What is Passive Sensor?

Author: Li Ai
Source: Ulink Media

What is Passive Sensor?

Passive sensor is also called energy conversion sensor. Like the Internet of Things, it does not need external power supply, that is, it is a sensor that does not need to use external power supply, but also can obtain energy through external sensor.

We all know that sensors can be divided into touch sensors, image sensors, temperature sensors, motion sensors, position sensors, gas sensors, light sensors and pressure sensors according to different physical quantities of perception and detection. For passive sensors, the light energy, electromagnetic radiation, temperature, human movement energy and vibration source detected by sensors are potential energy sources.

It is understood that passive sensors can be divided into the following three categories: optical fiber passive sensor, surface acoustic wave passive sensor and passive sensor based on energy materials.

• Optical fiber sensor

Optical fiber sensor is a kind of sensor based on some characteristics of optical fiber developed in the mid 1970s. It is a device that converts a measured state into a measurable light signal. It consists of light source, sensor, light detector, signal conditioning circuit and optical fiber.

It has the characteristics of high sensitivity, strong electromagnetic interference resistance, good electrical insulation, strong environmental adaptation, remote measurement, low power consumption, and is increasingly mature in the application of the Internet of things. For example, the optical fiber hydrophone is a kind of sound sensor which takes the optical fiber as a sensitive element, and the optical fiber temperature sensor.

• Surface Acoustic Wave Sensor

Surface Acoustic Wave (SAW) sensor is a sensor that uses a surface acoustic wave device as a sensing element. The measured information is reflected by the change of the speed or frequency of surface acoustic wave in the SURFACE acoustic wave device, and is converted into an electrical signal output sensor. It is a complex sensor with a wide range of sensors. It mainly includes surface acoustic wave pressure sensor, surface acoustic wave temperature sensor, surface acoustic wave biological gene sensor, surface acoustic wave chemical gas sensor and intelligent sensor, etc.

Besides the passive optical fiber sensor with high sensitivity, can distance measurement, the characteristics of low power consumption, passive surface acoustic wave sensors use Hui frequency change guess the change of the velocity, so the change of the check to the outside measurement can be very precise, at the same time it the characteristics of small volume, light weight, low power consumption can let it get good thermal and mechanical properties, And ushered in a new era of wireless, small sensors. It is widely used in substation, train, aerospace and other fields.

• Passive Sensor Based on Energy Materials

Passive sensors based on energy materials, as the name implies, use common energy in life to convert electrical energy, such as light energy, heat energy, mechanical energy and so on. The passive sensor based on energy materials has the advantages of wide band, strong anti-interference ability, minimal disturbance to the measured object, high sensitivity, and is widely used in electromagnetic measurement fields such as high voltage, lightning, strong radiation field strength, high power microwave and so on.

Combination of Passive Sensors with Other Technologies

In the field of the Internet of Things, passive sensors are more and more widely used, and various kinds of passive sensors have been published. For example, sensors combined with NFC, RFID and even wifi, Bluetooth, UWB, 5G and other wireless technologies have been born.In passive mode, the sensor obtains energy from radio signals in the environment through the antenna, and the sensor data is stored in non-volatile memory, which is retained when power is not supplied.

And wireless passive textile strain sensors based on RFID technology, It combines RFID technology with textile materials to form equipment with strain sensing function. RFID textile strain sensor adopts communication and induction mode of passive UHF RFID tag technology, relies on electromagnetic energy to work, has miniaturization and flexibility potential, and becomes a potential choice of wearable devices.

At the end

Passive Internet of Things is the future development direction of the Internet of Things. As a link of passive Internet of Things, the requirements for sensors are no longer limited to miniature and low power consumption. Passive Internet of Things will also be a development direction worth further cultivation. With the continuous maturity and innovation of passive sensor technology, the application of passive sensor technology will be more extensive.