Input Frequency Research Articles

Multi-physics coupled numerical simulation study to optimize process parameters for electromagnetic stirring of semi-solid A356 aluminum alloy under the influence of skin effect

The electromagnetic stirring (EMS) method stands as a widely used technique in creating semi-solid aluminum alloy slurry due to its convenience and precision in parameter control compared to other methods. In this study, a comprehensive model that combines electromagnetics, flow, heat transfer and solidification was formed. By analyzing the influence of input current and frequency on the electromagnetic force, the behavior of various process parameters in velocity field and temperature field under influence of the skin effect is investigated. The aim is to find the optimal process parameters for production of slurry using the low-frequency EMS. The results show that within the investigated range, by adjusting the input current and frequency to 150 A and 15 Hz, higher fluid velocities and appropriate distribution of vortex zones can be observed, while achieving a uniform temperature field, the highest cooling rate and the minimum radial temperature difference. In addition, the sample prepared under the optimal process parameters shows that the melt edge is least affected by the skin effect, which leads to a higher stirring strength and a smaller overall grain size, which is consistent with the theoretical skin effect research found within the simulation section.

Small-strain stiffness of selected anthropogenic aggregates from bender element tests

Abstract This article presents a study on the stiffness of mixtures of anthropogenic materials derived from construction or demolition waste, specifically fine recycled concrete aggregates (fRCAs) with different fine fraction (FF) contents. The study investigated small-strain shear moduli via various signal interpretation methods, examining, above all, the time domain approaches and considering the influence of FF content. However, the inconclusive results from the bender element (BE) tests highlight the complexity of factors affecting shear wave velocity, which requires further research to refine the methodology and assess long-term performance in geotechnical applications. Selecting the correct test frequency and interpretation method is crucial to obtain accurate results. The BE test method should consider all relevant factors. At low input frequencies (≤5 kHz), the near-field effect affected the received signal for fRCA mixtures. At higher frequencies (around 14 kHz), the noise levels increased, thereby interfering with the S-wave travel time determination. Intermediate input frequencies (10.0 and 12.5 kHz) provided the representative shear modulus (G) values. The small-strain shear modulus (G max) of the fRCA compounds from the resonant column and BE tests was found to be in good agreement, despite differences in the test procedures themselves.

Shear Thickening Fluid and Sponge-Hybrid Triboelectric Nanogenerator for a Motion Sensor Array-Based Lying State Detection System.

Issues of size and power consumption in IoT devices can be addressed through triboelectricity-driven energy harvesting technology, which generates electrical signals without external power sources or batteries. This technology significantly reduces the complexity of devices, enhances installation flexibility, and minimizes power consumption. By utilizing shear thickening fluid (STF), which exhibits variable viscosity upon external impact, the sensitivity of triboelectric nanogenerator (TENG)-based sensors can be adjusted. For this study, the highest electrical outputs of STF and sponge-hybrid TENG (SSH-TENG) devices under various input forces and frequencies were generated with an open-circuit voltage (VOC) of 98 V and a short-circuit current (ISC) of 4.5 µA. The maximum power density was confirmed to be 0.853 mW/m2 at a load resistance of 30 MΩ. Additionally, a lying state detection system for use in medical settings was implemented using SSH-TENG as a hybrid triboelectric motion sensor (HTMS). Each unit of a 3 × 2 HTMS array, connected to a half-wave rectifier and 1 MΩ parallel resistor, was interfaced with an MCU. Real-time detection of the patient's condition through the HTMS array could enable the early identification of hazardous situations and alerts. The proposed HTMS continuously monitors the patient's movements, promptly identifying areas prone to pressure ulcers, thus effectively contributing to pressure ulcer prevention.

Multifunctional Intelligent Metamaterial Computing System: Independent Parallel Analog Signal Processing

Analog computing based on miniaturized surfaces has gained attention for its high‐speed and low‐power mathematical operations. Building on recent advances, an anisotropic space‐time digital metasurface for parallel and programmable wave‐based mathematical operations is proposed. Using frequency conversions, our metasurface performs 1st‐order and 2nd‐order spatial differentiations, integrodifferential equations, and sharp edge detection in spatially encoded images. The anisotropic nature of the meta‐particle enables independent and simultaneous operations for two orthogonal polarizations. Reconfigurability is achieved through tunable gate biasing of an indium tin oxide layer. Illustrative examples demonstrate that the metasurface's output signals and transfer functions closely match ideal transfer functions, confirming its versatility and effectiveness. Unlike other wave‐based signal processors, the design handles wide spatial frequency bandwidths, even with high spatial frequency inputs.

