Response Correction Methods Research Articles

A Novel and Reliable Pixel Response Correction Method (DAC-Shifting) for Spectral Photon-Counting CT Imaging.

Spectral photon-counting cone-beam computed tomography (CT) imaging is challenged by individual pixel response behaviours, which lead to noisy projection images and subsequent image artefacts like rings. Existing methods to correct for this either use calibration measurements, like signal-to-thickness calibration (STC), or perform a post-processing ring artefact correction of sinogram data or scan reconstructions without taking the pixel response explicitly into account. Here, we present a novel post-processing method (digital-to-analogue converter (DAC)-shifting) which explicitly measures the current pixel response using flat-field images and subsequently corrects the projection data. The DAC-shifting method was evaluated using a repeat series of the spectral photon-counting imaging (Medipix3) of a phantom with different density inserts and iodine K-edge imaging. The method was also compared against polymethyl methacrylate (PMMA)-based STC. The DAC-shifting method was shown to be effective in correcting individual pixel responses and was robust against detector instability; it led to a 47.4% average reduction in CT-number variation in homogeneous materials, with a range of 40.7-55.6%. On the contrary, the STC correction showed varying results; a 13.7% average reduction in CT-number variation, ranging from a 43.7% increase to a 45.5% reduction. In K-edge imaging, DAC-shifting provides a sharper attenuation peak and more uniform CT values, which are expected to benefit iodine concentration quantifications.

A study on “position-energy” response correction method based on monolithic crystal coupled SiPM array

A study on “position-energy” response correction method based on monolithic crystal coupled SiPM array

Accurate Correction of the "Bulk Response" in Surface Plasmon Resonance Sensing Provides New Insights on Interactions Involving Lysozyme and Poly(ethylene glycol).

Surface plasmon resonance is a very well-established surface sensitive technique for label-free analysis of biomolecular interactions, generating thousands of publications each year. An inconvenient effect that complicates interpretation of SPR results is the “bulk response” from molecules in solution, which generate signals without really binding to the surface. Here we present a physical model for determining the bulk response contribution and verify its accuracy. Our method does not require a reference channel or a separate surface region. We show that proper subtraction of the bulk response reveals an interaction between poly(ethylene glycol) brushes and the protein lysozyme at physiological conditions. Importantly, we also show that the bulk response correction method implemented in commercial instruments is not generally accurate. Using our method, the equilibrium affinity between polymer and protein is determined to be KD = 200 μM. One reason for the weak affinity is that the interaction is relatively short-lived (1/koff < 30 s). Furthermore, we show that the bulk response correction also reveals the dynamics of self-interactions between lysozyme molecules on surfaces. Besides providing new insights on important biomolecular interactions, our method can be widely applied to improve the accuracy of SPR data generated by instruments worldwide.

A comparison of instrument response correction methods: Post-processing and real-time methods

Industrial vibration monitoring often requires sensors with adjustable sensitivity and suitable frequency range. In practice, most industrial studies utilize either geophones (velocimeters) or accelerometers. In some cases, where low frequency content is of interest, larger sensor will be required. In difficult installation conditions, it can be advantageous to utilize smaller, higher frequency sensor elements (geophones or accelerometers) to simplify installation and maintenance. A frequency correction of sensors or the recorded waveforms will be needed to accommodate the frequency range of interest. Most accelerometers have relatively smaller sensitivity at low frequency which can affect the calculation of vibration velocity and displacement at low frequencies. Geophones are limited by their frequency response, which drops-off significantly their sensitivity below the resonant frequency of the sensor. Structural and ground vibrations that occur under the resonant frequency could be observed at test sites, but the recorded waveforms cannot be used directly for real-time assessment, and therefore it can be beneficial to artificially expand the frequency range below the sensor's frequency cutoff. Methods for such expansion, were developed and are well established in seismological studies and exploratory geophysics. Usually, these procedures are applied in data post-processing. These methods are not applicable when an operator requires real-time feedback of the measured vibrational amplitude, for example, monitoring of machinery foundations, where excitation control is necessary to avoid infrastructure damage.This paper presents an approach for instrument frequency extension in the necessary low-frequency range of common geophone elements in real-time applications and compares the results of the proposed technique in post-processing and in real time data collection systems.

