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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ultrasonic transducer apparatus for breaking a calculus or eliminating a tumor utilizing ultrasonic oscillations.
2. Description of the Related Art
As shown in FIG. 1, a conventional ultrasonic transducer apparatus of this type includes a driving unit 1 having a driving circuit 2, and an ultrasonic transducer probe 3 which has an ultrasonic transducer 4 and which is detachable from the
driving unit 1.
As shown in FIG. 2, an equivalent circuit of the ultrasonic transducer 4 includes an LCR series resonance circuit formed of an inductor S, a capacitor 6, and a resistor 7, and a dumping capacitor Cd connected in parallel with the LCR series
resonance circuit. When a voltage is applied to the ultrasonic transducer 4, currents il and id are supplied through the LCR series resonance circuit and the dumping capacitor Cd, respectively. Of the currents il and id, only the current il is
converted into ultrasonic oscillations. Therefore, it is most efficient to drive the ultrasonic transducer 4 at a resonance frequency of the LCR series resonance circuit. The resonance frequency of the series resonance circuit is referred to as a
mechanical resonance frequency ft for the ultrasonic transducer 4 hereinafter.
Since a conductance G of the ultrasonic transducer 4 is maximum at the mechanical resonance frequency ft, the frequency ft is a rightmost point in a graph of an admittance Y (=G+jB) of the ultrasonic transducer 4, as shown in FIG. 3. FIG. 3
shows a locus of the admittance Y obtained when an angular frequency .omega. is a variable. Reference symbol B denotes a susceptance; and .omega., a driving angular frequency (=2.pi.f).
The conventional driving circuit 2 includes a phase-locked loop (PLL) circuit to lock the driving frequency when the conductance is maximum. The PLL circuit controls the driving frequency to make a phase difference between a voltage applied to
the ultrasonic transducer 4 and a current supplied to the ultrasonic transducer 4, i.e., a susceptance, zero. As shown in FIG. 3, however, the center of an admittance characteristic circle of the ultrasonic transducer 4 is shifted in the positive
direction of the susceptance by a capacitive susceptance .omega.Cd of the dumping capacitor Cd. Therefore, a lock point (point at which a susceptance is zero) PR obtained by the PLL does not coincide with the mechanical resonance point ft (point at
which a conductance is maximum), i.e., the transducer 4 cannot be driven at the mechanical resonance frequency even if a phase difference between the voltage and the current is set to be zero. As a result, conversion efficiency of a driving signal into
ultrasonic oscillations is poor.
An apparatus to eliminate the above drawback is disclosed in Published Unexamined Japanese Utility Model Application No. 54-136943. As shown in FIG. 4, in this apparatus, the driving unit 1 includes an inductor Ld arranged in parallel with the
ultrasonic transducer 4 besides the driving circuit 2. According to this apparatus, as shown in FIG. 5, a capacitive susceptance .omega.Cd of the dumping capacitor Cd included in the ultrasonic transducer 4 can be canceled by an inductive susceptance
(=1/.omega.Ld) of the inductor Ld. As a result, as shown in FIG. 5, the center of the admittance characteristic circle of the equivalent circuit of the ultrasonic transducer 4 is positioned on the axis where the susceptance is zero, and the lock point
PR obtained by the PLL coincides with the mechanical resonance point ft. Therefore, the ultrasonic transducer 4 can be efficiently driven.
A capacitive susceptance of the dumping capacitor in the ultrasonic transducer probe is varied depending on its shape or the characteristics of the ultrasonic transducer included in the probe. For this reason, in the ultrasonic transducer
apparatus in which different types of ultrasonic transducer probes can be connected to the above-mentioned driving unit shown in FIG. 4, capacitive susceptances of dumping capacitors in the ultrasonic transducers of all probes cannot be canceled. In
other words, in a driving unit including only one inductor Ld, capacitive susceptances of different dumping capacitors cannot be perfectly canceled. Therefore, when various ultrasonic transducer probes are selectively connected to a driving unit as in
an ultrasonic medical treatment apparatus in accordance with a target to be treated, various ultrasonic transducers cannot be driven at respective optimal mechanical resonance points. As a result, driving efficiency is poor.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an ultrasonic transducer apparatus which reliably drives an ultrasonic transducer at its mechanical resonance frequency even when types of ultrasonic transducer in an ultrasonic transducer probe
connected to a driving unit are different so that capacitive susceptances of dumping capacitors are different, thereby efficiently converting a driving signal into ultrasonic oscillations.
