Magnitude Of Frequency Response Research Articles

Balanced Intermodulation Reference With Flat Frequency Response Using Nonlinearity Equalization

This letter proposes a balanced intermodulation (IM) reference source with constant IM magnitude-frequency response using the nonlinearity equalization method. In the design, the diode is working as the nonlinear source, while the excitation carriers are equalized versus frequency to stimulate diode; thus, a flat IM3 magnitude-frequency response can be obtained accordingly. The experiment demonstrates this designed IM source can provide flat IM3 magnitude-frequency response at 700 MHz, 1800 MHz, and 2600 MHz IM3 test bands with a fluctuation error less than 1.5 dB, while three typical reference magnitudes ranges from -80 dBm, -90 dBm to -100 dBm at 2 × 43 dBm are demonstrated also.

Designing Audio Equalization Filters by Deep Neural Networks

Audio equalization is an active research topic aiming at improving the audio quality of a loudspeaker system by correcting the overall frequency response using linear filters. The estimation of their coefficients is not an easy task, especially in binaural and multipoint scenarios, due to the contribution of multiple impulse responses to each listening point. This paper presents a deep learning approach for tuning filter coefficients employing three different neural networks architectures—the Multilayer Perceptron, the Convolutional Neural Network, and the Convolutional Autoencoder. Suitable loss functions are proposed for each architecture, and are formulated in terms of spectral Euclidean distance. The experiments were conducted in the automotive scenario, considering several loudspeakers and microphones. The obtained results show that deep learning techniques give superior performance compared to baseline methods, achieving almost flat magnitude frequency response.

Nonconventional measurements on insulation materials high voltage bushings and power cables using frequency response analysis method

AbstractPower utilities desire an alternate noninvasive test method for assessing the diagnostic status of power apparatus. The primary reason is to minimize the economic constraints and ensure lifetime and reliability of power apparatus within shorter duration. In this context, frequency response analysis (FRA) method is increasingly recommended. The underlying principle of fault diagnosis using FRA method focuses on correlating the insulation condition to the changes in the magnitude and phase frequency response function. Existing practices validates the usage of FRA method in ascertaining the insulation integrity of transformers. Further attempts to expand the potential of FRA in method in determining the insulation status of power apparatus other than transformers, lack scientific and experimental evidence. To fill this gap, a research on using FRA method in assessing the insulation condition of high voltage bushings and power cables is initiated. Initially, test samples of insulation materials that are commonly used in bushings and cables are selected. The chosen samples are prepared in such a way that they represent common defect conditions that inflict premature material degradation and failures. These samples are grouped accordingly, placed on test cells, subjected to nonconventional FRA tests and their diagnostic status are respectively ascertained through comparative analysis. Following this, the pertinent findings are validated on actual bushings and power cables installed on a power transformer. In summary, the findings of this studies not only validate the usage of FRA method but provides the missing scientific and technical evidences and indices that could be used for diagnosing power apparatus.

Statistical modeling of magnitudes of Brazilian in-home PLC and hybrid PLC-wireless channels

This paper focuses on the statistical modeling of the magnitudes of frequency responses of Brazilian in-home power line and hybrid power line-wireless in the frequency band from 1.7 up to 100 MHz.122The present work is based on the master thesis (T.F. do A. Nogueira, 2018) [1].In this regard, a method to obtain statistical models is detailed. The statistical modelings of these channels are based on measured data sets, which were acquired through a measurement campaign carried out in Brazilian residences. Numerical results show that Beta and Log-Normal are the best statistical distributions for modeling magnitudes of the frequency responses of Brazilian in-home power line and hybrid power line-wireless communication channels, respectively. Also, these magnitudes are non-stationary random processes.

