1978 Volume 34 Issue 4 Pages 234-241
The dynamical demagnatizing-field effect in the sound propagation along a piezomagnetic (or biased-magnetostrictivce) rod has been studied. The procedure of the analysis is almost the same as that in the piezoelectric case reported in the preceding paper. In the present case, however, the nature of the driving field differs from that in the piezoelectric case. Therefore the assumption[3] in the previous paper should be replaced by the following. [3'] The vibration is excited with the magnetic field produced by the electric current through a solenoid or driven by the alternating stress on the ends. The demagnetizing-field is given by (2. 5), and the inner and outer driving magnetic fields are given by eq. (2. 7), of which the amplitude h_0 is related to the current I by eq. (2. 9). Fundamental equations are given by [A] (2. 11) and [B] (2. 14). An exact solution is obtained as reported in the preceding paper in case of infinitely long rod. For the vibration of a finite bar, equations [A] and [B] are approximately solved under the condition [C] (4. 1') using the approximation K_a(y). The results are obtained as (4. 2), (4. 3), (4. 10) and (4. 11). The impedance of the vibrator is determined as (5. 6), and is further expressed in the alternative from (5. 7) using (5. 12) and (5. 13). In the case of small w, it is transformed to the simple forms of (5. 21) and (5. 22). It is noticed that the electrical behavior of the present piezomagnatic bar is rather of transverse-effect-type despite of its logitudinal-effect coupling, in contrast to the conculusion obtained for piezoelectric bar in the preceding paper. The resonance occuers at a frequency near the half-wavelength frequency 1/2l√ρs_<eff>, which decreases with increasing length as shown in Fig 1. Numerical values of the parameters are given in Fig. 2 to serve for a practical use in the electromechanical measurement.
