Pulse Width Of Signal Research Articles

A highly survivable X‐band low noise amplifier based on GaN HEMT technology and impact of pulse width on recovery time

AbstractGaN high electron mobility transistor (HEMT)‐based low noise amplifiers (LNAs) are an integral part of microwave receiver systems to enhance signal‐to‐noise ratio (SNR). The noise of LNA itself becomes critical for systems requiring high SNR, such as imaging and satellite communication systems. This paper discusses the design of a three‐stage LNA operating at the X‐band in the frequency range of 8.0–12.0 GHz. The amplifier's design and small signal, noise, and linearity characterizations are discussed. Stagewise analysis for gain, noise figure (NF), and matching network losses at the design stage results in achieving promising results. The proposed LNA provides a gain of 23.2 dB with dB gain ripple. Its NF is below 1.5 dB, output power at 1 dB gain compression is 16.4 dBm, and third‐order intercept point is 24.7 dBm at 10 GHz. LNA's survivability is validated to input stress as high as 42 dBm. This LNA is the best reported NF and survivability combination in the 8.0–12.0‐GHz frequency range. The reverse recovery time of LNA is measured under two different pulse conditions, and it has been shown that LNA has better recovery times for lower pulse width signals. This LNA finds its applications in radars and satellite communication systems.

Modelling of long-wave mid-infrared ultrashort pulse generation via difference frequency generation.

In this paper, a model of generating mid-infrared (MIR) ultrashort laser pulse through difference frequency generation (DFG) is established. The pulse evolution relationship among the pump, signal, and idler pulses during the DFG process, as well as the effects of crystal length, pulse energy of the pump and signal lights, pulse width, and other factors on the characteristics of the MIR pulse are explored. Furthermore, through simulations from the time domain to the frequency domain, the spectral characteristics and angular distribution of MIR were analyzed. DFG experimental data are also presented to support the model.

Optimization of fast output from SiPM array for pulse shape discrimination techniques at high counting rates

Plastic scintillators with pulse shape discrimination (PSD) capability, when combined with silicon photo-multipliers (SiPMs), enable the development of compact neutron detectors with lower power consumption and insensitivity to magnetic fields. However, the SiPM array has a significantly large pulse width of the output signal, which leads to discrimination difficulties at high counting rates. There are two outputs of a SiPM array: a standard output for energy measurement and a fast output for timing measurement. The pulse width of the standard output signal is in the range of hundreds nanoseconds, while the pulse width of the other one is in the range of tens nanoseconds. Fast output signals have traditionally been considered suitably for fast timing, however utilizing them for PSD has been little explored. In our previous work, we successfully implemented PSD by using fast output signals from a SiPM. Despite the obvious negative overshoot in fast signals, we achieved PSD of fast signals by using longer sampling times. However, this approach was still limited at high counting rates. This study proposes a compensation network for fast output signals, which is composed of a compensation unit consisting of a resistor and a capacitor. This design effectively compensates the overshoot of the fast output and shortens the pulse width from 60 ns to 44 ns. Additionally, it highlights the frequency amplitude differences between the neutron and gamma signals from fast output in the high-frequency component, thus improving the PSD capability of the fast output.

A three-dimensional coupled structure triboelectric nanogenerator for vertical and horizontal mechanical energy harvesting and fitness gait monitoring

Recently, the self-powered monitoring device used for wearable sensors has attracted attention from various industries. It is worth noting that previous self-powered sensors were mostly focused on unidirectional sensing and monitoring, and few sensors can achieve both longitudinal and transverse sensing functions simultaneously. Here, we designed an arched and stacked coupling structure triboelectric nanogenerator (AS-TENG) to harvest horizontal and vertical mechanical energy. Meanwhile, the AS-TENG can simultaneously achieve sensing effects on longitudinal pressure and transverse pulling force. According to the results, the pulling force sensing sensitivity of AS-TENG can reach 2.415 V N−1, and the pressure sensing sensitivity of AS-TENG can arrive at 2.78 V N−1. Furthermore, under longitudinal 6 Hz mechanical motion excitation, the open-circuit voltage (Voc) and short circuit current (Isc) of AS-TENG can reach 28.21 μA and 173.25 V, respectively. The transfer charge (Qsc) of AS-TENG can arrive at 169.7 nC. The AS-TENG can achieve a maximum output power of 2.02 mW at a 3 MΩ load. Moreover, the sensing signal pulse width of AS-TENG can reach 180 ms, which is higher than the traditional arch structure’s 110 ms, indicating the unique advantages of AS-TENG in future fitness monitoring. This study provides a 3D triboelectric multi-directional sensor that will serve the fields of intelligent wearable fitness and sports.