Surface response correction method of light intensity detector in high energy laser measurement

Surface response correction method of light intensity detector in high energy laser measurement

Individual transducer impulse response characterization method to improve image quality of array-based handheld optoacoustic tomography.

The physical properties of each transducer element play a vital role in the quality of images generated in optoacoustic (photoacoustic) tomography using transducer arrays. Thorough experimental characterization of such systems is often laborious and impractical. A shortcoming of the existing impulse response correction methods, however, is the assumption that all transducers in the array are identical and therefore share one electrical impulse response (EIR). In practice, the EIRs of the transducer elements in the array vary, and the effect of this element-to-element variability on image quality has not been investigated so far, to the best of our knowledge. We hereby propose a robust EIR derivation for individual transducer elements in an array using sparse measurements of the total impulse response (TIR) and by solving the linear system for temporal convolution. Thereafter, we combine a simulated spatial impulse response with the derived individual EIRs to obtain a full characterization of the TIR, which we call individual synthetic TIR. Correcting for individual transducer responses, we demonstrate significant improvement in isotropic resolution, which further enhances the clinical potential of array-based handheld transducers.

High-order nonlinear response correction method for infrared radiation detector

The infrared detector can generate nonlinear response error when the Fourier transform infrared spectrometer is used for implementing the radiometric calibration or observing the high temperature targets. Based on the relationship between the incident radiation intensity and the electron concentration in the optical conduction band, the mechanism of the nonlinear response error caused by the high incident photon flow is analyzed. According to Planck radiation law and interference principle, the effect of nonlinear error on spectrum is studied by simulating blackbody radiation data with nonlinear error. It is found that the nonlinear response with a different order has a different influence region, and the higher-order nonlinear response has a wider influence range and generates a larger nonlinear response error. By the general nonlinear response correction method the nonlinear response coefficient is obtained through constructing the nonlinear response model of the interference data and then the spectral distortion produced by the detector is corrected. According to the convolution iteration method, the polar orbit meteorological satellite CrIS constructs the convolution equation to correct the second-order nonlinear response by taking the low-wave number band of 50－500 cm&lt;sup&gt;–1&lt;/sup&gt; as the characteristic region. The European Meteorological Agency’s Airborne Infrared Interferometer Evaluation System (ARIES) selected two feature areas, 50－500 cm&lt;sup&gt;–1&lt;/sup&gt; and 2000－2500 cm&lt;sup&gt;–1&lt;/sup&gt;, and iteratively corrected the second-order and third-order nonlinear response. The gradient descent method is often used to solve the optimization problems of unconstrained multivariate functions. Based on the gradient descent algorithm, an iterative method suitable for correcting the high-order nonlinear response errors is proposed in this paper. In this method, the information about the iteration point is obtained by constructing the nonlinear response function of the high-order detector and setting the appropriate iteration initialization. According to the initial value of the iteration and the information about the known iteration point, the gradient of the iteration variable is calculated to determine the iteration value of the next unknown variable, thus quickly searching for the global minimum point and determining the nonlinear response coefficient. We use Fourier transform infrared spectrometer to carry out radiometric calibration experiment and compare the effects of three correction methods: convolution, cross iteration and gradient descent method. The results show that the three correction methods can effectively reduce the nonlinear error, and improve the fitting extent by 0.15%, 0.29% and 0.39% respectively. The spectral data corrected by gradient descent method are more accurate.

