Measured Frequency Response Research Articles

Managing deviant data in spatial frequency response (SFR) measurement by outlier rejection

The edge-based Spatial Frequency Response (e-SFR) method was first developed for evaluating camera image resolution and image sharpness. The method was described in the first version of the ISO 12233 standard. Since then, the method has been applied in a wide range of applications, including medical, security, archiving, and document processing. However, with this broad application, several of the assumptions of the method are no longer closely followed. This has led to several improvements aimed at broadening its application, for example for lenses with spatial distortion. We can think of the evaluation of image quality parameters as an estimation problem, based on the gathered data, often from digital images. In this paper, we address the mitigation of measurement error that is introduced when the analysis is applied to low-exposure (and therefore, noisy) applications and those with small analysis regions. We consider the origins of both bias and variation in the resulting SFR measurement and present practical ways to reduce them. We describe the screening of outlier edge-location values as a method for improved edge detection. This, in turn, is related to a reduction in negative bias in the resulting SFR.

Development of 3-way loudspeaker system with trapezoidal enclosure

3-way loudspeaker system can manage middle and high frequencies with less distortion compared to 2-way loudspeaker system. It can operate in optimized ranges thus eliminating driver's excursion. The combination of 3 drivers, including the subwoofer, the midrange, and the tweeter, connected with a suitable 3-way crossover can produce high performance loudspeaker system that can disperse full range frequencies form 20Hz to 20kHz. Even though they come with high sensitivity and high performance to deliver the listener's need and satisfaction, sometime the price tag is too high and unaffordable. However, it is not impossible to build a 3-way loudspeaker system. The crucial steps and procedures include measuring the selected driver's impedance and compliance state, the driver's frequency response and designing the desired enclosure shape for the 3-way loudspeaker system. The air volume measurement result,Vas recorded good quality factor, Q which is 1.24. From the frequency response measurement, the constructed loudspeaker system has good performance at higher frequency as the frequency response ranges from 4kHz to 18kHz. There were some difficulties during component's selection for crossover's fabrication, however, the project is considered as successful, and the trapezoidal shape is deemed suitable for any 3-way loudspeaker system design.

PIC-integrable high-responsivity germanium waveguide photodetector in the C + L band.

We report the demonstration of a germanium waveguide p-i-n photodetector (PD) for the C + L band light detection. Tensile strain is transferred into the germanium layer using a SiN stressor on top surface of the germanium. The simulation and experimental results show that the trenches must be formed around the device, so that the strain can be transferred effectively. The device exhibits an almost flat responsivity with respect to the wavelength range from 1510 nm to 1630 nm, and high responsivity of over 1.1 A/W is achieved at 1625 nm. The frequency response measurement reveals that a high 3 dB bandwidth (f3dB) of over 50 GHz can be obtained. The realization of the photonic-integrated circuits (PIC)-integrable waveguide Ge PDs paves the way for future telecom applications in the C + L band.

Wideband Synthetic-Aperture Millimeter-Wave Spatial-Channel Reference System With Traceable Uncertainty Framework

This paper describes a wideband synthetic-aperture system and the associated Fourier processing for generating high-resolution spatial and temporal estimates of the signal propagation environment in wireless communication channels at millimeter-wave frequencies. We describe how to configure the synthetic aperture system for high angular resolution by sampling the progression of signal phase across a large planar area in space. We also show how to synthesize discrete measurements of the channel frequency response taken sequentially over a wide bandwidth to create power delay profiles (PDPs) in specified angular directions with high delay resolution. We provide a rigorous uncertainty analysis that can be made metrologically traceable to fundamental physical standards. This uncertainty framework can propagate the errors inherent in the measured signals through to the final channel estimates and derived parameters such as root-mean-square delay or angular spread. We illustrate use of the system in conjunction with two different analysis tools to extract both narrowband and wideband parameter estimates from the synthetic aperture, allowing its use as a stand-alone channel sounder or as a tool for verifying the performance of wireless devices.

Active vibration control for milling operations including frequency response function uncertainties

Active vibration controllers are designed to mitigate chatter vibrations and increase the productivity of machines. Such controllers, however, often do not perform well in real applications if uncertainties are present in the system. In this study, a controller design is presented for a test configuration, where the actuation is utilized by an electromagnetic actuator. The robust stability charts, which take into account the bounded uncertainties in the measured frequency response functions (FRFs), are calculated in frequency domain using the zero-order approximation method. The predictions for the experimental configuration are validated in cutting tests.

