Zaifang Xi

A kind of coating method of GaN-MOCVD graphite susceptor

A novel coatingmethod for the GaN-MOCVD graphite susceptor is proposed in the paper, whichmeans that the upper surface and sides of the graphite susceptor are covered with a low emissivity material coating, and the surface under the susceptor is covered with a high emissivity SiC coating. By using finite element analysis software COMSOL Multiphysics, the temperature field of the susceptors without coating, with common SiC coating, and with improved coating is obtained and compared, which shows that the susceptor with the improved coating not only increases the heating efficiency of the heater, but also improves the temperature uniformity of the substrate, which can be of great benefit to the film growth. In addition, this improved coating for the susceptor has the same heating sensitivity as the common SiC coating.

Novel compact dual-band-notched ultra-wideband printed antenna with a parasitic circular ring strip

A simple and compact printed ultra-wideband antenna with dual-band-notched characteristics is presented. The proposed antenna is composed of a rectangular patch and a modified ground plane. The rectangular patch is etched onto a lossy FR4 substrate. A circular ring strip parasitizes the rectangular patch embedded by a U-shaped slot. Two inverted-L slits and a rectangular slit are embedded onto the ground plane. Some bandwidth enhancement and band-notched techniques are applied in the antenna structure for broadening the bandwidth and generating notches. The simulated and measured results show that the proposed antenna offers a very wider bandwidth ranging from 3.04 to 17.30 GHz, defined by the return loss less than −10 dB, with dual-notched bands of 3.30–4.20 and 5.10–5.85 GHz covering the 3.3/3.7 GHz WiMAX, 3.7/4.2 GHz C-band, and 5.2/5.8 GHz wireless local area network systems. Furthermore, the proposed antenna presents relatively high antenna gain and quasi-omnidirectional radiation patterns.

Upconversion NaYF 4 nanoparticles for size dependent cell imaging and concentration dependent detection of Rhodamine B

Upconversion nanoparticles (UCNPs) based on NaYF4 nanocrystals with strong upconversion luminescence are synthesized by the solvothermal method. The emission color of these NaYF4 upconversion nanoparticles can be easily modulated by the doping. These NaYF4 upconversion nanocrystals can be employed as fluorescence donors to pump fluorescent organic molecules. For example, the efficient luminescence resonant energy transfer (LRET) can be achieved by controlling the distance between NaYF4:Yb3+/Er3+ UCNPs and Rhodamine B (RB). NaYF4:Yb3+/Er3+ UCNPs can emit green light at the wavelength of ∼540 nm while RB can efficiently absorb the green light of ∼540 nmto emit red light of 610 nm. The LRET efficiency is highly dependent on the concentration of NaYF4 upconversion fluorescent donors. For the fixed concentration of 3.2 µg/mL RB, the optimal concentration of NaYF4:Yb3+/Er3+ UCNPs is equal to 4mg/mL which generates the highest LRET signal ratio. In addition, it is addressed that the upconversion nanoparticles with diameter of 200 nm are suitable for imaging the cells larger than 10 µm with clear differentiation between cell walls and cytoplasm.

Low-Complexity robust capon beamforming based on reduced-rank technique

Existing robust Capon beamformers achieve robustness against steering vector errors at a high cost in terms of computational complexity. Computationally efficient robust Capon beamforming approach based on the reduced-rank technique is proposed in this paper. Theproposed method projects the received data snapshots onto a lower dimensional subspace consisting of the matched filters of the multistage Wiener filter (MSWF). The subsequent adaptive beamforming will then be performed within this subspace. The combination of the benefit of the robust adaptive beamforming and the reduced-rank technique improves the performance on combating steering vector errors and lowering the computational complexity.

A novel miniaturized antenna with multiple band-notched characteristics for UWB communication applications

ABSTRACT A novel miniaturization planar ultra-wideband antenna with triple-notched bands is proposed. The antenna mainly consists of an elliptical patch, a rectangular split-ring patch with a π-shaped slit and a T-shaped slit, and two small additional patches. Two different type slits are adopted to realize multiple-notched bands and reduce the antenna size. The designed antenna has a small dimension of 17 × 16 × 1.6 mm3. The simulated and measured results show the antenna has a very wide impedance bandwidth of 2.96–19.0 GHz with Return Loss less than −10 dB, except triple notched bands of 3.30–3.72, 5.13–5.82 and 7.04–7.92 GHz, respectively, covering the WiMAX, WLAN and X-band systems. Furthermore, surface current distributions, gain, efficiency, radiation patterns and group delay characteristics of the antenna are also discussed. The results show that the antenna has high radiation efficiency, stable radiation pattern and lower group delay time.

Joint DOA and DOD estimation in bistatic MIMO radar without estimating the number of targets

Existing subspace-based direction finding methods for multiple-input multiple-output (MIMO) radar assume perfect knowledge about the dimension of the signal or noise subspace, which is hard to be established without prior knowledge of the signal environment. In this paper, an efficient method for joint DOA and DOD estimation in bistatic MIMO radar without estimating the number of targets is presented. The proposed method computes an estimate of the noise subspace using the power of R (POR) technique.Then the two-dimensional (2D) direction finding problem is decoupled into two successive one-dimensional (1D) angle estimation problems by employing the rank reduction (RARE) estimator.