Electronic Filter Research Articles

Fiber Bragg grating tuning with notch-type spring device

This paper presents a notch-type spring mechanism based on the traction principle for tuning fiber Bragg gratings, which magnifies the displacement of piezoelectric actuators. Practical tuning ranges up to 8 nm and tuning times below 20 ms are demonstrated. Oscillations that affect the device due to the rapid voltage change applied to the actuator are mitigated using either an electronic filter or a viscoelastic neutralizer technique.

Performance Comparison of Electronic PMD Equalizers for Coherent PDM QPSK Systems

Polarization division multiplexed (PDM) quadrature phase-shift keying (QPSK) coherent optical systems employ blind adaptive linear electronic equalizers for polarization-mode dispersion (PMD) compensation. In this paper, we compute the performance of various adaptive, fractionally spaced, feed-forward electronic equalizers, using the outage probability as a criterion. A parallel programming implementation of the multicanonical Monte Carlo method is developed, which automatically performs concurrent loop computation on multicore processors, for the estimation of the tails of the outage probability distribution. The constant modulus algorithm (CMA), the decision-directed least mean squares (DD-LMS), and their combination are applied for the adaptation of electronic equalizer filter coefficients. In the exclusive presence of PMD, we demonstrate that half-symbol-period-spaced CMA-based adaptive electronic equalizers perform slightly better than their DD-LMS counterparts, at links with strong PMD, whereas the opposite holds true at the weak PMD regime. It is shown that the successive application of CMA and DD-LMS with 20 complex, half-symbol-period-spaced taps per finite impulse response filter is adequate to reduce the outage probability of coherent PDM QPSK systems to less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> , for a mean differential group delay of more than twice the symbol period.

Structural Modal Analysis Based on HHT and Butterworth Filter

Structural signal is taken self-adaptive decomposition by Hilbert-Huang Transform mainly composed of the EMD(empirical mode decomposition) and HT(Hilbert Transform), which is especially suitable for structural projects in the non-linear, non-stationary signal analysis through local characteristic. However, some weak signal may be ignored by EMD resulting in modal missing. Butterworth filter is an electronic filter designed to have flat frequency response. Considering the influence of noise , Hilbert-Huang Transform and Butterworth band pass filter are applied together to process the structural signal in order to obtain the frequency, damping ratio and mode shapes of the structure more precisely in this paper. Numerical Simulation results show that the proposed method in this paper could identify the modal parameters effectively and accurately.

Optimized retrieval of primary care clinical prediction rules from MEDLINE to establish a web-based register

Objectives Identifying clinical prediction rules (CPRs) for primary care from electronic databases is difficult. This study aims to identify a search filter to optimize retrieval of these to establish a register of CPRs for the Cochrane Primary Health Care field. Study Design and Setting Thirty primary care journals were manually searched for CPRs. This was compared with electronic search filters using alternative methodologies: (1) textword searching; (2) proximity searching; (3) inclusion terms using specific phrases and truncation; (4) exclusion terms; and (5) combinations of methodologies. Results We manually searched 6,344 articles, revealing 41 CPRs. Across the 45 search filters, sensitivities ranged from 12% to 98%, whereas specificities ranged from 43% to 100%. There was generally a trade-off between the sensitivity and specificity of each filter (i.e., the number of CPRs and total number of articles retrieved). Combining textword searching with the inclusion terms (using specific phrases) resulted in the highest sensitivity (98%) but lower specificity (59%) than other methods. The associated precision (2%) and accuracy (60%) were also low. Conclusion The novel use of combining textword searching with inclusion terms was considered the most appropriate for updating a register of primary care CPRs where sensitivity has to be optimized.

Minimizing UV noise in supercritical fluid chromatography. I. Improving back pressure regulator pressure noise

