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The ultrasonic sensor is developed by exploiting ultrasonic characteristics.

2014/9/28      view:
The ultrasonic sensor is developed by exploiting ultrasonic characteristics. Ultrasonic is a kind of vibration wave whose frequency is higher than the sound wave and is generated by power exchange chip vibrating drove by voltage.It carries advantages of high frequency, short wave length and little diffraction .it is also with good direction and can spread directionally as rays. Its ability to penetrate liquid and solid is quite good .In the sunshine opaque solid, it can penetrate tens of meters in depth.Ultrasonic generates significant reflection and form reflected sound . When it encounters a moving object, it will generate Doppler Effect.Therefore ultrasonic as a detective method is widely used in industries, national defense , biomedical science etc. Sensors which can generate and receive ultrasonic are called ultrasonic sensors. People trend to call it ultrasonic transducer or ultrasonic probe.
The ultrasonic probe is mainly composed of a piezoelectric wafer. It can receive and emit ultrasonic. Low power ultrasound probe can be used to detect and it has different structures such as straight probe (P-wave), oblique probe (transverse), surface acoustic wave (SAW) probe, Lamb wave probe (Lan Mubo), double probe (reflection, a probe, a receiving probe) etc
The core of ultrasonic transducer is the piezoelectric wafer in the plastic or metal shell. Materials that compose the water may have many kinds. The chip size, its diameter and thickness can be different, so the performance of each probe can be different.We should know its performance before use.The main performance index of the ultrasonic sensor include:
(1)Working frequency. The working frequency is the resonance frequency of piezoelectric wafer。When the added AC voltage frequency equals to the resonance frequency of the chip. It generates the maximum energy output and the sensitivity is the highest.
(2)Working temperature. Due to the piezoelectric material Curie point is generally high while the service voltage of ultrasonic probe for diagnosis use is quite small ,so its the working temperature is low and the sensor can work for quite a long time without failure. Ultrasonic sensor for medical use generates high temperature while working so it needs extra refrigeration equipment.
(3)Sensitivity.It manly depends on the manufacturing chip itself. When the Electromechanical coupling coefficient is high, the sensitivity is high. Otherwise the sensitivity is low accordingly.
Structure and working principle.
When a voltage is applied to the piezoelectric ceramic, it changes while the voltage and frequency change .On the other hand, when the the piezoelectric ceramic vibrates ,it generates a charge. When applying a signal to the so called
piezoelectric bimorph element which is composed of two pieces of piezoelectric ceramics or a piezoelectric ceramic and a metal sheet, it bends and vibrates and then emits ultrasound.On the contrary, when applying ultrasonic vibration to the piezoelectric bimorph element, it will generate a signal. According to the above function, piezoelectric ceramic can be used to make ultrasonic sensor.
Such as ultrasonic sensor,which has a  composite type vibrator flexibly fixed on the base.This kind of vibrator is a combination of a resonator,a bimorph vibrator composed of metal plate and a piezoelectric ceramic piece.Resonator forms a horn shape, the purpose of which is to effectively radiate ultrasonic generated by vibration and to effectively gather all the ultrasound in the center part of the vibrator.
Ultrasonic sensor for outdoor use must have good sealing performance, so as to prevent the invasion of dust, rain and dew.Piezoelectric ceramic is fixed in the top of the inner side of the metal box body.The base is fixed on the opening end of the box body and is covered by resin. For industrial robot use ultrasonic sensor, its precision is required to reach 1mm and should has strong ultrasonic radiation.
Using the bending vibration of the conventional bimorph vibrator, at frequencies higher than the case of 70kHz, it is impossible to achieve this objective.Therefore, in the high frequency detection, piezoelectric ceramic must use the vertical thickness vibration mode.In this case, The matching of acoustic impedance of piezoelectric ceramics and air becomes very important.The acoustic impedance of piezoelectric ceramic is 2.6 * 107kg/m2s, and the acoustic impedance of the air is 4.3 * 102kg/m2s.The difference of 5 power will result in a large number of loss on the surface of a piezoelectric ceramic vibration and radiation.A special material adhered to the piezoelectric ceramics, as acoustic matching layer, can realize the matching with the acoustic impedance of air.This kind of structure can make the ultrasonic sensor work normally even if the frequency is as high as hundreds of KHZ.
The principle and application of ultrasonic distance sensor technology
Ultrasonic distance sensor can be widely used in material level (luquid level) monitoring,robot collision avoidance,all kinds of ultrasonic proximity switch ,burglar alarm and other related fields. It is reliable and easy to stall. Water proof, ,emission angle small, high sensitivity, this kind of sensor can easily connect to the industrial display instrument and provides a transmitting probe of the larger angle.