The quest for a truly wireless world has long been hindered by the physical limitations of Radio Frequency (RF) power transfer. From efficiency drops over distance to the persistent headache of electromagnetic interference (EMI), current methods of powering the Internet of Things (IoT) remain tethered to bulky batteries or proximity to power outlets. However, a breakthrough from the Institute of Science Tokyo (ISCT) promises to shift the paradigm. Professor Tomoyuki Miyamoto and his research team have unveiled a sophisticated Optical Wireless Power Transmission (OWPT) system that leverages adaptive optics and AI-guided beam control to deliver energy to IoT devices up to five meters away—effectively bridging the gap between theoretical potential and practical deployment.
The Core Innovation: Adaptive Optics and Artificial Intelligence
At the heart of the ISCT’s new system is the transition from static, inefficient light-casting to dynamic, intelligent beam management. Traditional optical systems struggle with "beam divergence," where light scatters over distance, drastically reducing the energy density at the receiver.
To combat this, the research team implemented a double-layer lens architecture. This setup features a liquid lens with a tunable focal length paired with a fixed imaging lens. By dynamically adjusting the liquid lens, the system suppresses beam expansion, allowing the light to remain tightly focused over greater distances. In experimental trials, this design achieved power delivery eight times higher at a three-meter range compared to previous fixed-optics iterations.
The "intelligence" of the system comes from a sophisticated AI-guided targeting mechanism. Using an RGB-IR depth camera and a convolutional neural network (CNN) based on a single-shot object-detection algorithm, the system identifies multiple photovoltaic (PV) receivers in a room. A motorized reflector then pivots to track these devices. To ensure functionality in low-light or total darkness, the team applied retroreflective sheets—similar to those found on high-visibility safety gear—to the edges of the PV modules. These sheets reflect the system’s IR sensor output, providing the AI with a high-contrast map of the target, regardless of ambient lighting conditions.
A Chronology of Development: From 2019 to Present
The road to this five-meter milestone has been marked by iterative engineering challenges and incremental successes.
- 2019 – The Proof of Concept: Professor Miyamoto and his team debuted their first LED-based OWPT approach. While it successfully demonstrated the viability of using LEDs for wireless power, it was limited by fixed optics and a range of only one meter. The system was prone to significant power attenuation, and it lacked the robustness required for real-world environmental changes.
- 2020–2023 – Refinement and Simulation: During this period, the team focused on overcoming the "divergence" problem. Through extensive ray-tracing simulations, they mapped the relationship between LED collection, beam spot size, and transmission distance, leading to the development of the adaptive liquid-lens system.
- 2024 – Integration of AI: Recognizing that hardware alone could not solve the issue of targeting multiple moving or static receivers, the team integrated the CNN-based detection system. This moved the project from a "fixed-point" transmitter to a dynamic, "smart" power source capable of sequential charging.
- 2025–2026 – Experimental Validation: The team successfully demonstrated the ability to power five differently sized PV receivers scattered across a lab at distances ranging from two to four meters, with peak transmission capabilities hitting the five-meter mark.
Supporting Data and Technical Metrics
The performance of the ISCT system challenges the dominance of traditional RF power solutions. While RF systems are hampered by free-space propagation losses, the LED system utilizes the inherent directional stability of optics.
- Transmission Efficiency: The current system operates at an overall optical efficiency of approximately 56%. The team has set a target of 80% for the next phase of development.
- Distance Capabilities: While five meters is the demonstrated experimental range, current simulations suggest that the beam can remain sufficiently focused up to 10 meters, provided the optical hardware is further optimized.
- Operational Versatility: The system proved reliable in both fully illuminated and completely dark environments, with the latter utilizing the IR-based retroreflective detection method to maintain a lock on PV receivers at up to four meters.
- Power Density: By concentrating energy into a narrow beam, the system avoids the safety pitfalls of high-intensity lasers while maintaining significantly higher power density than diffuse light or standard RF waves.
The Case for LEDs Over Lasers
In the race for long-range wireless power, laser-based systems have often been touted as the frontrunner due to their ability to bridge distances of several dozen meters. However, Professor Miyamoto emphasizes that LEDs offer a superior profile for indoor environments, particularly where human safety is a priority.
"The lower radiance and power density of LEDs make it easier to design systems that comply with optical safety requirements," Miyamoto told EE Times. "LEDs are also relatively cheap, have long operating lifetimes, and can be integrated into lighting-like modules, making them a natural fit for smart building infrastructure."
While lasers may be necessary for industrial-scale, long-distance power delivery, the LED approach is perfectly calibrated for the "meter-scale" needs of smart buildings, factories, and automated farms. The lower barrier to entry regarding safety regulations and component cost makes the LED-based OWPT a more viable candidate for rapid commercialization.
Implications for the Future of IoT
The implications of a reliable, long-range, wireless power source are profound for the Internet of Things ecosystem. Currently, the "battery problem"—the need to periodically replace or recharge thousands of sensors in a smart factory or office building—remains a major operational bottleneck.
1. Smart Infrastructure and Industrial IoT (IIoT)
In factories, sensors monitoring vibration, temperature, and humidity are often placed in hard-to-reach locations. Hardwiring these devices is expensive and labor-intensive, while battery replacements create significant maintenance overhead. An LED-based overhead lighting system that doubles as a power grid could provide continuous, autonomous operation for these devices.
2. Sustainable Smart Buildings
As buildings move toward higher levels of automation, the density of sensors is increasing. An OWPT-enabled environment would reduce the millions of tons of battery waste generated annually by IoT devices, contributing to a more sustainable, circular economy.
3. Agricultural Efficiency
In controlled-environment agriculture (CEA) or indoor vertical farms, power delivery is constant and vital. The ISCT system’s ability to target multiple receivers at varying distances allows for a centralized power hub to support a diverse array of environmental monitoring sensors, reducing the complexity of the internal facility wiring.
Looking Ahead: Scaling and Integration
Despite the success of the current laboratory demonstrations, the path to commercialization involves several critical hurdles. Professor Miyamoto has outlined a clear roadmap for the next phase of development:
- Thermal Compensation: The liquid lens is susceptible to thermal drift, which can affect the focal length and, by extension, the precision of the beam. The team is working to characterize the temperature-focal length relationship to implement active thermal management.
- Component Miniaturization: The next step is to integrate the optical source, power electronics, and control circuitry into a singular, compact module that can be installed similarly to standard office lighting fixtures.
- Industry Partnership: Miyamoto is actively seeking industry partners for product integration and qualification. "If we can now get an industry partner to look at product integration and qualification, we will be able to build a pilot system relatively quickly," he noted.
The transition from a laboratory experiment to a ceiling-mounted reality requires rigorous testing for long-term reliability and adherence to international safety standards. However, with the foundational research now in place, the prospect of "power-over-light" is closer than ever. By replacing the tether of the battery with the reach of an LED beam, the ISCT team is not just improving a technology; they are potentially unlocking the next era of infrastructure, where power is as ubiquitous and accessible as the light we use to see.
