Working principle ?
Ultrasonic sensor is the use of ultrasonic characteristics of the sensor developed. Ultrasonic is a vibration frequency higher than the sound wave mechanical waves, vibration generated by the transducer chip in the voltage excitation, it has a high frequency, short wavelength, small bypass phenomenon, especially good directionality, can become a ray and directional propagation and other characteristics. Ultrasonic penetration of liquids, solids, especially in the sun opaque solids, it can penetrate the depth of tens of meters. Ultrasound encounters impurities or interfaces will produce significant reflections to form reflections into echoes, and can produce the Doppler effect when it encounters moving objects. Therefore, ultrasonic detection is widely used in industry, national defense, biomedical and other aspects of ultrasound as a means of detection, must produce ultrasound and receive ultrasound. To complete this function is the device ultrasonic transducer, customarily known as ultrasonic transducer, or ultrasonic probe.
Structural composition ?
Ultrasonic transducer is mainly composed of piezoelectric wafer, can transmit ultrasound, but also can receive ultrasound. Small power ultrasonic probe is mostly used as a detection role. It has many different structures, can be divided into straight probe (longitudinal wave), oblique probe (transverse wave), surface wave probe (surface wave), Lamb wave probe (Lamb wave), double probe (a probe reflection, a probe to receive) and so on. The heart of an ultrasound transducer is a piezoelectric wafer in its plastic jacket or metal jacket. There can be many different materials that make up the wafer. The size of the wafer, such as diameter and thickness, also varies, so the performance of each transducer is different, and we must know its performance beforehand before using it.
The main performance indicators of ultrasonic sensors ?
(1) operating frequency. Operating frequency is the piezoelectric chip *** vibration frequency. When the frequency of the AC voltage added to its ends and the chip *** vibration frequency is equal, the output energy is the largest, the highest sensitivity. ?
(2) Operating temperature. Because the Curie point of piezoelectric material is generally higher, especially when the diagnostic ultrasound probe using less power, so the operating temperature is lower, can work for a long time without failure. Medical ultrasound transducers have higher temperatures and require separate refrigeration equipment. ?
(3) sensitivity. Depends largely on the manufacturing wafer itself. High electromechanical coupling coefficient, high sensitivity; vice versa, low sensitivity. ?
As in the case of ultrasonic transducers, a composite vibrator is flexibly fixed to the base. The composite vibrator is a combination of a resonator and, a dual piezoelectric wafer element vibrator consisting of a metal wafer and a piezoelectric ceramic wafer. The resonator is horn shaped for the purpose of efficiently radiating ultrasonic waves generated due to vibration and efficiently causing the ultrasonic waves to collect in a central part of the vibrator. ?
Ultrasonic sensors for outdoor use must be well sealed against dew, rain and dust. The piezoelectric ceramic is secured to the inside of the top of the metal cassette. The base is fixed to the open end of the cassette and is covered with resin. For ultrasonic sensors for industrial robots, an accuracy of 1 mm and strong ultrasonic radiation are required.