Piezoelectric transducers

Details Piezoelectric transducers Piezoelectric transducers

1998-11-17

2001-02-27

Barnie, Rexford (Department: 2743)

Electrical audio signal processing systems and devices

Electro-acoustic audio transducer

Electrostrictive, magnetostrictive, or piezoelectric

C381S191000

Reexamination Certificate

active

06195440

ABSTRACT:

BACKGROUND ART
Loudspeakers employing a piezoelectric transducer capable of propagating surface acoustic waves to drive a diaphragm have been proposed as an alternative to moving coil loudspeakers. Such a device was described by Martin in U.S. Pat. No. 4,368,401 and later Takaya in U.S. Pat. No. 4,439,640. Both inventions dealt with attaching a disc shaped piezo to a diaphragm. Martin's device used a thick glue layer (10 to 50% of the carrier plate thickness) between a carrier plate and the piezo ceramic. The adhesive layer served to attenuate resonance. Any displacement in the piezoelectric is directly related to the applied electrical potential.
One disadvantage to utilizing transducers employing a piezoelectric element is that such materials are very costly and that a substantial expense would be involved to utilize a sufficiently sized piezo electric material to drive large diaphragms. Another disadvantage is that piezoelectric materials are as a rule comparatively brittle and do not deform well. Consequently, if one attempts to have piezoelectric materials conform to the curvature of an irregularly shaped diaphragm they may shatter or break, resulting in necessary expense.
Therefore it would be advantageous to attempt to reduce the cost of using piezoelectric elements in a transducer and to adapt them is such a way to a diaphragm so as to reduce the possibility of having the piezo be damaged.
BRIEF DESCRIPTION OF THE INVENTION
The present invention involves a transducer which is utilized to drive a diaphragm, in particular a comparatively large diaphragm. The transducer is comprised of a piezoelectric layer, (or a layer of some other material covered with a layer of piezo-electric material) capable of propagating flexural acoustic waves, which piezoelectric material typically is a flat layer placed on top of a substrate layer which has essentially the same degree of rigidity (as measured by its Young's modulus and thickness) as the piezoelectric electric material, but has more rigidity than the diaphragm material so that when the substrate material is distorted by the motion of the piezoelectric material the diaphragm will move accordingly. In this regard, the thickness of the substrate may be optimized to the properties of the piezoelectric material. The substrate will be larger in surface area than the piezoelectric element in order to impart motion to a larger area of the diaphragm. The invention also comprises utilizing multiple transducers on a single diaphragm to extend the frequency range. In this case larger transducers would be used to produce low frequencies and smaller transducers would be used to produce higher frequencies. The use of multiple transducers serves to increase the motion imparted to the diaphragm and, hence, the volume or loudness of the sound.


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