Input Frequency Research Articles

A Continuous Time Domain Direct Identification Method for Unsteady Fluid Dynamic Model in Incompressible Flow

To identify the unsteady fluid dynamic model for a solid moving in the fluid, a new identification method that operates in the continuous time domain is proposed. It is illustrated that this new identification method is more accurate and appropriate for identifying unsteady fluid dynamic model in incompressible flow in comparison with the classical frequency domain or discrete domain method. This new method is applied to identify the unsteady fluid dynamic models of a NACA0012 airfoil and the effect of the fluid viscosity on the model parameter is analyzed. The result shows that the added mass in viscous flow is dependent on the input signal frequency and is exactly the added mass in inviscid flow when the frequency approaches infinity. Based on this discovery, the long controversy on the relationship of added mass between viscous and inviscid flow is solved. Then, the enlightenment of this discovery on the identification of both linear and nonlinear unsteady aerodynamic model in incompressible flow is illustrated. At last, the advantage of the new acquired unsteady fluid dynamic model is discussed in comparison with the classical quasi-steady aerodynamic model.

Brillouin Amplifier Noise Limiting With a Semiconductor Optical Amplifier for Coherent Communication Applications

Suppression of Brillouin amplifier intensity noise is demonstrated by use of a semiconductor optical amplifier (SOA) at its output to enhance application of its narrowband gain for boosting the carrier to noise ratio (CNR) of spectral lines in coherent communications. This utilizes the fast recovery time of the SOA gain in saturation to limit distortions induced when Brillouin gain is reduced from its maximum by detuning of the input frequency or state of polarization relative to the backward propagating pump. Although the SOA carrier dynamics associated with the varying gain also converts intensity noise to phase distortion, the similarly low bandwidth in the tens of megahertz range as for Brillouin gain permits its removal in communication applications by the same digital signal processing used to compensate the similarly slow phase error from coherent detection with a local oscillator laser. When applied to a spectral line with initial poor CNR of 19.5 dB/0.1 nm that is then boosted by Brillouin gain but at detuned input frequency of ∼±10 MHz from optimum (or 67% of a 30 MHz gain bandwidth), the SOA improves use of the SBA output as a carrier of 72 Gb/s 64-QAM signals with up to 2 dB higher <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> -factor at the receiver. Overall, SBA's benefit for noise suppression in combination with the SOA is extended to more flexible and wider ranging input parameters.

Improved Branch Energy Balance Control for Three-Phase to Single-Phase Modular Multilevel Converter for Railway Traction Power Supply

Maintaining the branch energy balance poses a huge challenge to controller design of many modular multilevel converter (MMC) topologies. Aiming at railway traction power supply system application of a three-phase to single-phase MMC with equal input and output frequency, this article proposes a branch energy balance control with an improved common-mode voltage selection. As a result, the capacitor voltage oscillations as well as circulating currents are reduced greatly. As the MMC is a complicated periodic time-varying system, an average theory is used to simplify the analysis and controller design. The controllability analysis of the system is carried out and the results show that the proposed branch energy balance control is controllable under most load conditions. In addition, the stability of the branch energy balance system is validated through frequency response. Finally, experimental results verify the effectiveness of the control scheme by an 18-cell model based on the RT-LAB platform.

A Dual-Band Differential Intraoral Antenna and System for Wireless Data and Radiative Near-Field Power Transfer

