Impedance Transfer Function Research Articles

Improvement of Commercial Vehicle Seat Suspension Employing a Mechatronic Inerter Element

To further improve the ride comfort of commercial vehicles, a seat ISD (Inerter–Spring–Damper) suspension utilizing a mechatronic inerter is proposed in this paper. Firstly, a five-DOF (degree-of-freedom) commercial vehicle seat ISD model was built. Then, the positive real network constraint conditions of a biquadratic impedance transfer function were determined, and the meta-heuristic intelligent optimization algorithm was used to solve the parameters. According to the solution, the impedance transfer function was obtained and the specific network structure was realized by network synthesis. Lastly, this study compares the vibration isolation performance of the mechatronic ISD suspension of the vehicle seat with that of a passive suspension. In comparison to passive seat suspension, the seat mechatronic ISD suspension reduces seat vibration transmissibility by 16.33% and vertical acceleration by 16.78%. Results indicate that the new suspension system can be an effective improvement in ride comfort.

Impedance models for single and two degree of freedom linings with an improved data base and local non-linearity

Previously developed predictive models for impedance of single-degree-of-freedom and two-degree-of-freedom acoustic linings driven by a broad band acoustic source are reexamined. Two issues are addressed, the first being improvement of the conventional perforate face sheet impedance model. Data correlations based on flow bench measurements of steady flow pressure drop are reevaluated with emphasis on low flow velocity to improve the consistency of the prediction of linear resistance. In addition, for two-degree-of-freedom linings, face sheet mass reactance is modified to account for the presence of the septum. The second issue addresses the implication that for a non-linear lining, with impedance a function of the local sound pressure level, the installed performance of the lining depends on the local impedance, as opposed to impedance based on the source sound pressure level. This is investigated in the benchmarking of the impedance models by comparison of the acoustic transfer function predicted by a propagation code with the imbedded impedance model and transfer function measurements made in a grazing flow duct test facility. The propagation code is extended to make the non-linear behavior of the lining model dependent on the local acoustic spectrum, introducing an additional level of non-linearity and an iterative application of the propagation code. A principal conclusion is that with no grazing flow both the lining model and grazing flow duct transfer function measurements show a significant effect of local variation of the acoustic spectrum. With increasing grazing flow Mach number, this effect is reduced and effectively disappears at the highest Mach number. With increasing grazing flow Mach number the grazing flow contribution to face sheet resistance dominates and tends to mask the non-linear behavior of the component of resistance not related to grazing flow.

Testing the absorption coefficient of 3D printed perforated panels

Sound absorption is common in most studios, but most residential spaces are not designed for good acoustics. While these rooms are non-ideal, they are sometimes used to record sounds and need to absorb unwanted frequencies. Perforated 3D printed panels have the potential to make inexpensive and modular home treatments. In order to determine if these panels would be effective, the absorptive properties need to be evaluated. There are several ways to test sound absorption, including the in situ subtraction method and the impedance tube transfer function method. Reference materials were used to test the effectiveness of both measurement methods. 3D printed perforated panels were then designed and the absorption was tested. Each surface was tested with the subtraction method, and many different setups for the equipment were tested to find the ideal setup for the most accurate absorption coefficient. The results show varying success. The 3D printed panels were then tested with the transfer function method. An impedance tube was made using PVC pipes and was used to test the transfer function method. This method showed varying results for the absorption coefficient tested, and results will be presented.

