Simple Yet Robust Triboelectric Harvester Powers Sweat-Sensing Patch

您将学到什么：

• Caltech团队如何使用灵活的电路板创建可穿戴的汗水传感器。
• 涉及创建能量收获传感器的材料。

It’s not news that you can use the triboelectric effect—electricity generated by the friction of motion between two suitable materials—to generate tiny but useful amounts of energy to power body-mounted devices and their sensors. However, many of these energy harvesters require complex fabrication steps and lack ruggedness or flexibility for normal body wear and normal associated normal wear.

Now, a team at the California Institute of Technology (Caltech) has developed a wearable sweat sensor that’s powered by a simple-to-fabricate triboelectric harvester, which is based on a thin sandwich of materials (Teflon, copper, and polyimide) attached to the person's skin. As the person moves, these sheets of material rub against a sliding layer made of copper and polyimide to generate small amounts of electricity.

What is new, noted Wei Gao, assistant professor of medical engineering in the Andrew and Peggy Cherng Department of Medical Engineering and project leader, is how the research team manufactured the nanogenerator. “This is not something new, concept-wise. But instead of using fancy materials, we use commercially available flexible circuit boards," he said. "This material is cheap and very durable and mechanically robust over long periods of time."

为什么要专注于汗水？研究人员指出，汗水是一种具有吸引力且可访问的培养基，具有许多分子生物标志物，包括电解质，代谢产物，氨基酸，激素和可穿戴传感器可以分析的药物。被称为独立式摩洛电纳米生成器（FTENG）功率可穿戴汗液传感器系统（FWS³），该集成单元通过低功耗蓝牙链接无线地报告数据，从而消除了对连接器的需求以及添加到设计的许多问题。

该项目导致了一个非常健壮，可实现的无电池可穿戴平台，可通过基于FTENG的灵活印刷电路板（FPCB）有效地从身体运动中提取动力。完整的单元是一个高效，可穿戴的，低功率的无线传感器电路以及单个FPCB平台上的微流体汗液传感器贴片，可以动态监视键汗生物标志物（例如pH和NA）⁺，并产生相对较高的功率输出约为416 mW/m²(Fig. 1)。

1.无电池FW³用于无线和非侵入性分子监测。（a）示意图说明FWS³that integrates human motion energy harvesting, signal processing, microfluidic-based sweat biosensing, and Bluetooth-based wireless data transmission to a mobile user interface for real-time health status tracking. (B and C) Optical images of an FPCB-based FWS³，可以戴在人侧躯干上。比例尺，4厘米。（d）基于FPCB的FTENG的示意图，带有光栅滑块和互化定子。（e）FWS的示意图³showing a microfluidic-based sweat sensor patch interfacing with the flexible circuitry. (F) System-level block diagram showing the power management, signal transduction, processing, and wireless transmission of the FWS³从fteng到生物传感器，再到用户界面。（资料来源：Yu Song，加利福尼亚理工学院）

为了制造FTENG，该团队使用了一系列类似于PCB制造的步骤来制造焊料，使用电镍/浸入式金（ENIG）沉积（ENIG）沉积以及polytetra-fluoroethylene（PTFE - Teflon）涂层进行定子涂层(Fig. 2)。The rectangular interdigitated slider (44 × 42 mm) has 10 “digits,” while the stator (60 × 38 mm) has 15.

2. Fabrication process of the slider and the stator of the FTENG. Steps (i-vi) are compatible to the commercial FPCB fabrication process. (Source: California Institute of Technology)

Output of the FTENG was modeled and measured on the bench under multiple scenarios;图3shows data extracted from one such run.

3.FTENG的输出性能。(一)波形of output voltages of an FTENG under a working frequency of 0.5 Hz. (B) Cycling stability of output performance of a FTENG after 20,000 cycles under a working frequency of 2 Hz. (Source: California Institute of Technology)

The schematic diagram of the circuit and the high-level flow chart of the operating firmware shows the interconnection and interplay among the many elements（图4）。

4. FWS的系统级集成和评估³。（a）无电池FWS的示意图³由FTENG模块，生物传感器界面，仪器放大器，能量收获的PMIC，电压调节器和BLE PSOC模块组成。（b）FWS的运行流³信号处理和数据传输。（c）FWS的功耗³在操作过程中。（d）FWS连续运行期间电容器的实时电位（242 µF）³在不同的工作频率下使用三板fteng。(E) Validation of data transmission from an FWS³在不同的工作频率下使用三板fteng。（f）FWS时电容器充电过程的长期稳定性³以1.5 Hz的工作频率运行。(Source: California Institute of Technology)

In addition to physical and electrical modeling and bench tests, the project team did evaluations with live subjects to validate the results and enhance the project credibility（图5）。

5. On-body evaluation of the FWS³for wireless, dynamic perspiration analysis. (A) Output waveforms of a six-panel FPCB-based FTENG during various exercises. (B and C) Real-time potential of the capacitor charged by an FTENG (B) and the average charging time for each package transmission (C) when a subject is running on a treadmill for 1 hour at a constant speed of 9 km/hour. The ratio in (C) represents the percentage of charging cycles (with charging duration within a given time range) out of all the charging cycles. When the potential reaches 3.3 V, the capacitor is discharged due to the Bluetooth Low Energy (BLE) data transmission. (D) Optical image of a subject on a treadmill wearing an FWS³和手机。（e）实时汗水和NA⁺levels are obtained wirelessly from the wearable system charged by a lithium battery and by an FTENG during constant-speed running. (Source: Yu Song, California Institute of Technology.

A description of the rationale, various stages, and results of this multidisciplinary project can be found in an 11-page, readable paper published in the journal科学进步, “无线电池可穿戴汗液传感器由人类运动驱动。” It’s accompanied by a 38-pageSupplementary Materials提供有关制造，布置和测试的其他详细信息的纸张。