Frequency-dependent Gain Research Articles

Bode gain-phase relation beyond the minimum phase condition

The Bode gain-phase relation links the phase shift introduced by a causal, linear and time-invariant system with its frequency-dependent magnitude gain. The relation, which is widely used in system theory and electronics, was first derived by H. W. Bode for a transfer function described, in the Fourier (Laplace) domain, by rational functions of frequency, where the numerator fulfills the so-called minimum-phase condition, according to which the polynomial numerator of the frequency-domain transfer function has no zeroes in the upper-half (right-half) of the complex ω-plane (s-plane). Here we discuss a general derivation that widens the range of applicability of the relation beyond the minimum phase condition, allowing the presence of zeroes and encompassing cases in which delays occur. Both these features are widely present in real physical systems, thus endowing the new proof with a broader range of validity.

Lyric intelligibility of musical segments for older individuals with hearing loss

Understanding lyrics is a major barrier to enjoying music for people with hearing loss. To improve lyric understanding through machine-learning, metrics need to be informed by the experiences of the target population. Currently, there are no data on lyric-recall ability of older individuals with hearing loss. Twelve older participants with mostly mild-sloping hearing loss listened to and recalled 100 segments of popular music that varied in genre, duration and word count. In each trial, participants heard a randomly chosen segment twice with a 5-s interstimulus interval over headphones at an A-weighted level of 65 dB plus individualised frequency-dependent nonlinear gain. The proportion of words heard correctly varied greatly across samples, from 0 to 100%, and varied as a function of genre, similar to past studies with different populations. Individual intelligibility across samples was correlated with age; sample intelligibility across individuals, however, was not correlated with word count or rate. Improving sung-lyric intelligibility is a different challenge from spoken-speech enhancement for those with hearing loss. Not only does the enhancement need to be considered within the overall enjoyment of the music, but the variation in results—as seen in the current study—reflects variations in genre, orchestration and vocal quality in sung music.

Wavelet LQR based gain scheduling for power regulation and vibration control of floating horizontal axis wind turbine with double-pitched rotor

This paper introduces a wavelet-based linear quadratic regulator (LQR) control strategy for double-pitched rotor systems of an offshore horizontal axis wind turbines. A comprehensive aero-servo-elastic model incorporating bending-torsion coupling is developed to assess the performance of the proposed controller under combined turbulent wind and wave loading. The weight matrices of the classical LQR algorithm are optimized using a nonlinear optimization scheme. Additionally, frequency-dependent gain scheduling is proposed using wavelet transform where the analytic Morse wavelet serves as the basis function. The resulting LQR algorithm operates in the time-frequency domain and solves scale-dependent Algebraic Riccati equations to determine optimal gains. Numerical simulations demonstrate the superior performance of the proposed gain scheduling compared to the classical LQR approach. The effectiveness of the algorithm is evaluated across various flow conditions and wind-wave misalignment, with benchmark results used for performance comparison.

Airy pulse dynamics in semiconductor optical amplifier with dispersive gain

We analytically as well as numerically study the Airy pulse dynamics in semiconductor optical amplifier (SOA) with dispersive gain. The frequency dependent gain of the SOA not only modifies the temporal shape of the Airy pulse but also alters the peak power of the Airy pulse. The study finds that the trajectory of the Airy pulse can be manipulated by the gain induced dispersion and the linewidth enhancement factor. Moreover, the gain dispersion introduces upchirp during the propagation that suppresses the Airy pulse acceleration in anomalous group velocity dispersion while the acceleration is pronounced when the dispersion is normal.

Automated Koala call detection using a cochlea model

Estimating koala populations is challenging, making surveys costly and often imprecise. This study examines the feasibility of recognising koala calls from audio recordings using a bio-inspired acoustic approach. In the work, we propose to use the Cascade of Asymmetric Resonators with Fast-Acting Compression (CAR-FAC) cochlea model to pre-process koala recordings and a support vector machine (SVM) for classification. The frequency-dependent gain and bandwidth properties of the CAR-FAC model in pre-processing noisy data are discussed and investigated. To evaluate the effectiveness of the proposed method, it is compared with an FFT-based system as a baseline method. The baseline methodology uses a Mel-spectrogram pre-processing and the same linear classifier as the proposed method as the back-end. In summary, we achieved 96.7% accuracy for the proposed system.

