There is a need to develop low-cost and compact frequency reconfigurable antennas with continuous tuning capability. Existing approaches rely on dedicated electrical, mechanical, or MEMS-based reconfigure the antenna, which requires extra components fabrication steps. In this paper, we propose physics-based approach realize tunable helical based shape memory alloy (SMA). By utilizing temperatur...

A radio frequency identification (RFID) system consists of a reader, a writer, and a tag. Filmtype half-wavelength dipole antennas (shown in Fig. 1.1) have been used as tag antennas in many applications [1]. The antenna performance is governed by the electric current in the tag. When the abovementioned antenna is mounted on the surface of a metallic object, the radiation characteristics are ser...

Plasma densities produced by halfand full-wavelength (HW and FW) helical antennae in helicon discharges are compared. It is found that HW antennae are more efficient than FW ones in producing plasma downstream from the antenna. The measured wave amplitudes and the apparent importance of downstream ionization do not agree with computations.

in this work, a design of quadrifilar helical antenna with characteristics of compact, wideband and circular polarization is presented. It is achieved by combining the ways of tuning the different dimensions of the pairs of bifilars, and a feeding structure for providing the self-phasing technique. Both of simulated and measured results are reported in this study.

We present optimization results obtained for two type of antennas using evolutionary algorithms. A quadrifilar helical UHF antenna is currently flying aboard NASA’s Mars Odyssey spacecraft and is due to reach final Martian orbit insertion in January, 2002. Using this antenna as a benchmark, we ran experiments employing a coevolutionary genetic algorithm to evolve a quadrifilar helical design in...

A novel method for excitation of RF B1 field in high-field (3-T) magnetic resonance imaging (MRI) systems using a subject-loaded quadrifilar helical antenna as an RF coil is proposed, evaluated, and demonstrated. Design, analysis, characterization, and evaluation of the novel coil when situated in a 3-T MRI bore and loaded with different phantoms are performed and cross-validated by extensive n...

The CD spectra of a range of antenna complexes from several different species of purple photosynthetic bacteria were recorded in the wavelength range of 190 to 930 nm. Analysis of the far UV CD (190 to 250 nm) showed that in each case except for the B800-850 from Chr. vinosum the secondary structure of the light-harvesting complexes contains a large amount of a-helix ( 2 5 0 % ) and very little...

A practical, small-size, dual-helical antenna array mounted on a mobile handset model is designed for use as diversity/MIMO receiving antennas. The array is rigorously studied with respect to its diversity performance and the achievable channel capacity. It is found that a very low correlation coefficient, a high diversity gain, an equal-mean branch SNR, and a relatively matched input impedance...

This paper presents results of delay spread and path loss measurements across a large college campus, and illustrates how antenna gain and polarization should be selected for line-of-sight microwave links between buildings. Two line-of-sight links were used with three different types of antennas to determine best polarizations and pointing angles. Measurements show multipath is most severe when...