Fig. 6.
Time domain pulse/echo response and normalized frequency spectrum of the first element of the annular array.(The X-cut quartz target was about 5 mm away from the array; The -6dB bandwidth of the signal is 90%.)
Time domain pulse/echo response and normalized frequency spectrum of the first element of the annular array.(The X-cut quartz target was about 5 mm away from the array; The -6dB bandwidth of the signal is 90%.)