Preparation and performance of capacitive sensors with biomimetic skin wrinkle structure
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摘要: 随着智能可穿戴技术的快速发展，柔性电容式传感器因其制备工艺简单及优良的电学性能，在健康监测、人机交互、电子皮肤等领域展现出广阔的应用前景。本文围绕提升电容式传感器的检测范围和耐久性为目标，提出了一种基于聚二甲基硅氧烷(PDMS)和可膨胀微球复合介电层的仿生皮肤褶皱结构的电容式传感器。用SEM分析了介电层的结构形貌，并研究了该传感器的电学性能和人体适用性。结果表明：电容式传感器具有较宽的检测范围(0-242 kPa)、高灵敏度(
0.0079 kPa−1)、快速响应时间(230 ms)以及优异的稳定耐久性(9500 次循环)；同时，还具有较好的非接触感测性能，其非接触灵敏度为0.59%/cm。在实际应用中，该传感器可用于监测手指、手腕、膝盖等关节的弯曲运动，以及眨眼、张口等细微的生理信号。该电容式传感器在运动监测和健康监测领域具有潜在的应用价值。Abstract: With the rapid development of intelligent wearable technology, flexible capacitive sensors have shown broad application prospects in fields such as health monitoring, human-computer interaction, and electronic skin due to their simple preparation process and excellent electrical property. In order to improve the detection range and durability of the capacitive sensors, a capacitive sensor based on polydimethylsiloxane (PDMS) composite dielectric layer and expandable microsphere imitating the skin wrinkle structure is proposed. The structural morphology of the dielectric layer was evaluated by SEM and the electrical properties and human suitability of the sensor were investigated. The results show that the capacitive sensor has a wide detection range (0-242 kPa), high sensitivity (0.0079 kPa−1), fast response time (230 ms), and excellent stable durability (9500 cycles). It also has good non-contact sensing performance with a non-contact sensitivity of 0.59%/cm. In practical applications, this sensor can accurately monitor bending movements of joints such as fingers, wrists and knees, as well as subtle physiological signals such as blinking and opening the mouth. The capacitive sensor has potential applications in the field of motion monitoring and health monitoring. -
图 2 聚二甲基硅氧烷(PDMS)-可膨胀微球介电层和纯PDMS介电层的微观形貌：(a) 可膨胀微球膨胀前的SEM照片；(b)可膨胀微球膨胀后的SEM照片；(c) PDMS-可膨胀微球介电层光学显微镜照片；(d) PDMS-可膨胀微球介电层的SEM照片；(e) PDMS-可膨胀微球介电层实物照片；(f) PDMS-可膨胀微球介电层横截面的SEM照片；(g) 纯PDMS介电层的SEM；(h) 纯PDMS介电层横截面的SEM照片。
Figure 2. Microscopic morphology of polydimethylsiloxane (PDMS)-expandable microsphere dielectric layer and pure PDMS dielectric layer: (a) SEM image of expandable microspheres before expansion; (b) SEM image of expandable microspheres after expansion; (c) PDMS-expandable microsphere dielectric layer optical microscope picture; (d) SEM image of PDMS-expandable microsphere dielectric layer; (e) Photographic of PDMS-expandable microsphere dielectric layer; (f) SEM image of PDMS-expandable microsphere dielectric layer cross-section; (g) SEM of pure PDMS dielectric layer; (h) SEM image of pure PDMS dielectric layer cross-section.
图 3 电容式传感器的传感机制示意图
Figure 3. Schematic diagram of sensing mechanism of capacitive sensor
图 4 电容式传感器压力传感性能：(a) 压力灵敏度；(b) 不同压力下的电容响应；(c) 在2 kPa压力下对传感器进行循环施压的电容响应数据；(d-e) 响应/回复时间；(f) 压力耐久性；(g) 电容式传感器性能对比图
Figure 4. Capacitive sensor pressure sensing performance: (a) Pressure sensitivity; (b) Capacitive response at different pressures; (c) Capacitive response data for cyclic pressure application to the sensor at 2 kPa pressure; (d-e) Response/recovery time; (f) Pressure durability; (g) Performance comparison of capacitive sensors
图 5 电容式传感器非接触性能：(a) 非接触传感示意图；(b) 非接触灵敏度；(c) 不同距离下的电容响应；(d) 不同手指根数的电容响应(5 cm高度)；(e) 非接触耐久性
Figure 5. Capacitive sensor non-contact performance: (a) Non contact sensing schematic diagram; (b) Non-contact sensitivity; (c) Capacitive response at different distances; (d) Capacitive response for different number of fingers (5 cm height); (e) Non-contact durability
图 6 电容式传感器关节弯曲运动应用：(a) 手指弯曲；(b) 手腕弯曲；(c) 膝盖弯曲；(d) 走路
Figure 6. Capacitive sensors for joint bending motion applications: (a) Finger bending; (b) Wrist bending; (c) Knee bending; (d) Walking
图 7 电容式传感器生理信号监测：(a) 眨眼；(b) 张口；(c) 吞咽
Figure 7. Capacitive sensor physiological signal monitoring: (a) Blinking; (b) Opening the mouth; (c) Swallowing
图 8 电容式传感器在外加压力下的响应演示：(a1-b2) 传感器对快速触摸和重量压力的电容响应；(c1-d2) 检测各种重复动作，包括点击鼠标和抓烧杯；(e-g) 检测指尖、不锈钢圆柱体和尺子尖对传感器的重复敲击
Figure 8. Demonstration of the capacitive sensor in response to exerted pressures: (a-b) Capacitive response of the sensor to fast touch and weight pressure; (c-d) Detection of various repeated actions, including clicking the mouse and grasping the beaker; (e-g) Detection of the repeated strikes of the sensor by fingertips, stainless steel cylinders and ruler tips
图 9 电容式传感器用于摩斯密码应用：(a) 阿拉伯数字和英文字母摩斯密码表；(b-c) 不同阿拉伯数字的摩斯密码电容信号；(d-e) 不同英文字母的摩斯密码电容信号；(f) 不同单词的摩斯密码电容信号
Figure 9. Capacitive sensors for morse code applications: (a) Morse code table of Arabic numerals and English letters; (b-c) Morse code capacitive signals with different arabic numerals; (d-e) Morse code capacitive signals for different alphabets; (f) Morse code capacitive signals for different words
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