Wearable wireless devices are rapidly moving into the mainstream of society, led by the health and fitness markets. Advances in mobile communications and battery technology, miniaturized electronics, high performance materials, and app software have turned bulky wearable computing gear designed for the military into lightweight, energy-efficient, and fashionable wearable devices.
As more functional and fashionable devices hit the market, the focus is shifting from fashion to usability. It will soon be critical to deliver wire-equivalent connectivity for wearable devices, sometimes at very high data rates.
High Speed Wireless
With an avalanche of new wearables, it is important to find ways to supply low-latency high speed data connections to enable truly demanding use cases such as augmented reality. This is particularly true for high-density wearable computing scenarios, such as public transportation, where existing wireless technology may have difficulty supporting stringent application requirements wearable devices, sometimes at very high data rates.
For instance, if 25 out of 50 passengers in a conventional bus want to use Bluetooth communications for their headsets at the same time, there is barely enough bandwidth. That is for an average of 0.5 wearable devices per passenger. In the near future, we could be seeing five devices per passenger.
The reality is that existing wireless protocols are a compromise between simplicity, efficiency, and flexibility. For wearables, this is a problem as data needs to get from the device to a place where it can be used. And the volume of sensor-based devices is increasing at an incredible rate. A panel of experts assembled by ECN cited forecasts of 10 trillion sensors by 2027, not including RFID devices. “To handle that much information, the industry needs to miniaturize antennas and examine how much bandwidth sending data away from a device will require. Or, data processing can be done on the device itself, if the battery life and a way to extract the data can be integrated.”
The design and fabrication of wearable electronics require embedding electronic components inside clothes or wearable accessories that do not compromise the appearance and usability of the product. Per standards in the fashion industry, wearable technology must be useful, comfortable, and must not be intrusive to the user, who must be able to carry out daily activities without any movement limitation or additional burdens.
According to a team of researchers at the University of Salento,
Considering these requirements, either near-field or far-field wireless technologies may successfully serve the purpose for both data and power transmission. To guarantee a seamless integration of electronic devices and antennas in wearable and portable accessories, it is crucial to select appropriate materials and fabrication techniques. To this purpose, the use of nonconventional materials such as textile materials, conductive threads, electrotextile fabrics, and nonwoven conductive fabrics should be preferred.
Some wearable antennas for far-field Wireless Power Transmission (WPT) links have been proposed, such as a multifrequency rectifying antenna (rectenna) where the multiband behavior is obtained by using a slotted annular-ring microstrip antenna. The overall system is a multilayer structure using two layers of pile and a thermoadhesive layer at each interface between pile and conductive fabric. In addition, two textile logo antennas fabricated by means of a self-adhesive nonwoven conductive fabric have been presented. For near-field WPT links for wearable applications, a system using two resonators on a layer of leather has been proposed.
Battery Technology for Wearables
Batteries for wearables need to be small, thin, lightweight, and rarely charged. But battery technology has been slow to change. Li-Ion dominates thus far. Lithium Polymer is also an attractive choice for lightweight batteries.
According to battery expert Dr. Manfred Leimkühler, “Li-Ion coin cells may be fine for sensors and other very low power wearable devices, but they struggle to keep up with the demands of more capable wearables, such as fitness bands and smartwatches. Extending the battery life is critical for these types of devices to gain market acceptance and for the wearables market.”
Advances in wireless charging, battery management, ultra-low power conversion, low power solutions such as Bluetooth and microcontrollers, even energy harvested from the body are in development to extend the battery life of wearable designs.
For flexible wearables, a new design strategy has emerged. Instead of changing the chemistry or thinning the device, a special arrangement of cells makes the existing batteries flexible or even foldable.
Regardless of the specific wearable application, batteries need to be packaged to absorb internal impact energy. PORON® polyurethane materials and BISCO® silicone foams withstand collapse that can happen due to the stresses of compression and temperature in battery packs over time. This Compression Set Resistance (C-set resistance) Resistance can help extend the life of the battery by continuing to seal and absorb shock. These unique materials from Rogers Corporation also have a unique ability to act as a spring by retaining a very consistent level of force across a range of compressions. This allows the designer more flexibility and reliability in packaging of the battery pack due to the ability to predict the cushioning material’s behavior across varied dimensional tolerances.