Sawtooth Waveform Research Articles

Periodic low-frequency electric field structures in a magnetized non-thermal auroral plasma

The theoretical explanation of electric field structures associated with density depletion in the Earth's upper ionosphere is presented. Using the quasi-neutrality hypothesis, the effect of excess energetic electron species is studied on the evolution of nonlinear low-frequency ion-cyclotron and ion-acoustic waves in a magnetized auroral plasma. The dynamics of the cold ion beam is governed by the fluid equations and the electron is treated as energetic species with non-thermal density distribution. Numerical computations appear in a series of periodic oscillations, such as spiky, sawtooth and sinusoidal waveforms. The present model can generate up to 18 mV/m electric field amplitude, which is in the range of the FREJA satellite measurements in the auroral acceleration region.

Simple and Flexible Photonic Microwave Waveform Generation With Low RMSE of Square Waveform

A simple and flexible photonics-assisted approach based on an integrated polarization-division multiplexing Mach–Zehnder modulator (PDM-MZM) and a balanced photodetector (BPD) to generating microwave waveform is proposed. The sub-MZMs of PDM-MZM are biased at peak and null points. Square and trapezoid waveforms are generated by controlling the PC and driven sinusoidal signal power. Triangle and sawtooth waveforms are also obtained with the help of a 90° microwave phase shifter (MPS). The proposed approach features simple structure, flexible frequency tunability, and easy implementation. Moreover, the problem of high root-mean-square error (RMSE) of square waveform is solved by this approach for the first time. An experiment is conducted to verify the approach. Different waveforms with the repetition rates of 3 and 5 GHz are generated. The RMSE of square waveform is reduced from 0.3328 to 0.2048 which is the lowest RMSE to the best of our knowledge.

Hardware implementation of single phase three-level cascaded h-bridge multilevel inverter using sinusoidal pulse width modulation

<span lang="EN-US">In this paper a hardware implementation of single-phase cascaded H-bridge three level multilevel inverter (MLI) using sinusoidal pulse width modulation (SPWM) is presented. There are a few interesting features of using this configuration, where less component count, less switching losses, and improved output voltage/current waveform. The output of power inverter consists of three form, that is, square wave, modified square wave and pure sine wave. The pure sine wave and modified square wave are more expensive than square wave. The focus paper is to generate a PWM signal which control the switching of MOSFET power semiconductor. The sine wave can be created by using the concept of Schmitt-Trigger oscillator and low-pass filter topology followed by half of the waveform will be eliminated by using the circuit of precision half-wave rectifier. Waveform was inverted with 180º by circuit of inverting op-amp amplifier in order to compare saw-tooth waveform. Two of PWM signal were produced by circuit of PWM and used digital inverter to invert the two PWM signal before this PWM signal will be passed to 2 MOSFET driver and a 3-level output waveform with 45 Hz was produced. As a conclusion, a 3-level output waveform is produced with output voltage and current recorded at 22.5 Vrms and 4.5 Arms. The value of measured resistance is 0.015 Ω that cause voltage drop around 0.043 V. Based on the result obtained, the power for designed inverter is around 100W and efficiency recorded at 75%.</span>

Indicators of Airway Secretion Weight in Mechanically Ventilated Subjects.

Clinicians may use adventitious breath sounds on lung auscultation and a "sawtooth" pattern on the ventilator expiratory flow waveform as indicators of the need for chest physiotherapy for airway-secretion clearance in mechanically ventilated patients. This study seeks to identify potential clinical and novel indicators of the weight of airway secretions cleared from a single session of chest physiotherapy in mechanically ventilated subjects. We recorded airway crackles using artificial airway acoustic sound monitoring and computerized lung-sound amplitude using artificial airway acoustic sound detection and compared them to standard clinical assessments in 71 mechanically ventilated subjects immediately prior to a single session of chest physiotherapy. Correlational analyses were undertaken between the weight of airway secretions obtained after the single session of chest physiotherapy as the dependent variable and novel assessments, clinical assessments, patient characteristics, and ventilator parameters as the independent variables. Multiple linear regression analyses were then used to determine the best model to predict the weight of airway secretions obtained from the single chest physiotherapy session. Data are reported as mean and median as appropriate. Significance was set at P < .05. 71 mechanically ventilated subjects were included for analysis. Statistically significant associations with the weight of airway secretions included the presence of a sawtooth waveform on expiration and the novel assessment of average airway crackles during inspiration. The best predictive model of the weight of airway secretions included the presence of the sawtooth waveform on expiration and ventilator tidal volume. Simple clinical assessments used in this study were able to independently predict the weight of airway secretions cleared during a single session of chest physiotherapy. The novel assessments used in this investigation did not add any further value.

