Digital Array Research Articles

Establishment of a Digital Laminography facility at the Malaysian Nuclear Agency

Digital Laminography (DL) is a technique that enables the estimation of indication depth from a set of digital projection radiographs. It allows the engineers or researchers to visualize and measure the depth from the object’s surface. The technique applies to welded components and non-metal applications such as composite materials. The technique also allows users to understand engineering problems and further analyze the cause of failures. Malaysian Nuclear Agency is pursuing the building and establishment the DL system at its facility. A gantry is designed to hold a 225kVp X-ray tube that is mechanically moved slowly. A 100 µm pixel size Digital Detector Array (DDA) is used to capture the images. This paper highlights simulation and a preliminary assessment to understand the physics and appropriate steps to build a DL system. It discusses the simulation and experimental study of exposure parameters and setup by digital radiographic testing (RT-D) of known imperfections of a welded steel plate before performing the DL measurement. The radiographic images and their achieved contrast sensitivity and image quality are analyzed according to ISO 17636-2. The results of simulations and experiments demonstrate a good and consistent ability to measure the depth and extension of the reconstructed imperfections within ± 1 mm regarding the actual size and position.

Shaped pattern synthesis for hybrid analog–digital arrays via manifold optimization-enabled block coordinate descent

Hybrid analog–digital (HAD) architecture is a promising means to realize large-scale arrays owing to the judicious trade-off between system performance and hardware complexity. This paper investigates the beampattern shaping of HAD arrays through minimizing the beampattern matching error between desired and actual patterns. Due to the nonconvex constraints on analog and digital weights and the nonconvex nonsmooth objective function, the resultant codesign is NP-hard. To address this issue, we create an efficient algorithm by leveraging block coordinate descent (BCD) and Riemannian manifold optimization. We first equivalently represent the objective function as a smooth bi-quadratic function by introducing a uni-modulus auxiliary variable. Subsequently, we alternatingly optimize the scaling factor, digital weights, analog weights and auxiliary variable under the BCD framework, where the simultaneous update of analog weights and auxiliary variable is recast as uni-modular constrained quadratic programming which is efficiently solved by Riemannian Newton method, and the digital weights have a global optimal solution via Lagrangian multiplier method. We also derive an explicit convergence condition of this algorithm. Numerical results demonstrate that the proposed algorithm has superior performance and faster convergence speed than alternative algorithms, and produces nearly the same mainlobe gain as fully digital arrays with significantly fewer radio-frequency chains.

Receiving Paths Improvement of Digital Phased Array Antennas Using Adaptive Dynamic Range

In contemporary radar technology, the observation and detection of objects with low radar cross-sections remains a significant challenge. A multi-functional radar model employing a digital phased array antenna system offers notable advantages over traditional radar in addressing this issue. Nonetheless, to fully capitalize on these benefits, improving the structure of the receiving path in digital transceiver modules is crucial. A method for improving the digital receiving path model by implementing a matched filter approach is introduced. Given that the return signals from objects are often lower than the internal noise, the analog part of the digital transceiver modules must ensure that its dynamic range aligns with the level of this noise and the weak signal. The output signal level of the analog part must correspond to the allowable input range of the analog-to-digital converter. Improvements in the receiving path to achieve a fully matched model can reduce errors in the phase parameters and amplitudes of the useful signal at the output. The simulation results presented in this paper demonstrate a reduction in amplitude error by approximately 1 dB and a phase error exceeding 1.5 degrees for the desired signal at the output of each receiving path. Consequently, these improvements are expected to enhance the overall quality and efficiency of the spatial and temporal accumulation processes in the digital phased array antenna system. Furthermore, to maintain the matched filter model, we also propose incorporating an adaptive “pseudo-expansion” of the linear gain range. This involves adding a feedback stage with an automatic and adaptive bias voltage adjustment for the intermediate-frequency preamplifier in the analog part of the receiving path. Simulations to qualitatively verify the validity of this proposal are conducted using data from practical operational radar system models.

