Researchers in India have fabricated a new type of wearable antenna on polyester fabric that can be worn by military personnel to monitor their health status.
The flat and flexible antenna measures roughly 3 cm in length and nearly 4 cm in width, and operates at around 3.37 GHz for WiMAX (Worldwide Interoperability for Microwave Access) applications.
"Our goal is to make wearable antenna which can be embedded in the jacket worn by soldiers in remote locations. We can connect the antenna to different sensors such as temperature, pressure and ECG sensors and the data can be transmitted to a remote server. The antenna can sense and communicate data in a non-intrusive manner. This way we can monitor the health of soldiers," says Dr. P. Mohanan from Cochin University of Science and Technology, Kochi, India, reports The Hindu.
Wearables antennas embedded in smart textile are nothing new, but continuous research is pursued to make them more flexible, more efficient, and safer to wear.
Typically, making wearable antennas involves the use of thin copper films clad onto glass-reinforced epoxy substrates, which make them relatively inflexible. Alternatively, copper ink can be screen printed onto the substrates, including fabric. However, copper ink tends to permeate through the fabric during screen printing. It also is oxidized readily, and can affect the effectiveness of the antenna.
These challenges have been addressed through a new wearable antenna fabrication method devised by scientists at the Materials Science and Technology Division at the National Institute for Interdisciplinary Science and Technology (CSIR-NIIST), Thiruvananthapuram, Kerala, India.
Instead of copper, the researchers used silver ink for printing the bottom electrode on the polyester fabric as well as the E-shaped patch antenna. In order to prevent the ink from passing through the textile, the fabric was made over 1 mm thicker by hot-pressing three layers of polyester interlaid with polyacrylate sheets, which acted as an adhesive to bind the whole fabric material. Next, the fabric was dip-coated with a PVC polymer to reduce the fabric's surface roughness from 341 nanometers to about 15 nanometers, and to make it more water-resistant — an important requirement for embedded electronics.
"To overcome the problem of surface roughness, we coated the fabric with a polymer (polyvinyl butyral or PVB) to make the surface smooth and hydrophobic,” says Dr. K.P. Surendran, co-author of the paper published in Smart Materials and Structures. ”We can increase the degree of hydrophobicity by coating another polymer that is more hydrophobic."
When smart clothing is worn, wearable antennas tend to lose their radiation efficiency as the electrical contacts between the metal ink particles on the patch and bottom electrode get disrupted as the fabric flexes. Surendran says, however, that the radiation efficiency of his team’s wearable antenna "did not deteriorate even when bent for cycles of 10 up to 100 times."
While the effects of radiofrequency exposure emitted by wearable electronics on the human body are still being debated, Surendran claims that, "The bottom electrode protects the body from radiation. So wearable antennas are safe."