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JP2006319713

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DESCRIPTION JP2006319713
PROBLEM TO BE SOLVED: To provide an ultrasonic probe for transmitting a low voltage signal to
a signal transmission cable between an ultrasonic transducer and an observation device, boosting
the voltage in the vicinity of the ultrasonic transducer, and applying the boosted voltage to the
transducer. SOLUTION: When an ultrasonic transducer 6a for transmitting and receiving an
ultrasonic wave and a drive signal for driving the ultrasonic transducer are input, a high voltage
is generated based on the drive signal, and the high voltage is increased. The above-mentioned
subject is solved by the ultrasonic probe provided with the high voltage generating means 7
made to apply to a sound wave vibrator. [Selected figure] Figure 1
Ultrasonic probe and intracorporeal insertion type ultrasonic diagnostic apparatus mounted with
the same
[0001]
The present invention relates to a body cavity insertion type ultrasonic diagnostic apparatus
equipped with an ultrasonic transducer.
[0002]
Ultrasonic diagnostic methods are in widespread use in which ultrasonic waves are emitted
toward the wall of a body cavity, and an internal state of the body is imaged and diagnosed from
the echo signals.
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An ultrasound endoscope scope is one of the equipment used for this ultrasound diagnostic
method.
[0003]
In an ultrasonic endoscope, an ultrasonic probe is attached to the tip of an insertion portion to be
inserted into a body cavity, and this ultrasonic probe converts an electric signal into an ultrasonic
wave and emits it into a body cavity, or in a body cavity It receives the reflected ultrasonic waves
and converts them into electrical signals.
[0004]
Conventionally, ceramic piezoelectric material PZT (lead zirconate titanate) has been used as a
piezoelectric element for converting an electric signal to ultrasonic waves in an ultrasonic probe,
but a silicon semiconductor substrate is processed using silicon micromachining technology.
Capacitive micromachined ultrasonic transducers (hereinafter referred to as c-MUTs) have
attracted attention.
This is one of the elements collectively called micromachine (MEMS: Micro Electro-Mechanical
System, microminiature electrical and mechanical composite).
[0005]
By the way, recently, diagnostic modalities called harmonic imaging have been in the spotlight
because they enable unprecedented high-precision ultrasound diagnosis. Therefore, in the
intracavitary insertion type ultrasound diagnostic apparatus, standard equipment of this
diagnostic modality is used. It has become essential. Therefore, further broadening of the
ultrasonic transducer has been desired.
[0006]
As described above, in recent years, a capacitive ultrasonic transducer (cMUT) using a
micromachine process is attracting attention. This cMUT is not only free of heavy metals such as
lead but also can easily obtain wide band characteristics. Therefore, it is suitable for the above-
05-05-2019
2
mentioned harmonic imaging.
[0007]
FIG. 19 shows an example of a conventional cMUT. This figure is the cMUT disclosed in Patent
Document 1. The ultrasound transducer is formed by a plurality of capacitive micromachined
ultrasound transducers (cMUTs). Each cell constituting the cMUT has a charged vibration plate
206. The charged vibration plate 206 capacitively faces the oppositely charged substrate 205.
[0008]
The diaphragm 206 is bent toward the substrate 205 by the bias charge. Further, the substrate
205 has a central portion 28 which is raised with respect to the center of the diaphragm 206 so
that the charge of the cell has the maximum density at the center of the vibration of the
diaphragm 206. The drive pulse waveform fed to the cell is pre-distorted for harmonic operation.
This is done in view of the non-linear operation of the device in order to reduce the distortion of
the transmitted ultrasound signal in the harmonic band.
[0009]
The cMUT cell may be integrated with an auxiliary transducer circuit such as bias charge
regulator 201 as it is fabricated by conventional semiconductor processing. cMUT cells can also
be processed by microstereolithography. As such, cells are formed using a variety of polymers
and other materials.
[0010]
The ultrasonic observation apparatus is provided with a high breakdown voltage switch in the
ultrasonic probe in order to operate by the harmonics. In the ultrasonic observation apparatus,
pulse generation means and control means are provided. The pulse generation means can output
a pulse having an arbitrary waveform and an arbitrary voltage value. The control means controls
the outputs of the high withstand voltage switch and the pulse generation means based on the
scanning timing of the ultrasonic transducer.
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[0011]
On the other hand, the applicant of the present invention has proposed a method of applying a
DC voltage application timing only for a time synchronized with an rf signal application timing
(Patent Document 2). FIG. 20 shows an example (part 2) of a conventional ultrasonic transducer
driving method. This figure shows a test probe disclosed in Patent Document 3. In addition to
known circuits, this test probe is to minimize the effects of electrical interference caused by the
relatively long connection cable between the test probe and the ultrasound signal evaluation
device. , Including other actuation circuits. In Patent Document 3, the test probe includes the
above-described circuit, but the circuit is prevented from being excessively large. Also, the
operation is not difficult when performing the ultrasonic test.
[0012]
A transmitter circuit 210 is incorporated in the probe housing of the test probe. The transmission
circuit 210 includes a boost coil 211, a VMOS field effect transistor 213, a control circuit 214,
and a capacitor 215. The VMOS field effect transistor 213 performs an ON / OFF operation by
the control signal 212.
[0013]
The transmission circuit 210 operates as follows. The high density charge is charged in the
capacitor 215 through the booster coil 211. When the charge amount of the capacitor 215
becomes maximum, a control signal is output from the control circuit 214 to the switch drive
terminal of the VMOS field effect transistor 213. Then, the VMOS field effect transistor 213 is
turned on. Then, discharge occurs in a closed circuit by the ON resistance, the resistor 216 and
the capacitor 215. The voltage generated in the resistor 216 by the discharge current is applied
to the piezoelectric vibrator.
[0014]
However, to increase the voltage induced by this method, the inductance of the booster coil 211
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4
must be increased. As a result, resonance occurs between the capacitor 215 and the coil 211,
resulting in a driving pulse including ringing. This ringing signal is applied to the piezoelectric
vibrator as it is, leading to a decrease in S / N.
[0015]
FIG. 21 shows an example (part 3) of a conventional ultrasonic transducer driving method. FIG.
21A shows an ultrasonic diagnostic apparatus disclosed in Patent Document 4. As shown in FIG.
FIG. 21 (b) is a simplified version of FIG. 21 (a). Although Patent Document 4 is not necessarily
intended to prevent the ringing described above, it is disclosed to minimize the effect of electrical
interference due to a long connection cable.
