Acoustic transducer

• US 6,353,277 B1
• Filed: 07/07/2000
• Issued: 03/05/2002
• Est. Priority Date: 08/23/1997
• Status: Expired due to Fees

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Inventors: Hahn-Jose, Thomas
• Primary Examiner(s): Dougherty, Thomas M.
• Application Number:
  US09/486,191
• Time in Patent Office: 606 Days
• Field of Search: 310/324, 310/328, 310/357
• US Class Current: 310/324
• CPC Class Codes: B06B 1/0603 using a piezoelectric bender, e.g. bimorph
• CPC Class Codes: B06B 1/0611 in a pile
• CPC Class Codes: B06B 1/0644 using a single piezoelectric element B06B1/0688 takes precedence
• CPC Class Codes: B06B 1/0688 with foil-type piezoelectric elements, e.g. PVDF
• CPC Class Codes: H04R 17/00 Piezoelectric transducers; Electrostrictive transducers piezoelectric or electrostrictive elements in general H10N30/00; details of piezoelectric or electrostrictive motors, generators or positioners H10N30/00

Abstract

An acoustic transducer, especially an air transducer, including a piezoceramic disk (10). The object of the invention is to provide an improved transducer of this type for more efficiently converting electromagnetic waves into mechanical waves and vice versa. To this end, a combination of a piezoceramic disk (10) and a membrane (8) is provided, the membrane being configured as a monomorphic flexural resonator and being composed of an epoxy-hollow glass sphere mixture or of a material which is similar in terms of its acoustic properties. The planar vibration mode (4) in the piezoceramic is converted into a thickness vibration (6) using Poisson'"'"'s ratio. After the conversion, this thickness vibration is then adapted to the propagation medium, especially air, by a coupling layer having a low acoustic impedance.

Claims

1. An acoustic transducer comprising a composite sandwich having a piezoceramic disk and a diaphragm which form a monomorphous flexural vibrator, and a coupling layer,

wherein the piezoceramic disk has a planar vibration mode which is convertible by a cross-contraction ratio to a thickness vibration mode which, after transformation by the coupling layer of low acoustic impedance, is adaptable to a propagation medium, and

wherein the diaphragm has a thickness corresponding to approximately a quarter wavelength of a resonance frequency of the vibration thickness mode of the piezoceramic disk.

2. An acoustic transducer according to claim 1, wherein said transducer is an air transducer, and the propagation medium is air.

3. An acoustic transducer according to claim 1, wherein center frequencies f2 and f3 of the resonance frequencies of the thickness vibration mode of the piezoceramic disk and of a flexural vibration mode of the membrane are different.

4. An acoustic transducer according to claim 1, wherein a center frequency f3 of the diaphragm is greater than a center frequency f2 of the thickness vibration mode of the piezoceramic disk by a factor in a range from 1.0 to 2.0.

5. An acoustic transducer according to claim 4, wherein the center frequency f3 of the diaphragm is greater than the center frequency f2 of the piezoceramic disk by a factor in a range from 1.05 to 1.3.

6. An acoustic transducer according to claim 1, wherein a center frequency f1 of the resonance of a housing vibration is lower than a center frequency f2 of the thickness vibration mode of the piezoceramic by a factor in a range from 0.35 to 0.7.

7. An acoustic transducer according to claim 6, wherein the center frequency f1 of the resonance of a housing vibration is lower than the center frequency f2 of the piezoceramic by a factor in a range from 0.4 to 0.6.

8. An acoustic transducer according to claim 1, wherein the piezoceramic and the diaphragm are coupled by a thin hard adhesive layer.

9. An acoustic transducer according to claim 1, wherein the thickness resonance of the piezoceramic is applied to the total useful frequency of the transducer, and the flexural vibration f3 frequency of the diaphragm is slightly above the total useful frequency.

10. An acoustic transducer according to claim 1, wherein the diaphragm is configured as part of a transducer housing.

11. An acoustic transducer according to claim 1, wherein the center frequency f2 of the thickness vibration is about 142 kHz and the center frequency f3, which is determined by the monomorphous flexural vibration, is about 160 kHz.

12. An acoustic transducer according to claim 1, wherein the transducer has a cup-shaped housing filled with a damping material or a backing.

13. An acoustic transducer according to claim 1, wherein a transducer housing is provided containing damping material.

14. An acoustic transducer according to claim 13, wherein said damping material comprises at least one material selected from the group consisting of aluminum oxide, tungsten and polymers.

15. An acoustic transducer according to claim 1, wherein the diaphragm is composed of a mixture of epoxy and hollow glass balls.

16. An acoustic transducer comprising:

a composite sandwich of a piezoceramic disk and a diaphragm which form a monomorphous flexural vibrator, and

a coupling layer of low acoustic impedance,

wherein a planar vibration mode in the piezoceramic disk is convertible by way of a cross-contraction ratio to a thickness vibration mode, said thickness vibration mode being transformable by said coupling layer to adapt said thickness vibration mode to a propagation medium.

17. A method of transducing acoustic energy, comprising:

forming a monomorphous flexural vibrator from a composite sandwich of a piezoceramic disk and a diaphragm,

converting a planar vibration in the piezoceramic disk to a thickness vibration by way of a cross-contraction ratio, and

transforming the thickness vibration via a coupling layer of low acoustic impedance to adapt the thickness vibration to a propagation medium.