A 62.2dB SNDR Event-Driven Level-Crossing ADC with SAR-Assisted Delay Compensation Loop for Time-Sparse Biomedical Signal Acquisition.

This paper proposed an event-driven clockless level-crossing ADC (LC-ADC) suitable for biomedical applications. Thanks to the LC loop, the sampling rate of the converter automatically adapts to the input activities. Activity-dependent power consumption and data compression can thus be realized, saving system power, especially during time-sparse signal acquisition. Meanwhile, a SAR-assisted loop is exploited to resolve the loop-delay-induced distortion in conventional LC-ADC. Therefore, the resolution and power efficiency of the LC-ADC are improved effectively while maintaining the event-driven feature. Implemented in a 55nm process, the proposed LC-ADC achieves a scalable power consumption and a peak SNDR of 62.2dB for a 20kHz input. It also achieves a Walden FoM of 29.7fJ/conv.-step and a Schreier FoM of 158.6dB, which is best in class, without using off-chip calibration. Sub μW power is realized when the input frequency is below 1.5kHz. The proposed LC-ADC is also verified by simulated electrocardiogram (ECG), neural spike, and electromyogram (EMG) signals. It provides a ~7X data compression for ECG input, providing an attractive solution for time-sparse signal acquisition in biomedical applications.

An instrumentation amplifier with series switch pseudo resistor DC-servo loop realizing 0.16-Hz high-pass corner

This paper presents an instrumentation amplifier for electrocardiogram (ECG) signal recording. A DC servo loop (DSL) based on a series-switch pseudo resistor (S2PR ) is utilized to suppress the effect of the unavoidable electrode DC offset effectively. The two-step pulse generation circuit realizes two sets of pulse signals with shallow duty cycles, and the pulse signals drive the path switches and virtual switches in the S2PR, respectively. Virtual switches reduce the channel charge injection effect, and finally, a great equivalent resistance with high linearity is realized. The continuous DSL realized based on S2PR can suppress the electrode DC offset of ±180 mV. At the same time, the active area of the DSL is significantly reduced. The proposed instrumentation amplifier is realized in a standard 0.18-μm CMOS process. Simulation results show the DSL designed with a 1.8-V supply introduces a 0.16-Hz high-pass corner. The power consumption of the S2PR-DSL is 92.7 μW. The gain of the instrumentation amplifier is 39.8 dB, and the input-referred noise at the TT corner is 1.78 μVrms over a bandwidth of 0.5 Hz to 150 Hz. The input impedance of the instrumentation amplifier is 772.2 MΩ, when the input signal frequency is 50 Hz, and the total harmonic distortion (THD) of a 10-mVpp input sinusoidal signal at 9.033 Hz is −61.6 dB.

Differential effects of stimulation frequency on isometric and concentric isotonic contractile function in human quadriceps.

Electrically evoked contractions are used to assess the relationship between frequency input and contractile output to characterize inherent muscle function, and these have been done mostly with isometric contractions (i.e., no joint rotation). The purpose was to compare the electrically stimulated frequency and contractile function relationship during isometric (i.e., torque) with isotonic (i.e., concentric torque, angular velocity, and mechanical power) contractions. The knee extensors of 16 (5 female) young recreationally active participants were stimulated (∼1-2.5 s) at 14 frequencies from 1 to 100 Hz. This was done during four conditions, which were isometric and isotonic at loads of 0 (unloaded), 7.5%, and 15% isometric maximal voluntary contraction (MVC), and repeated on separate days. Comparisons across contractile parameters were made as a % of 100 Hz. Independent of the load, the mechanical power-frequency relationship was rightward shifted compared with isometric torque-frequency, concentric torque-frequency, and velocity-frequency relationships (all P ≤ 0.04). With increasing load (0%-15% MVC), the isotonic concentric torque-frequency relationship was shifted leftward systematically from 15 to 30 Hz (all P ≤ 0.04). Conversely, the same changes in load caused a rightward shift in the velocity-frequency relationship from 1 to 40 Hz (all P ≤ 0.03). Velocity was leftward shifted of concentric torque in the unloaded isotonic condition from 10 to 25 Hz (all P ≤ 0.03), but concentric torque was leftward shifted of velocity at 15% MVC isotonic condition from 10 to 50 Hz (all P ≤ 0.03). Therefore, isometric torque is not a surrogate to evaluate dynamic contractile function. Interpretations of evoked contractile function differ depending on contraction type, load, and frequency, which should be considered relative to the specific task.NEW & NOTEWORTHY In whole human muscle, we showed that the electrically stimulated power-frequency relationship was rightward shifted of the stimulated isometric torque-frequency relationship independent of isotonic load, indicating that higher stimulation frequencies are needed to achieve tetanus. Therefore, interpretations of evoked contractile function differ depending on contraction type (isometric vs. dynamic), load, and frequency. And thus, isometric measures may not be appropriate as a surrogate assessment when evaluating dynamic isotonic contractile function.

