Filter Pulse Research Articles

Perfect pulse filtering under simultaneous incidence at the same frequencies with waveform-selective metasurfaces

We present a new concept of metasurface filters to preferentially extract pulsed waveforms at a constant frequency from a complex superimposed input signal. This filtering capability is realized using circuit-based metasurfaces, denoted waveform-selective metasurfaces, that behave according to the pulse duration of the incident wave. Importantly, our metasurface filters overcome a long-lasting issue of eliminating unnecessary pulses under simultaneous incidence without relying on variables that are commonly used for modulation schemes, e.g., frequency, time, and spatial variation (angular dependence). Such simultaneous filtering is made possible by integrating several types of waveform-selective metasurface unit cells with delay lines and successive interference cancellation processes. Moreover, we show that our concept can be extended to incorporating broadband signals, additional pulses, and variables used for existing modulation schemes. Our study therefore provides a higher degree of freedom to control electromagnetic waves and phenomena with possible applications including wireless power transfer and communications.

Counting Efficiency and Neutron/Gamma Ratio for KDP: Tl+ and UPS-923A Scintillators in a Single Photone Detection Mode

This research related to registration of the fast neutrons with a detector based on the inorganic KDP: TL+ mono crystal (KH2PO4 potassium dihydrogen phosphate) and plastic UPS-923A. The crystal of the KDP: TL+ detector grown from a water solution by the method of lowering the temperature. The high concentration of hydrogen nuclei in the KDP: TL+ crystal grid makes it possible to detect neutron radiation with an efficiency comparable to polystyrene scintillators. KDP: TL+ crystals have a high radiation resistance (up to 1010 neutrons/cm2), which significantly expands the spectrum of their application in high-energy physics applications, intense neutron fields. In this work, we used a technique for recording the detector response in the photon counting mode and pulse filtering mode. Since the detector operates on the principle of detecting gamma quanta from the reactions (n, n 'γ), (n, n' γ)res, (n, γ)cap and others, this makes it possible (in a filtering mode) to isolate the mechanisms of cascade generation processes in the volume of the detector caused by secondary gamma quanta from excited states of compound nuclei. The gamma quanta of the elastic scattering reaction (n, n' γ) for the KDP: TL+ scintillator nuclei are the start of the cascade process of the discharge of excited isomeric states of the input, intermediate, and final nuclei. Measurements of the detection efficiency of fast neutrons were carried out with a KDP: TL+ crystal of size 18x18x42 mm in spherical geometry. The obtained detector reviews in units of impulse / particle for sources and 239Pu-Be and 137Cs were 3.57 and 1.44. In this case, a broadband path with a speed of 7 ns was used. In addition, the counting efficiency of the narrow-band tract measured simultaneously with a processing time of 1 μs and 6.4 μs. The received response from the KDP: TL+ detector (in units of impulse/particle) for both sources 239Pu-Be and 137Cs was 0.09 and 0.00029. The n/γ ratio coefficient was 310. The given measurements of a polystyrene-based scintillator size of 40×40×40 mm. The received response in a single photon-counting mode from the plastic detector (in units of impulse/particle) for both sources 239Pu-Be and 137Cs was 19.4 and 3.9. The n/γ ratio coefficients for detectors are also given: KDP: TL+ - 2.47 and UPS-923A - 4.97 in the 7 ns mode. The statistical error in measurements of the neutron detection efficiency was about ~ 5%.

A Robust Principal Component Analysis for Outlier Identification in Messy Microcalorimeter Data.

A principal component analysis (PCA) of clean microcalorimeter pulse records can be a first step beyond statistically optimal linear filtering of pulses toward a fully nonlinear analysis. For PCA to be practical on spectrometers with hundreds of sensors, an automated identification of clean pulses is required. Robust forms of PCA are the subject of active research in machine learning. We examine a version known as coherence pursuit that is simple and fast and well matched to the automatic identification of outlier records, as needed for microcalorimeter pulse analysis.

A supervised machine learning approach using naive Gaussian Bayes classification for shape-sensitive detector pulse discrimination in positron annihilation lifetime spectroscopy (PALS)

Abstract The acquisition of high-quality and non-artefact afflicted positron lifetime spectra is crucial for a profound analysis, i.e. the correct lifetime spectra decomposition for retrieving the true information. Since the introduction of digital positron lifetime spectrometers, this is generally realized by applying detector pulse discrimination with the help of software-based pulse filtering regarding area and/or shape of the detector pulses. Here, we present a novel approach for shape-sensitive detector pulse discrimination applying supervised machine learning (ML) based on a naive Bayes classification model using a normally distributed likelihood. In general, naive Bayes methods find wide application for many real-world problems such as famously applied for email spam filtering, text categorization or document classification. Their algorithms are relatively simple to implement and, moreover, perform extremely fast compared to more sophisticated methods in training and predicting on high-dimensional datasets, i.e. detector pulses. In this study we show that a remarkable low number of less than 20 labelled training pulses is sufficient to achieve comparable results as of applying physically filtering. Hence, our approach represents a potential alternative.

