Rectangular Waveform Research Articles

Visibility and annoyance of the phantom array effect varies with age and history of migraine

The phantom array effect (PAE) is a series of repeated images that may be perceived when a person moves their eyes in large saccades across a light source (or a specular reflection of that light source) that is modulating in output over time. Fifty-five people, including a group of 25 who experience migraine, evaluated the visibility and annoyingness of phantom arrays produced by 85 unique temporal light modulation waveforms (including sine, rectangular, complex and DC waveforms) generated using an LED placed against a black background. Those with migraine exhibited higher average visibility compared to those without migraine ( p = 0.019) and were relatively more sensitive at higher frequencies ( p < 0.001). Younger participants also found more stimuli to be visible ( p < 0.001). The threshold sensitivity function was similar to that developed for the phantom array visibility measure (PAVM), and PAVM was effective in predicting visibility ( R2 = 0.87 for the relevant region of PAVM < 3). While those in the migraine group did not report seeing the PAE more often in everyday life at a statistically significant level, they reported being more annoyed by it and having more unwanted physiological responses (headaches, eye fatigue and distraction/disorientation). Members of the migraine group were also more likely to have changed their behaviour in architectural spaces (such as leaving a restaurant with ‘flickering’ lights). In the four hours after completing the experiment, 64% of the migraine group (vs. 19% of the non-migraine group) reported experiencing discomfort or an adverse reaction. In particular, 41% reported experiencing a headache (vs. 8% for those in the non-migraine group).

Photonic Generation of Arbitrary Microwave Waveforms with Anti-Dispersion Transmission Capability

We propose and demonstrate a photonic-assisted approach for generating arbitrary microwave waveforms based on a dual-polarization dual-parallel Mach–Zehnder modulator, offering significant advantages in terms of tunability of repetition rates and anti-dispersion capability. In order to generate diverse microwave waveforms, two sinusoidal radio frequency signals with distinct frequency relationships are applied to the dual-polarization dual-parallel Mach–Zehnder modulator. By adjusting the power of the applied sinusoidal radio frequency signal, the power ratio between these orthogonal polarized optical sidebands can be changed, and thereby desired radio frequency waveforms can be obtained after photoelectric conversion. In our proof-of-concept experiment, we systematically varied the repetition rate of triangular, rectangular and sawtooth waveforms. Meanwhile, we calculated the Root Mean Square Error (RMSE) to assess the approximation error in each waveform. The RMSEs are 0.1089, 0.2182 and 0.1185 for the triangular, rectangular and sawtooth microwave waveforms with repetition rate of 8 GHz, respectively. Furthermore, after passing through 25 km single mode fiber, the optical power decreased by approximately 5.6 dB, which verifies the anti-dispersion transmission capability of our signal generator.

Preservation of vision by transpalpebral electrical stimulation in mice with inherited retinal degeneration.

The potential neuroprotective and regenerative properties of electrical stimulation (ES) were studied in rhodopsin knockout mice (Rho -/- ), a murine model of inherited retinal degeneration. The study focused on assessing the impact of varying ES frequencies on visual functions and photoreceptor cell survival in Rho -/- mice. To elucidate the impact of electrical stimulation on cone survival, Rho -/- mice received either sham or transpalpebral ES using biphasic ramp or rectangular waveforms at 100µA amplitude, starting at sixweeks of age. The treatment duration spanned from one to three weeks. The optimal treatment frequency of ES sessions was determined by applying ES every one, two, or three days in three separate groups of Rho -/- mice. The sham group received daily treatments without the application of ES. Our study revealed significant improvement of visual function in Rho -/- mice following daily or every-other-day noninvasive transpalpebral ES, as evidenced by electroretinogram and optomotor response-based visual behavior assays. Concurrently, assessment of outer nuclear thickness and immunohistochemistry for the cone photoreceptor cell marker PNA demonstrated pronounced increases in the survival of rods and cones and improvement in the morphology of the inner and outer segments. This study underscores the protective effect of non-invasive ES in rhodopsin knockout-induced retinal degenerative disorders, providing a foundation for developing targeted therapeutic interventions for retinitis pigmentosa.

