Beam Synthesis Technique Research Articles

Efficient Angle-of-Arrival Estimation of Lens Antenna Arrays for Wireless Information and Power Transfer

Antenna design and angle-of-arrival (AoA) estimation are critical to the efficiency of wireless information and power transfer. The AoA estimation is challenging for energy-efficient lens antenna arrays (LAAs), due to discrete sets of fixed discrete Fourier transform (DFT) beams. This paper presents a novel fast and accurate approach for the AoA estimation of LAAs. The key idea is that we prove the two differential outputs of three adjacent lens beams, referred to as “DFT beam differences (DBDs),” that are the strongest at the two sides of an AoA. They are easy to identify and robust to noises, and their powers are proved to provide an accurate estimate of the AoA. Another important aspect is a new beam synthesis technique which produces different beam widths based on DFT beams and practical 1-bit phase shifts in real time. As a result, the angular region containing the AoA can exponentially narrow down, and the two strongest DBDs can be quickly identified. The proposed approach can operate in coupling with successive interference cancellation to estimate the AoAs of multiple paths. Simulations show that the proposed approach is able to outperform the state of the art by orders of magnitude in terms of accuracy. The power transfer efficiency can be dramatically improved.

Suppression of ion-implantation induced porosity in germanium by a silicon dioxide capping layer

Ion implantation with high ion fluences is indispensable for successful use of germanium (Ge) in the next generation of electronic and photonic devices. However, Ge readily becomes porous after a moderate fluence implant (∼1×1015 ion cm−2) at room temperature, and for heavy ion species such as tin (Sn), holding the target at liquid nitrogen (LN2) temperature suppresses porosity formation only up to a fluence of 2×1016 ion cm−2. We show, using stylus profilometry and electron microscopy, that a nanometer scale capping layer of silicon dioxide significantly suppresses the development of the porous structure in Ge during a Sn− implant at a fluence of 4.5×1016 ion cm−2 at LN2 temperature. The significant loss of the implanted species through sputtering is also suppressed. The effectiveness of the capping layer in preventing porosity, as well as suppressing sputter removal of Ge, permits the attainment of an implanted Sn concentration in Ge of ∼15 at.%, which is about 2.5 times the maximum value previously attained. The crystallinity of the Ge-Sn layer following pulsed-laser-melting induced solidification is also greatly improved compared with that of uncapped material, thus opening up potential applications of the Ge-Sn alloy as a direct bandgap material fabricated by an ion beam synthesis technique.

Beam Synthesis Technique for Array Antenna Based on Projection Matrix Algorithm

Beam Synthesis Technique for Array Antenna Based on Projection Matrix Algorithm

Beam Synthesis Technique for Array Antenna Based on Projection Matrix Algorithm

Beam Synthesis Technique for Array Antenna Based on Projection Matrix Algorithm

Superhard Tungsten Tetraboride Films Prepared by Pulsed Laser Deposition Method

Attempts to synthesize and/or theoretically predict new superhard materials are the subject of an intense research activity. The trials to deposit them in the form of films have just began. WB(2) (77 wt % WB(2) and 23 wt % WB(4)) and WB(4) (65 wt % WB(4) and 35 wt % WB(2)) polycrystalline bulk samples were obtained in this work via electron beam synthesis technique and, subsequently, used as targets for films preparation by the pulsed laser deposition method. The targets were irradiated by a frequency-doubled Nd:glass laser with a pulse duration of 250 fs. The films grown on SiO(2) substrates at 600 °C were characterized by X-ray diffraction, scanning electron and atomic force microscopies, and Vickers microhardness technique. The deposited films are composed of WB(4). The intrinsic film hardness, calculated according to the "law-of-mixtures" model, lies in the superhardness region 42-50 GPa.

