A new microwave exposure system for biological experiments with well-defined exposure conditions and improved control of the exposure parameters consisting of variable frequency power source, coaxial to waveguide transition, matching network and single-mode resonant cavity with movable shorting plunger was fabricated and characterized. The introduction of a biological sample into a resonant cavity has a large impact on its field configuration and port impedance. As such, the properties, geometry and position of the biological sample become a part of the electrical properties of the microwave circuit. With that change, the electrical properties of the resonant cavity, such as impedance, quality factor and resonant frequency, also change. In this study, an appropriate coupling system with effective power transfer and an algorithm to tuning and coupling of resonant cavity in resonance before and after the introduction of biological sample have been proposed. This procedure will lead to a known dose distribution within the biological sample and allow a better comparison with other studies. Coupling of the electromagnetic energy into a resonant cavity was experimentally investigated. Graphical representation of cavity impedance in case of undercoupled, critically coupled and overcoupled cavity has been presented. Critical coupling of an empty resonant cavity has been accomplished at voltage standing wave ratio (VSWR) 1.01, at resonance frequencies 900 and 947.5 MHz. Critical coupling with the introduction of a biological sample has been accomplished at VSWR ≤ 1.07 for frequency bandwidth 1 MHz and VSWR ≤ 1.5 for frequency bandwidth up to 5 MHz with central frequency 947.5 MHz.
During the past decade, cold plasma sources have gained much attention regarding sources operating at atmospheric pressure. The preferred plasma device to this point has been dielectric barrier discharges. In this work, we present well-known surface-wave-sustained microwave discharge operating at 2.45 GHz. This atmospheric pressure plasma torch can sustain low wall thickness, and dielectric permittivity) vary temperature and length of discharge. The purpose of this work is to precisely determine the working conditions at which this plasma source can be used in direct contact with biological objects.
The purpose of this work was to investigate the impact of user's positions in close space over the variations of SAR distribution in human head induced from mobile phone under the worst case conditions. The ''worst case'' considered in this paper refers to conditions that include (1) a half-wavelength dipole antenna, placed near the model of human head-SAM phantom; (2) a vertically oriented dipole antenna, parallel to the side walls of closed space for maximum reflection; (3) metallic closed space acts as a resonant cavity; and (4) 360 randomly selected observation points. We also used a free space model for comparative purposes. The maximum 1-and 10-g average SAR and average SAR in whole-exposed object probability density function curves have been derived to illustrate the percentage of SAR values that have been induced inside SAM for different locations of user in the closed space. The obtained results show that in more than 86.7% of all investigated user's positions in the metallic closed space, the induced maximum 1-g average SAR in user's head is in the boundaries of ±10% of maximum 1-g average SAR, when the user use mobile phone in free space. This relationship keep still at maximum 10-g average SAR, where in 85.9% from all investigated user's positions, SAR values are in boundaries of ±10% of maximum 10-g average SAR in free space. The results showed that closed space causes more significant changes on average SAR in wholeexposed object than maximal SAR values. When we estimated the average SAR in whole-exposed SAM in 85% from all investigated user's position in closed space, the induced SAR is higher than SAR values in free space model. It can be noted that the highest obtained SAR values in closed space were with 8.5% (for 1 g), 6.7% (for 10-g average SAR), and 15.1% (for average SAR in whole SAM) higher than these of the free space.
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