The use of an artificial neural network for acoustic selections headphone filters

The article aims to examine the influence of various acoustic materials on the usable properties of headphones. Acoustic materials act as filters that modify the incident acoustic waves by attenuating specific frequency components of the acoustic signals. They can therefore be called acoustic filters because they affect the frequency response (bandwidth) of the headphones in question. Therefore, the choice of acoustic materials in headphones with a specific design can have a significant impact on their psychoacoustic properties. Calibrating your headphones is critical to ensure they don't amplify, attenuate or introduce any coloration to your frequencies. To address this problem, a dedicated test setup was designed and constructed to evaluate the frequency response of selected headphone models using seven different acoustic materials (acoustic filters). The final selection of the acoustic filter was made using an artificial neural network. The article presents the measurement methodology, and the obtained frequency response measurements were analyzed and compared.

Frequency-response measurement of forward scattering clutters in water by using vortex beams

Frequency-response measurement of forward scattering clutters in water by using vortex beams

Settling Time Optimization in Wire Bonder Systems via Extremum-Seeking Control1

Adequate tuning of control laws is essential for high positioning accuracy, large system throughput, and reliability in high-end mechatronic and robotic systems. However, a population of such systems generally shows slight variations in dynamic responses due to, e.g., manufacturing tolerances, different disturbance situations, or position-dependent dynamics. Given the time-consuming nature of controller design, even by experienced control engineers, typically just one control law is designed for the whole system population based on worst-case bounds on variations in dynamic responses, resulting in a loss of individual system performance. The main contribution of this paper is the development of an automated controller tuning approach, based on extremum-seeking control, for settling time optimization via individual controller tuning. While other automated controller tuning methods exist, the developed approach allows inclusion of closed-loop stability and robustness constraints based solely on non-parametric frequency-response measurements of open-loop plant dynamics, and therewith directly optimizes transient system performance in a purely data-based manner. The proposed approach has been applied in simulation in an industrial case study for settling time optimization in point-to-point motions of a wire bonder system. In this case study, the effectiveness of the approach has been shown by achieving significant performance increases of 39.4% and 40.6% compared to controllers designed by experienced control engineers using manual loop-shaping techniques and a frequency-based auto-tuner, respectively, without needing manual tuning effort.

Sensitivity Analysis and Robust Assignment of Natural Frequencies for Vibrating Systems Using the Receptance Method

This paper presents a new receptance-based method for the robust assignment of natural frequencies. This method aims to address the deviation of the actually achieved natural frequencies for target natural frequencies when assigning natural frequencies, which usually arises due to uncertainties in passive structural modifications (i.e. mass and stiffness modifications). The mathematical expression is derived for the sensitivity of the target natural frequency to the uncertainties in modification parameters, which are subsequently employed to characterize the potential deviations of the target natural frequencies in the total differential form. The obtained deviation expression is integrated into the optimization calculation of the natural frequency assignment as an extra penalty term to boost the acquisition of highly robust modification parameters. The proposed robust assignment method, as a non-probabilistic technique, can be employed without any knowledge of the probabilistic distribution of uncertainty in modification parameters. Moreover, it uses only the measured frequency response functions (FRFs), preserving the advantage of the receptance method not needing a numerical model. Two numerical examples and a comparison with a typical eigenstructure assignment method (reported in the literature) demonstrate that the proposed method can provide highly robust modification parameter solutions. The application of the proposed method to the natural frequency assignment of a laboratory water-filled pipeline system gives experimental evidence of its effectiveness.

Sensitivity enhanced fiber optic temperature sensor based on optical carrier microwave photonic interferometry with harmonic Vernier effect

A sensitivity enhanced fiber optic temperature sensor based on optical carrier microwave interferometry (OCMI) with harmonic Vernier effect is proposed and experimentally demonstrated. The sensor is composed of two cascaded Mach–Zehnder interferometers (MZIs) with different optical length differences. Harmonic Vernier effect in microwave frequency domain is generated due to the free spectral range (FSR) difference in the microwave frequency response. Temperature sensing is realized by detecting the intersection of the inner envelopes of the measured frequency response curve. Experimental results demonstrate that sensitivity up to 580.45kHz/°C has been obtained by employing the harmonic Vernier effect, whose sensitivity amplification factor is up to 18.61. Through the application of harmonic Vernier effect in microwave domain, the amplification factor can be easily adjusted with much higher manufacturing tolerance and alleviate the measurement range restriction induced by the periodic frequency response.