Filtering of pulses from particle detectors using neural networks by dimensionality reduction

This article presents a comparison between different filtering methods based on dimensionality reduction for pulses generated on particle detectors . This reduction has been carried out using Neural Networks (NNs). In particular, three topologies have been used: Autoencoders (AEs), Denoising Autoencoders (DAEs) and Restricted Boltzmann Machines (RBMs). A detailed explanation of these methods, a noise reduction analysis, filtering with simulated data and processing of pulses from a neutron detector have been carried out to verify the feasibility of using these NNs as pulse filters.

Filtering of pulses from particle detectors by means of Singular Value Decomposition (SVD)

This paper presents a novel methodology to filter pulses coming from particle detectors. It is based on variable-in-time convolutions in which one of the operands is the input pulse and the other is a vector that changes with every convolution step. This is equivalent to multiply every incoming pulse by a filtering matrix. The coefficients of this matrix are computed by applying a Singular Value Decomposition (SVD) factorization over a set of training pulses. A detailed explanation of this SVD-filtering methodology, a noise filtering analysis, simulations and filtering of pulses coming from a neutron monitor were carried out to verify its feasibility.

Improved fission neutron energy discrimination with 4He detectors through pulse filtering

This paper presents experimental and computational techniques implemented for 4He gas scintillation detectors for induced fission neutron detection. Fission neutrons are produced when natural uranium samples are actively interrogated by 2.45MeV deuterium-deuterium fusion reaction neutrons. Fission neutrons of energies greater than 2.45MeV can be distinguished by their different scintillation pulse height spectra since 4He detectors retain incident fast neutron energy information. To enable the preferential detection of fast neutrons up to 10MeV and suppress low-energy event counts, the detector photomultiplier gain is lowered and trigger threshold is increased. Pile-up and other unreliable events due to the interrogating neutron flux and background radiation are filtered out prior to the evaluation of pulse height spectra. With these problem-specific calibrations and data processing, the 4He detector's accuracy at discriminating fission neutrons up to 10MeV is improved and verified with 252Cf spontaneous fission neutrons. Given the 4He detector's ability to differentiate fast neutron sources, this proof-of-concept active-interrogation measurement demonstrates the potential of special nuclear materials detection using a 4He fast neutron detection system.

Improvement of the GERDA Ge Detectors Energy Resolution by an Optimized Digital Signal Processing

GERDA is a new generation experiment searching for neutrinoless double beta decay of 76Ge, operating at INFN Gran Sasso Laboratories (LNGS) since 2010. Coaxial and Broad Energy Germanium (BEGe) Detectors have been operated in liquid argon (LAr) in GERDA Phase I. In the framework of the second GERDA experimental phase, both the contacting technique, the connection to and the location of the front end readout devices are novel compared to those previously adopted, and several tests have been performed.In this work, starting from considerations on the energy scale stability of the GERDA Phase I calibrations and physics data sets, an optimized pulse filtering method has been developed and applied to the Phase II pilot tests data sets, and to few GERDA Phase I data sets. In this contribution the detector performances in term of energy resolution and time stability are here presented.The improvement of the energy resolution, compared to standard Gaussian shaping adopted for Phase I data analysis, is discussed and related to the optimized noise filtering capability. The result is an energy resolution better than 0.1% at 2.6 MeV for the BEGe detectors operated in the Phase II pilot tests and an improvement of the energy resolution in LAr of about 8% achieved on the GERDA Phase I calibration runs, compared to previous analysis algorithms.

A 2.0 Gb/s Clock-Embedded Interface for Full-HD 10-Bit 120 Hz LCD Drivers With 1/5-Rate Noise-Tolerant Phase and Frequency Recovery

A 2.0 Gb/s clock-embedded interface for LCD drivers, Advanced-PPmL¿, has been developed for high-speed data transfer and reduced area in transmission media. Only one pair of differential signals is needed to control the LCD driver and to display images. A newly developed 1/5-rate phase frequency detector helps achieve a 25% power reduction compared with a half-rate architecture. Pulse filtering of phase control signals and a 4B5B-based interface protocol have been developed for noise-tolerant clock recovery. Power consumption in the clock and data recovery (CDR) is 93 mW with a 3.0 V supply. The rms jitter in the recovered clock is 11 ps when a PRBS7 pattern is used.

