An ultrasonic sensor is a contactless sensor that uses ultrasonic waves as the detection medium. Practically, it consists of a transmitter and a receiver; the transmitter uses ultrasonic waves converted from electrical signals as the medium for transmission, and the receiver converts the received ultrasonic waves to electrical signals.
Generally, the transmitter emits ultrasonic waves towards an object, and the receiver receives the reflected waves, so that the existence of and the distance from the object can be identified.
Piezoelectric ceramics are capable of converting mechanical energy to electrical energy (piezoelectric effect) and electrical energy to mechanical energy (inverse piezoelectric effect). The piezoelectric effect and inverse piezoelectric effect allow the transmission and reception of ultrasonic waves.
When voltage is applied to a piezoelectric ceramic, it expands and contracts in the thickness direction and, accordingly, in the direction perpendicular to the thickness.
In a unimorph structure where a piezoelectric ceramic is bonded to a metal plate, expansion and contraction in the perpendicular direction become the force that causes the entire unimorph transducer to bend. This flexion movement allows the emission of ultrasonic waves. Also, when ultrasonic vibration is applied to the transducer, the inverse piezoelectric effect causes the flexion movement of the transducer, generating electrical signals.
|1||Piezo & Transducer|
|2||Case (plastic resin)|
|4||Vibrating plate (metal plate)|
|Usage||For both transmission and reception|
|Center frequency||38.5 kHz±2.5％|
|Max. input voltage||30 Vpp|
|Operating temperature and humidity range||-40～85℃ 85% RH or less|
|Storage temperature and humidity range||-40～85℃ 85％85% RH or less(There must be no condensation)|
[Distance measurement] Robots, drones, car back sonars, etc.
[Sensing/detection] Automatic traffic signal switch, intruder alarm system, etc.
[Ultrasonic communication systems]
|High-temperature exposure||+85℃||100 hours|
|High-temperature and humidity exposure||+85℃ 85％RH||100 hours|
|Low-temperature exposure||-40℃||100 hours|
|Thermal shock||-40°C (30 min.) <=> +85°C (30 min.) (Short between terminals 1 and 2)
|Vibration||Maximum amplitude: 1.2 mm; frequency: 10 to 20 Hz||Two hours each for three directions|
|Room-temperature operation||Frequency: 40 kHz; block pulse: 30Vp-p||1,000 hours|
Measurement of the distance to an object (measurement of pulse reflection time)
The distance to an object is measured by measuring the time between the emission of ultrasonic waves from the ultrasonic sensor towards the object and the return of the reflected wave.
Oscillating frequency/40 kHz, block pulse (voltage: 10Vpp)
Burst cycle/10 ms
The voltages of transmitted and received waveforms are measured using an oscilloscope.
Measurement locations: transmitted waveforms‒Point A, received waveforms‒Point B
The aerial ultrasonic wave propagation velocity V [m/s] is represented by the following equation.
V = 331.5 + 0.6071t (t: ambient temperature)
T [s], the time between the emission of ultrasonic waves and the return of reflected waves, is represented by the following equation, where d [m] is the distance from the ultrasonic sensor to the object.
T = 2d / V
Thus, the distance from the ultrasonic sensor to the object can be measured.