ENLARGING SAR PATCH-MAPPING AREA BY ANTENNA BEAM SCAN

The approach for enlargement of SAR patch mapping area by antenna beam scan is investigated, which serves for moderate fine-resolution mapping of medium-sized terrain patches. The scanning angular velocity and the scanning angular scope are determined respectively. The angular velocity of the scanning antenna is controlled to scan over just one azimuth 3 dB beam width in the time interval during which the radar platform moves over one synthetic aperture length determined from the desired cross-range resolution, radar wavelength, nominal slant range, and squint angle. The scanning angular scope is mainly determined by the azimuth width of the terrain patch, nominal slant range, squint angle, platform velocity, and azimuth beam width. Finally, the related experimental results of an airborne SAR are presented. The linear range-Doppler algorithm is employed in image formation after motion compensation is conducted to remove the effect of transnational motion of the radar platform relative to the map center.

Collection efficiency of a monitor parallel plate ionization chamber for pencil beam scanning proton therapy

The collection efficiency of monitor parallel plate ionization chambers is the main uncertainty in the beam control of pencil beam scanning systems.Existing calculation methods for collection efficiency in photon or passive scattering proton systems have not considered the characteristics of non-uniform charge density in pencil beam scanning systems.In this study,Boag’s theory was applied to a proton pencil beam scanning system.The transverse distribution of charge density in the ionization chamber was considered to be a Gaussian function and an analytical solution was derived to calculate collection efficiency in the beam spot area.This calculation method is called the integral method and it was used to investigate the effects of beam parameters on collection efficiency.It was determined that collection efficiency is positively correlated with applied voltage,beam size,and beam energy,but negatively correlated with beam current intensity.Additionally,it was confirmed that collection efficiency is improved when the air filling the monitor parallel plate ionization chamber is replaced with nitrogen.

TEMPLATE MATCHING ALGORITHM OF RADAR BEAM SCAN TYPE RECOGNITION

Phased array radar has been applied broadly because of its sound performance.But signal of phased array radar is of a wide variety of types.Therefore,recognition of phased array radar is the most puzzling aspect of the whole emitter identification domain.To solve the problem,the article proposes the method that identifies phased array radar by pulse amplitude information,and studies the phased array radar,models transmit signal of them,and receiving signal by radar countermeasure reconnaissance receiver.From constructing template of pulse train's amplitude vector of mechanical scanning radar,computing distance of samples and standard template,finding threshold of the template matching arithmetic,the article puts forward the template matching algorithm of radar beam scan type recognition to identify phased array radar automatically.

Reformatted method for two-dimensional detector arrays measurement data in proton pencil beam scanning

The spatial resolution of a commercial two-dimensional(2D)ionization chamber(IC)array is limited by the size of the individual detector and the center-to-center distance between sensors.For dose distributions with areas of steep dose gradients,inter-detector dose values are derived by the interpolation of nearby detector readings in the conventional mathematical interpolation of 2D IC array measurements.This may introduce significant errors,particularly in proton spot scanning radiotherapy.In this study,by combining logfile-based reconstructed dose values and detector measurements with the Laplacian pyramid image blending method,a novel method is proposed to obtain a reformatted dose distribution that provides an improved estimation of the delivered dose distribution with high spatial resolution.Meanwhile,the similarity between the measured original data and the downsampled logfilebased reconstructed dose is regarded as the confidence of the reformatted dose distribution.Furthermore,we quantify the performance benefits of this new approach by directly comparing the reformatted dose distributions with 2D IC array detector mathematically interpolated measurements and original low-resolution measurements.The result shows that this new method is better than the mathematical interpolation and achieves gamma pass rates similar to those of the original low-resolution measurements.The reformatted dose distributions generally yield a confidence exceeding 95%.

