Acoustic wave transducer device

Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices

Reexamination Certificate

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C310S31300R, C310S311000, C310S319000

Reexamination Certificate

active

06310429

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to acoustic wave transducer devices, for example microphones, hydrophones, sonar systems, etc.
BACKGROUND TO THE INVENTION
Note that although the present invention relates generally to acoustic waves and to acoustic wave receivers/transducers, for clarity we will refer to the most common examples, namely sound waves and microphones. Some classes of microphone transducer technologies which are known to the audio community are: carbon, condenser, moving-coil (or “dynamic”) and piezoelectric. Using these technologies microphones with varying sensitivity to direction, proximity, impedance and frequency can be constructed. Some of these are: cardioid, pressure gradient, and microphone array. The existing background literature in this field is extensive, however, some very good technology reviews are described in references: L. Beranek, Acoustics, American Institute of Physics, New York, N.Y., 1986; and L. E. Kinsler,
Fundamentals of Acoustics,
John Wiley & Sons, Inc., New York, N.Y., 1982. In addition, microphone manufacturers (for example B&K Shure and Electrovoice) have application notes and product literature which describe the performance of these devices.
Indeed, the review articles and the current literature describe a need for microphone systems which have increasingly larger signal to noise ratio, and increasingly larger directional sensitivity (i.e., increased sensitivity to acoustic waves originating from a particular direction). While the devices described above address these needs to some degree, problems still exist. For example, current state-of-the-art microphones with relatively high signal to noise ratios tend to be sufficiently large to scatter the waves, thus affecting the received sound waves. This is problematic as it both distorts the signal produced by the microphone, as well as changes the waves for subsequent receivers or listeners.
Other background information which may be useful in understanding the invention and the techniques described herein is found in: Horowitz and Hill,
The Art of Electronics,
McGraw-Hill; S. W. Golomb,
Shift Register Sequences,
Aegean Park Press, 1982; and G. Arfken,
Mathematical Methods for Physicists,
Academic Press, Inc., New York, N.Y., 1985, which are all hereby incorporated by reference.
SUMMARY OF THE INVENTION
In accordance with a broad aspect of the present invention there is provided an acoustic wave transducer device comprising a material which produces a voltage signal dependent on the shape of the material and on the pressure applied to the material by an acoustic wave, wherein said material is of an irregular shape.
A material such as PVDF (polyvinylidene fluoride) can be used. Materials like PVDF have been used to form transducers before, but have not been formed into sheets with irregular shapes, as described herein, or have been coupled to signal processor which uses the shape of the transducer sheet as described herein.
Preferably, the shape of a sheet of material which forms the transducer is selected in order to advantageously convolve acoustic signal information with a width function dependent on the shape of the sheet. Thus the transducer can be used to produce desired voltage signals representing the convolution of an input signal with a known function by shaping said transducer according to said known function. Alternatively, a signal processor can deconvolve a voltage signal produced by the sheet into a signal indicative of the pressure applied to the transducer by an acoustic wave in order to determine the acoustic signal information. The acoustic signal information is a time dependent function carried by said acoustic wave which is often useful as it represents desired information, for example voice or music carried by sound waves.
The shape of the sheet can be thought of as encoding spatial information about the acoustic wave into the voltage signal produced by the sheet, which is useful in order to preferentially extract desired acoustic signal information.
In accordance with another aspect of the invention there is provided an acoustic wave transducer device comprising:
a material which produces a voltage signal dependent on the shape of the material and on the pressure applied to the material by an acoustic wave, wherein said material is of a predetermined shape; and
a signal processor for producing an output signal indicative of the pressure applied to the material by processing said voltage signal using said predetermined shape.
As the material is cut to a predetermined shape the signal processor can produce an output signal, indicative of the pressure applied to the material by the acoustic wave, by processing said voltage signal using said predetermined shape. Thus the signal processor includes a memory for storing shape function data dependent on said predetermined shape and uses the shape function data to produce the output signal. The predetermined shape can be defined in terms of a width function and a shape function. The shape function data depends on the width function.
In particular, the transducer produces a voltage signal which represents the convolution of the width function with the acoustic signal information in the acoustic wave. The signal processor subsequently uses the stored shape function data to deconvolve the voltage signal to retrieve the acoustic signal information (i.e., produces an output signal, indicative of the pressure applied to the material by the acoustic wave).
According to another aspect of the invention there is provided a method of making an acoustic wave transducer device comprising the steps of:
selecting a mathematical relation with orthogonal properties; transforming said relation to form a width function; and forming a transducer whose shape depends on said width function.
According to such a method, a transducer may be formed from at least one sheet of material which produces a voltage signal dependent on the shape of the sheet and on the pressure applied to the sheet by an acoustic wave. Preferably the shape of said transducer is derived from said width function such that the shape has an irregular width which varies with the length of the transducer, and a length which is longer then the longest wavelength of the acoustic waves to be received.
Advantageously, a transducer device can be formed which produces a higher signal to noise ratio than conventional transducers. Preferably such a transducer device includes means for increasing the sensitivity of the device to acoustic waves originating from a selected direction. Preferably said transducer device comprises a sheet (or sheets) with negligible thickness, an irregular width which varies along the length of the sheet, and a length which is longer then the longest wavelength of the acoustic waves to be received, said sheet having a sheet axis and wherein said means for increasing the sensitivity of the device to acoustic waves originating from a selected direction comprises means for selecting an angle between said sheet axis and said selected direction.


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Proceedings of the Second Technical Conference on Telecommunications R & D in Massachusetts; University of Massachusetts Lowell, MA 01854; Mar. 12, 1996.
The Interactive Balloon: Sensing, Actuation, and Behavior in a Common Object by J.A. Paradiso; IBM Systems Journal, vol. 35, NOS 3&4, 1996—0018-8670/96.

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