Study on resonance characteristic of continuous co‐phase traction power supply system

In order to solve the power quality problems and eliminate the neutral sections in the railway, the implementation of the continuous co-phase traction power supply system (CCTPSS) is the development trend of the future. However, various parameters of the compensator in CCTPSS have a huge impact on the resonance, which will possibly change the original resonance characteristic of the railway. Therefore, the parameters design of the compensator has become a difficult problem to be solved. An optimization mode method is proposed in this paper to obtain the influence of the compensator on the resonance characteristic of CCTPSS and the optimal solution of each parameter is obtained with the goal of suppressing resonance and minimizing the cost. Firstly, the impedance analysis and transfer function analysis are used to establish models for CCTPSS. It is found that the equivalent harmonic impedance of the traction substation decreases after adding the compensator, which will inevitably cause the resonance frequency to increase. By comparing the resonance points of the original traction power supply system (TPSS) and CCTPSS, the results show that the parameters of the compensator have a greater influence on the resonance point in CCTPSS. At last, taking the CCTPSS based on LCL-type reactive power comprehensive compensator (RPCC) as an example to carry out the optimization mode method, the result proves that this method is not only beneficial to the suppression of harmonic resonance, but also helpful for reducing the cost of the RPCC.

Structural Characteristics and Sound Absorption Properties of Waste Hemp Fiber

In order to realize high-efficiency and high-value recycling of waste hemp fibers, the macromolecular structure, the supramolecular structure, and the morphological structure of waste hemp fibers were investigated by using Fourier transform infrared spectroscopy, X-ray diffractometry, upright metallurgical microscopy, and scanning electron microscopy. According to its structural characteristics, the sound-absorbing mechanism of waste hemp fiber was analyzed, and the reason for the good sound-absorbing performance of waste hemp fiber was clarified. The acoustic impedance transfer function test was used to analyze and compare the sound-absorbing performance of waste hemp fiber and several other fiber aggregates that could be used in the field of sound-absorbing, and the sound-absorbing performance of a waste hemp fiber composite material was tested. The research revealed that: the sequence of sound-absorbing performance of several fiber aggregates was cotton fiber, waste hemp fiber, wool fiber, and polyester fiber; that waste hemp fiber had excellent high-frequency sound-absorbing performance, with a maximum sound absorption coefficient of 0.95; and that the maximum sound absorption coefficient of the waste hemp fiber composite reached 0.93. Therefore, the waste hemp fiber has excellent sound-absorbing properties and has high application value in the field of sound absorption.

Structural characteristics and sound absorption properties of different kinds of waste feather fibers

There are millions of tonnes of waste feathers every year from the booming poultry industry. To rationalize the utilization of waste feather resources, waste chicken feather fibers, waste duck feather fibers, and waste goose feather fibers were used as reinforcement materials, and polybutylene succinate was used as matrix materials to prepare sound absorbing composite materials. The acoustic impedance transfer function method was used to test the sound absorption performance of the sound absorbing composite materials with different feather fibers. The results showed that the sound absorbing composite materials with waste duck fibers had the best sound absorption performance. Fourier transform infrared spectrometer, X-ray diffraction, and scanning electron microscope were used to analyze the macromolecular structure, aggregation structure, and morphological structure of different kinds of waste feather fibers. According to the structure, the mechanism of sound absorption was analyzed, and the reason why the fibers of different kinds of waste feathers (chicken feather, duck feather and goose feather) had good sound absorption performance was clarified. It was clear that this unique structure endowed it with the characteristics of light weight and good sound absorption. So the waste feather fibers have high application value in the field of sound absorption.

Physics-Based Greedy Algorithm for Reliable Fast Frequency Sweep in Electromagnetics via the Reduced-Basis Method

A reliable fast frequency sweep model order reduction (MOR) process is detailed. A reduced-basis approximation is taken into account to accurately and efficiently describe the electromagnetic field in a frequency band of analysis. The reduced-basis space is made up of snapshots of the electric field adaptively chosen on a physics-based greedy algorithm. Following a theoretical analysis starting from time-harmonic Maxwell’s equations, in- band eigenresonances are shown to significantly contribute to the electric field in the band of analysis. An impedance matrix transfer function description of the microwave circuit is used and a pole-residue expansion of this matrix-valued impedance transfer function is detailed. A fundamental physical property is identified, from which a straightforward a posteriori error estimator arises, namely, matrix residues in the pole-residue expansion of the impedance transfer function must be rank-1. This cheap computation is well-suited for fast greedy algorithm strategies in adaptive construction of the reduced-basis approximation. Contrary to what has been previously done, a straightforward physics-based greedy algorithm that does not need to scan the whole frequency band of interest to enrich the reduced-basis approximation is proposed. Finally, actual microwave applications illustrate the capabilities and efficiency of the new physics-based a posteriori error estimator in the proposed methodology.

