Figure 3 shows an obtained frequency characteristics of the sound pressure level dependent on the frequency and the depth. The range of the frequency and the depth above 190dB (re. 1mPa at 1m) can be found in this figure. The Q values are less than 4, which means the frequency band width over 50Hz, at all the depth measured in this experiment.

　

2-2　Long term operation test of the driving units of 200Hz source

ATOC sound source is operated with 70Hz frequency, transmission interval of 4 hour, the repetition cycle of 6 times a day, and duration time of 1 time is 30 minutes. Therefore, total drive cycle N_total for 10 years are

N_total = 70^Hz × 1800^second × 6^time × 365^day × 10^year = 2.7594 × 10^9time　　(1).

The driving unit for the 200Hz sound source constitutes the oscillatory system by adding the mass of the aluminum block to both ends of giant magnetrostrictive rod of 20mm diameter and 120mm length, as it is shown in Fig. 1. The prestress to the rod is given with tightening by three bolts, and the magnetic circuit which consists of permanent magnet and yoke put in both ends of the rod gives the magnetic bias. The driving force is arising by the excitation of current in the solenoid coil in the circumference of the rod. The resonant frequency of the unit is about 1150Hz. Therefore, drive hour T_unit of the unit which corresponds to the duration of 30 minutes for the 70Hz sound source is

T_unit = 1800^second × 70^Hz / 1150^Hz

= 109^second　　(2),

but the drive hour was set to be 1 minute in order to reduce the temperature rise of the giant magnetrostrictive rod. The drive interval is 5 minutes, and the idle period for 15 minutes is put every 50 time for cooling-off period of the rod.

Fig. 4　Temperature variation of the giant magnetostrictive rod on power (1 minute) and off power (5 minutes) state.

Fig. 5　Variation of strain for giant, magnetostrictive rods at 1150Hz.

BACK　　　CONTENTS　　　NEXT