Ultrasonic SensorsBasic knowledge about ultrasonic sensors: What can you do with ultrasonic sensors?

Here we present examples of what you can do with ultrasonic sensors, with regard to the use of sound waves for “detection.”

Features and operating principle of ultrasonic sensors

The “ultrasonic waves” employed by ultrasonic sensors are a type of sound wave. Sound waves with a frequency of 20 kHz or above, which are inaudible to the human ear, are called ultrasonic waves.
Depending on the frequency band, ultrasonic waves can be conveyed via any medium, whether gas, liquid, or solid, but the propagation speed differs depending on the acoustic impedance of the substance they are travelling though.
Ultrasonic waves can be utilized in different ways, such as distance detection by sensing reflected ultrasonic waves and presence detection by sensing fluctuation in ultrasonic waves. When used in distance detection applications, ultrasonic sensors can be used to detect transparent materials such as plastic or glass, unlike optical distance sensors.
The operating principle of ultrasonic sensors makes use of changes in the voltage polarity of a piezoelectric ceramic element to generate air vibration from expansion and contraction (ultrasonic waves).

Types of ultrasonic sensors available from Murata and precautions

Murata only offers ultrasonic sensors designed to be used with air as the medium, not water or solids. Four varieties of ultrasonic sensors are available: open structure type, drip-proof type, high-frequency type, and SMD type. Each type has its own features, with some being suitable only for specific applications. For details, refer to the lineup page for each type.
In addition, the sensors contain no circuitry. Either create your own circuits, referring to the basic reference circuit diagrams on the website, or obtain suitable circuits from a manufacturer of IC devices.
On the website you will find basic knowledge about the characteristics, etc., of ultrasonic waves, application examples, lists of unsuitable applications, more detailed precautions, frequently asked questions, and more. Please feel free to make use of these resources.

Distance detection

By measuring the reflection time of ultrasonic waves it is possible to calculate the distance to an object. The color of the object does not matter, and it is possible to sense reflections even from objects made of transparent glass or acrylic.

The time from the start of transmission until reflected waves are received is measured.
Time × speed of sound (approx. 340 m/s) = distance to object (round trip)

Object presence detection

The presence or absence of reflected waves can be used to determine whether an object is present or absent. This means it is possible to detect the presence of an object without making contact with it. Presence detection can be performed over a wide range within the range of directionality.

Using ultrasonic waves to detect the presence or absence of objects.

State detection

It is possible to detect moving objects based on fluctuations in the waveforms of ultrasonic waves. And although it is not possible to detect the amount of movement directly, it is possible to detect the distance to the object as it comes closer.

  • It is possible to detect the state of a location (changes in the sound field) based on fluctuations in the combined signals from reflected and direct waves.
  • It is not possible to detect the amount of movement.
  • Possible only when a separate sensor is used for reception.