A Space–Time Coding Array Sidelobe Optimization Method Combining Array Element Spatial Coding and Mismatched Filtering

Digital array radar (DAR) can fully realize digitalization at both the transmitting and receiving ends. However, the development of freedom at the transmitting end is far from mature. So, the new concept of multi-dimensional waveform coding array has appeared, which can optimize the transmitting resources in space–time/frequency waveform or another dimension. Space–time coding array (STCA) is a typical kind of multi-dimensional waveform coding array, which can make full use of the high degree of freedom at the transmitting end. It realizes emission diversity by introducing a small time delay between different transmission array elements. In this paper, an optimization method for STCA, which combines the array spatial coding at the transmitting end and mismatched filter design at the receiving end, is proposed. This method aims to solve the sidelobe problems of STCA: the inherent resonance phenomenon and the resolution loss problem. The experimental verification and quantitative comparative analysis prove the effectiveness of the proposed method. The resolution is restored to the ideal level under the premise of maintaining the beam-scanning ability and ultra-low sidelobe, and the resonance phenomenon caused by spectrum discontinuity is eliminated simultaneously.

Особенности структурного синтеза алгоритмов обработки радиолокационной информации при многочастотном наблюдении

Setting and solving the problem of structural synthesis of the algorithm for detecting and measuring parameters of mobile objects against the background of correlated interference and noise in multi-frequency radar surveillance systems based on multibeam digital antenna arrays are considered. The processing algorithm is synthesized under the assumption of Gaussian observation statistics with separate spatial and temporal characteristics of signals and interference. As part of the study, a phenomenological model of the radar situation was developed, adequate to the formation of observations in multi-frequency space-time signal processing systems against the background of correlated interference and noise. On its basis, a structure of an optimal, in terms of Bayesian quality criteria, algorithm for detecting a multi-part signal at the outputs of multipath digital antenna arrays is obtained. On the basis of the adaptive Bayesian approach, ways of solving the problem of detecting and measuring parameters of mobile objects in conditions of multi-frequency observations with parametric a priori uncertainty about interference characteristics are determined. Recommendations on selection of adaptive algorithms for radar information processing in case of non-stationary observations are given. The results of structural synthesis make it possible to present processing in the form of a multichannel system in space, time and radial speed. Sufficient statistics on the set of radiation frequencies are accumulated. This view opens up a wide range of possibilities for using parallel computing systems. It is shown that the obtained algorithms can serve as the basis for detecting the beginning of maneuvering of an observation object at the stage of primary processing of radar information.

(Invited) Analog Computing with High Precision and Programmability Enabled by Memristors

While digital computing dominates the technological landscape, analog computing distinguishes itself with superior energy efficiency and high throughput. However, its historical limitation in precision and programmability has confined its application to specific and low-precision domains, notably in neural networks. The escalating challenge posed by the analog data deluge calls for versatile analog platforms. These platforms must not only exhibit exceptional efficiency but also boast reconfigurability and precision.Recent breakthroughs in analog devices, such as memristors, have laid the groundwork for unparalleled analog computing capabilities. Leveraging the multifaceted role of memristors, we introduce memristive field-programmable analog arrays (FPAAs), mirroring the functionality of their digital counterparts, field-programmable digital arrays (FPGAs). To elevate precision, we delve into the origins of reading noise, successfully mitigating it and achieving an unparalleled 2048 conductance levels in individual memristors—equivalent to 11 bits per cell, setting a record precision among diverse memory types. Acknowledging the persistent demand for single or double precision in various applications, we propose and develop a circuit architecture and programming protocol. This innovation enables analog memories to attain arbitrarily high precision with minimal circuit overhead. Our experimental validation involves a memristor System-on-Chip fabricated in a standard foundry, demonstrating significantly improved precision and power efficiency compared to traditional digital systems.The co-design approach presented empowers low-precision analog devices to perform high-precision computing within a programmable platform. This demonstration underscores the transformative potential of analog computing, transcending historical limitations and ushering in a new era of precision and efficiency.

