Christopher I. Duff

A Millimeter-Wave Gyroelectric Waveguide Isolator

In this paper, a new type of millimeter-wave waveguide isolator is demonstrated. After developing an analytical model for a rectangular waveguide loaded with stratified media, all the modes propagating through the structure are found. Isolators are then designed by utilizing the frequency ranges where high nonreciprocal attenuation is identified. Here, an isolator is designed to work within the Ka-band by loading a WR-28 waveguide with a transversely magnetized indium antimonide (InSb) slab cooled to 77 K. Measured performance shows more than 20-dB isolation with 1-dB insertion loss, which agrees with theoretical predictions. Moreover, the effects of changing the magnetic bias (

New Microwave Antenna Structures for Treating Gastro-Oesophageal Reflux Disease (GERD)

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Observations on the sensitivity of on-wafer cascode cell S-parameter measurements due to probing uncertainties

) and adding dielectric layers above the InSb slab were analyzed theoretically and verified through measurement. Results prove the possibility of achieving high isolation using a weaker magnetic bias by topping the gyroelectric slab with dielectric layers. Nonreciprocal behavior was also demonstrated using an isolator working at 105 GHz, where simulated results show more than 33-dB isolation with 1.16-dB insertion loss. The results presented in this paper could pave the way toward the realization of nonreciprocal components working in the submillimeter-wave and terahertz frequency ranges, where the performance of the classical ferrite device deteriorates.

Active Millimeter-Wave Radiometry for Nondestructive Testing/Evaluation of Composites—Glass Fiber Reinforced Polymer

The design and initial pre-clinical evaluation of microwave traveling-wave antenna structures to deliver high-frequency microwave energy with controlled depth of penetration of the electric field to produce controlled ablation around the inner wall of the oesophagus (confined to the mucosal layer) at the junction between the stomach and the oesophagus is described in this paper. The structures were fabricated using flexible microwave substrates to enable them to be attached to the outer wall of oesophageal balloons for introduction into the oesophagus. It is shown that the uniform electromagnetic field produced along the length of the structure produces controlled circumferential tissue ablation, which could be used to tighten the muscles in the lower oesophageal sphincter, where the stomach connects to the oesophagus, to reduce or eliminate regurgitation and acid exposure to the oesophagus, a condition known as gastro-oesophageal reflux disease. This paper also presents the results obtained from in-vitro tissue studies and initial in-vivo work carried out using the porcine model. This is the first study to assess the use of microwave energy to treat medical conditions associated with the oesophagus.

Broadband THz imaging of composite materials

On-wafer probing accuracy limitations affect measurement repeatability for potentially unstable circuits. Here we present a 2×25 μm pHEMT cascode cell on 2 mil GaAs substrate measured from 0.045-110 GHz. The S-parameter measurements carried out for the same device using two different on-wafer measurement systems, one PNA based (Sys-1) and the other a 8510XF VNA (Sys-2), differed by up to 2 dB in gain above 50 GHz. Measurements were performed using a Cascade Microtech probe station after applying on-wafer LRRM calibration on WINCAL XE using the same set of standards. Sys-1 used Cascade infinity probes; Sys-2 Cascade ACP probes. A maximum difference in measured gain of 1.1 dB at 85 GHz was observed with variation in probe position. As |S22| for the cascode configuration is > 1, measured gain is highly sensitive to the output termination. The extra pad metallization due to differing probe position was modeled as a negative shunt capacitance (-5 fF), effectively de-embedding the extra pad capacitance.

A Q-band gyroelectric waveguide isolator

Manufacture and in-service assessment of composite materials can be challenging since there is, yet, no standard method for testing them. Nevertheless, regular inspection is necessary to maintain the structural integrity. This paper describes a nondestructive, broadband noise mapping method that uses a millimeter-wave radiometer to detect defects in composite materials. The

Electrosurgical ablation apparatus and a method of ablating biological tissue

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Nondestructive Testing of Thermal Barrier Coated Turbine Blades Using Microwave Techniques

-band system is configured for transmission mode measurement in which an amplified photonic source illuminates a glass fiber reinforced polymer containing machined defects. A high sensitivity radiometer is used for imaging the sample. The radiometer consists of a Schottky diode-based frequency tripler and a fundamental mixer.

Cascode cell analysis for ultra-broadband GaAs MMIC component design applications

Imaging composite materials is a challenging task due to the continual improvement in material quality and inspection demands. This paper describes a novel broadband THz noise mapping technique that performs active imaging of composite materials. The transmission measurement consists of an amplified photonic noise source to illuminate the sample and a W-band Schottky diode based radiometer to obtain the intensity profile as a function of scan position. The experimental set-up and preliminary results are presented.

Microwave nondestructive evaluation of thermal barrier coated turbine blades using correlation analysis

This paper presents a waveguide isolator working in the Q-band by utilising the gyroelectric effects of magnetised semiconductors. After developing an exact mathematical approach for analysing a rectangular waveguide loaded with layered media, the complex propagation constants for a WR-22 waveguide loaded with an Indium Antimonide (InSb) slab at 77 K are calculated. It is found that the structure exhibits strong nonreciprocity for a range of frequencies when the InSb is biased with a specific D.C. magnetic flux. This behaviour is then utilised to design an isolator working at 48 GHz by magnetically biasing the InSb with a D.C. magnetic flux of 0.6 T. Next, the performance of this isolator is verified via simulation and measurements, and both resulted in more than 21 dB isolation at the frequency of operation. Unlike classical ferrite nonreciprocal devices, the operation of the gyroelectric devices can be extended up to the THz frequency ranges. This potential is demonstrated here by proposing another isolator to work at 143 GHz by loading a 4 mm long WR-06 waveguide with InSb slab at 77 K, and biasing it with a magnetic flux of 0.15 T. Simulation results show more than 30 dB isolation at the frequency of operation, which prove the advantages of utilising the gyroelectric effects in designing compact millimetre and sub-millimetre wave waveguide isolators.