Editorial for the special issue on advances in forward and inverse surrogate modeling for high‐frequency design

Editorial for the special issue on advances in forward and inverse surrogate modeling for <scp>high‐frequency</scp> design

Hydrocarbon identification using the AVO response correction method based on high-resolution complex spectral decomposition

Amplitude-variation-with-offset (AVO) technique is one of the primary quantitative hydrocarbon discrimination methods with prestack seismic data. However, the prestack seismic data are usually have low data quality, such as nonflat gathers and nonpreserved amplitude due to absorption, attenuation, and/or many other reasons, which usually lead to a wrong AVO response. The Neogene formations in the Huanghekou area of the Bohai Bay Basin are unconsolidated clastics with a high average porosity, and we find that the attenuation on seismic signal is very strong, which causes an inconsistency of AVO responses between seismic gathers and its corresponding synthetics. Our research results indicate that the synthetic AVO response can match the field seismic gathers in the low-frequency end, but not in the high-frequency components. Thus, we have developed an AVO response correction method based on high-resolution complex spectral decomposition and low-frequency constraint. This method can help to achieve a correct high-resolution AVO response. Its application in Bohai oil fields reveals that it is an efficient way to identify hydrocarbons in rocks, which provides an important technique for support in oil and gas exploration and production in this area.

Model Correction and Optimization Framework for Expedited EM-Driven Surrogate-Assisted Design of Compact Antennas

Design of compact antennas is a numerically challenging process that heavily relies on electromagnetic (EM) simulations and numerical optimization algorithms. For reliability of simulation results, EM models of small radiators often include connectors that significantly contribute to evaluation cost. In this letter, a response correction method for antenna models without a connector, based on a so-called network unterminating concept, has been proposed. Unterminating allows for obtaining electrical parameters of the connector embedded in the EM antenna model. They can be then utilized to refine the reflection responses of the EM antenna model without the connector. The refined model has been optimized using a novel trust-region-based method. It exploits the information gained from unsuccessful iterations to improve the accuracy of the model and prevent premature convergence of the algorithm. The proposed design approach has been demonstrated using two antenna structures and compared to benchmark algorithms.

光子计数探测器的响应函数标定及校正方法

光子计数探测器的响应函数标定及校正方法

High-Resolution Lamb Wave Inspection in Viscoelastic Composite Laminates

Lamb wave inspection is a promising structural health monitoring method for carbon fiber reinforced plastic laminates. The optimal design of the excitation waveform based on Lamb wave pulse compression is an effective way to improve the inspection resolution in elastic plates. However, due to the viscoelastic property of the composite materials, the material damping effect will influence the amplitude response of the output signals; thus, the current design strategy is no longer applicable. The purpose of this paper is to develop an excitation waveform design strategy based on pulse compression to meet the demands of high-resolution Lamb wave inspection in composite materials. Different parameters that affect the design of excitation such as material damping effect, amplitude response, relative frequency bandwidth, and the selection of excitation waveform are considered synthetically. In addition, an excitation waveform design strategy based on the corrected amplitude response is also established to eliminate the effect of material damping and thus achieve better detection resolution. Finally, an experiment was carried out on a quasi-isotropic composite plate. The experimental results validate the robustness of the amplitude response correction method and the effectiveness of the excitation waveform design strategy.

Response features and circuit decomposition for accelerated EM‐driven design of compact impedance matching transformers

ABSTRACTIn this letter, a procedure for low‐cost simulation‐driven design optimization of compact impedance matching transformers is presented. The proposed methodology exploits a bottom‐up design with the design requirements for the entire transformer circuit being translated into specifications for its building blocks, here, compact microstrip resonant cells. These elementary cells are optimized using response features which permits considerable numerical savings compared to conventional approach. Subsequently, the entire circuit is fine‐tuned using local response surface approximation models and response correction methods. A three‐section 50‐to‐100 Ω transformer is designed for demonstration purposes. Its optimized design is obtained at the computational cost corresponding to only 31 evaluations of the high‐fidelity electromagnetic transformer model, despite large number of geometry parameters to be adjusted (here, 15). © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2130–2133, 2016