Acoustic and structural damping properties of fibrogranular composites made of jute and crumb rubber

Synthetic materials are mostly used in sound absorption and structural damping that cause harm to the environment and living beings. Previous studies have shown that jute and jute-derived composites are excellent sound-absorbing fibrous materials. The recent study also shows that the inclusion of granular particles like crumb rubber in the fiber enhances sound absorption. Fibrogranular material of natural and recycled material is an alternative to synthetic material. This study aims to characterize the effect of granular material, i.e., crumb rubber with the jute fiber, to understand the effect of granular particles on the jute fiber for sound absorption and the structural damping properties. Further, the size of crumb rubber is varied to understand its effect on the sound-absorbing and structural damping properties. The impedance tube transfer function method is used to measure the acoustic properties for normal incidence of sound. Then the measured acoustic properties are used to inverse characterize using the classical porous material model to evaluate the non-acoustic parameters, which is further used to characterize the structural damping properties based on the existing methodologies. The study discusses the sound absorption and structural damping properties of jute and crumb rubber fibrogranular composite

Rapid characterization of efficient system level ESD protection strategy using coupling transfer function

This study details a new technique for the fast and efficient design and analysis of system level electrostatic discharge (ESD) protection strategy using developed coupling transfer impedance function. The transfer coupling characteristics from the zapping point to the victim location on a DUT can be computed using coupling transfer gain function. Subsequently, it is integrated with an ESD current source in a SPICE type circuit simulator for the fast and efficient analysis of induced ESD coupling noise and the design of the appropriate ESD protection scheme with the suitable choice of ESD protection device (diodes, SCR, GGNMOS, GCNMOS etc.). The study discusses the different protection schemes i.e. primary, secondary and double ESD protections, and the effect of the selected diode types and ESD stressing levels on the employed protection strategy. The proof-of-concept is validated through the rapid design of suitable system level ESD protection strategy for a microstrip-line PCB, high-speed mobile device memory module, and a portable notebook motherboard.

Geolectric field measurement, modelling and validation during geomagnetic storms in the UK

Significant geoelectric fields are produced by the interaction of rapidly varying magnetic fields with the conductive Earth, particularly during intense geomagnetic activity. Though usually harmless, large or sustained geoelectric fields can damage grounded infrastructure such as high-voltage transformers and pipelines via geomagnetically induced currents (GICs). A key aspect of understanding the effects of space weather on grounded infrastructure is through the spatial and temporal variation of the geoelectric field. Globally, there are few long-term monitoring sites of the geoelectric field, so in 2012 measurements of the horizontal surface field were started at Lerwick, Eskdalemuir and Hartland observatories in the UK. Between 2012 and 2020, the maximum value of the geoelectric field observed was around 1 V/km in Lerwick, 0.5 V/km in Eskdalemuir and 0.1 V/km in Hartland during the March 2015 storm. These long-term observations also allow comparisons with models of the geoelectric field to be made. We use the measurements to compute magnetotelluric impedance transfer functions at each observatory for periods from 20 to 30,000 s. These are then used to predict the geoelectric field at the observatory sites during selected storm times that match the recorded fields very well (correlation around 0.9). We also compute geoelectric field values from a thin-sheet model of Britain, accounting for the diverse geological and bathymetric island setting. We find the thin-sheet model captures the peak and phase of the band-passed geoelectric field reasonably well, with linear correlation of around 0.4 in general. From these two modelling approaches, we generate geoelectric field values for historic storms (March 1989 and October 2003) and find the estimates of past peak geoelectric fields of up to 1.75 V/km in Eskdalemuir. However, evidence from high voltage transformer GIC measurements during these storms suggests these estimates are likely to represent an underestimate of the true value.

