Electroacoustic transducer

Abstract

An electroacoustic transducer is provided that combines the properties and advantages of the known concepts of the thickness mode transducer and of the bending transducer with each other. For this purpose, an electroacoustic transducer is provided, which includes a housing and an oscillating structure. The oscillating structure is formed by at least one piezoelectric element, a diaphragm, and an acoustic transmitter. It is provided that the diaphragm is designed as a bending transducer, and the acoustic transmitter is designed as a thickness mode transducer.

Claims

1. An electroacoustic transducer for emitting sound waves to an external environment and sensing sound waves received from the external environment, comprising: a housing; an oscillating structure including a piezoelectric element, a diaphragm above the piezoelectric element, and an acoustic transmitter above the diaphragm, so that the diaphragm is at a first side of the acoustic transmitter and the external environment is at a second side of the acoustic transmitter that is opposite the first side of the acoustic transmitter; and an electrical connecting device contacting an electrode of the piezoelectric element, wherein: the diaphragm is connected to the piezoelectric element; the acoustic transmitter includes a first surface and a second surface in parallel to the first surface; the first surface of the acoustic transmitter is coupled to the diaphragm; the diaphragm is a bending transducer; the acoustic transmitter is a thickness mode transducer; the electroacoustic transducer is configured to perform the emission by the electrical connecting device applying a voltage to the piezoelectric element, the piezoelectric element responding to the applied voltage by causing the diaphragm to oscillate with a first flexural oscillation, the first flexural oscillation of the diaphragm exciting a component of the acoustic transmitter to oscillate with a thickness mode oscillation, by which thickness mode oscillation the acoustic transmitter emits a sound wave to the external environment; and for the sensing, the acoustic transmitter is configured to be excited by a sound wave received from the external environment, by which excitation the acoustic transmitter is configured to excite the diaphragm to oscillate with a second flexural oscillation that generates a voltage signal at the piezoelectric element, which the electrical connecting device is configured to tap and evaluate to characterize the sound wave received from the external environment.

2. The electroacoustic transducer as recited in claim 1, wherein: the first surface of the acoustic transmitter is coupled to a first surface of the diaphragm, and a second surface of the diaphragm is connected to the piezoelectric element.

3. The electroacoustic transducer as recited in claim 2, wherein the diaphragm is bonded to the piezoelectric element.

4. The electroacoustic transducer as recited in claim 1, wherein the acoustic transmitter includes a rod-shaped element and a plate.

5. The electroacoustic transducer as recited in claim 4, wherein: the plate is part of a lining element, and the housing is joined to an inside surface of the lining element in such a way that the electroacoustic transducer is not visible from the outside.

6. The electroacoustic transducer as recited in claim 5, wherein the lining element is a bumper.

7. The electroacoustic transducer as recited in claim 5, wherein the plate has a lower material thickness compared to a surrounding area of the lining element.

8. The electroacoustic transducer as recited in claim 7, wherein a ratio between a diameter of the plate to a thickness of the plate is approximately 10/1.

9. The electroacoustic transducer as recited in claim 4, wherein: the rod-shaped element is held on the housing with the aid of a bearing structure that is situated at a height of the rod-shaped element which corresponds to a node of a resonance oscillation of the oscillating structure.

10. The electroacoustic transducer as recited in claim 4, wherein the rod-shaped element has a decreasing cross-sectional area at least one of in a direction of the first surface connected to the diaphragm and in a direction of an end face connected to the plate.

11. The electroacoustic transducer as recited in claim 4, wherein: the rod-shaped element has at least one mounting aid element that includes one of a recess and an elevation on an end face facing the plate, the plate includes at least one complementary mounting aid element on a surface facing the end face, and a centrical positioning of the rod-shaped element and of the plate is achieved as a result of an engagement of the mounting aid element and the complementary aid element in each other.

12. The electroacoustic transducer as recited in claim 4, wherein the rod-shaped element extends longitudinally from the diaphragm to the plate, with a first edge of the rod being connected to a top surface of the diaphragm and a second edge of the rod being connected to a bottom surface of the plate, the diaphragm, rod, and plate thereby forming an ‘I’ shape in cross-section.

13. The electroacoustic transducer as recited in claim 4, wherein: an upper surface of the diaphragm is attached to an underside of the housing; the rod-shaped element extends longitudinally, from the upper surface of the diaphragm to an underside of the plate, within an interior space of the housing; and an underside of the plate is above a top surface of the housing.

14. The electroacoustic transducer as recited in claim 13, wherein a width or diameter of the interior space widens at a bottom end of the housing.

