Devices as "rectenna"s and "nantenna"s, as well as contact-less energy sources and re-chargers og electronics energy accomulating devices are prognosticates as perspective energy sources
At microwave frequencies rectenna arrays have been shown to be around 80 percent effcienct some of this work was done as early as the 1960's. At optical or terahertz frequencies the rectenna approach seems less reasonable for a couple of reasons. First the sources are often broadband, while the devices may be resonant or narrowband, so it may be less likely to capture a significant portion of the energy. 2nd instead of having real rectification, the metal insulator metal tunneling junctions often only show some nonlinearity, thus the rectification is not strong. Third, depending on the approach it seems like there will be difficulties with phase, or how to coherently accumulate the energy. Fourth, with lots of elements, there are also lots of interconnects and that also implies loss. That can imply heating in some situations. All of that said, there are enough clever people working on it that there may be some progress.
If a source is narrow band that changes things some. For example, the world record for collecting power from a laser by using a semiconductor photodetector that is tuned to the laser wavelength probably approaches 60 or 70 percent. Much higher than a solar cell. Using wide band gap semiconductors there have been people trying to pattern the surfaces to encourage only narrow band polarized infrared light to come out. Some call it phonon engineering.
In terms of using inductive coupling, those techniques are reaching the market to charge cell phones or even potentially electric vehicles. OF course the range is very short.
@Dear Dr. John Muth! Thank you for interesting and competent ansver! In my opinion, an other aspect of discussion can be directed to possibilities to create directed beam from utilized energy, that will characterize the distance of the energy transfere?
dear colleagues, what do you think about the transfer of energy by creating a waveguide in air(waveguide, stimulating air(laser, microwave radiation, or both) and create a plasma in the air with an empty Central part and so forth) for the flow according to the obtained waveguide current, electromagnetic radiation, laser coherent, microwave. Is it possible to pass thus high energy?? I also thought possibly it may be a jet of gas or liquid for a contact to use for the same purpose, without ionization? Thinking and the search for promising ways of energy transfer for drones, quadcopters and other small air transport