Cryogenic VCSEL microwave-optical model for laser frequency response prediction and e–h recombination lifetime analysis

Cryogenic vertical-cavity surface-emitting lasers (VCSELs) for high-speed computing and energy-efficient data links have recently received considerable interest due to the microcavity laser bandwidth enhancement at low operating power. In this work, microwave on-wafer measurements of VCSELs for frequencies up to 50 GHz are performed over temperatures down to 82 K. Subsequently, we applied parasitic de-embedding techniques to develop a microwave-optical laser model. Based on the bias-dependent measurement of laser frequency responses and laser model, the photon and electron–hole (e–h) recombination lifetimes are accurately extracted to explain the physics of laser bandwidth enhancement and the behavior of resonances. Finally, we demonstrate that the VCSEL can deliver a modulated bandwidth of >60 GHz at a low operating current, I = 3 mA, for delivering >120 Gb/s non-return-to-zero data to establish an energy-efficient optical link at 82 K.

Frequency-domain stability methods for reset control systems

Reset controllers have the potential to enhance the performance of high-precision industrial motion systems. However, similar to other non-linear controllers, the stability analysis for these controllers is complex and often requires parametric model of the system, which may hinder their applicability. In this paper a frequency-domain approach for assessing stability properties of control systems with first and second order reset elements is developed. The proposed approach is also able to determine uniformly bounded-input bounded-state (UBIBS) property for reset control systems in the case of resetting to non-zero values. An illustrative example to demonstrate the effectiveness of the proposed approach in using frequency response measurements to assess stability properties of reset control systems is presented.

Linear Matrix Inequality Approach to Designing Damping and Tracking Control for Nanopositioning Application

This paper presents a method to extend the eigenstructure assignment based design of the Positive Position Feedback (PPF) damping controller to the family of well-known second-order Positive Feedback Controllers (PFC) namely: (i) the Positive Velocity and Position Feedback (PVPF) and (ii) the Positive Acceleration Velocity and Position Feedback (PAVPF) using appropriate eigenstructure assignment. This design problem entails solving a set of linear equations in the controller parameters using Linear Matrix Inequalities (LMI) to specify a convex design constraint. These damping controllers are popularly used in tandem with a tracking controller (typically an integrator) to deliver high-bandwidth nanopositioning performance. Consequently, the closed-loop performance of all three controllers (PPF, PVPF and PAVPF) employed in tandem with suitably gained integral tracking loops is thoroughly quantified via relevant performance metrics, using measured frequency response data from one axis of a piezo-stack actuated x-y nanopositioner.

Photonic scheme for broadband frequency response measurement of PDs.

We report a scheme to measure the broadband frequency response of photodetectors (PDs) with the capacity of self-calibration. The optical carrier at f 0 is modulated through one modulator, and this modulator is driven by a microwave signal with a fixed frequency f 1 to produce the carrier-suppressed double sideband optical signals f 0-f 1 and f 0+f 1. The frequency interval of the optical signals is 2f 1. Subsequently, the two optical signals are sent to another modulator driven by a swept microwave signal f m. Two pairs of carrier-suppressed double sideband signals with a high signal-to-noise ratio are generated. The frequencies of these signals are f 0-f 1-f m,f 0-f 1+f m, f 0+f 1-f m, and f 0+f 1+f m. After the PD under test, the frequency response can be extracted from the amplitude of the microwave signals at 2f 1, 2f 1-2f m, and 2f 1+2f m. Two PDs in our laboratory are experimentally characterized from 0.1 to 40GHz with a resolution of 100MHz. Compared with the traditional vector network analyzer swept method, the proposed method extends the measurement range from f m(max) to 2f 1+2f m(max) and has the capacity of self-calibration to eliminate the influence caused by the modulator frequency response on the measurement results.

Modeling, analysis, and demonstration of a carrier-injection electro-absorption modulator at 2 µm on Ge-on-Si platform.

In this paper, a carrier-injection electro-absorption modulator (EAM) at 2 µm is demonstrated on Ge-on-Si platform. The EAM shows a compact size and high modulation efficiency due to the strong free-carrier electroabsorption (FCEA) effect in Ge. A modulation depth of 40 dB can be obtained under the injection current of only 420 mA. Small-signal frequency response measurement is performed and a small-signal equivalent circuit model is proposed. Based on reflection coefficients and equivalent circuit, the frequency response of carrier-injection EAM is discussed in detail. The 500 Mbps open eye diagram verifies the data-processing capacity of our EAM at 2 µm wavelength for its application in biological, chemical molecular detection, and infrared imaging systems.

