A metal-mesh achromatic half-wave plate (HWP) has been designed, manufactured, and tested for potential use in millimeter and submillimeter astronomical instruments. The prototype device presented here is based on a 12-grid Shatrow [IEEE Trans. Antennas Propag. 43, 109 (1995)] recipe to operate over the frequency range of 120-180 GHz. Transmission line modeling and finite-element analysis [Ansoft HFSS website: http://www.ansoft.com/hfss/] were used to optimize the design geometrical parameters in terms of the device transmission, reflection, absorption, phase-shift, and cross-polarization as a function of frequency. The resulting prototype device was constructed and characterized using incoherent radiation from a polarizing Fourier transform spectrometer to explore its frequency and polarization behavior. These measurements are shown to be in excellent agreement with the models. Lists of the achieved HWP performance characteristics are reported.
[Show abstract][Hide abstract] ABSTRACT: The successful European Space Agency (ESA) Planck mission has mapped the
Cosmic Microwave Background (CMB) temperature anisotropy with unprecedented
accuracy. However, Planck was not designed to detect the polarised components
of the CMB with comparable precision. The BICEP2 collaboration has recently
reported the first detection of the B-mode polarisation. ESA is funding the
development of critical enabling technologies associated with B-mode
polarisation detection, one of these being large diameter half-wave plates. We
compare different polarisation modulators and discuss their respective
trade-offs in terms of manufacturing, RF performance and thermo-mechanical
properties. We then select the most appropriate solution for future satellite
missions, optimized for the detection of B-modes.
"This design uses capacitive and inductive metal-mesh geometries which each generate a frequency dependent phase shift with opposite sign. A first device fabricated from 6 capacitive grids and 6 inductive separated by air/vacuum gaps using accurately etched annular spacers demonstrated a bandwidth of 40 % (60 GHz) with a center frequency of 150 GHz . Here we describe a procedure for optimizing the design of this type of HWP and present measurements of a device fabricated with a new process using dielectric spacers between the metallized sheets fused together with a hot pressing technique to make a solid self-supporting disc . "
[Show abstract][Hide abstract] ABSTRACT: We describe a novel multilayered metal-mesh achromatic half-wave plate (HWP) for use in astronomical polarimetric instruments. The HWP is designed to operate across the frequency range from 125 to 250 GHz. The wave plate is manufactured from 12 layers of thin film metallic inductive and capacitive grids patterned onto polypropylene sheets, which are then bonded together using a hot-pressing technique. Transmission line modeling and three-dimensional electromagnetic simulations are used to optimize the parameters of the metal-mesh patterns and to evaluate their optical properties. A prototype HWP has been fabricated, and its performance is characterized in a polarizing Fourier transform spectrometer. The device performance is consistent with the modeling, although the measured differential phase shift for two orthogonal polarizations is lower than expected. This difference is likely to result from imperfect patterning of individual layers and misalignment of the grids during manufacture.
"Components fabricated using this technique have been used in a number of THz cameras and spectrometers     . More recently, the same technique has been used to manufacture half-wave plates using aligned metallic patterns with air-gap spacing between the layers . These traditional metal mesh components are not considered metamaterials because their electromagnetic properties are not independent of their thickness, i.e. they cannot be characterized as having a bulk electric permittivity and magnetic permeability. "
[Show abstract][Hide abstract] ABSTRACT: We describe a novel artificial dielectric material which has applications at
millimetre and submillimetre wavelengths. The material is manufactured from
layers of metal mesh patterned onto thin polypropylene sheets which are then
bonded together using a hot pressing process to provide planar rugged discs
which can be reliably cycled to cryogenic temperatures. The refractive index of
this material can be tuned by adjusting the geometry and spacing of the
metal-mesh layers. We demonstrate its usage by designing and characterising a
broadband anti-reflection coating for a Z-cut crystalline Quartz plate. The
coating was fabricated and applied to the quartz using the hot press technique
and characterized using a Fourier Transform Spectrometer. The performance is
shown to be in good agreement with HFSS and transmission line modelling
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