Improving load capacity of stick-slip actuators in both driving directions via a shared driving foot

Stick-slip piezoelectric actautors are promising actautors with prinicipally unlimited stroke and positioning resolution. However, it is challenged with a low load capacity, which limits the field of application. Various types of compliant driving foot were proposed in literature to improve the load capacity but the improved load capacity is direction-dependent. To improve the load capacity in both forward and backward directions, this paper proposes an approach via a shared driving foot. The basic idea is to employ two piezoelectric actuators and a shared driving foot to work in a way that either forward or backward driving is a stick-slip process and both involve a clamping action during the ‘stick’ phase and a releasing action during the ‘slip’ phase, so that a large driving force/load capacity can be achieved in both driving directions. Following this approach, a shared driving foot was proposed and designed. Finite element simulations were carried out and have validated that the designed driving foot can realize the proposed approach as desired. A prototype was built and tested and the effectiveness of the proposed approach has been validated by experiments. Under the sawtooth waveform voltage of 100 V at 1 kHz, the prototype achieved a free-load forward and backward driving speed as large as 18.6 mm s−1 and 16 mm s−1 respectively and a load capacity larger than 2 kg for both driving directions. Under a driving load of 2 kg, it can still move stably with forward and backward driving speeds of 1.8 mm s−1 and 0.6 mm s−1 respectively.

Effect of power parameters on micro-discharge induced by corona discharge

This research mainly describes the generation and diagnosis of plasma using a wire-plate discharge device driven by different power supplies, aimed at investigating the effect of driving source parameters on micro-discharge induced by a corona. The influence of parameters such as waveform, duty ratio and bias voltage on discharge characteristics was explored preliminarily. Experiment results show that the determination of volt-ampere characteristics under different driving source waveforms indicates that the application of square and pulse waveforms shows great advantages over that of sawtooth and sinusoidal waveforms. Similarly, the photo-thermal effects of the system were investigated by comparing the high-voltage electrode temperature and relative emission intensity of N2 (C3Пu → B3Пg, 0–0, 337 nm), where square and pulse waveforms also achieved better performance. But the pulse waveform had a slight advantage over the square waveform in terms of energy conversion. Further, investigations of the duty ratio and bias voltage applied on the pulse waveform were conducted, and the results indicate that the duty ratio could effectively improve the discharge power and thermal effect to a certain extent; however, the application of bias voltage on the pulse signal had little influence on the discharge power and thermal effect.

Photonic microwave waveform generation based on dual-wavelength time domain synthesis technology

&lt;sec&gt;Microwave waveforms, such as square waveforms, sawtooth waveforms and triangle waveforms are widely used in radar communication, electronic measurement and medical imaging and so on. Using photonic microwave technology to generate arbitrary microwave waveforms has been a research hotspot.&lt;/sec&gt;&lt;sec&gt;In this paper, a photonic microwave waveform generation scheme based on dual-wavelength time domain synthesis is proposed and experimentally demonstrated. Used in this scheme mainly are two lasers, two single-drive Mach-Zehnder modulators, a wavelength division multiplexer and a tunable optical delay line. The two Mach-Zehnder modulators are respectively biased at different operating points. When two beams with different wavelengths are superimposed in the time domain, different microwave waveform outputs can be generated. Therefore, by adjusting the bias voltage and modulation depth of the modulator, the phase and amplitude of the modulated optical signal can be controlled, and finally the photonic microwave waveform is generated.&lt;/sec&gt;&lt;sec&gt;At first, the generation mechanism of square waveform, sawtooth waveform and triangle waveform are analyzed, and the comparisons among ideal square waveform, sawtooth waveform, triangle waveform and their third-order waveforms are made through the simulation analysis. It is verified that third-order waveforms become close to the ideal waveforms. Since the proposed scheme produces higher-order components, and the waveforms of the first three orders are the same as the ideal waveforms, so the scheme has good waveform generation capability. And then square waveform, sawtooth waveform and triangle waveform with a repetition rate of 2.5 GHz are successfully generated experimentally. Thus, experimental results are well consistent with the theoretical analyses. In addition, the system also has good tunable characteristics. By changing the modulation frequency of the modulator, the frequency tuning of the output photonic microwave waveforms can be realized, and square waveform, sawtooth waveform and triangular waveform with a repetition rate of 5 GHz are also experimentally achieved. The repetition rate of the generated microwave waveform is mainly limited by the bandwidth of modulator and electrophotonic detector, so the devices with higher bandwidth can be used to generate arbitrary waveform with a higher repetition rate. Therefore, the scheme has good application prospects.&lt;/sec&gt;