Uncertainty Quantification of CMOS Active Filter Circuits: A Non-Intrusive Computational Approach Based on Generalized Polynomial Chaos

Semiconductor fabrication technologies as applies to the nanometer-era paradigms of nowadays have rendered uncertainty quantification analyses through component-level parameters compulsory and indispensable. Frequency responses of CMOS active filters are invariably observed to be affected by probabilistically modelled parameter deviations, and in this article the focus is on the fast and accurate quantification of the uncertainties pervading CMOS active filters in terms of their magnitude frequency responses. Previous work dominantly has preference for the widely recognized non-intrusive Monte Carlo methods, which bring about a disproportionately high computational burden. Also discomfitures are observed to arise due to apparently inadequate ensemble volumes and a limited variety of distribution functions that are chosen to be utilized, along with seemingly insufficient means of resulting data visualization and the lack of accurate probabilistic quantification. Generalized Polynomial Chaos (gPC) based stochastic spectral techniques, which usually offer reduced computational complexity with respect to Monte Carlo, targeting CMOS active filters do not seem to have drawn much attention; the few related publications offer utility in a limited scope of electronic components. In this article, we carry out uncertainty quantification analyses in order to compute partial or approximate stochastic characterizations of the magnitude frequency responses of several multi-component CMOS active filter circuits with the gPC-based stochastic collocation technique. The pertaining inherent non-intrusive nature is exploited, and the stated issues associated with the previous work are addressed. We utilize a stokhos-based MATLAB/C++ toolbox of our own design, on whose software architecture, features, and facilities we provide profound details, and present performance comparisons with Monte Carlo along with intuitive and insightful comments, in an endeavor to suggest that such observations may prove to be beneficial to circuit designers.

A novel hybrid coordinates multiple decoupled phase‐locked loop under nonideal grid conditions

AbstractA novel hybrid coordinates multiple decoupled phase‐locked loop (HCMD‐PLL) is presented to improve the performance of the PLL under nonideal grid conditions. Based on the Clark transform and the first‐order low‐pass filter, the complex coefficient filter is derived to analyze phase‐locked loop. It is different from the phase‐locked loop with a complex coefficient filter. On this basis, the multiple‐complex‐coefficient band‐pass filter of HCMD‐PLL is derived, and the equivalent transfer function of the decoupling of the fundamental positive sequence, negative sequence and harmonic components is obtained, and the magnitude and phase frequency responses are analyzed. The fundamental positive sequence component is extracted without phase shift and amplitude attenuation under the nonideal grid conditions, eliminating the effect of specific‐order harmonics components because the amplitude is attenuated to zero. And the specific‐order harmonic component can also be extracted precisely. The interaction from the various specific components is eliminated. The stability of the system is analyzed by the pole distribution of the closed‐loop system. The stationary αβ coordinate system for PLL is adopted to suppress the change of the grid voltage. Simulation and experimental results verify the effectiveness of the HCMD‐PLL. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Fractional-Order Phase Shifters with Constant Magnitude Frequency Responses

This contribution presents and experimentally analyzes the idea how to reach the constant magnitude as well as the phase response in the fractional-order (FO) phase when shifting two-ports. The straightforward method employing the automatic gain control circuit (AGC) in a cascade after so-called constant phase block approximating FO integrator or differentiator is studied. The variable gain amplifier utilized in AGC and simple RC-based FO constant phase elements (approximating capacitors with order alpha = 1/4 and alpha = 1/2 as an example) connected in the feedback of operational amplifier-based integrator are established in the experimental setup. The operation indicated in three decades (between 100 Hz and 100 kHz) is evaluated. The known solutions of the standard FO phase shifting circuits are discussed and generally compared with the features obtained in this paper, together with the supposed effects of AGC on their performances.

Coupling Capacitor Voltage Transformers Models and Impacts on Electric Power Systems: A Review

Coupling capacitor voltage transformers (CCVTs) are the predominant devices used in high voltage systems to provide scaled-down voltage signals for metering, protection, and control devices. The performances of these devices are subject to errors due to the transient behavior of CCVTs, so that the use of CCVT digital models is essential for studying power systems in order to predict how the equipment dynamics affect protective relaying performances. In this review paper, the authors put together complete information regarding five realistic CCVT digital models available in the literature and perform a detailed sensitivity analysis of their magnitude and angle frequency responses, as well as their influence on phasor estimation, distance protection, and fault location techniques.

