Wearables are gaining popularity amongst end-users for a variety of use cases. The market shows an increasing trend in demand for wearable solutions, which have gained widespread popularity in various fields, including medicine, security, entertainment, and industrial have seamlessly integrated into our daily lives, from the health and fitness trackers that count our steps, take ECG, track our sleep, to the smartwatches that notify us of incoming messages and complement other features of smartphones. These small, often stylish devices have become indispensable, providing real-time data and improving our quality of life.

Wearables, which non-invasively connect the physical and digital worlds, monitor our health, track fitness, and even link us to the Internet of Things (IoT). Despite their capabilities, current wireless charging methods in wearables, such as those used in fit-bits, primarily rely on inductive chargers and face limitations. However, their reliance on battery power significantly constrains usability and design.

Microwave Wireless Power Transmission (MW-WPT) is emerging as a potential solution to overcome some of these challenges, enabling continuous power supply without physical connectors.

Saying so, there are other wireless power solutions such as ones based on RF, Infrared and NFC which are also being considered for wearable applications. Here in this blog we specifically look at MW-WPT.

Enter Microwave Wireless Power Transfer (MW-WPT)

Imagine a world where your smartwatch or fitness tracker never runs out of battery. This futuristic scenario is closer to reality thanks to Microwave Wireless Power Transfer (MW-WPT). Microwave WPT involves the transmission of power from a source to a receiver via microwave frequencies. The fundamental components include a power transmitter (source), a receiver (rectenna), and an efficient transmission medium.

Key Components of Microwave Wireless Power Transfer (MW-WPT)

• Transmitter: The transmitter converts electrical power into microwave radiation using high-frequency oscillators and amplifiers.
• Receiver (Rectenna): The rectenna, a rectifying antenna, captures microwave energy and converts it back into direct current (DC) power.
• Transmission Medium: Microwave frequencies (typically ranging from 1 GHz to 300 GHz) are utilized for their ability to penetrate various materials and provide a focused beam.

The Process involves:

• Energy Harvesting: Capturing ambient microwave energy from the environment.
• Rectennas: Specialized antennas that receive microwaves and rectify them to DC power.
• SWIPT (Simultaneous Wireless Information and Power Transfer): A sophisticated system that can transmit both power and data using the same microwave signal.

Let’s delve into the viability of using Microwave WPT for charging wearable devices in detail:

Advantages of Microwave WPT for Wearables:

1. Flexibility and Mobility: Microwave WPT systems can be designed to be compact and lightweight, which is crucial for wearables. This allows for flexibility in integration into various forms of clothing and accessories without significantly impacting the user’s mobility or comfort.
2. Efficiency: Modern advancements in Microwave WPT technology have improved efficiency, making it feasible to transmit power over short distances with minimal loss. This is essential for wearable devices, where every bit of energy efficiency matters to prolong battery life.
3. Continuous Charging: Unlike traditional wired charging or even some wireless charging methods, Microwave WPT can potentially offer continuous charging as long as the wearable device remains within range of the transmitter. This eliminates the need for users to periodically plug in or place their wearables on a charging pad.
4. Integration with Wearable Designs: Microwave WPT can be integrated into the design of wearables more seamlessly compared to other power transfer technologies. This integration can be done in ways that are aesthetically pleasing and functionally effective, enhancing the user experience.

Challenges and Considerations for Microwave WPT:

1. Safety Concerns: Microwave frequencies used for power transfer raise safety concerns regarding human exposure to electromagnetic radiation. Regulations and standards must be strictly adhered to in the design and deployment of Microwave WPT systems to ensure they are safe for continuous use near the human body.
2. Power Efficiency: While efficiency has improved, Microwave WPT systems still face challenges in achieving high enough efficiency levels, especially over longer distances or when there are physical obstacles between the transmitter and receiver. Energy loss can occur due to absorption by environmental elements or reflection.
3. Cost and Complexity: Developing and deploying Microwave WPT systems can be costly and technically complex, particularly when aiming for high efficiency and reliability. This could impact the affordability and widespread adoption of such technology in consumer wearables.
4. Interference and Regulation: Microwave WPT operates in frequency bands that are subject to regulatory constraints and potential interference issues with other wireless technologies. Ensuring compatibility and compliance with local regulations is crucial for deployment.

