Multi-element System Research Articles

The art of back-of-the-envelope paraxial raytracing

Paraxial raytracing is a valuable tool for making quick back-of-the-envelope calculations in optical system design. Its popularity has been highly diminished as a consequence of the growing sophistication of computer-aided raytracing and the availability of powerful computers. The availability of raytracing computer programs does not harm in itself the usefulness of graphical raytracing, but it makes people forget, or never learn the basics of graphical raytracing. In this paper, some of the basic concepts of graphical raytracing are presented, along with some examples that illustrate how it can be applied to multielement systems. The mastering of the methods presented in this paper constitute some of the fundamentals required in the use of any optical software. Such knowledge is absolutely necessary for the conception of novel optical systems.

Development of a personal dosimetry system based on optically stimulated luminescence of α-Al 2O 3 : C for mixed radiation fields

To develop a personal (OSL) optically stimulated luminescence dosimetry system for mixed radiation fields using α-Al 2O 3 : C, a discriminating badge filter system was designed by taking advantage of its optically stimulable properties and energy dependencies. This was done by designing a multi-element badge system for powder layered α-Al 2O 3 : C material and an optical reader system based on high-intensity blue light-emitting diode (LED). The design of the multi-element OSL dosimeter badge system developed allows the measurement of a personal dose equivalent value H p( d) in mixed radiation fields of β and γ. Dosimetric properties of the personal OSL dosimeter badge system investigated here were the dose response, energy response and multi-readability. Based on the computational simulations and experiments of the proposed dosimeter design, it was demonstrated that a multi-element dosimeter system with an OSL technology based on α-Al 2O 3 : C is suitable to obtain personal dose equivalent information in mixed radiation fields.

A novel high-accuracy microstereolithography method employing an adaptive electro-optic mask

A new stereo-photolithography technique to create three-dimensional micro-components using a planar, layer-by-layer, process of exposure has been developed. With this procedure, it is possible to build components with dimensions in the range 50μm–50mm, and feature sizes as small as 5μm with a resolution of less than 1μm. This newly developed system consists of eight elements: a Computer Aided Design environment supporting solid or surface modelling; a resin bath with an integrated high resolution translation stage and component built platform; an ultraviolet laser light source operating at 351.1nm; an optical shutter; a diffractive optical element designed to re-distribute the irradiance of the laser beam from a Gaussian to a top-hat profile; a polysilicon thin film twisted nematic SVGA resolution (800×600) spatial light modulator; a multi-element lithographic reduction lens system; and a comprehensive control system. In this paper, the experimental set-up is described and examples of the microcomponents fabricated by the system are shown.

Techniques and tools for obtaining symmetrical performance from tilted-component systems

Tilted-component systems are known to be characterized by aberrations with unusual field dependences, such as decentered coma and binodal astigmatism. In this paper, the origin of binodal astigmatism in a multielement system from the contributions of individual surfaces is explained in an intuitive manner, as a logical extension of the ordinary aberrations known to all optical designers. The insight provided by this graphical model allows an understanding of why the astigmatism of any given system behaves the way it does, and what needs to be done to convert it to ordinary quadratic behavior, so that what remains can be corrected by a final, rotationally symmetric subsystem. Conditions under which ordinary behavior may be obtained from a system of tilted ele- ments are explored. It is shown that a certain type of symmetry of the primary aberrations may be obtained (regardless of the tilt angles) if the initial, untilted system is monocentric. Graphical displays of the aberra- tion types are used to explore the behavior of the system across the field, and direct optimization of the Zernike coefficients is used to guide the performance of the system. © 2000 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(00)00807-2) Subject terms: optical design; tilted-component systems; nonsymmetric systems; unobscured reflective systems.

Capacities of multi-element transmit and receiveantennas:Correlations and keyholes

Multi-element system capacities are usually thought of as limited only by correlations between elements. It is shown that degenerate channels, called 'keyholes', may arise under realistic assumptions which have zero correlation between the entries of the channel matrix H and yet only a single degree of freedom.