Intraoral tongue drive system (iTDS) is a promising assistive technology for rehabilitating disabled persons. This article proposes a radiative near field power transfer (RNF-PT) system comprising an intraoral differential rectenna (rectifying antenna) and external power transmitter (RNF-Tx). A dual-band compact differential intraoral antenna operating in the Industrial, Scientific and Medical (ISM) band (2.45 GHz) and midfield band (1.9 GHz) is proposed for the data and power transmission modes, respectively. The proposed differential antenna and rectifier were designed and fabricated individually using a Rogers RT/duroid 6010 substrate. The differential rectifier shows a simulated conversion efficiency of 89.3% for a radio frequency (RF) input power of 14.78 dBm at 1.9 GHz with a 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{k}\Omega $ </tex-math></inline-formula> load. The maximum transmission coefficient of −25.95 and −24.93 dB was achieved at a separation of 22 mm for the closed and opened mouth conditions, respectively. The measured impedance bandwidths of the proposed antenna in both the closed and open mouth of the test subject are around 10% in the midfield band and around 9.5% in the ISM band, respectively. The measured peak gain in the minced pork and saline solution was −20.48 dBic, −18.25 dBic at the frequency of 1.9 GHz and −18.54 dBi, and −16.88 dBi at the frequency of 2.45 GHz, respectively. The specific absorption rate (SAR) values have also been analyzed through simulations for both data and power transmission modes and are found acceptable in the closed and open mouth placements. Based on these acceptable SAR values, the link margin was theoretically calculated where it could communicate over a reasonable distance. Thus, the proposed intraoral differential antenna with a rectifier is ideal for data and PT support in iTDS-based applications.

Ultrasonic damage detection in lithium-ion cells with localized thermal abuse histories

Electric vehicles require nearly 1000 individual lithium-ion batteries to provide appropriate power and capacity. It has recently been shown that ultrasonic inspection can detect localized heating in a LIB cell with a combination of input frequencies and propagation paths [J. Acoust. Soc. Am. 152, A283 (2022)]. However, monitoring the thermal conditions of every cell in a battery pack is highly challenging to implement. This work explores the use of ultrasonic inspection to diagnose LIB cells with damage histories due to local, thermal abuse. LIBs were interrogated with ultrasonic waves while subjected to electrical and thermal loading, specifically, standard charge-dischargecycling followed by moderate localized thermal abuse and another phase of charge-discharge cycling. Ultrasonic signals from each portion of the test and data for the cycling before and after heating are directly compared for indicators of past abuse. Experimental data are compared to a transfer-matrix model to simulate the time-of-flight (TOF) through an individual cell using temperature-specific material properties for individual components to simulate the effect of heat on TOF. Experimental results indicate that deviations in time-domain features of the received signals can be used to detect previous thermal abuse via ultrasonic testing during charge-discharge cycling after thermal abuse.

Blocker-Tolerant Inductor-Less Harmonic Selection Wideband Receiver Front-End for 5G Applications

A blocker-tolerant harmonic selection receiver front-end with RF bandwidth of 6.5 GHz to support the fifth-generation (5G) sub-6 GHz band is presented. The proposed N-path switching filter-based receiver employs harmonic recombination blocks at the baseband (BB) to select the desired local oscillator (LO) harmonics and suppress blockers. It is demonstrated how the configuration of two feed-forward N-path switching filters and BB harmonic recombination stage can be reconfigured to select the first harmonic of the switching frequency at the low-frequency band (0.5–1.9 GHz) and the third LO harmonic at the high-frequency band (1.95–6 GHz). Thus, the proposed architecture has the capability of supporting an RF input frequency of up to 6 GHz while the switching frequency operates up to 2 GHz. Higher harmonic selection in addition to the fundamental helps to reduce the power consumption and required input frequency of the multiphase LO clock generator. An RF receiver prototype is fabricated in a TSMC 130-nm CMOS technology. It achieves a 5 dB noise figure (NF), −16.6 dBm in-band input-referred third-order intercept point (IIP3), and 9 dBm out-of-band (OOB) IIP3, respectively, at the low-frequency band (0.5–1.9 GHz). The 2nd–5th harmonic rejection ratios (HRRs) are higher than 44 dB without any calibration. The receiver can tolerate a 0 dBm blocker at a 180 MHz offset from a 1 GHz switching frequency with an NF of 9.4 dB. Over the high-frequency band (1.95–6 GHz), the receiver’s NF is less than 7.1 dB. Moreover, in-band IIP3, OOB IIP3, and first HRR are higher than −21 dBm, 7 dBm, and 39 dB, respectively. The receiver achieves an S11 better than −10 dB over 0.5–6 GHz, and has a total power consumption of 17–22.5 mW from a 1.2 V supply.