According to the present invention, there is provided an ultrasonic transducer apparatus comprising a probe including an ultrasonic transducer formed of a series connection of an inductor, a resistor, and a capacitor, and a dumping capacitor
connected in parallel with the series connection; a driving unit detachably connected to the probe and including a driving circuit for supplying to the ultrasonic transducer a driving signal having a frequency where a phase difference between a voltage
applied to the ultrasonic transducer and a current supplied to the ultrasonic transducer is substantially zero, and an inductor connected in parallel with the ultrasonic transducer; and an impedance matching element arranged in at least one of the probe
and the driving unit and having an impedance corresponding to a capacitive susceptance of the dumping capacitance.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention
may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention and, together with the general description given above and the detailed description of
the preferred embodiments given below, serve to explain the principles of the invention.
FIG. 1 is a block diagram of a conventional ultrasonic transducer apparatus;
FIG. 2 is an equivalent circuit diagram of an ultrasonic transducer;
FIG. 3 is a graph of an admittance characteristic for explaining an operation of the conventional apparatus shown in FIG. 1;
FIG. 4 is a block diagram of another conventional ultrasonic transducer apparatus;
FIG. 5 is a graph of an admittance characteristic for explaining an operation of the conventional apparatus shown in FIG. 4;
FIG. 6 is a block diagram of an ultrasonic transducer apparatus according to a first embodiment of the present invention;
FIG. 7 is a block diagram showing the first embodiment with another ultrasonic transducer probe;
FIG. 8 is a block diagram of a driving circuit for the first embodiment;
FIG. 9 is a block diagram of an ultrasonic transducer apparatus according to a second embodiment of the present invention;
FIG. 10 is a block diagram of the second embodiment with another ultrasonic transducer probe;
FIG. 11 is a block diagram of an ultrasonic transducer apparatus according to a third embodiment of the present invention;
FIG. 12 is a block diagram of the third embodiment with another ultrasonic transducer probe;
FIG. 13 is a block diagram of an ultrasonic transducer apparatus according to a fourth embodiment of the present invention;
FIG. 14 is a block diagram of an ultrasonic transducer apparatus according to a fifth embodiment of the present invention;
FIG. 15 is a block diagram of the fifth embodiment with another ultrasonic transducer probe;
FIG. 16 is a block diagram of an ultrasonic transducer apparatus according to a sixth embodiment of the present invention;
FIG. 17 is a block diagram of the sixth embodiment with another ultrasonic transducer probe;
FIG. 18 is a block diagram of an ultrasonic transducer apparatus according to a seventh embodiment of the present invention;
FIG. 19 is a block diagram of the seventh embodiment with another ultrasonic transducer probe;
FIG. 20 is a block diagram of an ultrasonic transducer apparatus according to a eighth embodiment of the present invention;
FIG. 21 is a block diagram of an ultrasonic transducer apparatus according to a ninth embodiment of the present invention; and
FIG. 22 is a graph of an admittance for explaining an operation of the apparatus in the ninth embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
An ultrasonic transducer apparatus according to preferred embodiments of the present invention will be described hereinafter with reference to the accompanying drawings.
