John Volakis, Director of the ElectroScience Laboratory, holds a prototype communications antenna embroidered into cloth. Photo by Al Zanyk, courtesy of Ohio State University.
To make communications devices more reliable, Ohio State University researchers are finding ways to incorporate radio antennas directly into clothing, using plastic film and metallic thread. They report a new antenna design with a range four times larger than that of a conventional antenna worn on the body – one that is used by American soldiers today. The Ohio State system takes elements from previous research and combines them in a new way, with the addition of a unique computer control device that lets multiple antennas work together in a single piece of clothing.
Journal IEEE Antennas and Wireless Propagation Letters – Omnidirectional Vest-Mounted Body-Worn Antenna System for UHF Operation
We present an omnidirectional UHF body-worn antenna specifically designed for vests worn by law enforcement agencies. Typically, body-worn antennas suffer from pattern nulling that decreases communication reliability. The proposed antenna system consists of a compact diversity module (79 × 41 × 28 mm3) and four antennas mounted on a typical body-worn vest to achieve an omnidirectional pattern. Each antenna element is carefully designed for body-worn mounting onto fitted vests and can operate at UHF frequencies with reasonable on-body gain. Radiation patterns are calculated and validated via measurements. Performance is also evaluated in an indoor environment for several realistic human activities. Comparison to a simple whip monopole antenna is also provided.
The result is a communications system that can send and receive signals in all directions, even through walls and inside a building, without a need for the wearer to carry an external antenna.
When antennas make contact with the human skin, however, the body tends to absorb radio signals and form a short circuit – a fact driven home by the recent difficulties with the antenna placement on the iPhone 4. Also, if an antenna is improperly placed, a person’s body can block it when he or she moves against a wall or other obstacles.
The Ohio State system overcomes these problems by surrounding the body with several antennas that work together to transmit or receive a signal, no matter which way a person is facing. An integrated computer control device senses body movement and switches between the antennas to activate the one with the best performance given the body’s position.
The engineers created a prototype antenna by etching thin layers of brass on a commercially available plastic film, called FR-4. The film is light and flexible, and can be sewn onto fabric.
They attached it into a vest at four locations –chest, back, and both shoulders. The computer controller – a metal box a little smaller than a credit card and an inch thick – was worn on a belt.
In laboratory tests, the experimental antenna system provided significantly greater signal strength compared to a conventional military “whip” antenna, enabling a range of communications four times larger.
Perhaps most importantly, the new antenna system worked in all directions, even as researchers tested it inside the hallways of the ElectroScience Lab, where doors and windows would normally interfere with the signal.
Chen currently estimates that the antenna systems, as demonstrated in the prototype, would cost $200 per person to implement, but mass production would bring that cost significantly down.
In the meantime, the engineers are working on printing antennas directly onto clothing, and embroidering antennas into clothing with metallic threads. A typical home sewing machine is now part of their laboratory equipment, and early tests have shown that the swirly designs they’ve embroidered into fabrics such as cotton – and even taffeta – can work as functional antennas.
That’s why Volakis envisions the technology to be adaptable for the general public. The elderly or disabled could wear clothing that would let them communicate in case of emergency, without the stigma they might feel in wearing a more visible assistive device.
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