Ziqiang Yang

Properties of obliquely incident electromagnetic wave in one-dimensional magnetized plasma photonic crystals

Properties of obliquely incident electromagnetic wave in one-dimensional (1D) magnetized plasma photonic crystals (PPCs) are studied in this paper. Based on the continuous boundary condition of electromagnetic wave in 1D PPC, transfer matrix equation and dispersion equation of transverse magnetic polarization are deduced, and the properties of dispersion and transmission relation in terms of external magnetic field, collision frequency, and dielectric constant of dielectric and incident angles are investigated, respectively. Results show that gap location and gap width can be effectively controlled by adjusting external magnetic field as well as incident angle, and increasing collision frequency has little effect on gap width while larger dielectric constant of dielectric leads to more gaps.Properties of obliquely incident electromagnetic wave in one-dimensional (1D) magnetized plasma photonic crystals (PPCs) are studied in this paper. Based on the continuous boundary condition of electromagnetic wave in 1D PPC, transfer matrix equation and dispersion equation of transverse magnetic polarization are deduced, and the properties of dispersion and transmission relation in terms of external magnetic field, collision frequency, and dielectric constant of dielectric and incident angles are investigated, respectively. Results show that gap location and gap width can be effectively controlled by adjusting external magnetic field as well as incident angle, and increasing collision frequency has little effect on gap width while larger dielectric constant of dielectric leads to more gaps.

Defect modes in one-dimensional magnetized plasma photonic crystals with a dielectric defect layer

By using transfer matrix method, properties of one-dimensional magnetized plasma photonic crystals with a dielectric defect layer are studied. Results show that several defect modes appear within the photonic band gaps; periodic number and collision frequency only affect transmission magnitude of the defect modes; the external magnetic field and incident angle control both the transmission magnitude and frequency of the defect modes; thickness and dielectric constant of the defect layer determine both the number and frequency of the defect modes. This phenomenon may be useful in designing of narrow band filters or multi-channel filters.

Three-dimensional simulation of super-radiant Smith-Purcell radiation

A simulation of coherent and super-radiant Smith-Purcell radiation is performed in the gigahertz regime using a three-dimensional particle-in-cell code. The simulation model supposes a rectangular grating to be driven by a single electron bunch and a train of periodic bunches, respectively. The true Smith-Purcell radiation is distinguished from the evanescent wave, which has an angle independent frequency lower than the minimum allowed Smith-Purcell frequency. We also find that the super-radiant radiations excited by periodic bunches are emitted at higher harmonics of the bunching frequency and at the corresponding Smith-Purcell angles.

COMPUTATION OF ELECTROMAGNETIC DOSIMETRY FOR HUMAN BODY USING PARALLEL FDTD ALGORITHM COMBINED WITH INTERPOLATION TECHNIQUE

To enhance the flexibility of the parallel FDTD for the analysis of the bio-electromagnetic problems, a universal and efficient interpolation technique based on the super-absorbing boundary principle is presented, which can improve the interpolation accuracy and ensure the stability of the parallel FDTD iterative procedure. Using this technique, we calculate the SAR (Specific Absorption Rate) values in the head for two different human-body postures. In the iteration procedure of parallel FDTD, the data are exchanged between adjacent subdomains with the interpolation technique. Thus, the meshes can be created in local coordinates, which makes it convenient to build the human model in the different posture and use position for FDTD computing. The results show that the change of human-body posture only brings about a slight decrease (within 6.8%) in the peak SAR values, whereas the SAR values in the brain, as a critical organ, are sensitive to the change of the body posture, and it increases by 28% at maximum for the 1-g averaged peak SAR.

Reduce the start current of Smith-Purcell backward wave oscillator by sidewall grating

A sidewall grating for the Smith-Purcell device is proposed to enhance the coupling of the optical mode with the electron beam and, consequently, relax the stringent requirements to the electron beam. With the help of three-dimensional particle-in-cell simulations, it has been shown that, comparing with the general grating, the usage of a sidewall grating improves the growth rate and dramatically shortens the time for the device to reach saturation. It is also found that the sidewall grating holds the potential to reduce the start current for the operation of a Smith-Purcell backward wave oscillator.

Dispersion properties of a 2D magnetized plasma metallic photonic crystal

This is a study on a 2D magnetized plasma-filled metal photonic crystal (PMPC). We analyze the dispersion relation of the magnetized PMPC by using the finite-difference time-domain method. Results show a cutoff frequency for the PMPC, and two flat bands and new forbidden band gaps appear due to the external magnetic field. Adjusting the external magnetic field can control the positions of the flat bands, cutoff frequency, and location and width of the local gap. These results provide theoretical basis for designing tunable photonic crystal devices.

A novel Smith-Purcell free electron laser

An experiment on a novel Smith–Purcell free electron laser (FEL) is described in this paper. The FEL is driven by a relativistic sheet electron beam of middle energy. The high frequency system of the device is a quasi-optical resonator composed of a diffraction grating and a three-mirror reflector. Coherent radiation with a peak power of tens of kW at the 3 mm waveband is sucessfully detected from an experimental facility. The main experimental parameters are: sheet beam energy from 400 kV to 500 kV; pulse length of voltage 70 ns; pulse beam current 0.2 kA; synchronous guide magnetic field up to 1.2 T with 10 ms pulse length; and grating period 2.2 mm.

Numerical computation of dispersion curves for symmetric and asymmetric modes in an arbitrary cylindrical metal SWS

A method of quickly and accurately getting the dispersion curves for both symmetric and asymmetric modes in arbitrary slow-wave structures is investigated analytically. A universal dispersion equation is derived by utilizing the field theory and expressing the slow-wave structures profile in a finite Fourier series. In principle, this method can be applied to arbitrary axisymmetric profiles. As examples, numerical results for three typical slow-wave structures (namely, rippled-wall, disk-loaded, and modified disk-loaded structures) are presented.

A 3–50 GHz Ultra-Wideband PHEMT MMIC Balanced Frequency Doubler

A novel configuration of ultra-wideband (UWB) GaAs PHEMT monolithic microwave integrated circuit balanced frequency doubler is presented. By using two different terminal impedances of the common-source/common-gate active balun, the doubler exhibits UWB characteristic with more than a four octave frequency range. From 3 to 50 GHz, the measured conversion gain and fundamental frequency suppression of the doubler are better than -4 dB and 15 dB.

A Novel Smith-Purcell FEL

A novel Smith-Purcell FEL with a relativistic electron beam of middle energy and a quasi-optical resonator composed of diffraction grating and three mirror reflector is described in this paper. Coherent radiation with peak power of tens of KW at 3 mm waveband is successfully detected from an experimental facility characterized by beam energy of 400-500 KeV, pulse length of 70 ns, pulse beam current of 0.2 KA, and pulse guide magnetic field of up to 1.2 T.