[0016]
In FIG. 21, the ultrasonic probe 220 and the ultrasonic observation device 221 are described.
Ultrasonic signals are transmitted and received from an ultrasonic transducer 222 provided in
the ultrasonic probe to ultrasonically scan the subject. The ultrasound diagnostic apparatus 221
can obtain an ultrasound tomographic image based on the received ultrasound signal.
[0017]
In the ultrasonic probe 220, a high withstand voltage switch 223 is provided. In the ultrasonic
observation apparatus, a pulse generation unit 227 and a control unit 228 are provided. The
pulse generation means 227 can output a pulse having an arbitrary voltage value with an
arbitrary waveform. The control means 228 controls the outputs of the high withstand voltage
switch 223 and the pulse generation means 227 based on the scanning timing of the ultrasonic
transducer.
[0018]
Such a configuration does not increase the size of the electric circuit inside the ultrasonic probe.
In addition, a high voltage pulse signal for driving an ultrasonic transducer can be efficiently
generated in the probe. And while being able to obtain the good ultrasonic image which is not
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5
influenced by the interference in a cable, it is possible to hold down the noise radiated to the
outside small. Also, since there are no resonating elements in the circuit, no ringing occurs. JP-A2004-503313 JP-A-2004-176039 JP-B-63-026341 Patent No. 3062313 Y. Nakamura, Y.
Adachi, "Piezoelectric transformer using a lithium niobate single crystal", The Institute of
Electronics, Information and Communication Engineers Dissertation, A, Vol. J80-A, no. 10, pp.
1694-1698, October 1997
[0019]
However, in the prior art, in order to apply a high pulse voltage to the piezoelectric vibrator, it is
necessary to increase the output voltage of the amplifier. The high voltage pulse is transmitted
through the long connection cable as it is.
[0020]
Ultrasound endoscopes require a long signal transmission cable between the ultrasound
transducer and the observation device. However, transmitting a high voltage signal to the cable is
a source of RF noise, which is not preferable. It is desirable that the voltage transmitted to the
cable is a low voltage, and a voltage high enough to receive a sufficient echo signal is applied
only in the vicinity of the ultrasonic transducer only when transmitting an ultrasonic wave.
[0021]
In a body cavity insertion type ultrasonic diagnostic apparatus, a long cable is wired between an
ultrasonic transducer and a signal control unit. Generally, the application of high voltage pulses is
required, and the effect of RF noise radiation or flight in the cable has been a problem.
[0022]
In addition, capacitive micromachine ultrasound transducers (cMUTs) that have wide bandwidth
that can be compatible with harmonic imaging that is indispensable as a diagnostic modality in
recent years and that are environmentally friendly need not only high voltage pulse application
but also high DC voltage to be superimposed. there were.
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[0023]
Also, the inductor requires space.
Therefore, in the apparatus described in Patent Document 2, there is a problem that the
ultrasonic probe can not be miniaturized or can not be integrated. In addition, since high-voltage
pulses having a sharp rise and fall are transmitted between the observation device and the
ultrasonic probe, the noise radiated to the outside becomes large, and the restriction on the noise
can not be cleared.
[0024]
In view of the above problems, the present invention transmits a low voltage signal to the signal
transmission cable between the ultrasonic transducer and the observation device, boosts it in the
vicinity of the ultrasonic transducer, and applies the boosted voltage to the transducer. An
ultrasound probe and a body cavity insertion type ultrasound diagnostic apparatus are provided.
[0025]
According to the invention described in claim 1 of the above-mentioned subject, when an
ultrasonic transducer for transmitting and receiving an ultrasonic wave and a drive signal for
driving the ultrasonic transducer are inputted, the drive signal is input. By providing a high
voltage generating means for generating a high voltage based on the high voltage and applying
the high voltage to the ultrasonic transducer, the ultrasonic probe being disposed close to each
other at the tip thereof. Can be achieved.
[0026]
According to the invention described in claim 2, the above-mentioned problem is that the
ultrasonic transducer is a capacitive ultrasonic transducer (cMUT) manufactured using a
micromachine manufacturing process. This can be achieved by providing the ultrasonic probe
according to claim 1 characterized by
[0027]
According to the invention as set forth in claim 3, the above-mentioned problem is characterized
in that the ultrasonic transducer is a piezoelectric transducer (p-MUT) manufactured using a
micromachine manufacturing process. This can be achieved by providing the ultrasonic probe
according to claim 1.
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[0028]
According to the invention set forth in claim 4 of the present invention, the high voltage
generation means outputs a direct current high voltage based on the drive signal when the drive
signal is a direct current low voltage. This can be achieved by providing the ultrasonic probe
according to claim 1.
[0029]
According to the invention set forth in claim 5 of the present invention, when the drive signal is a
direct current low voltage, the high voltage generation means outputs an alternating current high
voltage based on the drive signal. This can be achieved by providing the ultrasonic probe
according to claim 1.
[0030]
According to the invention described in claim 6, the above-mentioned problem is that, in the case
where the drive signal is an AC low voltage, the high voltage generation means outputs a DC high
voltage based on the drive signal. This can be achieved by providing the ultrasonic probe
according to claim 1.
[0031]
According to the invention described in claim 7, the above-mentioned problem is that, when the
drive signal is an AC low voltage, the high voltage generation means outputs an AC high voltage
based on the drive signal. This can be achieved by providing the ultrasonic probe according to
claim 1.
[0032]
According to the invention as set forth in claim 8, the above-mentioned problem is characterized
in that the frequency of the drive signal of the alternating current high voltage is substantially
equal to the resonance frequency of the ultrasonic transducer. This can be achieved by providing
the ultrasonic probe according to claim 5 or 7.
[0033]
According to the invention as set forth in claim 9, the above object provides the ultrasonic probe
according to claim 5 or 7, wherein the alternating current high voltage is a burst wave. It can be
achieved by
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[0034]
According to the invention as set forth in claim 10, the high voltage generating means has a
boosting means for boosting the voltage of the drive signal. This can be achieved by providing an
ultrasound probe.
[0035]
According to the invention as set forth in claim 11, the above object is achieved by providing the
ultrasonic probe according to claim 10, wherein the boosting means is an electromagnetic
transformer. it can.
[0036]
According to the invention as set forth in claim 12, the above object can be achieved by
providing the ultrasonic probe according to claim 10, wherein the pressure raising means is a
piezoelectric transformer. .