Current State and Future Outlook:

The viability of Microwave WPT for charging wearables (and possibly many other applications), seems promising but is still in the development and refinement stage. Researchers and engineers continue to explore ways to improve efficiency, reduce costs, and enhance safety to make Microwave WPT a practical solution for everyday use.

This technology promises to keep our wearables charged and opens up possibilities for entirely new applications.

Healthcare Applications

One of the most exciting developments is in healthcare. Wearables with microwave WPT are being designed to continuously monitor physiological parameters like ECG, oxygen saturation, and activity levels. Imagine a smart textile that can track your heart rate and send the data directly to your doctor, all without needing to be recharged. This technology is not just a convenience; it has the potential to save lives by providing real-time health monitoring and alerts.

Sustainable Electronics

Another significant trend is the push towards sustainable electronics. Wearables are becoming more energy-efficient, with researchers developing ways to reduce power consumption and extend battery life. Integrating Microwave WPT into wearables means that these devices can harvest energy from their surroundings, reducing the need for frequent charging and making them more environmentally friendly.

Advanced Sensing and Communication

Microwave WPT is also enhancing the capabilities of wearables through advanced sensing and communication technologies. Low-power and passive communication systems, such as RFID and backscattering transponders, are being integrated into wearables. These technologies allow wearables to communicate with other devices and systems without significant power, making them more efficient and functional.

Material Innovation

The materials used in wearables are also evolving. Researchers are developing flexible semiconductors and textile-based batteries that can be integrated into fabrics. These innovations make wearables more comfortable and durable, ensuring they can withstand the rigours of daily use while providing continuous power through microwave WPT.

Recent Advances in Microwave WPT for Wearables

Microwave WPT is being looked at in detail by companies and aspiring academicians/electrical engineers. Few wireless power technology solution providers are already developing MW-WPT solutions for a wide range of applications. The new generation of electrical engineers sees it promising and has presented some interesting white-papers papers on various aspects of Microwave WPT.

At the Wireless Power Transfer and Conversion Expo (WPTCE) 2024 in Japan, which WAWT attended and conducted panel and industry sessions, Microwave Wireless Power Transfer (WPT) garnered significant attention, particularly for its advancements and potential applications.

One notable area of progress is in Far-Field Rectenna Technology. Recent studies have demonstrated that textile-based rectennas can achieve efficiencies comparable to their rigid counterparts. This breakthrough allows for flexible and wearable implementations without sacrificing performance, making it feasible to integrate power reception directly into everyday clothing and accessories.

Near-field and Multi-Mode WPT Networks have made significant strides. By leveraging near-field resonant inductive power transfer (IPT) and multi-coil systems, engineers have developed solutions capable of delivering higher power levels over short distances. Consequently, these systems are particularly well-suited for wearable applications. They offer enhanced link efficiencies and extend operational ranges while maintaining compact form factors.

Moreover, Hybrid WPT Systems have emerged as a promising approach. These systems combine near-field and far-field technologies, blending broadband antennas with inductive coils to optimize power reception. This hybrid approach not only enhances power output but also improves efficiency across varying distances and orientations. Importantly, it adheres to rigorous safety standards.

To summarize, microwave WPT is poised to revolutionize the wearable technology landscape. Providing a reliable and efficient way to power such devices wirelessly addresses one of the most significant challenges facing wearables today. As researchers continue to innovate and refine this technology, the day when our wearables are always charged and ready to go is not far off. Indeed, the future of wearables is not just smart; it’s wirelessly powered.

About Wired and Wireless Technology (WAWT)

Wired and Wireless Technologies (WAWT), is a strategic technology analyst and consultancy firm. Its comprehensive research data, insights and market intelligence on the wireless power market titled ‘Wireless Power Intelligence Service’, covers various types of wireless power technology solutions such as inductive, resonance, NFC, RF, infrared or MW-based. WAWT monitors the development and adoption of various types of wireless power solutions across 30+ key application markets across automotive, consumer, computing, wearables, hearables, medical/healthcare, smart home, industrial, robotics, retail, infrastructure, and other sectors. Research also provides market size estimation and forecast of adoption of wireless power technology across market segments.

Reach out to our subject matter experts (SMEs) by emailing analyst@wawt.tech and following our LinkedIn page (WAWT) for the latest market estimates and forecasts, trends, insights and updates on wireless power/charging and allied technologies.