Printed circuits on irregular shapes; sweat-powered batteries; indoor photovoltaics.

Printing circuits on irregular shapes Researchers at Pennsylvania State University have proposed a method of printing biodegradable circuits on irregular and complex shapes.

"We are trying to make circuits directly on free-form 3D geometric structures," said Huanyu "Larry" Cheng, a professor in the Department of Engineering Science and Mechanics (ESM) at Pennsylvania State University. "Printing on complex objects can realize the future Internet of Things, in which circuits can connect various objects around us, whether it is smart home sensors, robots that perform complex tasks together, or devices placed on the human body."

The printing method uses a thin film covered with ink made of zinc nanoparticles. The film is attached to the mask cover layer on the target surface. The researchers then pulsed high-energy xenon lamps through thin films. Within a few milliseconds, the energy from this light is enough to excite the particles and transfer them to the new surface through the template.

In the test of this method, the researchers printed on glass beakers and shells. The transferred zinc forms a conductive electronic circuit that can be used as a sensor or antenna.

The researchers demonstrated a new printing method that uses pulsed light to transfer electronic circuits to shells, as shown in the picture. (Photo credit: Jennifer McCann/Pennsylvan State University)

The team stated that the printing process is faster and more cost-effective than other technologies because it does not require expensive equipment or vacuum time. Cheng pointed out that these circuits are also biodegradable. "Our electronic products are upgraded every two years or so, which will generate a lot of electronic waste. Looking to the future, if our electronic products are environmentally friendly enough to flush into the toilet, then their use will be much better for the environment."

Cheng added that biodegradability also allows for the safe destruction of equipment. "If your device is only encrypted with software, it can always be cracked and there is a potential for information leakage. This biodegradable device can be physically destroyed, so data cannot be recovered; it provides what traditional silicon devices cannot solve. Unique opportunity."

They also developed a method to extend the life of printed zinc circuits by immersing them in a solution containing copper or silver. They plan to study ways to make the process suitable for mass manufacturing and optimize its printing on the skin.

Sweat-powered battery Researchers at Nanyang Technological University in Singapore have developed a stretchable battery powered by sweat.

The battery consists of printed silver sheet electrodes that can generate electricity in the presence of sweat. When silver flakes come into contact with sweat, its chloride ions and acidity can agglomerate the silver flakes, thereby increasing their electrical conductivity. This chemical reaction also causes current to flow between the electrodes.

When the battery is stretched, the resistance will further decrease. Researchers also pointed out that it can withstand the stress of daily activities, including repeated stress and sweating.

The battery is flat, measuring 2 cm x 2 cm, and is designed to be fixed to a soft and sweat-absorbing textile that can be stretched and connected to wearable devices such as watches, wristbands or armbands.

"By using ubiquitous products, sweat, we can find a more environmentally friendly way to power wearable devices without relying on traditional batteries. It is an almost guaranteed source of energy produced by our bodies. We want batteries It can power all kinds of wearable devices," said Lee Pooi See, professor and dean of the Graduate School of NTU.

The stretchable fabric has water absorption and can retain moisture, so when the sweat rate is not consistent, the battery can still maintain power.

Lu Jian, a researcher at the School of Materials Science and Engineering at NTU, added that this battery does not contain toxic ingredients. "Traditional batteries are cheaper and more common than ever, but they are usually made of unsustainable materials that are harmful to the environment. They are also potentially harmful in wearable devices, and damaged batteries may spill toxic liquids on human skin. . Our equipment can provide a real opportunity to completely eliminate these toxic materials."

In the test, a person who wears a battery on his wrist and rides on a stationary bicycle for 30 minutes can generate 4.2 V and 3.9 mW of output power, which is enough to power commercial temperature sensor devices and send data. Connect to a smartphone via Bluetooth .

Researchers plan to continue to study the battery, including its interaction with different components of sweat and the influence of factors such as body temperature.

Indoor Photovoltaics Researchers at the National Institute of Standards and Technology (NIST) believe that using photovoltaics to capture indoor artificial light is a viable way to power small sensors.

"People in this field have assumed that photovoltaic modules can be used to power IoT devices in the long run, but we have not really seen the data to support this before, so this is the first step that we can pull it off, "NIST Mechanical Engineer Andrew Shore said.

The team tested small modular photovoltaic devices made of different materials: gallium indium phosphide (GaInP), gallium arsenide (GaAs) and silicon.

The researchers placed the cm-wide module under a white LED located in an opaque black box to block external light sources. During the experiment, the LED produced light at a fixed intensity of 1000 lux, which was comparable to the light level in a well-lit room. For silicon and GaAs photovoltaic modules, the efficiency of immersion in indoor light is lower than sunlight, but the performance of GaInP modules under LEDs is much better than sunlight. Both GaInP and GaAs modules significantly surpass silicon indoors, converting 23.1% and 14.1% of LED light into electrical energy, respectively, while the power conversion efficiency of silicon is 9.3%.

They connected the lowest performing but cheapest silicon device to an example IoT device, in this case a temperature sensor. When the silicon photovoltaic device is placed under the LED, it can wirelessly transmit temperature readings to a nearby computer, powered only by the silicon module. Two hours later, they turned off the light in the black box, the sensor continued to run, and its battery was depleted at half the charging speed.

"Even with low-efficiency mini modules, we found that we can still provide more energy than wireless sensors," Shore said, and suggested that solar modules designed for outdoor use can be used in indoor applications, especially when lighting is required. Of commercial applications in continuous use.

The researchers plan to study the performance of indoor photovoltaics in typical residential scenarios.

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