Experimental Evaluation of Higher Order Stability Zones Using a Digitally Operated Quadrupole Mass Filter.

Recent improvements to the comparison-based method of digital waveform generation increased the reproducibility of the waveforms so that the higher-order Mathieu stability zones can be accessed reliably. Digitally driven quadrupole mass filters access these zones using a fixed AC voltage and rectangular waveforms that are defined by a duty cycle. In this context, the duty cycle is the fraction of the waveform period where the waveform remains in the high state. Because digitally driven quadrupoles navigate stability using a duty cycle, there is no need to apply a resolving DC offset between electrode pairs. Accessing the higher stability zones using a conventional resonantly tuned RF requires the use of thousands of AC and DC voltages making the mode of operation less accessible with these devices. Stability zones higher than (1,1) and (2,1) have theoretical resolving powers that are on the order 1,140 and 3,447 at fwhm which drives efforts to practically access these operational conditions. Accessing these zones digitally requires the use of extremely precise waveforms. In a previous effort, waveform generation produced waveforms to reliably access the (1,1) and (2,1) zones without impacting performance. However, recent work found more improvement was needed to reliably access neighboring higher stability zones. Derived from that work, it was determined that a waveform resolution of ∼10 ppm or less was needed to reliably access the (3,1) and (3,2) zones. The present work utilized digital waveforms that achieve this level of precision to experimentally access and characterize attributes of the (3,1) and (3,2) zones. This work dives into the investigation of different beam energies to overcome the destabilizing fringing fields, improve transmission, and their overall effect on the experimental resolving power and signal-to-noise. In addition, the AC voltage of the driving RF was varied to understand the effects on the initial ion beam energy that is needed to achieve balanced separation and how the overall signal-to-noise is affected. Lastly, an assessment was made on the effects of the temporal parameters of a digital mass scan on peak sensitivity, peak fidelity, and overall duration for a scan.

Refining Heisenberg’s principle: A greedy approximation of step functions with triangular waveform dictionaries

In this paper, we consider a step function characterized by a real-valued sequence and its linear expansion representation constructed via the matching pursuit (MP) algorithm. We utilize a waveform dictionary based on the triangular function as part of this algorithm and representation. The waveform dictionary is comprised of waveforms localized in the time–frequency domain. In view of this, we prove that the triangular waveforms are more efficient than the rectangular waveforms used in a prior study by achieving a product of variances in the time–frequency domain closer to the lower bound of the Heisenberg Uncertainty Principle. We provide a MP algorithm solvable in polynomial time, contrasting the common exponential time when using Gaussian windows. We apply this algorithm on simulated data and real GDP data from 1947–2024 to demonstrate its application and efficiency.

Modeling of a linear ion trap with driving rectangular waveforms.

We consider the operation of a digital linear ion trap with resonant radial ejection. A sequence of rectangular voltage pulses with a dipole resonance signal is applied to the trap electrodes. The periodic waveform is piecewise constant, has zero mean, and is determined by an asymmetry parameter : one value is taken on interval and another on , where is the RF period. Ion mass scanning is performed by varying the asymmetry parameter and amplitude of the negative pulse part with time. The ion oscillation frequencies and acceptance of the linear trap are calculated. The dependence of the ion mass to charge ratio on the parameter is . The maximum value is about kDa for typical parameters of the linear trap: frequency 0.5 MHz, rod radius 4 mm, and negative pulse amplitude 1 kV. The dipolar excitation frequency is 0.125 MHz at which the LIT acceptance is maximal.

Time-resolved laser-induced fluorescence spectroscopy using CW diode laser for diagnostics of argon-ion velocity distribution near AC-biased electrode.

