Huacheng Zhu

Fast algorithm for electromagnetic pulse heating on dispersive medium

In this paper we present a fast time-domain algorithm to study the electromagnetic pulse heating on dispersive medium. Using the proposed fast algorithm, the long heating process can be compressed by accelerating thermal conduction and scaling the power dissipation density. Comparing with the previous computation of several pulse periods, the proposed algorithm can deal with the heating process up to billions of pulse periods. Besides, employing the proposed algorithm, we study a 2D water post heated by electromagnetic pulses. The results reveal that comparing with continuous microwave heating, pulse heating cannot improve temperature uniformity or enhance heating efficiency.

Study on stability of electric field in multimode microwave heating cavity

Microwave heating has been widely used and the heating uniformity is related to the characteristics of electric field. In this paper, we investigate the stability of electric field in a multimode microwave cavity by analyzing the spectrum and the condition number of integral equation. Results show that the stability of the electric field is mainly dependent on microwave frequency, the permittivity of heating object and cavity geometrical parameters. Particularly, when the heating object has a low loss factor, the electric field is generally unstable. Namely, a tiny shift of the parameters mentioned above will result in dramatic changes of electric field distribution. Besides, the instability of the electric field increases with the lower loss, the higher microwave frequency or the larger permittivity of the heating object.

Power-combining based on master–slave injection-locking magnetron*

A microwave power-combining system composed of two Panasonic 2M244-M1 magnetrons based on master–slave injection-locking is demonstrated in this paper. The principle of master–slave injection-locking and the locking condition are theoretical analyzed. Experimental results are consistent with the theoretical analysis and the experimental combined efficiency is higher than 96%. Compared with the external-injection-locked system, the power-combining based on the master–slave injection-locking magnetron is superior by taking out the external solid-state driver and the real-time phase control system. Thus, this power-combining system has great potential for obtaining a high efficiency, high stability, low cost, and high power microwave source.

Bivariate characterization and measurement for effective permittivity of esterification reactions at 2450 MHz for multiphysics simulation

The aim of the present work is to obtain effective permittivity of the reaction mixture during esterification reac- tions that can be used in a dynamic simulation environment and analysis the dielectric properties during the reaction process. Microwave heating serves as an excellent tool for carrying out such reactions and the multiphysics simulations need effective permittivity as one of the most important inputs. In this work, we perform the esterification reaction between ethanol, acetic acid and butyric acid using a temperature cycle in order to measure the effective permittivity of the reaction mixture. The ob- tained result is fitted using a bivariate function of the concentration of one of the products of the reaction and temperature of the mixture. The computed results show good agreement with measured values with maximum errors for the synthesis reactions of ethyl butyrate and ethyl acetate being 4.94% and 3.68%, respectively.

Implicit Function and Level Set Methods for Computation of Moving Elements During Microwave Heating

It is popular to use moving elements to improve heating uniformity during microwave heating under some situations. However, it is still a challenge to simulate moving elements during microwave heating due to the complexity of mathematical modeling. In this paper, a novel continuous algorithm based on implicit function and level set methods is developed to compute this heating process. By introducing the implicit function and level set methods, the moving region’s properties are set as a function of space coordinate and time, which means that the movement of the elements is represented by the variation of the parameters. In addition, with the coordinate transformation, the coupling process of electromagnetic field and heat transfer in microwave heating can be performed. A 2-D applicator model and a 3-D applicator model with a rotating turntable are used to illustrate the proposed method in detail. Experiments are also conducted to testify the validity of the proposed method. The results obtained by the proposed method are in accordance with those obtained by experiments. Moreover, compared with conventional methods, the proposed method is more accurate and efficient.