Improved firefly algorithm based optimal design of special signal blocking IIR filters

This work proposes the design/implementation of special signal blocking IIR filters (SBIIRFs) to meet some of the general applications in modern electronics and measurement system engineering, employing a robust swarm and evolutionary optimization algorithm. Especially SBIIRFs are the basic supplement for the development of sophisticated digital measuring instruments. Lower order IIR filters are considered for faster output response hence, make suitable in online applications. Best coefficients of these filters are searched proposing a modified version of the recent firefly algorithm (FA), known as improved firefly algorithm (IFA) in order to provide stable frequency magnitude response. The proposed IFA enhances exploration ability of the classical FA due to an additional random difference term in its mathematical model. The efficacy of the proposed IFA is measured considering its performance over the optimal design of SBIIRFs in contrast to classical FA, particle swarm optimization, and real-coded genetic algorithm.

Design of Non-overshooting Fractional-Order PD and PID Controllers for Special Case of Fractional-Order Plants

This study focuses on shaping the transient response of special case of fractional-order systems by using fractional-order PD (FOPD) and fractional-order PID (FOPID) controllers. For a plant with a fractional-order pole, a FOPID controller is designed in which the orders of its derivative and integral terms are considered equal to the commensurate order of the plant while for an integrating plant with a fractional-order pole, a FOPD controller is designed. The region of controller parameters is extracted to obtain a closed-loop system with a monotonically decreasing magnitude–frequency response. This leads to a non-overshooting or low-overshoot step response. The gain crossover frequency and phase isodamping conditions are employed to select appropriate controller parameters among the mentioned region. The numerical examples are provided to show the efficiency of the proposed FOPD and FOPID controllers.

Electromagnetic shunt damping with negative impedances: Optimization and analysis

Dynamic vibration absorbers (DVA) are classic and effective devices to reduce the amplitude of vibration sustained by structures. A promising alternative to the DVAs is the electromagnetic shunt damper (EMSD), in which the electrical shunt circuit serves as the absorbing oscillator. The objective of this paper is to carry out optimum designs of an EMSD connected to a resistive-inductive-capacitive (RLC) shunt circuit, by adopting three different calibration strategies: the fixed points theory, H2 optimization criterion and maximum damping criterion. The aforementioned optimization strategies are appropriate to different excitation scenarios: harmonic, random and transient vibration, respectively. Analytical expressions of optimal parameters are formulated in terms of the ratio of external inductance in the shunt and inherent inductance of electromagnetic transducer. Lower bounds of inductance ratio in the region of stability are also specified for each strategy, based on which the ultimate attainable performance of EMSDs can be predicted. Numerical investigation underlines that including a negative inductance in the shunt always contributes to reduce the frequency response magnitude, broaden the absorbing area around targeted vibration mode, increase the damping performance, and thereby accelerate the decay rate of transient vibration.

Characterization and epitope identification of the T cell response in non-allergic individuals exposed to mouse allergen

BackgroundExposure to airborne allergens is a frequent trigger of respiratory allergy and asthma in atopic individuals. While allergic patients suffer hypersensitivity reactions to these allergens, non-allergic individuals do not exhibit clinical symptoms despite environmental exposure to these ubiquitous allergen sources. The aim of this study was to characterize T cell responses in non-allergic laboratory workers, who are heavily exposed to mice allergens (Exposed Non-Allergics, ENA) and compare this data to previously published T cell responses measured in mouse (MO)-allergic patients. METHODS: Peripheral mononuclear cells (PBMC) from ENA subjects were expanded for 2 weeks in vitro with mouse urine extract and screened for IFNγ and IL-5 cytokine production in response to mouse antigen-derived peptides by ELISPOT. Ex vivo T cell reactivity in the ENA cohort was performed after 6hr stimulation with peptide pools by intracellular staining of CD154. ResultsVigorous responses were detected, associated with 147 epitopes derived from 16 mouse antigens. As expected, responses in ENA subjects were somewhat lower than those observed in MO-allergics for both responder frequency and overall response magnitude. While responses in allergics were polarized towards IL-5 production and associated with low IFNγ production, ENA responses were not polarized. The composition of targeted antigens and epitopes was overall similar between the two cohorts, with the majority of T cell reactivity directed against Mus m 1 and other major urinary proteins. However, kappa-casein precursor and odorant binding protein Ib were more abundantly recognized in MO-allergics compared to ENA subjects. Additionally, T cell responses against oligopeptides derived from the low molecular weight fraction of mouse urine were also assessed. Interestingly, no difference in the response frequency, magnitude or polarization between MO-allergic and ENA individuals was observed. Finally, assessment of ex vivo T cell activation also revealed T cell reactivity in the ENA cohort, with a non-significant trend for lower responses compared to MO-allergics. ConclusionExposure to mouse induces potent T cell responses in non-allergic individuals, targeting similar epitopes as seen in allergic patients.