Simulation-driven design of compact ultra-wideband antenna structures

Purpose – The purpose of this paper is to investigate strategies and algorithms for expedited design optimization and explicit size reduction of compact ultra-wideband (UWB) antennas. Design/methodology/approach – Formulation of the compact antenna design problem aiming at explicit size reduction while maintaining acceptable electrical performance is presented. Algorithmic frameworks are described suitable for handling various design situations and involving simulation models without and with response gradients available. Numerical and experimental case studies are provided demonstrating feasibility of solving real-world miniaturized antenna design tasks. Findings – It is possible, through appropriate combination of the global and local optimization methods, surrogate modeling techniques and response correction methods, to find optimum dimensions of antenna structures that minimize antenna size while maintaining acceptable electrical performance. Design optimization can be performed at practically feasible computational costs. Research limitations/implications – The study summarizes recent advances in miniaturization-oriented design optimization of UWB antennas. The presented techniques reach far beyond the commonly used design approaches based on parameter sweeps and similar hands-on methods, particularly in terms of automation, reliability, and reduction of the computational costs of the design processes. Originality/value – The proposed design problem formulation and algorithmic frameworks proved useful for rapid design of compact UWB antenna structures, which is extremely challenging when using conventional methods. To the knowledge, this is the first attempt to efficient solving of this type of design problems, especially in the context of explicit antenna size reduction.

Low-cost multi-objective optimization and experimental validation of UWB MIMO antenna

Purpose – The purpose of this paper is to validate methodologies for expedited multi-objective design optimization of complex antenna structures both numerically and experimentally. Design/methodology/approach – The task of identifying the best possible trade-offs between the antenna size and its electrical performance is formulated as multi-objective optimization problem. Algorithmic frameworks are described for finding Pareto-optimal designs using auxiliary surrogate models and two alternative approaches to design refinement: response correction techniques and co-kriging. Numerical and experimental case studies are provided to demonstrate feasibility of solving real-world and complex antenna design tasks. Findings – It is possible, through appropriate combination of the surrogate modeling techniques (both data driven and physics based) and response correction methods, to find the set of alternative designs representing the best possible trade-offs between conflicting design objectives, here, electrical performance and size. Design optimization can be performed at practically feasible computational costs. Research limitations/implications – The study demonstrates feasibility of automated multi-objective design optimization of antennas at low computational cost. The presented techniques reach beyond the commonly used design approaches based on parameter sweeps and similar hands-on methods, particularly in terms of automation, reliability and reduction of the computational costs of the design processes. Originality/value – Multi-objective design of antenna structures is very challenging when high-fidelity electromagnetic simulations are utilized for performance evaluation of the structure at hand. The proposed design framework permits rapid optimization of complex structures (here, MIMO antenna), which is hardly possible using conventional methods.

Strategies for computationally feasible multi-objective simulation-driven design of compact RF/microwave components

Purpose – Strategies for accelerated multi-objective optimization of compact microwave and RF structures are investigated, including the possibility of exploiting surrogate modeling techniques for electromagnetic (EM)-driven design speedup for such components. The paper aims to discuss these issues. Design/methodology/approach – Two algorithmic frameworks are described that are based on fast response surface approximation models, structure decomposition, and Pareto front refinement. Numerical case studies are provided demonstrating feasibility of solving real-world problems involving multi-objective optimization of miniaturized microwave passives and expensive EM-simulation models of such structures. Findings – It is possible, through appropriate combination of the surrogate modeling techniques and response correction methods, to identify the set of alternative designs representing the best possible trade-offs between conflicting design objectives in a realistic time frame corresponding to a few dozen of high-fidelity EM simulations of the respective structures. Research limitations/implications – The present study sets a direction for further studied on expedited optimization of computationally expensive simulation models for miniaturized microwave components. Originality/value – The proposed algorithmic framework proved useful for fast design of microwave structures, which is extremely challenging when using conventional methods. To the authors’ knowledge, this is one of the first attempts to surrogate-assisted multi-objective optimization of compact components at the EM-simulation level.

