Finite Impedance Research Articles

Experimental study on the acoustic properties of monofilament fabrics

The traditional machining perforated sound absorption structure has high processing cost and inconvenient installation and disassembly, so that how to efficiently and economically manufacture submillimeter micropores still remains a challenge. In this study, a kind of flexible microporous sound absorbing material was obtained by weaving a polymer artificial fiber covered with ethylene polyester fiber, and the relationship between the sound absorption performance of the curtain and the porosity of the pass and fabric was obtained through the finite element simulation model and impedance tube experiment. The mechanism parameters of wide-band flexible microporous material with high sound absorption performance are obtained, which guide the design of a kind of sound absorption material with lower production cost and easy installation and disassembly.

An epsilon‐near‐zero circuit based on half‐mode SIW with enhanced integrability for applications of narrowband large group delay

AbstractThe tunneling effect of an epsilon‐near‐zero (ENZ) is exploited to fulfill a narrowband large group delay by using a compact half‐mode substrate integrated waveguide structure built on thin substrate. The ENZ channel possesses a finite input impedance at the tunneling frequency point, and the finite input impedance can be matched to the final I/O port simply by a quarter wavelength impedance transformer. Thus, the enhanced integrability is realized in a planar form in the proposed circuit comparing to the conventional waveguide ENZ channel. Meanwhile, in the real ENZ channel, the effective impedance is observed to be close to 50 Ω, so that the ENZ can be connected with 50 Ω microstrip directly, which has been experimentally validated. The final measured net group delay is 1.36 ns at 3.08 GHz with 3.6 dB insertion loss, and the proposed method provides an alternative for the group delay engineering.

Ultra-Generalized Continuous Class F Power Amplifier with Finite Third-Harmonic Load Impedance

This paper proposes the ultra−generalized continuous class F (UCCF) mode, which combines the influences of the drain current conduction angle and overdriven transistor on the drain current waveform to achieve a broader finite third-harmonic load impedance space. The UCCF mode uses α to describe the magnitude of the drain current conduction angle and pcr to describe the drain current peak-clipped ratio. An analysis of the effects of pcr and α on the linearity and efficiency of the UCCF model is presented, establishing a robust theoretical foundation for achieving a balance between these two characteristics. Additionally, an examination of how pcr and α influence the load impedance design space is conducted, demonstrating that the UCCF mode not only offers a broader finite third-harmonic load impedance space but also expands the fundamental and second-harmonic load impedance design space. For practical validation, a PA with frequency of 2.05–2.65 GHz is designed based on CGH40010F. The test results show that S11 is less than −15 dB, the drain efficiency is 67.0–73.2%, and the output power is 40.1–41.0 dBm. The linearity is tested using a 5G NR (New Radio) signal with a bandwidth of 100 MHz and a peak-to-average power ratio of 8 dB at 2.35 GHz. The worst adjacent channel power ratio (ACPR) is −34.8 dBc without digital predistortion (DPD), and −57.8 dBc with DPD. An average output power (Pave) of around 32.4 dBm and an average DE (DEave) of 34.39% were obtained.

On the use of ground-board mounted microphones for outdoor noise measurements

Outdoor noise measurements made by a microphone mounted into or on an acoustically rigid thin board lying on the ground can be affected to some degree by diffraction from the edges of the board due to the thickness of the board or the finite impedance of the surrounding ground. This can result in the sound pressure level varying over the top surface of the board and deviating from the 6 dB increase (relative to the incident sound field) expected if the board was very thin and the surrounding ground was also acoustically rigid. In this paper, an experimental and numerical investigation is carried out to assess the variation in the sound pressure level over the top surface of the ground-board from sound incident at several different angles. The experiments utilise a probe microphone flush-mounted into a 0.4 m diameter circular thin metal ground-board slightly protruding from a simulated grass-covered field in an anechoic chamber. The experiments are repeated on an outdoor grass-covered field and compared. The effect of different installation methods such as the flush-mounted probe microphone, inverted microphone, and a side-set microphone are also investigated. The variation of the sound pressure level on the top surface of the ground-board due to diffraction from the edges of the board is shown. It is also shown that the presence of the microphone body begins to affect the noise measurements from a frequency of 3 kHz. The results presented in this paper suggest that narrow-band noise measurements using a microphone mounted on a circular ground-board installed on a grass-covered surface can deviate by more than 3 dB from the nominal 6 dB increase above the incident field level.