A series‐fed frequency scanning antenna for millimeter wave wireless communication

AbstractIn the realms of 5G and the upcoming 6G communications, the millimeter‐wave bands offer substantially greater bandwidth. However, due to their propagation characteristics, aligning antennas becomes a challenging issue, particularly at the node side in industrial and vehicular network applications. Angle‐scanning antennas can significantly enhance communication reliability or provide new possibilities for spatial multiplexing. Previous studies have predominantly concentrated on frequency‐scanning antennas characterized by either low‐gain individual units or expensive digital arrays. Consequently, there has been a scarcity of solutions that are both cost‐effective and high‐gain. In this study, a method is proposed for achieving frequency scanning by extending the feed lines between elements. Based on this approach, a millimeter‐wave high‐gain serial‐feed frequency‐scanning antenna is developed. This antenna operates within the 60–64 GHz millimeter‐wave ISM (Industrial, Scientific, and Medical) band and is capable of performing a 10 scan in the E‐plane. Moreover, the antenna maintains a width of less than half a wavelength, allowing for the assembly of multiple antennas into a MIMO array.

Development of conductive carbon-based interdigitated electrode array integrated with microfluidic channel for blood glucose sensing

PurposeThis study aims to provide a microfluidic blood glucose sensing platform based on integrated interdigitated electrode arrays (IDEAs) on a flexible quartz glass substrate, adhering closely to pertinent electrochemical characterizations.Design/methodology/approachSensors are the key elements of the modern electronics era through which all the possible physical quantities can be detected and converted into their equivalent electrical form and processed further. But to make the sensing environment better, various types of innovative architectures are being developed nowadays and among them interdigitated electrodes are quite remarkable in terms of their sensing capability. They are a well-qualified candidate in the field of gas sensing and biosensing, but even their sensitivities are getting saturated due to their physical dimensions. Most of the thin film IDEAs fabricated by conventional optical lithographic techniques do not possess a high surface-to-volume ratio to detect the target specified and that reduces their sensitivity factor. In this context, a classic conductive carbon-based highly sensitive three dimensional (3D) IDEA-enabled biosensing system has been conceived on a transparent and flexible substrate to measure the amount of glucose concentration present in human blood. 3D IDEA possesses a way better capacitive sensing behavior compared to conventional thin film microcapacitive electrodes. To transmit the target biological analyte sample property for the detection purpose to the interdigitated array-based sensing platform, the design of a microfluidic channel is initiated on the same substrate. The complex 3D Inter Digital array structure improves the overall capacitance of the entire sensing platform and the reactive surface area as well. The manufactured integrated device displays a decent value of sensitivity in the order of 5.6 µA mM−1 cm−2.FindingsDevelopment of a low-cost array-based integrated and highly flexible microfluidic biochip to extract the quantity of glucose present in human blood.Originality/valuePotential future research opportunities in the realm of integrated miniaturized, low-cost smart biosensing systems may arise from this study.

Orbital-Rail-Type Automatic Inspection Device for Pipeline Welds Using Radiation Dose Prediction Results from FLUKA Simulation

Pipeline welds typically do not have secondary reinforcement, rendering welds highly vulnerable to leakage accidents caused by the movement of gases or liquids. Therefore, identifying internal defects in welds through radiographic testing (RT) is critical for a visual and quantitative evaluation of weld defects. In this study, we developed a device that can automatically inspect the circumferential connection between pipes by applying a digital radiography testing (DRT) technique that can convert radiation signals into real-time electrical signals by using a digital detector array (DDA). Gamma rays were used to minimize spatial constraints in the inspection environment and optimization was performed to satisfy quality requirements set by international standards. Furthermore, FLUKA simulation was performed to predict radiation intensity for accurate radiation leakage identification to enable the shielding design to be supplemented with lead rubber. This measure considerably reduces the safe distance for radiation leakage during field testing. The results confirmed the feasibility of a novel automated inspection technique that integrates automatic inspection devices and ensures safety using radiation, the byproduct of which is a hazardous material.

Adaptive digital antenna array signal processing algorithm based on LDL decomposition

Two algorithms for inverting correlation matrices of digital antenna array signals are compared: LDL decomposition and the fringing method. The idea of comparing algorithms was to take into account the limitations on the length of the input data mantissa in the process of space-time processing using FPGAs. It has been found that rounding errors in the signal processing process in FPGAs can lead to the destruction of the directivity pattern. This is due to the fact that when implementing various algorithms for matrix inversion, the distribution of errors in the channels becomes interconnected. This means that when implementing adaptive antenna arrays on FPGAs, it is necessary to carefully choose the length of the mantissa and the conversion algorithm. In this regard, an algorithm for signal processing in an adaptive antenna array is proposed, its difference from the known ones is that when implemented on FPGAs, floating-point arithmetic of limited mantissa bit is used. When comparing two computationally efficient matrix inversion algorithms (the LDL method and the fringing method), the LDL method has higher stability. It was found that with an increase in the rank of the correlation matrix, the effect of rounding errors will be stronger. In this regard, it is necessary to determine in advance at what ratio of power sources and internal noise it is planned to use an adaptive processor.