An optimal self-heating strategy for lithium-ion batteries with pulse-width modulated self-heater

Battery self-heating technology has emerged as a promising approach to enhance the power supply capability of lithium-ion batteries at low temperatures. However, in existing studies, the design of the heater circuit and the heating algorithm are typically considered separately, which compromises the heating performance. In this paper, an optimal self-heating strategy is proposed for lithium-ion batteries with a pulse-width modulated self-heater. The heating current could be precisely controlled by the pulse width signal, without requiring any modifications to the electrical characteristics of the topology. Meanwhile, the heating process is further optimized with a particle swarm optimization algorithm to balance the heating time and energy efficiency. The effectiveness of the proposed heating strategy is validated on the designed self-heater. Experimental results show that the proposed heating strategy can effectively shorten the heating time by at least 12.5% and improve energy efficiency by more than 3.4% when compared with existing heating strategies. Moreover, no obvious capacity fade is observed after 500 repeated heating processes.

Widely tunable NCPM-KTA OPO based on non-collinear phase-matching in a four-mirror ring cavity.

Based on non-collinear phase-matching (PM), a new method for widely tunable wavelength was proposed and demonstrated in a four-mirror ring cavity of non-critical phase-matching (NCPM) KTiOAsO4 (KTA) optical parametric oscillator (OPO). Wavelength tuning range of 141 nm from 1535.56 nm to 1676.73 nm was achieved by moving one mirror of ring cavity back and forth. The tuning theory and tuning method of non-collinear PM were analyzed in detail. The output energy and pulse width of signal were measured and compared in collinear and non-collinear PM condition. This method is also applicable to OPOs of other nonlinear crystals based on four-mirror ring cavity.

Research on the Coupling Effect of HIRF on UAV

The electromagnetic environment of low-altitude airspace has become extremely complex due to the rapid advancement of radio technology. In particular, the electromagnetic energy of HIRF (High Intensity Radiation Field) that is frequently emitted by radar, radio stations, radios, and various ships/airborne impacts negatively aircraft flight safety. In this paper, based on the modeling of a consumer UAV, the HIRF effect is simulated using UWB-HPM, and the electric field variation law at key position and antenna coupling law of the UAV under plane wave irradiation in different directions are analyzed with the help of CST simulation software. The results show that for front-door coupling, the shorter the pulse width of the interference signal is, the stronger the interference for the antenna is, while for back-door coupling, irritation direction and pulse width play a significant role in the coupling effect.

Experimental Study of High Power Microwave Injection in Radar Receiving Front-end

In order to study the tolerance threshold and damage process of radar receiving front end against high power microwave pulse attack, the relationship between the damage of receiving front end and injected signal power, pulse width, and duration was obtained by injection test. The experimental results show that the damage of PIN limiter by high power microwave is a slow worsening process near the damage threshold. Based on the test results, the radar withstanding range of high-power microwave weapon attack is calculated theoretically, which can provide theoretical support for the radar receiving front-end design.

On-chip all-optical second-order ordinary differential equation solver based on a single microdisk resonator.

This paper proposes an all-optical second-order ordinary differential equation (SODE) solver based on a single microdisk resonator. We validate the feasibility of our structure for constant and complex coefficient SODE solutions for Gaussian and super-Gaussian pulses. The results demonstrate a good agreement between the solutions obtained with the designed structure and those obtained through mathematical calculations for both constant and complex coefficient SODEs. We also discuss the influence of input optical signal pulse width on solution result deviations. Furthermore, we validate the capability of the designed structure to achieve tunable solutions for complex-coefficient SODEs with a tuning power of less than 10 mW. The device footprint is approximately 20×30 μm2, and it is 3-4 times smaller than the current smallest solving unit. The maximum Q-factor reaches 9.8×104. The proposed device avoids the traditional approach of cascading two resonators for SODE solving. Moreover, achieving mode alignment within the same resonator reduces the process challenges associated with aligning multiple devices in a cascade. Furthermore, it offers wider applicability for solving SODEs, namely, the ability to solve both constant and complex coefficient SODEs with complete derivative terms.