Controlling the ion velocity in an ion sheath by applying an alternating current (AC) voltage to an electrode and/or a substrate is critical in plasma material processes. To externally control the velocity distribution of incident ions on a substrate, the application of tailored-waveform AC voltages instead of sinusoidal voltages has garnered interest in recent years. In this study, to investigate temporal changes in ion-velocity distributions, we developed a time-resolved laser-induced fluorescence spectroscopy (LIF) system using a continuous-wave diode laser as an excitation-laser source. A time-resolved LIF system entails the capture of temporally continuous and spectrally discrete LIF spectra during an AC voltage cycle. By measuring temporal changes in the LIF signal intensity at various excitation-laser wavelengths, the argon-ion velocity distribution near the electrode following the AC voltage can be characterized. The results of applying sinusoidal, triangular, and rectangular bias waveforms indicate that the LIF measurement scheme proposed herein can be used to investigate the dynamic behavior of ion-velocity distributions controlled by tailored-waveform AC voltages.

Increasing Isolation Efficiency Using a Segmented Quadrupole Mass Filter Operated with Rectangular Waveforms.

The performance of a segmented quadrupole mass filter operated with rectangular waveforms and capacitively coupled rectangular waveforms applied to the prefilters was examined on a home-built quadrupole-Orbitrap platform. For peak widths of 50 m/z, 100% isolation efficiency was achieved, which fell to approximately 20% for 5 m/z peak width for a rectangular waveform of 150 V0-p. Due to a small exit aperture following the mass filter, peak structure was observed in both experimental peak shapes and those simulated using SIMION. A larger radius quadrupole was examined and achieved similar performance. While the segmented quadrupole does remove the defocusing effects of the fringing fields, the ion beam is only slightly refocused due to the low RF voltage which limits achievable gains in isolation efficiency.

Optimal transcorneal electrical stimulation parameters for preserving photoreceptors in a mouse model of retinitis pigmentosa.

JOURNAL/nrgr/04.03/01300535-202419110-00034/figure1/v/2024-03-08T184507Z/r/image-tiff Retinitis pigmentosa is a hereditary retinal disease that affects rod and cone photoreceptors, leading to progressive photoreceptor loss. Previous research supports the beneficial effect of electrical stimulation on photoreceptor survival. This study aims to identify the most effective electrical stimulation parameters and functional advantages of transcorneal electrical stimulation (tcES) in mice affected by inherited retinal degeneration. Additionally, the study seeked to analyze the electric field that reaches the retina in both eyes in mice and post-mortem humans. In this study, we recorded waveforms and voltages directed to the retina during transcorneal electrical stimulation in C57BL/6J mice using an intraocular needle probe with rectangular, sine, and ramp waveforms. To investigate the functional effects of electrical stimulation on photoreceptors, we used human retinal explant cultures and rhodopsin knockout (Rho-/-) mice, demonstrating progressive photoreceptor degeneration with age. Human retinal explants isolated from the donors' eyes were then subjected to electrical stimulation and cultured for 48 hours to simulate the neurodegenerative environment in vitro. Photoreceptor density was evaluated by rhodopsin immunolabeling. In vivo Rho-/- mice were subjected to two 5-day series of daily transcorneal electrical stimulation using rectangular and ramp waveforms. Retinal function and visual perception of mice were evaluated by electroretinography and optomotor response (OMR), respectively. Immunolabeling was used to assess the morphological and biochemical changes of the photoreceptor and bipolar cells in mouse retinas. Oscilloscope recordings indicated effective delivery of rectangular, sine, and ramp waveforms to the retina by transcorneal electrical stimulation, of which the ramp waveform required the lowest voltage. Evaluation of the total conductive resistance of the post-mortem human compared to the mouse eyes indicated higher cornea-to-retina resistance in human eyes. The temperature recordings during and after electrical stimulation indicated no significant temperature change in vivo and only a subtle temperature increase in vitro (~0.5-1.5°C). Electrical stimulation increased photoreceptor survival in human retinal explant cultures, particularly at the ramp waveform. Transcorneal electrical stimulation (rectangular + ramp) waveforms significantly improved the survival and function of S and M-cones and enhanced visual acuity based on the optomotor response results. Histology and immunolabeling demonstrated increased photoreceptor survival, improved outer nuclear layer thickness, and increased bipolar cell sprouting in Rho-/- mice. These results indicate that transcorneal electrical stimulation effectively delivers the electrical field to the retina, improves photoreceptor survival in both human and mouse retinas, and increases visual function in Rho-/- mice. Combined rectangular and ramp waveform stimulation can promote photoreceptor survival in a minimally invasive fashion.

