Miniaturized wireless medical wearables

Traditionally, small chip antennas used in radio-frequency (RF)-enabled medical devices have required a designated ground keep-out area to minimize interference from other components and ensure the ideal radiation pattern for wireless signals. In some cases, this reserved space takes as much as 15mm x 20mm of the printed circuit board.

However, alternatives allow the chip antenna to mount directly above metal surfaces, so up to 20% of the space traditionally reserved for the keep-out area is no longer required. This enables designers to reduce the product’s overall size, miniaturizing next-generation medical biosensors and wearables where miniaturized printed circuit boards (PCBs) and coin-cell batteries often limit the form factor.

Mobile biosensors, wearables

Powered sensor devices that can be located near, attached to, or implanted in the body monitor physiological signs such as temperature, blood pressure and pulse rate, and the market continues to grow. These smart devices monitor fitness, health, environment, lifestyle, and behavior. Tracked biological parameters include vital signs, sleep, emotions, stress, breathing, movement, effort, posture, gait, body shape, lesions, mental acuity, toxins, blood glucose, ECGs, and drug adherence.

Collected information wirelessly transmits to nearby cell phones, remote monitoring stations, or through Wi-Fi to back-end servers for further analysis, assessment, and decision-making.

Among the products already incorporating this type of technology are adhesive bandages that contain built-in sensors measuring heart rhythm, respiratory rate, and temperature.

Embedded chip antennas

To transmit and receive RF wireless signals in the appropriate frequency range, smart devices must contain small RF chip antennas embedded on the PCB or behind the scenes, underneath the product’s encasement.

Chip antennas radiate and receive electromagnetic waves as other types of antennas, but the most notable difference is their small size. While today’s mobile phones incorporate a minimum of 4 antennas and up to 13 in some models, wearable devices may contain only 1 or 2.

To work properly, chip antennas have typically been ground-plane dependent – 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 must typically be placed on the edge of the board in an isolated section, free from ground and metal components that would distort its radiation. Without the isolation distance, antenna performance is signi?cantly affected.

“The keep-out area is fundamental to ensure 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 electromagnetic interference (EMI) chip filters.

According to Carmona, Johanson Technology has been able to eliminate the requirement for a designated ground keep-out area by optimizing materials (ceramics and inks), manufacturing processes, and RF circuit design.

The 2.4GHz antenna mounts directly onto the metal ground plane; measures 2mm x 5mm; and is designed for small coin-cell battery operated IoT, 2.4 BLE, wearable, ISM, ZigBee, and 802.11-standard applications where metal or a battery/display covers the entire length or side of the PCB.

“With PCB real estate at a premium, the size and placement of the chip antenna is critical because, as everything gets smaller, it becomes increasingly difficult to place more components on the board,” Carmona explains. “Therefore, design engineers are looking to component manufacturers to deliver miniaturized solutions that occupy next-to-no real board space.”

Design assistance

The antenna’s design is also critical to range and performance. With medical devices, radio interference or some other glitch could interrupted connectivity.

There can be legal ramifications as well. As with any wireless device, products that use RF technology, including Bluetooth, to collect or transmit information, are subject to regulation by the Federal Communications Commission (FCC). Therefore, it is critical the device perform at the designated frequency and the design and placement of the antenna is critical to proper tuning.

Despite the critical nature of the antenna, Carmona says it is often overlooked until late in the design process, at which point optimal antenna performance may not be achievable within the space provided.

To assist with chip antenna design and selection, Johanson Technology offers a program where design engineers can send in a miniaturized device and the company will tune the antenna for optimum functionality.

“A chip antenna that can be mounted over a ground plane opens up many applications for products to incorporate wireless,” Carmona says. “To date, we have received everything from smart shirt buttons to jewelry and other wearables in various shapes and sizes.”