Researchers who are working to develop wearable electronics have reached a milestone: They are able to embroider circuits into fabric with 0.1 mm precision — the perfect size to integrate electronic components such as sensors and computer memory devices into clothing.
With this advance, a team at Ohio State University have taken the next step toward the design of functional textiles — clothes that gather, store, or transmit digital information. With further development, the technology could lead to shirts that act as antennas for your smart phone or tablet, workout clothes that monitor your fitness level, sports equipment that monitors athletes’ performance, a bandage that tells your doctor how well the tissue beneath it is healing — or even a flexible fabric cap that senses activity in the brain.
That last item is one that John Volakis, Professor of Electrical Engineering at Ohio State, and research scientist Asimina Kiourti are investigating. The idea is to make brain implants, which are under development to treat conditions from epilepsy to addiction, more comfortable by eliminating the need for external wiring on the patient’s body.
In Volakis’ lab, the functional textiles, also called “e-textiles,” are created in part on a typical tabletop sewing machine — the kind that fabric artisans and hobbyists might have at home. Like other modern sewing machines, it embroiders thread into fabric automatically based on a pattern loaded via a computer file. The researchers substitute the thread with fine silver metal wires that, once embroidered, feel the same as traditional thread to the touch.
The shape of the embroidery determines the frequency of operation of the antenna or circuit, explained Kiourti.
The shape of one broadband antenna, for instance, consists of more than half a dozen interlocking geometric shapes, each a little bigger than a fingernail, that form an intricate circle a few centimeters across. Each piece of the circle transmits energy at a different frequency, so that they cover a broad spectrum of energies when working together — hence the “broadband” capability of the antenna for cell phone and internet access.
The researchers previously had to stack the thicker thread in two layers, one on top of the other, to make the antenna carry a strong enough electrical signal. But by refining the technique that she and Volakis developed, Kiourti was able to create the new, high-precision antennas in only one embroidered layer of the finer thread. So now the process takes half the time: only about 15 minutes for the broadband antenna mentioned above.
She’s also incorporated some techniques common to microelectronics manufacturing to add parts to embroidered antennas and circuits.
One prototype antenna looks like a spiral and can be embroidered into clothing to improve cell phone signal reception. Another prototype, a stretchable antenna with an integrated RFID (radio-frequency identification) chip embedded in rubber, takes the applications for the technology beyond clothing. (The latter object was part of a study done for a tire manufacturer.)
Yet another circuit resembles the Ohio State Block “O” logo, with non-conductive scarlet and gray thread embroidered among the silver wires “to demonstrate that e-textiles can be both decorative and functional,” Kiourti said.
They may be decorative, but the embroidered antennas and circuits actually work. Tests showed that an embroidered spiral antenna measuring approximately six inches across transmitted signals at frequencies of 1 to 5 GHz with near-perfect efficiency. The performance suggests that the spiral would be well-suited to broadband internet and cellular communication.
In other words, the shirt on your back could help boost the reception of the smart phone or tablet that you’re holding – or send signals to your devices with health or athletic performance data.
[Photo by Jo McCulty, courtesy of The Ohio State University.]
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