Contrast-based notch-to-crack transfer function for digital radiography

To simulate cracks, a series of slits with depths ranging from 17.2% to 40% of 301 stainless steel (SS) plate thickness are fabricated for this study. The examination includes a microfocus X-ray tube and a digital detector array (DDA) with 75 ??m pixel pitch. The basis of this study is to determine the effect of detector scintillator blur, noise and pixelation on the contrast of the resultant radiographic image and, ultimately, on the detectability of a crack. Many crack detectability studies are performed on notched plates rather than true cracks. As the notch width becomes smaller than a pixel, the grey value of the image it generates will be averaged over the entire footprint of the pixel. Therefore, the contrast with neighbouring (no notch) pixels is reduced. This study develops a relationship between the material property, detector parameters, notch geometry and expected contrast that would result from the radiograph image. This relationship can be used as a transfer function towards evaluating the resultant contrast from a notch and extrapolating the results towards a hairline crack.

The main directions of enhancement of digital antenna arrays

The development of modern radio electronic systems causes an increase in the requirements for the parameters of antenna devices (AU) and causes the transition from previously used mirror antennas and passive phased array antennas (FAA) to active FAA (AFAA), the considerable advantage of which is a significant reduction in energy losses of transmitted and received signals by reducing the distance of the low-noise amplifier input and output of power amplifier to the antenna element. Further development of the AU is the transition from AFAA with analog beamforming to digital antenna arrays (DAR) with digital beamforming, the advantages of which are due to the possibility of forming multibeam receiving and transmitting radiation patterns with independent control of the direction and shape of the beams, as well as the possibility of flexible change of operating modes. The use of a DAR with two-dimensional electronic scanning provides a significant increase in the efficiency of radio-electronic systems. Thus, their use in radar provides a gain in the efficiency of using the time, energy, frequency and spatial resources of radar with CAR up to 13 times compared with radar with passive FAA and AFAA with one-dimensional scanning. The disadvantages of the DAR are the high cost and increased energy consumption due to the installation of active elements in each transceiver channel, as well as the long time required to create new products, associated with a large amount of software and a complex structure for building a CAR. To overcome these disadvantages, manufacturers of antenna arrays and developers of the radio-electronic element base are creating new technical solutions. The main directions of development of technologies for the production of DAR functional devices that reduce the cost and reduce the time needed to create new products are shown: the development of common modules that allow you to create scalable DAR, increasing the integration of microwave monolithic integrated circuits with the placement of the maximum number of transceiver channels on one chip, increasing the integration of ASIC, including ADCs, DACs and digital signal processing devices, increasing the clock frequencies of digital functional nodes, as well as the development of circuit solutions for building nodes with low energy consumption.

Method for measuring radiation patterns of digital antenna arrays

Formulation of the problem. The Digital Beamforming Antenna Arrays (DBAA) are widely used as the directional antennas in radio systems today. However, such arrays typically do not have a radiofrequency output. Consequently, the standard methods for measuring the Radiation Patterns (RP), based on the transmitting of a monochromatic probing signals, reception of the signals in the far field, as well as measuring the output power of the antenna array, cannot be used to measure the RP of the DBAA. The method considered in this work involves the transmitting a probing signal modulated by a pseudonoise sequence and processing the DBAA output signal at the zero intermediate frequency (base-band) using a matched filter or a correlator. Target. A method for measuring the radiation pattern of the DBAA is considered, based on the correlation processing of its output signal. Results. The paper presents a description of the setup for measuring the DBAA RP, as well as a mathematical explanation of the measurement procedure. It is shown that the accuracy of the RP measurement depends on the Signal-to-Noise Ratio (SNR) at the outputs of the receivers of the DBAA channels, and the number of array channels and the number of symbols of the pseudonoise sequence used for the modulation of the radiated signal. The error in the RP measurement decreases by 3 dB each time as the number of the DBAA channels or the number of symbols of the pseudonoise sequence used in the measurements is doubled. This result is confirmed by simulation the measurement of RP of the eight- and sixteen-channel linear DBAA using pseudo-noise sequences of maximum length (M-sequences) with a number of symbols equal to 1023 and 2047. Practical significance. The proposed method does not require the usage of the up-converter to convert the base-band DBAA output signal from the base-band to a carrier frequency, and it also does not require the usage of a power meter for measurement the analog signal at the output of this converter.

