超音波振動子諸定数の自動測定法

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The characteristics of a magnetostrictive or piezoelectric transducer whose equivalent representation is a circuit shown in Fig. 1 can be described by four constants ; resonance frequency f_0, mechanical Q, motional admittance Y_<m0> at resonance, and damped admittance Y_d. An automated method for measuring these constants rapidly and accurately is proposed, which utilizes a technique of automatic tracking of the transducer resonance by means of perturbing the driving frequency. The output voltage V_0 of the differential circuit shown in Fig. 2 is proportional to the motional current of the transducer. The frequency of the driving voltage V_d is modulated by a sinusoidal perturbation signal of low frequency f_p. Then, the amplitude modulation of V_0 occurs as illustrated in Fig. 3. The center frequency of V_d is controlled so that the f_p-component of the envelope V_a of the modulated V_0 vanishes. The center frequency gives f_0. A system for the measurement is shown in Fig. 6. The value of f_p is desired to satisfy Inequality (3) for speedy f_0-tracking (See Fig. 7). The amplitude-modulation degree k_p in V_0, when the tracking is over, is related to the frequency deviation Δf and the mechanical Q as shown in Fig. 4. For a small perturbation, the relation can be expressed by Equation (2). Thus, Δf is automatically controlled so that k_p is equal to a constant value. The mechanical Q can be obtained from the controlled value of Δf. A system for the measurement is shown in Fig. 8. The value of f_p must satisfy Inequality (4) for accurate measurements (See Figs. 9 and 10). Fig. 11 shows examples of the required time for measuring Q. During these measurements, V_d must be kept constant. the constant-voltage control system in shown in fig. 12. The value of Y_<m0> can be read from the voltmeter in this system. Before the measurements mentioned above, the variable resistance R in the differential circuit (Fig. 2) is automatically adjusted so as to detect the motional current. The damped admittance Y_d can be obtained from the controlled R. In order to advance the accuracy of measuring Y_d the driving voltage V_d of the balanced-modulated wave, of which the center frequency is near resonance, is employed on the basis of a property of motional admittance as shown in Fig. 5. A system for this measurement is shown in Fig. 13. As shown in Figs. 14 and A1, providing the modulating frequency f_D is larger than 15% of f_0, the error of measured Y_d is sufficiently small. An arrangement for measuring all the constants simultaneously is shown in Fig. 15. Measured results for a ferrite transducer (Figs. 16(a) and (b)) show that the method proposed here can be applied to measurements of a higher vibration level than customary manual methods.
社団法人日本音響学会の論文
1977-10-01

超音波振動子諸定数の自動測定法

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