Transient simulations and theoretical modeling of near-junction heat conduction in GaN-on-diamond HEMT

Under high-power working conditions, accurate predictions of the maximum temperature and thermal resistance distribution in devices during transient states are essential for monitoring the health status of the devices. In this work, the heat conduction characteristics of GaN-on-diamond high electron mobility transistors (HEMTs) near the junction region under transient conditions with thermal impedance are systematically investigated with the aid of finite element simulations and thermal impedance analyses. The effects of pulse characteristics, thermal properties of different layers on the maximum temperature and thermal resistance of the device are discussed specifically. The results show that pulse characteristics have a significant effect on the maximum temperature of the device. The shorter the pulse switching time is, the higher the maximum temperature will be. Regarding the effects of the thickness of the GaN layer, the maximum temperature initially decreases and then increases, with the lowest maximum temperature observed at 1.7 μm. As the TBR increases uniformly from 10 to 40 m2K/GW, the temperature increases by approximately 4 % per 10 m2K/GW. The analyses on the thermal resistance show that the GaN layer occupies the largest proportion of thermal resistance, while the diamond substrate occupies the smallest. The optimal substrate thickness is obtained by analyzing the thermal penetration depth in the substrate for working conditions with various pulse widths. For diamond substrate, the optimal thickness at a pulse width of 5 μs is about 25 μm, and increases as the increase in pulse width. At the end, a modified Cauer RC model is proposed for predicting the transient maximum temperature based on heat spreading analysis. The difference between the maximum temperatures predicted by the model and the finite element simulations is within 8 %.

Acoustic modes in a rectangular flow duct with a wall of finite acoustic impedance value

The acoustic field in a rectangular flow duct of infinite length was numerically investigated. One of the walls of the duct was assumed to have finite acoustic impedance while the other three were rigid walls. Uniform flow profile was also assumed. The propagation constants, namely, complex wave numbers, were calculated for various impedance values and the Mach numbers of the flow from the boundary condition on the finite impedance wall derived by Myers. First, we calculated the propagation constant without uniform flow. If all four walls are rigid and the frequency of the sound is under the cut-off frequency, only zeroth mode propagates along the duct and higher modes decay rapidly. In contrast, if one wall has a finite impedance value, two modes can have comparable amount of attenuation. The acoustic field in the duct would be a superposition of those less decaying modes depending on the inlet condition. As for the flow effect, the attenuation tends to be decreasing in fair wind, and vice versa. This tendency, however, is not general because the propagation constant moves on the complex plane in intricate manner.

A Resistance Augmented Parallel-T RC Network Gives Over Unity Gain

We examine, in this paper, how a non-zero source impedance and a finite load impedance affect the response characteristics of the well-known parallel-T RC null network. In the process, by taking the complement of the null filter, it is shown that the two additional impedances help in producing a band-pass characteristic with over unity gain in a certain range of frequencies. A comprehensive step-by-step analysis is carried out for both configurations, which is followed by simulation. The special case of infinite load impedance is also considered, along with results of simulation, which also show the same feature of over unity gain.

Investigation of time domain measurement of electrochemical impedance spectrum in low frequency range for lithium-ion batteries using preset equivalent circuit model

A time domain measurement technique using a preset equivalent circuit model consisting of many series-connected resistor and capacitor parallel elements was examined as a measurement method of the electrochemical impedance spectrum of a lithium-ion battery excluding the apparent impedances from open circuit voltage change in the low frequency range. At first, a comprehensive experimental study was carried out to determine the standard condition of the applied signal suitable for this technique. It was established that an impedance spectrum from several tens of microhertz to several tens of millihertz can be accurately measured by selecting a proper, small rate and long duration constant current charge or discharge as the applied signal. Next, impedance spectra excluding the apparent impedances from open circuit voltage change were measured under various conditions using this technique, and basic characteristics of the impedances of the solid state diffusion processes of lithium that exist in the corresponding low frequency range were investigated. It was revealed that the impedance spectrum excluding the apparent impedances from open circuit voltage change in the low frequency range, from several tens of microhertz to several tens of millihertz, can be reasonably separated into two finite length Warburg impedances that can be clearly characterized by difference in their diffusion time constant values and in the state of charge dependence of their diffusion resistances. An Arrhenius type temperature dependence was confirmed for both of their diffusion resistances.

