New wearable patch can detect hazards in the environment

Imagine getting a warning about toxic gas or contaminated water not through a phone notification you might not check right away, but through a buzz you feel directly against your skin.

Researchers have built exactly that: a wearable patch that detects environmental hazards such as dangerous gases or heavy metals in water and immediately alerts the wearer through vibration.

The same team also adapted the underlying technology into an “e-skin” that lets robots detect and avoid hazards on their own.

Faster warnings when seconds matter

The work was led by Erim Uzunoğlu, a PhD student at North Carolina State University (NC State). 

Existing sensors can already detect environmental hazards and send notifications to a smartphone, but the team wanted to improve on that.

The researchers had two main goals. First, they wanted to miniaturize the sensors and integrate them into a wearable patch that could identify potential hazards.

“If you’re coming into contact with a hazardous substance, you need to know as quickly as possible,” said Uzunoğlu.

Because people may not check a phone notification right away, the team built haptic technology into the patch so it vibrates immediately after detecting a hazard, allowing the wearer to respond more quickly.

Breakthrough technology in a tiny patch

The team built a square patch slightly smaller than a driver’s license, yet packed with a surprising amount of technology. 

Inside the patch are a microcontroller that acts as its brain, a small battery, and sensors that can monitor six different environmental hazards. A tiny actuator serves as the haptic motor, vibrating against the skin when the device detects a hazard.

The exterior incorporates an array of thin-film photovoltaic cells, allowing the device to harvest solar power continuously while being worn, helping stretch its limited battery life further.

Designing a buzz you can’t miss

Simply having a vibrating motor wasn’t enough on its own. The sensation needed to register with the wearer in a meaningful way.

“Just having a buzzing motor isn’t enough; you need to actually feel it,” said co-author Oluwatobi Ojuade, a PhD student at NC State. “We designed tiny textured surfaces that sit at the interface between the motor and your skin, almost like a miniature pattern of bumps.”

“By changing the size and spacing of those bumps, we could control how the vibration is perceived against your skin. That let us fine-tune the sensation so it grabs your attention instead of feeling like a faint buzz you might miss.”

The device goes a step further by triggering a distinct vibration pattern, or “haptic sequence,” for each hazard it detects.

That means wearers don’t just know something is wrong. They can identify which specific environmental hazard they’re dealing with based on how the patch vibrates against their skin.

Solar power keeps it running 

Early testing showed real promise for the concept.

“In proof-of-concept testing, we found that the device did a good job of detecting hazardous substances and immediately triggering the haptic response,” Uzunoğlu said.

“We also found the energy-harvesting technology did a good job of extending the battery life. Coupled with the sensors’ low power demands, this allows the device to function for around 24 hours.”

A full day of operation is an important milestone for a device this small. It allows the patch to function as a true all-day wearable instead of requiring frequent recharging or replacement.

From human to robot skin

While developing the wearable patch, the researchers began wondering whether the same underlying concept could work for robots instead of people. That would give machines the ability to detect and respond to environmental hazards on their own.

The question led to the development of what the team calls e-skin.

The e-skin works by layering the sensor patch over a layer of piezoelectric material. When a sensor detects a hazard, it triggers the haptic response.

The resulting vibration against the piezoelectric layer generates an electrical signal that the robot can detect and interpret.

In proof-of-concept testing, the e-skin allowed quadrupedal robots to detect hazards and alter their routes to avoid them.

This shows that the same sensing framework built for human safety could extend naturally into autonomous hazard avoidance for robotics.

Off-the-shelf parts

The researchers built both the patch and the e-skin largely from off-the-shelf components rather than custom-engineered parts.

“The patch and e-skin are largely made using off-the-shelf components, with very few custom-engineered elements,” said co-corresponding author Amay Bandodkar, an assistant professor of electrical and computer engineering at NC State. 

“That should make it easier to scale up the technology moving forward. The concept is extremely flexible – the sensor array is modular, so you can add or remove sensors that monitor for whichever hazards are most relevant.”

The same basic patch design could theoretically be adapted for many different uses.

By changing which hazards the wearable patch detects, it could support workplace safety, environmental monitoring, or disaster response.

A breakthrough years in making

For Lilian Hsiao, co-corresponding author and an associate professor of chemical and biomolecular engineering at NC State, the achievement represents the culmination of a long-standing technical challenge.

“It’s quite amazing to see that we can encode tactile signals into materials with different properties,” she said. “It’s something that has been very challenging to do in the past, especially in real-world situations where people would want to wear the device.”

“Combining something people would wear with sophisticated sensing capabilities and the ability to alert the user is something we’ve been working toward for a long time.”

The study is published in the journal Device.

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