Enhancement of 10 MHz single element ultrasonic transducers based on alternating current polarized PIN-PMN-PT single crystals

The piezoelectric properties of [001] oriented PIN-PMN-PT single crystals under traditional direct current polarization (DCP) and alternating current polarization (ACP) were investigated, and the 10 MHz single-element ultrasonic transducers were designed and fabricated based on DCP and ACP PIN-PMN-PT crystals, as well as DCP PZT ceramics as comparison. The results showed that used an alternating electric field with the amplitude range of 10-18 kV/cm, polarization frequency of 10-20 Hz and 10-25cycles, the piezoelectric coefficient (d33) of the crystal increased from 1147 to 1570pC/N, which was 37% higher than DCP. Moreover, the relative dielectric constant (epsilon 33T /epsilon 0) rose from 4396.84 to 5361.36, and the electromechanical coupling coefficient (kt) improved from 53% to 56.5%. Ultrasonic transducers based on the different polarization methods were designed, fabricated and investigated in this paper. The results showed that the echo amplitude of 1.7 V, - 6 dB bandwidth of 55.04%, and the relative sensitivity of - 35.34 dB was achieved in the ultrasonic transducers based on the ACP PIN-PMN-PT crystal, which were 0.54 V, 10.73%, and 3.3 dB higher than those of DCP crystal transducers, and 0.79 V, 28.52% and 5.58 dB higher than DCP PZT ceramic transducers. The work provided an effective route to improve piezoelectric properties in PIN-PMN-PT crystals using ACP and then to enhance the performances of the ultrasonic transducers.