Compensation of body shake errors in terahertz beam scanning single frequency holography for standoff personnel screening

In the terahertz（THz） band, the inherent shake of the human body may strongly impair the image quality of a beam scanning single frequency holography system for personnel screening. To realize accurate shake compensation in imaging processing, it is quite necessary to develop a high-precision measure system. However, in many cases, different parts of a human body may shake to different extents, resulting in greatly increasing the difficulty in conducting a reasonable measurement of body shake errors for image reconstruction. In this paper, a body shake error compensation algorithm based on the raw data is proposed. To analyze the effect of the body shake on the raw data, a model of echoed signal is rebuilt with considering both the beam scanning mode and the body shake. According to the rebuilt signal model, we derive the body shake error estimated method to compensate for the phase error. Simulation on the reconstruction of point targets with shake errors and proof-of-principle experiments on the human body in the 0.2-THz band are both performed to confirm the effectiveness of the body shake compensation algorithm proposed.

Evaluation of Single Field Uniform Dose (SFUD) Proton Pencil Beam Scanning (PBS) Planning Strategy for Lung Mobile Tumor Using a Digital Phantom

Purpose: To quantitatively evaluate four different Proton SFUD PBS initial planning strategies for lung mobile tumor. Methods and Materials: A virtual lung patient’s four-dimensional computed tomography (4DCT) was generated in this study. To avoid the uncertainties from target delineation and imaging artifacts, a sphere with diameter of 3 cm representing a rigid mobile target (GTV) was inserted into the right side of the lung. The target motion is set in superior-inferior (SI) direction from ?5 mm to 5 mm. Four SFUD planning strategies were used based on: 1) Maximum-In-tensity-Projection Image (MIP-CT);2) CT_average with ITV overridden to muscle density (CTavg_muscle);3) CT_average with ITV overridden to tumor density (CTavg_tumor);4) CT_average without any override density (CTavg_only). Dose distributions were recalculated on each individual phase and accumulated together to assess the “actual” treatment. To estimate the impact of proton range uncertainties, +/?3.5% CT calibration curve was applied to the 4DCT phase images. Results: Comparing initial plan to the dose accumulation: MIP-CT based GTV D98 degraded 2.42 Gy (60.10 Gy vs 57.68 Gy). Heart D1 increased 6.19 Gy (1.88 Gy vs 8.07 Gy);CTavg_tumor based GTV D98 degraded 0.34 Gy (60.07 Gy vs 59.73 Gy). Heart D1 increased 2.24 Gy (3.74 Gy vs 5.98 Gy);CTavg_muscle based initial GTV D98 degraded 0.31 Gy (60.4 Gy vs 60.19 Gy). Heart D1 increased 3.44 Gy (4.38 Gy vs 7.82 Gy);CTavg_only based Initial GTV D98 degraded 6.63 Gy (60.11 Gy vs 53.48 Gy). Heart D1 increased 0.30 Gy (2.69 Gy vs 2.96 Gy);in the presence of ±3.5% range uncertainties, CTavg_tumor based plan’s accumulated GTV D98 degraded to 57.99 Gy (+3.5%) 59.38 Gy (?3.5%), and CTavg_muscle based plan’s accumulated GTV D98 degraded to 59.37 Gy (+3.5%) 59.37 Gy (?3.5%). Conclusion: This study shows that CTavg_Tumor and CTavg_Muscle based planning strategies provide the most robust GTV coverage. However, clinicians need to be aware that the actual dose to OARs at distal end of target may increase. The study also indicates that the current SFUD PBS planning strategy might not be sufficient to compensate the CT calibration uncertainty.

Metamaterial beam scanning leaky-wave antenna based on quarter mode substrate integrated waveguide structure

In this paper, we first propose a metamaterial structure by etching the same two interdigital fingers on the upper ground of quarter mode substrate integrated waveguide（QMSIW）. The simulated results show that the proposed QMSIWbased metamaterial has a continuous phase constant changing from negative to positive values within its passband. A periodic leaky-wave antenna（LWA）, which consists of 11 QMSIW-based metamaterial unit cells, is designed, fabricated,and measured. The measured results show that the fabricated antenna achieves a continuous beam scanning property from backward-43° to forward ＋32° over an operating frequencyrange of 8.9 GHz–11.8 GHz with return loss better than 10 d B.The measured antenna gain keeps consistent with the variation of less than 2 d B over the operating frequency range with a maximum gain of 12 d B. Besides, the measured and simulated results are in good agreement with each other, indicating the significance and effectiveness of this method.

