At present, many wearable biosensors, data transmitters, and similar personal health monitoring devices are already very advanced, and are getting smaller and smaller. However, these devices still require a lot of energy to maintain their work, and the power supply may be large and bulky.
A new study from Trisha Andrew, a material chemist at the University of Massachusetts, and her doctoral student Linden Allison shows that they have now developed a new fabric that can collect body heat and provide it for small wearable microelectronic devices such as activity trackers. power. Related research results are published in the online version of "Advanced Materials Technology".
Trisha Andrew explained that, theoretically, human body heat can use the difference between human body temperature and the surrounding cooler air to generate energy, which is a "thermoelectric effect". In this way, materials with high electrical conductivity and low thermal conductivity can transfer charge from areas with higher temperature to areas with lower temperature.
Studies have shown that the human body can obtain a small amount of electrical energy during the 8-hour working day, but the special materials currently required are either expensive, toxic, or inefficient. Trisha Andrew said: "We have developed a new method to add biocompatibility, flexibility and light weight polymer film to cotton cloth for daily use, so that it has a sufficiently high thermoelectric performance and can generate a higher thermal voltage, It can drive small devices to operate normally. "
In this study, the researchers used the natural low heat transfer characteristics of wool and cotton to create a thermoelectric garment that can maintain a temperature gradient on an electronic device called a "thermoelectric stack." The electronic device can convert heat into electrical energy even when it is continuously worn for a long time. This is a very realistic and feasible solution to ensure that the conductive materials are stable in terms of electrical, mechanical and thermal energy.
Trisha Andrew said: "In essence, we used the basic insulation properties of the fabric to solve a long-standing problem in the equipment industry."
Specifically, they printed a conductive polymer, a persistent P-doped polymer (PEDOT-Cl), by steam printing on a high-density woven and a medium-density commercial cotton fabric to make a full fabric Thermopile. Then, they integrated this thermopile on a specially designed wearable ring. When people wear this ring on their hands, they can generate a thermal voltage greater than 20 mV.
The researchers rubbed or washed the coated fabric in hot water to evaluate the wear resistance of the PEDOT-Cl coating, while evaluating the performance of the coating by scanning electron micrographs. The results show that this coating has no cracks and delamination, and will not wear the coating after mechanical washing, and can confirm the mechanical strength of the PEDOT-Cl coating by steam.
Subsequently, they measured the conductivity of the coating surface using a special probe, and found that loose fabrics exhibited higher conductivity than tight fabrics. They emphasized that the electrical conductivity of these two fabrics remained basically unchanged after rubbing and mechanical washing.
The researchers used thermal imaging cameras to find that the volunteers ’wrists, palms, and upper arms radiated the most heat, so Trisha Andrew and colleagues made a flexible thermoelectric fabric ring that can be worn on these body parts. They pointed out that the outer part of the ring-shaped device exposed to the air was isolated from body temperature by the thickness of the gauze, and only the uncoated side was in contact with the skin, thereby reducing the allergic reaction to PEDOT-Cl.
The researchers noticed that sweating significantly increased the heat and pressure output of the elastic arm ring, which is not surprising, because they found that wet cotton is considered to be a better thermal conductor substance than dry fabric. By inserting a layer of heat-reflective plastic between the wearer's skin and the wristband, they can turn off heat transfer at will.
“Compared with traditional production equipment, the reactive vapor coating process produces a wear-resistant fabric thermopile with a significantly higher thermoelectric potential rate factor at low temperatures. In addition, we also describe the most natural integration of thermopile into clothing design. Good practice. "Trisha Andrew said. (Liu Yiyang)
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