Our bodies send out hosts of signals — chemicals, electrical pulses, mechanical shifts — that can provide a wealth of information about our health. But electronic sensors that can detect these signals are often made of brittle, inorganic material that prevents them from stretching and bending on the skin or within the body. Recent advances have made stretchable sensors possible but their changes in shape can affect the data produced and many sensors cannot collect and process the body's faintest signals.
A new sensor design incorporates a patterned material that optimizes strain distribution among transistors, creating stretchable electronics that are less compromised by deformation. The researchers also created several circuit elements with the design, which could lead to even more types of stretchable electronics.
To design the electronics, the researchers used a patterned strain-distribution concept. When creating the transistor, they used substrates made of elastomer — an elastic polymer. They varied the density of the elastomer layers, meaning some remained softer while others were stiffer while still elastic. The stiffer layers — termed “elastiff” by the researchers — were used for the active electronic areas.
The result was transistor arrays that had nearly the same electrical performance when they were stretched and bent as when they were undeformed. In fact, they had less than five percent performance variation when stretched with up to 100 percent strain. The team also used the concept to design and fabricate other circuit parts including NOR gates, ring oscillators, and amplifiers. NOR gates are used in digital circuits, while ring oscillators are used in radio-frequency identification (RFID) technology. By making these parts successfully stretchable, the researchers could make even more complex electronics.
The stretchable amplifier they developed is among the first skin-like circuit that is capable of amplifying weak electrophysiological signals — down to a few millivolts. That's important for sensing the body's weakest signals like those from muscles. The signals can be processed and amplified directly on the skin.
The design is being assessed as a diagnostic tool for ALS. By measuring signals from muscles, the researchers hope to better diagnose the disease while gaining knowledge about how the disease affects the body. They also hope to test the design in electronics that can be implanted within the body and to create sensors for all kinds of bodily signals.