Ultrasound transducers for measuring distance

Ultrasounds transducers for measuring distances are commonly used in robotics, automotive parking sonars. Ultrasound distance measuring is non -contact measuring method – radiation and reception of ultrasound waves. Ultrasound waves are mechanical acoustic waves with frequencies more than 20kHz. Normally human cannot hear frequencies above 20kHz while some animals can. For instance bats use ultrasound location of objects. Dolphins communicate with each other using ultrasound signals.

Ultrasound interacts with hard body and part of incoming wave energy is reflected back, in other words – it is back scattered. So direct wave towards object is back scattered widely – up to 180°. If object is moving – received frequency differs because of Doppler effect. Lets say simple example – parking sonar. Distance to object can be calculated very simply by formula:


Where t- time period between transmitted and received signals; v – ultrasound speed; α – signal angle to object. If signal is perpendicular to object then cos(α)=1.



Each Ultrasound transducer has its impedance characteristics. Usually operation frequency is at lowest impedance point where sensitivity is highest:



Typical transducer operates at 32kHz. If working mode is continuous then two transducers are needed: one for transmission and second for reception of wave signals. If impulse is used, then only one transducer is enough as Ultrasound transducer can operate as transmitter and receiver.

Ultrasound is generated pretty simply. It is because of special properties of material which is used to deformate because of voltage applied. When some frequency applied (usually resonance) then ultrasound plate starts mechanically oscillate and generate sound. In reception mode transducer plate generates voltage because of material deformation forced by mechanical waves:



Of course there is whole physics pf piezoelectrics which I won’t discuss here. And typical transducer used in Ultrasound distance measuring transducer often used in parking systems looks like in picture bellow:




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