Transfer Function Measurements Research Articles

Simplified Simulation and Measurement of the Signal Transfer Function of a Continuous-Time Pipelined Analog-to-Digital Converter

The continuous-time pipeline (CTP) analog-to-digital converter is a power- and area-efficient realization of an anti-alias filter + ADC cascade. The signal transfer function (STF), which is the transfer function of the anti-alias filter, is an important property of the CTP ADC. It is conventionally characterized by exciting the ADC with multiple input sinusoids. We demonstrate that a single-tone excitation is enough to determine the STF of the CTP ADC over its useful frequency range. The theory is supported by measurement results from a three-stage CTP ADC designed in a 65 nm CMOS process. The converter, equivalent to a sixth-order anti-alias filter + ADC, achieves 70 dB SNDR in a 100MHz bandwidth while sampling at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{s}= 800$ </tex-math></inline-formula> MHz.

Estimation of the Optimal Spherical Harmonics Order for the Interpolation of Head-Related Transfer Functions Sampled on Sparse Irregular Grids

Conventional individual head-related transfer function (HRTF) measurements are demanding in terms of measurement time and equipment. For more flexibility, free body movement (FBM) measurement systems provide an easy-to-use way to measure full-spherical HRTF datasets with less effort. However, having no fixed measurement installation implies that the HRTFs are not sampled on a predefined regular grid but rely on the individual movements of the subject. Furthermore, depending on the measurement effort, a rather small number of measurements can be expected, ranging, for example, from 50 to 150 sampling points. Spherical harmonics (SH) interpolation has been extensively studied recently as one method to obtain full-spherical datasets from such sparse measurements, but previous studies primarily focused on regular full-spherical sampling grids. For irregular grids, it remains unclear up to which spatial order meaningful SH coefficients can be calculated and how the resulting interpolation error compares to regular grids. This study investigates SH interpolation of selected irregular grids obtained from HRTF measurements with an FBM system. Intending to derive general constraints for SH interpolation of irregular grids, the study analyzes how the variation of the SH order affects the interpolation results. Moreover, the study demonstrates the importance of Tikhonov regularization for SH interpolation, which is popular for solving ill-posed numerical problems associated with such irregular grids. As a key result, the study shows that the optimal SH order that minimizes the interpolation error depends mainly on the grid and the regularization strength but is almost independent of the selected HRTF set. Based on these results, the study proposes to determine the optimal SH order by minimizing the interpolation error of a reference HRTF set sampled on the sparse and irregular FBM grid. Finally, the study verifies the proposed method for estimating the optimal SH order by comparing interpolation results of irregular and equivalent regular grids, showing that the differences are small when the SH interpolation is optimally parameterized.

Estimating the State of Charge of Lithium-Ion Batteries Based on the Transfer Function of the Voltage Response to the Current Pulse

There are several methods for estimating the SoC of lithium-ion batteries that use electrochemical battery models or artificial intelligence and intelligent algorithms. These methods have numerous advantages but are complex and computationally intensive. This paper presents a new method for estimating the SoC of lithium-ion batteries based on identifying the transfer function of the measured battery voltage response to the charging current pulse. It is assumed that the transfer function of the battery changes with the state of charge. In the learning phase, a reference table of known SoCs and associated transfer functions is created. The parameters of these transfer functions form the reference points in hyperspace. In the phase of determining the unknown SoC of the battery, the parameters of the measured transfer function form a point in hyperspace that is compared with the reference points of the transfer functions for known SoCs. The unknown SoC of the battery at the particular measurement time is obtained by finding the two reference points closest to the point of unknown SoC using the Euclidean distance and a linear interpolation based on this distance. The method is simple, computationally undemanding, insensitive to measurement noise, and has high accuracy in SoC estimation.

Automated human temporal-bone experiments

Abstract Temporal-bone (TB) experiments are useful for the investigation of middle-ear and inner-ear transfer properties, and the analysis and development of active or passive middleear prostheses or related devices. To acquire the mechanical middle-ear (ME) response, the Laser-Doppler vibrometry (LDV) is utilized as a preferred method. In most setups, the exact measurement point chosen on the biological structure of interest as well as the direction of the corresponding vibration measurement is not precisely defined and of unknown reproducibility. Hence, an automated setup controlling coordinates of TB and measurement direction is developed and tested. To test the reproducibility, TBs were measured with ER7C and ER10C probe microphones employing a small industrial robot to position the TB to the ME points of interest and align it to the laser beam. The position and vibration data acquired at the same locations at different points of time were processed and compared. Measured transfer functions indicate noticeable differences at some frequency ranges. Nonetheless, the reproducibility of positioning to repeatedly measured points proved itself relatively accurate, if no manipulations in the setup are made. In conclusion, the current study shows that automated LDV TB measurement system is in principle capable to adapt to the changes in setup during intermediate preparation steps. With more acquired data, the setup stability and reproducibility can be more precisely verified, and additional improvements can be made.