Characterization of the crystalline quality of β-SiC formed by ion beam synthesis

The ion beam synthesis (IBS) technique is applied to form crystalline silicon carbide (SiC) for future optoelectronics applications. Carbon ions at 80 and 40keV were implanted into (100) high-purity p-type silicon wafers at room temperature and 400°C, respectively, to doses in excess of 1017ions/cm2. Subsequent thermal annealing of the implanted samples was performed in a vacuum furnace at temperatures of 800, 900 and 1000°C, respectively. Elastic recoil detection analysis was used to investigate depth distributions of the implanted ions and infrared transmittance (IR) measurement was used to characterize formation of SiC in the implanted Si substrate. Complementary to IR, Raman scattering measurements were also carried out. Levels of the residual damage distribution of the samples annealed at different temperatures were compared with that of the as-implanted one by Rutherford backscattering spectrometry (RBS) in the channeling mode. The results show that C-ion implantation at the elevated temperature, followed by high-temperature annealing, enhances the synthesis of crystalline SiC.

GaN nanodot fabrication by implant source growth

By using implant source growth, an ion beam synthesis technique where implanted ions are used as a growth source for nanostructures, we have fabricated self-assembled GaN nanodots on SiO2. The fabrication method consists of implanting Ga ions into a 60nm thick thermally grown SiO2 layer by using a focused ion beam system followed by annealing under an NH3 flux. The morphology, crystal structure, and optical properties of the GaN nanodots are also shown and discussed.

TEM investigation of ion beam synthesized semiconducting FeSi2

Abstract Both as-implanted and annealed semiconducting FeSi 2 samples fabricated using ion beam synthesis technique were studied by transmission electron microscopy. A continuous buried silicide layer with larger precipitates and sharper interfaces formed during annealing at 900 °C for 18 h. Different orientation relationships between the silicide grains and the silicon substrate were found. The existence of a large variety of parallel lattice plane pairs with the available small mismatches between the two phases results in these preferred orientation relationships.

A contoured beam synthesis technique for planar antenna arrays with quadrantal and centro-symmetry

A method is described for the synthesis of planar array antennas with prescribed contoured beams. The technique utilizes a transformation which divides the problem into two decoupled subproblems. One subproblem involves the determination of certain coefficients of the contour transformation in order to achieve the required footprint contours. The number of coefficients which need to be used depends on the complexity of the desired contour, but is very small in comparison to the number of planar array elements. The other subproblem consists of a linear array shaped beam synthesis, for which there already exist powerful methods for determining appropriate element excitations. The size required for this prototype linear array depends on the number of contour transformation coefficients used and the size of the final planar array. Simple formulas then determine the final planar array excitations from the information forthcoming from the above two subproblem solutions. >

New trends in SIMOX

Recent developments of the SIMOX technology, in which a silicon-on-insulator structure is synthesized by high-dose implantation of oxygen into Si, have been reviewed. A problem with these structures is that the Si layer generally contains a high density of dislocations (10 8–10 9 dislocations/cm 2). However, recently three different methods have been reported in which the density of these defects was reduced to less than 10 5 dislocations/cm 2 by optimization of the implantation conditions. These methods have been discussed and relations have been established between the processing conditions, the steady-state point defect concentrations and the microstructure of the material. The relations may be used as guidelines for further improvement of these structures. The success of the SIMOX technology has also stimulated the research on the synthesis of other compounds in Si. In general the structures formed by the ion beam synthesis technique are not only of good quality, but they frequently exhibit unique features, illustrating the potential of the SIMOX and other ion beam synthesis techniques.

Synthesis of heteroepitaxial Si/CoSi2/Si structures by Co implantation into Si

Heteroepitaxial Si/CoSi2/Si structures have been formed in both (100) and (111)Si by high-dose implantation of Co. During the implantation, Co is incorporated in the Si lattice as CoSi2 with the same orientation as the Si substrate. Upon annealing the implanted Co distribution is transformed into an epitaxial Si/CoSi2/Si layered structure. Sputtering of Si during the implantation of Co was studied using an implanted Si3N4 marker layer. The Si/CoSi2/Si/Si3N4/Si multilayer structure that is formed in this way demonstrates the potential of the ion beam synthesis technique.