Signal Generation Process Research Articles

Generalizable and precise control based on equilibrium-point hypothesis for musculoskeletal robotic system

PurposeThe purpose of this study is realizing human-like motions and performance through musculoskeletal robots and brain-inspired controllers. Human-inspired robotic systems, owing to their potential advantages in terms of flexibility, robustness and generality, have been widely recognized as a promising direction of next-generation robots.Design/methodology/approachIn this paper, a deep forward neural network (DFNN) controller was proposed inspired by the neural mechanisms of equilibrium-point hypothesis (EPH) and musculoskeletal dynamics.FindingsFirst, the neural mechanism of EPH in human was analyzed, providing the basis for the control scheme of the proposed method. Second, the effectiveness of proposed method was verified by demonstrating that equilibrium states can be reached under the constant activation signals. Finally, the performance was quantified according to the experimental results.Originality/valueBased on the neural mechanism of EPH, a DFNN was crafted to simulate the process of activation signal generation in human motion control. Subsequently, a bio-inspired musculoskeletal robotic system was designed, and the high-precision target-reaching tasks were realized in human manner. The proposed methods provide a direction to realize the human-like motion in musculoskeletal robots.

A Modified Variable Power Angle Control for Unified Power Quality Conditioner in a Distorted Utility Source

The distorted supply voltage degrades the control performance of a unified power quality conditioner (UPQC). This problem causes incorrect calculations in the harmonic identification and reference signal generation processes. This paper proposes a modified harmonic identification of the UPQC. The reference compensating current calculation for the shunt active power filter (shunt APF) is developed using the sliding window with the Fourier analysis (SWFA) method. In addition, the variable power angle control (PAC) is applied to operate the reference signal generation of the series APF and the shunt APF of the UPQC. Under the distorted voltage and nonlinear load conditions, the proposed approach can provide accurate reference compensating signals and successfully share the load reactive power compensation between the shunt APF and the series APF. In this work, a three-phase, three-wire power system with linear and nonlinear loads was implemented. The proposed method was validated using the processor-in-the-loop technique on an eZdsp™ F28335 board and the MATLAB/Simulink program. The testing results indicated that SWFA has excellent filtering performance and enhances harmonic identification compared to the operation without any filter or with low pass filters (LPF). With the proposed approach, the percentage of total harmonic distortion of voltage and current could be maintained within the IEEE519-2022 standard, and the magnitude of the RMS voltage across the load was in the recommended range specified by ANSI C84.1-2016.

A mathematical model for simulating photoacoustic signal generation and propagation in biological tissues

Photoacoustic (PA) medical imaging is a crossbred technique relying on light-induced ultrasonic waves due to the PA effect phenomenon recorded primarily in 1880 by A. G. Bell. Numerical simulation, also known as in-silico, studies assist scientists in minimizing incorrect PA experiments in both in-vitro and in-vivo. Numerical modeling techniques help to achieve a fast simulation process in contrast to pure mathematics alone. However, if a suitable facilitated mathematical model can be established prior to applying numerical modeling, it will be of great interest to the whole numeric model. Numerous mathematical equations, theorems, and propositions have been proposed to model the whole PA signal generation and propagation process in biological media. However, most of them are complicated and difficult to be understood by researchers, especially beginners. That’s why this paper was introduced. Our paper aims to simplify the understanding of the generation and propagation process of biomedical PA waves. We have developed a facilitated mathematical model for the entire process. The introduced developed mathematical model is based on three steps: (1) pulsed laser stimulation, (2) light diffusion, and (3) PA stress wave generation and propagation. The developed mathematical model has been implemented utilizing COMSOL Multiphysics, which relies on the finite element method (FEM) numerical modeling principle. The in-silico time-dependent study's results confirmed that the proposed mathematical model is a simple, efficient, accurate, and quick starting point for researchers to simulate biomedical PA signals' generation and propagation process utilizing any suitable software such as COMSOL multiphysics.

