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A team of researchers from Sejong University in South Korea has successfully used infrared light to transmit power wirelessly over a distance of 30 meters. When testing the wireless laser charging system, the researchers safely transmitted 400mW of light and used it to power an LED light.
“We could use this technology to wirelessly power IoT sensors in smart homes or digital signage (displays) in large shopping malls and other places,” Jinyong Ha, who led the study, told indianexpress.com via email. Ha also envisions industrial applications of this technology in places where the use of wires could pose security risks. The research results were published in an article in Optics Express in September.
The system developed by the researchers consists of a transmitter and a receiver. When both are in line of sight of each other, they can be used to deliver light-based energy. However, the system will go into safe power mode, where it will stop transmitting power if an obstacle comes between the transmitter and receiver. This aims to minimize the risks associated with the system.
The transmitter has an erbium-doped fiber optic amplifier (EDFA) power supply that has a wavelength of 1,550 nm. According to the researchers, this wavelength range is safe and poses no danger to human eyes or skin at the intended power level. The EDFA was first invented in 1987 and is commonly used to compensate for signal loss in fiber optic transmission over long distances.
The receiving unit consists of a photovoltaic cell and a spherical retroreflector with a ball lens that helps reduce the scattering of light emitted by the transmitter and focuses it on the photovoltaic cell for maximum efficiency. The researchers found that the performance of the system was strongly dependent on the refractive index of the spherical lens, and that a refraction of 2.003 was the most effective.
During experimental testing, the transmitter could provide 400 mW of optical power at a distance of 30 meters. The receiver’s 10 x 10 millimeter photovoltaic cell was able to convert the light energy into 85 mW of electrical energy, which was used to power the LEDs. The researchers also demonstrated the safety of the system by placing a human hand between the transmitter and receiver. At this point, the system went into low power mode, producing low intensity light so it did no harm.
“Efficiency can be significantly improved. Since we are now using 1550 nm light, we have a low efficiency photovoltaic cell (GaSb). If we use infrared light with a wavelength of about 900 nm, the efficiency can be improved by 40 percent,” Ha said. Currently, the photovoltaic cell is made of gallium arsenide (GaAs). This can be turned off for other materials that will be more effective at different wavelengths to increase efficiency.
The team is now working to increase the efficiency of the system and scale it up so that it can be used for IoT sensors in smart factories before the technology finds further applications.
