A three-dimensional spaced structure piezoresistive knitted sensor with three-dimensional sensing capability machine-integrated

Infineon / Mitsubishi / Fuji / Semikron / Eupec / IXYS

A three-dimensional spaced structure piezoresistive knitted sensor with three-dimensional sensing capability machine-integrated

Posted Date: 2024-01-13

Background introduction

Smart textiles provide highly comfortable sensing methods and interfaces for sensing body motion parameters in daily life. Knitting, a traditional textile manufacturing method, enables completely seamless one-piece preparation in electronic textiles. However, current planar braided sensors are only used to sense strain in the horizontal plane. This study proposes a new machine-integrated three-dimensional spacer structure piezoresistive knitted sensor with three-way sensing capabilities. This structure can detect not only the pressure in the vertical direction, but also the strain in the horizontal direction of the warp/weft yarn, and can sense pressure below 2kPa. The paper tested three sizes of spacer knitted sensors in terms of mechanical properties, stability, and response to external factors such as sweat and washing. Then, the impact of material selection on sensor performance is evaluated and the experience of material selection is summarized.

In addition, this study tested single sensors and multiple sensor arrays in several fine or large motion sensing application scenarios. Test results show that the machine-integrated knitted piezoresistive sensor can detect body movements from multiple directions (vertical direction, warp and weft horizontal directions). Furthermore, this knitted sensor is customizable and can be easily and seamlessly integrated into knitted garments. This knitted sensor structure is versatile and can be made from a variety of materials for highly sensitive multi-directional strain/pressure sensing, making it a highly compatible sensor structure for wearable applications and ready for mass production.

Figure 1. Schematic diagram of a spacer structure knitted three-way piezoresistive sensor for integrated integration and wearable applications.

Article Highlights

Existing knitted structure sensors are difficult to meet the strain and pressure sensing requirements for all-round motion detection because: (1) Planar/two-dimensional knitted sensors can only sense deformation on the horizontal plane. However, human kinematics involves the dynamic detection of multi-directional motion parameters, and unidirectional motion monitoring can hardly meet the needs of complex motion monitoring tasks. Therefore, three-dimensional knitted structures are needed for the perception of complex motion parameters. (2) The human body has requirements for the comfort threshold of wearable products (up to 2000-3500Pa), and most existing commercial film/textile sensors cannot meet the small-scale measurement requirements of wearable products. Therefore, there is a need to develop small-range textile sensors for comfortable body wear.

This paper designs and evaluates a three-dimensional spaced braided piezoresistive sensor based on one-piece braiding technology for small measurement ranges below 2kPa and multi-directional pressure/strain sensing. Due to the three-dimensional spacer structure, compression or tension causes the spacer braided sensor to deform, which can cause its resistance to change, making it a sensitive pressure/strain sensor structure (see Figure 2). The sensor responds to both pressure in the vertical direction and strain in the horizontal direction (warp and weft direction). The sensor adopts machine-integrated weaving technology, which can be made of different materials and sizes into customized integrated wearable devices for various body movement detection.

Figure 2. (a) Schematic diagram of the three-way sensing structure of the spacer knitted sensor; (b) Cross-sectional view of the sensor model; (c) Surface SEM image and (d) cross-sectional view of the spacer knitted sensor; (e) Different sizes Surface and (f) cross-sectional view of the spacer knitted sensor sample; (g) model rendering of the knitted sensor compressed in the vertical direction; and (h) model rendering of the knitted sensor stretched in the weft horizontal direction.

Partial graphic analysis

Figure 3. Basic sensing performance of spacer knitted sensors: (c) Sensitivity test of pressure sensor - three sizes; (d) Measurement of strain sensing in the horizontal direction for three sizes of sensors.

Figure 4. (a) Sensitivity comparison of fabric pressure sensors; (b) Gauge coefficient comparison between knitted strain sensors.

Figure 5. (ab) SEM images of the spacer knitted sensor before and after the stability cycle test; (c) Air permeability test results of pure cotton fabric, the spacer knitted sensor of this project and the TPU film; (d) Spacer knitted Perspiration test of the sensor; and (e) washing test of the spacer woven sensor.

Figure 6. Application of spacer braided sensors for real-time fine movement monitoring: (a) finger flexion, (b) neck flexion, and (c) post-exercise respiration. Real-time detection of large movements: (d) knee bending, (e) wrist bending up and down, (f) arm bending 60°, 90°, 145°, (g) detection using a sensing array made of multiple spaced woven sensors interactive gestures on a smartwatch strap, and (h) detecting whether the driver's body is in a relaxed or focused state using a spaced woven sensor array on the top.


The work was published in the journal under the title "Three-directional Spacer-knitted Piezoresistant Strain and Pressure Sensor for Electronic Integration and On-body Applications"ACS Applied Materials & Interfacesand was selected as a cover story. This research was supported by the National Natural Science Foundation of China and the Guangdong Provincial Natural Science Foundation of China.

Corresponding Author:Ziqian Bai, Southern University of Science and Technology, Shouxiang Jiang, Hong Kong Polytechnic University

First author:Mengqi Jiang

Review Editor: Liu Qing

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