A 3D Non-Stationarity and Consistency Model for Cooperative Multi-Vehicle Channels

In this paper, based on the irregular shaped geometry-based stochastic modeling (IS-GBSM) approach, a novel three-dimensional (3D) model for cooperative multi-vehicle communication channels is developed. By employing the cooperative communication technology, multi-vehicles can form a platoon to cooperatively transmit data streams, which can achieve distributed multiple-input multiple-output (MIMO) system performance. The proposed cooperative IS-GBSM distinguishes static and dynamic clusters, where continuously arbitrary vehicular movement trajectories (VMTs) of dynamic clusters and multi-vehicles are imitated. A new method, which combines frequency-dependent path gain and spectral clustering algorithm in machine learning (ML), is proposed to model cooperative space-time-frequency (S-T-F) non-stationarity with cooperative time-space (T-S) consistency. Based upon Poisson and Bernoulli processes, the developed method can also model the disappearance of links/sub-channels due to the destruction of transceivers by missiles in an optional manner. Therefore, the proposed cooperative IS-GBSM can further mimic an actual military cooperative communication scenario, i.e., cooperative multiple-unmanned ground vehicle (multi-UGV) communications for Mosaic Warfare. From the proposed cooperative IS-GBSM, typical channel statistics are derived. Simulation results show that cooperative S-T-F non-stationarity with cooperative T-S consistency is mimicked and the influences of vehicular traffic density (VTD) and VMT on channel statistics are investigated. Finally, simulation results fit well with the ray-tracing-based results, confirming the accuracy of the proposed cooperative IS-GBSM.

Hyperpolarization-activated cation channels shape the spiking frequency preference of human cortical layer 5 pyramidal neurons.

Discerning the contribution of specific ionic currents to complex neuronal dynamics is a difficult, but important, task. This challenge is exacerbated in the human setting, although the widely-characterized uniqueness of the human brain as compared to preclinical models necessitates the direct study of human neurons. Neuronal spiking frequency preference is of particular interest given its role in rhythm generation and signal transmission in cortical circuits. Here, we combine the frequency-dependent gain (FDG), a measure of spiking frequency preference, and novel in silico analyses to dissect the contributions of individual ionic currents to the suprathreshold features of human L5 neurons captured by the FDG. We confirm that a contemporary model of such a neuron, primarily constrained to capture subthreshold activity driven by the hyperpolarization-activated cyclic nucleotide gated (h-) current, replicates key features of the in vitro FDG both with and without h-current activity. With the model confirmed as a viable approximation of the biophysical features of interest, we applied new analysis techniques to quantify the activity of each modeled ionic current in the moments prior to spiking, revealing unique dynamics of the h-current. These findings motivated patch-clamp recordings in analogous rodent neurons to characterize their FDG, which confirmed that a biophysically-detailed model of these neurons captures key inter-species differences in the FDG. These differences are correlated with distinct contributions of the h-current to neuronal activity. Together, this interdisciplinary and multi-species study provides new insights directly relating the dynamics of the h-current to suprathreshold spiking frequency preference in human L5 neurons.Significance StatementUnderstanding the contributions of individual ionic currents to neuronal activity is vital, considering the established role of ion channel modifications in neuropsychiatric conditions. We combine in vitro characterization of the spiking frequency preference of human L5 cortical pyramidal neurons via the frequency-dependent gain (FDG) with new analyses of a biophysically-detailed computational model of such a neuron to delineate the connection between the dynamics of the hyperpolarization-activated cyclic nucleotide gated (h-) current prior to spiking and key properties of the FDG. By further determining that both these FDG properties and h-current dynamics are distinct in analogous rodent neurons, we provide convincing evidence for the key role of the h-current in the suprathreshold frequency preference of human L5 cortical neurons.

Analytic theory of coupled-cavity traveling wave tubes

Coupled-cavity traveling wave tube (CCTWT) is a high power microwave vacuum electronic device used to amplify radio frequency signals. CCTWTs have numerous applications, including radar, radio navigation, space communication, television, radio repeaters, and charged particle accelerators. Microwave-generating interactions in CCTWTs take place mostly in coupled resonant cavities positioned periodically along the electron beam axis. Operational features of a CCTWT, particularly the amplification mechanism, are similar to those of a multicavity klystron. We advance here a Lagrangian field theory of CCTWTs with the space being represented by one-dimensional continuum. The theory integrates into it the space-charge effects, including the so-called debunching (electron-to-electron repulsion). The corresponding Euler–Lagrange field equations are ordinary differential equations with coefficients varying periodically in the space. Utilizing the system periodicity, we develop instrumental features of the Floquet theory, including the monodromy matrix and its Floquet multipliers. We use them to derive closed form expressions for a number of physically significant quantities. Those include, in particular, dispersion relations and the frequency dependent gain foundational to the RF signal amplification. Serpentine (folded, corrugated) traveling wave tubes are very similar to CCTWTs, and our theory applies to them also.