Microwave Power System Based on a Combination of Two Magnetrons

Currently, microwave energy is utilized for many diverse industrial applications because of its various advantages including its eco-friendliness. Low-cost, high-efficiency, and high-power industrial microwave sources are in urgent demand. In this paper, we propose a low-cost quasi-coherent power-combining system based on a combination of two magnetrons. We have analyzed and built a low-loss waveguide-based applicator combined with specific phase. This system utilizes the coupling of the combiner to quasi-lock the slave magnetron. A waveguide phase shifter lies in the slave magnetron branch to adjust the phase difference between the master and slave magnetrons’ signals to achieve high resultant efficiency. Based on theory, the phase difference between the master and the injected slave magnetrons has been numerically calculated and analyzed. The phase difference changes periodically when the slave magnetron is quasi-locked to the master magnetron and the periodicity increases with the injection ratio. Experimental results show the resultant efficiency of the proposed system can reach as high as 92% when using several suitable waveguide components. The investigation also provides guidelines for further microwave power combination systems with multiple sources.

Understanding of microwave heating in a novel designed cavity with monopole antennas

This research presents a novel designed cavity system for improving microwave heating efficiency. Microwave heat- ing at 2.45 GHz with monopole antennas in a cavity is compared with the conventional magnetron heating on a tylose block. The model for both heating methods was first validated versus experimental results and showed excellent agreement. The antenna heating in a cavity significantly improved the heating rate and uniformity in the tylose sample. The cavity heating method exhibited nearly twice the efficiency as sample sizes increased. The cavity design improves the microwave absorption and final temperature uniformity substantially over the traditional microwave oven. Notably within the first 60 seconds, the non-uniformity in temperature distribution begins to decrease in the cavity while the magnetron method still shows increasing temperature non-uniformity. The novel use of antennas in a cavity demonstrates the potential for a controllable and selectable microwave heating system that improves power efficiency, heating rate, and temperature uniformity over conventional mi- crowave heating.

Modeling and experimental studies of a side band power re-injection locked magnetron*

A side band power re-injection locked (SBPRIL) magnetron is presented in this paper. A tuning stub is placed between the external injection locked (EIL) magnetron and the circulator. Side band power of the EIL magnetron is reflected back to the magnetron. The reflected side band power is reused and pulled back to the central frequency. A phase-locking model is developed from circuit theory to explain the process of reuse of side band power in SBPRIL magnetron. Theoretical analysis proves that the side band power is pulled back to the central frequency of the SBPRIL magnetron, then the amplitude of the RF voltage increases and the phase noise performance is improved. Particle-in-cell (PIC) simulation of a 10-vane continuous wave (CW) magnetron model is presented. Computer simulation predicts that the frequency spectrums peak of the SBPRIL magnetron has an increase of 3.25 dB compared with the free running magnetron. The phase noise performance at the side band offset reduces 12.05 dB for the SBPRIL magnetron. Besides, the SBPRIL magnetron experiment is presented. Experimental results show that the spectrum peak rises by 14.29% for SBPRIL magnetron compared with the free running magnetron. The phase noise reduces more than 25 dB at 45-kHz offset compared with the free running magnetron.

Broadband complex permittivity determination using a two-port U-shaped coplanar waveguide with artificial neutral network algorithm

A two-port U-shaped Coplanar Waveguide (U-CPW) used for broadband complex permittivity measurement of high loss solutions is presented. Compared with the one-port measurement device, this two-port U-CPW coupled with artificial neural networks algorithm has the ability of reducing the multiple-solutions. Also, the measured T/R (transmission/reflection) coefficients were used instead of simulated reflection coefficients for training the neural networks that enhanced the accuracy of measurement results. Two real-valued neural networks associated with the U-CPW are used to reconstruct the two parts of the complex permittivity separately from the measured T/R coefficients. First, a large number of measured T/R coefficients of broadband frequency points of ethanol-water mixtures along with their theoretical complex permittivity are used to train two separate neural networks. Second, the trained networks are employed to reconstruct the complex permittivity of other solutions using the measured T/R coefficients. Compared with the results of Cole-Cole equation, the reconstructed results of methanol-water mixtures and ethanol-methanol mixtures at different volume fractions have been obtained with sufficient degree of accuracy in the frequency range 1-3 GHz at 20 ◦ C. For predicted values using the developed artificial neural network (ANN) architecture and those obtained from literature, the average relative errors of real and imaginary parts of complex permittivity are 2.27% and 2.12%, respectively.