Unified model of lithium-ion battery and electrochemical storage system

Nowadays, energy storage systems are of paramount importance in sectors such as renewable energy production and sustainable mobility because of the energy crisis and climate change issues. Although there are various types of energy storage systems, electrochemical devices such as electric double layer capacitors (EDLCs), lithium-ion capacitors (LiCs), and lithium-ion batteries (LiBs) are the most common because of their high efficiency and flexibility. In particular, LiBs are broadly employed in many applications and preferred in the mobility sector, where there is a need for high energy and high power. To ensure good operating conditions for a battery and limit its degradation, it is important to have a precise model of the device. The literature contains numerous equivalent circuit models capable of predicting the electrical behavior of an LiB in the time or frequency domain. In most of them, the battery impedance is in series with a voltage source modeling the open circuit voltage of the battery for simulation in the time domain. This study demonstrated that an extension of a model composed exclusively of passive elements from the literature for EDLCs and LiCs would also be suitable for LiBs, resulting in a unified model for these types of electrochemical storage systems. This model uses the finite space Warburg impedance, which, in addition to the diffusion process of lithium\\lithium ions in the electrodes\\electrolyte, makes it possible to consider the main capacitance of the battery. Finally, experimental tests were performed to validate the proposed model.

Bottom-up approaches for rapid on-demand design of modular metaporous structures with tailored absorption

As a new trend in the studies on sound-absorbing structures design, customizable metaporous structures (MPSs) have drawn a great deal of interest due to their distinct advantages, which include designable broadband absorption, light weight, and low thickness. Conventional finite element-based design methods, such as trial-and-error and iterative optimization, are inefficient and expensive in terms of computational resources. Inspired by the widely used bottom-up method, in this study, we develop a data-driven metaheuristic optimization framework to accomplish the rapid on-demand design for a novel modular metaporous structure (MMPS) of only 30mm thickness from the local to the global level. Two cascade variants of the genetic algorithm (GA) are employed for local optimization and global customized design, accordingly. The local design level involves the development of a surrogate-assisted genetic algorithm (SAGA) for design space optimization. On the basis of the structural dataset, a well-tuned convolutional neural network (CNN) model is developed for expediting the forward prediction of the acoustic properties of the two-dimensional (2D) MPS. In the subsequent phase, the validated CNN model is combined with SAGA to expedite the fitness evaluation for optimizing the structural units. At the global design stage, the developed SAGA is coupled with the population initialization process of an elitist genetic algorithm (EGA) to achieve inverse design for the MMPS with customizable broadband absorption based on the optimized design space. Furthermore, an acoustic measurement is performed on the fabricated MMPS samples to validate the finite element method (FEM) simulation and impedance design method. The utilization of this optimization method opens up fresh possibilities not solely for the customized design of sound-absorbing structures, but also for optimization processes in various other domains. Meanwhile, the proposed MMPS with customizable broadband absorption in a thickness of 30mm could well be utilized for noise reduction in a variety of practical applications.

Towards Personalized Control for Powered Knee Prostheses: Continuous Impedance Functions and PCA-Based Tuning Method.

Optimizing control parameters is crucial for personalizing prosthetic devices. The current method of finite state machine impedance control (FSM-IC) allows interaction with the user but requires time-consuming manual tuning. To improve efficiency, we propose a novel approach for tuning knee prostheses using continuous impedance functions (CIFs) and Principal Component Analysis (PCA). The CIFs, which represent stiffness, damping, and equilibrium angle, are modeled as fourth-order polynomials and optimized through convex optimization. By applying PCA to the CIFs, we extract principal components (PCs) that capture common features. The weights of these PCs serve as tuning parameters, allowing us to reconstruct various impedance functions. We validated this approach using data from 10 able-bodied individuals walking. The contributions of this study include: i) generating CIFs via convex optimization; ii) introducing a new tuning space based on the obtained CIFs; and iii) evaluating the feasibility of this tuning space.

Sound absorption of space-coiled metamaterials with soft walls

Integrating soft components into acoustic metamaterials is an extremely promising way to enhance their adjustability and reconfigurability. Herein, we report a type of space-coiled metamaterials using soft walls to construct internal channels, denoted as soft-wall space-coiled metamaterials (SSM), exhibiting superior sound absorption performance at low frequencies. The physical mechanism of the SSM is revealed through finite element simulations and sound impedance tube-based experiments. It is demonstrated that the exceptional sound absorption of the SSM originates from the strong coupling effect between the friction-like dissipation along the internal channel and the deformation-like dissipation in the soft wall. The experimental results show that the fabricated SSM sample with a subwavelength thickness (<1/25 wavelength) features near-perfect sound absorption (reaching 0.97 at 615 Hz) and a broad half-power bandwidth (1.6 times that of the rigid-wall space-coiled metamaterials sample with the same geometric dimensions). Moreover, the SSM has excellent sound absorption performance under oblique incidence even when the incident elevation angle reaches 75°. This work may bring inspiration for developing soft-components-integrated acoustic metamaterials with compact, adjustable, and reconfigurable characteristics.

