoustical reflection plate 5 was set to and the angle d, of the outer acoustical reflection plate 7 was set to 45. Under the same conditions, when the angle d1, of the outer acoustical reflection plate 7 was set to a directivity of 10 of the half value angle was obtained.

Referring now to FIG. 5, another preferred and alternative embodiment of the present invention is shown in a plane view (A), in a sectional view (B), taken along the line b-b of the plane view, and in a sectional view (C) taken along the line c-c of the plane view. In FIG. 5, the outer acoustical reflection plate 7 is beveled and the acoustical shielding plate 8 is placed on top of the beveled portion as shown in FIG. 5(A).

It should now be apparent that in accordance with the present invention, acoustic or electrical oscillations emitted from both the inner and outer surfaces of the cylindrically shaped electroacoustical transducer element thereof which are of opposite phase to each other can, by the provision of a pair of reflection plates, be changed in the axial direction such that the phases of the acoustic or electrical oscillations are made to coincide, whereby the power of usable acoustical or electrical oscillation is greatly increased. Moreover, it should now be apparent that with the present invention the directivity of the acoustic or electrical oscillations can be readily changed by properly selecting the angles of both of the acoustical reflection plates thereof.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. Thus, for example, although ordinarily the sectional view of extent of the acoustic or electrical oscillations emitted from conventional transducers is generally of a circular nature, it is possible to attain various shapes within the extent of directivity by properly shielding a portion of the transducer with an acoustical shield plate. Thus, for example, instead of a circular shaped emission, a square, rectangular or the like shaped beam may be obtained. Additionally, while the present invention has been illustrated to show the cmittance of an acoustical oscillation by exciting the transducer with an electrical signal, it should be readily understood that the transducer could be utilized to emit an electrical signal by exciting the same with an acoustical oscillation. Thus, the transducer of the present invention can be utilized for receiving, as well as transmitting acoustical signals. Moreover, while the present invention has been described as emitting an acoustical signal of the ultrasonic type, the invention is not so limited and may be equally used for transmitting acoustical sounds in other ranges, such, for example, as in the audible range. It is therefore to be understood that within the scope of the appended Claims, the invention may be practiced otherwise than as specifically described herein.

WHAT IS CLAIMED AS NEW AND DESIRED TO BE SECURED BY LETTERS PATENT OF THE UNITED STATES IS:

1. An electroacoustical transducer comprising:

a cylindrically shaped electroacoustical transducer element,

a first conical acoustical reflection plate having a given acoustical impedance mounted within said transducer element for changing the direction of transmission of acoustical oscillations therefrom, and,

a second acoustical reflection plate having an acoustical impedance which is the same as said given acoustical impedance, said second acoustical reflection plate mounted in said electroacoustical transducer abutting an exterior surface of said transducer element for changing the direction of transmission of acoustical oscillations therefrom, said first and second reflection plates having different respective reflecting angles relative to said electroacoustical transducer element for producing different length transmission paths between said transducer element and said first and second reflection plates so that the phases of all of the acoustical oscillations reflected from said first and second reflection plates will substantially coincide with each other in the axial direction of the cylindrically shaped electroacoustical transducer element.

2. A transducer according to claim 1, wherein said second acoustical reflection plate is a conical shape and is beveled at the upper edge thereof.

3. A transducer according to claim I, wherein a shielding plate is mounted to said transducer for shielding a part of said transducer to control the acoustical directivity thereof.

Claims

1. An electoacoustical transducer comprising: a cylindrically shaped electroacoustical transducer element, a first conical acoustical reflection plate having a given acoustical impedance mounted within said transducer element for changing the direction of transmission of acoustical osciallations therefrom, and, a second acoustical reflection plate having an acoustical impedance which is the same assaid second acoustical reflection plate mounted in said electroacoustical transducer abutting an exterior surface of said transducer element for changing the direction of taansmission of acoustical oscillations therefrom, said first and second reflection plates having different respective reflecting angles relative to said electroacoustical transducer element and said first and second reflection plates so that the phases of all of the acoustical oscillations reflected from said first and second reflection plates will substantially coincide with each other in the axial direction of the cylindrically shaped electroacoustical transducer element.

2. A transducer according to claim 1, wherein said second acoustical reflection plate is a conical shape and beveled at the upper edge thereof.