Scanning Linear Array Research Articles

Pareto optimal synthesis of the linear array geometry for minimum sidelobe level and null control during beam scanning

In this work, synthesis of the linear array geometry is put forward as a constrained vector optimization problem whose components are to meet the minimum sidelobe level (SLL) and control of the wide/narrow null placement during beam scanning whose range can vary from zero to the wide bands. As these synthesis objectives generally conflict with each other, nondominated solutions are acquired using the Nondominated Sorting Genetic Algorithm- II (NSGA-II) as a fast nondominated genetic sorting algorithm. Then, the Pareto frontiers are obtained using these trade-off solution sets between the maximum SLL, null control, and scanning range to provide a view of all design options. Thus, the pattern features resulted from these Pareto frontiers are valid for any chosen main beam direction within its full prescribed beam scanning range. The same Pareto optimal synthesis procedure can be applied to a thinned linear antenna array. A thinned linear antenna array is obtained by a simple genetic optimization by rounding the excitation amplitudes either to 1 or 0 to minimize the maximum of side lobe level (MSLL) during the beam scanning within the prescribed region as stated in the multiobjective function. Finally, some typical Pareto optimal radiation patterns of the scanning arrays are synthesized with only perturbating the positions of the array elements, and their full electromagnetic wave simulations are also completed to examine the resulted mutual coupling effects between the elements of the arrays. It can be concluded that the Pareto optimal synthesis procedure gives the scanning linear antenna arrays with successful radiation performance. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.

Design and Characterization of the I-ImaS Multi-Element X-Ray Detector System

I-ImaS (Intelligent Imaging Sensors) is a European project aiming to produce new, intelligent X-ray imaging systems using novel APS sensors to create optimal diagnostic images. Initial systems have been constructed for medical imaging; specifically mammography and dental encephalography. However, the I-ImaS system concept could be applied to all areas of X-ray imaging, including homeland security and industrial QA. The I-ImaS system intelligence is implemented by the use of APS technology and FPGAs, allowing real-time analysis of data during image acquisition. This gives the system the capability to perform as an on-the-fly adaptive imaging system, with the potential to create images with maximum diagnostic information within given dose constraints. The I-ImaS system uses a scanning linear array of scintillator-coupled 1.5-D CMOS Active Pixel Sensors to create a full 2-D X-ray image of an object. This paper describes the parameters considered when choosing the scintillator elements of the detectors. A study of the positioning of the sensors to form a linear detector is also considered, along with a discussion of the potential losses in image quality associated with creating a linear sensor by tiling many smaller sensors. Preliminary results show that the detectors have sufficient performance to be used successfully in the initial mammographic and encephalographic I-ImaS systems that are currently under construction.

The sensitivity threshold of IR devices based on array photodetectors

A noise model of IR staring arrays is proposed that takes into account the combined action of the spatial and temporal components of the noise. It is used as a basis for obtaining simple relationships for calculating the sensitivity threshold of IR staring devices. How the residual spatial noise affects the relationship in the sensitivity between a staring array and a scanning linear array of photosensitive elements is considered. It is shown that the operation of IR staring devices under conditions of incomplete suppression of spatial noise makes it possible to narrow the spectral range.

Non-contact velocity compensation system for handheld scanners

In this paper, we present a method for compensating for variations in the scanning speed of hand-held scanners that does not require physical contact between the scanning device and the scanned surface. In existing scanning devices the scanning linear array is placed parallel to the paper width (main scan direction) and moves perpendicularly to its axis (sub-scan direction). The speed with which the array moves determines the scanning resolution along the sub-scan direction. If the scanner is moved manually as in a handheld scanner the velocity with which the array moves along the sub-scan direction varies, thus causing distortions of the scanned images. In this paper, we present a system that can estimate these velocity variations using local contrast estimates. This system is unique in that it does not require contact between image source and scanning head, it can therefore be used by visually impaired users in a variety of environments. The presented velocity compensation system provides a post-compensation (apparent) velocity in the range of 1.2 : 1 for an initial (real) velocity variation of 10 : 1.

Image reconstruction from multiple 1-D scans using filtered localized projection

The state-of-the-art procedure for image acquisition in downlooking remote sensing and astronomical applications is to use scanning linear arrays. These consist of discrete IR solid-state detectors. We consider the spatial resolution that may be attained with such an array. The individual detectors in the array are typically significantly larger than the blur spot of the imaging optics. Hence a naive recombination of data would produce images which are limited in resolution by the size of the detectors. However, the information content of all available data, including intentional overlap of successive scans and rescans of the same area from different directions, may include much higher spatial frequencies. In the following, we outline a method of filtered localized projection (FLP) which attempts to reconstruct these higher frequencies. Mathematically, FLP consists of a localized summation or projection followed by an inverse-filter operation in analogy to filtered backprojection of computed tomography. The FLP method is applied, using a linear array, to simulated data for staggered parallel scans and to multiple scan directions. Effects of noise and limitations of the approach are discussed.

