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The microwave-to-plasma energy conversion efficiency and the ease of plasma self-ignition are critical factors affecting the applications for microwave plasma sources (MPSs). This study presents a novel MPS utilizing dielectric wedges for self-ignition and improved energy conversion. Firstly, we crafted a dielectric wedge with a gradient refractive index, guiding the electric field from air to dielectric materials and facilitating microwave propagation along the dielectric in a waveguide. Through electromagnetic simulation, we explored how the size and permittivity of the dielectric wedge affect the electric field distribution. Then, the MPS based on the dielectric wedge was designed. In this configuration, a dielectric tube encloses the discharge tube, connecting to dielectric wedges to guide electromagnetic waves to the plasma. We analyzed the MPS performance using the Drude model, evaluating microwave energy conversion efficiency across various electron densities and collision frequencies. The results were compared with a commonly used MPS based on a tapered waveguide, demonstrating the proposed MPS has wider applicability across different operation conditions. Finally, experiments under low pressures were conducted using various gases, showing an average energy conversion efficiency of approximately 40% higher than the tapered waveguide MPS. The experiments also indicate the proposed MPS has a greater capability of self-ignition at lower power levels. These findings highlight the efficacy of incorporating dielectric wedges to enhance MPS performance, making it conducive for broader industrial applications. [ABSTRACT FROM AUTHOR]

Cancer is a significant disease that often results in severe side effects from traditional treatments. Microwave hyperthermia has emerged as a minimally invasive, highly effective, and low‐toxicity treatment option that has gained widespread use in recent years. The primary objective of this study is to develop and assess a miniaturized slit patch antenna designed to operate at 2450 MHz for hyperthermia therapy. The octagonal antenna patch features four symmetrical slots to reduce its size, enhance directional radiation, and improve focusing and penetration depth. Additionally, a metal cavity is incorporated at the top of the antenna to create a gap between the antenna and the skin, allowing for skin heat dissipation, improved impedance matching, reduced outgoing radiation, and enhanced directional radiation. The performance of the antenna is assessed based on specific absorption rate (SAR), penetration depth (PD), and effective field size (EFS). Subsequently, the antenna is fabricated and tested in pork tissue, with the measured results demonstrating good agreement with the simulated outcomes. [ABSTRACT FROM AUTHOR]

A compact high-power four-port circulator aiming to simplify the conventional, complex, and bulky injection-locking magnetron system is proposed. To reduce the performance deterioration and the risk of ferrite rupture under long-term high-microwave-power condition, the method of breaking a monolithic ferrite into three discrete ferrites in a conventional three-port circulator is proposed. To miniaturize the size and cost of the four-port circulator, a butterfly-shaped waveguide structure is proposed, with a stub inserted into the cavity at the central point and with no connecting waveguide. Multiphysics simulation results show that the temperature coefficient of variation (COV) at the surface of the discrete ferrites is 12.4% lower than that of a monolithic ferrite circulator, with input microwave power of 10 kW. The size of the proposed four-port waveguide circulator is 27% less than the assembly of two three-port circulators, and way smaller than a conventional differential phase shift circulator (DPSC). The simulated and measured S-parameters match well, and the measured power capacity of the fabricated circulator is higher than 3 kW (limited by the experimental condition). A magnetron is successfully locked using only one designed compact circulator. The research in this paper promotes the development of injection-locking magnetron and provides a design example for the compact, high-power circulator. [ABSTRACT FROM AUTHOR]

This study investigates the counterintuitive behaviors of a microwave‐induced atmospheric pressure plasma jet (APPJ) under the influence of an external electrostatic field applied by one or a pair of parallel electrode plates subjected to DC voltages. The findings demonstrate that the plasma jet consistently deflects toward the electrode plate with an electrostatic potential, irrespective of the direction of the applied field. The deflection becomes more pronounced with increasing voltage on the electrode plate until the ionic wind generated by the high voltage significantly affects the jet's behavior. Remarkably, a negative voltage induces a greater deflection compared to a positive voltage. To further investigate this discovery, the dielectric properties and the non‐neutral characteristics of the APPJ are analyzed, and the simulations of the electric field distribution reveal a non‐uniform distribution, which plays a crucial role in understanding the mechanism behind the observed behaviors of the plasma jet. This study provides a comprehensive understanding of the underlying mechanism driving the observed phenomena and sheds light on the collective behavior of plasma jets under non‐uniform electric fields. The findings of this study offer valuable guidelines for investigating and controlling the behavior of APPJs. [ABSTRACT FROM AUTHOR]

In this paper a low profile circularly polarized annular ring slot antenna (CPARSA) with high gain is presented. An inverted U-shaped meandered slot is cut at the inner patch of annular ring to obtain the circularly polarized (CP) radiation. This annular slot loaded ground plane on a substrate thickness of 0.5 mm results in a very low profile (0.009λ0) antenna in term of free space wavelength at its center operating frequency. The largest side lengths of octagonal shaped antenna are 0.89λ0 × 0.89λ0 according to its center frequency. Measured impedance bandwidth of 23.54% from 5.4 GHz - 7.0 GHz (for |S11| ≤ -10 dB) and AR bandwidth (AR

A novel design of a coplanar waveguide (CPW) feed antenna array with circular polarization (CP) and a high front-to-back ratio is described. The proposed CP array is achieved by using a compact CPW–slotline transition network etched in the ground plane. The measured results show that this kind of feeding method can improve the impedance bandwidth, as well as the axial ratio bandwidth of the CP antenna array and provide adequate gain. The proposed array can achieve a 6.08% impedance bandwidth and a 4.10% CP bandwidth. Details of the antenna design and experimental results are presented and discussed.

Permittivity is an important aspect of the design of microwave devices. In order to design microwave devices that are more suitable for the excitation of air plasmas, this paper presents a method for the on-line measurement of the relative permittivity of an atmospheric pressure air plasma with 2.45 GHz microwaves. First, a ridged waveguide is designed and constructed to excite the air. Using the ridged waveguide, the plasma can be excited and measured simultaneously. An artificial neural network trained with simulated data is integrated into the system to invert the dielectric constant of the air plasma being measured. At a power of 786 W and an airflow rate of 1250 L/h, the real and imaginary parts of the permittivity are obtained to be −1244 and 60, respectively. The forecasted errors on the real part and the imaginary part of the relative permittivity are kept at around 5% and 3%. The Drude model is used to construct a relationship between the electronic and dielectric properties. This diagnostic method is simple to operate and has a high degree of generality. It should be useful in the design of microwave plasma devices and can greatly improve the efficiency of microwave plasma equipment. [ABSTRACT FROM AUTHOR]