2-D localization system utilizing M-sequence encoded laser beam scanning

In this paper, as the active position measurement system, a novel method for a two-dimensional localization system using M-sequence signal is proposed. The feature of this system is to realize a position measurement only by scanning the encoded laser beams from fixing points to a measurement field, and by observing it. First, both the system configuration and encoding method were practically considered, and an order and an initial value of M-sequence signal were selected for encoding. This method is based on discrete angle measurement therefore the resolution has its own limitation. To overcome this limitation, analogue phase shift detecting method was introduced. System design was performed and applied to position measurement experiments. The experimental results show that the measurement error of the analogue method is 1/3 of that of the discrete method.

Robustness Evaluation of a Novel Proton Beam Geometry for Head and Neck Patients Treated with Pencil Beam Scanning Therapy

Background: To evaluate the robustness of head and neck treatment using proton pencil beam scanning (PBS) technique with respect to range uncertainty (RU) and setup errors (SE), and to establish a robust PBS planning strategy for future treatment. Methods and Materials: Ten consecutive patients were planned with a novel proton field geometry (combination of two posterior oblique fields and one anterior field with gradient dose match) using single-field uniform dose (SFUD) planning technique and the proton plans were dosimetrically compared to two coplanar arc VMAT plans. Robustness of the plans, with respect to range uncertainties (RU = ± 3% for proton) and setup errors (SE = 2.25 mm for proton and VMAT), in terms of deviations to target coverage (CTV D98%) and OAR doses (max/mean), were evaluated and compared for each patient under worst case scenarios. Results: Dosimetrically, PBS plans provided better sparing to larynx (p = 0.005), oral cavity (p < 0.001) and contralateral parotid (p = 0.004) when compared to VMAT. CTV D98% variations were higher from SE than from RU for proton plans (-1.1% ± 1.3 % vs -0.4% ± 0.7% for nodal CTV and -1.4% ± 1.2 vs -0.4% ± 0.5% % for boost CTV). Overall, the magnitudes of variation of CTV D98% to combined SE and RU were found to be similar to the impact of the SE on the VMAT plans (-1.6% ± 1.9% vs -1.7% ± 1.4% for nodal CTV and -1.9% ± 1.6% vs -1.3% ± 1.5% for boost CTV). Compared to VMAT, a larger range of relative dose deviations were found for OARs in proton plans, but safe doses were maintained for cord (41.8 ± 3.6 Gy for PBS and 41.7 ± 3.9 Gy for VMAT) and brainstem (35.2 ± 8.4 Gy for PBS and 36.2 ± 5.1 Gy for VMAT) in worst case scenarios. Conclusions: Compared to VMAT, proton plans containing three SFUD fields with superior-inferior gradient dose matching had improved sparing to larynx, contralateral parotid and oral cavity, while providing similar robustness of target coverage. Evaluation of OAR dose robustness showed higher sensitivities to uncertainties for proton plans, but safe dose levels were maintained for cord and brainstem.

Angle amplifier in a 2D beam scanning system based on peristrophic multiplexed volume Bragg gratings

In this paper,a 2D angle amplifier based on peristrophic multiplexed volume Bragg gratings is designed and prepared,in which a calculation method is firstly proposed to optimize the number of channels to a minimum.The induction of peristrophic multiplexing reduces the performance difference in one bulk of the grating,whereas there is no need to deliberately optimize the fabrication process.It is revealed that a discrete 2D angle deflection range of±30°is obtained and the relative diffraction efficiency of all the grating channels reaches more than 55%with a root-meansquare deviation of less than 3.4%in the same grating.The deviation of the Bragg incidence and exit angles from the expected values is less than 0.07°.It is believed that the proposed 2D angle amplifier has the potential to realize high-performance and large-angle beam steering in high-power laser beam scanning systems.