Numerical Research on the Effects of Process Parameters on Microdroplet Jetting Characteristics by Piezoelectric Printhead

The precision and consistency of the microdroplet jetting procedure are crucial for the casting sand mold’s performance during binder injection. The generation and jetting of microdroplets in piezoelectric printheads were examined in this study in relation to changes in specific jetting process parameters. Using finite element analysis and a simplified physical model of a microdroplet jetting device, an electromechanically coupled model of a microdroplet jetting device was created in order to study the characteristics of microdroplet jetting. A volume-of-fluid model was also created in order to study the microdroplet jetting process and perform repeatability tests. The effects of altering nozzle radius, actuation pulse width, intake velocity, and fluid viscosity on microdroplet jetting properties were then investigated using the models. We were able to control the development of satellite droplets thanks to the knowledge we gained about how each process parameter affected droplet status. This study demonstrates how the radius of the nozzle and the pulse width of the piezoelectric actuation signal have a significant impact on the jetting properties of piezoelectric printheads and the production of microdroplets. The quantitative correlations between process factors and jetting characteristics can be used to optimize microdroplet production and reduce droplet size. Finally, this study will help create control systems for microdroplet jetting operations and enhance the precision of 3D printed casting sand molds.

An Inverse Class-E Power Amplifier for Ultrasound Transducer.

An inverse Class-E power amplifier was designed for an ultrasound transducer. The proposed inverse Class-E power amplifier can be useful because of the low series inductance values used in the output matching network that helps to reduce signal distortions. Therefore, a newly designed Class-E power amplifier can obtain a proper echo signal quality. The measured output voltage, voltage gain, voltage gain difference, and power efficiency were 50.1 V, 22.871 dB, 0.932 dB, and 55.342%, respectively. This low voltage difference and relatively high efficiency could verify the capability of the ultrasound transducer. The pulse-echo response experiment using an ultrasound transducer was performed to verify the capability of the proposed inverse Class-E power amplifier. The obtained echo signal amplitude and pulse width were 6.01 mVp-p and 0.81 μs, respectively. The -6 dB bandwidth and center frequencies of the echo signal were 27.25 and 9.82 MHz, respectively. Consequently, the designed Class-E power amplifier did not significantly alter the performance of the center frequency of the ultrasound transducer; therefore, it could be employed particularly in certain ultrasound applications that require high linearity and reasonable power efficiency.

Research on the characteristics of micro planar capacitance sensor for multi wear particle detection

Wear particles are rich in information about the running state of mechanical equipment. Identifying wear particles is of great importance for monitoring and maintaining the safety and reliability of mechanical equipment. This paper investigated the characteristics of the micro planar capacitance sensor used for wear particle detection. The structural parameters of the micro planar capacitance sensor were optimized through finite element numerical simulation. The influences of excitation frequency and particle velocity on the sensor characteristics were studied through different experiments. The results show that when the excitation frequency is 1.8 MHz, and the particle velocity is 4 mm/s, the sensor has higher sensitivity for particle recognition. The relationship between the sensor signal pulse width and particle velocity is a power function. The sensor can distinguish and detect various metal and non-metallic particulate pollutants and recognize 78 μm iron particles and 165 μm copper particles. This study provides a new method for wear condition monitoring.

Research on the detection of silica/phenolic composite surface cracks using instantaneous high-power xenon lamp-induced chirp-pulsed radar thermography

In this present study, the high-power instantaneous xenon lamp-induced chirp-pulsed radar thermography was introduced to detect the surface crack of the silicon/phenolic composite which was widely used in the engine nozzle insulation sleeve. Two crack defect specimens were artificially made and detected by chirp-pulsed radar thermography to verify the detection ability of this approach. The cracks of two specimens were made by the diamond scribing process and laser ablation respectively. The differences between them were analyzed by the crack defect detection experiment. The crack defect made by the diamond scratching method is more consistent with the real situation according to the experimental results. The chirp-pulsed radar signal was extracted by the time/frequency signal extraction algorithms [cross-correlation (CC) and dual-orthogonal demodulation algorithms (DOD)]. The influence of parameters such as the power of xenon lamps, excitation frequency, reference pulse width or pulse time, and reference signal delay time on the detection results is mainly investigated by quantitative detection experiments. The results demonstrated that the CC peak and DOD amplitude are more sensitive than the phase when detected the surface crack of silica/phenolic composites. Meanwhile, the reflective phenomenon of the specimen’s surface has a great impact on the detection results. The larger the excitation parameters (such as the excitation frequency and the signal pulse width), the larger the contrast of the crack defect and the smaller the signal-to-noise ratio (SNR). The delay time of the reference signal has a small impact on the SNR and contrast of crack detection. In summary, instantaneous high-power xenon lamp-induced chirp-pulsed radar thermography can realize the reliable quantitative detection of surface cracks of silicon/phenolic composite.

