JPH0514997

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DESCRIPTION JPH0514997
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
drive circuit for an ultrasonic transducer, and more particularly to a drive circuit for a
piezoelectric ultrasonic transducer.
[0002]
2. Description of the Related Art Conventionally, as a method of tuning the frequency by a
transmitter having an ultrasonic transducer as a load, the sound transmitted from the ultrasonic
transducer is detected by a microphone provided outside and the maximum sound pressure is
obtained. Control the transmission frequency, or control the transmission frequency so that the
current flowing through the ultrasonic transducer is maximized, or detect the phase difference
between voltage and current, and control the transmission frequency so that the phase difference
becomes zero. And the resonance point was detected.
[0003]
Among the above-described conventional frequency tuning methods, the method of using the
microphone externally is required a circuit for receiving the signal of the microphone and
detecting the level in addition to the transmitting circuit, It has the disadvantage of being
structurally large.
[0004]
In addition, in the method of controlling so as to maximize the current flowing through the
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ultrasonic transducer, the resonance point does not necessarily coincide with the minimum value
of the circuit impedance according to the value of the circuit constant, and the Q of When the
value is high, there is a disadvantage that a slight frequency deviation inevitably affects the
transmission output of the ultrasonic transducer.
[0005]
Furthermore, in the method of detecting the phase difference between the voltage and current
generated in the circuit, if an unnecessary signal such as noise is superimposed on the waveform
rise, it is assumed that the phase difference is zero where the actual phase difference is not zero.
There is a drawback that the decision of
[0006]
An object of the present invention is an ultrasonic transducer that eliminates the abovementioned drawbacks, eliminates the need for an external microphone, enables driving at an
optimum frequency even when the Q value is high, and eliminates the influence of noise at
waveform rise. To provide a drive circuit for the
[0007]
A driving circuit for an ultrasonic transducer according to the present invention is a driving
circuit for an ultrasonic transducer for driving an ultrasonic transducer at a predetermined
frequency, which is applied to the ultrasonic transducer. Means for controlling the drive
frequency so as to always maximize the product of the drive voltage and the drive current
flowing through the ultrasonic transducer.
[0008]
Moreover, the drive circuit of the ultrasonic transducer of the present invention has a
configuration in which the ultrasonic transducer targets a piezoelectric ultrasonic transducer.
[0009]
Next, the present invention will be described with reference to the drawings.
[0010]
FIG. 1 is a block diagram of an embodiment of the present invention.
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[0011]
The configuration of the present embodiment includes a piezoelectric ultrasonic transducer 6
represented by an equivalent circuit, a frequency controller 1 that generates a transmission
frequency and performs frequency control corresponding to the displacement of the resonance
point of the ultrasonic transducer 6; The power amplification circuit 2 generates driving power
for driving the ultrasonic transducer 6, the output transformer 3, the voltage detection circuit 4
detecting an applied voltage to the ultrasonic transducer 6, and the driving current of the
ultrasonic transducer 6 A current detection circuit 5 to be detected, a matching coil 7 for series
resonance with the ultrasonic transducer 6, a multiplier 10 for multiplying the detected drive
voltage and the drive current, and a filter for removing noise included in the waveform after
multiplication 11 and a peak detector 12 which detects the peak value after multiplication and
controls the frequency controller 1 so as to always maximize the detected peak value.
[0012]
Next, the operation of this embodiment will be described.
[0013]
The frequency controller 1 generates a transmission frequency and is power amplified by the
power amplifier 2.
[0014]
The output of the power amplifier 2 is applied to the ultrasonic transducer 6 via the output
transformer 3.
[0015]
The voltage detection circuit 4 divides and extracts the drive voltage of the secondary example of
the output transformer 3 and sends it to the multiplier 8 as a detection voltage 8.
[0016]
The current detection circuit 5 detects the drive current and sends it to the multiplier 10 as a
detection current 9.
[0017]
The ultrasonic transducer 6 has the matching coil 7 inserted in series and is set in a series
resonance state.
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[0018]
FIG. 2 is a characteristic diagram showing an example of the moving admittance loop (b) in the
state where the moving admittance loop (a) and the resonance frequency are shifted in the
normal state of the ultrasonic transducer.
[0019]
The sharpness of resonance Q of the piezoelectric ultrasonic transducer exhibiting a dynamic
admittance loop in a normal state as shown in FIG. 2A is shown as Q = f0 / (f2-f1).
Here, f0 is the resonance frequency, and f1 and f2 are the points of intersection with the
dynamic admittance loop drawn 45 degrees up and down from the cut point P of the dynamic
admittance loop on the conductance G axis.
When driving at this resonance frequency f0, transmission of the maximum output can be
secured.
[0020]
However, when Q is high, even if the resonance frequency slightly shifts due to an external factor
such as water pressure application, the position of the resonance frequency on the dynamic
admittance loop largely moves as shown in FIG. If it transmits by f0, the maximum output can not
be secured. In this case, it is necessary to transmit at the frequency f3.
[0021]
FIG. 3A shows the characteristics of the capacitive reactance XC 13 of the ultrasonic transducer
6 with high Q and the inductive reactance XL 14 of the matching coil 7 for series resonance in
the normal state.
Since the Q of the ultrasonic transducer 6 is high, the value of the capacitive reactance XC 13
largely changes as shown in FIG.
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Assuming that the frequency of the resonance point is f0 at the beginning, the product of voltage
and current is maximum, but the frequency remains unchanged even if the resonance frequency
f0 shifts to f3 in FIG. 3 (b). If it transmits by f0, the multiplication value of voltage and current
will fall.
On the other hand, the frequency is controlled to transmit at the frequency of f3 so as to
maximize the multiplication value.
[0022]
The multiplier 10 receives the detection voltage 8 and the detection current 9 and takes their
multiplication value.
[0023]
The multiplied value is passed through the filter 11 to remove unnecessary components such as
noise, and then the peak value is detected by the beak detector 12.
[0024]
The peak value detected by the peak value detector 12 is provided to the frequency controller 1,
and the output frequency is controlled so that the peak value detected by the peak detector 12 is
maximized, thus the transmission frequency corresponding to the deviation of the resonance
frequency. It is adaptively changed, and always sends the maximum output.
[0025]
As described above, according to the present invention, the drive voltage of the ultrasonic
transducer is multiplied by the value of the drive current, and the drive frequency is controlled so
that the product is always maximized. Even in the case where the Q value of is high, it is possible
to drive the ultrasonic transducer at an optimal frequency, and there is an effect that the
additional microphone is unnecessary and miniaturization can be achieved.
[0026]
In addition, there is an effect that it is possible to remove the erroneous setting of the frequency
due to the noise at the rising of the waveform when detecting by the phase difference between
the drive voltage and the drive current.
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