Non-Intrusive Accelerometer-Based Sensing of Start-Of-Combustion in Compression-Ignition Engines

<div class="section abstract"><div class="htmlview paragraph">A non-intrusive sensing technique to determine start of combustion for mixing-controlled compression-ignition engines was developed based on an accelerometer mounted to the engine block of a 4-cylinder automotive turbo-diesel engine. The sensing approach is based on a physics-based conceptual model for the signal generation process that relates engine block acceleration to the time derivative of heat release rate. The frequency content of the acceleration and pressure signals was analyzed using the magnitude-squared coherence, and a suitable filtering technique for the acceleration signal was selected based on the result. A method to determine start of combustion (SOC) from the acceleration measurements is presented and validated. In-cylinder pressure (used to calculate heat release rate) and accelerometer data were collected on a 1.9-L compression-ignition direct-injection engine (Z19DTH) over a wide range of speeds (1000-3250 RPM) and loads (2-8 bar IMEP<sub>g</sub>), for single- and double-injection strategies, and for fuels of several different cetane numbers (35.5 and 48.5). The relationship between engine block acceleration and the time derivative of heat release rate was verified using the experimental results and indicates that unsteadiness in the rate of heat release is the driving factor for the engine block acceleration signal. The accelerometer-based method developed allows detection of SOC for the main injection with a root mean square error less than 0.75 CAD for the range of conditions tested in this work.</div></div>

Biased learning under ambiguous information

This paper proposes a model of how biased individuals update beliefs in the presence of informational ambiguity. Individuals are ambiguous about the actual signal-generating process and interpret signals according to the model that can best support their biases. This paper provides a complete characterization of the limit beliefs under this rule. The presence of model ambiguity has the following effects. First, it destroys correct learning even if infinitely many informative signals can be observed. When the ambiguity is sufficiently high, individuals can justify their biases, leading to belief extremism and polarization. Second, an ambiguous individual can exhibit greater confidence than a Bayesian individual with any feasible model perception. This phenomenon comes from a novel complementary effect of different models in the belief set.

Proton-Induced Thermoacoustic Process as Linear-Time-Invariant System

This article presents a cross-domain model that defines and sets the acoustic signal generation process due to the fast dose deposition induced by a proton beam penetrating an energy absorber. The proposed model reduces the complex iono-acoustic energy transformation process to a simple impulse-response of a linear-time-invariant (LTI) system and is validated by comparing LTI output simulation results (in both time and frequency domain) with experimental acoustic signals emitted by a physical proton beam at 20 MeV and 70–120-ns pulse time width. Thanks to the intrinsic simplicity of the system, it is possible to predict and estimate the effective acoustic power at the sensor and the resultant beam range measurement precision. More importantly, the information coming from LTI simulations provides well-defined methodologies that allow to increase acoustic signal amplitude from +3 up to +9 dB and to improve the measurement precision of the beam range localization (up to +/ − 0.3 mm versus +/ − 0.6 mm state of the art for 200-MeV energy and 75-mGy total dose).

RF Acquisition System Based on μTCA for Testing of High-Gradient Acceleration Cavities

The radio frequency (RF) laboratory hosted in the Corpuscular Physics Institute (IFIC) of the University of Valencia is designed to house a high-power and high-repetition-rate facility to test normal conduction RF accelerator cavities in the S-Band (2.9985 GHz) in order to perform R&D activities related to particle accelerator cavities. The system, which manages the entire process of RF signal generation, data acquisition and closed-loop control of the laboratory, is currently based on a modular and compact PXI platform system. This contribution details the development of a platform with similar features, but which is based on open architecture standards at both the hardware and software level. For this purpose, a complete system based on the μTCA platform has been developed. This new system must be able to work with accelerator cavities at other operating frequencies, such as 750 MHz, as well as to explore different options at firmware and software levels based on open-source codes.

