Simulation and experimental study of a K-band extended interaction oscillator for microwave processing systems.

High-power microwave sources have been widely applied for material processing in scientific research and manufacturing. The development of stable, high-frequency, high-power microwave sources is essential for achieving efficient microwave processing. This study proposes using a square doubly reentrant coupled-cavity as the slow-wave resonant structure in a K-band extended interaction oscillator (EIO). This design allows for ease of fabrication and high-power capability. The EIO is designed to operate in single 0-mode. The simulation results show that the competing π/5-mode can be effectively suppressed by properly choosing the width and location of the output coupler. The simulation and experiments successfully demonstrate stable, single-mode, tunable, high-performance operation of the EIO. The experimental measurements show a maximum output power of 1.776 kW (18.56% electronic efficiency), and a wave frequency of 24.324 GHz at a beam voltage of 17.4 kV and beam current of 550 mA. The EIO microwave source is suitable for interdisciplinary applications that require higher heating rates and greater uniformity.

High performance and high power circularly polarized horn antenna for K-band microwave processing systems.

A single-ridged K-band circularly polarized horn antenna offering excellent performance has been developed by improving the polarization conversion and manufacturing complexity. The numerical and experimental results are consistent showing the return loss of this antenna to be less than -20 dB and the axial ratio at the boresight direction to be less than 0.7 dB in the frequency range from 23.5 GHz to 24.5 GHz. In addition, the gain of this antenna is higher than 20 dB. The newly designed circularly polarized horn antenna has a simple structure and outperforms many existing circular polarization devices in high-power operations.

A microwave applicator for uniform irradiation by circularly polarized waves in an anechoic chamber.

Microwave applicators are widely employed for materials heating in scientific research and industrial applications, such as food processing, wood drying, ceramic sintering, chemical synthesis, waste treatment, and insect control. For the majority of microwave applicators, materials are heated in the standing waves of a resonant cavity, which can be highly efficient in energy consumption, but often lacks the field uniformity and controllability required for a scientific study. Here, we report a microwave applicator for rapid heating of small samples by highly uniform irradiation. It features an anechoic chamber, a 24-GHz microwave source, and a linear-to-circular polarization converter. With a rather low energy efficiency, such an applicator functions mainly as a research tool. This paper discusses the significance of its special features and describes the structure, in situ diagnostic tools, calculated and measured field patterns, and a preliminary heating test of the overall system.

Efficient heating with a controlled microwave field.

To uncover the intriguing non-thermal microwave effect, an experiment was conducted using an amplifier rather than an oscillator as the radiation source, which was injected into an applicator with strong electromagnetic field enhancement. The characteristics of the applicator are discussed and the enhancement of the microwave field is illustrated and explained. Thermal distribution is simulated based on the calculated microwave field profile. It was demonstrated that the proposed system heated a SiC susceptor to a temperature of 637 °C with the input power of 60 W. The reasons for such an efficient heating are discussed.

Drug release from interpenetrating polymer networks based on poly(ethylene glycol) methyl ether acrylate and gelatin.

In order to develop new materials for biomedical and pharmaceutical applications, interpenetrating polymer networks (IPNs) based on poly(ethylene glycol) methyl ether acrylate (PEGMEA) and gelatin were synthesized. These two materials were cross-linked sequentially using N,N'-methylene bisacrylamide (NMBA) and glutaraldehyde (Glu). Two series of IPNs gels were synthesized by applying different amounts of PEGMEA and gelatin in the initial feed. Sequential IPNs were prepared by polymerizing and cross-linking PEGMEA in the presence of gelatin using redox initiators (e.g., ammonium peroxydisulfate (APS) and N,N,N',N'-tetramethyl ethylenediamine (TEMED)), as well as NMBA as the cross-linking agent. Gelatin in firm gel was then cross-linked with 1% glutaraldehyde. The swelling kinetics, mechanical properties and drug-release behavior of these IPNs were analyzed. The surface properties were examined by scanning electron microscopy. The results indicated that the swelling ratio decreased with an increase in the content of both PEGMEA and gelatin in the IPNs. PEGMEA/gelatin-based full-IPNs had a significantly higher shear modulus (G) and cross-linking density (rho) when the content of PEGMEA was increased. The drug loading was very high due to the full-IPN structure. The drug-release velocity was mainly affected by the content of PEGMEA.