Digital antenna array based on programmable logic integrated circuits for mobile radio networks

Currently, there is a need to develop new technical solutions for antenna systems for central (base) stations of mobile radio networks, which not only have improved electrical characteristics, but also allow them to adjust from intentional and unintended interference, while providing a reliable communication channel between several correspondents. The purpose of the work is to develop methods for constructing digital antenna arrays with adaptive DN control for VHF mobile radio networks. The presented solution of the ring car allows you to form the DN in the specified directions, to work in multipath mode, as well as the proposed solutions of ring cars can be used both in the center (base) stations of mobile radio communication systems and on mobile objects operating, including in the relay mode.

Design and Implementation of Digital Down Converter for WiFi Network

This paper introduces a field-programmable gate array (FPGA)-based digital down converter (DDC) processing a sampling frequency of about 3.64 GHz to a down-converted frequency of 28.4375 MHz to match the IEEE 802.11ah Wi-Fi HaLow standard. The proposed DDC uses a polyphase mixer(PM) and a resampling filter. The PM adopts parallel coordinate rotation digital computer (CORDIC) processors and lowpass filter arrays to reduce high-speed data rates with minimum resource utilization. Again, the resampling filter employs a cascaded integrator comb (CIC) filter associated with a parallel prefixed adder (PPA) and a multi-channel systolic finite impulse response (FIR) filter implemented with canonical expression, attaining optimum hardware cost. Converting floating-point to fixed-point data types provides significant resource savings. Finally, the improved design is coded in the Xilinx Vivado synthesis tool and successfully tested on the FPGA Kintex-7 device. In contrast to other recent architectures, the proposed design substantially reduces area requirements and power utilization. The Matlab tool verifies the design to achieve an acceptable spurious-free dynamic range (SFDR) of 115 dB.

Characterization of Rigid and Flexible Digital Detector Arrays Using ASTM E2597/E2597M-22

ASTM E2597/E2597M-22 is a standard that summarizes a standard practice for characterization of digital detector arrays (DDAs) by manufacturers. The standard consists of a series of tests intended to deliver quantitative results for a given model of detector’s characteristics as they should perform upon sale. It was written for use in characterizing rigid detectors, but the tests are applicable to bendable DDAs, utilized for single viewing. Bendable DDAs, unlike their rigid counterparts, are made to conform around parts being inspected, such as pipes, in a similar application to film and computed radiography for imaging curved objects. As bendable DDAs are made using the same scintillators as flat panel DDAs and have similar pixel pitch and resolution capabilities, it is expected that the results from most characterization tests should be similar. Conformable DDAs produce similar imaging results as rigid DDAs but have the flexibility of use for curved surfaces. They offer a valuable tool for customers currently using film and CR who are looking to expedite their inspections or move away from use of consumable products. We performed these characterization procedures on conformable DDA models and rigid DDA models utilizing proprietary INDUSTREX software developed by Carestream Health, Inc. The experimental results are presented as part of this paper.

Exposure Factors for Flexible Digital Detector Arrays

Exposure factors (R factors) provide guidance in gamma radiography applications. The exposure time is calculated for a specific source type, activity, thickness of steel, desired exposure factor for a target film density or pixel value, and source-to-detector distance (SDD). R factors to produce target film densities of 2.0, 2.5, 3.0, and 3.5 were published for M100, MX125, T200, AA400, and HS800 films. Digital R factors are now published for Carestream rigid and flexible digital detector array (DDA) products. The flexible DDA’s are bent repeatedly around curved surfaces for single wall viewing, as radiography codes and standards require that the detector be in direct contact with the weld whenever practical. The R factor tables are published along with the supporting data used to calculate them, which are provided in graphical format for each condition. Iridium, selenium, and cobalt radioisotope sources were utilized for the generation of the data. Radiographers utilize the tables provided to enter the R factor into a commercially available phone-based calculator to determine the exposure time required to obtain the target optical density or grey value through the base metal. R factors are meant to be a starting point only, as other factors related to the part geometry and technique impact the required exposure.

