Hongchun Yang

A NEW TRIPLE-BAND CPW-FED MONOPOLE ANTENNA FOR WLAN AND WIMAX APPLICATIONS

A new CPW-fed antenna with triple-band is presented for simultaneously satisfying wireless local area network (WLAN) and world interoperability for microwave access (WiMAX) applications. The investigated antenna consists of a T-shaped monopole with a trapeziform ground plane and two parasitic elements to generate tripleband. The design methodology is outlined and the overall size is 32× 15× 1 mm3. This antenna was numerically designed using Ansoft HFSS simulation software package. The measured 10 dB bandwidth for return loss is from 2.35 to 2.71 GHz and 3.35 to 3.72 GHz and 4.9 to 6.1 GHz, covering all the 2.4/5.2/5.8 GHz WLAN bands and 2.5/3.5/5.5GHz WiMAX bands.

Effects of interatomic potential on He bubble creation by cascades in α -iron

The effects of using different interatomic potentials in molecular dynamics (MD) simulations of the formation of He-vacancy clusters within displacement cascades in α-Fe are investigated using two sets of potentials. Simulations of cascades produced by primary knock-on atoms of energy Ep=1–20keV were performed in α-Fe containing a concentration of substitutional He atoms varying from 1to5at.% at an irradiation temperature of 100K. Although the effects of interatomic potentials on the nucleation of He-vacancy clusters induced by cascades are relatively small, the number and size of He-vacancy clusters produced are significantly different for the different potentials employed in this study. Thus, these differences may influence the microstructural evolution predicted in damage accumulation models that use the results from MD cascade simulations as input. The observed differences in postcascade configurations can be attributed mainly to the differences in the Fe–Fe and Fe–He potentials.

Photoresistances of semi-insulating GaAs photoconductive switch illuminated by 1.064 μm laser pulse

The Shockley–Read–Hall model (SRHM) and its simplified model (SSRHM) were used to describe the characteristics of a photoconductive semiconductor switch (PCSS) made from a semi-insulating (SI) gallium arsenide (GaAs) chip, biased at low voltage, and illuminated by a 1.064 μm laser pulse. These characteristics include the free carrier densities, dynamic photoresistance, and time evolution of output pulses of the PCSS. The deep donor EL2 centers in SI GaAs play a dominant role in both the SRHM and SSRHM as electrons at EL2 unionized centers are strongly excited by the subband-gap photons at the wavelength of 1.064 μm. Theoretical modeling on the evolution of the experimental measured output pulses led to a two-step micromechanism of electron excitation process within the GaAs chip. The minimum photoresistances predicted by the SSRHM are in good agreement with experimental measurements, which confirms the dominant role of EL2 in the generation of electric pulses from a SI GaAs photoconductivity switch on whi...

A Novel Wideband Dielectric Resonator Antenna

A novel wideband dielectric resonator antenna is proposed. This antenna is comprised of a dielectric hemispherical shell made of high permittivity material and a ground made of low permittivity material. A conformal patch is used as the excitation structure. A quasi-omnidirectional radiation pattern in the upper half space and an impedance bandwidth up to 40% can be achieved in the simulation results. And the parameters affected the resonant frequency and bandwidth are studied.

DESIGN OF DUAL BAND FILTER BASED ON A NOVEL DGS STRUCTURE

This letter presents a dual-band bandpass fllter (BPF) using interdigital coupling lines with a new defected ground structure (DGS) pattern. Traditional DGS structures are mainly used to realize wide bandstop characteristics. In this letter, by introducing a pair of coupling stubs in the aperture of the DGS, a narrow passband can be achieved within a wide stopband, so a dual-band bandpass fllter can be implemented. An equivalent circuit model is derived to describe the fllter. And the circuit simulation result agrees well with the EM simulation one. The position and bandwidth of the two passbands can be designed and adjusted independently. In order to verify the theory, a dual-band bandpass fllter is designed, fabricated and measured. The simulated and measured results are in good agreement.