FIG. 6 is a block diagram showing an arrangement of the first embodiment. A driving unit 12 includes a driving circuit 14, an inductor 16, and connection terminals 18, 20, 22, and 24. Output terminals of the driving circuit 14 are respectively
connected to the connection terminals 18 and 24. The inductor 16 is connected between the connection terminals 18 and 24. An inductance of the inductor 16 is constant, i.e., L1. The inductor 16 includes intermediate taps at positions corresponding to
inductances L2 and L3 (L1>L2>L3), respectively. The intermediate taps corresponding to the inductances L2 and L3 are connected to the connection terminals 20 and 22, respectively. More specifically, the inductances between the terminals 18 and 24
can be switched to the inductance L1, L2, or L3.
An ultrasonic transducer probe 26 includes an ultrasonic transducer 28 having an equivalent circuit shown in FIG. 2, and a connector 30 connected to the driving unit 12 through the connection terminals 18, 20, 22, and 24.
When this embodiment is applied to an ultrasonic medical treatment apparatus, the probe includes a horn or a pipe (not shown) for efficiently transmitting ultrasonic oscillations of the ultrasonic transducer 28 to a morbid part. Such a probe is
known as a Langevin-type transducer probe.
The ultrasonic transducer 28 is connected between the connection terminals 18 and 24. It is assumed that a capacitance of a dumping capacitor in the ultrasonic transducer 28 is Cd1. The probe 26 is detachably connected to the driving unit 12
through the connector 30. More specifically, another ultrasonic transducer probe 26a of another type having an ultrasonic transducer 28a as shown in FIG. 7 can be connected to the driving unit 12. It is assumed that the dumping capacitance of the
ultrasonic transducer 28a is Cd2.
The connector of each probe includes a wiring for connecting the connection terminal 18 to the connection terminal 20 or 22 or does not include the wiring so as not to connect the connection terminal 18 to other connection terminals at all in
accordance with the capacitance of the dumping capacitor of the ultrasonic transducer. More specifically, when the probe is connected to the driving unit, an inductor for providing an inductive susceptance having an absolute value equal to that of a
capacitive susceptance of the dumping capacitor in the ultrasonic transducer is connected in parallel with the ultrasonic transducer, and the capacitive susceptance (positive) of the ultrasonic transducer is canceled by the inductive susceptance
(negative) of the inductor 16.
A detailed arrangement of the driving circuit 14 is shown in FIG. 8. An output from a voltage-controlled oscillator 36 is supplied to the connection terminals 18 and 24 through an amplifier 38 and a transformer 40. Phases of an output voltage
and an output current from the amplifier 38 are detected, and detection results are input to a phase comparator 42. A phase difference between the output voltage and the output current is applied to the control terminal of the oscillator 36 through a
low-pass filter 44. Thus, the driving circuit 14 includes a PLL circuit for locking a driving frequency at the mechanical resonance frequency where the susceptance of the ultrasonic transducer 28 of the ultrasonic probe is substantially zero, i.e., a
conductance is maximum.
As described above, according to the first embodiment, a plurality of intermediate taps are arranged at the inductor 52 in the driving unit 12 to provide a plurality of inductances, and the wiring in the connector 30 of the probe 26 is varied in
accordance with a capacitive susceptance of the dumping capacitor in the ultrasonic transducer 28. Therefore, an inductance corresponding to the capacitive susceptance of the dumping capacitor can be selectively connected in parallel to the ultrasonic
transducer 28. Even if a different kind of probe is connected to the driving unit 12, a capacitive susceptance of the dumping capacitor can be perfectly canceled by the inductive inductance of the inductor 16. Therefore, the ultrasonic transducer has
admittance characteristics shown in FIG. 5, and a lock point obtained by the driving circuit 14 having the PLL circuit coincides with the mechanical resonance point of the ultrasonic transducer. As a result, when another ultrasonic oscillator probe is
connected to this driving unit 12, the driving circuit 14 can reliably drive the ultrasonic transducer 28 at its mechanical resonance point. This apparatus allows an improvement of efficiency achieved when a calculus is broken, or a tumor is eliminated. Note that the number of taps is not limited to three. When the number of types of probe is increased, the number of taps may be increased in accordance with the number of types of probe.
