Communications – electrical: acoustic wave systems and devices – Signal transducers
Patent
1991-01-02
1992-07-07
Eldred, J. W.
Communications, electrical: acoustic wave systems and devices
Signal transducers
367163, 367180, 367157, 310334, 310800, H04R 1700
Patent
active
051289059
DESCRIPTION:
BRIEF SUMMARY
This invention relates to acoustic field transducers.
Transduction of acoustic fields is required in a variety of applications where low-frequency vibration is encountered including geophysics, engineering, mechanical design and development, control systems, intrusion alarm systems, environmental noise monitoring, various medical monitoring systems, triggering, impact sensing, microphonics and hydrophonics.
In a known prior proposal disclosed in U.S. Pat. No. 4,326,275 a piezo-electric transducer element is used. The element is ceramic and flexural and gives rise to an acceleration sensitive device.
It is an object of the present invention to provide a new and improved form of acoustic field transducer. It is a further object to provide an acoustic field transducer which is velocity sensitive. It is a still further object to provide a new and improved method of acoustic field transduction.
Accordingly the present invention provides in one of its aspects an acoustic field transducer comprising an elastic membrane made of piezo-electric material peripherally held in stretched condition with static strain and having a major surface area which is free to move in response to acoustic field variations, means for coupling acoustic field variations to the membrane, and electrical conductor means connected to the membrane for collecting signals piezo-electrically generated by the membrane due to strain variations which are a measure of said acoustic field variations.
The present invention in another of its aspects also provides an acoustic field transducer comprising a rigid hollow support structure capable of being coupled to an acoustic field, the support structure housing an assembly forming an inertial reference mounted for movement relative to the support structure in one translational direction, the assembly including at least one elastic membrane made of piezo-electric material peripherally held in stretched condition with static strain and having a major surface area which is free from contact with the support structure and which extends transversely to said one direction, means interconnecting the support structure and the assembly to transfer to the inertial reference motion of the support structure via the membrane and to effect variations in the strain of the membrane consequential to said motion in said direction of translation, and electrical conductor means connected to the membrane for collecting signals piezo-electrically generated by said membrane due to strain variations which are a measure of said acoustic field variations coupled to the support structure, the assembly having a mechanical resonance frequency at or below which the transducer is sensitive to acoustic field frequencies, the output of the transducer being proportional to the relative velocity of motion between the inertial reference and the support structure.
The present invention also provides an acoustic field transducer comprising a hollow support structure capable of being coupled to an acoustic field, the support structure housing at least one elastic membrane made of piezo-electric material peripherally held in stretched condition with static strain and having a major surface area which is free from contact with the support structure, driver means connected to a flexural part of the support structure and engaging part of said major surface area to effect variations in the strain of the membrane consequential to movements of the driver means relative to the membrane and which are a measure of said acoustic field variations coupled to the flexural part of the support structure.
The present invention also provides a method of transducing acoustic fields comprising providing an elastic membrane made of piezo-electric polymeric material, holding the membrane in a static strain stretched condition, applying acoustic field variations to a part of the membrane which is free to move in a gaseous medium, and collecting piezo-electrically generated signals from the membrane as a measure of the acoustic field variations.
Each membrane may
REFERENCES:
patent: 4051395 (1977-09-01), Taylor
patent: 4315433 (1982-02-01), Edelman et al.
patent: 4354134 (1982-10-01), Micheron
patent: 4782469 (1988-11-01), Granz et al.
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