Numerical Optimization of an Open-Ended Coaxial Slot Applicator for the Detection and Microwave Ablation of Tumors

A multiobjective optimization method for a dual-mode microwave applicator is proposed. Dual-modality means that microwaves are used apart from the treatment, and also for the monitoring of the microwave ablation intervention. (1) The use of computational models to develop and improve microwave ablation applicator geometries is essential for further advances in this field. (2) Numerical electromagnetic–thermal coupled simulation models are used to analyze the performance of the dual-mode applicator in liver tissue; the sensitivity evaluation of the dual-mode applicator’s sensing mode constrains the set of optimal solutions. (3) Three Pareto-optimal design parameter sets are derived that are optimal in terms of applicator efficiency as well as volume and sphericity of the ablation zone. The resulting designs of the dual-mode applicator provide a suitable sensitivity to distinguish between healthy and tumorous liver tissue. (4) The optimized designs are presented and numerically characterized. An improvement on the performance of previously proposed dual-mode applicator designs is achieved. The multiphysical simulation model of electromagnetic and thermal properties of the applicator is applicable for future comprehensive design procedures.

Evaluation of Microwave Applicator Design on Electromagnetic Field Distribution and Heating Pattern of Cooked Peeled Shrimp

Non-uniform temperature distribution within solid food is a major problem associated with microwave heating, which limits industrial applications. Therefore, an experimentally validated 3D model was proposed to study the effect of microwave applicator geometry on the electromagnetic field distribution and heating pattern of shrimp under different processing conditions. Simulation results were compared with physical experiments, in which a cooked peeled shrimp sample was heated using two different laboratory-scale microwave applicators (rectangular and cylindrical cavities). For the rectangular applicator, the temperature distribution within the shrimp, when examined in cross-section, was more homogeneous compared to that of the cylindrical applicator. The results showed the influence of the complex shape of the food on the temperature distribution during microwave heating, as well as of process parameters (input power and geometry cavity). Moreover, this modelling method could provide a better understanding of the microwave heating process and assist manufacturing companies to evaluate a suitable microwave applicator according to their specific purpose.

On microstructural and mechanical properties of 21-4-N nitronic steel joint developed using microwave energy

In the current experimental work, an effort has been made to explore the feasibility of fusion joints of 21-4-N nitronic steel employing microwave heating. These fusion joints were developed inside a domestic microwave applicator operating at 900 W. Microwave energy was used to fabricate the joints in hybrid heating mode by converting electromagnetic energy into heat at 2.45 GHz. Charcoal and SiC plates were used as susceptor and separator, respectively, and nickel powder was used as the interface material. The developed joints were characterized for their microstructural and mechanical properties. The microstructures indicate a complete fusion of nickel interfacing powder with the faying surfaces. XRD results show the formation of metallic nitrides and carbide phases (Cr2N, Fe3N, and Fe2C) and the FeNi phase at the weld zone. Furthermore, the observed average tensile strength of the fusion joints was approximately 61% of base metal. The reduction in the stress and elongation compared to the base metal were 38.67% and 12.68%, respectively. The average microhardness of the microwave joints was monitored as 407 ± 69.27 HV. The results indicate the feasibility of fusion joints of nitronic steel using microwave energy.

Investigation of Microwave Ablation Process in Sweet Potatoes as Substitute Liver

The microwave ablation technique to destroy cancer tissues in liver is practiced clinically and is the subject of ongoing research, e.g., ablation monitoring. For studies, liver tissue from cattle or pigs is often used as a substitute material. In this work, sweet potato is presented as an alternative material for microwave ablation experiments in liver due to similar material properties. Sweet potatoes as a substitute for liver have the advantages of better handling, easy procurement and stable material properties over time for microwave ablation experiments. The dielectric constant and electrical conductivity of sweet potato are characterized for temperature variation with the help of high-temperature dielectric probe. Furthermore, a test setup is presented for microwave ablation experiments in which a bowtie slot antenna matched to sweet potato is placed on its surface to directly receive the microwave power from a self-developed microwave applicator inserted into a sweet potato 4 cm below the surface antenna. A high-power source was used to excite the microwave powers up to 80 W and a spectrum analyzer was used to measure the signal received by the surface antenna. The experiments were performed in an anechoic chamber for safety reasons. Power at 50 W and 80 W was stimulated for a maximum of 600 s at the 2.45 GHz ISM band in different sweet potato experiments. A correlation is found between the power received by the surface antenna and rise of temperature inside sweet potato; relative received power drops from 1 at 76 ∘C to 0.6 at 88 ∘C (max. temperature) represents a 40% relative change in a 50 W microwave ablation experiment. The received power envelope at the surface antenna is between 10 mW and 32 mW during 50 W microwave ablation. Other important results for 10 min, 80 W microwave ablation include: a maximum ablation zone short axis diameter of 4.5 cm and a maximum ablation temperature reached at 99 ∘C, 3 mm away from the applicator’s slot. The results are compared with the state of the art in microwave ablation in animal liver. The dielectric constant and electrical conductivity evolution of sweet potato with rising temperature is comparable to animal liver in 50–60 ∘C range. The reflection loss of self-developed applicator in sweet potato is below 15 dB which is equal to reflection loss in liver experiments for 600 s. The temperature rise for the first 90 s in sweet potato is 76 ∘C as compared to 73 ∘C in liver with 50 W microwave ablation. Similarly, with 80–75 W microwave ablation, for the first 60 s, the temperature is 98 ∘C in sweet potato as compared to 100 ∘C in liver. The ablation zone short-axis diameter after 600 s is 3.3 cm for 50 W microwave ablation in sweet potato as compared to 3.5 cm for 30 W microwave ablation in liver. The reasons for difference in microwave ablation results in sweet potato and animal liver are discussed. This is the first study to directly receive a signal from microwave applicator during a microwave ablation process with the help of a surface antenna. The work can be extended to multiple array antennas for microwave ablation monitoring.

Processing strategy for high strength Ni-based hybrid composite clad on SS 316L steel through microwave heating

Processing of nickel-based high strength composites and alloys is a difficult and thought-provoking task. In this work, a strategy of heating through microwaves radiation is utilized to process the high strength hybrid Ni-based composite clad on SS 316L steel surface containing 15% (WC-8Co) and 5% Mo. The premixed composite powder was placed on the steel surface and irradiated with domestic microwave applicator having 2.45 GHz fixed frequency and 900 W power. The hybrid clad was successfully developed within 12–15 min of microwave exposure. The processed clad was subjected to various metallurgical and mechanical characterizations to understand the microstructures and phase changes. Microstructural analysis study revealed that the clad of ∼0.85 mm thickness was obtained and presence of dispersed reinforced particles of WC-8Co and Mo in nickel matrix were observed. Some inter-metallic phases of W2C, Ni2Mo4C, Ni4W and NiSi2 were observed in the clad. The average microhardness of the composite clad was712 ± 58 HV. The microwave processed clad exhibited a flexural strength of 852 ± 6 MPa with deformation index of 35 × 10−5 mm/N. Further, the sliding wear study revealed that the sliding velocity of 1.0 m/s favoured the formation of oxide tribo layers. The various mechanisms of wear revealed by the analysis of worn-out surfaces were abrasion, adhesion, surface pull-out and deformation of surfaces. The microwave processed clad revealed significant improvement in wear resistance in comparison to the steel substrate.