A Novel Online Monitoring Strategy for the Localized Grounding Insulation Defect of Converter Transformers Based on Converter Switching States Control

Power electronic converters are operated under rapid and frequent switching actions. Large electrical stresses and various current harmonics have critical effects on insulation ageing and reliable operation of converter transformers. In this article, a novel online monitoring strategy for the localized grounding insulation defect is proposed based on the control of converter switching states (CSS). First, a transfer function (TF) measurement is developed using switching transient voltages. Analytical expression of the TF is derived that can separate the effects of defect location and ageing severity. Then, a CSS control method is proposed by inserting six designated CSS sequences, which can identify the phase with defect and evaluate defect location and ageing severity. Next, the monitoring strategy is established in the procedure of CSS control, testing, data processing, and evaluation. Finally, online experiments are performed to validate the effectiveness of the proposed CSS-control-based monitoring strategy. The resonance trace is shown as a powerful tool whose slope and magnitude are utilized to evaluate location and severity, respectively. The main advantage of the proposed strategy is that it can be implemented conveniently and reliably, with no extra hardware requirement and little effect on the normal operation of converter system.

Modelling of a hydraulic system coupled with lumped masses

ABSTRACT A coupled hydraulic-mechanical system with a lumped parametric mechanical part has been set up, measured and mathematically modelled in the frequency domain. The main focus of this article is the identification of unknown system parameters, which depends on the models of coupling and dissipation. The set-up under investigation can be excited hydraulically, by flow rate, or mechanically, by force. The responding pressures of the hydraulic subsystem and the accelerations of the mechanical subsystem are measured, from which transfer functions between excitation and system states can be calculated. The property of reciprocity is used for the processing of measurement data. With a suitable two-step strategy and non-linear optimization unknown system parameters can be identified from measurements. Additionally, the agreement of model and measurement and the physical meaningfulness of these parameters are examined. The proposed model succeeds in predicting measured transfer functions, whose data weren't used for the identification of model parameters.

Determination and utilization of blocked forces

Path analysis approaches rely on measured transfer functions, and measured sources or responses. For vibratory path analysis, the focus is commonly on determining forces that are hard to measure directly. There are three commonly applied strategies: 1) blocked force analysis, 2) pseudo force, and 3) classical transfer path analysis. These three strategies will be surveyed, and then the usefulness of the blocked force approach will be illustrated on two practical examples. Blocked forces are determined using correlated or uncorrelated assumptions for low or high frequencies, respectively. Suggested guidelines for selecting the number of blocked forces are detailed and demonstrated.

Quantifying the Surface Strain Field Induced by Active Sources with Distributed Acoustic Sensing: Theory and Practice.

Quantitative dynamic strain measurements of the ground would be useful for engineering scale problems such as monitoring for natural hazards, soil-structure interaction studies, and non-invasive site investigation using full waveform inversion (FWI). Distributed acoustic sensing (DAS), a promising technology for these purposes, needs to be better understood in terms of its directional sensitivity, spatial position, and amplitude for application to engineering-scale problems. This study investigates whether the physical measurements made using DAS are consistent with the theoretical transfer function, reception patterns, and experimental measurements of ground strain made by geophones. Results show that DAS and geophone measurements are consistent in both phase and amplitude for broadband (10 s of Hz), high amplitude (10 s of microstrain), and complex wavefields originating from different positions around the array when: (1) the DAS channels and geophone locations are properly aligned, (2) the DAS cable provides good deformation coupling to the internal optical fiber, (3) the cable is coupled to the ground through direct burial and compaction, and (4) laser frequency drift is mitigated in the DAS measurements. The transfer function of DAS arrays is presented considering the gauge length, pulse shape, and cable design. The theoretical relationship between DAS-measured and pointwise strain for vertical and horizontal active sources is introduced using 3D elastic finite-difference simulations. The implications of using DAS strain measurements are discussed including directionality and magnitude differences between the actual and DAS-measured strain fields. Estimating measurement quality based on the wavelength-to-gauge length ratio for field data is demonstrated. A method for spatially aligning the DAS channels with the geophone locations at tolerances less than the spatial resolution of a DAS system is proposed.