Physical and MAC layer simulation of IEEE 802.15.4c protocol in transformer terminal unit

IEEE 802.15.4c protocol is suitable for large-scale process control applications with ultra-low complexity, low cost and low power consumption. It is particularly suitable for wireless communication standard used in TTU (transformer terminal unit). Based on the introduction of IEEE 802.15.4c protocol, the physical and MAC (media access control) layer simulation program of IEEE 802.15.4c protocol in TTU is written in MATLAB. In the program, the Gaussian noise with different SNRs (signal-to-noise ratios) is used to simulate noise of signal, and the spread spectrum O-QPSK (offset-quadrature phase shift keying) is used to modulate signal. Based on this, the process of signal generation, signal transmission and signal reception is simulated. The influences of SNR, threshold of sliding autocorrelation method and order of filter on BER (bit error rate) are investigated. The results reveal that the BER of simulation is significantly lower than the theoretical value, and the former is only about 2/5 of the latter when the SNR varies from -2 dB to 6 dB. The threshold of sliding autocorrelation method has a big influence on BER. The threshold corresponding to the minimum BER ranges from 0.4 to 0.6. The order of filter has little influence on BER.

Simulation of the physical process of neural electromagnetic signal generation based on a simple but functional bionic Na+ channel

The physical processes occurring at open Na+ channels in neural fibers are essential for the understanding of the nature of neural signals and the mechanism by which the signals are generated and transmitted along nerves. However, there is a less generally accepted description of these physical processes. We studied changes in the transmembrane ionic flux and the resulting two types of electromagnetic signals by simulating the Na+ transport across a bionic nanochannel model simplified from voltage-gated Na+ channels. The results show that the Na+ flux can reach a steady state in approximately 10 ns due to the dynamic equilibrium of the Na+ ion concentration difference between both sides of the membrane. After characterizing the spectrum and transmission of these two electromagnetic signals, the low-frequency transmembrane electric field is regarded as the physical quantity transmitting in the waveguide-like lipid dielectric layer and triggering the neighboring voltage-gated channels. Factors influencing the Na+ flux transport are also studied. The impact of the Na+ concentration gradient is found to be higher than that of the initial transmembrane potential on the Na+ transport rate, and introducing the surface-negative charge in the upper third channel could increase the transmembrane Na+ current. This work can be further studied by improving the simulation model; however, the current work helps to better understand the electrical functions of voltage-gated ion channels in neural systems.

Fronto-occipital mismatch responses in pre-attentive detection of visual changes: Implication on a generic brain network underlying Mismatch Negativity (MMN)

Current theories of pre-attentive change detection suggest a regularity or prediction violation mechanism involving a frontotemporal network. Modulations of the early inferior frontal cortex (IFC) mismatch response representing the effort in comparing a stimulus to the prediction, the superior temporal cortex (STC) response indicating deviance detection, and the late IFC response representing prediction model updating were consistently demonstrated in auditory change detection using event-related optical signal (EROS). If the prediction violation hypothesis is universal, a generic neural mechanism should be found in all sensory modalities. We postulated a generic fronto-sensory cortical network underlying the prediction violation mechanism: the IFC is responsible for non-modality-specific prediction processes while the sensory cortices are responsible for modality-specific error signal generation process. This study examined the involvement of the IFC-occipital cortex (OC) network in visual pre-attentive change detection. The EROS mismatch responses to deviant bar arrays violating a fixed orientation regularity (low in regularity abstractness) were compared to that of deviant violating a rotational orientation regularity (high in abstractness) while the information available for establishing the prediction model was manipulated by varying the number of standards preceding the deviants. Modulations of the IFCOC mismatch response patterns by abstractness and train length reflected the processing demands on the prediction processes and were similar to that of the IFC-STC network in auditory change detection. These findings demonstrated that the fronto-sensory cortical network is not unique to auditory pre-attentive change detection and provided supports for a universal neural mechanism across sensory modalities as suggested by the prediction violation hypothesis.