The Effect of Input Flooding and Explicit Instruction on L2 Acquisition of English Inverse Scope

This article investigates how different types of input and instruction can affect L1-Mandarin L2-English learners’ acquisition of English inverse scope. English quantifier–negation sentences such as All the kids didn’t climb the tree are ambiguous between a surface-scope reading (‘none of the kids climbed the tree’) and an inverse-scope reading (‘it is not the case that all the kids climbed the tree’), while the Mandarin equivalent only has the surface-scope reading. Inverse scope can be challenging even for advanced learners, due to its low frequency in naturalistic input and/or its complex form–meaning mapping. The present study implemented an intervention with inverse scope: learners received either input flooding (increased frequency) or explicit instruction (explicit explanations about form–meaning mappings). For learners receiving explicit instruction, acceptance of inverse scope increased significantly after instruction. In contrast, learners receiving input flooding did not show significant improvement; results from debriefing questionnaires indicated that learners in the input flooding group failed to either notice the target structure or further process the input. This suggests that input flooding alone is not as effective as explicit instruction in learning a property that has complex form–meaning mapping, such as inverse scope.

Temperature Rise Characteristics and Experimental Study of Magnetorheological Dampers Under Different Excitations

The magnetorheological damper converts the mechanical energy of vibration into its own thermal energy, and the thermodynamic energy is expressed as the temperature rise. In this study, according to the principle of temperature rise, the temperature rise of the magnetorheological damper is established theoretical model by using the simplified one-dimensional heat transfer model of a fluid element and the lumped parameter method under the action of sine harmonic wave motion and triangular wave motion, as well as using the finite element software COMSOL to simulate the internal temperature fields of the damper. The results show that the temperature values of the damper are different, there are high-temperature areas and low-temperature areas, and the temperature rise mainly comes from the heating of the coil. The different frequency and amplitude of the excitation signal, as well as the input current, will affect the internal temperature of the damper. The temperature rise increases with the increase of input current, amplitude, and frequency, which is verified on the built testbench for the temperature rise characteristics. The change trend of the theoretical calculated value, the simulated value, and the tested value is consistent; and there is an error within the allowable range. By comparison, the temperature rise trend is basically the same for the three methods; but, when comparing with the application of sine harmonic wave motion, the temperature rise of the magnetorheological damper is 5°C higher than the triangular wave motion under the same operating condition.

Do learners need semantics to spell syntactic markers? Plural spellings in real vs. pseudowords in a French L2 setting

Inaudible syntactic markers are especially difficult to spell. This paper examines how 455 fourth graders spell silent French plural markers in a dictation with real and pseudowords after one year of formal French instruction (L2). The Generalized Linear Mixed Model analysis shows first that noun plural spelling (real and pseudo) is a strong predictor for verb and adjective plural spelling. Second, the performance on real verb plural is higher than the performance on real adjective plural. In contrast, the performance on pseudoadjective plural is higher than on pseudoverb plural. Our findings indicate the strong influence of semantics and frequency in instruction input on plural spelling: noun plural is semantically grounded, and nouns are most frequent in the curriculum. Verbs and verb plural are also frequent, and inflection is mostly taught by means of memorizing the verb inflection paradigm. Adjectives are taught least frequently. The findings are discussed in the context of French L2 instruction, as the extremely low results on adjectives and pseudoverbs seem to be a consequence of instruction methods.

Frequency-domain analysis of aperiodic control loops with identically distributed delays

Extending classical frequency domain analysis to systems with time-varying delays remains a challenge in the systems and control field. These systems are receiving a renewed interest due to emergent control applications in which the use of shared communication and computation resources induce severe time-varying delays in the loop. Here, an extension of frequency domain analysis is proposed for aperiodic control loops with time-varying delays, assumed to be independent and identically distributed and to follow an exponential distribution. In aperiodic control loops, the actuation is updated immediately after a delayed sensor measurement arrives at the controller. In the present framework, the amplitudes of expected values and variances of output responses to sinusoidal inputs are plotted as a function of the input frequency. This plot allows for inferring the behavior of the response to general input signals. The usefulness of the results is illustrated in the control of a double integrator with delayed measurements.