Statistical Analysis of the Measurement Noise in Dynamic Impedance Spectra.

Different strategies can be used to acquire dynamic impedance spectra during a cyclic voltammetry experiment. The spectra are then analyzed by fitting them with a model using a weighted non‐linear least‐squares minimization algorithm. The choice of the weighting factors is not trivial and influences the value of the extracted parameters. At variance with the classic electrochemical impedance spectroscopy, dynamic impedance measurements are performed under non‐stationary conditions, making them typically more prone to errors arising from the voltage and current analog‐to‐digital conversion. Under the assumption that the noise in the voltage and current signals have a constant variance along the measurement and that it is uncorrelated between distinct samples, we calculate an expression for the expected variance of the error of the resulting immittances, which considers the specific procedure used to extract the spectra under the time‐varying nature of the measurements. The calculated variance of the error is then used as a rigorous way to evaluate the weighting factors of the least‐squares minimization, assuming that the fitted model is ideally exact and that there are no systematic errors. By exploring two classical electrochemical systems and fitting the measured spectra with a transfer function measurement model, namely with the Padé approximants, we show that the variance evaluated with our method captures the frequency dependence of the resulting residuals and can be used for reliably performing the complex non‐linear least‐squares fitting procedure.

Estimating uncertainty for the instrument transfer function measurement of 3D scanners.

Spatial resolution is an important aspect of many optical instruments. It is defined as the ability of surface-topography measuring instruments to distinguish closely spaced surface features. Following convention, spatial resolution can be defined as the spatial frequency response of the instrument, known as the instrument transfer function (ITF). In this paper, we describe the step-artifact approach for estimating the ITF for 3D scanners, discuss step artifact characterization and validation approaches, and present a method to estimate the combined uncertainty of the ITF measurement. The approach is demonstrated using the EinScan-Pro 3D scanner. A step artifact is used for the measurement that takes advantage of the cleaving properties of a single-side polished silicon wafer. The uncertainty analysis includes simulations to estimate the contribution due to influencing factors such as the alignment of the step artifact to the measurement axis, the diffuse versus specular scattering properties of the step edge, and various processing parameter choices.

Case study: Simulating and measuring the vibration and radiated sound of a large industrial chiller

This paper presents a case study for measuring and simulating the vibration and radiated sound for a large complex industrial chiller. We describe a simulation framework based on statistical energy analysis (SEA), which is populated using a hybrid mix of analytic, numerical, and measurement techniques. This hybrid approach was motivated by preliminary measurements of vibration and sound from the operating chiller, as well as a series of vibroacoustic transfer functions measured during quiescent non-operating conditions. Some components, like the chiller condenser shell, are modally dense and well suited to statistical estimates of SEA parameters like modal density and coupling between the shell modes and internal and external acoustic spaces. Other components, like the discharge pipe between the compressor and condenser shell, have only a few well separated modes with low damping. This component is better modeled using mobilities either measured or calculated using finite element analysis. We estimate other parameters like internal and coupling loss factors using a mix of analytics and measurements where appropriate. We validate the general model by comparing simulated and measured transfer functions between the discharge pipe and condenser shell — the components that radiated the most sound. We estimate structure-borne and fluid-borne input powers from the compressor using inference techniques based on transfer function measurements at quiescent conditions and averaged surface vibrations measured at operating conditions. This inference approach allows for estimating input powers over any chiller operating condition. Simulated vibrations and radiated sound are generally within 3 dB of measurements for several operating conditions. This case study provides a useful general methodology for modeling and measuring the vibroacoustics of chillers and other complex machinery

Determination of the heat conduction transfer function within the thermoacoustic instability limit cycle in a Rijke tube

In this work, experimental measurements of the heat conduction transfer function (HCTF) within the limit cycle of thermoacoustic instabilities were conducted associated with a feedback controller. The responses of the heat conduction from the heater to the air in the vicinity to the oncoming flow disturbance can be described as the HCTF. When self-excited thermoacoustic instability occurs, it is not possible to measure the HCTF. The measurement experiment is twofold. Firstly, the active feedback control is applied to suppress the self-excited thermoacoustic oscillation in the Rijke tube. Secondly, the two-microphone method is applied to achieve the measurement of the HCTF at different working conditions. Experimental results show that the mean air flow velocity has an effect on the attenuation time of the thermoacoustic oscillation. Both of the mean air flow velocity and the electric-heating power have a significant effect on HCTFs.