Sequential LMBA Design Technique for Improved Bandwidth Considering the Balanced Amplifiers off-State Impedance

This work proposes a design technique to improve the bandwidth of sequential load-modulated balanced amplifiers (SLMBAs). It is theoretically demonstrated that a finite off-state impedance of the balanced power amplifiers (BPAs) degrades the overall SLMBA performance, especially between the two efficiency peaks, i.e., when the BPAs start to operate. Moreover, it is shown that this issue is especially important when high-power devices are considered. The new proposed design technique optimizes the load trajectory of the BPAs, by properly designing their output matching networks, considering the actual off-state impedance. The method avoids the use of the conventional narrowband compensation offset lines strategy, being able to obtain optimum efficiency and output power performance when the BPAs are turned on across wide bandwidths. The proposed design technique is explained and validated with a practical 1.3–2.1-GHz 200-W GaN HEMT-based SLMBA prototype.

A modal expansion method for simulating reverberant sound fields generated by a directional source in a rectangular enclosure

The prediction of reverberant sound fields generated by a directional source is of great interest because practical sound sources are not omnidirectional, especially at high frequencies. For an arbitrary directional source described by cylindrical and spherical harmonics, this paper developed a modal expansion method for calculating the reverberant sound field generated by such a source in both two-dimensional and three-dimensional rectangular enclosures with finite impedance walls. The key is to express the modal source density using the cylindrical or spherical harmonic expansion coefficients of the directional source. A method based on the fast Fourier transform is proposed to enable the fast computation of the summation of enclosure modes when walls are lightly damped or rigid. This makes it possible to obtain accurate reverberant sound fields even in a large room and/or at high frequencies with a relatively low computational load. Numerical results with several typical directional sources are presented. The efficiency and the accuracy of the proposed method are validated by the comparison to the results obtained using the finite element method.

On the modelling of ground-board mounted microphones for outdoor noise measurements

This paper presents a boundary element method for calculating the sound pressure level on and above a ground-board placed on an infinite ground plane with constant impedance. This method uses the Green's function for the Helmholtz equation in a half-space bounded by an infinite impedance plane and therefore avoids the complications which occur when modeling the ground as a finite impedance plane (which results in diffraction from the edges of the ground plane). Two formulations are presented: the first one models a finite thickness ground-board, whilst the second one models a zero-thickness ground-board with the upper surface coplanar with the ground plane. The method is validated against an equivalent finite element method simulation and example calculations are presented for typical ground-board designs used for outdoor noise measurements on different ground impedance planes and incidence angles. It is shown that the sound pressure level on the upper surface of a ground-board placed on a non-rigid ground can vary significantly and that this variation is dependant on the ground impedance, angle of incidence and frequency. These findings are consistent with previous investigations and highlight the fact that noise measurements made using ground-board mounted microphones on a non-rigid ground are dependant on the impedance of the surrounding ground surface. The method presented in this paper could be used to develop corrections to straightforwardly account for this effect.

Loudspeaker array beamforming for sound projection in a half-space with an impedance boundary.

Sound projection is a method of using highly focused sources to project sound onto reflective surfaces to create the impression of surround sound, which can be realized via beamforming using loudspeaker arrays. Generally, these devices are mounted near a surface with a finite acoustic impedance, such as a TV accent wall. The beamforming performance degrades in this half-space with an impedance boundary when the filters are designed using transfer functions measured in the free field. This paper proposes a model for predicting the beamforming performance in a half-space with an impedance boundary in terms of the transfer functions in the free field. A mathematical model is presented, and the results are compared with practical measurements for a 16-driver line array in real-use environments. The results show that reflections from the boundary lead to "dark bands" in the beam, causing the beam to deviate from the designed direction. Using filters designed with transfer functions calculated by the proposed model yields improved beamforming performance.

Circuit Simulator Compatible Model for the Ring-Dot Piezoelectric Transformer

A lumped-element equivalent circuit model for the ring-dot piezoelectric transformer (PT) is derived based on a one-dimensional analysis of the radial vibration mode. Initially, equations for the magnitudes of force, vibration velocity at the boundaries of each Section of the device are derived based on the piezoelectric constitutive equations and using Kirchhoff plate theory. Similarly, equations for the amplitudes of input and output currents are derived from the electric displacement field and Gauss’ law. From this analytical approach, an equivalent circuit model is developed and, using a Taylor expansion, approximated as the Mason equivalent circuit. A key contribution of this work is the development of a circuit simulator compatible model which can be used by electronic engineers, without in-depth knowledge of the underlying material science, to design ring-dot PTs for power conversion applications. The resulting model is verified against both COMSOL finite element simulations and experimental impedance measurements. Compared to COMSOL, the model estimates the resonant circuit elements to within 1% and the input and output capacitance are estimated to within 10%. Experimental results match the simulation to within 10% for most parameters, and 1% for resonant frequency. [2022-0154]

