Collaborative Research: RF-MEMS Phase Modulators for Millimeter-wave Polarimeter Array

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Measurements of the linear polarization of the cosmic microwave background (CMB) offer a unique probe of the early universe. The currently most-successful model of modern cosmology includes an epoch of rapid expansion of space-time shortly after the Big Bang. Gravity waves, excited during this inflationary epoch, propagate through the universe and interact at much later times to impart a distinctive polarization pattern to the CMB. Detection of this gravity-wave signature would have profound consequences for both cosmology and high-energy physics. Not only would it establish inflation as a physical reality, a detection would test physics at energies above 10^15 GeV, more than 12 orders of magnitude beyond what is accessible in particle accelerators, yielding new insight into the nature of Grand Unification and quantum gravity.The predicted polarization signal in the CMB is weak and its measurement complicated by much brighter emission from the Milky Way galaxy. To effectively separate these two components, measurements must be accurate and made over a wide range in frequency. One of the most promising techniques for efficiently measuring the polarization of the CMB is in constructing many-pixel, integrated polarimeter arrays in which the signal in each channel is "chopped" electrically between opposing polarization states on time scales (~100 Hz) much shorter than those associated with the observing conditions. To date, these integrated polarimeters have lacked one key item: low-capacitance, low-insertion loss switches that can operate at cryogenic temperatures for long periods of time.The MEMS devices to be developed by PI's Barker and Kogut are Micro-Electro-Mechanical switches that appear to satisfy all of the necessary criteria for completing these "polarimeters on a chip". Central to this specialized effort is the combination of state-of-the-art development facilities at the University of Virginia Microfabrication Laboratories and the Detector Development Laboratory at NASA's Goddard Space Flight Center. Together these facilities enable fabrication and cryogenic testing of sophisticated electrical networks operating at frequencies up to 250 GHz.Going beyond the development of a technique for obtaining fundamental information about the early history of our Universe, the work to be carried out under this award will involve graduate and undergraduate students in the science and engineering of mm-wave instrumentation and produce new technologies that will benefit emerging applications in the fields of remote sensing and wideband communications.