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.

Inverse problem solutions in NDE can be broadly classified as model-based approach and system-based approach. In model-based approach an accurate forward model is used in an iterative framework to provide a defect shape that minimizes the error between the measured signal and a simulated signal. However this approach results in repeated executions of a three dimensional forward model in each iteration, making it computationally demanding. This paper presents a direct approach to inversion using principles of time reversal. The feasibility of the approach is demonstrated via application to microwave NDE data. A two-dimensional finite difference time domain model for simulating the propagation of forward and time reversed wave fields is first developed. The key advantage of the approach is that it provides a model-based inversion method that is not iterative. Simulation and experimental results validating the approach are presented. © 2011 American Institute of Physics.

A miniaturised frequency selective surface (FSS) with λ0/7 x λ0/7 unit cell at the pass band centre frequency is presented for millimetre wave remote sensing. A resonant corner convoluted square ring (CCSR) is loaded with non-resonant cross dipole (CD) for tri-band spectral response. Rectangular patches integrated in the CCSR are used to optimise the coupling between the CD and CCSR to reject 50-60 GHz (B1) and 170-195 GHz (B3), and transmit 87-91 GHz (B2). The FSS fabricated on 175 μm thick quartz with 3721 unit cells indicates polarisation and angle stable transmission response.

In this work we present a microwave sensor for noncontact monitoring of liquid level at high temperatures. The sensor is a high gain, directional conical lensed horn antenna with narrow beam width (BW) designed for operation over 10 GHz - 15 GHz. Sensor design and optimization was carried out using 3D finite element method based electromagnetic (EM) simulation software HFSS®. A rectangular to circular waveguide feed was designed to convert TE10 to TE11 mode for wave propagation in the conical horn. Swept frequency simulations were carried out to optimize antenna flare angle and length to achieve better than -10 dB return loss (S11), standing wave ratio (SWR) less than 2.0, 20° half power BW (HPBW) and 15 dB gain over 10 GHz - 15 GHz. The sensor was fabricated using Aluminum and was characterized in an anechoic test box using a vector network analyzer (E5071C, Agilent Technologies, USA). Experimental results of noncontact level detection are presented for boiling water in a metal canister.

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.

An electric field sensor is fabricated on a 125 micron thick flexible dielectric substrate for electromagnetic (EM) nondestructive material inspection at 915 MHz. The sensor consists of an electrically short dipole antenna and a radio frequency (RF) diode detector connected to a pair of high impedance screen printed carbon lines. The DC component of the rectified diode voltage conveyed across the high impedance lines is measured using a data acquisition circuit. Sensor measurements are validated with simulated data for a conformal patch antenna operating at 915 MHz. Sensor performance for EM nondestructive testing (NDT) is evaluated using phantom defects in low loss dielectric slabs. Preliminary results indicate sensor utility for EM NDT and support further testing on realistic defects.

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.

Targeted heating with minimal dose to neighboring tissues is possible with intra cavitary microwave applicators as they can treat tumors within/or nearby body cavities. Here we present an intra cavitary applicator for hyperthermia treatment of gynecological cancers at 434 MHz. A 3D numerical model of the applicator with conformal patch antenna in muscle tissue is studied for rectangular patch, variations of bow tie and spiral antennas. Antenna performance is evaluated in terms of size, return loss, bandwidth, specific absorption rate (SAR) and effective field surface (EFS). Fish tailed bow tie and spiral patches exhibited ≤-25 dB return loss and ≥25 MHz bandwidth compared to other shapes. EFS of spiral antenna is larger than fish tail. However, ratio of EFS to patch area indicates larger volumetric power deposition for fish tailed bow tie. From simulation results, it can be concluded that an array of fish tailed bow tie and/or spiral patch antennas would provide adjustable heating profile with high power deposition.

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.

The feasibility of non-contact and non-destructive evaluation (NDE) of planar aerospace dielectric composites using microwave is examined in this paper. Free space microwave measurement set up includes spot focusing horns to gather the scattering parameters of the composites with the help of (Gated-thru reflect line) G-TRL calibration. The dielectric properties are studied from the measured scattering parameters to characterize the material's defective and non-defective region. Particulate reinforced composite with an air gap of 0.1 mm thickness and 10 mm width is used for validation of the technique.