A Non-Stationary Model With Time-Space Consistency for 6G Massive MIMO mmWave UAV Channels

In this paper, a novel unmanned aerial vehicle (UAV) space-time-frequency (S-T-F) non-stationary channel model with time-space consistency for sixth generation (6G) massive multiple-input multiple-output (MIMO) millimeter wave (mmWave) wireless communication systems is proposed. In the proposed model, the line-of-sight (LoS) transmission and non-LoS (NLoS) transmission through ground reflection, single-clusters, and twin-clusters are modeled. Meanwhile, the three-dimensional (3D) continuously arbitrary trajectory and the self-rotation of UAV are imitated. To capture the time-space consistency and S-T-F non-stationarity simultaneously, a new UAV-related non-stationary modeling algorithm that integrates the visibility region (VR), frequency-dependent path gain, and survival probability is developed for the first time. In this algorithm, the UAV-related parameters are considered, including UAV’s height, 3D moving velocity, and self-rotation angles. In the proposed model, the calculation of channel impulse response (CIR) is developed, which considers the cluster density index influenced by communication scenarios, frequency, UAV’s height, and the distance between transceivers. Some important channel statistical properties, such as S-T-F correlation function (STF-CF), Doppler power spectral density (DPSD), and stationary interval, are derived. Finally, simulation results match well with ray-tracing-based results, which verifies the utility of the proposed model.

Two stages of bandwidth scaling drives efficient neural coding of natural sounds.

Theories of efficient coding propose that the auditory system is optimized for the statistical structure of natural sounds, yet the transformations underlying optimal acoustic representations are not well understood. Using a database of natural sounds including human speech and a physiologically-inspired auditory model, we explore the consequences of peripheral (cochlear) and mid-level (auditory midbrain) filter tuning transformations on the representation of natural sound spectra and modulation statistics. Whereas Fourier-based sound decompositions have constant time-frequency resolution at all frequencies, cochlear and auditory midbrain filters bandwidths increase proportional to the filter center frequency. This form of bandwidth scaling produces a systematic decrease in spectral resolution and increase in temporal resolution with increasing frequency. Here we demonstrate that cochlear bandwidth scaling produces a frequency-dependent gain that counteracts the tendency of natural sound power to decrease with frequency, resulting in a whitened output representation. Similarly, bandwidth scaling in mid-level auditory filters further enhances the representation of natural sounds by producing a whitened modulation power spectrum (MPS) with higher modulation entropy than both the cochlear outputs and the conventional Fourier MPS. These findings suggest that the tuning characteristics of the peripheral and mid-level auditory system together produce a whitened output representation in three dimensions (frequency, temporal and spectral modulation) that reduces redundancies and allows for a more efficient use of neural resources. This hierarchical multi-stage tuning strategy is thus likely optimized to extract available information and may underlies perceptual sensitivity to natural sounds.

Performance Analysis on Interference and Frequency-to-Time Mapping Based Frequency Hopping Receiver

The receiving performance of a frequency hopping receiver based on interference and frequency-to-time mapping are analyzed. The broadening of the receiving passband induced by high frequency hopping speed is theoretically analyzed. The spurious-free dynamic range (SFDR), the frequency-dependent RF gain, and the average signal-to-noise ratio (SNR) corresponding to the RF gain are theoretically derived to indicate the receiving performance. Experimental verifications on the SFDR and RF gain were conducted. The SFDR of the passband at 7.21 GHz is 77.23 dBc, and for the passbands located from 7 GHz to 23 GHz, the SFDR variance is below 3.2 dB, which fits well with the simulated results with the difference of less than 3.7 dB. The RF gain for passbands located from 2.6 GHz to 40.9 GHz were tested, and the difference is less than 2 dB compared to the theoretical results.

Doppler Gyroscopes: Frequency vs Phase Estimation.

We consider the fundamental roles of frequency versus phase in parameter estimation, specifically in the Sagnac effect. We describe a novel, ultrasensitive gyroscope based on the extremely steep frequency-dependent gain of a liquid crystal light valve. We provide compelling experimental evidence that the Doppler shift is fundamental in the Sagnac effect giving clarity to a long-debated question. We experimentally show orders of magnitude improvement in sensitivity relative to the standard quantum limit of a gyroscope based on phase estimation.

Frequency-segmented power amplification using multi-band radio frequency amplifiers to produce a high-voltage pulse.