Impedance Circuit Model of Grid-Forming Inverter: Visualizing Control Algorithms as Circuit Elements

The impedance model is widely used for analyzing power converters. However, the output impedance is an external representation of a converter system, i.e., it compresses the entire dynamics into a single transfer function with internal details of the interaction between states hidden. As a result, there are no programmatic routines to link each control parameter to the system dynamic modes and to show the interactions among them, which makes the designers rely on their experience and heuristic to interpret the impedance model and its implications. To overcome these obstacles, this article proposes a new modeling tool named as impedance circuit model, visualizing the closed-loop power converter as an impedance circuit with discrete circuit elements rather than an all-in-one impedance transfer function. It can reveal the virtual impedance essence of all control parameters at different impedance locations and/or within different frequency bandwidths, and show their interactions and coupling effects. A grid-forming voltage source inverter is investigated as an example, with considering its voltage controller, current controller, control delay, voltage/current dq-frame cross-decoupling terms, output-voltage/current feedforward control, droop controllers, and three typical virtual impedances. The proposed modeling tool is validated by frequency-domain spectrum measurement and time-domain step response in simulations and experiments.

Advanced Impedance-Based Control Design for Decoupling Multi-Vendor Converter HVDC Grids

A progressive interconnection of existing HVDC links to form grids and the development of completely new HVDC grids from different vendors are expected shortly. One of the current challenges of such endeavour is unintended interactions due to independently designed controllers. This article proposes a design methodology for decentralized controllers to mitigate such interactions in multi-vendor voltage source converter (VSC)-HVDC grids. The approach presented relies on the unique stand-alone input-output impedance transfer function of each VSC, and the global impedance transfer function as seen from each terminal after interconnection with other VSCs. Subsequently, network-level controllers are designed by attempting to match the global responses at selected locations based on a novel interaction analysis, to the unique transfer function model of the vendors at the corresponding location. This approach reduces the entire problem to an impedance matching problem. We demonstrate the efficacy and flexibility of both the methodology and the designed controllers in mitigating interactions due to the independent design of VSC controllers through nonlinear simulations on a four-terminal droop controlled HVDC grid.

Structural characteristics and sound absorption properties of poplar seed fibers

In order to make reasonable utilization of poplar seed fibers, their macromolecular structure, supramolecular structure and morphological structure were analyzed by means of a biological microscope, scanning electron microscope, Fourier transform infrared spectrometer and X-ray diffractometer, and the relationship between the structure of poplar seed fiber and its sound absorption performance was explored. The acoustic impedance transfer function method was used to test the sound absorption performance of poplar seed fiber, kapok fiber, cotton fiber, wool fiber and hemp fiber aggregates that could be used in the field of sound absorption. The results showed that the order of sound absorption properties of the five fiber aggregates was as follows: kapok fiber, poplar seed fiber, cotton fiber, wool fiber, hemp fiber. The special structure of poplar seed fiber meant it had excellent sound absorption performance in the entire tested frequency range. The poplar seed fiber aggregate had a wide sound absorption frequency band and the maximum sound absorption coefficient reached 0.84, which has high application value in the field of sound absorption.

Sound Absorption Performance of the Poplar Seed Fiber/PCL Composite Materials.

Composite materials were prepared by the hot pressing method using poplar seed fibers and polycaprolactone (PCL) as the raw materials to solve the problems related to the recycling of waste fibers. The effects of mass fraction of poplar seed fibers, the volume density, and thickness on the sound absorption performance of the resulting composite materials were studied. The sound absorption coefficient curves of the composite material were obtained by the acoustic impedance transfer function method. The sound absorption coefficient of the composite material that was prepared under the optimal process conditions was higher than 0.7, and the effective sound absorption frequency band was wide. According to the box counting dimension method, which is based on the fractal theory, the fractal dimensions of the composite materials were calculated while using the Matlab program. The relationships between the fractal dimensions and the volume densities, mass fractions of poplar seed fibers, and thicknesses of the composite materials were also analyzed. Subsequently, the quantitative relationship between the fractal dimension and the sound absorption property parameters of the composite material was established in order to provide a theoretical basis for the design of the sound absorption composite material.

