Microwave Endometrial Ablation (MEA) is a technique that can be used for the treatment of abnormal uterine bleeding. The procedure involves sweeping a specially designed microwave applicator throughout the uterine cavity to achieve an ideally uniform depth of tissue necrosis of between 5 and 6mm. We have performed a computer analysis of the MEA procedure in which finite element analysis was used to determine the SAR pattern around the applicator. This was followed by a Green Function based solution of the Bioheat equation to determine the resulting induced temperatures. The method developed is applicable to situations involving a moving microwave source, as used in MEA. The validity of the simulation was verified by measurements in a tissue phantom material using a purpose built applicator and a calibrated pulling device. From the calculated temperatures the depth of necrosis was assessed through integration of the resulting rates of cell death estimated using the Arrhenius equation. The Arrhenius parameters used were derived from published data on BHK cells. Good agreement was seen between the calculated depths of cell necrosis and those found in human in-vivo testing.
Microsulis, in conjunction with the University of Bath have developed a set of novel microwave applicators for the ablation of soft tissues. These interstitial applicators have been designed for use in open surgical, laparoscopic and percutaneous settings and range in diameter from 2.4 to 7 mm. A 20 mm diameter flat faced interface applicator was developed as an adjunct to the open surgical interstitial applicator and has been applied to the treatment of surface breaking lesions in hepatobiliary surgery. Taken as a complete tool set the applicators are capable of treating a wide range of conditions in a safe and efficacious manner.
The modality employs a radiated electromagnetic field at the allocated medical frequency of 2.45 GHz and powers between 30 and 150 Watts. Computer simulations, bench testing, safety and efficacy testing, ex-vivo and in-vivo work plus clinical trials have demonstrated that these systems are capable of generating large volumes of ablation in short times with favourable ablation geometries. Clinical studies have shown very low complication rates with minimal local recurrence. It is considered that this modality offers major advantages over currently marketed products.
The technique is considered to be particularly safe as it is quick and there is no passage of current obviating the requirement for grounding pads. Since the microwave field operates primarily on water and all soft tissues with the exception of fat are made up of approximately 70% water the heating pattern is highly predictable making repeatability a key factor for this modality.
The fabrication of air-filled rectangular metal-pipe waveguide using a lithographically-based technique has recently been reported. This type of waveguide, together with other passive components such as antennas, couplers, mixers and filters may offer a realistic route to terahertz frequency integrated circuits in view of the compatibility of the fabrication technique with those of standard semiconductor processing. In this contribution, we report the fabrication of a range of waveguide components for operation at frequencies of up to 300 GHz. These measurements represent the highest frequency characterization study so far reported for a micromachined passive structure of this type and provide proof of TE<SUB>10</SUB> propagation with the expected cut-off frequency. Numerous measurements have been taken using G-band (WR-F) guide which show an attenuation loss of approximately 0.6 dB per guide wavelength at 200 GHz. This low value of attneuation shows that these micromachined waveguide are viable components for use in integrated circuits at terahertz frequencies. The insertion loss repeatability (due to mismatch effects at the ports of the waveguides) has been measured and has been shown to be better than plus or minus 0.5 dB. Preliminary results are presented for J-band (WR-3) waveguide which clearly shows the cut off frequency.
A new technique is reported for micro-machining millimeter and submillimeter-wave rectangular waveguide components using an advanced thick film UV photoresist known as EPON<SUP>TM</SUP> SU-8. The recent introduction of this resist has been of great interest to the millimeter-wave and terahertz micro-machining communities, as it is capable of producing features up to 1 mm in height with very high aspect ratios in only a single UV exposure. It therefore represents a possible low-cost alternative to the LIGA process. S-parameter measurements on the new rectangular waveguides show that they achieve lower loss than those produced using other on-chip fabrication techniques, they have highly accurate dimensions, are physically robust, and cheap and easy to manufacture.
We report on the work being undertaken at Bath University in collaboration with British Aerospace on subharmonic mixers using planar GaAs diodes. This project has been underway for several years but recent results at 160 GHz using air-bridged diodes are very promising. We shall present these results together with our most recent work on the modelling of subharmonic mixers.