Self-Powered, Wireless Sensing Platform May Take Wearable Electronics to the Next Level

Flexible electronics are often used in sensors that monitor a patient’s condition, such as heartbeat, pulse rate, oxygen or glucose levels, physical movements, and other key life signs indicators. The work by monitoring and recording data derived from sensors that are in contact with the patient’s skin, perspiration, or bodily fluids.

However, these sensor-based devices are battery-operated and require periodic recharging, which is inconvenient and can also  break the continuity of monitoring, causing delays. Although flexible, self-charging power units have been created using stretchable energy harvesters and power management circuits with energy storage units, they are often unreliable and emit low, intermittent, or unstable output power, especially when they are being stretched or deformed. These power units are also complex to design and expensive to manufacture. 

“There is a significant need for environmentally friendly, efficient, self-charging sensors that can monitor patients’ vital signs without contributing to their physical or financial stress,” said Huanyu Cheng, assistant professor of engineering science and mechanics at The Pennsylvania State University and also a member of  the university’s Materials Research Institute.

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Cheng is an expert in the development of wearable sensor technologies and products.  Since joining the department of engineering  in 2015,  Cheng has engineered several innovative, sensor-driven medical products such as wearable head scanners, needle-free glucose monitors, and printable electronics.

Now, Cheng and his research team have done it again. They have developed a prototype of a self-powered, wireless, sensing platform made from graphene foam that captures and stores kinetic energy from the movements of the wearer, creating a self-powered, ongoing power supply for medical sensors and devices.
 

How It Works

 
To gain widespread acceptance, the next generation of flexible sensors must have improved power-charging capabilities, with either longer-lasting batteries or, even better, self-powered, sustainable power supplies that are reliable enough to continuously drive sensitive, increasingly multi-functional skin sensors and wireless transmission modules.

Cheng focused on graphene-based materials because they are lightweight, flexible, and highly conductive. Graphene consists of a single layer of hexagonally arranged carbon atoms. With a laser, layered graphene foams can be created in various shapes and dimensions at low cost. When designed for a specific application, graphene can harvest energy from human body movements and store it as electrical energy in flexible micro-supercapacitors.
 
“3D porous foams with high specific surface area and excellent charge transport provide an efficient flow of triboelectric [a type of contact electrification] electrons in triboelectric nanogenerators,” said Cheng. “The surface coating or doping with second laser irradiation on these foams can also form a 3D composite to provide high energy density in micro-supercapacitor arrays. The integration of a triboelectric nanogenerator and power management circuits with micro-supercapacitor arrays can then efficiently harvest intermittent mechanical energy from body movements into stable power output.”

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The self-powered, wireless medical sensor harvests energy from the kinetic motion of the user, which then powers the micro-supercapacitors, which monitor the user’s movements, thus creating a cyclical charge for the device. 
 
“The generated stable, yet high, power with adjustable voltage and current outputs drives various stretchable sensors and wireless transmission modules to wirelessly measure pulse, strain, temperature, electrocardiogram, blood pressure, and blood oxygen,” Cheng said. “This self-powered, wireless, wearable sensing platform paves the way to wirelessly detect clinically relevant biophysical and biochemical signals for early disease diagnostics and healthy aging.”
 

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Cheng has developed an innovative technology that can fabricate a porous graphene foam-based, self-powered, stretchable health monitor, which could revolutionize electronics in medical devices and across other industries. Even better, “the foams and their composites, when patterned into various geometries, can create various deformable sensors on large scale at low cost,” Cheng said.
 
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This work has created a general yet programmable platform for the next generation of self-powered wearable electronics. Future research will focus on developing and validating the stretchable sensing platform in clinically relevant settings for both in-patient and out-patient applications. 
 
Cheng’s low-cost manufacturing approach for making the self-powered wireless sensing platform has already generated considerable interest from large firms, start-up companies, and venture capitalists, who all recognize the potential of the device and want to be considered for future commercialization opportunities. Most recently, in December 2021, Meta Reality Labs, Facebook’s technology development branch, awarded Cheng $150,000 in unrestricted funds to advance biodegradable, stretchable, energy-generating systems.
 
Mark Crawford is a science and technology writer in Corrales, N.M.