An Improved Constant Active Power Control for Three-Phase Buck Rectifier Under Unbalanced Input Voltages and Wide AC Input Frequency

An Improved Constant Active Power Control for Three-Phase Buck Rectifier Under Unbalanced Input Voltages and Wide AC Input Frequency

Optimum design of a novel Ku-band rasorber for RADAR warfare systems using ML neural network

The design, fabrication, and testing of a conformal Frequency Selective Rasorber (FSR) operating at A-T-A mode is designed for RADAR warfare systems. In the design of a miniaturized single-layer FSR element, multiple parameters influencing the absorption and transmission characteristics need to be optimized. This simulation using conventional methods consumes more simulation time. Thus, the geometrical parameters are optimized and predicted using supervised machine learning (ML) techniques to expedite the process. The multiple output regression neural network (MORNN) is used to generate multiple input and output features from the dataset. The ML algorithm is trained using the datasets generated from the electromagnetic solver using which a scalable FSR is synthesized. The reflection coefficient, (|S11|), and transmission coefficient (|S21|) are used as input data, and the dimension of the FSR unit cell for the user input frequency requirements are derived as output data. The extracted dimensions of the FSR offered a small mean square error (MSE) of 0.02 between the desired and observed results. The designed FSR offers absorption at 11.5 GHz and 18.9 GHz while the transmission window extends from 15.02 GHz to 16.09 GHz. The neural network results are endorsed using the EM simulation tool and validated by experimental measurements.

Implementation and Linearization of a Coupled Panel and Vortex Particle Method in State-Space Form

This paper describes the implementation and linearization of a coupled panel and vortex particle method in a state-variable form. More specifically, the coupled panel and vortex particle dynamics are formulated as a nonlinear system of ordinary differential equations in first-order form to be self-contained and inherently linearizable. Linearization of this coupled panel and vortex particle method is demonstrated via finite differencing and a novel analytical linearization technique to yield a linear time-invariant representation. The code is implemented in MATLAB® and validated against an open-source aerodynamic solver for a fixed wing in both stationary and unsteady conditions. The linearized models are verified against the nonlinear dynamics both in the time and frequency domains. Linearized models accurately represent the wake dynamics about the equilibrium condition for moderate amplitude inputs and for input frequencies covering the typical frequency range of flight dynamics and flight controls, i.e., 0.3–30 rad/s. Analytical linearization is shown to abate the cost of linearization over perturbation methods by O(n2), where n is the total number of states of the system. Linearized models of the coupled panel and vortex particle dynamics have applications in the flight dynamics of both fixed- and rotary-wing vehicles, where these dynamics can be used to augment the rigid-body dynamics. The coupled rigid-body and wake dynamics can be leveraged to assess the stability, response characteristics, and handling qualities of vehicles experiencing aerodynamic interactions between rotors, wings, and/or obstacles.

Full-Swing Nanosecond Delay Hybrid Level Shifter for Time-Critical Applications

A crucial component of digital integrated circuits with numerous power domains is the level shifter (LS). The traditional topologies are currently the mirror LS and cross-coupled LS. For full-swing level conversions from extremely low voltage to the nominal voltage of the supply, ahybrid LS is proposed in this paper, which is a combination of the current mirror LS and cross-coupled LS with a swing-aware output inverter. The proposed LS circuit is designed to ensure full swing, static current-free, and limited current-contention level conversions by preserving the benefits of the current mirror and cross-coupled LS, and using them to eliminate each other’s shortcomings. The proposed hybrid LS is designed and implemented by using 45-nm technology in Cadence Virtuoso tool. Pass transistors and current limiters with multiple thresholds are included for the suggested LS. The proposed LS provides voltage conversion from 0.10 V to 1.20 V. At alevel-shifting voltage of 0.20 V, the proposed hybrid LS at 1 MHz input frequency demonstrates a delay of 8.38 ns, an average power consumption of 3.81 µW, and an energy per transition of 26.64 fJ. Additionally, the suggested LS has low delay, good supply voltage scaling, and delay scalability.

A 30-60 GHz Broadband Low LO-Drive Down-Conversion Mixer with Active IF Balun in 65 nm CMOS Technology.