A Low‐Complexity Expectation Propagation Detector for OTFS

In this paper, we propose a low‐complexity expectation propagation (EP) detector for orthogonal time frequency space (OTFS) system with practical rectangular waveforms. In the high‐mobility scenario, OTFS is becoming a potential scheme for the sixth‐generation (6G) wireless communication system. However, the large size of the effective delay‐Doppler (DD) domain channel matrix brings unbearable computational complexity to the signal detection algorithm based on the matrix inversion. We propose a low‐complexity EP detector based on the sparsity and the block circulant structure of the effective channel covariance matrix in the DD domain. The proposed algorithm only requires log‐linear complexity. In addition, simulation results show that the proposed algorithm not only has the advantage of low complexity but also has good performance, which achieves a tradeoff between performance and complexity.

The Threat of Optical Transmission Jamming

In this paper, we investigate how data transmissions may be affected by various types of optical interference introduced into the fiber on purpose, via a clip-on coupler. The research proved that transmissions may be jammed completely using inexpensive equipment readily available on the market, provided that the attacker has physical access to the fiber optic cable. The most dangerous attacks rely on a typical, slowly modulated communication laser with a rectangular waveform. This study urges further research aimed at counteracting such attacks.

On the Doppler Squint Effect in OTFS Systems Over Doubly-Dispersive Channels: Modeling and Evaluation

Extensive work has demonstrated the excellent performance of orthogonal time frequency space (OTFS) modulation in high-mobility scenarios. Time-variant wideband channel estimation serves as one of the key compositions of OTFS receivers since the data detection requires accurate channel state information (CSI). In practical wideband OTFS systems, the Doppler shift brought by the high mobility is frequency-dependent, which is referred to as the Doppler Squint Effect (DSE). Unfortunately, DSE was ignored in overall prior estimation schemes employed in OTFS systems, which leads to severe performance loss in channel estimation and the consequent data detection. In this paper, we investigate DSE of wideband time-variant channel in delay-Doppler domain and concentrate on the characterization of OTFS channel coefficients considering DSE. The formulation and evaluation of OTFS input-output relationship are provided for both ideal and rectangular waveforms considering DSE. The channel estimation is therefore formulated as a sparse signal recovery problem and an orthogonal matching pursuit (OMP)-based scheme is adopted to solve it. Simulation results confirm the significance of DSE and the performance superiority compared with traditional channel estimation approaches ignoring DSE.

Effect of Current Waveforms during Directed Energy Deposition of 4043 Aluminum Alloy on Microstructure, Hardness, and Wear of Alloy.

Wire arc additive manufacturing (WAAM) was employed to fabricate 4043 aluminum alloy walls. To investigate the effects of sinusoidal, triangular, and rectangular waveforms of alternating current (AC) and their transients on the wall geometry, microstructure evolution, hardness, and wear properties were evaluated. The root mean square (RMS) current value was maximum for the rectangular and minimum for the triangular waveform. The section produced by the triangular waveform had the highest height-to-width ratio, indicating that this waveform can be a favorable choice for creating components using WAAM. The optical micrographs of the transverse cross-section of the printed sections revealed the grain structure produced with this waveform to be heterogeneous, having a columnar dendritic structure at the bottom and equiaxed at the top portion. The waveforms also had an impact on the hardness and wear characteristics of all the walls, which were attributed to their cooling rate.

