地中埋設物探査用受波器

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A Piezoelectric type receiver is a useful device to be placed on the ground surface for reception of impulsive echo signals from bodies buried in the underground, because it has a capability of receiving signals of wide frequency band, and is simple and small-sized in structure substantially. In this paper are described a means to get close contact of the receiver attachment with the ground surface, together with theoretical and experimental analyses about reception characteristics of the receiver. The receiver is composed of two PZT disks cemented on an aluminum attachment and an aluminum disk cemented on the PZT disks. In order to find a means to get close contact of the receiver attachment with the ground surface, experiments were performed by an apparatus shown in Fig. 2 with several receiver attachments shown in Fig. 1. The results are shown in Fig. 3 and Fig. 4, from which it was concluded that the contact surface of the receiver attachment with sharp V-grooves as shown in No. 4 of Fig. 1 is most suitable and insertion of grease-sand mixture (weight ratio 1 : 3) between the attachment surface and the ground (sand) produces a close contact. Equation (6) expresses the relation between the sound pressure p of the incident plane wave and the output voltage E_o of the receiver placed on the ground surface. Fig. 6 shows the frequency characteristics of the receiver sensitivity calculated by Eq. (6). Fig. 6 indicated that the receiver sensitivity in the low frequency range increases proportional to frequency and the maximum sensitivity is obtained at Ω=1, and the receiver sensitivity decreases a little even in the higher frequency range in case of low mechanical Q. Eq. (11) and Eq. (12) express the radiation resistance and the stiffness of the receiver respectively. Fig. 7 gives the relation between mass M_T and diameter 2a of the receiver as functions of wavelength λ_po and mechanical Q calculated by Eq. (16), using ρ_s=1. 45 g/cm^3 and B=0. 1486. M_T and 2a can be determined from this chart by giving λ_po and Q. Eq. (17) expresses the output of the receiver when the waveform of the incident sound is impulsive. Measurements of the mechanical resonance frequency and the mechanical Q of the receiver placed on the ground surface were carried out in order to justify the theoretical expressions. Fig. (8) and Fig. (9) show the sound source, the receiver and the measuring apparatus used in the measurement. For the sound source, an electromagnetic induction type sound source was used. Resonance frequency in the transmitting electrical circuit was changed by three steps of 5 kHz, 1. 82 kHz and 0. 87 kHz. Mass of the receiver was changed by five steps of 260g, 420g, 600g, 1200, g and 2460g by rescrewing the brass rod with various weights in the main body of the receiver. in Fig. 10, the waveform of the receiver output in case of 0. 87 kHz driving current frequency and 1200g mass of receiver is shown. Resonance frequencies were obtained from periods of the received sound waveforms except for the first half cycle. in Fig. 11, the results are compared with the theoretical values of the mechanical resonance frequencies calculated by Eq. (13) using c_p=300 m/s (measured value). Mechanical Q's were obtained from decay curves of the envelope of the received sound waveforms. In Fig. 12, the results are compared with the theoretical values calculated by Eq. (14). From the fact that the measured values agree with the calculated ones with reasonable accuracy, it is confirmed that the radiation impedance of the receiver is expressed by Eq. (11) and Eq. (12).
社団法人日本音響学会の論文
1973-08-01

地中埋設物探査用受波器

スポンサーリンク

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スポンサーリンク