E-Skin Sensors Go Chipless and Batteryless

Flexible, wearable devices promise VR and medical-monitoring applications

2 min read
Illustration of a golden patch on a forearm. A red ring attached to gold piping hovers above it, with colored rings radiating between them.

MIT engineers fabricated a chip-free, wireless electronic “skin.” The device senses and wirelessly transmits signals related to pulse, sweat, and ultraviolet exposure, without bulky chips or batteries.

Jun Min Suh/MIT

Wearable sensors now often help keep track of vital signs, but these devices usually rely on bulky microchips and batteries. Now scientists have invented a new microscopically thin “electronic skin” that can wirelessly transmit data about the body’s heart rate and chemistry, all without chips or batteries.

Recent advances in flexible and stretchable circuits and sensors have enabled the emergence of electronic skin, or e-skin, which sticks onto the body like an electronic version of tape. These devices often find use as health-monitoring platforms to keep track of wellness and fitness.

In order for e-skin devices to find broader use in daily life, they need to communicate data wirelessly. However, this means e-skins typically rely on rigid microchips that limit flexibility and consume a lot of power.

Now scientists have devised new chipless, wireless electronic skins that “are very thin and imperceptible, because our e-skins do not use thick and rigid integrated-circuit chips,” says study cosenior author Jeehwan Kim, a materials scientist at MIT. “Also, whereas integrated-circuit chips generate a lot of heat because of high power consumption, our e-skins do not. Thus, our e-skins can be worn over long periods—for example, weeks—without causing discomfort or skin injury.”

The new electronic skin employs sensors that examine acoustic waves rippling across the surfaces of materials. Modern cellphones now each possess dozens of acoustic devices to manipulate these kinds of surface acoustic waves.

These sensors are made of pure single-crystalline gallium nitride membranes only 200 nanometers thick. These extraordinarily thin piezoelectric films can convert electric signals to sound waves and vice versa.

The scientists reasoned that each gallium nitride membrane would possess its own inherent vibration frequency that its piezoelectric nature would convert into an electrical signal, the frequency of which a smartphone wireless receiver could detect. Any change in the electronic skin’s physical condition would affect its mechanical vibrations, resulting in detectable changes to its electrical signals, all without the need for a chip or battery in the sensor.

In the new study, the researchers combined these gallium nitride membranes with gold, titanium, and other materials to help serve as the e-skin's antenna. They incorporated the device onto a silicone rubber patch just 20 micrometers thick, or about one-fifth the diameter of the average human hair.

In experiments, the scientists placed the e-skin on volunteers’ wrists and necks. They were able to monitor changes in the surface acoustic waves of the device related to pulse and heart rate, “which can be useful when tracking exercise and trying to detect heart abnormalities,” Kim says.

The researchers found e-skin can continuously monitor heart rate and pulse for about 17 hours per day for a week, demonstrating its wearable and reusable nature. Such wireless mechanical sensors could also find use in virtual reality and other entertainment applications that wirelessly detect motions of users, Kim says.

When the researchers paired the sensors with thin-membrane detectors, changing sodium levels on the skin could be sensed—for instance, when a volunteer held onto a heat pad and began to sweat. The electronic skin could be paired with other sensors to help analyze other chemicals, such as glucose to help monitor diabetes, or the stress hormone cortisol to keep track of depression and panic disorders, Kim says.

In addition, the scientists found that the sensors were sensitive to ultraviolet light. “Ultraviolet light information can be used to track the exact amount of sun exposure and prevent sunburns, or too little exposure to sunlight that might lead to vitamin D deficiency,” Kim says.

The scientists detailed their findings in the 19 August issue of the journal Science.

The Conversation (1)
Jonathan Tate17 Sep, 2022
INDV

Wonderful news - That is what we are hoping to do with MedChip.com

Europe Expands Virtual Borders To Thwart Migrants

Our investigation reveals that Europe is turning to remote sensing to detect seafaring migrants so African countries can pull them back

14 min read
A photo of a number of people sitting in a inflatable boat on the water with a patrol ship in the background.

Migrants in a dinghy accompanied by a Frontex vessel at the village of Skala Sikaminias, on the Greek island of Lesbos, after crossing the Aegean sea from Turkey, on 28 February 2020.

ASSOCIATED PRESS

It was after midnight in the Maltese search-and-rescue zone of the Mediterranean when a rubber boat originating from Libya carrying dozens of migrants encountered a hulking cargo ship from Madeira and a European military aircraft. The ship’s captain stopped the engines, and the aircraft flashed its lights at the rubber boat. But neither the ship nor the aircraft came to the rescue. Instead, Maltese authorities told the ship’s captain to wait for vessels from Malta to pick up the migrants. By the time those boats arrived, three migrants had drowned trying to swim to the idle ship.

The private, Malta-based vessels picked up the survivors, steamed about 237 kilometers south, and handed over the migrants to authorities in Libya, which was and is in the midst of a civil war, rather than return to Malta, 160 km away. Five more migrants died on the southward journey. By delivering the migrants there, the masters of the Maltese vessels, and perhaps the European rescue authorities involved, may have violated the international law of the sea, which requires ship masters to return people they rescue to a safe port. Instead, migrants returned to Libya over the last decade have reported enslavement, physical abuse, extortion, and murders while they try to cross the Mediterranean.

If it were legal to deliver rescued migrants to Libya, it would be as cheap as sending rescue boats a few extra kilometers south instead of east. But over the last few years, Europe’s maritime military patrols have conducted fewer and fewer sea rescue operations, while adding crewed and uncrewed aerial patrols and investing in remote-sensing technology to create expanded virtual borders to stop migrants before they get near a physical border.

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