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JPH10243498

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DESCRIPTION JPH10243498
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to
transducers for ultrasonic range finders or obstacle locators.
[0002]
2. Description of the Related Art Conventionally, an ultrasonic transducer having a structure in
which an umbrella-type reflector is combined with one cylindrical piezoelectric vibrator has been
used for traffic control of a car or obstacle detection in a railroad crossing.
[0003]
[Technical problems to be solved] The problem is that the cylindrical piezoelectric vibrator has a
high Q (generally Q = 100 or more), narrow bandwidth and poor distance resolution when used
for pulse radar or FM modulation. was there.
[0004]
[Means for Solving the Problems] In order to solve the above-mentioned problems, the present
invention uses an ultrasonic transducer having a comprehensively broad band characteristic by
using a plurality of transducers having slightly different resonance frequencies. By controlling
the amplitudes and phases of electrical signals for exciting a plurality of transducers, an
ultrasonic transducer having desired characteristics is realized.
04-05-2019
1
[0005]
DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention
will be described in detail with reference to the drawings in the case of n = 2 and n = 3.
[0006]
FIG. 1 is a block diagram of an ultrasonic transducer when n = 2.
That is, two cylindrical piezoelectric ceramic vibrators whose resonance frequencies are slightly
shifted are stacked in two stages to be combined with an umbrella-shaped reflector.
In this embodiment, in order to obtain vibrators having slightly different resonance frequencies,
the outer circumference of one of the vibrators 1 of a pair of cylindrical piezoelectric ceramic
vibrators 1 and 2 (resonance frequency: 31.336 kHz) of the same specification The resonance
frequency was lowered by adhering six lead spheres 3 (about 0.2 gr) at regular intervals on the
central line and applying mass addition.
In this manner, cylindrical piezoelectric vibrators having resonance frequencies fr1 = 30.664 kHz
(vibrator 1) and fr2 = 31.336 kHz (vibrator 2) were prepared.
The resonance characteristics of both vibrators were made to cross each other at the peak of -6
dB. In addition, in fixing these cylindrical vibrators, silicone rubber was used as an adhesive agent
in view of expecting a decrease in Q of the respective vibrators and mechanically exciting
independently of each other. The thickness of the adhesive layer 4 is about 1 mm. Further, in the
present embodiment, glass wool was filled in the cylinder as a sound absorbing material. FIG. 2
shows a block diagram of the measurement system. Although not shown in the drawings, the
amplitude and the phase of the applied electric signal can be arbitrarily controlled in exciting
each piezoelectric vibrator. Here, experiments were conducted in the case where both vibrators
were excited at the same voltage and in phase, and when the phase difference was shifted by 180
° at the same voltage, that is, excited in the opposite phase. A network analyzer 7 (Anritsu,
model MS420B) is used to excite the vibrator, the output signal level is fixed at +9 dBm, and the
radiation pressure from the transducer is changed while the frequency is changed. Condenser
microphone 8 (type B & K, model 4135) And an amplifier 9 (B & K Co., type 2636), and data
were again collected by the personal computer 10 through the network analyzer. Considering the
case of use in the far sound field for distance measurement, here we measured the frequency
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2
characteristics of the sound pressure at a point 1 m apart, which is considered to be a point
sufficiently distant on the central axis of the ultrasonic transducer . FIG. 3 and FIG. 4 show the
measurement results obtained when the vibrators 1 and 2 were excited at the same voltage and
in phase and at the same voltage and reverse phase (180 °), respectively. Both figures also show
the results when the respective transducers are excited alone. In FIG. 3, the peaks 13 and 14 at
the respective resonance frequencies of the two transducers remain as they are, but in FIG. 4 the
flat band characteristic 15 is obtained between them, and the broadband of the ultrasonic
transducer of this configuration can be realized . Next, an embodiment of n = 3 will be described.
Three cylindrical piezoelectric ceramic vibrators of vibrators 3, 4 and 5 were prepared. The
resonant frequencies of the three transducers are 37.60 kHz, 40.35 kHz and 42.60 kHz,
respectively. The center axes of these three transducers were aligned and stacked one on top of
the other to create a triple-layer ultrasonic transducer combined with a similar umbrella
reflector. With respect to this transducer, the amplitudes of the voltages applied to the respective
vibrators are equalized, and the result in the case where excitation is performed by giving a
phase difference of 180 ° only to the vibrator 4 whose resonance frequency has an
intermediate value is shown in FIG.
Moreover, the result at the time of exciting three vibrators by the same amplitude and the same
phase is shown in FIG. When excitation is performed with the same amplitude and in phase, a
deep depression is seen in the frequency characteristics, but when the vibrator 4 is excited in the
opposite phase, the depression becomes shallow and substantially flat band characteristics can
be obtained.
[0007]
As described above, according to the broadband ultrasonic transducer of the present invention,
the central axes of a plurality of cylindrical piezoelectric vibrators having slightly different
resonant frequencies are aligned in multiple layers and combined with an umbrella-type
reflector. A wide band characteristic can be obtained by controlling the phase and the amplitude
of the voltage applied to each vibrator. In an ultrasonic transducer using only one conventional
cylindrical piezoelectric vibrator, the band is narrow due to the high Q of the piezoelectric
vibrator, and sufficient distance resolution can not be obtained when it is used for pulse radar or
FM modulation. However, the realization of the broadband ultrasonic transducer of the present
invention enables the improvement of distance resolution and measurement accuracy. The same
effect can be expected even if a cylindrical magnetostrictive vibrator is used instead of the
cylindrical piezoelectric vibrator.
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3
[0008]
Brief description of the drawings
[0009]
It is a block diagram of an ultrasonic transducer when it is FIG. 1 n = 2.
[0010]
2 is a block diagram of the measurement system.
[0011]
FIG. 3 shows the measurement results when the vibrators 1 and 2 are excited at the same voltage
and in phase, respectively.
[0012]
Fig. 4 shows the measurement results in the case of excitation with the same voltage and reverse
phase (180 °).
[0013]
In the embodiment shown in FIG. 5n = 3, the measurement results in the case where the
amplitudes of the voltages applied to the respective vibrators are equalized and the phase
difference of 180 ° is given only to the vibrator 4 whose resonance frequency takes an
intermediate value. It is.
[0014]
It is a measurement result at the time of exciting three vibrators by the same amplitude and the
same phase in the Example of FIG. 6 n = 3.
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