Boolean chaos

We observe deterministic chaos in a simple network of electronic logic gates that are not regulated by a clocking signal. The resulting power spectrum is ultrawide band, extending from dc to beyond 2 GHz. The observed behavior is reproduced qualitatively using an autonomously updating Boolean model with signal propagation times that depend on the recent history of the gates and filtering of pulses of short duration, whose presence is confirmed experimentally. Electronic Boolean chaos may find application as an ultrawide-band source of radio waves.

Estimation Of Energy Expenditure From Wrist Attached Accelerometer Signal Using Movement Counting And Filtering

Activity monitoring from the wrist has yielded accurate results for estimation of time spent in bed rest and energy expenditure (EE) in walking, but the results have not been equally good in everyday tasks. Overestimation of EE has resulted when hands move a lot while whole body movement is low. Recently, complex multi-sensor measurement and computer approaches with pattern recognition have been tested to solve the problem. We used a simple 1-D accelerometer-based movement counter equipped with a pulse filtering procedure (European Patent 1532924), and exposed our method to selected everyday activities. PURPOSE: To determine the suitability of 1-D accelerometer measurement together with a movement counting and filtering procedure in estimation of EE in everyday activities. METHODS: 8 males (27 ± 5 years, BMI 24.0 ± 3.8 kgm-2, mean ± SD) and 7 females (32 ± 6 years, BMI 21.8 ± 1.5 kgm-2) wore a wrist watch type instrument equipped with 1-D accelerometer in laboratory conditions. The protocol included nine activities with various contributions of hand activity: rest, reading, playing with toys, computer work, hitting nails, packing a bag while standing, cleaning the floor and treadmill walking 3.5 km/h and 5.5 km/h. The instrument was tuned to low frequency movements (0.3-1.5 Hz) and it was programmed to register the movement if acceleration exceeded 0.1 g. Depending on whether the majority of movements were periodic or non-periodic, the filter only allowed one movement in 600 ms or 850 ms. Minute-by-minute movement count was transformed to METs using a non-linear relationship and body height based calibration factor. METs were transformed to kJ/min using WHO equations with age and body weight. Reference EE was measured with portable respiratory gas analysis system. Each activity lasted five minutes and the last three minutes of each activity were selected for analysis. RESULTS: Estimated energy expenditure correlated highly (r=0.88) with measured one. Difference between estimated and measured energy expenditure was 0.5 ± 3.1 kJ/min or -2 ± 27% (mean ± SD). The filtering diminished the overestimation in activities where hand movements dominate. CONCLUSIONS: 1-D accelerometer-based movement counter with simple filtering procedure provides accurate estimations of low-to-moderate intensity EE.

Ultrabroadband electromagnetic wave propagation in hydrocarbon reservoirs in the presence of an oil-water interface

Numerical experiments are applied to simulate propagation of broadband pulses which are transmitted by an electric dipole and travel in a uniform oil-bearing formation or in a layered reservoir with an oil-water interface. We calculate the frequency responses of the oil- and water-saturated layers as low-frequency filters for the propagating waves and find the respective cutoff frequencies. Attenuation rates are analyzed in the cases of incident nanosecond and picosecond pulses in uniform oil-bearing formations and those reflected from the oil-water interface. The low frequency filtering of pulses is investigated in terms of its effect on wave energy attenuation during propagation in oil-bearing rocks.

Fast-Light Based Pulse Compression in 2-D Photonic Crystal Waveguides

Chirped-pulse propagation close to a mini-stopband (MSB) in short photonic crystal (PhC) waveguides is studied using the 2-D finite-difference time-domain method. The group delay (GD) is calculated for different length waveguides and is shown to have a nonlinear relationship with length, implying that dispersion diagram based design approaches may not be applicable in these cases. Pulse compression is then observed directly in the time domain, and a GD-based analysis is used to explain the results. It is shown that the fast-light or negative GD region that is found within the MSB plays a more important role than pulse filtering effects, which can also induce compression. The GD analysis is then used to find the optimum length waveguide for the maximum pulse compression, and this is found to be in agreement with direct time-domain results. Finally, a different PhC waveguide structure is studied based on square holes, which results in an increased GD and, hence, increased pulse compression.