TCR and CD28 Concomitant Stimulation Elicits a Distinctive Calcium Response in Naive T Cells.

T cell activation is initiated upon ligand engagement of the T cell receptor (TCR) and costimulatory receptors. The CD28 molecule acts as a major costimulatory receptor in promoting full activation of naive T cells. However, despite extensive studies, why naive T cell activation requires concurrent stimulation of both the TCR and costimulatory receptors remains poorly understood. Here, we explore this issue by analyzing calcium response as a key early signaling event to elicit T cell activation. Experiments using mouse naive CD4+ T cells showed that engagement of the TCR or CD28 with the respective cognate ligand was able to trigger a rise in fluctuating calcium mobilization levels, as shown by the frequency and average response magnitude of the reacting cells compared with basal levels occurred in unstimulated cells. The engagement of both TCR and CD28 enabled a further increase of these two metrics. However, such increases did not sufficiently explain the importance of the CD28 pathways to the functionally relevant calcium responses in T cell activation. Through the autocorrelation analysis of calcium time series data, we found that combined but not separate TCR and CD28 stimulation significantly prolonged the average decay time (τ) of the calcium signal amplitudes determined with the autocorrelation function, compared with its value in unstimulated cells. This increasement of decay time (τ) uniquely characterizes the fluctuating calcium response triggered by concurrent stimulation of TCR and CD28, as it could not be achieved with either stronger TCR stimuli or by co-engaging both TCR and LFA-1, and likely represents an important feature of competent early signaling to provoke efficient T cell activation. Our work has thus provided new insights into the interplay between the TCR and CD28 early signaling pathways critical to trigger naive T cell activation.

Hyperfine Intrinsic Magnitude and Phase Response Measurement of Optical Filters Based on Electro-Optical Harmonics Heterodyne and Wiener–Lee Transformation

An electro-optical heterodyne scheme is proposed and demonstrated for magnitude- and phase-frequency response measurement of optical filters based on harmonics heterodyne and Wiener–Lee transformation. The method consists of an acousto-optic frequency shifter and a phase modulator located in a frequency-shifted heterodyne interferometer. The minimum phase-frequency response is simultaneously extracted from the measured magnitude–frequency response with the help of Kramers–Kronig relations and the Wiener–Lee transformation. As compared with the single-sideband-based or double-sideband-based methods, our method eliminates small-signal assumption and features an immunity to undesired spurious sidebands, enabling harmonic sideband sweeping with even-folded measuring frequency range. Prior to the conventional frequency-shifted heterodyne methods, the method enables simultaneous extraction of intrinsic magnitude and phase frequency responses for most optical filters by introducing the Wiener–Lee transformation. A phase-shifted fiber Bragg grating is measured for extracting the frequency responses in the proof-of-concept experiment with the frequency resolution up to 50 kHz and frequency range of 80 GHz by using a frequency-swept modulation of 20 GHz.