[0037]
According to the invention as set forth in claim 13, the above object can be achieved by
providing the ultrasonic probe according to claim 12, characterized in that the piezoelectric
transformer is of a Rosen type. .
[0038]
According to the invention as set forth in claim 14, the above-mentioned subject is the ultrasonic
probe according to claim 12 characterized in that the piezoelectric transformer is made of
lithium niobate. It can be achieved by
[0039]
According to the invention as set forth in claim 15, the high voltage generating means further
converts the drive signal into an alternating current signal when the drive signal is a direct
current signal. This can be achieved by providing the ultrasonic probe according to claim 10,
comprising oscillating means for outputting to the boosting means.
[0040]
According to the invention as set forth in the claim 16, the high voltage generating means further
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applies a DC bias voltage to the AC high voltage outputted from the boosting means. The present
invention can be achieved by providing an ultrasonic probe according to claim 10, characterized
in that
[0041]
According to the invention as set forth in claim 17, the above-mentioned problem is that the DC
bias applying means comprises a first AC high voltage and a second AC high voltage outputted
from the voltage boosting means. Summing means for branching to a high voltage, DC
conversion means for converting the first AC high voltage into DC, and addition for adding the
DC voltage output from the DC conversion means and the second AC high voltage It can be
achieved by providing an ultrasonic probe according to claim 16, characterized in that it
comprises means.
[0042]
According to the invention as set forth in claim 18, the above-mentioned problem is that the
addition means superimposes the second alternating current high voltage on the period in which
the direct current voltage is generated. This can be achieved by providing the ultrasonic probe
according to claim 17.
[0043]
According to the invention as set forth in claim 19, the above-mentioned problem is that,
according to the invention as set forth in claim 19, the period during which the direct current
voltage is generated does not exceed 10 μsec. Can be achieved by providing
[0044]
According to the invention as set forth in claim 20, the above-mentioned problem is
characterized in that the adding means is provided with means for blunting the rise and fall of
the DC voltage. This can be achieved by providing an ultrasound probe.
[0045]
According to the invention as set forth in claim 21, the above-mentioned problem is
characterized in that the p-MUT is formed on a silicon substrate, and further, a switch circuit and
a rectifier are provided on the silicon substrate. This can be achieved by providing the ultrasonic
probe according to Item 3.
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[0046]
According to the invention as set forth in the claim 22 of the present invention, the abovementioned problem is the ultrasonic probe according to claim 2, characterized in that the cMUT
is an electret condenser using an electret film. It can be achieved by
[0047]
According to the invention set forth in claim 23, the above-mentioned subject can form at least
one of a step-up transformer, a switch circuit, a rectifier and a charge amplifier on or in the
silicon substrate of the cMUT. This can be achieved by providing the ultrasonic probe according
to claim 2, characterized in that
[0048]
According to the invention as set forth in claim 24, the above problem is to integrate a switch
circuit, a rectifier and a charge amplifier using a semiconductor process on or in a silicon
substrate constituting the cMUT. This can be achieved by providing the ultrasonic probe
according to claim 2 which is characterized.
[0049]
According to the invention as set forth in claim 25, the above object is achieved by the invention
according to claim 25. In the semiconductor process, a switch circuit, a rectifier, an adder, a delay
circuit, and a charge amplifier are formed on or in a silicon substrate having the cMUT The
present invention can be achieved by providing an ultrasonic probe according to claim 2,
characterized in that it is integrated using
[0050]
According to the invention described in claim 26, the above-mentioned problem is to provide a
body cavity insertion type ultrasonic diagnostic apparatus comprising the ultrasonic probe
according to any one of claims 1 to 25. It can be achieved by
[0051]
By using the present invention, it is possible to transmit only a low voltage signal to the cable and
efficiently generate a high voltage pulse for driving an ultrasonic transducer in the probe without
enlarging the electric circuit inside the ultrasonic probe. it can.
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Moreover, the influence of the noise resulting from a cable can be prevented.
[0052]
First Embodiment In this embodiment, a body cavity insertion type ultrasonic diagnostic
apparatus in the case of using a piezoelectric vibrator as an ultrasonic vibrator will be described.
[0053]
FIG. 1 is a block diagram of a circuit configuration of a body cavity insertion type ultrasonic
diagnostic apparatus using a piezoelectric vibrator as an ultrasonic vibrator in the present
embodiment.
In the figure, a body cavity insertion type ultrasonic diagnostic apparatus 1 includes an insertion
portion 2 and an observation device 5.
[0054]
The insertion portion 2 has an elongated tubular shape for insertion into a body cavity.
The insertion part 2 is comprised from the ultrasonic probe 3, a bending part, and the flexible
tube part 4 in an order from a front end side.
The ultrasonic probe 3 is provided with an ultrasonic transducer, and transmits and receives
ultrasonic signals.
The bending portion is a bendable portion located at the rear end of the ultrasonic probe 3.
The flexible tube portion is positioned at the rear end of the curved portion to be thin and long
and flexible.
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[0055]
The ultrasonic probe 3 incorporates a piezoelectric vibrator 6 a and high voltage generation
means 7.
A coaxial cable 8 (core wire 8 a and shield wire 8 b) is built in the inside of the bending portion
and the flexible tube portion 4.
[0056]
The observation device 5 has functions of generating a control signal to turn on / off the high
voltage / high speed SW, outputting a low voltage RF pulse signal, processing the received signal
and converting it into an image signal.
[0057]
The cable transmission signal Sg1 is transmitted from the observation device 5 to the high
voltage generation means 7 via the core wire 8a of the coaxial cable 8.
The high voltage generation means 7 outputs an AC high voltage when a DC low voltage is input,
and outputs an AC high voltage when an AC low voltage is input.
[0058]
The high voltage generating means 7 includes boosting means 7a (for example, an
electromagnetic transformer, a piezoelectric transformer).
The boosting unit 7a boosts the voltage (for example, 10 V or less) of the cable transmission
signal Sg1 to a predetermined value (for example, 50 V to several hundred V) in order to obtain a
voltage necessary to drive the vibrator.
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[0059]
Then, the high voltage generation means 7 transmits the boosted signal (vibrator drive signal)
Sg2 to the piezoelectric vibrator 6a.
Further, when an AC high voltage signal is outputted from the high voltage generating means 7,
the frequency of the AC high voltage signal is adjusted to be substantially equal to the resonance
frequency of the piezoelectric vibrator.