FIG. 9 is a block diagram showing the second embodiment. In the second embodiment, intermediate taps are arranged at an inductor in the same manner as in the first embodiment, and an inductance is selected upon selection of the tap. In the
second embodiment, each tap is positioned so that an inductance is multiplied, and the larger number of inductance levels than the number of taps can be obtained in accordance with a combination of the inductances between the taps.
A driving unit 50 includes the driving circuit 14, an inductor 52, and connection terminals 54, 56, 58, 60, 62, 64, and 66. Output terminals of the driving circuit 14 are respectively connected to the connection between the connection terminals
54 and 66. A total inductance of the inductor 52 is 32L, and the intermediate taps are arranged at positions where the inductances from the connection terminal 66 are L, 2L, 4L, 8L, and 16L, respectively. The taps corresponding to the inductances 16L,
8L, 4L, 2L, and L are connected to the connection terminals 56, 58, 60, 62, and 64, respectively.
An ultrasonic transducer probe 68 includes the ultrasonic transducer 28, and a connector 70 detachably connected to the driving unit 50 through the connection terminals 54, 56, 58, 60, 62, 64, and 66. The ultrasonic transducer 28 is connected
between the connection terminals 54 and 66. The connector 70 includes or does not include wirings for connecting arbitrary pairs of the connection terminals 54, 56, 58, 60, 62, 64, and 66 to each other in accordance with a capacitive susceptance of the
dumping capacitor in the ultrasonic transducer 28. For this reason, the inductance of the inductor 52 can be varied in 32 ways of L to 32L depending on interconnections of the connection terminals. Thus, the connector 70 includes the wiring for
determining an inductance of the inductor 52 so that the inductive susceptance of the inductor 52 connected in parallel with the ultrasonic transducer 28, when the probe 68 is connected to the driving unit 50, is equal to a capacitive susceptance of the
ultrasonic transducer. In the arrangement shown in FIG. 9, the connection terminals 56 and 58, and the connection terminals 60 and 62 are connected to each other; the inductance of the inductor 52 is set to be 22L. In another probe 68a shown in FIG.
10, the connection terminals 54 and 56, and the connection terminals 62 and 64 are connected to each other; the inductance of the inductor 52 is set to be 14L.
According to the second embodiment, the capacitive susceptance of the dumping capacitor can be canceled by the inductive inductance of the inductor in the same manner as in the first embodiment. In addition, the inductance of the inductor can be
varied in a large number of levels. Therefore, this apparatus can be applied to various ultrasonic probes as compared with that in the first embodiment. Even if a new type of ultrasonic oscillator probe is manufactured, the capacitive susceptance of a
dumping capacitor can be reliably canceled by changing wiring in the connector without increasing the number of intermediate taps of the inductor and changing the structure of the driving unit.
FIG. 11 is a block diagram showing the third embodiment. In the third embodiment, an inductance of an inductor is varied in accordance with the type of probe connected to a driving unit, i.e., a capacitive susceptance of a dumping capacitor, in
the same manner as in the first and second embodiments. Although the inductance is varied in a stepped manner upon selection of the tap in the first and second embodiments, a core of a coil of the inductor is slid to continuously change the inductance
in the third embodiment.
A driving unit 74 includes the driving circuit 14, an inductor 76, and connection terminals 78 and 80. Output terminals of the driving circuit 14 are respectively connected to the connection terminals 78 and 80, and the inductor 76 is connected
between the connection terminals 78 and 80. A ferrite core 82 is inserted in a coil of the inductor 76. One end of the ferrite core 82 is fixed to a part of a housing of the driving unit 74 through a spring 84. The spring 84 is biased in its extending
direction, and the core 82 is biased in the right direction in FIG. 11.
An ultrasonic oscillator probe 86 includes the ultrasonic transducer 28, and a connector 88 detachably connected to the driving unit 74 through the connection terminals 78 and 80. The ultrasonic transducer 28 is connected between the connection
terminals 78 and 80. The connector 88 holds a bar 90 for pushing the other end of the ferrite core 82 against a biasing force of the spring 84 when the probe 86 is connected to the driving unit 74. One end of the bar 90 is fixed in the connector 88.