Effect of initial/tail of the pulse waveform on surface morphology of AZ31 magnesium alloy laser spot welding

Effects of initial/tail of the pulse waveform on coupling efficiency and surface morphology of AZ31 magnesium alloy laser spot welding is investigated. Research shows that initial ramp-up waveform can improve the laser spot welding absorptance, but with limited effect (0.88 → 0.9), and melting time of ramp-up waveform is longer than rectangular for equal pulsed energies, making the welding energy coupling efficient and diameter larger. The ramp-down waveform can extend duration (9 ms → 12 ms) of molten pool above melting point temperature (630 °C), increase Marangoni number (R1: 29.29, R2: 32.11, R3: 23.70, R4: 26.62), slow down cooling rate (3 × 106 °C/s → 1 °C/s) and recoil pressure (R3: 52.90 P0 → 12.16 P0, R4: 95.95 P0 → 20.58 P0) of instantaneous closure of rectangular waveform, reduce the sensitivity of welding defects such as overfill, undercut and spatter, and improve the surface morphology of laser welding spots.

The effects of catalyst conductivity and loading of dielectric surface structures on plasma dynamics in patterned dielectric barrier discharges

Dielectric barrier discharges (DBDs) are promising tools for air pollution removal and gas conversion based on excess renewable energy. Catalyst loading of dielectric pellets placed inside the plasma can improve such processes. The effects of such metallic and dielectric catalyst loading on the discharge are investigated experimentally. A patterned DBD is operated in different He/O2 mixtures and driven by a pulsed rectangular voltage waveform. Hemispherical dielectric pellets coated by different catalyst materials at different positions on their surface are embedded into the bottom grounded electrode. Based on phase resolved optical emission spectroscopy the effects of different catalyst materials and locations on the streamer dynamics are investigated. The propagation of cathode directed positive volume streamers towards the apex of the hemispheres followed by surface streamers, that move across the structured dielectric, is observed for positive applied voltage pulses. Coating the apex with a conducting catalyst results in attraction of such streamers towards the apex due to charging of this surface, while they avoid the apex in the presence of a dielectric catalyst. Surface streamers, that propagate across the hemispheres, are stalled by conducting catalysts placed on the embedded pellets as rings of different diameters, but propagate more easily across dielectric coatings due to the presence of tangential electric fields. Reversing the polarity of the driving voltage results in the propagation of negative streamers across the patterned dielectric and attenuated effects of catalytic coatings on the streamer dynamics.

Temporal light modulation: Data processing and metric calculations

There are multiple metrics used in research and industry to describe the visibility of temporal light modulation (TLM), colloquially referred to as ‘flicker’. However, the metrics are not straightforward to calculate, and the values sometimes vary according to sampling rates. This work addresses the vagaries in processing TLM waveform data and calculating the metrics. For each TLM metric, its sensitivity to sampling rate is presented, followed by recommendations for improving the reliability and consistency of calculated metrics. Appropriate sampling rates are proposed according to the nature of the waveform and metric. The analyses of this paper are based on ideal waveforms without noise or instability, but the effects of sampling rate also apply to real-world waveforms. Some metrics, such as the Stroboscopic Visibility Measure, were relatively stable (i.e. produced the same value regardless of sampling rate) – within the ranges for which they are defined – for sinusoidal and/or rectangular TLM waveforms. In contrast, short-term flicker indicator [Formula: see text] and perceived modulation [Formula: see text] values exhibited greater variability based on sampling rate. Metric values from sinusoidal waveforms were generally more stable than those from rectangular waveforms, although [Formula: see text] showed inconsistency even with sinusoidal TLM.

A low sampling rate method for the monopole UWB impulse parameter monitoring using waveform transformation

In ultra-wideband (UWB) impulse parameter monitoring, amplitude and pulse width measurements are crucial for detecting and classifying unknown impulse signals. Meanwhile, mass sampling data and the complexity of the current measurement technologies are the limitations of real-time and continuous monitoring. It urges to adopt a simple method that reduces the sampling rate without sacrificing accuracy. This article suggests a novel approach for the monopole UWB by analog signal preprocessing before sampling. A peak detector and integrator are utilized to retain the impulse amplitude and the area inside the impulse for a period, which is the so-called waveform transformation. A low-speed two-channel synchronous ADC samples the output signals from the peak detector and the integrator to determine the amplitude and the area. In the signal process, we demonstrate the concept that pulse width value equals the division of area and amplitude. Due to the distorted amplitude caused by the response time of the peak detector, the relationship between the distorted amplitude, the actual amplitude, and the pulse width is analyzed and examined based on the response function. Finally, the actual amplitude and pulse width are acquired and calculated by solving two equations. In terms of impulse waveform, rectangular and Gaussian waveform factors are developed and applied in the measurement. The proof-of-concept experimental results of a 0.68 V/ 18.8 ns rectangular impulse at a 10 Msps sampling rate is 0.711 V/ 17.00 ns with 4.56 %/ 9.57% relative error, tested and verified.