[0060]
The vibrator drive signal Sg2 is input to one of the electrodes of the piezoelectric vibrator 6a to
apply a voltage to the electrode.
The other electrode of the piezoelectric vibrator 6a is connected to the shield wire 8b of the
coaxial cable 8 and grounded.
Therefore, the piezoelectric vibrator vibrates due to the voltage difference between the
electrodes, and an ultrasonic wave is emitted from the surface of the piezoelectric vibrator 6a.
[0061]
Hereinafter, an embodiment in which an electromagnetic step-up transformer and a piezoelectric
transformer are used as the boosting unit 7a will be described.
The electromagnetic boost transformer can drive a relatively low impedance load because the
output impedance is relatively low.
On the other hand, the piezoelectric transformer has a high boosting efficiency and is
miniaturized as compared with the electromagnetic booster transformer.
05-05-2019
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[0062]
Example 1 FIG. 2 is a block diagram of a circuit configuration of a body cavity insertion type
ultrasonic diagnostic apparatus using an electromagnetic step-up transformer as boosting means
in the present example.
The high voltage generating means 7 in the present embodiment comprises a step-up
transformer 10, a rectifier 11, and a switch 12.
[0063]
The step-up transformer 10 includes a step-up transformer primary coil 10a and step-up
transformer secondary coils 10b and 10c.
The switch 12 has switch terminals 12a, 12b, 12c and 12d.
The switch 12 is for switching between ultrasonic wave transmission and ultrasonic wave
reception.
The switch 12 is in a state in which the switch terminals 12c and 12d are in conduction except at
the time of ultrasonic wave transmission (in a state where a DC voltage is not applied to the
switch drive terminal).
[0064]
At the time of ultrasonic wave transmission, the cable transmission signal Sg1 is transmitted
from the observation device 5 and is input to the step-up transformer primary coil 10a of the
step-up transformer 10.
Then, a boosted AC signal is generated in step-up transformer secondary coils 10b and 10c.
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In the present embodiment, the cable transmission signal Sg1 is a burst wave having a specific
frequency.
[0065]
The high voltage output from the step-up transformer secondary coil 10c side is converted to a
direct current through the rectifier 11 to be a direct current voltage.
When the DC voltage is applied to the switch drive terminal of the switch 12, the switch
terminals 12a and 12b are conducted.
[0066]
Then, the high voltage output from the step-up transformer secondary coil 10b is applied to one
of the electrodes of the piezoelectric vibrator 6a, passing between the conducting switch
terminals 12a and 12b.
The transducer drive signal Sg2 output from the step-up transformer secondary coil 10b is a
higher voltage burst wave in which the amplitude of the cable transmission signal Sg1 is
increased.
[0067]
When a high voltage is applied, the piezoelectric vibrator 6a vibrates and an ultrasonic wave is
emitted from the surface of the piezoelectric vibrator 6a.
At the time of ultrasonic wave reception, the cable transmission signal Sg1 is not transmitted
from the observation device 5, so that no high AC voltage is generated by the step-up
transformer 10.
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Therefore, no voltage is applied to the switch drive terminal of the switch 12, so the switch
terminals 12c and 12d are in a conductive state.
[0068]
At this time, when the piezoelectric vibrator 6a receives an ultrasonic wave, it converts the
ultrasonic wave into an electric signal.
The ultrasonic wave reception signal Sg3 converted into the electric signal is transmitted to the
observation device 5 through the core wire 8a of the coaxial cable 8 through the switch terminal
12c-12d.
[0069]
From the above, by installing the high voltage generating means 7 in the vicinity of the
piezoelectric vibrator 6a, a low voltage signal is transmitted to the cable, and high voltage pulses
for driving the piezoelectric vibrator are efficiently generated in the ultrasonic probe. be able to.
Moreover, the influence of the noise resulting from a cable can be prevented.
[0070]
Example 2 FIG. 3 is a block diagram of a circuit configuration of a body cavity insertion type
ultrasonic diagnostic apparatus using a piezoelectric step-up transformer as a step-up unit in the
present embodiment.
The high voltage generation means 7 in the present embodiment is composed of a piezoelectric
transformer 20, a resistor (DC resistance) 21, a rectifier 11, and a switch 12.
[0071]
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The piezoelectric transformer 20 includes a piezoelectric vibrator 20a, a piezoelectric
transformer primary electrode 20b, a ground electrode 20c, and a piezoelectric transformer
secondary electrode 20d.
The switch 12 is in a state in which the switch terminals 12c and 12d are in conduction except at
the time of ultrasonic wave transmission (in a state where a DC voltage is not applied to the
switch drive terminal).
[0072]
The cable transmission signal Sg1 is transmitted from the observation device 5 at the time of
ultrasonic wave transmission.
In the present embodiment, the cable transmission signal Sg1 is a burst wave having a specific
frequency. The cable transmission signal Sg1 is input to the piezoelectric transformer primary
side electrode 20b of the piezoelectric transformer 20. Then, a high voltage is output from the
piezoelectric transformer secondary side electrode 20d. The vibrator drive signal Sg2 output
from the piezoelectric transformer secondary electrode 20d is a higher voltage burst wave in
which the amplitude of the cable transmission signal Sg1 is increased.
[0073]
The voltage input to the primary side electrode 20b is grounded via the DC resistance 21, so
displacement current due to the voltage input to the primary side electrode 20b also flows to the
DC resistance 21 and both ends of the DC resistance 21 rise. Generate power. This voltage is
converted to direct current through the rectifier 11 to be a direct current voltage. When the DC
voltage is applied to the switch drive terminal of the switch 12, the switch terminals 12a and 12b
are conducted. Then, a high voltage vibrator drive signal Sg2 is transmitted to the piezoelectric
vibrator 6a through the switch terminals 12a-12b.
[0074]
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The cable transmission signal Sg1 is not transmitted from the observation device 5 at the time of
ultrasonic wave reception. Therefore, no current flows in the direct current resistance 21 and the
SWs 12a and 12b do not conduct, so that no high voltage is generated by the piezoelectric
transformer 20. Therefore, no voltage is applied to the switch drive terminal of the switch 12, so
the switch terminals 12c and 12d are in a conductive state.
