How do ultrasonic sensors work?

Ultrasonic sensors are devices that convert ultrasonic signals into other energy signals (usually electrical signals) to measure distance from the sensor to the target object. Ultrasonic wave is a mechanical wave with a vibration frequency higher than 20KHz and it has the characteristics of high frequency, short wavelength, small diffraction phenomenon, especially good directivity, which can become rays and propagate directionally.

Ultrasonic sensor can be used as ultrasonic distance sensor to measure the distance of a target object, detect the presence of as well as the movement of the object by applying the electrical signals to the 40khz ceramic transducer (transmitter) to transmit ultrasonic waves and convert the reflected sound into electrical signals(refer to the picture).

A pair of ultrasonic sensor is composed of a transmitter and receiver which are available as separate units or embedded together as single unit. The below image shows the Manorshi 40KHz ultrasonic transmitter and receiver.(You can find more information on Manorshi website: www.manorshi.com)

Working of Ultrasonic Sensors

Ultrasonic transmitter uses a piezoceramic crystal attached with a conical metal sheet. When an electrical voltage is applied to the piezoceramic, it vibrates with continuous expansion and contraction. As a result, as per the property of piezoelectric material, ultrasonic waves are generated which propagates straight because of the conical shape of the resonator.

Ultrasonic receivers work on the exact opposite concept. When the ultrasonic wave strikes through the resonator, the connected vibrator (metal plate) vibrates. By sticking the vibration of the piezoelectric ceramic disc to the vibrator, a current is generated according to the characteristics of the piezoelectric ceramic material. This current is further taken from the two external leads.

In short, ultrasonic sensors can both transmit and receive ultrasonic waves. When transmitting ultrasonic waves, it converts electrical energy into ultrasonic waves; when receiving echoes, it converts the vibration of ultrasonic waves into electrical signals, so it is called "ultrasonic transducer".

Performance characteristics of ultrasonic sensors

Due to the structural characteristics of the circular piezoelectric wafer, the emitted ultrasonic waves have a certain directivity, and the cross-section of the beam is similar to an ellipse, so the detection range is limited. The detection angle of the horizontal plane is 120 degrees, and the detection angle of the vertical plane is 60 degrees.

Features of Ultrasonic sensors

1. Simple structure and convenient manufacturing;

2. Not easily interfered by environmental electromagnetic fields;

3. Ultrasound is not sensitive to light and color, and can be used to identify transparent and poorly reflective objects.