Angle diversity for nondirected wireless infrared communication

We outline the benefits and challenges of using angle diversity in nondirected wireless infrared (IR) communications systems. Multiple transmitter beams and multiple narrow field-of view receivers reduce the path loss, multipath distortion, and background noise of the channel, which leads to improved range. We also discuss practical considerations for multielement angle diversity systems, including channel characterization and suboptimal detection techniques. Maximal-ratio combining provides nearly optimal performance up to 100 Mb/s for the angle diversity systems considered. The design and performance of a prototype angle diversity IR communication system are discussed. The prototype can maintain 70 Mb/s at a P/sub e/ of 10/sup -9/ over a 4-m range.

First experimental characterization of ROTOR: the new switched-current VLSI amplifier for X-ray spectroscopy with silicon drift detectors

In this paper we present the results of an experimental characterization of ROTOR, a new VLSI shaping amplifier conceived for multi-anode Silicon Drift Detectors, or other multi-element solid-state X-ray detection systems. The readout scheme is suitable for the demanding requirements of new X-ray spectroscopy experiments with synchrotron light, like X-ray holography, where both high count-rates and good energy resolutions are required. The circuit, which is of time-variant nature, features a trapezoidal weighting function obtained by means of a switched-current technique. A first prototype of the circuit, integrated with the 1 /spl mu/m/5 V JFET/CMOS technology of the Fraunhofer-Institut, Duisburg (Germany), has been characterized in spectroscopy measurements with a Silicon Drift Detector. The experimental results are presented and discussed in the work.

On the advantages of the use of the three-element detector system for measuring EDXRD patterns to follow the crystallisation of open-framework structures

Time-resolved energy-dispersive X-ray diffraction (EDXRD) studies, employing a new detector technology, of a range of crystallisations of open framework materials are described. We consider four distinct categories of phenomena where new information has been gained specifically from the use of the multi-element (as opposed to the single element) detector system. The systems investigated are: (a) the competitive formation of small-pore and large-pore aluminophosphates (AlPO's), and the effect of concentration of CoII in the mother liquor (precursor gel) in directing the relative amounts of AlPO-18 (AEI) and chabazite (CHA) structures that are formed; (b) the influence of both template (structure directing) molecules and synthesis time on the stabilities of the AlPO-5 (AFI) structures; (c) a study of both the rate of formation of the open framework titanosilicate (ETS-10) structure and the dissociation rate of crystalline TiO2 used in the preparation of ETS-10; and (d) tracking of the intermediate formed during the synthesis of the gallophosphate structure known as ULM-3. The advantages of using a three-element detector configuration are illustrated.

Reliability of mechanical and phased-array designs for serial intravascular ultrasound examinations--animal and clinical studies in stented and non-stented coronary arteries.

Both mechanical and multi-element intravascular ultrasound designs have potential advantages and limitations that may impact on their value for clinical and research purposes. Determination of the reproducibility of measurements is critical before a given system can be used in studies such as regression of atherosclerosis trials. We performed serial intravascular ultrasound imaging with catheters using mechanical and phased-array designs in stented and non-stented coronary arteries in dogs and in patients. Both systems correlated well for areas (r > or = 0.90, p < 0.0001) and diameters (r > or = 0.84. p < 0.0001) in dogs and in patients. There was a slight difference between multi-element and mechanical designs for measurements of area (mean difference in dogs and in patients: -0.24 and 0.96 mm2, p < 0.055) and diameter (-0.08 and 0.16 mm, p < 0.0001). The reproducibility of the multi-element system for reanalysis of the same frames and for analysis of serial pullbacks was similar to the same measurements with the mechanical system (r > or = 0.96 for all measurements). The differences in absolute and relative variability between the mechanical and phased-array designs, both for reanalysis of same frames and serial pullbacks, were very small. Although multi-element and mechanical intravascular ultrasound designs are not strictly interchangeable, their similar reproducibility and the small differences in measurements demonstrate that both designs are acceptable alternatives for trials of regression of atherosclerosis. Determination of the variability for serial pullbacks of both designs was also important to assess the statistical power of such trials.

