JPH10243498A - Broad band ultrasonic wave transducer employing cylindrical piezoelectric vibrator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transducer with a high frequency band characteristic and enhanced distance resolution and measurement accuracy by controlling a phase and an amplitude of a voltage applied to respective vibrators. SOLUTION: Cylindrical piezoelectric ceramic vibrators 1, 2 whose resonance frequencies are set with a slight deviation are stacked in two stages and they are combined with an umbrella type reflector 5. In order to slightly deviate the resonance frequencies of the vibrators, six lead balls 3 are adhered on a center line of an outer circumference of the vibrator 1 at an equal interval to add the mass of the vibrator 1 in a couple of the cylindrical piezoelectric ceramic vibrators 1, 2 of the same specifications so as to reduce the resonance frequency of the vibrator 1. The resonance frequency of the vibrator 1 is set to 30.664kHz and the resonance frequency of the vibrator 2 is set to 31.336kHz. In the case of exciting the vibrators 1, 2 with a voltage at the same phase, the peaks of the respective resonance frequencies of the vibrators 1, 2 remain as they are, but the part between the peaks provide a flat frequency band characteristic thereby realizing the broad band characteristic of the ultrasonic wave transducer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transducer for an ultrasonic range finder or an obstacle detector.

[0002]

2. Description of the Related Art Conventionally, an ultrasonic transducer having a structure in which a single cylindrical piezoelectric vibrator is combined with an umbrella-shaped reflector has been used for traffic control of automobiles or detection of obstacles at railroad crossings.

[0003]

[Technical Problems to be Solved] Cylindrical piezoelectric vibrators have a high Q (generally Q = 100 or more), and have a narrow bandwidth and poor distance resolution when used in a pulse radar system or an FM modulation system. was there.

[0004]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides an ultrasonic transducer having a wide band characteristic by using a plurality of transducers having slightly different resonance frequencies. An ultrasonic transducer having desired characteristics is realized by controlling the amplitude and phase of an electric signal for exciting a plurality of transducers.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with n = 2 and n =
The case of 3 will be described in detail with reference to the drawings.

FIG. 1 is a configuration diagram of an ultrasonic transducer when n = 2. That is, a cylindrical piezoelectric ceramic vibrator whose resonance frequency is slightly shifted is stacked in two stages and combined with an umbrella-shaped reflector. In this embodiment, in order to obtain a resonator having a slightly different resonance frequency, a pair of cylindrical piezoelectric ceramic resonators 1 having the same specification are used.
And a lead ball 3 (approximately 0.2 gr) on the center line of the outer periphery of one of the vibrators 1 having a resonance frequency of 31.336 kHz
The resonance frequency was lowered by applying the mass by bonding the pieces at equal intervals. In this manner, cylindrical piezoelectric vibrators having resonance frequencies fr ₁ = 30.664 kHz (vibrator 1) and fr ₂ = 31.336 kHz (vibrator 2) were prepared. The resonance characteristics of both vibrators have a peak of -6.
They crossed each other at the dB point. In fixing these cylindrical vibrators, silicone rubber was used as an adhesive in view of the expectation that the Q of each vibrator would be reduced and mechanically independent excitation. The thickness of the adhesive layer 4 is about 1 mm. Further, in this embodiment, the cylinder was filled with glass wool as a sound absorbing material. FIG. 2 shows a block diagram of the measurement system. Although not shown in the figure,
Upon excitation of each piezoelectric vibrator, the amplitude and phase of an applied electric signal can be arbitrarily controlled. Here, experiments were performed for the case where both vibrators were excited at the same voltage and the same phase, and the case where they were excited at the same voltage and the phase difference was shifted by 180 °, that is, when they were excited in the opposite phase. A network analyzer 7 (Anritsu Corporation, M
S420B type) and the output signal level is +9 dB.
m, and changing the frequency while changing the frequency, the condenser microphone 8 (B & K
, 4135) and amplifier 9 (B & K, 2636)
, And data was collected again by the personal computer 10 through the network analyzer. Considering the case of using in a distant sound field for distance measurement, here, the frequency characteristic of the sound pressure at a point 1 m away, which is considered to be a point sufficiently far away on the center axis of the ultrasonic transducer, was measured. . 3 and 4 show the case where the vibrators 1 and 2 are excited at the same voltage and the same phase, respectively, and the same voltage and the opposite phase (180 °).
The measurement results obtained for the case where the excitation was performed are shown. Both figures also show the results when each vibrator is excited independently. 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, a flat band characteristic 15 is obtained between them, and a wider band of the ultrasonic transducer having this configuration can be realized. . Next, an embodiment in which n = 3 will be described. Vibrator 3,
Four and five cylindrical piezoelectric ceramic vibrators were prepared. The resonance frequency of each of the three vibrators is 37.60k
Hz, 40.35 kHz, and 42.60 kHz. The three transducers were superposed in order with their central axes aligned, and a triple structure ultrasonic transducer combined with a similar umbrella-shaped reflector was produced. With respect to this transducer, the amplitude of the voltage applied to each transducer is made equal, and only 180
FIG. 5 shows the results when excitation was performed with a phase difference of ゜.
FIG. 6 shows the results when three vibrators are excited with the same amplitude and the same phase. When excited at the same amplitude and same phase, a deep dent is observed in the frequency characteristic, but when the oscillator 4 is excited at the opposite phase, the dent becomes shallow, and a substantially flat band characteristic is obtained.

[0007]

As described above, the broadband ultrasonic transducer of the present invention has a plurality of cylindrical piezoelectric vibrators having slightly different resonance frequencies, which are superposed one on another with the central axes thereof aligned.
A broadband characteristic is obtained by controlling the phase and the amplitude of the voltage applied to each of the vibrators by using a structure combined with an umbrella-shaped reflector. In a conventional ultrasonic transducer using only one cylindrical piezoelectric vibrator, the bandwidth is narrow due to the high Q of the piezoelectric vibrator, and a sufficient distance resolution cannot be obtained when the ultrasonic transducer is used in a pulse radar system or an FM modulation system. However, the realization of the broadband ultrasonic transducer of the present invention makes it possible to improve the distance resolution and the measurement accuracy. Similar effects can be expected by using a cylindrical magnetostrictive vibrator instead of the cylindrical piezoelectric vibrator.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an ultrasonic transducer when n = 2.

FIG. 2 is a block diagram of a measurement system.

FIG. 3 is a measurement result when vibrators 1 and 2 are excited at the same voltage and in the same phase, respectively.

FIG. 4 is a measurement result in a case where excitation is performed at the same voltage and opposite phase (180 °).

FIG. 5 is a diagram showing a case where, in the embodiment of n = 3, the amplitudes of the voltages applied to the respective vibrators are made equal, and only the vibrator 4 having an intermediate resonance frequency is excited by giving a phase difference of 180 °. Is the measurement result.

FIG. 6 is a measurement result when three vibrators are excited with the same amplitude and the same phase in the example of n = 3.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mitsuo Ikehara 3-9 Izumi Park, Izumi-ku, Sendai-shi, Miyagi Pref. 3-19 Izumi Park, Izumi-ku, Sendai-ku, Japan

Claims (1)

[Claims] It consists of a structure in which the central axes of n cylindrical piezoelectric vibrators whose resonance frequencies are slightly different from each other are aligned in n stages so as to maintain a mechanically independent vibration form, and combined with an umbrella-shaped reflector A broadband ultrasonic transducer obtained by controlling the phase and amplitude of a voltage applied to each transducer in an ultrasonic transducer.