Vertical dynamic response of a pile embedded in radially inhomogeneous soil based on fictitious soil pile model

The vertical dynamic response of a pile embedded in radially inhomogeneous soil is investigated while allowing for the vertical wave effect of soil. For most engineering applications, the soil adjacent to pile may be hardened or softened due to the construction disturbance effect of pile, leading to the radial inhomogeneity of soil which has a significant influence on the vibration characteristics of pile. To consider this problem, this paper introduced the vertical shear complex stiffness transfer model to simulate the radial inhomogeneity of the surrounding soil and underlying soil of pile. Then, the governing equations of pile-soil system subjected to vertical dynamic loading are established based on the fictitious soil pile model. By means of Laplace transfer method, vertical shear complex stiffness transfer method and impedance function transfer method, the analytical solution of the vertical dynamic impedance of pile head is derived in the frequency domain. The present solution is verified by comparing it with existing solution. Based on the present solution, a parametric study is conducted to study the influence of the construction disturbance effect of pile surrounding soil and underlying soil on the vertical dynamic response of pile head. The results show that, even if the surrounding soil of pile is hardened or softened within a very small range, the construction disturbance effect still has a remarkable influence on the vertical dynamic response of pile head.

Design and Analysis of Enhanced Mixer-First Receivers Achieving 40-dB/decade RF Selectivity

A “second-order” passive mixer-first receiver is proposed to improve channel selectivity, linearity, and noise figure (NF) in the presence of out-of-band blockers, by presenting an impedance that rolls off at 40 dB/decade as the load to an N-path filter. The synthesis of this impedance is described in a step-by-step manner starting from the required impedance transfer function to its actual circuit realization. Various tradeoffs and limitations of the architecture are described in detail, and layout-related techniques are also provided. Two integrated circuit prototypes were fabricated in 28-nm bulk CMOS as proof of concept for this circuit, including a low-power version. The receiver, capable of broadband operation from 0.2 to 2 GHz, achieves an out-of-band IIP3 of +33 dBm and a blocker P1dB of +12 dBm. Additionally, it achieves an NF of 4.4 dB with less than 2-dB degradation in NF for a 0-dBm blocker.

Impedance-Based Modeling and Common Bus Stability Enhancement Control Algorithm in DC Microgrid

In this paper, impedance modeling of a DC microgrid system consisting of a source and load converter, including an input filter, is performed. Impedance-based modeling has been used to derive mathematical models of the output impedance of the source converter and the input impedance of the load converter. The correlation between the converter interaction and system stability is analyzed based on the mathematical model. An impedance-based stability analysis is used to determine the system stability by analyzing the interactions among the converters in the DC microgrid system. Middlebrook’s stability criterion, which uses the impedance transfer function, is applied to determine system stability. Moreover, in this paper, a stability enhancement control algorithm is proposed to resolve the system instabilities resulting from interaction among the converters and the distortion caused by the harmonics emanating from the AC input. The proposed stability enhancement control algorithm consists of a feed-forward type virtual impedance (VI) and a proportional-resonant (PR) controller. The validity of the proposed method is demonstrated by the results of the response characteristics in the frequency domain, and the effectiveness of the proposed control algorithm is verified via simulations and prototype experimental models.