15. The electroacoustic transducer as recited in claim 4, wherein the electroacoustic transducer is configured so that: in the case of the emission, the first flexural oscillation excites the rod-shaped element, thereby causing the plate to emit the emitted sound wave to the external environment; and the sound wave received from the external environment excites the plate, the excitation of the plate exciting the rod-shaped element and the excitation of the rod-shaped element exciting the diaphragm to oscillate with the second flexural oscillation.

16. The electroacoustic transducer as recited in claim 15, wherein a top surface of the plate is exposed to the external environment, and the sound wave received from the external environment impinges upon the plate to cause the excitation of the plate.

17. The electroacoustic transducer as recited in claim 1, wherein the diaphragm is attached to the housing with the aid of a bearing structure.

18. The electroacoustic transducer as recited in claim 1, wherein: the piezoelectric element includes a design that is one of quadrangular, circular, annular, elliptic, and arbitrary, and the piezoelectric element is bonded to the diaphragm across a full surface.

19. The electroacoustic transducer as recited in claim 1, wherein a length of the electroacoustic transducer is equal to approximately half of a wavelength of a resonance oscillation of the oscillating structure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an electroacoustic transducer according to a first embodiment of the present invention.

(2) FIG. 2 shows an electroacoustic transducer according to a second embodiment of the present invention.

(3) FIG. 3 shows an electroacoustic transducer according to a third embodiment of the present invention.

(4) FIG. 4 shows the electroacoustic transducer according to the first embodiment of the present invention, together with a diagram of the deflection in the thickness direction of the acoustic transmitter.

DETAILED DESCRIPTION

(5) FIG. 1 shows a schematic longitudinal section through an electroacoustic transducer 1 according to a first embodiment of the present invention. Electroacoustic transducer 1 includes a housing 180 and an oscillating structure 110. Oscillating structure 110 includes a piezoelectric element 150, which in this example is designed as a piezoceramic disk. The piezoceramic disk is glued to bottom side 122 of diaphragm 120. The piezoceramic disk essentially has the same surface shape and size as diaphragm 120 and ends flush with diaphragm 120.

(6) When a corresponding voltage signal U is applied to piezoceramic disk 150, the same may cause diaphragm 120 to oscillate. Electrical connecting means 190 are provided for this purpose, which are contacted with electrodes of piezoelectric element 150 and are shown only schematically here.

(7) A rod-shaped element 145 is attached to top side 121 of the diaphragm. A first surface 141 of the rod-shaped element is connected to the diaphragm. The attachment may be carried out with the aid of screwing and/or welding and/or adhesive bonding, for example. Rod-shaped element 145 is attached, in particular bonded, with its second surface (end face) 146 to a plate 240. Plate 240 is connected in one piece to a lining element 200, which in this example is the bumper or a trim of a motor vehicle.

(8) Housing 180 is attached to the inner side of lining element 200, for example with the aid of adhesive bonding, whereby the electroacoustic transducer is not visible from the outside. Housing 180 is essentially cylindrical in this example and is made of a metal, such as aluminum. It has a high impedance (it is stiff and/or heavy) in parallel to the oscillating direction of rod-shaped element 145, so that the introduction of oscillations into housing 180 remains preferably low. Diaphragm 120 is mounted in an edge area 185 of housing 180. Housing 180 has a lower wall thickness in this edge area 185. Mounting 170 may be designed to be fixed, for example with the aid of clamping or adhesive bonding. Alternatively, mounting 170 may have a certain mobility, which is achieved in that the contact surface between diaphragm 120 and housing 180 is designed to be small, and thus flexible.

(9) Outwardly directed surface 142 of plate 240 is suitable for emitting and/or receiving sound waves. Together, plate 240 and rod-shaped element 145 form acoustic transmitter 140 according to the present invention, which is excitable by flexural oscillations of diaphragm 120 to carry out thickness mode oscillations. In the reception case, this principle is exactly reversed. Sound waves impinge on surface 142 and excite plate 240. The plate excites rod-shaped element 145, which in turn excites diaphragm 120 to carry out flexural oscillations. Since piezoelectric element 150 is glued to diaphragm 120, voltage signals are generated at piezoelectric element 150, which may be tapped by electrical connecting means 190 and further processed for evaluation. In general, oscillating structure 110 will oscillate at a certain resonance frequency. Longitudinal extension d of oscillating structure 110 corresponds to half a wavelength (λ/2) of the resonance oscillation. Longitudinal extension d is essentially determined by the length of rod-shaped element 145, which is why the same is also referred to as λ/2 thickness mode transducer.

