When wearable electronics devices disappear into clothes

Powered by “microsupercapacitors” woven into fabrics
December 17, 2015

The Athos Upper Body Package includes 14 built in sensors for real-time muscle and heart rate data. (credit: Athos)

Wearables will “disappear” in 2016, predicts New Enterprise Associates venture capital partner Rick Yang, cited in a Wednesday (Dec. 16) CNBC article — integrated “very directly into your everyday life, into your existing fashion sense to the extent that nobody knows you’re wearing a wearable,” he said.

For example, Athos makes smart workout clothes embedded with inconspicuous technology that tracks muscle groups, heart, and breathing rates, he noted.

But taking that next step in wearable technology means ditching bulky, clothes-deforming batteries. Supercapacitors (see “Flexible 3D graphene supercapacitors may power portables and wearables“), as discussed on KurzweilAI, are a perfect match for that. They work like tiny batteries, but unlike batteries, they can be rapidly charged and deliver more power quickly in a smaller space.

They’re a lot smaller and thinner than batteries. But still too bulky.

Weaving electronics into fabrics

Enter Case Western Reserve University researchers, who announced Wednesday that have developed flexible wire-shaped microsupercapacitors that can be embedded as microscopic-sized wires directly in fabrics. These provide three times higher capacitance than previous attempts to create microsupercapacitors, the researchers say.*

Wearable wires (credit: Tao Chen, Liming Dai/Energy Storage Materials)

In this new design, the modified titanium wire is coated with a solid electrolyte made of polyvinyl alcohol and phosphoric acid. The wire is then wrapped with either yarn or a sheet made of aligned carbon nanotubes, which serves as the second electrode.

The titanium oxide nanotubes, which are semiconducting, separate the two active portions of the electrodes, preventing a short circuit.

“They’re very flexible, so they can be integrated into fabric or textile materials,” said Liming Dai, the Kent Hale Smith Professor of Macromolecular Science and Engineering. “They can be a wearable, flexible power source for wearable electronics and also for self-powered biosensors or other biomedical devices, particularly for applications inside the body.”

The scientists published their research on the microsupercapacitor in the journal Energy Storage Materials this week. The study builds on earlier carbon-based supercapacitors.

Conductive inks

An article just published in Chemical & Engineering News (C&EN) profiles textiles printed with such stretchable embedded wiring and electronic sensors, which can transmit data wirelessly and withstand washing.

Smart socks (credit: Sensoria)

For example, “smart socks” incorporate stretchable silver-based conductive yarns that connect their sensors to a magnetic Bluetooth electronic anklet that transmits data to a mobile app to keep track of foot landings, cadence, and time on the ground.

The data are intended to help runners improve their form and performance. Two pairs of socks and an anklet cost $200.

C&EN also highlights another key technology: conductive inks, which are used by BeBop Sensors in a design for a thin shoe insole integrated with piezoresistive-fabric sensors and silicon-based electronics, which are capable of measuring a wearer’s foot pressure.

They’ve also developed a conceptual design for a car steering wheel cover that senses driver alertness and weight-lifting gloves that sense weight and load distribution between hands.

Mounir Zok, senior sports technologist for the U.S. Olympic Committee dates the beginning of wearable technology to 2002, when relatively small electronic devices first began to replace the probes, electrodes, and masks that athletes wore while tethered to monitoring equipment in training labs, C&EN notes.

Devices to measure heart rate, power, cadence, and speed can lead to improved performance for athletes, Zok explained. Many of the first wearable devices designed for track and field were cumbersome and interfered with performance. But the smaller, more flexible, less power-hungry devices available today are helping Zok and his colleagues better monitor athletic improvements.

* In a lab experiment, the microsupercapactitor was able to store 1.84 milliFarads per micrometer. Energy density was 0.16 x 10-3 milliwatt-hours per cubic centimeter and power density .01 milliwatt per cubic centimeter.

Abstract of Flexible and wearable wire-shaped microsupercapacitors based on highly aligned titania and carbon nanotubes

Wire-shaped devices, such as solar cells and supercapacitors, have attracted great attentions due to their unique structure and promise to be integrated into textiles as portable energy source. To date, most reported wire-shaped supercapacitors were developed based on carbon nanomaterial-derived fiber electrodes whereas titania was much less used, though with excellent pseudocapacitvie properties. In this work, we used a titanium wire sheathed with radially aligned titania nanotubes as one of the electrodes to construct all-solid-state microsupercapacitors, in which the second electrode was carbon nanotube fiber or sheet. The capacitance of the resulting microsupercapacitor with a CNT sheet electrode (1.84 mF cm−2) is about three time of that for the corresponding device with the second electrode based on a single CNT yarn. The unique wire-shaped structure makes it possible for the wire-shaped microsupercapacitors to be woven into various textiles and connected in series or parallel to meet a large variety of specific energy demands.