Equalization of Ti 6Al 4V alloy welded joint by scanning electron beam welding

The equalization of Ti 6Al 4V alloy welded joint with base metal on corrosion resistance, strength and ductility was studied. The solidification microstructure is transformed from 650 μm columnar grains to 100 μm equiaxed grains by scanning electron beam welding. The anodic polarization curve of 150 μm equiaxed grains coincides with that of base metal. Equal corrosion resistance between weld metal and base metal was obtained. Uniform microstructure and solute distribution are the basis of equalization. Corrosion rate of weld with 150 μm equiaxed grains is the lowest, 2.45 times lower than that of 650 μm columnar grains. Weld strength is 98% as much as that of base metal, yield strength ratio is 99.5%, which is 3.6% higher than that of base metal.

Investigation on gradient material fabrication with electron beam melting based on scanning track control

A new electron beam control system was developed in a general vacuum electron beam machine by assembling with industrial control computer, programmable logic control （PLC）, deflection coil, data acquisition card, power amplifier, etc. In this control system, scanning track and energy distribution of electron beam could be edited off-line, real-time adjusted and controlled on-line. Ti-Mo gradient material （GM） with high temperature resistant was fabricated using the technology of electron beam melting. The melting processes include three steps, such as preheating, melting, and homogenizing. The results show that the GM prepared by melting technology has fine appearance, and it has good integrated interface with the Ti alloy. Mo and Ti elements are gradually distributed in the inter.face of the gradient material. The microstructure close to the Ti alloy base metal is α ＋ β basket-waver grain, and the microstructure close to the GM is a single phase of β solid solution.

Multiple helical scans and the reconstruction of over FOV-sized objects in cone-beam CT

In cone-beam computed tomography （CBCT）, there are often cases where the size of the specimen is larger than the field of view （FOV） （referred to as over FOV-sized （OFS））. To acquire the complete projection data for OFS objects, some scan modes have been developed for long objects and short but over-wide objects. However, these modes still cannot meet the requirements for both longitudinally long and transversely wide objects. In this paper, we propose a multiple helical scan mode and a corresponding reconstruction algorithm for both longitudinally long and transversely wide objects. The simulation results show that our model can deal with the problem and that the results are acceptable, while the OFS object is twice as long compared with the FOV in the same latitude.

Molecular Beam Epitaxy Growth and Scanning Tunneling Microscopy Study of Pyrite CuSe2 Films on SrTiO3

We perform molecular beam epitaxy growth and scanning tunneling microscopy study of copper diselenide （CuSe2 ） films on SrTiO3 （001）. Using a Se-rich condition, the single-phase pyrite CuSe2 grows in the Stranski-Krastanov （layer-plus-island） mode with a preferential orientation of （111）. Our careful inspection of both the as-grown and post-annealed CuSe2 films at various temperatures invariably shows a Cu-terminated surface, which, depending on the annealing temperature, reconstructs into two distinct structures 2 ×√3 and √x ×√3-R30°. The Cu termi- nation is supported by the depressed density of states near the Fermi level, measured by in-situ low temperature scanning tunneling spectroscopy. Our study helps understand the preparation and surface chemistry of transition metal pyrite dichalcogenides thin films.

Theory of Z-scan technique using Gaussian-Bessel beams with a phase object

This paper reports the theoretical study of combining Z-scan technique with Gauss-Bessel （GB） beams beside a phase object （PO） to measure the third-order nonlinear susceptibility components. By using this method, the sign of refractive index which depends on the shape of the close aperture Z-scan curve can be easily determined. Meanwhile, the magnitude of nonlinear coefficients can also be deduced by theoretical fit. The proposed method is advantageous for high sensitivity and imposes a lower stress in the cases of fragile materials, since small pulse energy is enough for the measurement of nonlinear coefficients. Predictions of the models are compared with Gaussian Z-scan measurement and GB Z-scan measurement. By using GB beams with a PO, the sensitivity of Z-scan measurements is found to be a factor of over 60 times greater than for Gaussian beams and 2 times greater than for Gaussian-Bessel beams.

