Patent ID: 8829334

Claim:
A device for generating electric energy, comprising: a heat source for generating heat energy; a thermal emitter operative to receive said heat energy and to emit thermal radiation with black body emissivity; a housing forming a reflective cavity enclosing said heat source and said thermal emitter, and having a transparent window through which thermal radiation emitted by said thermal emitter is passed; photovoltaic cell means located outside said reflective cavity and positioned to receive thermal radiation passing through said transparent window, said cell means being operative to convert thermal radiation within a particular wavelength range into electric energy; and a band pass filter disposed outside of said reflective cavity and between said window and said photovoltaic cell means, said band pass filter having a first cutoff wavelength on one side of said particular wavelength range converted into electricity by said photovoltaic cell means, and a second cutoff wavelength on the opposite side of said particular wavelength range converted into electricity by said photovoltaic cell means, said band pass filter including, a non-resonant sub-wavelength aperture array consisting of a layer of metallic material forming a reflective thin film disposed between said window and said cell means, and having a film thickness greater than 30 nm and a plurality of transparent openings formed therein, the size and shape of said openings being selected to transmit thermal radiation having wavelengths shorter than said first cutoff wavelength, said reflective thin film being operative to reflect radiation having wavelengths longer than said first cutoff wavelength back to said emitter through said window, and a dichroic cold mirror interposed between said window and said reflective thin film, said dichroic cold mirror being operative to transmit thermal radiation having wavelengths longer than said second cutoff wavelength and to reflect radiation having wavelengths shorter than said second cutoff wavelength back to said emitter through said window, whereby radiation from said thermal emitter having wavelengths within the pass band of said band pass filter is transmitted to said photovoltaic cell means for conversion into electric energy, and thermal radiation having wavelengths outside said pass band is reflected back to said thermal emitter to be re-absorbed thereby to enhance the conversion efficiency of the device.