Overview
TOKYO —Toshiba Corporation has developed the world’s first microwave remote power transfer system that can wirelessly transfer power to remote locations while coexisting with wireless LANs (Wi-Fi). The developed system includes interference avoidance functions (*1) that allow efficient power transfer to targeted locations without disrupting local wireless LAN communications, along with technologies that enable efficient power reception regardless of the receiving antenna’s orientation (*2).
The practical application of remote power supplies requires the prevention of interference so that the power supply can coexist with wireless LANs. Previous technologies have yet to achieve such coexistence, but this new development now allows interference avoidance by detecting the presence or absence of wireless LAN signals in the vicinity and controlling the power supply beam accordingly. Highly efficient and stable power reception was achieved by combining vertical (vertically polarized) and horizontal (horizontally polarized) radio waves, and the feasibility of receiving approximately twice the average power of conventional systems was demonstrated.
This newly developed technology is also expected to contribute to digitalization and labor-saving initiatives at manufacturing sites and distribution warehouses. Such initiatives are made possible through the use of wireless LANs and numerous IoT sensors for industrial equipment. The developed technology makes it possible to operate sensors without batteries, allowing efficient and continuous sensing at continuously operating manufacturing sites and improved productivity through advances in digitalization and labor savings, while also contributing to efforts toward realizing a carbon-neutral society (*3).
Toshiba will present details of this technology at the 2023 Asia-Pacific Microwave Conference (APMC 2023), an international conference to be held in Taipei, Taiwan, on December 6 and 8.
This development was partly supported by Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), “Energy systems of an Internet of Energy (IoE) society” (Funding agency: JST), FY2018–2022.
Development background
With the widespread introduction of IoT technologies, the deployment of sensors in industrial equipment is expected to continue increasing. Reducing the cost of introducing IoT systems requires wireless sensors that avoid line stoppages due to breakages of sensor power cables and that allow free placement and retrofitting of sensors in production lines. Battery-based power supplies have many issues, such as limited operation times and increased maintenance costs due to the need for recharging and replacement. There is thus increasing demand for new power supply schemes, such as remote power supplies and microwave-based recharging. However, microwave-based power supplies can interfere with other nearby wireless systems, such as wireless LANs. In May 2022, microwave-based remote power supply systems in three frequency bands (920 MHz, 2.4 GHz, and 5.7 GHz) were approved for use in wireless power transfer systems in Japan. The 5.7 GHz band that Toshiba focuses on is the frequency band that can supply the highest amount of power and is thus expected to be utilized in industrial applications. However, that frequency is adjacent to that used for wireless LANs, making interference an area of particular concern. These technologies must coexist with wireless LANs if they are to be commercialized in Japan, but until now, there have been no such wireless power supply systems.
Another issue is that improving the power-receiving efficiency of each sensor installed in each location requires careful adjustment of the orientation of power-receiving antennas, reducing the degree of freedom for sensor installations.
Features of the technology
To address the above challenges, Toshiba has developed a microwave-based remote power supply system that incorporates new power-supply technology. The developed system detects the presence or absence of nearby wireless LAN signals and appropriately controls the power-supply process to avoid interference with the other wireless systems while aiming the power-supply beam to the targeted location. Another aspect is a novel power-receiving technology, which can extract power from the microwave supply with high efficiency but without requiring adjustment of the receiving-antenna orientation (Figure 1).
The developed power-supply technology successfully detected the presence or absence of nearby wireless signals with high accuracy over the wide frequency band (5.50–5.72 GHz) used by wireless LANs (Figure 2). When a wireless signal is detected, the power supply direction is changed to allow coexistence without interference to the wireless LAN. For the power supply, Toshiba developed a compact 25 × 40 cm housing that integrates a signal processing circuit that includes wireless signal coexistence functions, an amplification circuit, a phase control circuit, and a 64-element antenna. This system integrates all the functions necessary for power supply, while its compact size allows easy installations on ceilings and other locations. With this technology, the feasibility of power supply without interference to wireless LANs was demonstrated. Coexistence with the wireless LANs widely used in factories and plants means communication with and power supply to sensors can be completely wireless, further improving efficiency at production sites.
In addition, the developed power-receiving technology combines power simultaneously received from microwaves with two polarizations, horizontal and vertical. Efficiently supplying power in a remote microwave-based supply system requires alignment of wave polarizations, which are the directions of fluctuations of the electromagnetic field. An issue to date has been that power is received at maximal strength when the supply and receive antennas operate with the same polarization, but misalignments hinder power reception. By receiving and combining two types of radio waves, however, power can be received efficiently regardless of the orientation of a sensor’s receiving antenna (Figure 3). Toshiba demonstrated that the average power received at a distance of 1.5 m while rotating the angle of the developed receiver antenna is approximately twice that received by vertically or horizontally polarized antennas.
Future developments
Toshiba plans to proceed with verification testing at plants, warehouses, and other actual worksites. The company aims to commercialize the system in 2025 or later after resolving technical issues discovered through verification testing and considering trends in legal developments.
*1: This is the world’s first microwave-based remote power supply system that can coexist with 2.4 and 5.7 GHz wireless LAN systems, the bands in which high-power remote power supply is legally permitted. Based on a Toshiba survey conducted in December 2023.
*2: This is the world’s first successful demonstration of improved power-receiving efficiency with respect to polarization angle by controlling and combining power for each received polarization component. Based on a Toshiba survey conducted in December 2023.
*3: Remotely supplying power to battery-free sensors or those equipped with rechargeable batteries reduces the need to change batteries. The system thus increases productivity through digitalization and labor savings and furthermore contributes toward a carbon-neutral society.
Figure 1: Overview of a high-efficiency, microwave-based remote power supply system that can coexist with other wireless systems
Figure 2: Demonstration results (right) of detecting difficult-to-detect wireless LAN signals in a wide frequency band (5.5–5.72 GHz) with the developed integrated power supply (left)
Figure 3: Demonstration of a power receiver that performs highly efficient power reception regardless of the receiving antenna orientation