Achieving Directionality and Transmit Diversity via Integrating Beam Pattern Scanning (BPS) Antenna Arrays and OFDM

In this paper, we introduce a novel merger of antenna arrays with scanning beam patterns, and Orthogonal Frequency Division Multiplexing (OFDM) systems. Controlled time varying phase shifts are applied to the antenna array elements mounted at the base station with beam patterns directed toward the desired user. This creates a small beam pattern movement called Beam Pattern Scanning (BPS). In rich scattering environments BPS creates a time varying environment leading to time diversity exploitable at the receiver enhances its probability-of-error performance. Here, we apply OFDM signals to BPS antenna arrays, and we achieve: (1) directionality, which supports Space Division Multiple Access (SDMA);and (2) a time diversity gain, which leads to high performance. We discuss the structure of the base station antenna array and the OFDM receiver that exploits time diversity. We also introduce the merger of BPS and multi-carrier OFDM (MC-OFDM) systems. In MC-OFDM each bit is transmitted over all sub-carriers after serial to parallel conversion. BPS/ MC-OFDM receiver exploits both time diversity inherent in BPS, and frequency diversity inherent in MC-OFDM transmission technique. Simulation results show high Probability-of-error performance is achie- vable via BPS/OFDM and BPS/MC-OFDM schemes comparing to the traditional OFDM and MC-OFDM, respectively. Simulations also reveal that MC-OFDM system as well as its merger with BPS is capable of mitigating large Peak-to-Average Ratio (PAPR) problem in traditional OFDM system. In addition, performance simulations with coded OFDM (COFDM) and coded MC-OFDM (MC-COFDM) and their merger with BPS are studied.

THE GROWTH OF MONOCRYSTALLINE SILICON THIN FILM ON INSULATOR (SOI) BY SCANNING ELECTRON BEAM

An experiment for preparation of SOI films by using the scanning electron beam to modify the polycrystalline silicon on SiO2 is presented. This method takes on the epitaxial lateral growth of liquid phase with the crystallon to form monocrystalline silicon films. The effects of the beam power density, scanning velocity, temperature of the substrates and the construction of samples on the quality of the monocrystalline silicon films were discussed. A good experimental result has been obtained, the monocrystalline silicon zone is nearly 200×25μm2.

Z-scan analysis of high-order nonlinear refraction effect induced by using elliptic Gaussian beam

The irradiance of an elliptic Gaussian beam that is high enough to excite high-order nonlinear refraction effect is used to calculate the normalized on-axis transmittance function in the z-scan technique by introducing complex beam parameters which make the calculation simpler. The transmittance formula is applied to the first-, first two-, and first three-order nonlinearities. Numerical evaluation shows that the symmetry no longer holds when using an elliptic Gaussian beam instead of a circular Gaussian beam. A distortion is observed in the central part of the curve, which decreases as ellipticity increases. Moreover, the variation of the normalized peak-valley difference decreases as ellipticity decreases.

多通道ScanSAR成像算法研究

针对传统星载SAR系统分辨率和测绘带宽之间的矛盾,文章采用方位向偏置相位中心结合距离向波束扫描的多通道ScanSAR系统进行了成像算法研究.该算法采用方位向频域重构结合全孔径算法实现了多通道ScanSAR成像,使高分辨率和宽测绘带成像可以同时实现,通过7×7点阵成像仿真验证了该算法的有效性,为高分辨率宽测绘带SAR工程的实现奠定了基础.

Feature Extraction of Sectorial Scan Image of Thick-Walled Electron Beam Welding Seam Based on Principal Component Analysis

A feature extraction method was proposed to sectorial scan image of Ti-6Al-4V electron beam welding seam based on principal component analysis to solve problem of high-dimensional data resulting in timeconsuming in defect recognition. Seven features were extracted from the image and represented 87. 3% information of the original data. Both the extracted features and the original data were used to train support vector machine model to assess the feature extraction performance in two aspects: recognition accuracy and training time. The results show that using the extracted features the recognition accuracy of pore,crack,lack of fusion and lack of penetration are 93%,90.7%,94.7% and 89.3%,respectively,which is slightly higher than those using the original data. The training time of the models using the extracted features is extremely reduced comparing with those using the original data.