[0075]
At this time, when the piezoelectric vibrator 6a receives an ultrasonic wave, it converts the
ultrasonic wave into an electric signal. The ultrasonic wave reception signal Sg3 converted into
the electric signal is transmitted to the observation device 5 through the core wire 8a of the
coaxial cable 8 through the switch terminal 12c-12d. Here, the piezoelectric vibrator 6a is not
limited to a bulk piezoelectric vibrator, and may be a so-called p-MUT in which a piezoelectric
thin film is formed on a membrane. In this case, it is preferable to manufacture a Si substrate, and
to form the SWs 12a and 12b and the rectifier 11 on the Si substrate to promote
compactification.
[0076]
FIG. 4 shows an example of the configuration of a piezoelectric vibrator (p-MUT) manufactured
by the micromachine process in the present embodiment. In the p-MUT, a (void) 6a-3 is formed
on a silicon substrate 6a-4, and a membrane 6a-2 is formed above the cavity 6a-3. The
membrane 6a-2 includes a lower electrode 6a-5, and the lower electrode 6a-5 is provided on the
upper surface of the membrane. A piezoelectric film 6a-6 is formed on the upper surface of the
lower electrode 6a-5. An upper electrode 6a-1 is formed on the top surface of the piezoelectric
film 6a-6. A signal is transmitted to the lower electrode 6 a-5 via the switch 12. The upper
electrode 6a-1 is a ground electrode.
[0077]
Next, the piezoelectric transformer 20 will be described. FIG. 5 shows the basic and best studied
Rosen-type structure of the piezoelectric transformer (Non-patent Document 1). The common
ground electrode is attached to the left half of the lower surface of the plate. The piezoelectric
ceramic plate is polarized by applying a DC high voltage to the input portion in the thickness
05-05-2019
19
direction and the output portion in the length direction.
[0078]
When a voltage Vin at the resonance frequency of longitudinal vibration determined by the
dimension in the length direction is applied to the input electrode, the longitudinal vibration
occurs due to the piezoelectric transverse effect, and the high voltage Vout is applied to the
output electrode attached to the end through the piezoelectric longitudinal effect. Will occur. The
boost ratio Vout / Vin when the output terminal is not loaded is represented by the equation (1).
[0079]
Vout / Vin ∝ k31 k33 Q (L / T) (1) From this, if the product of the electromechanical coupling
coefficient k31 of the transverse effect and the electromechanical coupling coefficient k33 of the
longitudinal effect and the piezoelectric material having a large mechanical quality factor Q value
is used It is possible to construct a transformer with a large ratio.
[0080]
In this embodiment, lithium niobate (LiNbO3) is used as a piezoelectric transformer.
The piezoelectric transformer using LiNbO3 single crystal has the following features as
compared with the conventional piezoelectric transformer using ceramic.
[0081]
First, the LiNbO3 crystal does not need to be polarized so that the polarization direction is
orthogonal between the input part and the output part by applying a high DC voltage like
ceramic. In addition, it has a high Q value of 1 to 2 × 10 <4>. As k31 k33 is larger than ceramic,
a high boost ratio is obtained. In addition, the temperature rise during operation due to heat
generation is small. In addition, there is no internal stress in LiNbO3 and it is difficult to be
destroyed.
05-05-2019
20
[0082]
FIG. 6 shows a piezoelectric transformer using lithium niobate in the present example. The
piezoelectric transformer 30 includes a lithium niobate single crystal substrate 31, a voltage
input side electrode 32 (ie, a piezoelectric transformer primary side electrode 20b), a voltage
output side electrode 33 (ie, a piezoelectric transformer secondary side electrode 20d), and an
opposite electrode 33a. (Provided on the bottom of the lithium niobate single crystal substrate
31 so as to face the voltage output side electrode 33), stripe electrodes 34, 35, piezoelectric
transformer support portions 36a, 36b, input signal wiring 37, output signal wiring It consists of
38.
[0083]
When the lateral length of the lithium niobate single crystal substrate 31 is represented by L, the
lateral length of the voltage input side electrode 32 is L / 2. The piezoelectric transformer
support portions 36a and 36b are respectively provided at a position of L / 4 from the end, and
the reason will be described with reference to FIG. The piezoelectric transformer support
portions 36 a and 36 b are terminals for connecting the input signal wiring 37 and the output
signal wiring 38 to the voltage input side electrode 32 and the voltage output side electrode 33,
respectively.
[0084]
FIG. 7 shows the vibrational displacement when observed from the side direction of the lithium
niobate single crystal substrate 31 of FIG. 41 is a vibration neutral surface, and when a burst
wave is applied to the voltage input side electrode 32 through the input signal wiring 37, it
vibrates at a position L / 4 from the end as a node as a characteristic of lithium niobate (vibration
Displacement 42). Therefore, the piezoelectric transformer support portions 36a and 36b are
provided at the portions to be the nodes.
[0085]
The piezoelectric transformer support 36 b and the voltage output side electrode 33 are
electrically connected by the stripe electrodes 34 and 35. Then, the high voltage signal generated
05-05-2019
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on the surface of the voltage output side electrode 33 is transmitted through the stripe
electrodes 34 and 35 and output from the output signal wiring 38.
[0086]
Thus, the vibration of the lithium niobate single crystal substrate 31 can be prevented from being
inhibited compared to the case where the output signal wiring 38 is connected to the voltage
output side electrode 33. The voltage output side electrode 33 vibrates in the direction
perpendicular to the end face.
[0087]
FIG. 8 is a modification (part 1) of FIG. In FIG. 8, the voltage output side electrode 33 and the
output signal wiring 38 are electrically connected by the lead wire 51. FIG. 9 is a modification
(part 2) of FIG. In FIG. 9, the voltage output side electrode 33 and the output signal wiring 38 are
conducted by the lead wire 52.
[0088]
From the above, by installing the high voltage generating means 7 in the vicinity of the
piezoelectric vibrator 6a, a low voltage signal is transmitted to the cable, and high voltage pulses
for driving the piezoelectric vibrator are efficiently generated in the ultrasonic probe. be able to.
Moreover, the influence of the noise resulting from a cable can be prevented.
[0089]
Second Embodiment In this embodiment, a body cavity insertion type ultrasonic diagnostic
apparatus in the case of using a capacitive ultrasonic transducer (cMUT) using a micromachine
process as an ultrasonic transducer will be described.
[0090]
The structure of cMUT will be briefly described.
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22
First, a cavity (void, recess) is provided in a silicon substrate, and a lower electrode is disposed at
the bottom of the cavity. A membrane is formed above the cavity, and an upper electrode film is
included as one of the components of the membrane. The upper electrode film is a ground
electrode.