LOWPASS FILTER WITH WIDE STOPBAND AND SHARP SKIRT USING NOVEL DEFECTED GROUND STRUCTURE

A novel defected ground structure unit is presented in this paper. This structure is composed of a traditional dumbbell DGS and a pair of coupling stubs in the aperture. In contrast to a single finite attenuation pole characteristic offered by the conventional dumbbell DGS, the proposed DGS unit provides dual finite attenuation poles that can be independently controlled. By adjusting the position of the two attenuation poles, a much sharper skirt and wider stopband could be achieved. A lowpass filter with a cut off frequency of 3.2 GHz utilizing four cascaded novel DGS units is designed, fabricated and measured. This lowpass filter achieves a wide stopband with over 30dB attenuation up to 30 GHz. The results obtained from simulation and measurement have good agreement.

The high voltage nanosecond electric pulse generator based on a photoconductive semiconductor switch

A recently developed simulation algorithm based on the Shockley-Read-Hall model was used to describe the characteristics of the output pulses from the newly developed high voltage nanosecond electrical pulse generator (HVNEPG). The new HVNEPG was based on a semi-insulating Gallium Arsenide (GaAs) photoconductive semiconductor switch (PCSS) which was biased at high external electric field (26.7KV/cm) and illuminated by a laser at the wavelength of 1.064 micrometer for 1 nanosecond. A pulsed power supply and a Blumlein-like transmission line with a small equivalent capacitance were employed in the new HVNEPG which resulted in high voltage low jitters output pulses and a significantly prolonged lifetime of the PCSS under high electric field. The good agreement between the model simulation and the experimental measurements leads to the conclusion that the PCSS was operated in a linear mode under a higher than critical electric field.

Theoretical evaluations of electro-manipulation from Jurkat T cells exposed to pulsed electric fields (PEFs) with different time durations

The multilayer dielectric sphere model (MDSM) was used to analyze responses of Jurkat T cells to pulsed electric fields (PEFs). The dependence of voltages across nuclear plasma, nuclear envelope, cytoplasm and plasma membrane on different time durations of PEFs was calculated by employing the inverse laplace transformation (ILT) in time domain with Maple software. Cytochrome C release was considered as a secondary effect of PEFs when mitochondria substructures were taken into account. It is proposed that two-step process of Cytochrome C release can be realized by bioelectric impulse effect on mitochondria.

A Compact Wideband Antenna Integrated With a Pulse-Forming Line for Transient Pulse Radiation

A compact wideband antenna integrated with a pulse-forming line for transient pulse radiation is proposed in this paper. It can be used in the fields such as ultrawideband (UWB) radar, ground-penetrating radar, UWB communications, etc. This antenna is integrated with a solid-state switch and a planar Blumlein pulse-forming line. The dimension of the antenna is 300 mm × 300 mm × 3 mm. In the experiment, the switch was triggered by a laser with a wavelength of 1064 nm. The peak power of a single antenna was 14.45 MW when the applied voltage was 17 kV. A Gaussian doublet pulse with a duration of 1.5 ns and a peak-peak amplitude of 305.7 V/m at a distance of 2 m from the antenna along the main beam direction was recorded in the experiment. The measured waveform was in good agreement with the predicted one.

Microstrip-fed monopole antenna for UWB application

In this paper, we propose a planar microstrip-fed monopole antenna for UWB applications. The proposed antenna is designed from 3 to 20 GHz with VSWR below 2. By adding elliptical shaped cuts between monopole and the feed line, and add notch in the ground plane, the proposed antenna exhibits excellent broadband properties and stable radiation patterns. The proposed antenna has a size of 30times21 mm, and provides ultra-wide bandwidth from 3.0 to 20 GHz in order to satisfy the requirements of the current wireless communications systems. Meanwhile, by introducing a spurline on the feeding line, a narrow band-rejection operation can be realized.