(10) FIG. 4 schematically illustrates deflection A of the thickness mode oscillation in a diagram. The x axis corresponds to the longitudinal direction, and the y axis corresponds to the deflection of the oscillating structure. The deflection corresponds to half the wavelength of the oscillation. The maximum deflections occur at the corresponding ends x.sub.1, x.sub.2 of oscillating structure 110. In the center x.sub.m, the deflection is essentially zero, corresponding to a node.

(11) Metals, such as aluminum or stainless steel, may be used to manufacture diaphragm 120 and rod-shaped element 145. It is also possible to use plastic materials, which ideally have no glass transition temperature in the temperature range of −40° C. to +85° C. A combination of different materials is also possible. The length of the rod-shaped element is to be selected as a function of the selection of the transmitting frequency and the material used for rod-shaped element 145 and the propagation velocity of the sound waves associated therewith. To avoid oblique positions of rod-shaped element 145, in particular when rod-shaped element 145 is very long compared to the dimensions of plate 240 or diaphragm 120, rod-shaped element 145 may be fixed to housing 180 with the aid of a further bearing structure 175. Bearing structure 175 may preferably be situated at half the height h of rod-shaped element 145. This centrical position of bearing structure 175 is selected since the amplitude of the thickness mode oscillations is minimal there. The position corresponds to the node at position x.sub.m in the illustration according to FIG. 4.

(12) In the embodiment of the present invention shown in FIG. 1, diaphragm 120, rod-shaped element 145, housing 180, and plate 240 are designed as separate components. As an alternative, diaphragm 120 and rod-shaped element 145 may also be designed in one piece.

(13) As an alternative, diaphragm 120 may be implemented in one piece with housing 180 and/or housing 180 may be formed in one piece with plate 240 or lining element 200.

(14) To protect electroacoustic transducer 1 even better with respect to the outside from environmental influences, such as moisture or dust, still another cover (not shown) may be provided.

(15) FIG. 2 shows a second exemplary embodiment of an electroacoustic transducer 1 schematically in a longitudinal section. The fundamental composition and the function of electroacoustic transducer 1 correspond to the transducer shown in FIG. 1. Identical elements are denoted by the same reference numerals. Contrary to the electroacoustic transducer shown in FIG. 1, piezoelectric element 150 is designed to be smaller than diaphragm 120 in this exemplary embodiment. Piezoelectric element 150 is centrically attached to the bottom side of diaphragm 120. Diaphragm 120 and rod-shaped element 145 are designed in one piece. Electroacoustic transducer 1 shown in FIG. 2 additionally includes means 148, 248 as mounting aids of the system made up of rod-shaped element 145 and plate 240. For this purpose, a recess 148 is formed centrally on end face 146 of rod-shaped element 145 as a mounting aid element. In complementary fashion, plate 240 has an elevation 248 on its surface 246 facing end face 146. When rod-shaped element 145 and plate 240 are joined, elevation 248 engages in recess 148. In this way, it is ensured that the rod-shaped element is correctly positioned relative to plate 240. Deviations in the positioning may result in undesirable deviations in the radiation pattern and/or the resonance frequency of electroacoustic transducer 1; in particular, non-centrical force introductions into the involved structures may occur, whereby undesirable so-called “spurious oscillations” may be created in other coordinate directions. These deviations and undesirable effects are avoided due to the mounting aid elements.

(16) FIG. 3 shows a third exemplary embodiment of an electroacoustic transducer 1 schematically in a longitudinal section. The fundamental composition and the function of electroacoustic transducer 1 correspond to the transducer shown in FIG. 1. Identical elements are denoted by the same reference numerals. Contrary to the electroacoustic transducer shown in FIG. 1, in this exemplary embodiment rod-shaped element 145 is designed in such a way that it has a decreasing cross-sectional area in the direction of first surface 141 connected to diaphragm 120. In other words, rod-shaped element 145 has a tapering design in the direction of its end connected to diaphragm 120. The resulting reduced connecting surface between rod-shaped element 145 and diaphragm 120 causes oscillations of the diaphragm—in particular the flexural oscillations—to be impeded only little by the rod-shaped element. It is additionally or alternatively conceivable to also design the end of the rod-shaped element facing plate 240 in a tapering manner. In addition or as an alternative, it may be provided that one end face or both of end faces 141 and 146 of rod-shaped element 145 has/have a central recess, which causes the particular connecting surface between rod-shaped element 145 and diaphragm 120 or plate 140 to have an annular design. In this way, a further reduction in impediment of oscillations of diaphragm 120 or of plate 240 is achieved.