Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-06-05
2001-03-13
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C290S053000
Reexamination Certificate
active
06201336
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates, in general, to power generation from piezoelectric materials, and particularly to an improved DC bias scheme for improved efficiency use of various electrostrictive materials for piezoelectric power generation.
A recent development in the field of piezoelectric power generation from natural sources of energy and the like is the use of “field-induced piezoelectricity” in electrostrictive materials. Typically, electrostrictive materials have very weak piezoelectric characteristics (related to a materials parameter known as d
31
). However, if a DC bias is applied across the materials, e.g., by means of a pair of electrodes on opposite surfaces of an electrostrictive material such as polyurethane, the piezoelectric characteristics can be significantly increased and in proportion to the DC bias.
Circuit arrangements for applying a DC bias between electrodes are well known. In general, a DC bias voltage is applied through a large bias resistance serving to prevent significant DC current flow within the biasing circuit. A problem, however, is that the bias resistor in known arrangements is in parallel with the load of the generator system and, particularly in those instances where the load resistance is quite highs a significant portion of the AC power generated by the system is lost in the bias circuit.
SUMMARY OF THE INVENTION
A DC bias is applied to the ground side of an electroded piezoelectric device and is thus separated from the load by the inherent capacitance of the piezoelectric device. Additionally, a capacitor normally present in the prior art arrangement for isolating the DC bias from the load is used in the inventive arrangement for bypassing the AC power current around the bias resistor.
REFERENCES:
patent: 3801839 (1974-04-01), Yo
patent: 4139826 (1979-02-01), Pradal
patent: 4680498 (1987-07-01), Takasugi et al.
patent: 4816713 (1989-03-01), Change
patent: 5347870 (1994-09-01), Dosch et al.
Dougherty Thomas M.
Epstein, Esq. Michael Y.
Ocean Power Technologies, Inc.
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