E-Skin transmits Glucose Concentrations, Blood Pressure, Heart Rate, to Your Smartphone

Wearable sensors are ubiquitous thanks to wireless technology that enables a person’s glucose concentrations, blood pressure, heart rate, and activity levels to be transmitted seamlessly from sensor to smartphone for further analysis. Most wireless sensors today communicate via embedded Bluetooth chips that are themselves powered by small batteries. But these conventional chips and power sources will likely be too bulky for next-generation sensors, which are taking on smaller, thinner, more flexible forms.

Now MIT engineers have devised a new kind of wearable sensor that communicates wirelessly without requiring onboard chips or batteries. Their design, detailed today in the journal Science, opens a path toward chip-free wireless sensors. The team’s sensor design is a form of electronic skin, or “e-skin” — a flexible, semiconducting film that conforms to the skin like electronic Scotch tape. The heart of the sensor is an ultrathin, high-quality film of gallium nitride, a material that is known for its piezoelectric properties, meaning that it can both produce an electrical signal in response to mechanical strain and mechanically vibrate in response to an electrical impulse. The researchers found they could harness gallium nitride’s two-way piezoelectric properties and use the material simultaneously for both sensing and wireless communication.

In their new study, the team produced pure, single-crystalline samples of gallium nitride, which they paired with a conducting layer of gold to boost any incoming or outgoing electrical signal. They showed that the device was sensitive enough to vibrate in response to a person’s heartbeat, as well as the salt in their sweat, and that the material’s vibrations generated an electrical signal that could be read by a nearby receiver. In this way, the device was able to wirelessly transmit sensing information, without the need for a chip or battery.

Chips require a lot of power, but our device could make a system very light without having any chips that are power-hungry,” says the study’s corresponding author, Jeehwan Kim, an associate professor of mechanical engineering and of materials science, and a principal investigator in the Research Laboratory of Electronics. “You could put it on your body like a bandage, and paired with a wireless reader on your cellphone, you could wirelessly monitor your pulse, sweat, and other biological signals.”

Jeehwan Kim’s group previously developed a technique, called remote epitaxy, that they have employed to quickly grow and peel away ultrathin, high-quality semiconductors from wafers coated with graphene. Using this technique, they have fabricated and explored various flexible, multifunctional electronic films. In their new study, the engineers used the same technique to peel away ultrathin single-crystalline films of gallium nitride, which in its pure, defect-free form is a highly sensitive piezoelectric material.

The team looked to use a pure film of gallium nitride as both a sensor and a wireless communicator of surface acoustic waves, which are essentially vibrations across the films. The patterns of these waves can indicate a person’s heart rate, or even more subtly, the presence of certain compounds on the skin, such as salt in sweat.

Source: https://news.mit.edu/

Harvesting Clean Hydrogen Fuel Through Artificial Photosynthesis

A new, stable artificial photosynthesis device doubles the efficiency of harnessing sunlight to break apart both fresh and salt water, generating hydrogen that can then be used in fuel cells.

The device could also be reconfigured to turn carbon dioxide back into fuel.

Hydrogen is the cleanest-burning fuel, with water as its only emission. But hydrogen production is not always environmentally friendly. Conventional methods require natural gas or electrical power. The method advanced by the new device, called direct solar water splitting, only uses water and light from the sun.

If we can directly store solar energy as a chemical fuel, like what nature does with photosynthesis, we could solve a fundamental challenge of renewable energy,” said Zetian Mi, a professor of electrical and computer engineering at the University of Michigan who led the research while at McGill University in Montreal.

Faqrul Alam Chowdhury, a doctoral student in electrical and computer engineering at McGill, said the problem with solar cells is that they cannot store electricity without batteries, which have a high overall cost and limited life.

The device is made from the same widely used materials as solar cells and other electronics, including silicon and gallium nitride (often found in LEDs). With an industry-ready design that operates with just sunlight and seawater, the device paves the way for large-scale production of clean hydrogen fuel.

Previous direct solar water splitters have achieved a little more than 1 percent stable solar-to-hydrogen efficiency in fresh or saltwater. Other approaches suffer from the use of costly, inefficient or unstable materials, such as titanium dioxide, that also might involve adding highly acidic solutions to reach higher efficiencies. Mi and his team, however, achieved more than 3 percent solar-to-hydrogen efficiency.

Source: https://news.umich.edu/