The length of the bar 90 is determined in accordance with the capacitive susceptance of the dumping capacitor in the ultrasonic transducer 28. In the arrangement shown in FIG. 11, the length of the bar 90 is relatively long, and the bar 90 deeply pushes
the ferrite core 82 in. In contrast to this, in a probe 86a shown in FIG. 12, the length of the bar 90a is relatively short, and the bar 90a hardly pushes the ferrite core 82 in. Therefore, the position of the ferrite core 82 in the coil is varied in
accordance with the type of the probe 86, and the inductance of the inductor 76 is varied in accordance with a change in position of the core 82. More specifically, the lengths of the bars 90 and 90a are determined in accordance with the capacitive
susceptance of the dumping capacitor in the ultrasonic transducer 28, i.e., to move the ferrite core 82 so that an inductive susceptance of the inductor 76 equal to the capacitive susceptance can be provided. For this reason, the inductance of the
inductor 76 can be continuously varied.
According to the third embodiment, the capacitive susceptance of the dumping capacitor can be canceled by the inductive susceptance of the inductor in the same manner as in the first and second embodiments. In addition, the infinite number of
variations in inductance can be achieved. Therefore, this apparatus can be applied to various ultrasonic transducer probes as compared with those in the first and second embodiments. Even if a new type of ultrasonic transducer probe is manufactured,
the capacitive susceptance of the dumping capacitor can be reliably canceled by only changing the length of a bar in the connector without changing the structure of the driving unit.
FIG. 13 is a block diagram showing the fourth embodiment. In the fourth embodiment, an inductance can be varied by selecting an appropriate tap of the inductor in a driving unit in the same manner as in the first and second embodiments. This
selection is not performed by the wiring or the bar arranged in the probe, but by a current detector arranged in a driving unit.
A driving unit 94 includes the driving circuit 14, an inductor 96 with intermediate taps, a selector 98 for selecting the tap, a current detector 100, and connection terminals 102 and 104. Output terminals of the driving circuit 14 are
respectively connected to the connection terminals 102 and 104, and the inductor 96 is connected between the connection terminals 102 and 104. Each tap of the inductor 96 is connected to the connection terminal 102 through the selector 98. Therefore,
when the selector 98 is switched, the inductance between the connection terminals 102 and 104 can be varied. The current detector 100 is connected between a power source Vcc and the connection terminal 102.
An ultrasonic oscillator probe 106 is detachably connected to the driving unit 94 through the connection terminals 102 and 104, and includes the ultrasonic transducer 28 connected between the connection terminals 102 and 104, and a resistor 108
connected in parallel with the ultrasonic transducer 28. The resistance of the resistor 108 corresponds to the capacitive susceptance of the dumping capacitor in the ultrasonic transducer 28.
When the ultrasonic probe 106 is connected to the driving unit 94, the current detector 100 detects a current supplied through the resistor 108, i.e., the resistance of the resistor 108, and switches the selector 98 in accordance with the
detected value. One of the taps of the inductor 96 is connected to the connection terminal 102 to change the inductance of the inductor 96. Since the resistance of the resistor 108 corresponds to the capacitive susceptance of the ultrasonic transducer
28, the inductance of the inductor 96 can be varied in accordance with the capacitance of the dumping capacitor in the ultrasonic transducer 28. As a result, the capacitive susceptance of the dumping capacitor of the ultrasonic transducer 28 is canceled
by the inductive susceptance of the inductor.
According to the fourth embodiment, the capacitive susceptance of the dumping capacitor can be canceled by the inductive susceptance of the inductor in the same manner as in the first to third embodiments, and the structure of the probe 106 is
changed in accordance with the types of probe by merely changing the resistor 108. Therefore, even if any probe 106 is connected to this driving unit 94, driving at a resonance point can be performed.
