In addition to the sensing, data processing, and communication topics discussed in Part 1 of this blog, other key design aspects for wearables will be presented in this one. First up, the one that has a specific focus on power management.
Power management
Smartwatches, earbuds, and health monitor wearables typically operate on 300 to 1500 mWh batteries. For these and other wearable products, power management ICs (PMICs) must address challenges such as inefficient power conversion, limited battery life, and space constraints. In addition, many wearables require multiple voltage regulators to provide a variety of voltages.
Using a design technique called Single-Inductor Multiple-Output (SIMO) technology, a PMIC can have one shared inductor generate multiple independent and independently regulated output voltages from a single input. For example, one company used this approach in a PMIC designed specifically for wearables and ultra-portable devices. With its single inductor, it delivers three outputs at 91% efficiency and replaces three traditional converters and inductors in a 19 mm² footprint that is 50% smaller than the alternative.
As part of power management, two subcategories deserve special consideration: charging and energy harvesting.
Charging/energy harvesting
Wearables have unique design requirements for charging based on their small size that pose problems for physical connectors. The solution is wireless charging, and available design techniques provide choices for implementing it. As shown in Table 1, a variety of factors enter into the choice of the right one. The wireless connectivity is provided by inductive, magnetic resonance, and RF (electromagnetic) techniques.
For wireless charging, industry standards have been developed by the Wireless Power Consortium and the NFC Forum. Leveraging the existing Near Field Communication (NFC) antenna for both communication and power transfer, the NFC Wireless Charging Specification (NFC WLC) can deliver low-power charging—up to 1 watt—over distances of about 2 cm. NFC charging relies on a small antenna that already exists in billions of devices for connectivity and authentication. In contrast, inductive or resonance systems require relatively larger coils/antennas.
The Wireless Power Consortium (WPC) created its Qi Standard strictly for wireless power transfer (WPT).
Originally an exclusive feature on the 2020 iPhone 12 line, after five years, key parts of Apple’s MagSafe wireless charging are now also available on Android phones because Apple allowed their incorporation into WPC’s open Qi2.2 standard.
Far-field wireless charging, where wearables are charged from across the room using radio waves, infrared light, or lasers, is a possible future approach for wearables. Some startups have already demonstrated functional prototypes.
In addition to these established wireless techniques, researchers continue to investigate new approaches for wireless power transfer. For example, one group of university researchers used self-capacitance technology to remotely transfer wearer-generated power to the wearable or devices installed in hard-to-reach areas of the body. As shown in Figure 1, their system utilizes the self-capacitance of the person’s body to wirelessly transfer power from portions of the body that generate higher power density to energy-constrained wearable devices. Its inventors envision implementation in millimeter-scale wearables in the power range of ~10mW, in end-user applications such as:
- Hard-to-reach wearable technology (including smart contact lenses and mouth guards)
- Smart textiles and stitched sensors (sports performance monitors, flexible electronics/wearables)
Energy harvesting from different conversion technologies continues to be the design goal of many companies and researchers. The ultimate solution could be a combination of the two companies’ expertise. For example, working together, one company’s RF-based wireless charging technology combined with the other company’s energy harvesting technology that captures RF power promises to open up the market for wireless charging up to two meters away. The combined solution can be used for a diverse array of connected products for retail, industrial, and consumer applications, including ultra-small, location-flexible, RF charging for wearables, hearables, and low-power electronics.
Algorithms
As shown in Figure 2, one company has developed algorithms for wearables that use an Inertial Measurement Unit (IMU) input through a 9-axis sensor fusion algorithm based on accelerometer, gyroscope, magnetometer, and strong artificial intelligence (AI). It offers these algorithms to consumers for wearable and other applications. Specifically, the algorithms address fall monitoring, activity recognition, step counting, head posture control (left and right turn of head, nod, head shake), and 3D head tracking for an immersive audio experience.
By operating on most of the world’s well-known low-power microprocessors, single-chip and Bluetooth SoCs, the algorithm can collect large amounts of data based on multiple sensors and constantly improve results through machine learning to achieve higher accuracy and more stable motion recognition. Figure 3 shows the small footprint that can be achieved.
Other systems aspects
Other system design aspects that impact or promise to impact wearable products include the display, simulation technology, including digital twins, multi-physics, and more, to optimize board layout and address thermal limitations, faults, and more.
For more complete power-consuming consideration, the screens on displays/optical systems can consume 10 to 100 mW, while augmented reality (AR) optics/glasses often require <320 mW, and Global Positioning System (GPS) sensors can require 70 mW+ of power.
With general-purpose simulation software used in all fields of engineering, manufacturing, and scientific research, multi-physics system-level analysis allows designers to gain insights into how physics couplings influence overall system performance.
References
Revolutionizing Power Management For Wearable Power Management With SIMO Technology
Extending the Battery Life of Electronic Wearable Devices
Self-capacitance Power Transfer for Efficient Wireless Charging of Small Wearables | Washington University Office of Technology Management
Powering the Future of Wearables: Battery Charging Strategies
Wireless Charging 2.0: NFC Power for Wearables in 2026
Energous and Atmosic Achieve Industry First Interoperability Energy Harvesting Advancing Development of Wireless Charging Applications
CyweeMotion
The COMSOL Product Suite
What is Multiphysics?
Digital twin for personalized medicine development
Related EEWorld content
How can designers decrease power and increase functions in wearables: part 1
Low-power sensor fusion platform seamlessly integrates into wearables
How can sensors save energy and improve sensor node battery life?
How can energy harvesting be used in industrial applications?
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