In an optical wireless power transmission (OWPT) system, position and size of the photovoltaic device (PV) should be accurately determined from the light source position. Even though the detection of PV for OWPT has been studied and reported in some literature, the methods reported thus far are not so robust against varying background illumination. This study aims to solve such problems utilizing an image sensor which generates a differential absorption image from two wavelength images. Unnecessary background illumination presented in the two images is subtracted in the differential image. The differential image of the Si substrate target, which simulates PV, was detected by this sensor from a 104.5 cm distance. Signal illumination intensity was less than 1 μW/cm2 on the target, and detection accuracy was 3.1% for the diameter of the substrate and about 6.3% for the area. The system level requirement is derived, and they were verified by these results. The detection range of this sensor is shown to be expandable at the cost of, for example, increasing the receiver diameter of the image sensor or controlling the transmitter beam’s divergence. With the simple experiment apparatus, preliminary results of performance assessment were obtained and issues for performance improvement and potential of this image sensor were recognized.
Since optical wireless power transmission (OWPT) transmits power by light, which has a narrow diffraction angle feature, it is a strong candidate for wireless power transmission systems supporting long ranges. To develop a realistic operational OWPT system, clarification of system level requirements is essential. In this study, to fill a gap between the concept/initial demonstration and an operational system, the required conditions were analyzed regarding the effects of beam alignment and shaping on the power generation ratio which is a system level efficiency factor with extension from the formerly reported one-dimensional analysis to three-dimensional to include errors in all degrees of freedom is presented. This extension is regarded as an indispensable methodology to evaluate the system level performance of general OWPT systems. Numerical requirements for beam alignment and shaping are derived for both non-cooperative and cooperative OWPT. In non-cooperative OWPT, the direction of the solar cell module is fixed, and the transmitter aligns its beam with the module. In cooperative OWPT, the module and transmitter mutually align in the same direction. Though the cooperative OWPT is more restrictive than the non-cooperative one, its advantages were clarified.
In optical wireless power transmission (OWPT) systems, since beam size is finite, and relative position and attitude between transmitter and receiver is not always stationary, both beam alignment and shaping accuracies are important parameters. Analysis based on a power generation efficiency calculation model of general OWPT systems shows that their tolerances are quite demanding, especially for long range OWPT, and relaxation is inescapably necessary. This study introduces the fly eye lens as a candidate to relax these difficulties and, moreover, it features producing homogeneous irradiation onto the solar cell array. All of these are essential to OWPT systems. In this study, cooperative OWPT is discussed, in which solar cell array and power transmitter mutually align each other. Its efficiency calculation model is integrated with a fly eye module surrounded by reflective walls. System level requirements are analyzed regarding beam shaping and alignment in terms of power generation ratio, and it is clarified that this module largely relaxes requirements. In this module, beam power is confined within the module and will be eventually absorbed by the solar cell as the incident beam is within the acceptance angle. This feature avoids degradation of power generation ratio due to beam shape mismatch. These advantages bring progress towards building operational OWPT.
In optical wireless power transmission, position, size, and attitude of photovoltaic device (PV) must be determined from light source. A method proposed in the previous report is based on selective absorption characteristics of PV, and it is detected by differentiating images of strongly absorbable wavelength and one not. In this study, using two infrared wavelengths, two kinds of targets were detected by differential absorption imaging. One was a GaAs substrate which simulates diffuse rear surface, and the other was a real GaAs PV. It was found that the substrate’s reflective characteristic was diffuse, and the solar cell’s was mainly non-diffuse and accompanied by small diffuse component supporting wide-angle reflection. Using this feature, the position of the GaAs solar cell could be determined within a wide range of angle. Its attitude could also be determined with an accuracy of ±10 degrees to its normal. The position of diffuse GaAs substrate could be determined within a wide range of angles, and its attitude determination was proposed by exploiting its varying apparent size with tilt angle. Broad reflection characteristics of the GaAs substrate enabled attitude determination for a wide-angle range, and determination around normal would be erroneous.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.