Archeology shows that about 170,000 years ago, just before the penultimate Ice Age, people wore clothing. But even today, most modern people wear clothes that are hardly different from the earliest garments. However, this will change soon as flexible electronics are increasingly being woven into so-called "smart fabrics".
Many of them are already available for purchase, such as: Gaiters that produce soft vibrations for easier yoga, T-shirts that track player performance, and sports bras that monitor heart rate. Smart substances can be promising in healthcare (measuring heart rate and blood pressure of patients), in defense (monitoring the health and activity of soldiers), in cars (adjusting seating temperatures to provide more comfort to passengers), and even in smart cities (Communication of the signs) to be used with passers-by).
Ideally, the electronic components of these garments - sensors, data transmission antennas, and power supply batteries - are small, flexible, and barely perceived by their wearers. This applies today to sensors, many of which are even machine washable. Most antennas and batteries are solid and not waterproof. They must therefore be removed from the clothing before washing.
My work at Ohio State University's ElectroScience Laboratory aims to make antennas and power sources equally flexible and washable. In particular, we embroider electronics with conductive threads, which we call "E-threads", directly in fabrics.
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Antenna embroidery
The E-threads we work with are bundles of twisted polymer filaments to ensure strength. Each thread has a metal-based coating to conduct electricity. The polymer core of each filament is typically Kevlar or Zylon while the surrounding coating is silver. Dozens or even hundreds of these filaments are then twisted into a single E-thread, usually less than half a millimeter in diameter.
These e-threads can be easily used with standard embroidery equipment - the same computer-aided sewing machines that people use to write their names on sports jackets and sweatshirts every day. The embroidered antennas are light and as good as their rigid copper counterparts and can be as complicated as state-of-the-art PCBs.
Our e-threaded antennas can even be combined with normal threads in more complex designs, such as: By integrating antennas into company logos or other designs. We were able to embroider antennas on fabrics as thin as organza and as thick as Kevlar. Once embroidered, the wires can be connected to sensors and batteries by conventional soldering or flexible interconnecting components.
So far, we've been able to create smart hats that read deep brain signals for patients with Parkinson's or epilepsy. We've embroidered T-shirts with antennas that extend the range of Wi-Fi signals to the wearer's mobile phone. We also made mats and sheets to monitor infant body size to detect a range of early childhood illnesses. And we made foldable antennas that measure how much the fabric has bent or raised on a surface.
Go beyond the antenna
My lab also collaborates with other Ohio researchers, including chemist Anne Co and physician Chandan Sen, to produce flexible, miniature fabric-based power generators.
We use a process similar to ink jet printing to place silver and zinc dots alternately on the fabric. When these metals come into contact with sweat, salt solution or even liquid escapes from wounds, silver acts as a positive electrode and zinc as a negative electrode - and electricity flows between them.
We have generated small amounts of electricity by moisturizing the fabric - without additional circuitry or components. It is a fully flexible, washable power source that can be connected to other portable electronic devices, eliminating the need for conventional batteries.
This flexible, wearable electronics transforms clothing, both together and individually, into networked, sensitive communications devices that blend well with the fabric of the connected 21st century.
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