One Port Impedance Quantization For a Class of Annihilation Operator Linear Quantum Systems

This paper provides a procedure for building a one port impedance quantization involving annihilation operators only for a class of linear quantum systems having a positive real impedance transfer function matrix. Based on the positive real properties of these quantum systems, it is shown that it is possible to use the Brune algorithm in order to find an electrical circuit that can physically implement these quantum systems. This theory, illustrated for one-port circuits may be useful for the implementation of superconducting microwave circuits used in quantum filters found in the field of quantum computing.

A geothermal aquifer in the dilation zones on the southern margin of the Dublin Basin

SUMMARYWe present modelling of the geophysical data from the Newcastle area, west of Dublin, Ireland within the framework of the IRETHERM project. IRETHERM's overarching objective was to facilitate a more thorough strategic understanding of Ireland's geothermal energy potential through integrated modelling of new and existing geophysical, geochemical and geological data. The Newcastle area, one of the target localities, is situated at the southern margin of the Dublin Basin, close to the largest conurbation on the island of Ireland in the City of Dublin and surrounds. As part of IRETHERM, magnetotelluric (MT) soundings were carried out in the highly urbanized Dublin suburb in 2011 and 2012, and a description of MT data acquisition, processing methods, multidimensional geoelectrical models and porosity modelling with other geophysical data are presented. The MT time-series were heavily noise-contaminated and distorted due to electromagnetic noise from nearby industry and Dublin City tram/railway systems. Time-series processing was performed using several modern robust codes to obtain reasonably reliable and interpretable MT impedance and geomagnetic transfer function ‘tipper’ estimates at most of the survey locations. The most ‘quiet’ 3-hr subsets of data during the night time, when the DC ‘LUAS’ tram system was not operating, were used in multisite and multivariate processing. The final 2-D models underwent examination using a stability technique, and the final two 2-D profiles, with reliability estimations expressed through conductance and resistivity, were derived. In the final stage of this study, 3-D modelling of all MT data in the Newcastle area was also undertaken. Comparison of the MT models and their interpretation with existing seismic profiles in the area reveals that the Blackrock–Newcastle Fault (BNF) zone is visible in the models as a conductive feature down to depths of 4 km. The investigated area below Newcastle can be divided into two domains of different depths, formed as depth zones. The first zone, from the surface down to 1–2 km, is dominated by NE–SW oriented conductors connected with shallow faults or folds probably filled with less saline waters. The conductors are also crossing the surface trace of the BNF. The second depth domain can be identified from depths of 2–4 km, where structures are oriented along the BNF and the observed conductivity is lower. The deeper conductive layers are interpreted as geothermal-fluid-bearing rocks. Porosity and permeability estimations from the lithological borehole logs indicate the geothermal potential of the bedrock, to deliver warm water to the surface. The fluid permeability estimation, based on Archie's law for porous structures and synthetic studies of fractured zones, suggests a permeability in the range 100 mD–100 D in the study area, which is prospective for geothermal energy exploitation.

Nonlinear Hybrid Impedance Control for Steering Control of Rack-Mounted Electric Power Steering in Autonomous Vehicles

In this paper, we present an innovative approach to steering control, based on torque overlay, for the smooth and efficient transfer of the steering control from an autonomous driving system to the driver, and to control the pinion angle of the rack-mounted electric power steering for lateral control of an autonomous vehicle. The novelty of our approach lies in the formulation of hybrid impedance control, which employs steering control for both lateral and impedance controls. The proposed method, nonlinear hybrid impedance controller, consists of desired impedance pinion angle generator and a super-twisting sliding mode controller for pinion angle tracking. The desired impedance transfer function of the driver’s torque to the steering wheel angle reflects the driver’s torque to the steering control. The desired impedance pinion angle is generated using the desired impedance transfer function and the desired pinion angle derived by the lateral controller. The sliding mode control method is designed, based on a super-twisting algorithm for the pinion angle, to track the desired impedance pinion angle. Consequently, without the driver’s torque, the proposed method is activated as a pinion angle tracking controller for lateral control of an autonomous vehicle. Moreover, with the driver’s torque, the proposed method is activated as an impedance controller.