Analysis of a piezoelectric energy harvester system from footsteps of passersby

Piezoelectric materials can be used in applications designed to handle a wide range of input frequencies and forces to enable energy harvesting. Although several studies have been carried out on piezoelectric energy harvesting systems, this application is still under development. The purpose of this work is to analyze the behavior and the ability to generate electrical energy through the elements in piezoelectric tiles or platforms, specifically, piezoelectric disc elements with a diameter of 27 mm. To do this, a platform of about 130 x 75 cm was designed to capture the footsteps of people and transmit the impact force to sensors to determine the power generation capacity of the piezoelectric elements. Tests were carried out with people weighing between 75 kg and 85 kg and the measurements obtained made possible to identify the behavior of the system and to develop a mathematical model to estimate the energy generated through the platform. The piezoelectric elements used here proved to be fragile despite the different types of shock absorbers used to avoid their rupture. Therefore, it is recommended to delve into the design of protection mechanisms to extend the life of piezoelectric elements in energy collection systems.

A mathematical approach to estimate micro-displacement of a dental implant using electromagnetic Frequency Response Analysis

The aim of this paper is to formulate a mathematical model of dental prosthetic using single degree of freedom (SDOF) to assess the micro-displacement under electromagnetic excitation. Using Finite Element Analysis (FEA) and values from literature, stiffness and damping values of the mathematical model were estimated. For ensuring the successful implantation of dental implant system, monitoring of primary stability in terms of micro-displacement is crucial. One of the most popular techniques for the measurement of stability is the Frequency Response Analysis (FRA). This technique assesses the resonant frequency of vibration corresponding to the maximum micro-displacement (micro-mobility) of the implant. Among the different FRA techniques, the most common method is the Electromagnetic FRA. The subsequent displacement of the implant in the bone is estimated by equations of vibration. A comparison has been made to observe the variation in resonance frequency and micro-displacement due to varying input frequency ranges of 1–40 Hz. The micro-displacement and corresponding resonance frequency were plotted using MATLAB and the variation in resonance frequency is found to be negligible. The present mathematical model is a preliminary approach to understand the variation of micro-displacement with reference to electromagnetic excitation force and to obtain the resonance frequency. The present study validated the use of input frequency ranges (1–30 Hz) with negligible variation in micro-displacement and corresponding resonance frequency. However, input frequency ranges beyond 31–40 Hz is not recommended due to large variation in micromotion and corresponding resonance frequency.

A 12-Bit 1-GS/s Pipelined ADC with a Novel Timing Strategy in 40-nm CMOS Process

This paper presents a 1-GS/s12-bit pipelined analog-to-digital converter (ADC) fabricated in 40-nm CMOS technology that optimizes the settling time, bit error rate, and robustness. This ADC uses an improved timing called pre-quantization timing (PQT), which implements quantization in half the time of the sampling phase to maximize the output-settling time of the operational amplifier (op-amp). A complete clocking scheme along with a delay lock loop (DLL) is proposed to generate an accurate timing no matter how process, voltage, and temperature (PVT) change. Based on PQT, a high-speed comparator circuit is adopted to obtain a bit error rate (BER) below 10−15. Sample and hold amplifier (SHA) is used to guarantee robustness over the wide input frequency. Furthermore, a low-cost automatic calibration is implemented to correct residual curves, and inter-stage gain errors are also corrected. This ADC achieves a signal-to-noise-and-distortion ratio (SNDR) of 57.3 dB and a spurious-free dynamic range (SFDR) of 78.5 dB at a 227 MHz input frequency. The measured differential nonlinearities (DNL) and integral nonlinearities (INL) after calibration are ±0.7 LSB and ±1.50 LSB, respectively. The power consumption of the ADC core is 97.6-mW, and the Walden figure of merit (FoM) is 172.9-fJ/conversion-step.