Fabrication of Bulk Mg&amp;ndash;Cu&amp;ndash;Ag&amp;ndash;Y Glassy Alloy by Squeeze Casting

A new Mg 65 Cu 15 Y 10 Ag 10 alloy having large glass-forming ability has been developed to produce bulk Mg-based glass material. Partial replacement of Ag with Cu in a Mg 65 Cu 25 Ag 10 alloy led to a significant improvement of glass-forming ability. The addition of Ag significantly decreases the melting temperature and also satisfies conditions of a multi-element system with a deep eutectic, large atomic-size difference between its components and a large electronegativity difference between the components for good glass-forming ability. Injection casting produced bulk metallic glass of Mg 65 Cu 15 Y 10 Ag 10 alloy having a diameter up to 6 mm. Squeeze casting was able to produce larger bulk metallic glass with Mg 65 Cu 15 Y 10 Ag 10 alloy having diameter of 10 mm, due to the rapid heat extraction and undercooling of the liquid alloy, by applying pressure during solidification.

A novel VLSI processor for high-rate, high resolution spectroscopy

A novel time-variant VLSI shaper amplifier, suitable for multi-anode Silicon Drift Detectors or other multi-element solid-state X-ray detection systems, is proposed. The new read-out scheme has been conceived for demanding applications with synchrotron light sources, such as X-ray holography or EXAFS, where both high count-rates and high-energy resolutions are required. The circuit is of the linear time-variant class, accepts randomly distributed events and features: a finite-width (1–10 μs) quasi-optimal weight function, an ultra-low-level energy discrimination (∼150 eV), and a full compatibility for monolithic integration in CMOS technology. Its impulse response has a staircase-like shape, but the weight function (which is in general different from the impulse response in time-variant systems) is quasi trapezoidal. The operation principles of the new scheme as well as the first experimental results obtained with a prototype of the circuit are presented and discussed in the work.

Proposal of a New Method for Neutron Dosimetry Based on Spectral Information Obtained by Application of Artificial Neural Networks

A new method for the monitoring of neutron radiation is proposed. It is based on the determination of spectral information on the neutron field in order to derive dose quantities like the ambient dose equivalent, the dose equivalent, or other dose quantities which depend on the neutron energy. The method uses a multi-element system consisting of converter type silicon detectors. The unfolding procedure is based on an artificial neural network (ANN). The response function of each element is determined by a computational model considering the neutron interaction with the dosemeter layers and the subsequent transport of produced ions. An example is given for a multi-element system. The ANN is trained by a given set of neutron spectra and then applied to count responses obtained in neutron fields. Four examples of spectra unfolded using the ANN are presented.

A monolithic implementation of a switched-current "wheel" amplifier for multi-channel Silicon Drift Detectors

In this paper we present a new VLSI shaper amplifier suitable for multi-anode Silicon Drift Detectors, or other multi-element solid-state X-ray detection systems. The readout scheme has been conceived and developed for demanding applications with synchrotron light sources, such as X-ray holography or EXAFS experiments, where both high count-rates and high energy resolutions are required. The circuit is of time-variant nature, accepts randomly distributed events and features a finite-width (1.1 /spl mu/s) weight function, a low-level energy discrimination, a low power consumption (a few mW per channel) and a full compatibility with monolithic integration in CMOS technology. Its impulse response has a staircase-like shape, but the implemented weight function (which is in general different from the impulse response in time-variant systems) is quasi trapezoidal. A first prototype of the circuit is here described and the first experimental results are also reported.

Design of a large-area CsI(Tl) photo-diode array for explosives detection by neutron-activation gamma-ray spectroscopy

A design for a large area, position-sensitive gamma-ray spectrometer for use in imaging explosive materials is described. The design has been optimised for use in the energy range from 2 to 12 MeV. At 5 MeV, the spectral resolution of each CsI(Tl)-photodiode pixel is better than 3% FWHM. The multi-element detector system, when used in conjunction with a coded-aperture mask, is able to provide a “multi-colour” image of the scene when illuminated by a neutron source. The feasibility of using such a system to identify the unique elemental composition and location of the explosive materials is discussed.

