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www.us-tech.com
February, 2019
Miniaturizing Smart Wearables for Fitness and Activity Tracking
By Jeff Elliott T
raditionally, small chip antennas used in Bluetooth-enabled devices have required a designated ground “keep out” area to mini-
mize interference from other components and ensure the ideal radiation pattern for wireless sig- nals. In some cases, this reserved space can eat up as much as 0.6 x 0.8 in. (15 x 20 mm) of the PCB. However, with the drive to further miniatur-
ize connected, “smart” wearables for fitness and activity tracking, new tiny embedded chip anten- nas are now available that mount directly above metal surfaces to save as much as 20 percent of board space. This has major implications for manufactur-
ers of smart rings, bracelets, shoes, pants, shirts, and other apparel, since the PCB, along with its coin-cell batteries, typically dictates the minimum size of the electronics involved.
Smart Wearables A wave of “smart” wearable devices has
already entered the market to monitor everything from fitness and health to the physical environ- ment. Often equipped with gyroscope, accelerome- ter, temperature and pressure sensors, GPS and even microphones, these tiny devices can track vital signs, sleep, emotions, stress, breathing, movement, and even send/receive messages and alerts through text, audible sounds and colors. As with any connected device, this information can be shared wirelessly by Bluetooth to a smartphone. Among the products already incorporating
this type of technology are smart bracelets that monitor movement, body position and vital signs to detect if an elderly person has had a debilitating fall, a necklace that records voice memos before translating them into text, and even 8k gold plat-
ed rings with choice of gemstone that serve as activity trackers. Connected clothing and other apparel, such
as jeans and yoga pants, also now contain sensors designed to keep track of workouts and monitor body temperature, posture and movement.
one or two antennas. To work properly, chip antennas are typically
ground plane dependent, meaning they require an appropriately sized and positioned ground plane to form a complete, resonant circuit. While the PCB can serve as the ground plane,
the antenna itself must typically be placed on the edge of the board in an isolated section, which is free from ground and metal components that would distort its radiation. Without the isolation distance, the performance of the antenna is signif- icantly affected. “The ‘keep out area’ is fundamental to ensure
Tiny RF chip antennas are enabling a new generation of wearables.
Not to be outdone, the $130.3 billion retail
sports footwear market offers intelligent running shoes that connect to popular distance/speed track- ing apps while also measuring acceleration, cadence, ground contact time and other factors to improve performance.
Embedded Chip Antennas To make all this work, each device must con-
tain small RF chip antennas embedded on the PCB or behind the scenes underneath the product’s cas- ing. These chip antennas radiate and receive elec- tromagnetic waves like other types of antennas, but the most notable difference is their small size. In fact, today’s mobile phones incorporate a mini- mum of four antennas and up to 13 in some mod- els. Smaller wearable devices may only contain
the chip antenna can electromagnetically radiate to antenna applications, because everything affects the radiation pattern, including the package size, where the antenna is mounted and its proximity to the human body,” says Manuel Carmona of Johanson Technology, a manufacturer of high-frequency ceramic components, including chip antennas, High- Q capacitors and EMI chip filters. According to Carmona, Johanson Technology
has been able to eliminate the requirement for a designated ground keep out area through opti- mization of materials (ceramics and inks), manu- facturing processes and RF circuit design. The new 2.4 GHz antenna can now be mount-
ed directly onto the metal ground plane. The prod- uct measures 0.08 x 0.2 (2 x 5 mm) and is designed for small coin-cell battery-operated wearable applications where metal, a battery or display cov- ers the entire length or side of the PCB. “With PCB real estate at a prime, the size
and placement of the chip antenna is critical, because as everything gets smaller it becomes increasingly difficult to place more components on
Continued on page 74
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