A novel experimental procedure for lock-in thermography on solar cells

<abstract> <p>The occurrence of defects in solar cells is intrinsically related to a reduction in the efficiency and reliability of these devices. Therefore, monitoring techniques, such as lock-in thermography, electroluminescence and the I-V characteristic curve are adopted in order to evaluate the integrity of the solar cells. In the present work, a novel experimental procedure for the lock-in thermography of solar cells is proposed, aiming to improve the detection capability of the assay. Conventional techniques use pulse width modulation to operate the cell at a fixed point on the I-V curve. Instead, we propose a methodology based on a sinusoidal electric current excitation in order to extend the range of operational points that are close to the maximum power point as the cell operates in the field. Some traditional image processing techniques (principal component analysis, the fast Fourier transform and the four-step phase-shifting method) have been used to analyze the thermal images captured by an infrared camera during steady-state operation mode of the solar cells using both sinusoidal electric current signal and standard pulse width modulation procedures. Comparison between the results of both procedures found that this novel approach provides smoother and clearer delimitation of the defects. Furthermore, the contrast of the phase images was found to exhibit significant changes between the defective and non-defective regions for different modulation frequencies and types of defects. From the achieved results, it was possible to obtain a satisfactory characterization of the existing defects.</p> </abstract>

Broadband one-dimensional range profiles characteristic of rough surface in terahertz band

<sec>The one-dimensional (1D) range profile is an important back scattering characteristic of objective, which reveals the longitudinal distribution of radar cross section (RCS) along the detection beam. Since the shape and posture can be reflected by the 1D range profile, it is of great significance in military to determine the target orientation, velocity and whether it is armed. In this paper, broadband terahertz 1D-range-profile measurement system is built based on the time-domain spectroscopy (TDS) system. It is in bistatic configuration (bistatic angle of 9°) and the signal-to-noise ratio (SNR) is 34.5 dB, with a gold mirror used as a reflector. Benefiting from the ultrashort terahertz pulse width (full pulse width of 0.52 ps), the bandwidth covers the frequency range from 0.1 THz to 2.5 THz (peaked at 0.9 THz), corresponding to the range resolution on a submillimeter scale.</sec><sec>Firstly, the 1D range profiles of several objects in different shapes are measured, including the step, cylinder, step cone and their combination, which indicates that the geometric profile of the target in the detection direction is adequate to identify the shape feature of the target and proves the reliability of the 1D range profile measuring system based on TDS. Secondly, aluminum plates with different surface roughness in a range of 0–25 μm are also characterized. The Kirchhoff approximation theory and small perturbation method (SPM) are introduced to illustrate the characteristics of broadband terahertz 1D range profile related to the surface roughness of target. It is found that the scattering characteristic of metal object in the terahertz range is sensitive to surface roughness. If the surface roughness of the object is larger, the peak intensity of the 1D range profile will be weaker and the echo signal pulse width becomes wider. The rule is also applicable for the cases with different incident angles. Furthermore, it is revealed that the time delay of the 1D range profile in the bistatic system is related to the rotation direction of the target, which is useful in estimating the posture of the target. In summary, the characteristics of 1D range profile for metal objects relating to shape, surface roughness and posture are studied. The conclusions have certain guiding significance for the target detection and recognition of terahertz radar.</sec>

Development of a Highly Sensitive and Low Hysteresis Temperature Sensing System With PEDOT:PSS Containing Polymer Sensing Membrane

In our study, we have designed and developed a side-polished optical fiber (SPOF) pulsewidth modulation (PWM)-based sensing system that can detect temperatures from 21 °C (room temperature) to 70 °C. According to the proposed SPOF PWM system, the received sensing signal pulsewidth changes if the optical fiber temperature sensing element (TSE) gets heat. The pulsewidth changes due to a change in the refractive index (RI) of the heat-sensitive polymer membrane of the SPOF TSE. We applied poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) as the primary temperature-sensitive sensing material to make the heat-sensitive polymer sensing membrane of the designed TSE. To the best of our knowledge, it is the first temperature sensing system/device where the optical sensing element uses PEDOT:PSS containing polymer sensing membrane and the optical PWM technique. The sensitivity and linearity of the designed TSE were approximately 960 ns/°C and 0.997, respectively. A microcontroller ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{C}$ </tex-math></inline-formula> ) and readily available electronic component-based light detection and signal processing unit were designed to process the received sensing signal. The proposed temperature sensing system has different features: low cost, susceptibility, excellent hysteresis response, good reproducibility, highly stable performance, and others. The proposed SPOF TSE offers first response and recovery times of approximately 2.59 and 3.14 s, respectively. Finally, in our study, we compared the sensing performance of the proposed TSE with other temperature sensors in terms of the temperature measurement range, linearity, and response/recovery time. We found that the overall sensing performance of the proposed TSE is better than the other temperature sensors.

