Ultrasonic ranging sensor

        Ultrasonic sensors are sensors developed using the characteristics of ultrasound. Ultrasonic ranging sensors are sensors that convert ultrasonic signals into other energy signals (usually electrical signals). Ultrasound is a mechanical wave with a vibration frequency higher than 20kHz. It has the characteristics of high frequency, short wavelength, small diffraction phenomenon, especially good directivity, and can be ray and directional propagation. Ultrasound has a great ability to penetrate liquids and solids, especially in solids that are opaque to sunlight. Ultrasonic waves encountering impurities or interfaces will produce significant reflections to form reflected echoes, and touching moving objects can produce Doppler effect. Ultrasonic sensors are widely used in industry, national defense, biomedicine, etc.

The device that accomplishes this function is an ultrasonic sensor, which is traditionally called an ultrasonic transducer, or ultrasonic probe.

The main performance indicators of ultrasonic sensors

The core of an ultrasound probe is a piezoelectric chip in its plastic or metal jacket. There may be many kinds of materials constituting the wafer. The size of the wafer, such as diameter and thickness are also different, so the performance of each probe is different, we must understand its performance before use. The main performance indicators of ultrasonic sensors include:

    (1) Working frequency. The operating frequency is the resonance frequency of the piezoelectric wafer. When the frequency of the AC voltage applied to it is equal to the resonance frequency of the chip, the output energy is the largest and the sensitivity is also the highest.

    (2) Working temperature. Since the Curie point of piezoelectric materials is generally relatively high, especially when the ultrasonic probe for diagnosis uses less power, the working temperature is relatively low, and it can work for a long time without failure. Medical ultrasound probes have relatively high temperatures and require separate refrigeration equipment.

    (3) Sensitivity. It mainly depends on the manufacturing wafer itself. The electromechanical coupling coefficient is large and the sensitivity is high; otherwise, the sensitivity is low.

Structure and working principle

    When voltage is applied to piezoelectric ceramics, mechanical deformation will occur with changes in voltage and frequency. On the other hand, when the piezoelectric ceramic is vibrated, a charge is generated. Using this principle, when an electric signal is applied to a vibrator composed of two piezoelectric ceramics or a piezoelectric ceramic and a metal sheet, a so-called bimorph element, ultrasonic waves are emitted due to bending vibration. Conversely, when ultrasonic vibration is applied to a bimorph element, an electrical signal is generated. Based on the above effects, piezoelectric ceramics can be used as ultrasonic sensors.

    Like an ultrasonic sensor, a compound vibrator is flexibly fixed on the base. The composite vibrator is a combination of a resonator and a bimorph piezoelectric element vibrator composed of a metal sheet and a piezoelectric ceramic sheet. The resonator is in the shape of a trumpet, the purpose is to effectively radiate the ultrasonic waves generated due to vibration, and to effectively concentrate the ultrasonic waves in the central part of the vibrator.

    The advantages of the ultrasonic ranging sensor: the longitudinal resolution is high, and it can identify transparent, translucent and diffuse reflection objects; especially suitable for non-contact measurement in dark, humid and other harsh conditions; based on the ultrasonic sensor sensing system It is easy to realize miniaturization and integration.