Characterization of Vegard strain related to exceptionally fast Cu-chemical diffusion in Cu_2Mo_6S_8 by an advanced electrochemical strain microscopy method

Electrochemical strain microscopy (ESM) has been developed with the aim of measuring Vegard strains in mixed ionic-electronic conductors (MIECs), such as electrode materials for Li-ion batteries, caused by local changes in the chemical composition. In this technique, a voltage-biased AFM tip is used in contact resonance mode. However, extracting quantitative strain information from ESM experiments is highly challenging due to the complexity of the signal generation process. In particular, electrostatic interactions between tip and sample contribute significantly to the measured ESM signals, and the separation of Vegard strain-induced signal contributions from electrostatically induced signal contributions is by no means a trivial task. Recently, we have published a compensation method for eliminating frequency-independent electrostatic contributions in ESM measurements. Here, we demonstrate the potential of this method for detecting Vegard strain in MIECs by choosing Cu_2Mo_6S_8 as a model-type MIEC with an exceptionally high Cu chemical diffusion coefficient. Even for this material, Vegard strains are only measurable around and above room-temperature and with proper elimination of electrostatics. The analyis of the measured Vegards strains gives strong indication that due to a high charge transfer resistance at the tip/interface, the local Cu concentration variations are much smaller than predicted by the local Nernst equation. This suggests that charge transfer resistances have to be analyzed in more detail in future ESM studies.

Selection Method of Modulation Index and Frequency ratio for Getting the SPWM Minimum Harmonic of Single Phase Inverter

Harmonic content is an important parameter in relation to the power generated by inverter. In power conversion technology of inverter, sinusoidal pulse width modulation (SPWM) is the most popular used by many researchers. The advantages of SPWM inverter operation as a conversion technique compared to other inverter types can be seen from the low harmonic distortion in the output voltage of inverter. Therefore, the SPWM signal generation process becomes a determining factor for the performance of the overall system. This paper present the method for selecting the modulation index (ma) and frequency ratio (mf) using Cubic Spline Interpolation to get minimum harmonic of SPWM inverter that generated. Both parameters controlled with varied values digitally using microcontroller to generate SPWM, then the output of inverter with and without LC filter was investigated. The results show that the use of Cubic Spline Interpolation method in the selection of ma and mf precisely managed to produce SPWM inverter with minimum harmonic content. At the inverter output, the use of LC filter is not only useful for converting SPWM signals to sinusoidal waveforms but can also reduce harmonic content significantly less than 3 %.

Measurement and Evaluation of Electric Signal Transmission Through Human Body by Channel Modeling, System Design, and Implementation

Human body communications (HBCs), employing the human body as a signal transmission medium, can provide efficient and intuitive methods to form a network in the body. This article presents a comprehensive study for a highly reliable HBC system, including body channel modeling, transceiver design, and performance evaluation through implementation, in consideration of practical sensor network environments for wearable and implantable devices applicable to healthcare and biosignal acquisition. Body channel characteristics based on capacitive couplings, such as root mean square delay spread and mean path gain (MPG), were explored by measuring the body impulse responses under 12 experimental conditions, determined by the variation in body postures and device locations between the wrist and positions assumed under the scalp through a customized experimental setup with micropig-derived biomembranes (MBMs) used for wrapping the devices to emulate an implantable environment. The proposed transceiver design for digital transmission, including a preamble structure and signal modulation method supporting a maximum data rate of 1 Mb/s, was verified through the performance evaluations conducted for examining the frame detection probability and bit error rate (BER) in the body channel model at multiple operating frequencies of 32, 42, and 64 MHz. The proposed system reliability was demonstrated by the achievement of a BER of below <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${4.7\,\times \, }{10}^{-8}$ </tex-math></inline-formula> through battery-powered implemented devices with dimensions of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${30\times 30 }\,\,{\text {mm}}^{2}$ </tex-math></inline-formula> , comprising a digital signal processing module (DSPM) for signal generation and detection processes, and an analog front-end module (AFEM) for recovering the received signal from signal deterioration by severe path loss and time-dispersive effect in the body channel.

