Huang Kama

Study on the key problems of interaction between microwave and chemical reaction

Microwave has been found as an efficient heating method in chemical industry. However, in present days the interaction between microwave and chemical reactions has not been deeply understood, which restricts a wider application of high power microwave in chemical industry. In this paper, the key problems of interaction between microwave and chemical reaction are investigated, such as complex effective permittivity of chemical reaction, simulation of microwave heating on chemical reaction and non-thermal effect of microwave, which will enhance further knowledge of the mechanism of interaction between microwave and chemical reaction. Moreover, such an analysis is beneficial for handling with difficulties in application of microwave chemical industry.

High frequency response sensitivity of electrically large enclosure with aperture and its statistical analysis method

In this paper, the high frequency response sensitivity (HFRS) of the electromagnetic (EM) environment characteristics inside the electrically large enclosure with aperture under the external EM radiation and its corresponding statistical analysis method are discussed. Because of the immense computational cost due to the electrically large size and HFRS, it is difficult to assess the universal characteristics of the electromagnetic environment inside the enclosure according to the deterministic solution obtained by full wave analysis. The HFRS corresponding to the perturbations of the external excitation frequency and of the enclosure structure (equivalent to boundary conditions) are illustrated respectively. The space field distributions (the deterministic results) and corresponding probability distribution functions (PDFs) (the statistical results) of |E| inside the enclosure are given under different conditions. In the case of high frequency, the small changes of external excitation or geometric/physical structure of the enclosure can lead to great changes of the EM field distribution inside the enclosure, but its corresponding statistical characteristics are relatively stable. Therefore, adopting statistical method to analyse and describe the electromagnetic environment inside the electrically large enclosure is more reasonable. As soon as the modelling of the statistical characteristics is performed, the electromagnetic environment inside the enclosure can be reconstructed quickly, avoiding the high-cost full wave analysis.

The Measurement for Permittivity of Materials Based on Artificial Nerve Network

Effective complex permittivity measurements of materials are important in microwave engineering and microwave chemistry. Artificial neural network (ANN) computational module has been used in microwave technology and becomes a useful tool recently. A neural network can be trained to learn the behavior of an effective complex permittivity of material under microwave irradiation in a test system and it can provide a fast and accurate result for the permittivity of material. Thus, the on-line measurement has been realized. In this paper, a measurement system has been designed and the S-parameters are obtained by full-wave simulations to reconstruct the permittivity of material. Moreover, several organic solvents have been measured. The reconstructed results of the effective permittivities of solvents by means of the ANN agree well with previous published data.

Length determination of equivalent lines in asymptotic approach for high-frequency field coupling to transmission lines

The length determination rule of two equivalent lines in asymptotic approach for high-frequency field coupling to transmission lines is investigated. The induced current along transmission lines with different structure exposed to high frequency plane wave is calculated using asymptotic approach and full-wave analysis commercial software NEC respectively. Results show that the length of two equivalent lines recommended in literature sometimes leads to incorrect results. Length determination rule of equivalent lines is suggested according to induced current results obtained using different length of equivalent lines.

Statistical analysis of EM field distribution in electrically large enclosures with rectangle aperture of different sizes

In this paper, the electromagnetic (EM) environmental characteristics for electrically large enclosures under external EM illumination are discussed. Because of the immense computational cost and high frequency response sensitivity (HFRS), it is difficult to assess universal rules of the EM environment in the enclosure based on deterministic solutions. However, some of the field statistics are found to be quite well behaved and fairly insensitive to enclosure parameters. Therefore, statistical analysis of the EM field in the enclosures should be considered. Graphic lookup tables are presented, which permit estimating the mean and standard deviation of E-field strength quickly. The probability density functions (PDFs) of E-field components are also given and these curves are highly coincident with the ones obtained from an ideal reverberation chamber. These results allow a quick estimation of the EM statistical characteristics inside enclosures with different rectangle apertures.

A novel physical parameter extraction approach for Schottky diodes

Parameter extraction is an important step for circuit simulation methods that are based on physical models of semiconductor devices. A novel physical parameter extraction approach for Schottky diodes is proposed in this paper. By employing a set of analytical formulas, this approach extracts all of the necessary physical parameters of the diode chip in a unique way. It then extracts the package parasitic parameters with a curve-fitting method. To validate the proposed approach, a model HSMS-282c commercial Schottky diode is taken as an example. Its physical parameters are extracted and used to simulate the diodes electrical characteristics. The simulated results based on the extracted parameters are compared with the measurements and a good agreement is obtained, which verifies the feasibility and accuracy of the proposed approach.

A numerical analytic method for electromagnetic radiation accompanying with fracture of rocks

This paper studies Rabinovitchs compression experiments on granite and chalk and proposes an oscillating dipole model to analyse and simulate the electromagnetic radiation phenomenon caused by fracture of rocks. Our model assumes that the electromagnetic radiation pulses are initiated by vibrations of the charged rock grains on the tips of the crack. The vibrations of the rock grains are stimulated by the pulses of the cracks. Our simulations show comparable results with Rabinovitchs compression experiments. From the simulation results, it verifies an assumption that the crack width is inversely proportional to the circular frequency electromagnetic radiation, which is presented by Rabinovitch et al. The simulation results also imply that, by using our oscillating dipole model together with Rabinovitchs two equations about the crack length and crack width, we can quantitatively analyse and simulate the electromagnetic radiation phenomenon, which is induced from the fracture of the rocks.

Entropy description of measured information in microwave imaging

For the reconstruction of permittivity distribution in microwave imaging, the information quantity of measured data plays an important role for the reconstruction precision. And the information quantity depends greatly on the number of measurement points. So it is necessary to determine the number of measurement points in analysis and evaluation of a large number of measured data. In this paper, a mathematical methodology based on information entropy is proposed to describe the measured information and determine the required number of measurement points in microwave imaging. Moreover Bayesian theory is used to calculate the information entropy. Numerical tests show that the methodology proposed can describe the measured information effectively. As a result, this methodology can be applied to instruct how to determine the number of measurement points in microwave imaging.

Design and implement of the signal generator in the magnetic focused conductivity tomography system

To improve stability and performance of the signal source and sweeping detection, as well as to extract abundant and reliable signal, the direct digital synthesis technology was employed to design the generator of the source which formed sweeping frequencies of sine wave output from 1 to 20 MHz. The planar spiral coil was connected as an amplitude modulation circuit. The same coil adopted differential architecture for signal detection and extraction. The MC1595 was utilized to compose a phase detector in which difference of phases varies with the change of frequencies. A low pass filter was designed to filter the carry waves of the sweeping source. Thereby the system gained abundant data and its stability was improved. Further, the spatial resolution of the system was enhanced. All of the above favors the use of software in the magnetic focused conductivity tomography system (MFCT) to reconstruct the image of conductivity within the human body.

FDTD analysis to simulate interaction between microwave and chemical reaction

By coupling Maxwells equations, the Fourier equation of heat conduction and chemical reaction together, the FDTD method was used to simulate a simplified chemical reaction model under microwave irradiation. The chemical reaction process, temperature distribution and electromagnetic characters of the system can be obtained. This is useful for microwave chemistry applications.