A method of frequency-segmented power amplification using multiband radio frequency (RF) amplifiers was proposed to generate stable and arbitrary high-voltage pulses. The concept behind this method is that an arbitrary pulse with a specified duration and sharp edges can be reconstructed using only several frequencies, and most of the power is concentrated on the fundamental frequency. The high-voltage pulse can, therefore, be obtained by amplifying each segmented frequency and then combining it with the RF power combiners. To correct the frequency-dependent group delays and gain of the amplifier circuit and to perform fine-tuning of the pulse structure, a seed pulse is divided into several lines that have bandpass filters, variable delay lines, variable power attenuators, and main RF amplifiers. A prototype pulse amplifier was designed and fabricated based on this method to generate rectangular pulses for the electron beam chopper of an x-ray free-electron laser injector. Flat and stable pulses with a 2ns width of 0.2kV height, peak-to-peak flat top of 0.8%, and route-mean-squared peak jitter of less than 0.2% were successively generated in both single- and multi-bunch structures. In the future, this type of pulse generator will play an important role in accelerators that require complicated and precise beam handling at high repetition rates of kHz or MHz.

Analytic theory of multicavity klystrons

Multicavity Klystron (MCK) is a high power microwave vacuum electronic device used to amplify radio frequency (RF) signals. MCKs have numerous applications, including radar, radio navigation, space communication, television, radio repeaters, and charged particle accelerators. The microwave-generating interactions in klystrons take place mostly in coupled resonant cavities positioned periodically along the electron beam axis. Importantly, there is no electromagnetic coupling between cavities. The cavities are coupled only by the flow of bunched electrons drifting from one cavity to the next. We advance here a Lagrangian field theory of MCKs with the space being represented by a one-dimensional continuum. The theory integrates into it the space-charge effects, including the so-called debunching (electron-to-electron repulsion). The corresponding Euler–Lagrange equations are ordinary differential equations with coefficients varying periodically in the space. Utilizing the system periodicity, we develop the instrumental features of the Floquet theory, including the monodromy matrix and its Floquet multipliers. We use them to derive closed form expressions for a number of physically significant quantities. Those include, in particular, the dispersion relations and the frequency dependent gain foundational to the RF signal amplification. We assume that MCKs operate in the voltage amplification mode associated with the maximal gain.

A General 3D Non-Stationary 6G Channel Model With Time-Space Consistency

This paper proposes a novel general sixth-generation (6G) irregular-shaped geometry-based stochastic model (IS-GBSM) for millimeter wave (mmWave) massive multiple-input multiple-output (MIMO) wireless communication systems. The proposed IS-GBSM can model spherical wavefront propagation, high delay resolution, and three-dimensional (3D) space-time-frequency non-stationarity of channels with time-space consistency, and thus can be applied to integrated communication and sensing systems. To capture the 3D non-stationarity with channel consistency, a new hybrid method combining geometric and parametric methods is developed. Based on the geometric method, i.e., visibility region (VR), the smooth and consistent appearance and disappearance of clusters during array-time evolution are modeled. With the help of the parametric method, a frequency-dependent path gain is introduced, and a visible factor based on uniform continuity theorem and bounded variation function is further proposed to capture the soft cluster power handover during cluster array-time evolution. Key channel statistics of the proposed IS-GBSM are derived and investigated. Simulation results demonstrate that the space-time-frequency non-stationarity is modeled and time-space consistency is captured. Finally, the utility of the proposed IS-GBSM is verified by the excellent agreement between simulation results and measurement.

Analysis and suppression of subsynchronous oscillation of Rudong wind power through MMC-HVDC system

There may be complex interaction between the converter control systems of wind power and MMC-HVDC, which will lead to sub-/super-synchronous oscillation and threaten the safe and stable operation of the system. The relevant events have been reported in Guangdong Nan'ao, Shanghai Nanhui and Zhangbei projects. Rudong offshore wind power project is the first offshore wind power transmission system in China, and it is still under construction. Therefore, it is of great significance to carry out the research on the risk analysis and suppression measures of sub-synchronous oscillation in Rudong wind power MMC-HVDC system. First, the time-domain simulation model of Rudong wind power MMC-HVDC system is built in the PSCAD/EMTDC simulation model. Then, the effects of the number of wind turbine generators, wind power output and the parameters of MMC-HVDC controller on the sub-/super-synchronous oscillation characteristics of the system are further analyzed. Finally, the suppression measures based on supplementary frequency dependent gain control are proposed, the application position of the controller is discussed, and the parameter optimization method of the controller is given. The research content provides a certain guiding significance for the operation and control of Rudong wind power MMC-HVDC.