Quantification of Time-Domain Truncation Errors for the Reinitialization of Fractional Integrators

In recent years, fractional differential equations have received a significant increase in their use for modeling a wide range of engineering applications. In such cases, they are mostly employed to represent non-standard dynamics that involve long-term memory effects or to represent the dynamics of system models that are identified from measured frequency response data in which magnitude and phase variations are observed that could be captured either by low-order fractional models or high-order rational ones. Fractional models arise also when synthesizing CRONE (Commande Robuste d'Ordre Non Entier) and/or fractional PID controllers for rational or fractional systems. In all these applications, it is frequently required to transform the frequency domain representation into time domain. When doing so, it is necessary to carefully address the issue of the initialization of the pseudo state variables of the time domain system model. This issue is discussed in this article for the reinitialization of fractional integrators which arises among others when solving state estimation tasks for continuous-time systems with discrete-time measurements. To quantify the arising time-domain truncation errors due to integrator resets, a novel interval observer-based approach is presented and, finally, visualized for a simplified battery model.

Scavenging energy from aeroelastic vibrations for hybrid stall control in a fixed-wing micro aerial vehicle

Scavenging energy from aeroelastic vibrations was considered for a self-powered hybrid passive-active stall control system intended to improve the aerodynamic performance of fixed-wing micro aerial vehicles without exhausting available batteries. It was found that the passive component of the system generates intense streamwise vortices, which give rise to vortex-induced vibrations. Measured frequency response functions indicated accelerations in a wing prototype up to 0.1 g at relatively low frequencies, when it was operated at simulated flight conditions in a wind tunnel. Aiming to use this resource for additional power, a piezoelectric energy harvesting device was installed inside the wing and tuned for resonant response. Two electromechanical modeling approaches for the piezoelectric harvester were investigated, namely, an analytical model and finite elements simulations. A comparison with experimental results has shown that the latter approach is better equipped to deal with advanced designs, yielding accurate predictions in the present study. Extracted power and generated voltage were quantified as a function of the electric loading resistance. The reported data demonstrated that the proof of concept was achieved, so that a lightweight, low-consumption actuator for the active component of the stall control system can be powered by the energy of structural vibrations.

Полосно-пропускающий фильтр на цилиндрических волноведущих структурах со сложными металлическими гребнями

This paper shows the possibility of using a circular waveguide with radial ridges and annular segments of finite thickness as resonant diaphragms in the synthesis of band-pass cylindrical waveguide filters. An electrodynamic calculation and design of a band-pass waveguide filter based on round waveguides with thin plane-transverse metal resonant diaphragms has been carried out. The analysis of the electrodynamic parameters of the diaphragm from its geometrical dimensions is carried out. The results of a study of the resonant properties of a single diaphragm are presented. The results of comparing the frequency response of filters obtained by computer simulation with the measured frequency response of manufactured prototype filters are presented.

Investigation of Piezoelectric Energy Harvesting From Structural Vibration Induced by Rotating Machinery

Increasing energy consumption has led recent efforts towards energy harvesting technologies. Among them, piezoelectric energy harvesting with piezo-based sensors and energy harvesters have gained significant attention due to their applicability and efficacy for microscale power generation systems. Present study aims to investigate energy harvesting with piezoelectric materials from structural vibration propagating throughout the structure from vibration sources. For this purpose, a use case of a mechanical pump mounted on a steel foundation is chosen. A Finite Element (FE) model of the foundation of the pump with piezoelectric energy harvesters is developed and validated in an experimental setup. Measured frequency response functions (FRFs) show particularly good match with simulation results. Afterwards, a real measured acceleration data from the mechanical pump is applied. Simulations are performed and effectiveness of the piezoelectric energy harvester for two different locations are demonstrated. In this study, piezoceramic (PZT), PVDF polymer, ZnO film and a PMN-PT single crystal composite is considered as harvester material and the effectiveness of each piezoelectric material are compared.

The Power Transformer Winding Input Admittance and Frequency Response

The frequency response analysis is increasingly more widely used to estimate the electrical and mechanical condition of power transformer windings. The frequency response measurement procedure has been prescribed in the existing international and national standards. However, the interpretation of measurement results still remains a subject of discussion. Various approaches have been used to interpret the results, including an analysis of transformer windings’ complex impedances and admittances obtained by calculations from frequency responses. To improve the frequency response interpretation, the article presents an analysis of power transformer winding input and output currents and admittances based on simplified equivalent circuits. Qualitative and quantitative results are presented, which show that the admittances obtained from measured frequency responses differ essentially from the true input admittances of the windings. The main factors causing the differences between these winding admittances are considered. It is shown that despite the existing differences, the current through the neutral and the winding admittance determined from the measured frequency response can also be used in practice to determine the power transformer winding natural oscillation frequencies.