As described above, according to the first to fourth embodiments, there is provided an ultrasonic transducer apparatus which can reliably cancel a capacitive susceptance of the ultrasonic transducer by changing an inductance of the inductor
arranged in the driving unit in accordance with the capacitive susceptance. Therefore, even if the capacitive susceptance of the ultrasonic transducer is changed depending on a type of ultrasonic oscillator probe, the ultrasonic transducer can be driven
at its mechanical resonance point, thereby efficiently generating ultrasonic oscillations.
In the first to fourth embodiments, a change in capacitive susceptance of the ultrasonic transducer for each probe is compensated for by varying the inductance of the inductor arranged in the driving unit in accordance with the types of
ultrasonic probe. Other embodiments wherein a parallel circuit including an inductor and a capacitor is arranged in the driving unit and the capacitance is changed in accordance with types of ultrasonic probe, so that an inductive susceptance of the
driving unit is equivalently varied to compensate for a change in capacitive susceptance for each probe will be described hereinafter.
FIG. 14 is a block diagram showing the fifth embodiment. A driving unit 110 includes the driving circuit 14, an inductor 112, connection terminals 118, 120, 122, and 124, and capacitors 114 and 116. Output terminals of the driving circuit 14
are respectively connected to the connection terminals 118 and 124, and the inductor 112 is connected between the connection terminals 118 and 124. The capacitor 114 is connected between the connection terminals 120 and 124, and the capacitor 116 is
connected between the connection terminals 122 and 124. It is assumed that the capacitances of the capacitors 114 and 116 are C1 and C2, respectively.
An ultrasonic transducer probe 126 includes the ultrasonic transducer 28 and a connector 128 connected to the driving unit 110 through the connection terminals 118, 120, 122, and 124. The ultrasonic transducer 28 is connected between the
connection terminals 118 and 124. A dumping capacitance of the ultrasonic transducer 28 is assumed to be Cd1. The probe 126 is detachably connected to the driving unit 110 through the connector 128. More specifically, an ultrasonic transducer probe
126a having an ultrasonic transducer 28a of another type shown in FIG. 15 can be connected to the driving unit 110. It is assumed that the dumping capacitance of the ultrasonic transducer 28a is Cd2.
The connector of each probe includes a wiring for connecting the connection terminal 118 to the connection terminal 120 or 122 or does not include the wiring so as not to connect the terminal 118 to any connection terminals in accordance with the
capacitance of the dumping capacitor of the ultrasonic transducer. More specifically, the connector 128 has the wiring for connecting the capacitor 114 or 116 in parallel with the inductor 112. When the probe 126 is connected to the driving unit 110, a
susceptance (inductive property) obtained by the parallel circuit of the inductor 112 and the capacitor 114 or 116 cancels a capacitive susceptance of the dumping capacitor of the ultrasonic transducer.
This can be mathematically proved as follows. The capacitances of the capacitors 114 and 116 are determined to establish the following relationship with respect to the capacitance of the ultrasonic transducer which can be connected to the
driving unit 110:
Here, Ld is an inductance of the inductor 112.
The above equation represents that the susceptance at the mechanical resonance frequency is zero.
Thus, according to the fifth embodiment, when the ultrasonic transducer probe 126 is connected to the driving unit 110, a dumping capacitance Cd of the ultrasonic transducer can be reliably canceled. A lock point obtained by a PLL circuit in the
driving circuit 14 coincides with the mechanical resonance point of the ultrasonic transducer 28, and efficient driving can always be performed regardless of the types of ultrasonic transducer 28.
FIG. 16 is a block diagram showing the sixth embodiment. In the fifth embodiment, a capacitor is selected by the wiring in the connector of the ultrasonic probe in the similar manner to those in the first and second embodiments. In contrast to
this, in the sixth embodiment, a capacitor is mechanically selected by a member arranged in the connector in the similar manner to the third embodiment.
A driving unit 130 includes the driving circuit 14, an inductor 112, connection terminals 132 and 134, and ten capacitors 136 connected in parallel with the connection | | |