Stick‐Type Discharge Triboelectric Nanogenerator with Amplified Output Using a Conductive Spring

As technology develops over time, energy‐harvesting methods that generate sustainable energy have been highlighted worldwide. In energy harvesting, triboelectric nanogenerators (TENGs) have several advantages, such as a simple design, high efficiency, low cost, and accessibility. Although they are applied in various fields, TENGs have limitations regarding the low current output on the microampere scale due to a high surface charge, leading to air breakdown and field emission. In addition, TENGs are implemented under vacuum pressure with high mechanical input frequency to overcome the limitation. Nevertheless, the developed TENGs still retain critical problems, such as the inability to make packaging systems and device damage. This paper reports on the stick‐type discharge (SD) TENG that can provide an amplified current with outstanding durability by applying a conductive spring to solve the problem. Consolidating a dynamic electrode with an accumulated surface charge and low curvature spring and emitting a high electric field generate a milliampere current scale through electrons to flow directly with exceptional mechanical endurance. Thus, a multi‐SD‐TENG comprising four SD‐TENGs and a portable holder powers a warning light in daily life through a shaking motion.

Efficiency Analysis and Design Considerations of a Hysteretic Current Controlled Parallel Hybrid Envelope Tracking Power Supply

This paper presents the realization of an Envelope Tracking Power Supply (ETPS), for a sinusoidal envelope input signal. A parallel hybrid topology is chosen for the implementation. In this topology, a voltage-controlled Class-AB linear amplifier stage and a current-controlled switching converter stage operate in parallel. A hysteretic current control scheme is employed to control the operation of the switching converter. Block-level implementation of the ETPS is done using Simulink 2017b, continuous mode simulation. Simulations are performed using a sinewave input envelope signal = 1.94+ 1.2 sin(ω∙t). The input frequency varied from 1MHz to 60MHz. As the input frequency is increased, the ETPS moves from the linear to the non-linear region of operation. During the transition, the slew rates of the load current and the switching current match at a particular input frequency of 2MHz while the efficiency peaks. The maximum obtained efficiency while tracking the sinewave input signal is 82.3%. The way the efficiency can be optimized by focusing on the matching of the slew rates of load and switching currents is explained. Also, an insight into the study of various circuit parameters and the trade-offs that the designer needs to consider while designing an ETPS, is provided.

Using Repetitive Control to Enhance Force Control During Human–Robot Interaction in Quasi-Periodic Tasks

We investigated the use of repetitive control (RC) to enhance force control during human-robot interaction in quasi-periodic tasks. We first developed a two-mass spring damper model and formulated three different RCs under force control: a nth 1 order RC (RC-1), a nth 3 order RC designed for random period error (RC-RPE), and a nth 3 order RC designed for constant period error (RC-RPE). Then, we quantified the performance of these three RCs through simulations and experiments conducted on a bench top linear platform, subject to nominal cyclical inputs (input signal and RC frequency: 0.5 Hz), and subject to inputs with random and constant period errors. During evaluation, we compared the performance achieved with the RCs with the one achievable with a passive proportional controller (PPC), subject to known theoretical limits for passivity and coupled stability. In nominal simulation conditions, the RC-1 reduced force error most effectively to 0.7% of the error measured with PPC. In real-world nominal experiments the RC-RPE most effectively reduced force error to 17% of the error achieved with the PPC. Subject to inputs with constant period errors, the three RCs performed similarly and better than PPC for period error values below 0.02 Hz, with the RC-CPE performing the best above 0.02 Hz period error. Subject to inputs with random period errors, all RCs performed better than PPC up to 0.09 Hz of period error, with RC-1 significantly outperforming the two other RCs. Our results indicate that RC can be successfully integrated into force control schemes to improve performance beyond the one achievable with a PPC, in the range of period variability expected in applications such as assistance or rehabilitation of cyclical human movements.

