Detection based on “Ultrasonic Waves”
Comparison between ultrasonic sensors and optical sensors

Ultrasonic sensors use ultrasonic waves to measure distance. This section explains the differences from optical sensors, which are also used to measure distance.

Outline and detection principle

Comparison between optical sensors (reflective model) and ultrasonic sensors

Typical sensors used for distance measurement are optical sensors.
The following table shows the advantages and disadvantages when optical sensors and ultrasonic sensors are compared.
Note that this table is based on KEYENCE products.

Item Optical (reflective model) * Ultrasonic
Detectable target Detection is affected by target materials/colours Detection is unaffected by target materials/colours
Detecting distance 1000 mm max. 10 m max.
Accuracy High Low
Response speed Fast Slow
Dust/water Affected Unaffected
Measuring range Small Large
Item Optical (reflective model) * Ultrasonic
Detectable target Detection is affected by target materials/colours Detection is unaffected by target materials/colours
Detecting distance 1000 mm max. 10 m 32.8' max.
Accuracy High Low
Response speed Fast Slow
Dust/water Affected Unaffected
Measuring range Small Large

* Excluding the Time of Flight (TOF) type

What is ultrasonic?

“Ultrasonic” generally refers to a “high pitch sound that is inaudible to humans.” Sound is expressed by a unit called frequency (Hz). The greater the frequency, the higher the pitch of sound becomes. The unit Hz (hertz) means the number of oscillations per second. For example, a wave that oscillates 100 times in a second is expressed as 100 Hz. The audible range for humans is said to be between about 20 Hz and 20 kHz. In other words, ultrasonic waves have a frequency of 20 kHz or greater.

Familiar examples of devices using ultrasonic waves

In our ordinary life, the following ultrasonic sensors are used:
・Fish detector (used for fishery or bass fishing)
・Active sonar in a submarine (used for finding enemy submarines or battle ships)
・Back sonar for cars
(for detecting obstacles during backing a car to prevent single-car accident)

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