Knowledge based response correction method for design of reconfigurable N‐shaped microstrip patch antenna using inverse ANNs

SummaryArtificial neural networks (ANNs) have been often used for engineering design problems. In this work, an inverse model of a reconfigurable N‐shaped microstrip patch antenna which is formed by ANN is considered to find design parameters. For this task, knowledge‐based response correction consists of two steps, which include generating response using multilayer perceptron as a first step and correcting this response using knowledge based methods such as source difference, prior knowledge input, and prior knowledge input with difference as a second step. The proposed antenna has four states of operation controlled by two Positive‐Intrinsic‐Negative (PIN) diodes with ON/OFF states. The two‐step ANN models are inversely trained using the optimum of the resonant frequency parameter as the input and the physical dimensions of the proposed antenna as outputs of the multilayer perceptron. The outputs and, in some methods, the input parameters of the multilayer perceptron are sent as input to the knowledge‐based models while the obtained outputs from the two steps are the results of the new physical dimensions of the redesigned reconfigurable antenna that will be compared and analyzed. This input/output complexity of the proposed reconfigurable antenna allows an accurate and fast inverse model to be developed with less training data. Users may use this antenna and its ANN models to develop new products in the market where any frequency in the operating region can be given to the input to result an appropriate form of the new reconfigurable antenna. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Surrogate‐assisted design optimization of photonic directional couplers

SummaryIn this paper, computationally efficient simulation‐driven design optimization of integrated photonic couplers is discussed. The design process is conducted using variable‐fidelity electromagnetic (EM) simulations and surrogate‐based optimization (SBO) techniques. Two design case studies are considered: conventional directional coupler and a curved coupler. A particular choice of the SBO approach relies on a visual inspection of the low‐ and high‐fidelity coupler model responses as well as their correlations. The first structure is optimized using adaptively adjusted design specifications technique. Because of limited correlations between the high‐ and low‐fidelity EM models of the second structure, its optimal design is obtained using the additive response correction method. Subsequently, the design is fine‐tuned using local response surface approximations. As demonstrated through numerical results, utilization of the SBO techniques allows for considerable reduction of the design optimization time compared with direct handling of the high‐fidelity model. The total optimization cost of conventional and curved coupler corresponds to only 13.5 and 23.7 high‐fidelity model simulations, respectively. Copyright © 2015 John Wiley &amp; Sons, Ltd.

The effects of different calibration and frequency response correction methods on eddy covariance ozone flux measured with a dry chemiluminescence analyzer

Ozone (O3) flux (Fo) was measured over a wheat field in Yucheng, China, using the eddy covariance technique. A dry chemiluminescence fast-response O3 analyzer and a UV-absorption based slow-response O3 analyzer were used for measuring fast O3 concentration fluctuations and absolute concentrations, respectively. The main objective of this study was to determine a group of suitable methods for calculating Fo based on the performance of the two O3 analyzers in the field. We evaluated the effects of three calibration methods on Fo. These calibration methods include the ratio method (RM, it assumes that the fast-response analyzer’s signal-output is directly proportional to absolute ambient O3 concentration within a 30-min interval), the ratio offset method (ROM, it is based on the ratio method with analyzer’s offset modification), and the ratio variation method (RVM, it is based on the ratio method with the fast-response analyzer’s gain factor variation within a 30-min interval). Three frequency response corrections (analytic, revised analytic, and in-situ) for the estimation of Fo were also evaluated. Our results show that: (1) Compared to the O3 flux with the commonly-used method (RM), on average, the fluxes with ROM and RVM were decreased by about 9% and 7%, respectively. (2) Based on the spectral analysis, the fast-response O3 analyzer’s noise could cause random errors, but did not result in a systematic error in Fo. Tubing attenuation in O3 concentration fluctuations can cause up to 20% loss in Fo. (3) Frequency response corrections for Fo with the original analytic method, the in-situ method, and the revised analytic method were 34.6%, 23.8% and 25.4% on average, respectively.

Expedited EM-Driven Multiobjective Antenna Design in Highly Dimensional Parameter Spaces

A technique for low-cost multiobjective optimization of antennas in highly dimensional parameter spaces is presented. The optimization procedure is expedited by exploiting fast surrogate models, including coarse-discretization electromagnetic (EM) antenna simulations and response surface approximations (RSA). The latter is utilized to yield an initial set of Pareto nondominated designs that are further refined using response correction methods. Efficient handling of multiple geometry parameters is realized by the initial reduction of the solution space. Our approach is demonstrated using a 13-parameter triple trapezoidal, planar ultrawideband (UWB) monopole antenna.