Linear Applications Research Articles

Rotationally Adjustable Hyperthermia Applicators: A Computational Comparative Study of Circular and Linear Array Applicators.

Microwave breast hyperthermia (MH) aims to increase the temperature at the tumor location with minimal change in the healthy tissue. To this end, the specific absorption rate (SAR) inside the breast is optimized. The choice of the MH applicator design is important for a superior energy focus on the target. Although hyperthermia treatment planning (HTP) changes for every patient, the MH applicator is required to be effective for different breast models and tumor types. The linear applicator (LA) is one of the previously proposed applicator designs with linearly arranged antennas; however, it suffers from low focusing ability in certain breast regions due to its unsymmetrical geometrical features. In this paper, we propose to radially adjust the LA to obtain alternative excitation schemes without actually changing the applicator. Antipodal Vivaldi antennas were utilized, and the antenna excitations were optimized with particle swarm optimization (PSO). The comparison of the rotated and the fixed linear applicator, between 12-antenna circular and linear applicators, and finally, between a 24-antenna circular applicator are provided. Within the 12 rotation angles and two target locations that were analyzed, the 135° axially rotated linear applicator gave a 35% to 84% higher target-to-breast SAR ratio (TBRS) and a 21% to 28% higher target-to-breast temperature ratio (TBRT) than the fixed linear applicator. For the deep-seated target, the 135° rotated linear applicator had an 80% higher TBRS and a 59% higher TBRT than the 12-antenna circular applicator, while the results were comparable to the 24-antenna circular applicator.

Circuit model based predistortion technique for linear frequency modulation of voltage controlled oscillator

A voltage controlled oscillator (VCO) is a key component in a frequency modulated continuous wave reflectometer. The linear frequency modulation (LFM) of the VCO has been implemented by predistorting the tuning voltage waveform or by feedback control of the output frequency based on a phase locked loop. The latter has a better linearity but the frequency sweep rate is limited. The former has a relatively poor linearity but has the capability of a fast frequency sweep. In this paper, the predistortion technique is sophisticated to improve the linearity in applications of very fast LFM. The voltage waveform predistorted based on the static characteristics of VCO does not eliminate the nonlinearity completely because VCO’s behavior gets deviated from the static characteristics as the frequency sweep rate increases. The dynamic characteristics of the VCO are obtained by modeling the equivalent circuit inside the VCO as a low pass filter and simulating the circuit response numerically. The calculated voltage waveform is driven by an arbitrary waveform generator, and the output frequency of the VCO is experimentally measured to demonstrate the accuracy of the LFM. The techniques for frequency measurement and frequency linearization are described in detail and the results are presented.

An $E$ -Band Analog Predistorter and Power Amplifier MMIC Chipset

An analog predistorter and power amplifier (PA) MMIC chipset has been designed to improve the overall linearity for applications in wireless communication at the $E$ -band. The circuits have been implemented in a commercial 0.1 $\mu \text{m}$ InGaAs pHEMT process. The PA delivers an output referred 1-dB gain compression (OP1 dB) of 24 dBm, saturated output power of 27 dBm, and OIP3 of 32 dBm between 71 and 76 GHz. In combination with the analog predistortion circuit, the combined chipset improves carrier to third-order intermodulation ratio by 20 dB at an average output power of 21 dBm and at the same time increasing the OP1 dB by 2 dB to 26 dBm.

A Study of the Separation Efficiency in the Concentric-Tube Countercurrent Separation Process under Generalized Linear Applied Fields and with Recycles at Both Ends

Abstract The mathematical model for the separation of binary mixtures has been extended to a concentric-tube continuous-contact countercurrent column under generalized linear external fields and with recycles at both ends. An analytical solution is obtained by use of the orthogonal expansion method. Numerical results for separation in a thermal diffusion column are also illustrated.