Robert Sainati

An inverted-microstrip resonator for human head proton MR imaging at 7 tesla

As an extension of the previously developed microstrip transmission line (MTL) RF coil design, a high-frequency RF volume coil using multiple inverted MTL (iMTL) resonators for human head imaging at high magnetic field strength of 7 tesla (T) is reported. Compared to conventional MTL resonators, iMTL resonators can operate at higher frequency with lower losses and, thus, are suitable for designs of high-frequency RF volume coils with large coil size for human MR imaging and spectroscopy at high fields. An approach using capacitive terminations was analyzed and applied to the design of the iMTL volume coil for improving RF field homogeneity and broadening frequency-tuning range. A performance-comparison study was conducted between the prototype iMTL volume coil and a custom-built TEM volume coil at 7 T. The iMTL volume coil presents a comparable SNR and intrinsic B/sub 1/ homogeneity to the TEM volume coil. Phantom and the human head images acquired using the iMTL volume coil are also presented. The proposed iMTL volume coil provides an efficient and alternative solution to design high-frequency and large-size volume coils for human MR applications at very high fields.

Analog/RF physical layer issues for UWB systems

Ultra-wideband communications systems offer unique challenges and opportunities for RF circuit design. Proper understanding of the trade-offs that system specifications impose upon the circuit designer is essential in optimizing a system for UWB. The defining attribute of UWB is the wide fractional bandwidth of the signal. This wide bandwidth can be achieved in several ways: with carrierless systems, with a wide-bandwidth single carrier spread-spectrum system, with a multi-carrier system such as OFDM, via frequency hopping, or via some combination of these methods. This paper provides detailed impact analysis of wide fractional bandwidth on RF frontend circuits and examines the various tradeoffs. In particular, wide-bandwidth channels limit the instantaneous Q allowable in the signal path. This requires modifications of the traditional narrowband design methods. Some of the issues discussed in this paper include: issues of broadbanding, power impact, fast hopping tradeoffs, power amplifier, and antenna issues.

Comparative analysis of frequency selective surface geometry effect in Fabry-Perot Cavity antenna design

Fabry-Perot Cavity (FPC) antenna using a single radiating element with different frequency selective surface (FSS) is presented. The FSS designs are rectangular and square unit cells with rectangular and circular openings, respectively. A slot antenna is used as a primary source in the FPC antenna and the system is designed to operate in X-band. The effect of each FSS geometry on the radiation pattern of the source is investigated.

Microfluidic Near-Field Beam-Splitting Frequency Selective Surface for Fabry-Perot Cavity Antenna System

A microfluidic Fabry-Perot Cavity (FPC) antenna system is presented with split beam in the near-field. For this purpose, fluidic housing, which is made of polydimethylsilone (PDMS), is used and integrated into the FPC system. The FPC system consists of a slot antenna and frequency selective surface (FSS). Two FSS designs with rectangular apertures are considered: augmented and microfluidic FSS arrays. Each is designed, modeled, and tested for comparison in the FPC system.

Parametric study of near- and far-field performance of the Fabry-Perot cavity antenna system

This paper discusses the effects of varying the design parameters of the cavity or rectangular aperture in the frequency selective surface (FSS) of a Fabry-Perot Cavity (FPC) antenna system. The FPC system is excited by a coplanar-waveguide (CPW)-fed slot antenna. Theoretical results of the near-field distribution and far-field radiation pattern for each variation are shown to investigate the impact of the cavity height and FSS design parameters on the system.

Fabry-Perot Cavity antenna system with beam-splitting of near-field radiation

This paper describes the design and behavior of a Fabry-Perot Cavity (FPC) antenna system with split beam in the near-field and decreased beamwidth of the far-field pattern. The FPC antenna system is a coplanar waveguide (CPW)-fed slot antenna with 9 × 27 rectangular aperture unit cells in the frequency selective surface (FSS) oriented in horizontal and vertical directions. The far-field response has 3dB beamwidth of 21° and gain of 12.84 dBi at 11.2 GHz.

Reconfigurable frequency selective surface for fabry-perot cavity antenna system

This paper presents reconfigurable Fabry-Perot Cavity (FPC) antenna systems to switch one mode to other with respect to near- and far-field performance. The fluidic channel is created and integrated into the FPC system. The channel is filled with air or deionized (DI) water. The fluidic FPC systems are compared to a fixed FPC design without the fluidic housing. Simulation and measurement results are presented and discussed.

Analysis of coplanar waveguide feedline effect on Fabry-Perot Cavity antenna system performance

The effect of a coplanar waveguide (CPW) feedline on a Fabry-Perot Cavity (FPC) antenna system is investigated and the technique of mitigating feedline behavior in the FPC system is proposed. The FPC antenna system consists of a lumped-port excitation or coplanar waveguide (CPW)-fed slot antenna and frequency selective surface (FSS). The near-field distribution and far-field radiation patterns are assessed and discussed.

Fluidic switching and tuning of Fabry-Perot antenna

A Fabry-Perot Cavity (FPC) antenna with an integrated fluidic channel is proposed. The channel housing is filled with air or deionized (DI) water. The fluidic channel provides the control of the resonant frequencies of the FPC antenna and makes the antenna switch on/off. A tunable range is from 10.4GHz to 7.3GHz and from 11.7GHz to 11.1GHz when DI water is injected into the channel. The effects of the air and DI water in the FPC design are investigated.