A few days ago, the Shenzhen Science and Technology Innovation Committee disclosed the relevant content of the "14th Five-Year Plan for Shenzhen Science and Technology Innovation". The plan clarifies the main direction of "20+8" technology, that is, to carry out technological research around seven strategic emerging industries in Shenzhen, 20 industrial clusters and eight future industries. Among them, seven strategic emerging industries mentioned the need to carry out technical research in the field of new sensors.

Excerpt from "Shenzhen's 14th Five-Year Plan for Scientific and Technological Innovation"

As an important part of the Internet of Things, sensors need to acquire data accurately. It is like the "nerve terminal" of a product, which senses stimuli from the outside world and monitors changes in parameters. The smart sensor has brought it more diverse functions and gained more room for development. According to a recent Allied Market Research report, the global smart sensor market will grow at a compound annual growth rate (CAGR) of 18.6% by 2027 (from 2020 onwards), or $143.65 billion.

The passive Internet of Things that has emerged in recent years has also put forward higher requirements for sensors.

Passive IoT, which are essentially end nodes passive, have no power cords, no built-in batteries, and instead draw energy from the environment. In order to achieve "passive", the upstream end is put forward, which also gave birth to the emergence of passive sensors.

What is a passive sensor?

Passive sensor is also known as energy conversion sensor. Like the Internet of Things, it does not require external power supply, that is, it is a sensor that does not require external power supply, and can also obtain energy from external sources.

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 the physical quantities sensed and detected. For passive sensors, light energy, electromagnetic radiation, temperature, human motion energy, vibration sources, etc. detected by the sensor are all potential energy sources.

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

1. Optical fiber passive 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 the measured state into a measurable optical signal. It consists of a light source, a sensitive element, a photodetector, a signal conditioning circuit and an optical fiber.

Optical fiber sensors have the characteristics of high sensitivity, strong anti-electromagnetic interference, good electrical insulation, strong environmental adaptability, long-distance measurement, and low power consumption, and their applications in the Internet of Things are becoming more and more mature. For example, a fiber optic hydrophone is an acoustic sensor that uses an optical fiber as a sensitive element, as well as a fiber optic temperature sensor.

2. Surface acoustic wave passive sensor

A surface acoustic wave (SAW) sensor is a sensor that uses a surface acoustic wave device as a sensing element, and reflects the measured information through the change in the speed or frequency of the surface acoustic wave in the surface acoustic wave device, and converts it into Sensor with electrical signal output. It is a complex sensor type involving 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 and other types.

In addition to the characteristics of high sensitivity, long-distance measurement, and low power consumption of optical fiber passive sensors, surface acoustic wave passive sensors use vibration frequency changes to predict changes in propagation speed, so the measurement of changes in external detection quantities can be very effective. Accurate, at the same time, its small size, light weight and low power consumption allow it to obtain good thermal and mechanical properties, and also create a new era of wireless, small sensors. It is widely used in substations, trains, aerospace and other fields.

3. Passive sensors based on energy materials

Passive sensors based on energy materials, as the name suggests, use common energy sources in life to convert electrical energy, such as light energy, thermal energy, mechanical energy, etc. Passive sensors based on energy materials have the advantages of wide frequency band, strong anti-interference ability, minimal disturbance to the measured object, and high sensitivity. They are widely used in electromagnetic measurement fields such as high voltage, lightning, field strength in strong radiation areas, and high-power microwaves. .

Combining passive sensors with other technologies

In the field of the Internet of Things, the application of passive sensors is becoming more and more extensive, and various types of passive sensors have also appeared one after another. For example, sensors combined with wireless technologies such as NFC, RFID, and even wifi, Bluetooth, UWB, and 5G have been born.

In passive mode, the sensor draws energy from radio signals in the environment through an antenna, and sensor data is stored in non-volatile memory, which is retained when no power is supplied.

There are also wireless passive textile strain sensors based on RFID technology, which combine RFID technology with textile materials to form devices with strain sensing functions. RFID textile strain sensors use the communication and induction methods of passive UHF RFID tag technology, relying on electromagnetic It can work, has the potential of miniaturization and flexibility, and becomes a potential choice for wearable devices.

end

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

References:

Smart grid: "Research and Application Progress of Passive Sensors"

Silk Magazine: "Research Progress of Wireless Passive Textile Strain Sensor Based on RFID Technology"