A Washable Smart Garment? Two Startups Innovate E-Textiles With Conductive Ink and Water-Proof CircuitryMay 06, 2020 by Gary Elinoff
After 100 wash cycles, it was the fabric—not the electronics—that failed.
In most circumstances, it's a no-brainer that electronics plus a washing machine is a bad combination. But two Pittsburgh startups have found a way to work around the cumbersome task of removing all electrically-active components before washing a smart garment.
With Liquid X’s ink technology, electrical traces are printed directly into the garment. Powercast’s wireless recharger chips, a tiny battery, and associated circuity are then sealed within a waterproof package.
The image below displays two LEDs that will glow in a smart garment. The large black strip is the power receiving antenna printed with Liquid X ink.
E-textile presented at CES 2020. Image used courtesy of Powercast and Liquid X
In between is a Powercast chip harvesting power garnered from the antenna.
Electronic Garments on the Rise?
While smartwatches are one of the most common wearable devices, it seems that electronic garments or "e-textiles" are on the rise. Some researchers are pushing the possibilities of breathable, durable wearable fabric and sensor technology—some even inspired by octopus suckers. Others are focusing their attention on the elasticity of smart garments, discovering new ways to implement stretchable supercapacitors, batteries, and sensors.
Liquid X and Powercast are joining this movement for e-textile innovation by tapping into electrically-conductive ink and water-proof sealed components embedded discretely in fabric.
Liquid X’s Part in the Smart Garment
Liquid X is a manufacturer of particle-free inks that can be deposited directly onto e-textile fabric. This minimizes the processing steps, building conformally-coated conductive traces.
Durability tests for e-textiles using Liquid X particle-free ink. Image used courtesy of Liquid X
The traces are bendable, stretchable, and washable. Liquid X says that hardware, including ICs, can be mounted directly onto the traces via snaps, epoxy, or solder paste.
Scanning electron microscopic image of Liquid X’s ink on woven polyester fabric. Image used courtesy of Liquid X
Powercast’s Power Harvesting Chips
Powercast power harvesting chips, such as the P2110B, then convert RF into DC. DC is stored in a capacitor. When sufficient charge is garnered, the unit switches on an internal boost converter, which raises the programmed output level to charge a tiny battery.
Functional block diagram of the P2110B. Image used courtesy of Powercast
The power it can deliver is not insignificant; the P2110B can develop as much as 5.5 V at 50 mA. The device is optimized for the 902 MHz to 928 MHz RF band. Its dimensions are 0.625 in by 0.530 in. The unit is RoHS compliant. It operates over what Powercast describes as "the industrial temperature range."
In addition to smart garments, Powercast explains that the P2110B finds use in battery-free wireless sensors, charging small batteries, and in low-power electronics.
An Early Prototype at CES 2020
In January, the two Pittsburg-based companies jointly showcased a wirelessly rechargeable smart athletic shirt prototype. Representatives at the show explained that the electronics held true even after 100 wash cycles. "At that point, the fabric is actually what failed," remarked Bill Babe, VP of sales at Liquid X.
E-textile presented at CES 2020. Image used courtesy of Printed Electronics
The prototype demonstrated the concept of a shirt with two LEDs. Since then, the two companies have developed a more sophisticated version of the technology.
How Does Liquid X and Powercast Design the Smart Garment?
Once the circuit design is completed, the traces are written onto the fabric. This is comparable to depositing copper traces onto a PCB since the ink is highly conductive. The antenna used to absorb RF energy is also printed onto the garment.
The electrically-animated garment does not rely on random RF. Rather, RF energy from a Powercast RF transmitter is beamed onto the garment where it is intercepted by the antenna. It then passes onto a P2110B or similar device and is used to charge a tiny battery, serving as a source of power for the e-garment.
Mounted to the printed traces are LED devices. The fabric also has integrated RF wireless receivers (black), tuning components, and a 6" antenna. Image used courtesy of Powercast and Liquid X
Finally, the system is encapsulated in a waterproof bond to protect the circuitry during machine washing.
Where This Tech May Lead
An obvious use for this type of e-textile is in health monitoring. A shirt that covers an entire torso can make far better contact with human skin than the ½ a square inch or so of a smartwatch can. Depending on how long 5.5 V at 50 mA can be maintained between charges, tiny BLE transmitters can be included, and hospital garments with this capability can be used to monitor a patient's vital health parameters.
Before such a concept can pass the regulatory hurdles necessary for any medical device, it may find use in athletic applications when a person exercising wants to know his or her pulse rate. In future iterations of this design, the size of the harvesting chip may prove to be something of an obstacle.
Have you ever worked on a smart garment or e-textile design? Share your experience in the comments below.