Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2002-04-19
2004-08-10
Budd, Mark (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06774540
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sound converting apparatus for performing conversion between electric signals and ultrasonic waves, and more particularly to a sound converting apparatus operable to perform conversion between electric signals and ultrasonic waves at a low voltage.
2. Description of the Related Art
In recent years, there have been proposed various kinds of sound converting apparatus for performing conversion between electric signals and ultrasonic waves, viz. converting electric signals into ultrasonic waves or converting ultrasonic waves into electric signals used, for example, to probe the internal orgasm of the human body to assist the doctors in diagnosing the human body in the hospitals.
One typical example of the conventional sound converting apparatus is disclosed in Japanese Patent Laid-Open Publication No. 299799/1999. The conventional sound converting apparatus
700
herein disclosed is shown in FIG.
7
. The conventional sound converting apparatus
700
is adapted to emit ultrasonic waves converted from electric signals along a wave propagating direction Dp. The conventional sound converting apparatus
700
comprises a plurality of piezoelectric layers
76
a
,
76
b
, and
76
c
, each having a first surface and a second surface, and aligned one after another in a wave propagating direction Dp. The first and second surfaces of the piezoelectric layers
76
a
,
76
b
, and
76
c
are extending substantially parallel to an azimuthal direction Da perpendicular to the wave propagating direction Dp. The conventional sound converting apparatus
700
further comprises a plurality of electrodes, i.e., electrodes
77
,
79
,
80
, and
78
aligned one after another along the wave propagating direction Dp. The electrode
77
is held in contact with the second surface of the piezoelectric layer
76
c
. The electrode
79
is sandwiched between the piezoelectric layers
76
c
and
76
b
and held in contact with the first surface of the piezoelectric layer
76
c
and the second surface of the piezoelectric layer
76
b
. The electrode
80
is sandwiched between the piezoelectric layers
76
b
and
76
a
and held in contact with the first surface of the piezoelectric layer
76
b
and the second surface of the piezoelectric layer
76
a
. The electrode
78
is held in contact with the first surface of the piezoelectric layer
76
a
. The conventional sound converting apparatus
700
further comprises an electrically conductive film
84
electrically connecting the electrode
77
with the electrode
80
, and an electrically conductive film
85
electrically connecting the electrode
78
with the electrode
79
. The conventional sound converting apparatus
700
further comprises a signal line
87
electrically connected with the electrode
77
and a signal line
88
electrically connected with the electrode
78
. The signal lines
87
and
89
are operative to input an electrical signal to be applied to the piezoelectric layers
76
a
,
76
b
, and
76
c
to operate the conventional sound converting apparatus
700
.
As described above, the conventional sound converting apparatus
700
comprising a plurality of electrodes aligned one after another in the wave propagating direction Dp makes it possible to increase the electrical field intensity of an electric signal to be applied to the piezoelectric layers in comparison with a conventional sound converting apparatus comprising a single piezoelectric layer in the wave propagating direction Dp. This means that the electrical field intensity of an electrical signal, i.e., an operating voltage to be applied to the piezoelectric layers of the conventional sound converting apparatus
700
can be less than the operating voltage to be applied to the piezoelectric layer of the conventional sound converting apparatus comprising a single piezoelectric layer in the wave propagating direction Dp. This leads to the fact that the conventional sound converting apparatus
700
is operative at an operating voltage less than the operating voltage which the conventional sound converting apparatus comprising a single piezoelectric layer in the wave propagating direction Dp is operative at.
The conventional sound converting apparatus
700
thus constructed as above described, however, encounters such a problem that the conventional sound converting apparatus
700
is required to comprise electrically conductive films
84
and
85
for electrically connecting the piezoelectric layers
76
a
,
76
b
, and
76
c
. The conventional sound converting apparatus
700
thus constructed encounters another problem that the conventional sound converting apparatus
700
is required to increase the number of piezoelectric layers to be aligned in the wave propagating direction Dp in order to increase the electrical field intensity of an electric signal to be applied to the piezoelectric layers of the conventional sound converting apparatus
700
.
The present invention contemplates resolution of such problems.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a sound converting apparatus which is not required to comprise electrically conductive films for electrically connecting the piezoelectric layers.
It is another object of the present invention to provide a sound converting apparatus which can increase the electrical field intensity of an electrical signal to be applied to the piezoelectric layers without increasing the number of piezoelectric layers to be aligned in the wave propagating direction Dp.
It is a further object of the present invention to provide a sound converting apparatus which is simple in construction and operative at an operating voltage less than a conventional sound converting apparatus.
In accordance with a first aspect of the present invention, there is provided a sound converting apparatus for performing conversion between electric signals and ultrasonic waves, comprising: a plurality of oscillation bodies for emitting ultrasonic waves converted from the electric signals along a wave propagating direction; and a plurality of electrically conductive bodies each for electrically connecting the oscillation bodies; a plurality of signal lines for inputting electric signals to be applied to respective oscillation bodies; each of the oscillation bodies including a pair of piezoelectric layers respectively having inner surfaces and outer surfaces, extending substantially parallel to the wave propagating direction, the inner surfaces of respective piezoelectric layers opposing to each other; a pair of external electrodes respectively held in contact with the outer surfaces of respective piezoelectric layers and electrically connected with the electrically conductive bodies; and a dividing electrode sandwiched by and held in contact with the inner surfaces of the piezoelectric layers and electrically connected with the signal line, whereby piezoelectric layers respectively generate electric polarizations, directions of which are opposing to each other and extending substantially parallel to an azimuthal direction perpendicular to the wave propagating direction, and emit ultrasonic waves converted from the electric signals along the wave propagating direction when electrical fields are applied between the external electrodes and the dividing electrode in response to the electric signals. In the aforesaid sound converting apparatus, each of the oscillation bodies has a width with respect to the azimuthal direction and a thickness with respect to the wave propagating direction, and the ratio of the width to the thickness is within a range of from 0.1 to 0.8. In the aforesaid sound converting apparatus, the piezoelectric layers may be disposed in mirror symmetric relationship with respect to the directions of electric polarizations and each of the electrically conductive bodies is operative to electrically connect two oscillation bodies neighboring in the azimuthal direction.
In accordance with a second aspect of the present invention, each of the oscillat
Budd Mark
Matsushita Electric - Industrial Co., Ltd.
Pearne & Gordon LLP
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