Self-Calibrating Microwave Characterization of Broadband Mach–Zehnder Electro-Optic Modulator Employing Low-Speed Photonic Down-Conversion Sampling and Low-Frequency Detection

An approach to characterizing the microwave performance of an electro-optic Mach–Zehnder modulator (MZM) is proposed based on photonic down-conversion sampling. Through low-speed sampling, the magnitude response of the MZM at the input microwave frequency is transferred to the duplicate component in the first Nyquist frequency range, and can be measured via low-frequency detection and spectrum analysis. A proof-of-concept experiment is carried out to demonstrate the feasibility of the proposed method, where magnitude-frequency response and half-wave voltage versus frequency of a commercial MZM in the frequency range of 0–40 GHz have been accurately measured under a sampling rate of 96.9 MS/s. Both simulation and experimental results indicate that the proposed method can be implemented without any extra calibration.

Modeling Human Difference Threshold in Perceiving Mechanical Properties From Force

We discuss an extension of the basic principles underlying the human haptic just noticeable difference (JND) in perceiving a manipulator's mechanical properties from force feedback. Two cases are studied: first, the JND in perceiving the stiffness of manipulators with various masses and, second, the JND in perceiving the damping of a combined mass–spring–damper system with varying stiffness and mass. The extended JND laws are obtained through mapping psychophysical findings to JND formulations based on frequency response functions. We first present two human-factor experiments in which subjects discriminated between different levels of manipulator stiffness/damping while moving the manipulator with a prescribed sinusoidal deflection. For the two testing cases, both JNDs violate Weber's law: Due to the increases in mass, the normalized stiffness JND (the Weber fraction) decreases as the reference stiffness level increases; the damping JND for a constant reference damping increases with higher combined responses of stiffness and mass. On the basis of weighting the frequency response magnitude of mechanical properties, we performed model identification that fit the experimental observations and extended the JND laws for the two testing cases. Our extended JND laws indicate that, first, the stiffness and mass affect the stiffness JND in the same way, the stiffness JND is a fixed proportion of the combined frequency response of stiffness and mass, and, second, the frequency response magnitude of the damping JND is a fixed proportion of the frequency response magnitude of the combined system (the mass–spring–damper system).

Unsupervised selection of the singular spectrum components based on information theory for bioacoustic signal filtering

In this work, we present a comprehensive study of Singular Spectrum Analysis (SSA) applied to bioacoustics signal enhancement. The SSA method decomposes the signal into oscillatory components with physical meaning, allowing us to analyze different sound frequencies. One of the major SSA's challenges is how to choose those oscillatory components that will result in a better signal reconstruction, with less noise and distortion. We thus examine three entropy-based criterions for choosing such components. The quantifiers evaluated are: Amplitude Entropy, Spectral Entropy, and Permutation Entropy. The convergence of these quantifiers for different contamination conditions is provided. We then propose a grouping algorithm to arrange these components according to their entropy values. With the proposed rule, it is possible to identify the predominantly deterministic inner structure of the signal, in an unsupervised manner. We perform two different evaluations. First, we test a synthetic amplitude modulated signal contaminated with white, blue, pink, red, and violet color noises at 0 dB. Second, we analyze three audio calls of different anuran species recorded in the rainforest. The best quality of the recovered signal assessed through the Mean Square Error and the Signal-to-Distortion Ratio are 0.21 and 7.23 respectively for a white noise contamination applying the Permutation Entropy-based rule. Therefore, we conclude that our criterion is suitable for real scenarios under severe noise conditions, easily identifying trends and low-frequency components with a narrow band spectrum. Furthermore, we show how to derive an optimal FIR filter from SSA's components to build a specific filter bank for each species. We then present the magnitude–frequency response of the FIR filters of a bioacoustic anuran call.

