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Inside the world of designer antennas for wearables

Matt Hamblen | May 14, 2014
In some cases, custom antenna developers must account for how fat and skin affects a Bluetooth signal.

With the human body, there are different radio signal losses for bone, fat, and muscle that have to be taken into account in antenna design.

"It's a big mishmash of signal loss in a body," Venkat said. "If you implant something in a muscle layer, the signal reflects off the fat layer before it gets out and you lose a lot of that as heat. It's such a difficult process with so many different factors."

Venkat said he's absolutely confident that wearable devices aren't radiation hazards. "Bluetooth Low Energy is so weak that it's not going to impact health," he said.

Wearables, like smartphones, have to meet Specific Absorption Rate standards for the amount of radio frequency energy absorbed, as set by the Federal Communications Commission.

Venkat and Cambridge work with clients, some of them small startups, interested in designing wearable computers amid pressure to lower manufacturing costs and the final cost to consumers. With many smartwatches now selling for $150 to $200, there's plenty of pressure to cut costs to reach to more buyers.

Many times, to keep costs down, wearables are designed with low-cost off-the-shelf antennas without the flexibility or efficiency of a custom antenna that takes advantage of the materials and design of the wearable, he said.

Custom antennas potentially raise the materials price in a wearable by 10% to 15%, he estimated. Today, a small off-the-shelf antenna made of copper or ceramic could cost from 30 cents to 60 cents when purchased in bulk of 10,000 or more units.

Venkat estimated that 90% of wearables on the market today rely on the off-the-shelf, or reference design, antennas, mostly made by smaller companies. Companies like Samsung, which already produce smartwatches and smartbands, have the capacity to design custom antennas to fit the wearables being sold.

Some wearable antennas will be printed from copper on the inside of a wearable case to make the antenna larger and more efficient for wireless transmission, he predicted. For instance, a wearable shirt computer could have an antenna running the length of the shirt.

With better antennas, other benefits can result. A fitness buff wearing a smartwatch might not need to carry the smartphone while working out nearby, taking advantage of the maximum range of Bluetooth. And runners or bikers might even be able to communicate with Bluetooth Low Energy beacons arrayed along a path.

"The antenna will start to dominate how well that sensor information gets out," he said. "If you make more efficient use of the space inside a wearable, you can maximize performance."

 

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