UV microstereolithography system that uses spatial light modulator technology

A new stereophotolithography technique utilizing a spatial light modulator (SLM) to create three-dimensional components with a planar, layer-by-layer process of exposure is described. With this procedure it is possible to build components with dimensions in the range of 50 mum-50 mm and feature sizes as small as 5 mum with a resolution of 1 mum. A polysilicon thin-film twisted nematic SVGA SLM is used as the dynamic photolithographic mask. The system consists of eight elements: a UV laser light source, an optical shutter, beam-conditioning optics, a SLM, a multielement reduction lens system, a high-resolution translation stage, a control system, and a computer-aided-design system. Each of these system components is briefly described. In addition, the optical characteristics of commercially available UV curable resins are investigated with nondegenerate four-wave mixing. Holographic gratings were written at a wavelength of 351.1 nm and read at 632.8 nm to compare the reactivity, curing speed, shrinkage, and resolution of the resins. These experiments were carried out to prove the suitability of these photopolymerization systems for microstereolithography.

CdZnTe Array Detectors for Synchrotron Radiation Applications

An X-ray linear-array detector was fabricated using high-pressure Bridgman-grown CdZnTe. The detector area was 175 x 800 microm and the pitch size was 250 microm. The measured dark current for the test 16-element detector was as low as 0.1 pA at 800 V cm(-1) with excellent uniformity. Energy spectra were measured using a 57Co radiation source. Both a small-pixel effect and charge sharing were observed. For the arrays, an average 5.8% full width at half-maximum (FWHM) at the 122 keV photopeak was obtained with a standard deviation of 0.2%. A large-area detector (1 x 1 cm) of the same material before fabrication exhibited a low-energy tail at the photopeak, which limits the photopeak FWHM to 8%, typically due to hole trapping. At energies below 60 keV, charge sharing between elements was observed. The charge sharing was greatly reduced by providing a path to ground for unwanted charges. A prototype readout electronic system for an eight-channel array detector was developed. A readout system intended for a multielement solid-state detector system was also used. The array detector will be used for high-energy diffraction and Compton scattering measurements at the Advanced Photon Source.

A multi-DSP system for the neutron high resolution Fourier diffractometer

The multi-DSP data acquisition system for neutron time-of-flight spectrum measurements requiring fast real-time data processing is designed and is operated at the neutron High Resolution Fourier Diffractometer (HRFD). The use of high performance DSPs and front-end electronics based on flexible PLDs allows increasing of the efficiency of neutron diffractometers with a Fourier chopper and a multi-element detector system by the method of electronic time-focusing.

An approach to unfold the response of a multi-element system using an artificial neural network

An unfolding procedure is proposed which aims at obtaining spectral information of a neutron radiation field by the analysis of the response of a multi-element system consisting of converter type semiconductors. For the unfolding procedure an artificial neural network (feed forward network), trained by the back-propagation method, was used. The response functions of the single elements to neutron radiation were calculated by application of a computational model for an energy range from 10/sup -2/ eV to 10 MeV. The training of the artificial neural network was based on the computation of responses of a six-element system for a set of 300 neutron spectra and the application of the backpropagation method. The validation was performed by the unfolding of 100 computed responses. Two unfolding examples were pointed out for the determination of the neutron spectra. The spectra resulting from the unfolding procedure agree well with the original spectra used for the response computation.

Dead-time correction of a multi-element SSD for fluorescent XAFS.

The correct evaluation of the live time of a detection system is found to be important for correcting the counting loss of a multi-element detection system for fluorescent XAFS experiments. Synchronous resetting of preamplifiers and the suspension of electronics during the reset period is an effective method. The dead time of the incoming count rate should also be corrected, since its non-linearity cannot be neglected. A 19-element solid-state detector system which can count up to 3.7 x 10(5) counts s(-1) channel(-1) with <270 eV FWHM for Mn Kalpha has been realized; the dead time was independent of the incoming photon energy.

New method of computation of electrical Y-matrix for arbitrarily connected multielement SAW devices

We treat surface-acoustic wave (SAW) devices as an arbitrary multielement system. To describe it, a modified form of the chain matrix (E-matrix) is introduced. The E-matrix has a property of turning the calculation of the transfer matrix of this system into a simple multiplication procedure. This allows one to perform computation of electrical response of almost any type of SAW device since the total transfer matrix could be reduced to a Y-matrix. Examples and simulation results confirming the method described are shown.