Multi-Function Stretchable Sensor Platform Developed

14 August 2018. An engineering team created a system that combines multiple electronic sensors into a single 3-D stretchable device that can be worn on various body locations to monitor different functions. Researchers at University of California in San Diego describe their technology in yesterday’s issue of the journal Nature Electronics (paid subscription required).

The team from UC-San Diego’s research group led by electrical and computer engineering professor Sheng Xu is seeking ways to add more functions to stretchable and wearable electronics for monitoring a person’s health, while keeping down the amount of real estate these devices occupy. The lab’s approach is to go three-dimensional, stacking layers of electronic sensors on stretchable surfaces. While that concept may be easy to understand and feasible for rigid materials, making the idea work with fabrics and stretchable polymers was anything but simple.

“The problem isn’t stacking the layers,” says Xu in a university statement. “It’s creating electrical connections between them so they can communicate with each other,” Xu and colleagues address that issue by connecting the layers of circuits with lasers. In rigid materials, holes can be drilled allowing for conductive materials to link various layers, but that approach won’t work with stretchable materials or fabrics. The team instead uses black organic dyes that absorb and conduct energy from laser beams, thus allowing for electronic connections between layers of materials that bend and stretch. As long as the conductive regions of each layer overlap while stretched, electronic signals can be sent and received between layers.

For a proof-of-concept, the researchers created a system with 4 layers of circuits configured into a rubber-like stretchable polymer plastic. The individual circuits perform designated electronic functions, such as sensor, accelerometer, amplifier, and Bluetooth transmission. While each circuit is printed on rigid materials, they’re small enough to allow for the plastic layers encasing the chips to bend. And the individual layers are physically connected with tiny copper springs that enable the entire device to stretch and bend. The area of the device itself is about the same as a U.S. dollar coin that has a diameter of 26.5 millimeters, slightly more than 1 inch, and about the same 2 millimeter thickness.

The San Diego team demonstrated their system as a device with multiple functions. Worn on the chest, the system can measure heart rate like an electrocardiogram, while on the forehead it can detect brain signals like an electroencephalogram or EEG, and on the forearm, the device measures muscle activity. In addition, the prototype device can also measure respiration, skin temperature, and body motion. The system’s Bluetooth communications allow for transmitting signals up to 10 meters away. As the video below demonstrates, the communications and body motion functions make it possible for the device to control a remote robotic arm.

The device uses about 35.6 milliwatts of power, but Xu’s group is also working on stretchable lithium-ion batteries. The university says the lab is collaborating with industry partners to advance the technology to the point of clinical tests.

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