Influence of Vibration Waveform on MR Elastography

The purpose of this study was to investigate an influence of vibration waveform on magnetic resonance elastography (MRE). MRE is an innovative imaging technique for the non-invasive quantification of the elasticity of soft tissues through the direct visualization of propagating shear waves in vivo using a special phase-contrast magnetic resonance imaging sequence. Since the elasticity of soft tissue calculates from the wavelength of propagating shear waves, it is necessary to propagate sine-wave-shape shear wave at the target soft tissue. However, due to the various factors; i.e. overload of vibration generator, poor contact between imaging object and vibration pad, etc.; it may be difficult to generate a simple sine wave. This work was focused on change vibration waveforms; i.e. square wave, triangle wave, saw-tooth wave; which is induced by the various factors. Phantom experimental results demonstrated that when square and saw-tooth waveforms of 25 Hz vibration frequency, into the phantom, the waveform of propagating wave was not similar to sine waveform. It may influence on the MRE that in case of the waveforms has low frequency and square or saw-tooth like waveforms.

A Piezoelectric Stick-Slip Nanopositioning Stage With Ultra-High Load Capacity Realizing by Decoupling the Driving and Moving Units

The stick-slip piezoelectric stage plays an important role in micro-operation and industrial applications due to its nanometer resolution. However, under high load, the output performance of the piezoelectric stage will be seriously influenced. In order to overcome this limitation, this paper proposes a piezoelectric stick-slip nanopositioning stage with ultra-high load capacity by introducing the load unit to decouple the driving and moving units. A kinetic model of prototype is established to analyze the working process. And a series of experiments are carried out to explore the output performance of the prototype. The geometry of the prototype is 85 mm (Length)×50 mm (Width)×32 mm (Height), and the mass of it is 303 g. By using only one piezoelectric stack, this prototype can achieve load capacity more than 10 kg and driving capacity more than 47.62 [(mm/s)g/mW] in both directions. When there is free-load, under the sawtooth waveform of 100 V at 600 Hz, the velocity of the prototype can reach 4.75 mm/s and 4.86 mm/s in forward and backward directions respectively. Meanwhile, the forward and backward resolution of the prototype can attain 30 nm and 33 nm, respectively. When the load is 10 kg which is about 33 times larger than the weight of prototype, the velocity of the prototype is almost the same as the velocity under free-load.

Frequency diffraction management through arbitrary engineering of photonic band structures

It is of fundamental interest to control light diffraction in discrete optical systems. However, photon hopping in discrete systems is dominated by the nearest-neighbor coupling, limiting the realization of nonlocal diffraction phenomena. Here, we generalize the discrete diffraction from spatial to the frequency domain using optical phase modulators. By inducing long-rang couplings in the frequency lattice through periodic modulation signals, we find the lattice band structure can be artificially engineered, giving rise to the realization of arbitrary frequency diffraction. Particularly, we create linear, bilinear and semicircular band structures using sawtooth, triangular and semicircular modulation waveforms and realize the directional, bidirectional, omnidirectional frequency diffraction as well as the spectral "superlens". We also revisit frequency discrete Talbot effect and generalize the allowed incident period to arbitrary integers through band structure engineering. Moreover, as the frequency transition also carries a wave vector mismatch, an effective electric field will emerge, through which we can realize frequency Bloch oscillations that manifest the effects of arbitrary spectral routing and self-imaging. The study paves a promising way towards versatile spectrum management for both optical communications and signal processing.

Detection and Discrimination Thresholds for Haptic Gratings on Electrostatic Tactile Displays.

Designing algorithmsfor rendering haptic texture on electrostatic tactile displays requires a quantitative understanding of human perception. In this paper, we report detection and discrimination thresholds for haptic gratings rendered on such displays based on the waveform and amplitude of the applied voltage. The haptic gratings consist of functions that describe the variation in voltage amplitude as a function of the position of finger on the display. Four types of virtual haptic gratings are considered in two experiments. In Experiment I, we estimate the absolute detection thresholds of haptic gratings for four different voltage amplitude functions, consisting of spatial waveforms with sinusoidal, square, triangle, or sawtooth shape. In Experiment II, we report discrimination thresholds for haptic gratings at five reference values of the voltage amplitude (80, 120, 160, 200, and 240 Vpp) for each of the voltage amplitude functions used in Experiment I. The results indicate that the detection thresholds for the four virtual haptic gratings are between 30 and 36 Vpp, and that the JND increases with the increase of voltage amplitudes. In addition, the JNDs of the four virtual gratings differ significantly, with the lowest and highest values being given by the triangle and sawtooth waveform, respectively.