A 30~60 GHz broadband down-conversion mixer driven by low local oscillator (LO) power is presented. The down-conversion mixer utilizes an input signal coupling technique based on the Marchand balun to achieve broadband operation and achieves low LO power drive and low DC power consumption through the use of a weak inversion bias with Gilbert switching devices. The broadband conversion of single-ended to differential signals is achieved using the Marchand balun with compensation lines, and an equivalent circuit analysis is performed. For the intermediate frequency (IF) output, a self-biased IF trans-impedance amplifier with current reusing and an active IF balun structure are used to achieve signal amplification and single-ended signal output. Test results show that the proposed mixer achieves a conversion gain of -1.2 to 6.4 dB in an IF output bandwidth of 0.1 to 5 GHz at radio frequency (RF) input frequencies of 30 to 60 GHz and LO driving power of -10 dBm. The DC power consumption of the core mixing unit of the proposed mixer is 4.8 mW, and the DC power consumption including the IF amplifier is 28.3 mW. The proposed mixer uses a 65 nm CMOS technology with a chip area of 0.26 mm2.

Design and test of a sub-45 nm non-aligned double gate inverter in TCAD environment: static and dynamic analysis

ABSTRACT This work presents a sub-45 nm application-specific nanoscale single-device non-aligned double gate inverter (NADGI) with minimised gate and drain contacts. NADGI uses two devices of 25 nm channel length, i.e. NADGPFET and NADGNFET, giving maximum ON-current of 1.16 mA and 1.36 mA, respectively. The dynamic performance of the proposed structure was evaluated by applying ultra-high frequency, super-high frequency, and varying supply voltage/load capacitor. This work uses graphical method to determine the optimal supply voltage of the NADGI, the estimated values at 1 GHz and 10 GHz input frequency were 0.6 V and 0.7 V, respectively. When compared with the past works, the proposed inverter shows 82.4% improvement in propagation delay and 40% reduction in the supply voltage. Therefore, with improved design structure and response, the proposed inverter can be suitably used for high-frequency and low-power circuit design.

Dynamically frequency‐tunable and environmentally stable microwave absorbers

AbstractThe threat to information security from electromagnetic pollution has sparked widespread interest in the development of microwave absorption materials (MAMs). Although considerable progress has been made in high‐performance MAMs, little attention was paid to their absorption frequency regulation to respond to variable input frequencies and their stability and durability to cope with complex environments. Here, a highly compressible polyimide‐packaging carbon nanocoils/carbon foam (PI@CNCs/CF) fabricated by a facile vacuum impregnation method is reported to be used as a dynamically frequency‐tunable and environmentally stable microwave absorber. PI@CNCs/CF exhibits good structural stability and mechanical properties, which allows precise absorption frequency tuning by simply changing its compression ratio. For the first time, the tunable effective absorption bandwidth can cover the whole test frequency band (2−18 GHz) with the broadest effective absorption bandwidth of 10.8 GHz and the minimum reflection loss of −60.5 dB. Moreover, PI@CNCs/CF possesses excellent heat insulation, infrared stealth, self‐cleaning, flame retardant, and acid‐alkali corrosion resistance, which endows it high reliability even under various harsh environments and repeated compression testing. The frequency‐tunable mechanism is elucidated by combining experiment and simulation results, possibly guiding in designing dynamically frequency‐tunable MAMs with good environmental stability in the future.

Dielectrophoresis as an Adjunctive Technique for Fibroblast Cell Migration to Enhance Wound Closure

This study reports on DEP-based simulation and experimental validation of polystyrene (PS) beads and fibroblast cells for primary skin cell migration for enhancing wound closure. MyDEP software was used to calculate the numerical simulation of the Clausius-Mossotti factor (CMF). In order to examine particle trajectories based on input frequencies, the finite element technique (FEM) is used. The trajectories of PS beads and fibroblast cells were experimentally assessed to verify the impact of frequency applied on the polarisation of PS beads and fibroblast cells. The outcome illustrated the potential of employing FDEP to move particles and cells to regions of high and low electric field. Fibroblast cells exhibit negative dielectrophoresis (NDEP) at a broad range of frequencies. Thus, FDEP can be utilised for frequency optimisation to enhance wound closure.

