Such as an ultrasonic sensor, and the composite vibrator is flexibly fixed on the base. Composite vibrator is a combination of resonator and bimorph element vibrator composed of metal sheet and piezoelectric ceramic sheet. The resonator is horn-shaped so as to effectively radiate ultrasonic waves generated by vibration and effectively concentrate the ultrasonic waves at the center of the vibrator.
Ultrasonic sensors used outdoors must be well sealed to prevent the invasion of dew, rain and dust. Piezoelectric ceramics are fixed on the top of the metal box. The base is fixed at the open end of the box and covered with resin. For the ultrasonic sensor used in industrial robots, its accuracy is required to reach 1mm and it has strong ultrasonic radiation.
When the frequency is higher than 75kHz, it is impossible to achieve this goal by using the bending vibration of the conventional bimorph vibrator. Therefore, piezoelectric ceramics with vertical thickness vibration mode must be used in high frequency detection. In this case, it is very important to match the acoustic impedance of piezoelectric ceramics with air. The acoustic impedance of piezoelectric ceramics is 2.6× 107kg/m2s, while that of air is 4.3× 102kg/m2s. The difference of quintic power will lead to a large loss of vibration radiation surface of piezoelectric ceramics. A special material attached to piezoelectric ceramics can be used as an acoustic matching layer to match the acoustic impedance of air. This structure can make the ultrasonic sensor work normally even when the frequency is as high as several hundred kHz.