High-power Ti:Sapphire lasers: Temporal contrast and spectral narrowing

New extensions of the chirped pulse amplification (CPA) scheme designed specially for petawatt Ti:Sapphire lasers are considered. The two new schemes support a spectral bandwidth sufficient for 20 fs pulses and a temporal contrast of 1012. The Double CPA scheme consists of two CPA stages with an intermediate temporal pulse filtering for temporal contrast improvement. The scheme of Negative–Positive CPA amplification takes advantage of consecutive saturated amplification of down chirped and up chirped pulses. This allows a suppress imprint of gain narrowing, which usually limits the spectral bandwidth at the multi-terawatt power level, and reach the bandwidth in excess of 50 nm without using any direct spectral shaping of the pulse.

Simplified system configuration for real-time Fourier transformation of optical pulses in amplitude and phase

Real-time Fourier transformation (RTFT) of optical waveforms in amplitude and phase (i.e. transform-limited RTFT) is a fundamental operation that enables the realization of many interesting ultrafast signal processing applications, including wavelength-tunable optical pulse filtering, all-optical temporal correlations and convolutions and temporal imaging, among others. In this paper, we demonstrate that under certain conditions, a single time lens (quadratic-phase temporal modulator) followed by a suitable dispersive delay line can be used to implement transform-limited RTFT of optical pulses. The design specifications and constraints of the proposed transform-limited RTFT systems are derived and discussed. As compared with the conventional methods, the proposed design does not require the use of an input dispersive device preceding the time lens or a second time lens after dispersion, thus resulting in a simpler and more practical alternative for implementing TL-RTFT of optical signals. The feasibility of our proposal to operate on picosecond optical waveforms using electro-optic time lenses has been confirmed by numerical simulations.

Double chirped-pulse-amplification laser: a way to clean pulses temporally

We demonstrate a double chirped-pulse-amplification (CPA) Ti: sapphire laser system that includes two CPA stages with intermediate nonlinear temporal pulse filtering. The method makes it possible to reduce substantially the background of amplified spontaneous emission (ASE), including prepulses and postpulses. An ASE temporal contrast of 10(10) was demonstrated at 20 mJ of output energy and 50-fs pulse duration. The demonstrated scheme is applicable to petawatt power-level laser systems.

Intra-pulse Raman frequency shift versus conventional Stokes generation of diode laser pulses in optical fibers

We report experimental observations of stimulated Raman scattering in a standard fiber using a directly modulated DFB semiconductor laser amplified by two erbium-doped fibers. The laser pulse width was variably controlled on a nanosecond-scale; the laser emission was separated into two distinct regimes: an initial transient peak regime, followed by a quasi steady-state plateau regime. The transient leading part of the pump pulse containing fast amplitude modulation generated a broadband Raman-induced spectral shift through the modulation instability and subsequent intra-pulse Raman frequency shift. The plateau regime amplified the conventional Stokes shifted emission expected from the peaks of the gain distribution. The output signal spectrum at the end of a 9.13 km length of fiber for the transient part extends from 1550 nm to 1700 nm for a pump pulse peak power of 65 W. We found that the Raman-induced spectral shift is measurable about 8 W for every fiber length examined, 0.6 km, 4.46 km, and 9.13 km. All spectral components of the broadband scattering appear to be generated in the initial kilometer of the fiber span. The Stokes shifted light generation threshold was higher than the threshold for the intra-pulse Raman-induced broadened spectra. This fact enables the nonlinear spectral filtering of pulses from directly modulated semiconductor lasers.

Inertial effect handling method for CMOS digitalIC simulation

A method is presented for determining the occurrence of the inertial effect (pulse filtering) in CMOS digital logic gates to overcome the limitations of conventional approaches. It is based on accounting for individual input gate thresholds and a new scheduling mechanism, while maintaining compatibility with existing delay models.

An optimum digital signal processing for radiation spectroscopy

When resolution is a primary requirement in high performance spectroscopy systems, the signal pulse filtering should approach the theoretical optimum weighting function. This goal, almost impossible to reach with analog filtering especially when 1 ƒ noise is dominant, is achieved by the presented digital signal processor. It synthesizes the optimum weighting function by exploiting experimentally measured noise. The energy resolution dependence on the experimental settings is reported. Those include the number of samples acquired per pulse, the sampling frequency and the bandwidth of the antialiasing filter. An experimental comparison against the best analog filter shows an improvement of more than 10% in energy resolution.

Correction of counting losses of the preloaded fil ter pulse processor

By adapting noise filtering to individual pulse intervals, the Preloaded Filter (PLF) pulse processor (1) combines high resolution with optimum throughput efficiency. As a consequence, its output pulse interval distribution contains strong non-random components which render conventional ADC dead-time correction an impossibility. Quantitative correction of dead-time and pileup losses of the PLF processor may be achieved, however, with the Virtual Pulse Generator (2), together with a new, distribution-independent method of measuring ADC losses which is based on a pulse counting technique.