Dynamic control of the mode-locked fiber laser using a GO/PS modulator.

This Letter proposes a novel, to the best of our knowledge, transistor-like optical fiber modulator composed of graphene oxide (GO) and polystyrene (PS) microspheres. Unlike previously proposed schemes based on waveguides or cavity enhancement, the proposed method can directly enhance the photoelectric interaction with the PS microspheres to form a light local field. The designed modulator exhibits a distinct optical transmission change (62.8%), with a power consumption of <10 nW. Such low power consumption enables electrically controllable fiber lasers to be switched in various operational regimes, including continuous wave (CW), Q switched mode-locked (QML), and mode-locked (ML). With this all-fiber modulator, the pulse width of the mode-locked signal can be compressed to 12.9 ps, and the corresponding repetition rate is 21.4 MHz.

Modeling returned signal of a satellite laser altimeter over an urban area.

Modeling the returned signal of a satellite laser altimeter is a significant theoretical foundation for understanding the topography of the Earth. According to the lidar equation and working principle of laser altimeter, we establish the mathematical expression of the urban target response waveform (TRW) by using a definite integral formation. The characteristic parameters of the TRW, including signal energy, time delay, pulse width, and skewness are deduced in detail. Based on the specifications of the global ecosystem dynamics investigation laser altimeter and the assumption that the target is considered a rectangular plane, we simulate the influences of the geometrical parameters of the target, including the region area, the center geolocation, and the surface slope, on the TRW patterns and the characteristic parameters. The simulation results show that the TRW would present left-skewed and right-skewed patterns, with the exception that the center geolocation is nearly coincident with the laser footprint center. Such skewed distributions make the time delay derived from the TRW time centroid inaccurate for representing the range between the laser altimeter and the target center. In addition, the TRW energy is positively proportional to the region area and the proximity of the center geolocation to the laser footprint center and attenuated by the cosine of the surface slope. The root-mean-square pulse width is principally determined by the tangent of the surface slope. The simulation results contribute to a better understanding of the relationship between the TRW pattern and the geometrical parameters of the illuminated target. In particular, the characteristic parameters of the TRW can provide the detailed references for developing the waveform processing algorithm and the inversion of the surface elevation, the slope, and the reflectance. The returned signal in this paper may facilitate the application of the satellite laser altimeter over an urban area.

Improved Locating Method for Local Defects in XLPE Cable Based on Broadband Impedance Spectrum

The crosslinked polyethylene (XLPE) cable safety is affected by environmental factors and artificial defects during operation. This work proposes an improved locating method based on broadband impedance spectrum (BIS) to locate local defects in XLPE cables. The calculation process of the algorithm has been analyzed. The selection of the incident Gaussian signal and the peak recognition method have been discussed, where the pulse width of the Gaussian signal was found to be determined primarily by the upper limit frequency of the traveling wave transmitting in the cable. The centroid and function fitting methods were established to reduce the peak recognition error caused by the test sampling rate. This work verified the accuracy of the algorithm through experiments. A vector network analyzer (VNA) was used to test the BIS of the cable. A 20 m-long cable containing abrasion and an inserted nail with different depths was measured in the BIS test. It was found that the abrasion and the nail could be located. The locating deviation of abrasion was within ±1%, and the centroid and function fitting methods could effectively reduce the locating deviation. The locating deviation was within ±1% when the depth of the nail inserted into the cable accounted for less than 50% of the insulation thickness. When the depth exceeded 75% of the insulation thickness, the deviation of each method was more significant, and the maximum absolute value of the deviation was 4%.

A miniature fluorescence microscope for multi-plane imaging

Miniature fluorescence microscopes are becoming an increasingly established tool to investigate neural circuits in freely moving animals. In this work we present a lightweight one-photon microscope capable of imaging at different focal depths. The focal plane can be changed dynamically by modulating the pulse width of the control signal to a variable focus liquid lens, which is synchronized to the image sensor to enable changing focal plane between frames. The system was tested by imaging GCaMP7f expressing neurons in the mouse medial prefrontal cortex (mPFC) in vivo during open field test. Results showed that with the proposed design it is possible to image neurons across an axial scan of ~ 60 μm, resulting in a ~ 40% increase of total neurons imaged compared to single plane imaging.