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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 humans 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 a hard body, and part of incoming wave energy is reflected; in other words – it is backscattered. So direct wave towards an object is backscattered widely – up to 180°. If the object is moving – the received frequency differs because of the Doppler effect. Let’s say simple example – parking sonar. Distance to object can be calculated very simply by the formula:

L=v·t·cos()/2

T- the time period between transmitted and received signals; v – ultrasound speed; w± – signal angle to object. Suppose the signal is perpendicular to the object, then cos(w±)=1.

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

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

Ultrasound is generated pretty simply. It is because of the material’s special properties that are used to deformation because of the voltage applied. When some frequency applied (usually resonance), the 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 the whole physics of piezoelectric, which I won’t discuss here. And typical transducer used in Ultrasound distance measuring transducer often used in parking systems looks like in the picture below:

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