Sarcomeric Auto-Oscillations in Single Myofibrils From the Heart of Patients With Dilated Cardiomyopathy.

Left ventricular wall motion is depressed in patients with dilated cardiomyopathy (DCM). However, whether or not the depressed left ventricular wall motion is caused by impairment of sarcomere dynamics remains to be fully clarified. We analyzed the mechanical properties of single sarcomere dynamics during sarcomeric auto-oscillations (calcium spontaneous oscillatory contractions [Ca-SPOC]) that occurred at partial activation under the isometric condition in myofibrils from donor hearts and from patients with severe DCM (New York Heart Association classification III-IV). Ca-SPOC reproducibly occurred in the presence of 1 μmol/L free Ca2+ in both nonfailing and DCM myofibrils, and sarcomeres exhibited a saw-tooth waveform along single myofibrils composed of quick lengthening and slow shortening. The period of Ca-SPOC was longer in DCM myofibrils than in nonfailing myofibrils, in association with prolonged shortening time. Lengthening time was similar in both groups. Then, we performed Tn (troponin) exchange in myofibrils with a DCM-causing homozygous mutation (K36Q) in cTnI (cardiac TnI). On exchange with the Tn complex from healthy porcine ventricles, period, shortening time, and shortening velocity in cTnI-K36Q myofibrils became similar to those in Tn-reconstituted nonfailing myofibrils. Protein kinase A abbreviated period in both Tn-reconstituted nonfailing and cTnI-K36Q myofibrils, demonstrating acceleration of cross-bridge kinetics. Sarcomere dynamics was found to be depressed under loaded conditions in DCM myofibrils because of impairment of thick-thin filament sliding. Thus, microscopic analysis of Ca-SPOC in human cardiac myofibrils is beneficial to systematically unveil the kinetic properties of single sarcomeres in various types of heart disease.

Excitation of Ar, O2, and SF6/O2 plasma discharges using tailored voltage waveforms: control of surface ion bombardment energy and determination of the dominant electron excitation mode

Using tailored voltage waveforms (TVWs) to excite a low pressure, low-temperature plasma discharge, we compare the behavior of three gas mixtures, namely Ar, O2 and SF6/O2 mixtures, the last of which is currently used for the plasma-texturing of silicon wafers for photovoltaics. The primary goal of using TVWs is to control the ion bombardment energy at the surface of the wafer, and this control is demonstrated through retarding field energy analyzer (RFEA) measurements. However, the complicated electrical response of the plasma to such waveforms makes the ab initio prediction of the ion energy difficult, although by using said RFEA measurements, we show that it can be done approximately by using measured electrical data. In addition, we utilize the response of the plasma to mirror-image ‘sawtooth’ waveforms as a predictor of the dominant electron heating mode (α or drift-ambipolar, DA). At equivalent pressures and coupled powers, the Ar and O2 mixtures always display behavior associated with electropositive plasmas (a solely α heating mode). However, with the addition of SF6 to an O2 gas flow, a transition can be observed towards a behavior associated with a more electronegative plasma (i.e. a dominant DA heating mode). This crossover in the dominant heating mode is observed through the relative self-bias voltage for each type of sawtooth waveform, and is therefore a useful predictor of the dominant electron heating mode in low pressure, cold plasma discharges.

Focus on test, measurement, software, and instrumentation

Focus on test, measurement, software, and instrumentation

Multiple microwave waveform generation by a dual-loop optoelectronic oscillator

A self-starting multiple microwave waveform signal generator based on a dual-loop optoelectronic oscillator (OEO) is proposed. The structure of the dual-loop OEO with two wavelengths can suppress the random beating noise effectively and generate the microwave signal with low phase noise (−119.8 dBc/Hz at 10 kHz). Then square waveform is generated by setting the modulation index to be 1.15. Sawtooth (Reversed-sawtooth) waveform is obtained by combining a square and a frequency doubling sinusoidal signal which is got by setting the bias of the other MZM driven by OEO at the null point (maximum point). The triangular waveform is obtained by combining two oscillation signal envelopes with a relative 1/4 period time delay, when the modulation index of the MZM is set to 0.7555. The operation principle is theoretically analyzed and simulated. In experimental demonstration, full-duty-cycle and high quality square, sawtooth (reversed-sawtooth) and triangular waveform signals with low phase noise at 4.9641-GHz are achieved. An external synthesizer is replaced by the high-quality microwave signal in this structure.