[0091]
A unit consisting of a recess forming a cavity and a membrane covering the recess is called a cell.
And, an aggregate of a plurality of transducer cells is called a transducer element. The transducer
element is a minimum unit for inputting and outputting the drive control signal.
[0092]
The operation of the cMUT having such a configuration outline will be described. When a voltage
is applied to the pair of electrodes of the upper electrode and the lower electrode, the electrodes
are pulled apart, and when the voltage is set to 0, it returns to the original state. As a result of the
membrane vibrating by this vibration operation, an ultrasonic wave is generated, and the
ultrasonic wave is irradiated in the upper direction of the upper electrode.
[0093]
FIG. 10 is a block diagram of a body cavity insertion type ultrasonic diagnostic apparatus using a
capacitive ultrasonic transducer (cMUT) as an ultrasonic transducer in the present embodiment.
In FIG. 10, the piezoelectric vibrator 6a of FIG. 1 is replaced with a capacitive ultrasonic vibrator
(cMUT) 6b. The basic configuration and operation of FIG. 10 are the same as those of FIG.
[0094]
The high voltage generation means 7 in this embodiment outputs a DC high voltage when a DC
low voltage is input, outputs an AC high voltage when a DC low voltage is input, or inputs an AC
low voltage. When it is done, it outputs DC high voltage, and when AC low voltage is input, it
outputs AC high voltage, etc.
05-05-2019
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[0095]
The high voltage generating means 7 includes boosting means 7a (for example, an
electromagnetic transformer, a piezoelectric transformer).
The boosting unit 7a boosts the voltage (for example, 10 V or less) of the cable transmission
signal Sg1 to a predetermined value (for example, 50 V to several hundred V) in order to obtain a
voltage necessary to drive the vibrator.
[0096]
Further, when an AC high voltage signal is outputted from the high voltage generating means 7,
the frequency of the AC high voltage signal is adjusted to be substantially equal to the resonance
frequency of the electrostatic ultrasonic transducer. Hereinafter, an embodiment in which an
electromagnetic step-up transformer and a piezoelectric transformer are used as the boosting
unit 7a will be described. The electromagnetic boost transformer can drive a relatively low
impedance load because the output impedance is relatively low. On the other hand, the
piezoelectric transformer has a high boosting efficiency and is miniaturized as compared with the
electromagnetic booster transformer. Also, piezoelectric transformers are preferred for cMUTs
that require high impedance loading, as the output impedance is relatively high. Here, the cMUT
may not be a pure capacitor structure, but may be an electret capacitor using an electret film.
[0097]
Example 1 FIG. 11 is a block diagram of a circuit configuration of a body cavity insertion type
ultrasonic diagnostic apparatus using an electromagnetic step-up transformer as boosting means
in the present example. The high voltage generating means 7 in the present embodiment
comprises a step-up transformer 10, a rectifier 11, and a switch 12. These are similar to FIG. In
addition, a charge amplifier 60 is provided. The switch 12 is in a state in which the switch
terminals 12c and 12d are in conduction except at the time of ultrasonic wave transmission (in a
state where a DC voltage is not applied to the switch drive terminal).
[0098]
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24
The charge amplifier 60 has a function of performing impedance conversion (converting to high
impedance to low impedance), a function of detecting charges on the electrode surface of the
cMUT 6b, and a function as an amplifier. The function of detecting the charge is that the
ultrasonic wave emitted from the membrane surface of the cMUT 6b is reflected inside the body
cavity, and when the cMUT 6b receives the reflected wave, the membrane vibrates according to
the reception intensity of the reflected wave, Since the change of the charge on the upper
electrode according to the vibration occurs, it means the function of detecting the charge.
[0099]
At the time of ultrasonic wave transmission, the cable transmission signal Sg1 is transmitted
from the observation device 5 and is input to the step-up transformer primary coil 10a of the
step-up transformer 10. Then, a boosted AC signal is generated in step-up transformer secondary
coils 10b and 10c. In the present embodiment, the cable transmission signal Sg1 is a burst wave
having a specific frequency.
[0100]
The voltage output from the step-up transformer secondary coil 10c side is converted to a
rectifier 11 DC voltage. When the DC voltage is applied to the switch drive terminal of the switch
12, the switch terminals 12a and 12b conduct.
[0101]
Then, the high voltage output from the step-up transformer secondary coil 10b side is applied to
the lower electrode (upper side in the figure) of the cMUT 6b, passing between the conducting
switch terminals 12a and 12b. The transducer drive signal Sg2 output from the step-up
transformer secondary coil 10b is a higher voltage burst wave in which the amplitude of the
cable transmission signal Sg1 is increased.
[0102]
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25
When a high voltage burst wave is applied, the membrane of cMUT 6b vibrates and ultrasonic
waves are emitted from the membrane surface. At the time of ultrasonic wave reception, since
the amplitude of the cable transmission signal Sg1 is 0 in the time domain in which the drive
burst wave has not already occurred, the AC high voltage is not generated by the step-up
transformer 10. Therefore, since the voltage applied to the switch drive terminal of the switch 12
is zero, the switch terminals 12c and 12d are in a conductive state.
[0103]
At this time, when the cMUT 6b receives an ultrasonic wave, the cMUT 6b converts the ultrasonic
wave into an electric signal. The ultrasonic wave reception signal Sg3 converted into the electric
signal is transmitted to the observation device 5 through the core wire 8a of the coaxial cable 8
through the switch terminal 12c-12d.
[0104]
As mentioned above, by installing the high voltage generating means 7 in the vicinity of the
capacitive ultrasonic transducer 6b, the low voltage signal is transmitted to the cable, and the
capacitive ultrasonic transducer is driven in the ultrasonic probe. High voltage pulse can be
generated efficiently. Moreover, the influence of the noise resulting from a cable can be
prevented. As described above, cMUT is manufactured on a Si substrate using a micromachine
process, but components other than the step-up transformer, such as SW12, rectifier 11, and
charge amplifier can be formed on or in the Si substrate on which cMUT is formed. This makes it
possible to make it more compact.
[0105]
Example 2 FIG. 12 is a block diagram of a circuit configuration of a body cavity insertion type
ultrasonic diagnostic apparatus using a piezoelectric step-up transformer as a boosting means in
the present example. The high voltage generation means 7 in the present embodiment is
composed of a piezoelectric transformer 20, a resistor (DC resistance) 21, a rectifier 11, and a
switch 12. These are similar to FIG. Further, as in FIG. 11, a charge amplifier 60 is provided. The
switch 12 is in a state in which the switch terminals 12c and 12d are in conduction except at the
time of ultrasonic wave transmission (in a state where a DC voltage is not applied to the switch
05-05-2019
26
drive terminal).
