Frequency Selective Bolometers - Progress and Projections

We describe recent progress in the modeling and production of Frequency Selective Bolometers operating in the frequency range of 150-1500 GHz. The Frequency Selective Bolometer (FSB) functions by incorporating a bolometer element into a resonant structure to control the range of frequencies over which it absorbs. Both the bolometer absorber and the backshort are planar metal layers with periodic patterns that resonate at the desired frequency. The bolometer layer is resistive and absorbs the incident radiation at the desired frequency while the backshort is a low resistivity resonant pattern. The transmission, reflection, and absorption spectra of this two lay er structure are predicted with a numerical model and controlled by the design of the characteristics of the patterns. The key advantage to the FSB bolometer lies in the fact that the radiation not absorbed on the bolometer is transmitted through the device and passed on to subsequent FSB elements that are tuned to other frequencies. Thus a stack of FSB elements enables a multi-spectral single pixel with a geometry that can be close packed into an array of pixels. We describe the electromagnetic modeling and measurements of FSBs spanning 150 to 1500 GHz. The discussion is focused on two issues: prediction and control of the FSB passband and the projected high frequency limit of FSBs currently being produced. Results from FSBs produced for the SPEctral Energy Distribution (SPEED) receiver (150-350 GHz) are shown along with corresponding results from prototype FSBs for the Explorer of Diffuse high-z Galactic Emission (EDGE) telescope (300-1500 GHz).