Analysis of laser focusing effect on quantification of LII images

Laser-induced incandescence (LII) is a widely used technique for measuring soot concentrations. For flame applications LII is frequently deployed as a planar diagnostic to measure the two-dimensional soot field. However, when the laser sheet is focused, as is typical to reach the requisite laser fluence level and achieve good spatial resolution, the complex laser power dependence of the LII signal generation process can introduce a large variation in LII signal sensitivity across an LII image. In this work, this effect is quantified for the first time as a function of laser pulse fluence, using a typical planar LII excitation scheme with a clipped Gaussian YAG laser beam focused with a 1 m focal length lens. Furthermore, the cross-sectional energy distribution in the laser sheet was measured across the image plane, to relate the details of the laser sheet focal properties with the resultant LII behavior. The results show that a unique laser fluence level (referenced to the focal plane) exists whereby there is essentially no dependence of LII signal on position relative to the focal plane. However, at lower or higher fluences, the radial signals either decrease (low fluence) or increase (high fluence) rapidly with increasing distance away from the focal point. For measurements using an LII ‘plateau’ laser fluence level, as is usual in environments with significant optical depth (i.e. sufficiently strong soot levels), the LII signals are found to be 2.5X larger 40 mm away from the focal point. An analysis conducted by combining a previously measured LII fluence dependence for a top-hat laser profile with the laser sheet cross-sections measured in this work shows general agreement with the measured results for LII signal variation. Further, the sensitivity of LII signals at high fluences to the laser beam spatial profile, particularly away from the sheet focus, is highlighted.

Receiver Operating Characteristics for a Prototype Quantum Two-Mode Squeezing Radar

We have built and evaluated a prototype quantum radar, which we call a quantum two-mode squeezing radar (QTMS radar), in the laboratory. It operates solely at microwave frequencies; there is no downconversion from optical frequencies. Because the signal generation process relies on quantum mechanical principles, the system is considered to contain a quantum-enhanced radar transmitter. This transmitter generates a pair of entangled microwave signals and transmits one of them through free space, where the signal is measured using a simple and rudimentary receiver. At the heart of the transmitter is a device called a Josephson parametric amplifier (JPA), which generates a pair of entangled signals called two-mode squeezed vacuum (TMSV) at 6.1445 GHz and 7.5376 GHz. These are then sent through a chain of amplifiers. The 7.5376 GHz beam passes through 0.5 m of free space; the 6.1445 GHz signal is measured directly after amplification. The two measurement results are correlated in order to distinguish signal from noise. We compare our QTMS radar to a classical radar setup using conventional components, which we call a two-mode noise radar (TMN radar), and find that there is a significant gain when both systems broadcast signals at -82 dBm. This is shown via a comparison of receiver operator characteristic (ROC) curves. In particular, we find that the quantum radar requires 8 times fewer integrated samples compared to its classical counterpart to achieve the same performance.

Comprehensive Spectral Analysis of PWM Waveforms With Compensated DC-Link Oscillations

In the available literature, including reference books on the topic, the spectral analysis of voltage waveforms obtained through the use of pulse width modulation (PWM) relies on the assumption of an ideally flat voltage across the dc-link of a considered switching structure. Nevertheless, certain converter families (e.g., modular multilevel converter, characterized by the presence of distributed and floating dc-links), feature low-frequency oscillations of dc voltage within their switching stages. On these terms, the flat dc-link assumption cannot be considered valid from both theoretical and practical viewpoints. In case carrier-based modulation is employed, unless properly compensated through the modulation signal adjustments, the above mentioned voltage oscillations cause undesirable distortion of the converter currents. However, the very same adjustments of modulation signals introduce additional challenges in the spectral analysis of the voltage across the ac terminals of an observed switching stage. This article provides the ac terminals voltage analysis of a single half-bridge experiencing dc-link oscillations, which are compensated through the modulation signal generation process. PWM with the conventional triangular carrier is considered, while all the results are presented in a generalized form, making them easily extendable to cascaded structures. All of the presented results were experimentally validated.

Evaluation of a hybrid direct-indirect active matrix flat-panel imager using Monte Carlo simulation.