A model-based sliding mode control with intelligent distribution for a proportional valve driven by digital valve arrays

Parallel-connected digital valve arrays are commonly utilized in the pilot stage of the proportional directional valve to enhance dynamic performance and reliability. However, when the digital valve array is driven by a digital signal, it is difficult to optimally assign the signal pulses to each valve. If the assignment is not well executed, it can significantly reduce the switching uniformity of the digital valves or lead to performance degradation of the system. In this paper, a model-based sliding mode control strategy based on the intelligent distribution of control law is proposed and successfully applied to a proportional valve driven by digital valve arrays. The intelligent distribution strategy encompasses a logic distribution algorithm and a circular sliding distribution algorithm that automatically assigns control laws to different valves based on the rolling of the PWM signal cycle. Experimental results confirm that the proposed strategy not only simultaneously reduces the total number of valve switches and enhances the switching uniformity among the valves, but also adapts to the variation in the number of valves. The proposed strategy is not limited to the application of digital valve arrays, it is also applicable in other fields of multi-actuators driven by digital signals, and can simultaneously improve the control accuracy, lifetime, and maintenance friendliness.

A Low-Cost Wideband Digital Array Antenna Based on Stretch Processing Technique

Wideband digital phased array radar offers the advantages of high range resolution, which improves the recognition ability for multiple targets, group targets, and high-speed targets. Traditional wideband phased arrays use true time delay to compensate for aperture fill time; however, the cost increases significantly. In this paper, a wideband elemental digital array architecture based on the stretch processing method is proposed. By utilizing the time-domain and frequency-domain translation equivalence of the LFM (Linear Frequency Modulation) signal waveform, the equivalent aperture fill time is compensated for through frequency shift and phase shift after stretch processing. Compared to traditional wideband digital arrays, this method can dramatically reduce the required sampling rate and lower the requirements on antenna hardware, thereby reducing the manufacturing cost of system. A comprehensive analysis of the signal processing process and stretch processing method is provided. And an antenna array prototype is developed to verify the T/R channel compensation and wideband beamforming. Measured results show that the antenna is capable of ±60° scanning in azimuth plane and ±40° scanning in elevation plane, with a bandwidth of 500 MHz in S-band. The results demonstrate excellent wideband beam performance and accurate lobe scanning, which confirms the validity of the proposed wideband architecture for stretch processing, frequency shift, and phase shift. This method can be widely applied to the low-cost design and wideband performance improvement of wideband digital array radar.

Electrodynamic modeling of a four-channel antenna with an operating frequency band of octave

The actual problem of electrodynamic modeling of a four-channel antenna with an octave operating frequency range has been considered. The results of numerical electrodynamic modeling of a four-channel antenna have been presented. The considered antenna with an octave operating frequency range is a rectangular curtain comprising four independent non-equidistant channels. Numerical electrodynamic modeling of a four-channel antenna has been carried out in the ANSYS HFSS software package, with the convergence parameter DeltaS = 0.01. As a result of the simulation, the frequency characteristics of each channel have been obtained: VSWR, gain, reflection coefficient, directional pattern. The antenna provides a scanning angle as part of an ultra-wideband digital antenna array of at least ±30° in azimuth and from 0° to 60° in elevation. The gain of the antenna channels in the operating frequency range is not lower than 6 dB. According to the simulation results, the VSWR of each channel of the antenna in the operating frequency range does not exceed 2.55. To minimize the influence of mutual coupling of channels on the antenna characteristics, the distance from the phase centers of the curtain emitters to other elements of the ultra-wideband digital antenna array should be at least a wavelength in free space at the lower frequency of the operating frequency range. It has been shown that the considered four-channel antenna provides an octave operating frequency band and can be used as part of an ultra-wideband digital antenna array for direction finding of radiation sources.