Sound radiation by a vibrating circular plate located at the bottom of a non-rigid flanged circular cylindrical tube

The sound transmission through a non-rigid circular tube has been investigated in this study. For the same, the Neumann–Robin boundary value problem has been solved. The problem deals with sound radiation by considering a complex system consisting of a fluid filled in the circular cylindrical tube having a finite impedance and the half-space. The outlet of the tube is embedded into a rigid infinite flat screen. The fluid inside the tube is disturbed by a vibrating circular plate embedded at the bottom of the tube. A coupled system of partial differential equations governing the vibration of the plate and the fluid has been solved. For this purpose, the superposition of the two solutions has been applied: one is the Neumann boundary value problem in the form of the Dini series and the other is the correction for the impedance boundary in the form of a Fourier series. The continuity conditions at the tube outlet have been expressed in terms of the modal coupling acoustic impedance coefficients. The use of the radial polynomials together with Cerjan’s expansion greatly improve the numerical analysis. Application of the additional Fourier series helps to avoid finding the complex eigenvalues. Truncation conditions in the Dini series and in the Fourier series have been applied to assure valid and accurate numerical results for frequencies up to 8kHz, a tube radius from 30 to 70 mm, and a tube length from 3 to 7 times the tube radius with an arbitrary excitation of the plate. The selected tube materials range from being acoustically soft, such as mineral wool, to acoustically hard, such as a porous material. The other advantage of using the Dini and the Fourier series is that they require only real eigenvalues, and thus it is not necessary to find the cumbersome complex eigenvalues of the tube. One more advantage of the rigorous solution is that it automatically satisfies the radiation condition in the half-space, whereas the finite elements method always satisfies it approximately. The findings of this study can be summarized as follows: The main computational cost is associated with a relatively significant number of the Fourier expansion terms. As a result, for frequencies smaller than 1.2kHz, the first result can be obtained rapidly using the finite elements method. In addition, it has been shown that using the radial polynomials to calculate the coupling integrals enables faster calculations by at least 120 times.

Hybrid controller for mid-range mid-power audio application

A major reason for compromised audio quality with a coil-type loudspeaker is its complex impedance profile, which disturbs the intended algebraic linearity or linear phase behavior between the amplifier input and speaker driving force. Though switch-mode amplifiers are increasingly preferred in such audio systems owing to their superior energy efficiency, their inherent non-linearity and finite internal impedance further degrade audio reproduction. This paper investigates the effect of stated impedance on the loudspeaker driving current, hence on the loudspeaker driving force, and proposes a Hybrid controller-amplifier to enhance the proportionality between the audio reference and driving force without compromising on loudspeaker damping. The Hybrid amplifier combines a sliding mode controlled amplifier (SMCA) and a linear controller, designed after exhaustive modeling of the input–output behavior of the SMCA and best-fit approximation of the loudspeaker impedance. An 8 W, 500 Hz to 20 kHz prototype of the proposed amplifier is fabricated on the basis of the presented design. Time and frequency-domain results obtained with the experimental hardware are presented to validate the performance improvement.

Implementing a heuristic method to correct ground reflection effects observed in full-scale tactical aircraft noise measurements

In a recent study of noise from a T-7A-installed GE F404 engine, microphones along 38 and 76 m (125 and 250 ft) arcs were mounted 1.5 m (5 ft) above the ground to quantify human impact. While helpful for this purpose, the resulting multipath effects pose challenges for other acoustical analyses. For jet noise runup measurements, these effects are complicated by the fact that the noise source is extended and partially correlated and its spatial properties are frequency dependent. Furthermore, a finite-impedance ground surface and atmospheric turbulence affect interference nulls. This study applies a ground-reflection method developed previously [Gee et al., Proc. Mtgs. Acoust. 22, 040001 (2014)] for rocket noise measurements. The model accounts for finite ground impedance, atmospheric turbulence, and extended source models that are treated as coherent and incoherent arrays of monopoles. Application to the ground runup data to correct the 38 and 76 m spectra at a range of angles suggests the incoherent line source model is more appropriate at sideline angles whereas the coherent source model is more appropriate for upstream and downstream propagation. Comparisons with near-field data and similarity spectra show that, while imperfect, this method represents an advancement in correcting jet noise spectra for ground reflection effects. [Work supported by ONR Grant No. N00014-21-1-2069.]