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Battery-Free Sensor Patch Harvests Power from Body Heat

7 Feb 2016 7:41am, by

Today’s electronics are finicky and demanding, requiring frequent recharges to sustain their energy-hungry processes. But the inconvenience and unwieldy pervasiveness of today’s batteries for consumer products may soon become a thing of the past, as researchers are developing new kinds of wearable, energy-harvesting electronics, capable of extracting energy from the everyday movements and heat emitted by the human body. It’s all part of a recent trend in developing battery-free electronics, from devices that use power harvested from wireless signals, to biologically powered microchips.

As IEEE Spectrum reports, scientists at North Carolina State University’s Center for Advanced Self-Powered Systems of Integrated Sensors (ASSIST) are developing a wireless, wearable sensor patch that monitors the user’s hydration levels and sends the data to a smartphone, and is powered by energy harnessed from body heat.

Continuous Energy Harvesting

The prototype, which was showcased at the Consumer Electronics Show (CES) earlier this month, is one of the several flexible thermoelectric generator (TEG)-based electronic devices that the nanosystems engineering research center is currently developing. They are calling it a “Self-Powered and Adaptive Low-Power Sensing Platform (SAP), a battery-less, open architecture sensor system using continuous energy harvesting” to perform tasks like monitoring various biological functions.

The idea behind the design is to use thermoelectric materials to take advantage of the difference in the temperatures between the human body and its surrounding environment. This difference generates an energy gradient that can be directly transformed into electricity that powers the device, without the need for changing or recharging batteries.

ASSIST’s wearable skin patch looks somewhat like a hi-tech sticker, measuring about 7 square centimeters, and when in contact with your skin, is capable of producing 40 and 50 microwatts of electricity per square centimeter, based on a temperature difference of 3-degrees Celsius between skin and air. Employing a set of pliable thermoelectric generators (TEGs) connected as a series circuit, the amount of electricity produced depends on the temperature differential — when there’s a greater difference, that amounts to more electricity. The team found that the device can generate three times more electricity when there is more airflow, and when the wearer is engaged in more vigorous motions like walking or jogging.

The team notes that while this energy-harvesting wearable is not yet capable of generating enough energy to power an electronic display or GPS, it’s suitable for boosting a low-power processor and simple sensors like a heart rate monitor, hydration monitors, accelerometers, temperature and pressure sensors. Researchers are also working to integrate low-power Bluetooth capabilities into their prototype, enabling the device to communicate wirelessly with your phone without requiring any user input. The scientists are aiming to create unobtrusive, flexible and durable sensors that are powered by the human body, which can be comfortably worn for months on end.

Sensors will be everywhere

While long-term wearable sensors are beginning to emerge in things like flexible skin patches, biometric sensors have already appeared in recent years in various forms in smartwatches, smartglasses and in smart fitness clothing, measuring vitals like body temperature, muscle activity, galvanic skin response and even the chemical composition of sweat. Industry analysts predict that this growing market is poised to become even larger: according to market research firm IDTechEx, there will be 3 billion wearable sensors globally by 2025, in an industry with a projected worth of $5.5 billion. They could be everywhere, and whether they are in the lab or in the gym, wearable sensors will be delivering useful data for better workouts, as well as biomedical applications like health monitoring, improved rehabilitation, or clinical trials of pharmaceutical drugs.

Wearable biometric sensors could also be used outside of medicine, in affective computing applications like neuromarketing, where the emotional states of focus group test subjects are measured through physiological changes. The data gathered by these sensors are handled by algorithms that output useful information, which can ultimately be utilized for enhanced health outcomes, smarter advertising, more accurate scientific research and more intelligent AI.

In any case, with battery-free platforms now becoming a distinct possibility, you can expect biometric sensors to start popping up in clothing and accessories, to the unlikeliest of places — a bed that monitors sleep apnea, perhaps?

Read more over at IEEE Spectrum and ASSIST.

Feature image via Pixabay.

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