Recently, according to foreign media reports, American material chemists have developed a cloth that can collect heat from the human body. This cloth can provide power for small wearable devices. Trisha Andrew, a materials chemist at the University of Massachusetts, said that many wearable biosensors, data transmitters and similar personalized health monitoring devices have developed rapidly, and they have become more and more miniaturized. But they require a lot of energy, and the power supply is usually bulky.
Now, she and her doctoral student Linden Allison say they have developed a fabric that collects heat from the body to power small wearable microelectronic devices such as activity trackers.
Andrew and Allison explained that in theory, body heat can use the difference between body temperature and the surrounding cold air to generate electrical energy, that is, a "thermoelectric" effect.
But they pointed out that the special materials currently required are either very expensive, toxic, or inefficient. Andrew said: "What we have developed is a low-cost steam printing method that prints biocompatible, flexible and lightweight polymer films on cotton fabrics, which have sufficiently high thermoelectric properties to produce comparable The high thermal voltage is enough to drive a small device. "
In this work, the researchers used the natural low heat transfer properties of wool and cotton to create a thermoelectric garment that can maintain the temperature difference. The temperature gradient passes through an electronic device called a thermopile, which can convert heat into electrical energy even during long periods of continuous wear and tear.
She and Allison concluded: "In essence, we use the basic insulation properties of the fabric to solve a long-standing problem in the equipment industry." "We believe that for those equipment engineers and those interested in developing intelligence who are seeking to develop new energy sources for wearable electronics For designers of clothing, this work will be very interesting. "
Specifically, the fabric they created is a conductive polymer called persistent p-doped poly (3,4-ethyldioxythiophene) (PEDOT-Cl), which is printed on a tightly organized and A medium-structured commercial cotton fabric. They then integrated this thermopile into a specially designed wearable band, which generates a thermal voltage greater than 20 mV when worn on the hand.
The researchers tested the durability of the PEDOT-CI coating by rubbing or washing the coated fabric. The performance of the coating was evaluated by scanning electron micrographs. The results showed that the coating "does not crack or delaminate after washing or scratching, thus confirming the mechanical robustness of steam printed PEDOT-CI".
They measured the surface conductivity of the coating with a custom-made probe and found that looser tissue cotton exhibited higher conductivity than tighter tissue materials. They added that the electrical conductivity of these two fabrics "maintained the same after rubbing and washing."
The study found that they determined that the volunteers ’wrists, palms and upper arms radiated the most heat, so Andrew and Allison made elastic thermoelectric fabric knitted belts that can be worn in these areas. The exposed straps are insulated outside . Depending on the thickness of the yarn, only the uncoated side of the thermometer can contact the skin to reduce the risk of allergic reactions to PEDOT-CI.
The researchers noticed that sweat significantly increased the thermal voltage output of the stretch arm, which was not surprising, because they observed that wet cotton is a better thermal conductor than dry fabric. They can also switch off heat transfer at will by inserting a heat-reflecting plastic layer between the wearer's skin and the strap.
In general, they said, “we show that the reactive steam coating process creates a mechanically strong fabric temperature differenceâ€, which has a “significantly high thermoelectric power factor†in low temperature differences compared to traditionally produced equipment. "In addition, we also found that the best practice is to naturally integrate the thermometer into the garment, which allows a significant temperature gradient to be maintained across the thermometer despite continued wear and tear."
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