Kavitha Arunachalam

The performance of the genetic algorithm (GA) and particle swarm optimization (PSO) was compared to identify the best-suited algorithm for hyperthermia treatment planning (HTP) of breast cancer. Both algorithms were tested on four heterogeneous patient breast models derived from magnetic resonance (MR) images. Electromagnetic (EM) simulations indicate that PSO induces 5.7% less hotspot to target quotient (HTQ) compared to GA. However, coupled EM and thermal simulations of four patient models indicate that GA based HTP induces 1.25 °C - 3.87 °C higher average temperature in cancer tissue with limited thermal hotspots in healthy tissue when compared to PSO algorithm. This was observed to be due to the low power level assigned to each channel by PSO compared to GA. Coupled simulations of heterogeneous patient models indicate GA is a better global optimization algorithm for HTP of breast cancer.

In this work, we report a coaxial antenna consisting of a flexible Y-monopole with dual-band operation and low-profile wideband flexible ferrite choke for delivering localized HT treatment at shallow insertion depth of 50 mm inside the cervix using custom fabricated non-metallic intrauterine cervix tandem of 8 mm outer diameter and 1 mm wall thickness. Variable treatment coverage was achieved by selecting the excitation of the dual-band Y-monopole as 915 and 1300 MHz. The Y-monopole is a coaxial wire with a Y-split in the exposed inner conductor and wideband flexible ferrite sheet on the outer conductor to suppress the secondary current. The water loaded Y-monopole inside the intrauterine tandem cervix applicator with 15° bend angle resonated at 915 and 1300 MHz for arm lengths of 21 and 13.5 mm, respectively. The heating characteristics of Y-monopole was assessed using tissue-mimicking phantoms. Phantom measurements indicate dual band operation with power reflection coefficient $ \le - $24 dB at 915 and 1300 MHz. The measured extents of 25% axial specific absorption rate in tissue phantom at 915 and 1300 MHz is 39.4 and 28.4 mm, respectively. Localized power deposition with $\Delta T = 3 $ °C iso-contour of 46.3 mm × 39.2 mm and 37 mm × 31 mm along axial and radial directions was measured at 915 and 1300 MHz, respectively. Phantom measurements demonstrate the ability of the proposed antenna to deliver variable treatment volume to the cervix through 15° intrauterine tandem.

Patterned deposition of highly flexible transparent conducting materials is essential to realize stretchable optoelectronic devices. Silver nanowires (NWs) are suitable for these applications because they possess high electrical conductivity and good optical transparency. However, NWs have poor surface adhesion and large roughness. Embedding them in a conducting polymer, such as poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS), is one way to overcome these disadvantages without affecting the optoelectronic properties. However, this is normally a two-step deposition process and difficult to pattern directly. In this work, we have formulated a stable and printable nanocomposite ink consisting of Ag NWs and PEDOT:PSS. This ink can be directly used for patterned deposition in a single-step process. The printed film shows 86% transparency and 23 ω/sq sheet resistance, which is suitable for flexible transparent electrode applications. The printed film shows good adhesion and excellent stability to mechanical deformation, with less than 20% resistance variation after 10,000 bending cycles. The nanocomposite also exhibits improved thermal stability, planarity, reduced contact resistance, and good optical transparency when compared to pure Ag NWs. We demonstrate suitability of this nanocomposite using two applications -a printed transparent flexible antenna radiating at Wi-Fi frequencies and a printed transparent flexible heater suitable for antifogging applications. The nanocomposite properties make it suitable as a transparent electrode in flexible optoelectronic devices such as photovoltaics and light-emitting diodes.

Wire Electrical Discharge Machining (WEDM) is a specialized thermal machining process that uses electrical discharge erosion technique for conductive materials. A high potential difference across the inter-electrode gap between the wire electrode and the workpiece in the presence of dielectric fluid leads to the pulsed discharges. Several sensors have been investigated for adaptive control and monitoring of the WEDM process by detecting and classifying these discharges. The present work discusses the use of a magnetic near-field probe to detect radio frequency emissions during the machining process. Numerical modeling, fabrication, and probe characterization using Device-under-Test (DUT) have been done. The fabricated probe is able to detect the radio emissions corresponding to the pulsed discharge occurring in the inter-electrode gap.

Microwave hyperthermia makes use of microwaves to deliver heat to biological tissues. Real time temperature monitoring during treatment is important for efficacy and effectiveness of the treatment. Non-invasive methods such as CT, MR and ultrasound (US) have been actively researched for use in hyperthermia monitoring. US has inherent advantages of real-time imaging, portability and non-ionizing nature. It is also known from the literature that acoustic properties of tissue are sensitive to temperature and this has been harnessed to track the evolution of hotspot and temperature in high temperature zones encountered in ablation treatments. However, their usage in low temperature zones typically observed in hyperthermia appears to be less explored. This study introduces an improved method of regularized Kurtosis imaging (RKI) and compares its performance against regularized log spectral difference (RLSD) and regularized Nakagami imaging methods. The performance of these methods is compared against the ground truth estimated from IR thermal images in an experimental study on tissue-mimicking PAG-agar based phantoms. The error in the area estimated by RKI was 10.6%. The error in the lateral and axial co-ordinate of the centroid was 5.92% and 0.47%, respectively. The structural similarity index was 0.82 for RKI when compared with RLSD and RNI having score of 0.76 and 0.72, respectively. The results are promising and offer an alternative way to track the hotspot during microwave hyperthermia treatment.