Purpose: Monte Carlo simulations were used to evaluate the imaging properties of a composite direct-indirect active matrix flat-panel imager (AMFPI) with potentially more favorable tradeoffs between x-ray quantum efficiency and spatial resolution than direct or indirect AMFPIs alone. This configuration, referred to as a hybrid AMFPI, comprises a scintillator that is optically coupled to an a-Se direct AMFPI through a transparent electrode and hole blocking layer, such that a-Se acts as both a direct x-ray converter and an optical sensor. Approach: GEANT4 was used to simulate x-ray energy deposition, optical transport, and charge signal generation processes in various hybrid AMPFI configurations under RQA5 and RQA9 x-ray beam conditions. The Fujita-Lubberts-Swank method was used to quantify the impact of irradiation geometry, x-ray converter thicknesses, conversion gain of each layer, and x-ray cross talk between layers on detective quantum efficiency (DQE). Results: Each hybrid configuration had a greater DQE than its direct AMFPI layer alone. The DQE improvement was largest at low spatial frequencies in both front- and back-irradiation (BI) geometries due to increased x-ray quantum efficiency provided by the scintillator. DQE improvements persisted at higher frequencies in BI geometry due to preferential x-ray absorption in a-Se. Matching the x-ray-to-charge conversion gains of a hybrid AMFPI's direct and indirect detection layers affects its Swank factor and, thus, DQE(0). X-ray cross talk has a negligible impact on the of hybrid AMFPIs with sufficiently high optical quantum efficiency. Conclusion: An optimized hybrid AMFPI can achieve greater DQE performance than current direct or indirect AMFPIs.

Identification parameter system for mathematical modeling BLDC motor using transfer function models

The parameter system identification of Brushless Direct Current (BLDC) motorbike on electric bicycles is one of the important factors that support success in improving a stable and reliable control system. The purpose of this paper is to explain the mathematical modeling of BLDC motors by system identification parameters. The method of system identification parameters used in this study is experimentation, namely the pulse width modulation (PWM) signal generation process and the collection of input data in the form of current, voltage, and output data such as speed is carried out using sensors connected to the microcontroller. The input and output data are then simulated using the transfer function model found in the system identification toolbox in the MATLAB program. From the results of testing and simulations carried out on the BLDC motor system, a mathematical model was obtained in the form of a transfer function with third-order transfer function is the best fit value than the others. The sequential values of the transfer function 1, 2 and 3 are 69.81, -1945, and 83.34.

Phase Imbalance Optimization in Interference Linear Displacement Sensor with Surface Gratings.

In interferential linear displacement sensors, accurate information about the position of the reading head is calculated out of a pair of quadrature (sine and cosine) signals. In double grating interference schemes, diffraction gratings combine the function of beam splitters and phase retardation devices. Specifically, the reference diffraction grating is located in the reading head and regulates the phase shifts in diffraction orders. Measurement diffraction grating moves along with the object and provides correspondence to the displacement coordinate. To stabilize the phase imbalance in the output quadrature signals of the sensor, we propose to calculate and optimize the parameters of these gratings, based not only on the energetic analysis, but along with phase relationships in diffraction orders. The optimization method is based on rigorous coupled-wave analysis simulation of the phase shifts of light in diffraction orders in the optical system. The phase properties of the reference diffraction grating in the interferential sensor are studied. It is confirmed that the possibility of quadrature modulation depends on parameters of static reference scale. The implemented optimization criteria are formulated in accordance with the signal generation process in the optical branch. Phase imbalance and amplification coefficients are derived from Heydemann elliptic correction and expressed through the diffraction efficiencies and phase retardations of the reference scale. The phase imbalance of the obtained quadrature signals is estimated in ellipticity correction terms depending on the uncertainties of influencing parameters.

Biased Learning under Model Uncertainty

This paper proposes a model of how biased individuals update beliefs in the presence of informational ambiguity. Individuals are ambiguous about the actual signal-generating process and interpret signals according to the model that can best support their biases. This paper provides a complete characterization of the limit beliefs under this rule. The presence of model ambiguity has the following effects. First, it destroys correct learning even if infinitely many informative signals can be observed. When the ambiguity is sufficiently high, individuals can justify their biases, leading to belief extremism and polarization. Second, an ambiguous individual can exhibit greater confidence than a Bayesian individual with any feasible model perception. This phenomenon comes from a novel complementary effect of different models in the belief set.