Voltage Differencing Buffered Amplifier-Based Novel Truly Mixed-Mode Biquadratic Universal Filter with Versatile Input/Output Features

In this paper, a first-of-a-kind mixed-mode universal filter employing three VDBAs and three passive components, is proposed. The filter operates in all four modes and provides all five filter responses, namely voltage-mode (VM), current-mode (CM), trans-impedance-mode (TIM), or trans-admittance-mode (TAM). Additionally, the same filter topology can also work as a CM single-input-multi-output (SIMO) filter. A state-of-the-art comparison of various ‘voltage differencing’ variants of the voltage differencing buffered amplifier (VDBA)-based SIMO/MISO (single-input-multi-output/multi-input-single-output)-type biquad filters further highlight the significance of the presented research. In the proposed no passive component matching is required for generating the filter responses. The filter circuit also provides inbuilt tunability of the quality factor independent of the pole frequency. The non-ideal frequency dependent gain and component sensitivity analyses of the filter were also performed. The Silterra Malaysia 0.18μm process design kit (PDK) is employed to design and validated the proposed VDBA-based filter using the Cadence design software. The simulation results closely follow the theoretical predictions. To further verify the practical feasibility of the proposed filter, an experimental evaluation is also completed. The VDBA-based filter is implemented using off-the-shelf operational transconductance amplifiers Intersil CA3080, Texas Instruments LF356 op-amp, and Analog Devices AD844s. The filter is designed for a characteristic frequency of 100 kHz. The time and frequency domain measurement results indicate the proper functioning of the filter.

Flexible megahertz organic transistors and the critical role of the device geometry on their dynamic performance

The development of organic thin-film transistors (TFTs) for high-frequency applications requires a detailed understanding of the intrinsic and extrinsic factors that influence their dynamic performance. This includes a wide range of properties, such as the device architecture, the contact resistance, parasitic capacitances, and intentional or unintentional asymmetries of the gate-to-contact overlaps. Here, we present a comprehensive analysis of the dynamic characteristics of the highest-performing flexible organic TFTs reported to date. For this purpose, we have developed the first compact model that provides a complete and accurate closed-form description of the frequency-dependent small-signal gain of organic field-effect transistors. The model properly accounts for all relevant secondary effects, such as the contact resistance, fringe capacitances, the subthreshold regime, charge traps, and non-quasistatic effects. We have analyzed the frequency behavior of low-voltage organic transistors fabricated in both coplanar and staggered device architectures on flexible plastic substrates. We show through S-parameter measurements that coplanar transistors yield more ideal small-signal characteristics with only a weak dependence on the overlap asymmetry. In contrast, the high-frequency behavior of staggered transistors suffers from a more pronounced dependence on the asymmetry. Using our advanced compact model, we elucidate the factors influencing the frequency-dependent small-signal gain and find that even though coplanar transistors have larger capacitances than staggered transistors, they benefit from substantially larger transconductances, which is the main reason for their superior dynamic performance.

Kv2.1 Potassium Channels Regulate Repetitive Burst Firing in Extratelencephalic Neocortical Pyramidal Neurons

Abstract Coincidence detection and cortical rhythmicity are both greatly influenced by neurons’ propensity to fire bursts of action potentials. In the neocortex, repetitive burst firing can also initiate abnormal neocortical rhythmicity (including epilepsy). Bursts are generated by inward currents that underlie a fast afterdepolarization (fADP) but less is known about outward currents that regulate bursting. We tested whether Kv2 channels regulate the fADP and burst firing in labeled layer 5 PNs from motor cortex of the Thy1-h mouse. Kv2 block with guangxitoxin-1E (GTx) converted single spike responses evoked by dendritic stimulation into multispike bursts riding on an enhanced fADP. Immunohistochemistry revealed that Thy1-h PNs expressed Kv2.1 (not Kv2.2) channels perisomatically (not in the dendrites). In somatic macropatches, GTx-sensitive current was the largest component of outward current with biophysical properties well-suited for regulating bursting. GTx drove ~40% of Thy1 PNs stimulated with noisy somatic current steps to repetitive burst firing and shifted the maximal frequency-dependent gain. A network model showed that reduction of Kv2-like conductance in a small subset of neurons resulted in repetitive bursting and entrainment of the circuit to seizure-like rhythmic activity. Kv2 channels play a dominant role in regulating onset bursts and preventing repetitive bursting in Thy1 PNs.

Numerical computation of the nonlinear Schrödinger equation with higher order group velocity dispersion and frequency-dependent gain using the differential method

Numerical computation of the nonlinear Schrödinger equation with higher order group velocity dispersion and frequency-dependent gain using the differential method