Identification of Sine, Squire, Triangle and Sawtooth Waveforms with Uniform White and Inverse F Noises by Adaptive Neuro - Fuzzy Interface System

Identification of Sine, Squire, Triangle and Sawtooth Waveforms with Uniform White and Inverse F Noises by Adaptive Neuro - Fuzzy Interface System

Photonic microwave waveforms generation based on two cascaded single-drive Mach-Zehnder modulators.

A new photonic scheme for various waveforms generation has been proposed and demonstrated. In the scheme, two cascaded single-drive LiNbO3 Mach-Zehnder modulators serve as pulse shaper and the polarization-dependent character of the modulators is fully exploited and utilized. By arranging the polarization states of the incident light, two different spectra are achieved on two orthogonal polarization components respectively. Finally, the desired waveforms can be obtained by superimposing the photocurrents of the two orthogonal signals on a photodetector. The detailed theoretical analyses and simulations are given. In the experiment, square-shaped waveform, triangular waveform and sawtooth (or reversed-sawtooth) waveform are obtained successfully. Furthermore, an approach to smoothing the sawtooth waveform with fewer harmonics is suggested and verified.

An integrated charge-transfer relaxation oscillator without comparator

This letter presents a charge-transfer relaxation oscillator that achieves ultra-low power operation without comparator. The oscillator is implemented by charging or discharging the negative plate of the capacitor to a reference voltage through charge-transfer technique and the positive plate of the capacitor by a constant reference current, respectively. A special sawtooth waveform is generated, and a pseudo-inverter chain with delay compensation is adopted to determine the oscillation state. In the proposed structure, a conventional comparator has been eliminated to avoid comparator offset effect. The oscillator has been implemented with TSMC 0.18 $$\upmu $$ m CMOS process. The circuit operates in subthreshold region and consumes a total power of 85 nW. The circuit demonstrates a frequency variation less than 0.8%/V over 1.2–1.8 V, leading to a temperature coefficient of 33 ppm/ $$^{\circ }$$ C over − 40 to 80 $$^{\circ }$$ C.

Photonic microwave waveforms generation based on pulse carving and superposition in time-domain

A novel photonic approach for various microwave waveforms generation based on time-domain synthesis is theoretically analyzed and experimentally investigated. In this scheme, two single-drive Mach–Zehnder modulators are used for pulses shaping. After shifting the phase and implementing envelopes superposition of the pulses, desired waveforms can be achieved in time-domain. The theoretic analysis and simulations are presented. In the experimental demonstrations, a triangular waveform, square waveform, and half duty cycle sawtooth (or reversed-sawtooth) waveform are generated successfully. By utilizing time multiplexing technique, a frequency-doubled sawtooth (or reversed-sawtooth) waveform with 100% duty cycle can be obtained. In addition, a fundamental frequency sawtooth (or reversed-sawtooth) waveform with 100% duty cycle can also be achieved by the superposition of square waveform and frequency-doubled sawtooth waveform.

Pseudo-impulse tail current shaping for phase noise reduction in CMOS LC oscillators

In this paper, a low phase noise oscillator using tail current shaping method is presented. The current shaping is achieved using two paths for current disconnection and current injection, as a result of which, the total tail current is shaped to a sharp and sawtooth waveform, close to an impulse. Each switching transistor is ON only in 22% of an oscillation period, and tail current is mostly supplied to these transistors near the outputs peak points. In those moments, the oscillator sensitivity to noise sources is minimum. The proposed oscillator is designed and simulated in 0.18 μm RF CMOS technology with 1.8 V supply, and using the inductor model offered by the process, with quality factor of 11. Post layout simulations predict an oscillation frequency of 1.65 GHz, and phase noise of −127.7 dBc/Hz at 1 MHz offset, which is 6.3 dB better than that of simple cross coupled oscillator with the same core oscillator power consumption of 2.2 mW. The proposed circuit, however, consumes an extra power of about 1.9 mW for the added current shaping circuits. Compared to conventional tail current shaping technique, the proposed oscillator offers better tail current shaping, and a much higher start-up current and gain, which is desirable.