Piezoelectric transformer with segmented electrodes

Details Piezoelectric transformer with segmented electrodes Piezoelectric transformer with segmented electrodes

2000-02-11

2002-03-26

Ramirez, Nestor (Department: 2834)

Electrical generator or motor structure

Non-dynamoelectric

Piezoelectric elements and devices

C310S369000

Reexamination Certificate

active

06362559

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to piezoelectric transformers. More particularly, the present invention relates to a piezoelectric transformer having segmented electrodes on one or both faces of a piezoelectric ceramic disk. The transformer may be configured with a resonant feedback circuit that provides step up voltage transformation, and may provide voltage to multiple loads.
2. Description of the Prior Art
Wound-type electromagnetic transformers have been used for raising or lowering input voltages (step-up and step-down transformation, respectively) in internal power circuits of devices such as televisions or in charging devices of copier machines which require high voltage. Such electromagnetic transformers take the form of a conductor wound onto a core made of a magnetic substance. Because a large number of turns of the conductor are required to realize high transformation ratios, electromagnetic transformers that are effective, yet at the same time compact and slim in shape are extremely difficult to produce.
To remedy this problem, piezoelectric transformers utilizing the piezoelectric effect have been provided in the prior art. In contrast to the general electromagnetic transformer, the piezoelectric ceramic transformer has a number of advantages. The size of a piezoelectric transformer can be made smaller than electromagnetic transformers of comparable transformation ratio. Piezoelectric transformers can be made nonflammable, and they produce no electromagnetically induced noise.
The ceramic body employed in prior piezoelectric transformers takes various forms and configurations, including rings, flat slabs and the like. A typical example of a prior piezoelectric transformer is illustrated in FIG.
1
. This type of piezoelectric transformer is commonly referred to as a “Rosen-type” piezoelectric transformer. The basic Rosen-type piezoelectric transformer was disclosed in U.S. Pat. No. 2,830,274 to Rosen, and numerous variations of this basic apparatus are well known in the prior art as illustrated in
FIGS. 2 and 3
which show disk-shaped and annular Rosen-type piezoelectric transformers, respectively. The typical Rosen-type piezoelectric transformer comprises a flat ceramic slab
110
which is appreciably longer than it is wide and substantially wider than thick. As shown in
FIGS. 1 and 3
, a piezoelectric body
110
is employed having some portions polarized differently from others. In the case of the prior art transformer illustrated in
FIG. 1
, the piezoelectric body
110
is in the form of a flat slab which is considerably wider than it is thick, and having greater length than width. A substantial portion of the slab
110
the portion
112
to the right of the center of the slab, is polarized longitudinally, whereas the remainder of the slab is polarized transversely to the plane of the face of the slab. In this case, the remainder of the slab is actually divided into two portions; one portion
114
being polarized transversely in one direction, and the remainder of the left half of the slab, the portion
116
also being polarized transversely but in the direction opposite to the direction of polarization in the portion
114
. In the annular Rosen type transformer of
FIG. 3
, some portions of the annulus are polarized in the thickness direction, and the remaining portions are polarized in a circumference direction.
In order that electrical voltages may be related to mechanical stress in the slab
110
, electrodes are provided. If desired, there may be a common electrode
118
, shown as grounded. For the primary connection and for relating voltage at opposite faces of the transversely polarized portion
114
of the slab
110
, there is an electrode
120
opposite the common electrode
118
. For relating voltages to stress generated in the longitudinal direction of the slab
110
, there is a secondary or high-voltage electrode
122
cooperating with the common electrode
118
. The electrode
122
is shown as connected to a terminal
124
of an output load
126
grounded at its opposite end.
In the arrangement illustrated in
FIG. 1
, a voltage applied between the electrodes
118
and
120
is stepped up to a high voltage between the electrodes
118
and
122
for supplying the load
126
at a much higher voltage than that applied between the electrodes
118
and
120
.
An inherent problem of such prior piezoelectric transformers is that they have relatively low power transmission capacity. This disadvantage of prior piezoelectric transformers relates to the fact that little or no mechanical advantage is realized between the driver portion of the device and the driven portion of the device. This inherently restricts the mechanical energy transmission capability of the device, which, in turn, inherently restricts the electrical power handling capacity of such devices. Additionally, because the piezoelectric voltage transmission function of Rosen-type piezoelectric transformers is accomplished by proportionate changes in the x-y and y-z surface areas (or, in certain embodiments, changes in the x-y and x′-y′ surface areas) of the piezoelectric member, which changes are of relatively low magnitude, the power handling capacity of prior circuits using such piezoelectric transformers is inherently low.
Because the typical prior piezoelectric transformer accomplishes the piezoelectric voltage transmission function by proportionate changes in the x-y and y-z surface areas (or, in certain embodiments, changes in the x-y and x′-y′ surface areas) of the piezoelectric member, it is generally necessary to alternatingly apply positive and negative voltages across opposing faces of the “driver” portion of the member in order to “push” and “pull”, respectively, the member into the desired shape. Prior electrical circuits which incorporate such prior piezoelectric transformers are relatively inefficient because the energy required during the first half-cycle of operation to “push” the piezoelectric member into a first shape is largely lost (i.e. by generating heat) during the “pull” half-cycle of operation. This heat generation corresponds to a lowering of efficiency of the circuit, an increased fire hazard, and/or a reduction in component and circuit reliability.
Furthermore, in order to reduce the temperature of such heat generating circuits, the circuit components (typically including switching transistors and other components, as well as the transformer itself) are oversized, which reduces the number of applications in which the circuit can be utilized, and which also increases the cost/price of the circuit.
Another problem with prior piezoelectric transformers is, because the power transmission capacity of such prior piezoelectric transformers is low, it is necessary to combine several such transformers together into a multi-layer “stack” in order to achieve a greater power transmission capacity than would be achievable using one such prior transformer alone. This, of course, increases both the size and the manufacturing cost of the transformer; and the resulting power handling capacity of the “stack” is still limited to the arithmetic sum of the power handling capacity of the individual elements.
Another problem with prior piezoelectric transformers is that they are difficult to manufacture because individual ceramic elements must be polarized at least twice each, and the directions of the polarization must be different from each other.
Another problem with prior piezoelectric transformers is that they are difficult to manufacture because it is necessary to apply electrodes not only to the major faces of the ceramic element, but also to at least one of the minor faces of the ceramic element.
Another problem with prior piezoelectric transformers is that they are difficult to manufacture because, in order to electrically connect the transformer to an electric circuit, it is necessary to attach (i.e. by soldering or otherwise) electrical conductors (e.g. wires) to electrodes on the major faces of the cera

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