Left Handed Materials Research for Air Force Applications.

摘要

We have designed, fabricated, and measured low-loss, highly isotropic, sub-wavelength (lambda/radius approximatelky 15) single and dual- frequency antennas which operate between 1 and 2 GHz, but can be scaled to operate at higher or lower frequencies. Measurements indicate that we achieved a approximately 95% radiation efficiency while maintaining approximately 1dB gain anisotropy in phi for single frequency antennas and for the lower operating frequency of dual-frequency antennas, in agreement with simulations. For dual-frequency antennas, the higher operating frequency exhibits a lower 75-85% efficiency and somewhat higher (approximately 2%) gain anisotropy. We have optimized the sensitivity of our Varian E- 4 X-band EPR spectrometer and used it to measure potentially high Tc superconducting samples at temperatures in the range of 300K down to 4.2K. We also constructed a magnetic field coil to apply DC and modulation magnetic fields parallel to the RF magnetic field to allow us to discriminate between possible superconductivity and any paramagnetic signal which may be present in the sample being measured. Using our EPR spectrometer we have measured numerous balanced valence material samples, many of which show likely superconductivity at an onset temperature of about 17K with some having regions with possible superconducting onsets as high as 50K.