Closed-Form Discretization of Fractional-Order Differential and Integral Operators

This paper introduces a closed-form discretization of fractional-order differential and integral Laplacian operators. The proposed method depends on extracting the angle information from the phase diagram. The magnitude frequency response follows directly due to the symmetry of the poles and zeros of the finite ztransfer function. Unlike the continued fraction expansion technique, or the infinite impulse response of second-order IIR-type filters, the proposed technique generalizes the Tustin operator to derive a 1st, 2nd,3rd, and 4th-order discrete-time operators (DTO) that are stable and of minimum phase. The proposed method depends only on the order of the Laplacian operator. The resulting discrete-time operators enjoy a flat phase response over a wide range of the discrete-time frequency spectrum. The closed-form DTOs allow us to identify the stability regions of fractional-order discrete-time systems and to design discrete-time fractional-order PIλDµ controllers. The effectiveness of this work is demonstrated via several numerical simulation.

Carotid chemoreceptor control of muscle sympathetic nerve activity in hypobaric hypoxia.

What is the central question of this study? High-altitude hypoxia increases muscle sympathetic nerve activity (MSNA), but whether intravenous infusion of dopamine, to blunt the responsiveness of the carotid chemoreceptors, reduces MSNA at high altitude is not known. What is the main finding and its importance? Muscle sympathetic nerve activity was elevated after 15-17days of high-altitude hypoxia (3454m) compared with values at 'sea level' (432m). However, intravenous dopamine infusion to blunt the responsiveness of the carotid chemoreceptors did not significantly decrease MSNA either at sea level or at high altitude, suggesting that high-altitude sympathoexcitation arises via a different mechanism. High-altitude hypoxia causes pronounced sympathoexcitation, but the underlying mechanisms remain unclear. We tested the hypothesis that i.v. infusion of dopamine to attenuate carotid chemoreceptor responsiveness would reduce muscle sympathetic nerve activity (MSNA) at high altitude. Nine healthy individuals [mean (SD); 26 (4) years of age] were studied at 'sea level' (SL; Zurich) and at high altitude (ALT; 3454m; 15-17days after arrival), both while breathing the ambient air and during an acute incremental hypoxia test (eight 3min stages; partial pressure of end-tidal O2 90-45mmHg). Intravenous infusions of dopamine (3μgkg-1 min-1 ) and placebo (saline) were administered on both study days, according to a single-blind randomized cross-over design. Sojourn to high altitude decreased the partial pressure of end-tidal O2 (to ∼60mmHg) and increased minute ventilation [V̇E; mean±SEM, SL versus ALT: saline, 8.6±0.5 versus 11.3±0.6lmin-1 ; dopamine, 8.2±0.5 versus 10.6±0.8lmin-1 ; P<0.05] and MSNA burst frequency by ∼80% [SL versus ALT: saline, 16±3 versus 28±4burstsmin-1 ; dopamine, 16±4 versus 31±4burstsmin-1 ; P<0.05) when breathing the ambient air, but were not different with dopamine. Increases in MSNA burst frequency and V̇E during the acute incremental hypoxia test were greater at ALT than SL (P<0.05). Dopamine did not affect the magnitude of the MSNA burst frequency response to acute incremental hypoxia at either SL or ALT. However, V̇E was lower with dopamine than saline administration throughout the acute incremental hypoxia test at ALT. These data indicate that i.v. infusion of low-dose dopamine to blunt the responsiveness of the carotid chemoreceptors does not significantly decrease MSNA at high altitude.

Optical and electrical trade-offs of rib-to-contact distance in depletion-type ring modulators.

We present a study on electrical and optical trade-offs of the doping map in a ring modulator. Here, we investigate the effects of the high-doped region distance to edge of the waveguide sidewall. Four groups of ring modulators with different rib-to-contact distances are fabricated and measured where the key parameters such as extinction ratio, insertion loss, transmission penalty, and bandwidth are compared quantitatively. Small-signal responses for the selected ring modulators are simulated where results are in agreement with measurement results. We show that, at 4dB extinction ratio, decreasing the high-doped region distance to rib from 800nm to 350nm will increase the bandwidth by 3.8 ×. However, we observed 8.4dB increase the insertion loss. We also show that the high-doped region location affects the trade-off between bandwidth and frequency response magnitude at low frequencies. At 350nm, this trade off is 2.5 × and 3.8× more efficient compared to 550nm and 800nm, respectively.