Wireless sensors that stick to the skin to track your health

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BodyNet sticker and receiver

Popularity of wearable devices to monitor your health is growing. Change in consumer behaviour and need for awareness toward health is the reason for that. As people thrive to minutely quantify every action they do, the sensors that monitor those actions are growing lighter and less invasive. Remember the first body monitoring suit prototype? Was huge, bulky and full of wires. We have come a long way. Today we have wearable devices which monitors our pulse, heart rate, sleep time, step count and many more activities in a very intuitive non invasive method. With new development in sensor technology and flexible PCB, two crosstown rivals Stanford and Berkeley have built a prototype of a flexible sensors that can stick to your skin and track your health.

Under the project name BodyNet, engineers at Stanford have developed an experimental stickers that pick up physiological signals emanating from the skin, then wirelessly beaming these health readings to a receiver clipped onto clothing.

We tend to take our skin’s protective function for granted, ignoring its other roles in signaling subtleties like a fluttering heart or a flush of embarrassment. – TOM ABATE

These flexible stick-on sensors are built using some kind of metallic ink with a screen-printed antenna and sensors onto a stretchable sticker designed to adhere to skin and track pulse and other health indicators, and beam these readings to a receiver on a person’s clothing. While demonstrating it was applied to the wrist and abdomen of a subject to monitor the person’s pulse and respiration by detecting how their skin stretched and contracted with each heartbeat or breath. 

Another experiment was done by sticking these sensors on elbow and knee of a subject to track arm and leg motions by gauging the minute tightening or relaxation of the skin each time the corresponding muscle flexed.

Prof. Zhenan Bao said that this is just the beginning and they are planning to integrate more stick-on sensors that can monitor sweat and other secretions to track variables such as body temperature and stress. Her ultimate goal is to create an array of wireless sensors that stick to the skin and work in conjunction with smart clothing to more accurately track a wider variety of health indicators than the smart phones or watches consumers use today.

The BodyNet sticker uses RFID technology. It has an antenna that harvests a bit of the incoming RFID energy from a receiver on the clothing to power its sensors. It then takes readings from the skin and beams them back to the nearby receiver. So there is no need of a battery or rigid circuit that also makes these sticker comfortable to wear and prevent the stickers from stretching and contracting with the skin. Building such circuit and antenna is no easy task and engineers at Stanford spend close to 3 years in developing this technology. They created an antenna that could stretch and bend like skin. They did this by screen-printing metallic ink on a rubber sticker.

However, whenever the antenna bent or stretched, those movements made its signal too weak and unstable to be useful. To overcome this they developed a new type of RFID system that could beam strong and accurate signals to the receiver despite constant fluctuations. The battery-powered receiver then uses Bluetooth to periodically upload data from the stickers to a smartphone, computer or other permanent storage system.

bodynet_sticker-being-stretched

Working on a similar domain, A team of scientists at the University of California, Berkeley, is developing wearable skin sensors that can detect a number of physiological factors from your sweat. The goal of this project is not just to build sensors to monitor sweat but also to decode sweat composition to see how it is related to human health.

The new sensors contain a spiraling microscopic tube, or microfluidic, that wicks sweat from the skin. By tracking how fast the sweat moves through the microfluidic, the sensors can report how much a person is sweating, or their sweat rate. The microfluidics are also outfitted with chemical sensors that can detect concentrations of electrolytes like potassium and sodium, and metabolites like glucose.

In an experiment on the subject they first placed the sweat sensors on different spots on subjects bodies — including the forehead, forearm, underarm and upper back — and measured their sweat rates and the sodium and potassium levels in their sweat while they rode on an exercise bike.

They found that local sweat rate could indicate the body’s overall liquid loss during exercise, meaning that tracking sweat rate might be a way to give athletes a heads up when they may be pushing themselves too hard.

sweat sensor

The paper describing Stanford’s flexible sensor appeared this week in the journal Nature Electronics, while Berkeley’s sweat tracker was in Science Advances.

Stay tuned for more such updates on advance sensor tech.

Also read – 

MyoWare – Arduino Compatible Wearable Muscle Sensor Platform

 

 

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