Development of an in-ear microphone for individualized measurement of hearing protection device output

Hearing protection devices (HPDs) are designed to reduce the amplitude of sound reaching the ear, but can also distort the acoustical cues necessary for sound localization. In order to quantify the acoustic impact of an HPD on the signal reaching the tympanic membrane, the signals deep in the ear canal with and without the HPD must be compared. While some commercial microphone solutions for measuring in-ear pressures with HPDs exist, they are device-specific and/or may not provide reliable isolation of the microphone transducer from the (potentially high-intensity) ambient sound field. Here, we describe a new assembly using a small MEMS microphone attached to the end of a thin flexible circuit, which can be inserted either alongside or through virtually any HPD. Following a description of the electromechanical design of the assembly, we present measurements of insertion loss for HPDs with and without the microphone using an acoustic test fixture. These measurements demonstrate that the presence of the microphone does not significantly disrupt the sound attenuation characteristics of a range of HPDs. Preliminary measurements of insertion loss and head-related transfer functions in human subjects are also presented.

Improvements on sampling of point spread function in optical transfer function measurement.

Point spread function (PSF), which is the intensity distribution of optical system impulse response and usually acquired by imaging a single pinhole in experiment, can characterize the quality of optical imaging system. Faithful recording of the two-dimensional intensity distribution of PSF is key for accurate measurement of optical transfer function (OTF), however distortions in recorded PSF can be easily caused by a large sampling interval and the electronic noise of the detector. Under a given sampling interval, the position-phase difference between pixels and intensity signals can change the intensity distribution of acquired PSF remarkably, making the computed OTF or MTF (modulation transfer function) error prone. Aiming at problems existing in pinhole based MTF measurement methods, this paper developed a new method with underline physics similar to that of slanted edge method to realize sub-pixel sampling of PSF intensity by using accurate non-integer up-sampling matrix of separate binary pixels and applying random patterns shown on digital micro-mirror device (DMD) as target. Numerical simulations show that improvement on the discrete sampling of point spread function with this method is very helpful to improve anti-noise robustness and the accuracy of optical transfer function measurement.

Head-related transfer function measurements in a compartment fire.

The Personal Alert Safety System (PASS) is an alarm signal device carried by firefighters to help rescuers locate and extricate downed firefighters. A fire creates temperature gradients and inhomogeneous time-varying temperature, density, and flow fields that modify the acoustic properties of a room. To understand the effect of the fire on an alarm signal, experimental measurements of head-related transfer functions (HRTF) in a room with fire are presented in time and frequency domains. The results show that low-frequency (<1000 Hz) modes in the HRTF increase in frequency and higher-frequency modal structure weakens and becomes unstable in time. In the time domain, the time difference of arrival between the ears changes and becomes unstable over time. Both of these effects could impact alarm signal detection and localization. The receive level of narrowband tones is presented that shows that the fire makes the receive level of a source vary by > 10 dB. All of these effects could impact the detection and localization of the PASS alarm and have life safety consequences.

Effects of Converter Harmonic Voltages on Transformer Insulation Ageing and an Online Monitoring Method for Interlayer Insulation

Power electronic converter can produce massive voltage stresses on the connected transformer, with great effects on electrical ageing of the insulation. Such effects can be diverse upon different insulation components under different harmonic voltages, which have not been well clarified. This article aims at enhancing online monitoring of converter transformers from two aspects. First, electrical ageing evaluation models are developed for different types of transformer insulation. It is the first time to clarify the effects related to the component location and the ageing severity under differential-mode and common-mode (CM) voltages. Interlayer (IL) insulation faces a serious ageing threat and the line-lead component is aged with the severest degree. Second, CM voltages are used to build transfer function (TF) measurement for IL insulation monitoring. The key is to identify the optimal monitoring frequency with the highest sensitivity. Based on the analytical case introducing typical parameters, the TF performance is analyzed in different ageing conditions. Online experiments validate that the proposed method is effective and has good application prospect. The contributions lie in that the diverse ageing effects of converter harmonic voltages on different insulation components can be distinguished and online monitoring of IL insulation can be achieved effectively.