Controlling Collision-Induced Aggregations in a Swarm of Micro Bristle Robots

Systematically designing local interaction rules to achieve collective behaviors in robot swarms is a challenging endeavor, especially in micro robots, where size restrictions imply severe sensing, communication, and computation limitations. In such robot swarms, performing useful functions is often preconditioned on the formation of high-density aggregations which can facilitate collective signaling and information sharing. In this article, we present a systematic approach to control aggregation behaviors by leveraging the physical interactions in a swarm of 300 3-mm vibration-driven micro bristle robots that we designed and fabricated. We demonstrate the ability to control the degree of aggregation by varying the motility characteristics of the robots through global vibration frequency and amplitude inputs, after comprehensive characterization, modeling, and simulation of the locomotion dynamics and robot interactions. To quantify the degree of aggregation, we also introduce a new metric, the motility-induced phase separation index index, which unlike many existing methods does not require a scenario-specific tuning of parameters. Our investigations reveal how physics-driven interaction mechanisms can be exploited to achieve desired behaviors in minimally equipped robot swarms and highlight the specific ways in which hardware and software developments aid in the achievement of collision-induced aggregations.

Reconstructed Phase Voltages Based Power Following Control for Three-Phase Buck Rectifier Under Unbalanced Phase Voltages and Wide AC Input Frequency

In wide ac input frequency applications, such as more electric aircraft, ac input frequency of the three-phase buck rectifier varies in the range of 360–800 Hz. In this article, a reconstructed phase voltages based power following control for the three-phase buck rectifier under unbalanced input phase voltages in wide ac input frequency application is proposed. The input phase voltages are reconstructed to get more balanced modulation signals compared with the input phase voltages. The input currents are controlled to be in proportion to the reconstructed phase voltages to mitigate the imbalance of the input currents. The control strategy is simple and easy to be realized in digital. The analysis and design of the proposed control strategy and digital implementation are illustrated. An experimental prototype with 1.5 kW is built. The experimental results show that the sinusoidal input currents can be obtained when input phase voltages are unbalanced in wide ac input frequency application.

A Mixed Calibration Method of Time-to-Digital Converter for LiDAR Applications

This brief presents a mixed calibration method of time-to-digital converter (TDC) for Light Detection and Ranging (LiDAR) applications, which is primarily implemented by a feedback loop consisting of VCRO-based TDC, double-digital-to-analog converter (DDAC), encoder, sampling circuit, LSB-first algorithm (LSBFA) block, and analog buffer. Based on the external input frequency control code (FCC), the method automatically adjusts the DDAC output to control TDC. To ensure that the DDAC output meets the accuracy requirements, a voltage coverage strategy is proposed, which is implemented by an external code controlling the R-2R array. Furthermore, after the chip operation is stable, a voltage trimming approach is presented to avoid introducing drastic switching activity, which is implemented using an error comparator and an LSBFA block. The peak-to-peak INL and DNL of TDC are 1.81 LSB and 0.44 LSB, respectively.

Nonlinear response of laminar premixed flames to dual-input harmonic disturbances

In gas turbines, aero-engines and rocket engines, flames are always disturbed by perturbations of dual or multiple harmonic frequencies, resulting in corresponding combustion instability. This paper analyses the nonlinear response of laminar premixed flames to dual-input harmonic disturbances to further understand those associated combustion instability. Nonlinear results of flame dynamics were derived from analytical and numerical solutions of the G-equation. The spatial front-tracking of premixed flames was obtained, where types of nonlinear behaviors were classified and related mechanisms of that were elucidated. A dual-input flame description function (DIFDF) was proposed to separately determine global nonlinearities of flame responses of fundamental and higher harmonics frequencies under dual-input disturbances. The fundamental frequency response consists of linear and nonlinear components, and the higher harmonic frequency one is purely nonlinear. The DIFDF properties of conical and "V" flames were compared, with particular emphasis on their differences in nonlinear behavior. The spatial and global effects of the second input frequency on the flame kinematics perturbed by the first frequency were also clarified. Furthermore, the roles of perturbation amplitude and flame height in spatial flame dynamics and DIFDF were quantified.