Drive "smart clothing" with body heat

Many wearable biosensors, data transmitters, and similar personal health monitoring devices are now very advanced and are getting smaller and smaller. However, these devices still require a lot of energy to maintain the work, and the power supply can be large and cumbersome.

A new study from material chemist Trisha Andrew of the University of Massachusetts and her PhD student Linden Allison shows that they have developed a new fabric that can collect human body heat and provide it for small wearable microelectronic devices such as activity trackers. power. Relevant research results were published on the online edition of Advanced Materials Technology.

Trisha Andrew explained that in theory, human body heat can use the difference between human body temperature and the surrounding cold air to generate energy, which is a "thermoelectric effect." Materials with high electrical conductivity and low thermal conductivity can transfer charge from a higher temperature region to a lower temperature region in this way.

Studies have shown that the body can get a small amount of electrical energy in an 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 biocompatible, flexible and lightweight polymer films to everyday cotton fabrics with high enough thermoelectric properties to produce higher thermal voltages. Can drive small devices to work properly."

In this study, the researchers used the natural low heat transfer characteristics of wool and cotton to create a thermoelectric garment that maintains a temperature gradient across an electronic device called a thermopile. The electronic device can convert heat into electrical energy even in the case of continuous wear for a long time. This is a very realistic solution to ensure that conductive materials are continuously stable in terms of electrical, mechanical and thermal energy.

Trisha Andrew said: "In essence, we have used the basic insulation properties of fabrics to solve a long-standing problem in the equipment industry."

Specifically, they made a conductive polymer, a continuous P-doped polymer (PEDOT-Cl), printed on a high-density and a medium-density commercial cotton fabric by steam printing to make a full fabric. Thermoelectric stack. They then integrated the thermopile into a specially designed wearable ring that generated a thermal voltage greater than 20 millivolts when the ring was worn on the hand.

The researchers evaluated the wear resistance of the PEDOT-Cl coating by rubbing or washing the coated fabric in hot water while evaluating the performance of the coating by scanning electron micrographs. The results show that the coating has no cracks and delamination, and the mechanical coating does not wear the coating, and the mechanical strength of the steam-washed PEDOT-Cl coating can be confirmed.

Subsequently, they measured the surface conductivity of the coating using a special probe and found that the loose fabric exhibited higher conductivity than the compact fabric. They emphasize that the electrical properties of the two fabrics remain essentially unchanged after rubbing and mechanical washing.

Using thermal imaging cameras, the researchers found that volunteers had the highest amount of heat on their wrists, palms, and upper arms, so Trisha Andrew and colleagues created a flexible thermo-electric fabric ring that could be worn on these parts of the body. They pointed out that the outer portion of the ring device exposed to the air is isolated from the body temperature by the thickness of the gauze, while only the uncoated side is in contact with the skin, thereby reducing the allergic reaction to PEDOT-Cl.

The researchers noted that sweating significantly increased the hot-pressed output of the elastic armband, which is not surprising, as they found that wet cotton is a better thermal material than dry fabric. By inserting a layer of heat-reflecting plastic between the wearer's skin and the wristband, they can turn off heat transfer at will.

“Compared to conventional production equipment, the reactive steam coating process produces wear-resistant fabric thermopiles with significantly higher temperature-to-potential potential factors at low temperatures. In addition, we describe the most natural integration of thermoelectric stacks into apparel design. Good practice," said Trisha Andrew.