Real time digital thresholding of data from continuous scanning linear arrays

Some consequences of utilising the potential for real time digital thresholding on a line basis in an implemented system for fast image acquisition and analysis, the Edinburgh FIP-system, are discussed. The line by line approach may give rise to directionally dependent shape distortions of detected objects. The types of distortions encountered depend on the thresholding algorithm and the types of objects in question. The importance of the distortions is determined by the application for which the system is used. For application to metaphase finding the implemented dynamic thresholding scheme provides satisfactory results, which could not in any obvious way be improved by a corresponding two-dimensional alternative. For application to cervical smear screening an initial implementation of a local thresholding scheme is found inadequate. A straightforward software compensation is inhibited by the system's ‘interval-coding’, which on the other hand seems to provide a basis for alternative ways of surmounting the problem. The line by line approach imposes limitations on the applicability of the system, but many problems can be reformulated so as to allow solution in a fast line-scanning environment.

Detector for dual-energy digital radiography.

A detection scheme is described that allows one to accomplish dual-energy scanned projection digital radiography without switching the x-ray tube voltage. The method employs a high/low atomic number detector sandwich that simultaneously separates the x-ray beam transmitted by the patient into low and high energy components. To test the method, the response of a scanning linear array of energy-sensitive detectors was simulated, and bone and soft tissue images of an anthropomorphic chest phantom were obtained at 140 kVp. These were compared with similar images obtained by switching the x-ray tube voltage from 80 kVp to a heavily filtered 140 kVp. For comparable entrance skin exposures, the dual-energy detector images required a lower tube load and resulted in higher noise levels. The latter is attributable to the fact that the separation in energy between the high and low energy components is smaller with the dual-energy detector than with the voltage switching technique, and to misregistration problems associated with the simulation methodology. A detector design is also discussed that would result in improved energy separation and lower noise levels. In view of this possibility and the tube loading advantage, the method looks promising for digital scanned projection radiography.

Performance Analysis And Size Optimization Of Focal Planes For Point-Source Tracking Algorithm Applications

A number of applications require the precise tracking or position estimation of an object unresolved in the system optics. This paper evaluates several one-dimensional interpolation algorithms (odd N-point centroids, N = 3, 5, 7, 9, and three-point and five-point quadratic curve fits) designed to make these estimates to subpixel accuracy. Analytic, Monte Carlo, and experimental results are presented. The tracking sensor examined was a scanning linear array of infrared detectors assumed to be background-limited. The detector size and physical spacing were varied parametrically, with realistic fabrication constraints, to determine the relative performance and to obtain the optimum configuration. The optics blur spot was assumed Gaussian. The sources of error considered to affect the algorithm performance were the systematic algorithm bias, the random noise, and the postcalibration residual detector responsivity nonuniformities. Track accuracy improves with signal-to-noise ratio (SNR), until limited by algorithm inaccuracies or focal-plane nonuniformity. Among the algorithms tested, the three-point centroid performs best, provided that systematic algorithm bias is corrected. An experimental infrared tracking focal plane, used in a tracker simulation, closely confirmed the analysis. With the three-point algorithms, an experimental accuracy to smaller than 1/100 a detector (<1/250 a blur spot) was obtained at high signal-to-noise ratios.

Technical memorandum. Receiving analysis of the shaped cylindrical reflector antennna with an array feed

The receiving analysis of the shaped cylindrical reflector antenna is extended to cover the case where the reflector feed consists of a linear antenna array. Use of the theory is illustrated by considering the effects of finite reflector width on the secondary radiation characteristics of a planar reflector fed by a scanning linear array.

Simultaneous Multielement Quantitative Spectrochemical Analysis Using a DC Arc Source and a Computer Coupled Photodiode Array Spectrometer

Abstract Self scanning linear arrays of silicon photodiodes have been utilized as multichannel detectors in a variety of spectrochemical measurements (1,2,3,4). These arrays have densities of 1000 photodiodes per inch and can be thought of as completely solid state single line image sensors. In some earlier work (3) a spectrometer based on this detector was utilized for qualitative dc arc spectrochemical analysis. In this note we report on the utilization of an improved computer coupled photodiode array spectrometer system for simultaneous multielement quantitative analysis with a dc arc source.