What Are Smart Textile Sensors?

Smart textiles refer to textiles that can induce and react to external environmental stimuli, including intelligent thermostat textiles, shape memory textiles, waterproof and moisture permeable textiles, color changing textiles, and electronic information intelligent textiles.

The main components of electronic smart textiles include conductive textiles, signal acquisition sensors, driving units and control units, which can induce, feedback and respond to external stimuli.

Based on sensors, textiles that can only perceive the environment or users are called passive (passive) intelligent textiles; textiles that respond to environmental stimuli and integrate sensors and actuator devices are called active (active) intelligent textiles; textiles that perceive, react and adjust their behaviors to suit a given environment are called advanced intelligent textiles.

Sensors provide a neural system to detect signals, so in the passive smart materials, the existence of sensors is essential.

Sensor is a kind of detection device. By embedding the flexible or micro sensor into the fabric, it can induce various physical or chemical stimuli such as temperature, pressure, displacement and current.

At present, electronic intelligent textile sensors mainly include strain sensors, pressure sensors, inductance sensors and optical fiber sensors.

Strain sensor

Strain sensors are mainly used for monitoring vital signs, such as heart rate, respiration and blood pressure, and can be made into fabric sensors by integrating fibers with piezoresistive properties.

Because the fabric has a large area of contact with the skin, it means that it can be monitored in many parts of the body.

This kind of piezoresistive sensor is soft, light, sensitive, small in size and high resolution, and is well integrated with the fabric. When the fabric size changes slightly, the change of the conductive area leads to the change of resistance, so that the fabric deformation can be pformed into resistance change, and the body parameters can be monitored through signal analysis.

Carbon nanotube sensor for human respiration detection

Pressure sensor

Pressure sensor is a kind of sensor that receives the mechanical signal through a specific way by means of electrical signals. It is usually composed of mechanical induction and conversion device.

Pressure sensors can be divided into capacitive sensors and resistive sensors.

The capacitance sensor realizes the sensing function by changing the capacitance with the change of applied pressure.

There are fiber capacitive sensors made of fiber, which are made of conductive material and dielectric, and fabric type capacitance sensors made of fabric and dielectric.

The application of resistive sensor is very extensive. Its working principle is that the resistance of conductive material will change when it is subjected to pressure.

This kind of sensor is applied to smart clothing. When it is subjected to slight pressure changes, it will have obvious resistance changes. Therefore, the physiological indexes such as respiration and pulse can be measured by measuring the change of micro force.

Similarly, resistive sensors can be divided into fiber and fabric sensors.

The conductive materials commonly used for fiber resistance sensors are carbon nanotubes, graphene, and some non intrinsic conductive fibers. Fabric conductive resistance sensors are commonly conductive materials or conductive film materials. They have the softness of clothing requirements, and the conductive layers are all on the outside surface, which can detect pressure changes more sensitively.

Piezoresistive sensor for finger action detection

Inductive pducer

Inductance sensor is a pducer which uses electromagnetic induction to pform pressure or human action into the sensor of self inductance and mutual inductance of coil. It is also called inductive displacement sensor.

Inductive sensors can be divided into self induction and mutual inductance sensors according to the conversion principle. They can be divided into variable gap type, variable section type and screw type sensor according to their structure.

The inductive sensor has high resolution, good linearity and wide measuring range. Although it has defects such as zero signal and unfavorable high frequency dynamic measurement, it is more suitable for human monitoring intelligent textiles than other sensors.

Especially when the sensing coil of inductive sensor uses conductive textile material, it is more flexible than metal coil and is more suitable for smart textiles.

Optical fiber sensor

Optical fiber sensor is a sensor which monitors the physical quantities of the outside world by using the sensitive characteristics of optical fiber.

The principle is that when the light propagates in the optical fiber, the change of the external environment will cause the change of light intensity and polarization plane.

Optical fiber sensors are mainly composed of light sources, detectors and optical fibers. The widely used optical fiber sensing technologies include macro bending optical fiber sensors, micro bend optical fiber sensors and fiber Prague gratings.

The change of optical signal parameters can be pformed into relevant parameters of medical equipment. Because of its micro bending principle, macro bending principle, high sensitivity and anti electromagnetic interference property, it is suitable for combining with textiles and applied to medical health field.

Compared with electrical sensors, optical fiber sensors play an important role in the medical field, especially in the monitoring of heart rate and respiratory rate.

Optical fiber and fabric combination