Spectral and directional radiation characteristics of thin-film coated isothermal semitransparent plates

Abstract

An analysis is presented for prediction the effective spectral, directional radiation characteristics of an isothermal, semitransparent sheet surrounded on both sides by massive dielectrics. This sheet can be coated on one or both sides with one or more optically thin films. Such coated sheets are considered for their applicability as selective cover plates for solar collectors. Extensive computations have been performed to determine what thin film optical properties and film configurations yield the desired selectivity, i.e., high solar transmittance and at the same time high infrared reflectance. Sample results are presented to illustrate the effects of thin film real and imaginary indices of refraction on the spectral reflectance and transmittance of thin film coated glass sheets. Also, directional and polarization effects are considered for selected thin film-plate systems. Some potential candidate materials have been identified and spectral transmittances and reflectances of isothermal plates coated with thin films of these materials have been predicted.