A novel stick-slip piezoelectric actuator is developed based on a parallelogram flexible drive mechanism to minimize shear force

A piezoelectric actuator utilizing a parallelogram flexible mechanism is proposed. This actuator harnesses the parasitic motion generated by a parallelogram driven by a piezoelectric element. It differs from existing actuation mechanisms based on a similar principle in that the piezoelectric stack is positioned on the outside of the parallelogram flexible mechanism, thus protecting it from shear forces. Finite element simulations and experiments confirm this. The analysis was conducted using theoretical analysis and finite element simulation. The optimal drive angle for the parallelogram flexible mechanism was determined through finite element simulation. Additionally, a prototype actuator and an experimental measurement system were developed to assess the operational performance of the proposed piezoelectric actuator. When the driving frequency is 475 Hz and the locking force is 5 N, the motion of the actuator achieves a maximum speed of 5.65 mm s−1 and a maximum horizontal load of up to 113 g; when the input frequency is 1 Hz and the input minimum starting voltage is 8 V, the minimum displacement resolution is 30 nm. A comparative analysis of experimental results, theoretical calculations, and finite element simulation results demonstrates the feasibility of the structural design.

Equal levels of pre- and postsynaptic potentiation produce unequal outcomes.

Which proportion of the long-term potentiation (LTP) expressed in the bulk of excitatory synapses is postsynaptic and which presynaptic remains debatable. To understand better the possible impact of either LTP form, we explored a realistic model of a CA1 pyramidal cell equipped with known membrane mechanisms and multiple, stochastic excitatory axo-spinous synapses. Our simulations were designed to establish an input-output transfer function, the dependence between the frequency of presynaptic action potentials triggering probabilistic synaptic discharges and the average frequency of postsynaptic spiking. We found that, within the typical physiological range, potentiation of the postsynaptic current results in a greater overall output than an equivalent increase in presynaptic release probability. This difference grows stronger at lower input frequencies and lower release probabilities. Simulations with a non-hierarchical circular network of principal neurons indicated that equal increases in either synaptic fidelity or synaptic strength of individual connections also produce distinct changes in network activity, although the network phenomenology is likely to be complex. These observations should help to interpret the machinery of LTP phenomena documented in situ. This article is part of a discussion meeting issue 'Long-term potentiation: 50 years on'.

A hybrid SAR ADC with input range extension

—This paper proposes a differential 10-bit 1 MS/s successive approximation register (SAR) analog to digital converter (ADC) with input range (IR) extension. Employing 512 capacitor units and a reference voltage VREF, it attains a ±1.875VREF input range and a resolution of 10.91 bits. The hybrid SAR ADC decomposes the capacitive digital-to-analog converter (CDAC) into an incremental CDAC and a binary-weighted CDAC. For input signals larger than 0.75 VREF, the incremental CDAC is used to reduce the net sampling charge by biasing its capacitor bottom plates on proper reference voltage to implement input range extension. Furthermore, the increment CDAC contributes to enhancing linearity. The input frequency limitation is theoretically analyzed in the paper. This design is implemented with a 180-nm CMOS technology and achieves a 10.47 effective number of bits (ENOB). It consumes 26.8 μW at 1 MS/s with a 1.8-V supply and occupies an area of 0.0118 mm2.

Hybrid Printing of Conductive Traces from Bulk Metal for Digital Signals in Intelligent Devices.

In this article, we explore multi-material additive manufacturing (MMAM) for conductive trace printing using molten metal microdroplets on polymer substrates to enhance digital signal transmission. Investigating microdroplet spread informs design rules for adjacent trace printing. We studied the effects of print distance on trace morphology and resolution, noting that printing distance showed almost no change in the printed trace pitch. Crosstalk interference between adjacent signal traces was analyzed across frequencies and validated both experimentally and through simulation; no crosstalk was visible for printed traces at input frequencies below 600 kHz. Moreover, we demonstrate printed trace reliability against thermal shock, whereby no discontinuation in conductive traces was observed. Our findings establish design guidelines for MMAM electronics, advancing digital signal transmission capabilities.

Frequency importance functions in simulated bimodal cochlear-implant users with spectral holes.

Frequency importance functions (FIFs) for simulated bimodal hearing were derived using sentence perception scores measured in quiet and noise. Acoustic hearing was simulated using low-pass filtering. Electric hearing was simulated using a six-channel vocoder with three input frequency ranges, resulting in overlap, meet, and gap maps, relative to the acoustic cutoff frequency. Spectral holes present in the speech spectra were created within electric stimulation by setting amplitude(s) of channels to zero. FIFs were significantly different between frequency maps. In quiet, the three FIFs were similar with gradually increasing weights with channels 5 and 6 compared to the first three channels. However, the most and least weighted channels slightly varied depending on the maps. In noise, the patterns of the three FIFs were similar to those in quiet, with steeper increasing weights with channels 5 and 6 compared to the first four channels. Thus, channels 5 and 6 contributed to speech perception the most, while channels 1 and 2 contributed the least, regardless of frequency maps. Results suggest that the contribution of cochlear implant frequency bands for bimodal speech perception depends on the degree of frequency overlap between acoustic and electric stimulation and if noise is absent or present.