Experimental Evaluation of UWB Transmission Waveform with Body-Shadowing in an Indoor Environment

Wireless radio transmission performance in a realistic environment is a significant issue for designing and evaluating in short-range transmission technologies. Human body-shadowing is a significant propagation effect in an indoor wireless communication network. This paper presents the measurement model of impulse radio transmission with human body-shadowing in an indoor environment with IEEE 802.15.4 multipath impulse parameters. The impulse radio transfer function measurement model for the human body impulse radio transfer function with frequency band cover from 3 GHz to 11 GHz. The optimum system evaluation of impulse radio transmission is due to the human body and antennas. The characteristics of impulse radio transmission loss are using decay factor, log-normal standard, clusters, and ray arrival rate. The contributions of this research can be evaluating the human body impulse radio transfer function. And the design of the wireless radio system with the body shadowing effects and ambient environments.

Force detection sensitivity spectrum calibration of levitated nanomechanical sensor using harmonic coulomb force

Oscillators based on levitated particles are promising for the development of ultrasensitive force detectors. The theoretical performance of levitated nanomechanical sensors is usually characterized by the so-called thermal noise limit force detection sensitivity, which does not exhibit spectral specificity in practical measurements. To characterize the actual detection performance, we propose a method for the force detection sensitivity calibration of a levitated nanomechanical sensor based on the harmonic Coulomb force. Utilizing the measured transfer function, we obtained the force detection sensitivity spectrum from the position spectrum. Although the thermal noise limit force detection sensitivity of the system reached (4.39±0.62)×10−20N/Hz1/2 at 2.4×10−6mbar with feedback cooling, the measured sensitivity away from the resonance was of the order of 10−17N/Hz1/2 based on the existing detection noise level. The calibration method established in our study is applicable to the performance evaluation of any optical levitation system for high-sensitivity force measurements.

Evaluation of noise excitation as a method for detection of hypernasality

Hypernasality is a disorder where excess nasal resonance is perceived during speech, often as a result of abnormal coupling between the oral and nasal tracts known as velopharyngeal insufficiency (VPI). The most common cause of VPI is a cleft palate, which affects around 1 in 1650 babies, around ⅓ of whom have persistent speech problems after surgery. Current equipment-based assessment methods are invasive and require expert knowledge, and perceptual assessment methods are limited by the availability of expert listeners and differing interpretations of assessment scales. Spectral analysis of hypernasality within the academic community has resulted in potentially useful spectral indicators, but these are highly variable, vowel specific, and not commonly used within clinical practice.Previous works by others have developed noise excitation technologies for the measurement of oral tract transfer functions using resonance measurement devices (RMD). These techniques provide an opportunity to investigate the structural system abnormalities which lead to hypernasality, without the need for invasive measurement equipment. Thus, the work presented in this study adapts these techniques for the detection of hypernasality. These adaptations include augmentation of the hardware and development of the software, so as to be suitable for transfer function measurement at the nostrils rather than the mouth (nRMD). The new method was tested with a single participant trained in hypernasal production, producing ‘normal’ and hypernasal vowels, and the recordings validated through a listening test by an expert listener and calculation of nasalance values using a nasality microphone. These validation stages indicated the reliability of the captured data, and analysis of the nRMD measurements indicated the presence of a systematic difference in the frequency range 2 to 2.5 kHz between normal and hypernasal speech. Further investigation is warranted to determine the generalisability of these findings across speakers, and to investigate the origins of differences manifesting in the transfer functions between conditions. This will provide new insights into the effects of nasal tract coupling on voice acoustics, which could in turn lead to the development of useful new tools to support clinicians in their work with hypernasality.

Accuracy and precision of an edge-based modulation transfer function measurement method using a variable oversampling ratio

The edge-based method standardized in ISO 12233 approximates the modulation transfer function (MTF) as a function of horizontal or vertical spatial frequency by analyzing a supersampled edge profile obtained from the captured image of a slightly slanted bi-tonal edge. The method describes the slanted projection of pixels sampled in a square array into a linear array of subpixel-wide bins. An ad hoc correction is available to accommodate the diagonal MTF measurements. However, using a fixed oversampling ratio in the standard method degrades the accuracy and precision of the MTF estimates, owing to the periodic misalignment between the projection paths and the bin array. A new edge-based method using a variable oversampling ratio, OMNI-sine, has been proposed to remedy this misalignment. In this study, computer simulations were performed to demonstrate the accuracy and precision of the MTF estimates over a full range of finely sampled slant angles.