Plasma dynamics in a capacitively coupled discharge driven by a combination of a single high frequency and a tailored low frequency rectangular voltage waveform

Spatiotemporal dynamics in a capacitively coupled plasma discharge generated using a combination of 13.56 MHz sinusoidal voltage and 271.2 kHz tailored rectangular voltage is examined both experimentally and computationally. In the experiments, a fast-gated camera is used to measure the space and time-resolved emission at a wavelength of 750.39 nm from the Ar 2p1 1s2 transition. A particle-in-cell model is used to simulate the Ar plasma. The rectangular waveform is formed using 20 consecutive harmonics of 271.2 kHz, and the waveform duty cycle (DC) is varied between 5%–50%. The experiments and simulation show that excitation and argon metastable (Ar) production are primarily caused by electrons accelerated by the expanding sheath. Species generation occurs asymmetrically with more production happening adjacent to the powered electrode when the low frequency (LF) voltage is positive and vice versa. Densities of charged and excited-state neutral species decrease with increasing LF voltage due to the thinning of the plasma region and enhanced charged species loss at surfaces. At DC = 10%, the plasma responds strongly when the LF rectangular voltage switches from a small negative to a large positive voltage. Emission from the plasma and Ar production decrease considerably during this phase. When the LF voltage becomes negative again, species production and excitation remain suppressed for some time before returning to the pre-positive-pulse conditions. This reduction in plasma production is linked to the spike in electron current to the powered electrode during the positive LF voltage period, which depletes the electrons in the plasma bulk and adjacent to the grounded electrode and also raises the mid-chamber plasma potential. Plasma production suppression after the LF positive negative voltage transition lasts longer at higher LF voltage and lower high frequency voltage due to lower plasma density.

Optical Microwave Waveforms Generation Based on the Round-Trip Phase of the DFB Laser

In this paper, we theoretically and experimentally analyze the influence of the round-trip phase of distributed feedback (DFB) lasers on the harmonic-phase of photocurrent, caused by the external injection current. The results indicate that the harmonic-phase of photocurrent introduced by the round-trip phase (HPIRP) reduces with the increase of modulation depth at a fixed frequency. Then, based on the HPIRP of the DFB laser, a simple photonic generation method of optical microwave waveforms is proposed and verified. In this scheme, three lasers with different wavelengths are mainly used. By adjusting the tunable optical delay lines and attenuators, the amplitude and phase of the photocurrent of the three branches converted by the photodetector (PD) can be controlled individually. The photocurrent of the superposition of the three branches can be controlled properly to form the target waveform. Dispersive elements and complex microwave photonic filtering are not required. Through experiments, rectangular and triangular waveforms with a repetition frequency of 3.75 GHz are generated.

Design and implementation of a versatile H-bridge power supply for experiments on the STOR-M Tokamak

An H-bridge power supply has been developed for different experiments on the STOR-M tokamak. Four insulated-gate bipolar transistors (IGBTs) are used to guide the current to the load from a capacitor bank discharge. The timing signal to the gates of the IGBTs is controlled by a field programmable gate array (FPGA). The power supply can be programmed to drive either a sinusoidal current waveform to an inductive load or a bipolar rectangular current waveform to a resistive load. The maximum frequency and current tested for the sinusoidal current waveform are 25 kHz and 2200 A, respectively. For bipolar current waveforms, the maximum current tested is 1500 A at 3 kHz. The sinusoidal current to a set of helical coils was used for the Resonant Magnetic Perturbation (RMP) experiments and the bipolar rectangular current waveform was used for both the electrode biasing experiments and the RMP experiments on the STOR-M tokamak.