[0106]
The cable transmission signal Sg1 is transmitted from the observation device 5 at the time of
ultrasonic wave transmission. In the present embodiment, the cable transmission signal Sg1 is a
burst wave having a specific frequency. The cable transmission signal Sg1 is input to the
piezoelectric transformer primary side electrode 20b of the piezoelectric transformer 20. Then, a
high voltage is output from the piezoelectric transformer secondary side electrode 20d. The
vibrator drive signal Sg2 output from the piezoelectric transformer secondary electrode 20d is a
higher voltage burst wave in which the amplitude of the cable transmission signal Sg1 is
increased.
[0107]
The voltage applied to the input side is divided by the impedance between the DC resistance 21
and the electrodes 20b-20c, and the voltage-divided piezoelectric signals at both ends of the DC
resistance 21 are converted into a DC voltage by the rectifier 11. When the DC voltage is applied
to the switch drive terminal of the switch 12, the switch terminals 12a and 12b conduct. Then, a
high voltage vibrator drive signal Sg2 is applied to the cMUT 6b through the switch terminals
12a-12b.
[0108]
At the time of ultrasonic wave reception, since the amplitude of the cable transmission signal Sg1
is 0 in the time domain in which the drive burst wave has not been generated, the piezoelectric
transformer 20 does not generate a high voltage. Therefore, since the voltage applied to the
switch drive terminal of the switch 12 is zero, the switch terminals 12c and 12d are in a
conductive state.
[0109]
At this time, when the cMUT 6b receives an ultrasonic wave, the cMUT 6b converts the ultrasonic
05-05-2019
27
wave into an electric signal. The ultrasonic wave reception signal Sg3 converted into the electric
signal is transmitted to the observation device 5 through the core wire 8a of the coaxial cable 8
through the switch terminal 12d-12c.
[0110]
In the present embodiment, the SW 12, the rectifier 11, and the charge amplifier 60 are
integrated using a semiconductor process on or in the Si substrate constituting the cMUT, which
can be made more compact, which is preferable.
[0111]
Embodiment 3 In this embodiment, a body cavity insertion type ultrasonic diagnostic apparatus
including a DC bias pulse generating unit and an addition unit for adding an RF pulse and a DC
bias pulse will be described.
[0112]
FIG. 13 is a block diagram of a circuit configuration of the body cavity insertion type ultrasonic
diagnostic apparatus in the present embodiment.
In FIG. 13, a DC bias application means 70 is provided between the piezoelectric transformer
secondary electrode 20d and the switch terminal 12a in FIG.
[0113]
FIG. 14 shows the details of the DC bias application means 70 of FIG.
FIG. 15 shows waveforms of respective signals in the body cavity insertion type ultrasonic
diagnostic apparatus of FIG. The DC bias application means 70 includes an adder 71 and a
rectifier 72.
[0114]
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First, the cable transmission signal Sg1 is input to the piezoelectric transformer primary side
electrode 20b of the piezoelectric transformer 20 (for example, lithium niobate single crystal
substrate) (see FIG. 15A). Then, as described in the first embodiment, lateral effect piezoelectric
vibration is caused by the high voltage signal applied between the piezoelectric transformer
primary side electrode 20b of the piezoelectric transformer 20 and the ground electrode 20c,
and the thickness direction polarization 77 It is converted into longitudinal effect vibration by
action, and as a result, an alternating current signal 73 of high voltage is generated at the
electrode 20d.
[0115]
Then, an RF pulse 73, which is a high voltage signal, is output from the piezoelectric transformer
secondary electrode 20d. The high voltage RF pulse 73 output from the piezoelectric transformer
secondary electrode 20 d is input to the DC bias application unit 70.
[0116]
The RF pulse 73 is branched into two in the DC bias application means 70. One branched RF
pulse 74 (= 73) (see FIG. 15B) is input to the adder 71. The other branched RF pulse passes
through the rectifier 72 to become a DC bias pulse (see FIG. 15C) 75, and is input to the adder
71. The adder 71 adds the RF pulse 74 and the DC bias pulse 75, and outputs the result as a
vibrator drive signal Sg2 (see FIG. 15D). In FIG. 15 (d), 80 indicates a DC bias level.
[0117]
As described above, when the DC high voltage signal is output from the high voltage generating
means 7, both the high voltage DC signal and the high voltage AC signal are output to the adder
71 at substantially the same timing in the high voltage generating means 7. . It is for making it
easy to superimpose both signals. Specifically, when the DC high voltage signal is output from
the high voltage generating means 7, the generation period of the DC output signal 75 output
from the rectifier 72 is the same as the generation period of the AC output signal 74, or the AC
output signal It is set to be longer than the generation period of 74 so that the signals of both
parties can be easily superimposed.
05-05-2019
29
[0118]
That is, in FIG. 15, in order to make the pulse width of the DC output signal 75 longer than the
pulse width of the AC output signal 74, the DC output signal 75 is output first and then the AC
output signal 74 is superimposed. After the output 74 is completed, the output of the DC output
signal 75 is ended.
[0119]
More specifically, a trigger signal is generated at the rise timing of the DC bias pulse, and an RF
pulse is generated by the trigger signal after a set delay time has elapsed.
If this delay time is set too long, the RF pulse deviates from the DC bias pulse (does not overlap),
so an optimal delay time is set. Therefore, the adder 71 includes such a pre-processing function
(delay function).
[0120]
The DC output signal generation period should not exceed 10 μsec. This is because, if the pulse
width of the DC bias pulse is 10 μsec or more, even if there is an echo signal in the immediate
vicinity, it is superimposed on the transmission signal, the S / N of detection decreases, and the
diagnostic image of the region near the transducer It is because you can not obtain
[0121]
In addition, if the rising and falling of the high voltage DC output signal occur rapidly, the cMUT
may be broken. In order to prevent this, the rising and falling of the high voltage DC output
signal are slowed down. That is, since the steep rise and fall have high frequency components,
this high frequency component is bypassed by connecting a capacitor in parallel to the output
terminal to slow the rise and fall.