In the context of breast cancer detection, mechanical imaging is an emerging technique for screening breast cancer. In view of its promise, it deserves a detailed investigation. Development of material that can emulate tissue behavior is essential for research. This work is concerned with the fabrication of polymeric specimens to capture the mechanical behavior of human breast tissues. Three types of tissue phantoms are fabricated: fat, glandular and ductal carcinoma tissues. The fabricated phantoms are compared to available human breast tissue data obtained through compression tests and stress relaxation tests. Further, the fabricated tissue phantoms are subjected to stress relaxation tests to characterize their viscoelastic response. A finite strain viscoelastic constitute model is proposed to describe the mechanical response of the breast tissue phantoms. The model is calibrated using experimental data for phantom tissue specimens. Both phantom tissue specimens and model predictions show reasonable trends. The phantom tissues and model may be of utility in developing mechanical imaging setups.

Micro-scale removal of Cu from a dielectric substrate has applications in microelectronics, patch antenna fabrication and frequency selective surface (FSS) manufacturing. Pulsed laser-based micro-scribing of Copper (Cu) from a dielectric is a preferred technique to avoid the adverse effects of chemical etching, such as toxicity and corrosive nature of the etchant, difficulty in fabrication of mask etc. However, pulsed laser-assisted removal of Cu from a dielectric in the air will produce recast layer/ redeposit, oxide layer near the ablation zone and thermal damage to the dielectric is another challenge. In this study, a hybrid technique with nanosecond laser-activated electrochemical micro-scribing of Cu is demonstrated. The technique was extended to remove 35 μm Cu from Rogers-RO4003 dielectric with a thickness ≈0.75 mm to fabricate FSS samples in X-band. The Cu-deposited dielectric substrate was immersed in Sodium Chloride (NaCl) solution, the laser beam was directed through a negatively biased tool electrode and the sample was biased positively. In this hybrid technique, along with laser-assisted material removal, laser-activated electrochemical etching also removed Cu selectively. The laser irradiation coupled with the NaCl solution induced preferential micro-etching, resulting in improved surface morphology without re-deposition and recast layer and thermal protection to the dielectric substrate. The FSS sample produced with the laser-hybrid micro-scribing was working at 10.3 GHz.

The paper presents the numerical design and analysis of a compact microstrip patch antenna with superstrate for medical microwave radiometry at 1.3 GHz. The antenna design was optimized to obtain at least-10 dB power reflection coefficient, 100 MHz bandwidth centered at 1.3 GHz and localized power reception from deep seated tissue in homogeneous and layered tissue models mimicking the dielectric properties of the breast. Simulation results indicate that the optimized antenna with low loss superstrate meets the design criteria for passive deep tissue thermometry.

Steam generators (SGs) used in power plants have several hundreds of ferromagnetic SG tubes which are periodically inspected using non-destructive testing (NDT) methods. Pre-service and in-service inspections of these magnetic tubes are carried out using RFEC technique for plant safety and structural integrity. In this paper, a 3D numerical model was developed for SG tube inspection using remote field eddy current (RFEC) technique. The numerical model was used to estimate the electrical properties of the SG tube using RFEC signals gathered from a SG tube with machined defects. The influence of magnetic coupling between the surrounding SG tubes on defect detection was investigated for the estimated SG tube electrical properties. Simulations in the presence of six neighbouring SG tubes were carried out for centre to centre tube spacing of 32.2 mm with respect to the centre tube. Numerical simulations for the SG tube with machined defects indicated very good agreement with measurements for tube electrical conductivity σ of 2 MS/m and relative magnetic permeability μr of 30. Numerical simulations carried out to study the influence of magnetic coupling with the surrounding SG tubes indicated negligibly small perturbation in the simulated RFEC signal for a 2D groove defect in the centre tube and no false call in the centre tube for a 2D grove defect in the neighbouring tube.

The study of ferrite sleeve for realizing electrically short choke is reported in this work for coaxial antennas used in intracavitary microwave hyperthermia treatment. Electromagnetic simulations of intracavitary applicators with the optimized ferrite sleeve operating at 700, 915, and 2450 MHz demonstrated stable resonance and targeted power deposition independent of the insertion depth when compared to their unbalanced counterparts. Thermal simulations indicated spherical heating volume for the applicators with the ferrite sleeve. Intracavitary applicator prototypes of \boldsymbol {\lambda }/\mathbf {4} and \mathbf {3\lambda }/\mathbf {8} coaxial monopoles with the optimized ferrite choke indicated return loss more than 22, 27, and 22 dB at 700, 915, and 2450 MHz, respectively, for varying insertion depths (70-130 mm) in agreement with the simulations. Local electric field measurements at 915 MHz in phantom indicated 51% and 58% reduction in 25% field contour along the antenna axis for the \boldsymbol {\lambda }/\mathbf {4} monopole with \mathbf {0}.\mathbf {24\lambda } ferrite sleeve and \mathbf {3\lambda }/\mathbf {8} monopole with \mathbf {0}.\mathbf {12\lambda } ferrite sleeve, respectively. Specific absorption rate and thermal measurements in phantoms confirm that ferrite sleeve < \boldsymbol {\lambda }/\mathbf {4} is sufficient to choke the secondary current on coaxial monopole antennas for delivering targeted power deposition at varying tissue insertion depths.