[0122]
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30
Although the case of using the piezoelectric transformer has been described in this embodiment,
it may be used for an electromagnetic transformer. Since the broadband characteristics of the
cMUT depend on the DC bias, the broadband characteristics can be obtained by generating the
DC bias as described above, and ultrasonic diagnosis using harmonic imaging can be performed.
In the present embodiment, the components described in FIGS. 13 and 14, for example, the SW
12, the rectifiers 11 and 72, the adder 71, and the delay circuit (not shown) described above are
formed on or in the Si substrate on which the cMUT 6 b is formed. The charge amplifier 60 can
be integrated (integrated) using a semiconductor process, whereby further compactification is
realized, and a form preferable as an ultrasonic transducer for body cavity insertion can be
obtained.
[0123]
Fourth Embodiment FIG. 16 is a block diagram of a circuit configuration of a body cavity
insertion type ultrasonic diagnostic apparatus in the present embodiment. In the figure, a high
frequency oscillator 90 for generating an alternating current signal to be applied to the input
side of the boosting means 7a is further provided in the circuit of FIG. The piezoelectric
transformer is a device operated by an alternating current signal, and is configured for the
purpose of direct current voltage operation. That is, the signal 91 is a DC voltage signal, and the
high frequency oscillation circuit 90 is used as means for converting this into an alternating
current signal 92.
[0124]
FIG. 17 shows waveforms of respective signals in the body cavity insertion type ultrasonic
diagnostic apparatus of FIG. A DC pulse 91 (see FIG. 17A) is transmitted as the cable
transmission signal Sg1 and input to the high frequency oscillator 90. The high frequency
oscillator 90 raises the frequency of the DC pulse 91 and converts it into a burst wave 92 (see
FIG. 17B).
[0125]
The burst wave 92 is input to the piezoelectric transformer primary side electrode 20b of the
piezoelectric transformer 20 (for example, lithium niobate single crystal substrate), and the
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31
subsequent steps are the same as in the third embodiment (FIG. It corresponds to (a). FIG. 17 (c)
corresponds to FIG. 15 (b). FIG. 17 (d) corresponds to FIG. 15 (c). FIG. 17 (e) corresponds to FIG.
15 (d). ).
[0126]
By doing this, since the cable transmission signal Sg1 has a low frequency, there is no cable
signal loss, and the signal transmission signal Sg1 is unlikely to be affected by external or
external noises. Although the case of using the piezoelectric transformer has been described in
this embodiment, it may be used for an electromagnetic transformer.
[0127]
FIG. 18 is a block diagram of a circuit configuration of a body cavity insertion portion using an
array type ultrasonic transducer in the present embodiment. A plurality of capacitive ultrasonic
transducer array 100 and transducer elements (6b-1, 6b-2, 6b-3,..., 6b-n) shown in FIG. .
[0128]
FIG. 2 is a block diagram of a circuit configuration of a body cavity insertion type ultrasonic
diagnostic apparatus using a piezoelectric vibrator as an ultrasonic vibrator in the first
embodiment. A block diagram of a circuit configuration of a body cavity insertion type ultrasonic
diagnostic apparatus using an electromagnetic step-up transformer as a pressure rising means in
the first embodiment (Example 1) is shown. The block diagram of a circuit structure of a body
cavity insertion type | mold ultrasonic diagnosing device which uses a piezoelectric-type step-up
transformer as a pressure rising means in 1st Embodiment (Example 2) is shown. An example of
a structure of p-MUT in 1st Embodiment is shown. The structure of a Rosen type piezoelectric
transformer is shown. The piezoelectric transformer using lithium niobate in 1st Embodiment
(Example 2) is shown. The vibration displacement at the time of observing from the side direction
of the lithium niobate single crystal board | substrate 31 of FIG. 6 is shown. It is a modification
(the 1) of FIG. It is a modification (the 2) of FIG. FIG. 7 is a block diagram of a body cavity
insertion type ultrasonic diagnostic apparatus using a capacitive ultrasonic transducer (cMUT) as
an ultrasonic transducer in a second embodiment. The block diagram of a circuit structure of a
body cavity insertion type | mold ultrasonic diagnosing device which uses an electromagnetic
type step-up transformer as a pressure rising means in 2nd Embodiment (Example 1) is shown.
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32
The block diagram of a circuit structure of a body cavity insertion type | mold ultrasonic
diagnosing device using a piezoelectric-type step-up transformer as a pressure rising means in
2nd Embodiment (Example 2) is shown. The block diagram of the circuit structure of the in-vivo
insertion type ultrasound diagnosing device in 2nd Embodiment (Example 3) is shown. The detail
of the DC bias application means 70 of FIG. 13 is shown. FIG. 15 shows waveforms of respective
signals in the body cavity insertion type ultrasonic diagnostic apparatus of FIG. 14. The block
diagram of the circuit structure of the in-vivo insertion type ultrasound diagnosing device in 2nd
Embodiment (Example 4) is shown. FIG. 17 shows waveforms of respective signals in the body
cavity insertion type ultrasonic diagnostic apparatus of FIG. 16. The block diagram of the circuit
structure of the body cavity insertion part using the array-type ultrasonic transducer in 2nd
Embodiment (Example 4) is shown. An example of cMUT in the past is shown. An example (the 1)
of the control circuit using the drive circuit of the piezoelectric ultrasonic transducer in the past
is shown. An example (the 2) of the control circuit using the drive circuit of the piezoelectric
ultrasonic transducer in the past is shown.
Explanation of sign
[0129]
Reference Signs List 1 intracorporeal insertion type ultrasonic diagnostic apparatus 2 insertion
section 3 ultrasonic probe 4 bending portion and flexible tube 5 observation device 6a
piezoelectric vibrator 6a-1 upper electrode 6a-2 membrane 6a-3 cavity 6a-4 silicon substrate 6a
-5 Lower electrode 6a-6 Piezoelectric film 6b cMUT 7 High voltage generation means 7a
Boosting means 8 Coaxial cable 8 8a core 8b Shield wire 10 Boost transformer 10a Boost
transformer primary coil 10b, 10c Boost transformer secondary coil 11 Rectifier 12 Switch 12a,
12b, 12c, 12d Switch terminal 20 Piezoelectric transformer 20a Piezoelectric vibrator 20b
Piezoelectric transformer primary side electrode 20c Ground electrode 20d Piezoelectric
transformer secondary side electrode 21 Resistor (DC resistance) 60 Charge amplifier 70 DC bias
application means 71 Adder 72 Rectifier 90 High frequency Exciter
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