Pressure fluctuations and resulting refractive index changes, induced by the back pressure regulator (BPR) can be a significant source of UV detector noise in supercritical fluid chromatography (SFC). The refractive index (RI) of pure carbon dioxide (CO 2) changes ≈0.2%/bar at the most commonly used conditions in supercritical fluid chromatography (SFC) (40 °C and 100 bar), compared to 0.0045%/bar for water (CO 2 IS 44× worse). Changes in RI cause changes in the focal length of the detector cell which results in changes in UV intensity entering the detector. The change in RI (ΔRI/bar) of CO 2 decreases 8-fold at 200 bar, compared to 100 bar. A new back pressure regulator (BPR) design representing an order of magnitude improvement in the state of the art is shown to produce peak to peak pressure noise (PN p–p) as low as 0.1 bar, at 200 bar, and 20 Hz, compared to older equipment that attempted to maintain PN p–p < 1 bar, at <5 Hz. With this lower PN p–p, changes in baseline UV offsets could be measured as a function of very small changes in pressure. A pressure change of ±1 bar at 100 bar, common with some older BPR's, produced a UV baseline offset >0.5 mAU. A pressure change of ±0.5 bar representing the previous state-of-the-art, resulted in a UV offset of 0.3 mAU. Baseline noise <0.05 is required to validate methods for trace analysis. The new BPR, with a PN p–p of 0.1 bar, demonstrated UV peak to peak noise (N p–p) < 0.02 mAU with a >0.03 min (10 Hz) electronic filter under some conditions. This new low noise level makes it possible to validate SFC methods for the first time.

Combining Different Frequencies for Electrical Heating of Saturated and Unsaturated Soil Zones

AbstractIn situ electrical heating of soil was studied applying different frequencies: low‐frequency energy for resistive heating and radio‐frequency energy for dielectric heating. Steep temperature gradients were observed for each heating mode under the condition of the coexistence of saturated and unsaturated soil zones. By combining the two heating modes, this undesired effect can be avoided, thus allowing efficient soil remediation especially when organic phases are accumulated at the capillary fringe. A parallel application of both frequencies was demonstrated as the most suitable method to reduce temperature gradients. By using electronic filters, both electric fields can be established by only one electrode array. This innovative concept is especially applicable for optimizing thermal remediation of light non‐aqueous phase liquid contaminations or realizing thermally‐enhanced electrokinetic removal of heavy metals.

Hybrid Integrated Optical Phase-Lock Loops for Photonic Terahertz Sources

We present the first hybrid-integrated optical phase-lock loop (OPLL) for use in high spectral purity photonic terahertz sources. We have achieved the necessary short loop delay to lock a 1-MHz linewidth slave laser by hybrid integration of the slave laser and photodetector on a silicon motherboard with silica optical waveguides and combining this with a custom-designed low-delay electronic loop filter circuit. The laser and photodetectors are InP-based and are flip chip bonded to silicon daughter boards, which are in turn attached to the motherboard. Delay between the slave laser and photodiode was approximately 50 ps. The heterodyne between slave and master sources has a linewidth of less than 1 kHz and achieved phase noise less than -80 dBc/Hz at an offset of 10 kHz. The slave laser can be offset from the master source by 2-7 GHz, using a microwave oscillator. This integrated OPLL circuit was used with an optical comb source and an injection-locked laser comb filter to generate high spectral purity signals at frequencies up to 300 GHz with linewidths <;1 kHz and powers of about -20 dBm, while the two integrated lasers could deliver a tunable heterodyne signal at frequencies up to 1.8 THz.

The exact equation of motion of a simple pendulum of arbitrary amplitude: a hypergeometric approach

The motion of a simple pendulum of arbitrary amplitude is usually treated by approximate methods. By using generalized hypergeometric functions, it is however possible to solve the problem exactly. In this paper, we provide the exact equation of motion of a simple pendulum of arbitrary amplitude. A new and exact expression for the time of swinging of a simple pendulum from the vertical position to an arbitrary angular position θ is given by equation (3.10). The time period of such a pendulum is also exactly expressible in terms of hypergeometric functions. The exact expressions thus obtained are used to plot the graphs that compare the exact time period T(θ0) with the time period T(0) (based on simple harmonic approximation). We also compare the relative difference between T(0) and T(θ0) found from the exact equation of motion with the usual perturbation theory estimate. The treatment is intended for graduate students, who have acquired some familiarity with the hypergeometric functions. This approach may also be profitably used by specialists who encounter during their investigations nonlinear differential equations similar in form to the pendulum equation. Such nonlinear differential equations could arise in diverse fields, such as acoustic vibrations, oscillations in small molecules, turbulence and electronic filters, among others.

An Optically Tunable Optoelectronic Oscillator

An optically tunable optoelectronic oscillator (OEO) implemented by employing a two-port optical phase modulator without using any electronic microwave filters is proposed and experimentally demonstrated. The key device in the system is the two-port phase modulator, which functions, in conjunction with a dispersive element in the loop, to form a high-Q microwave filter to perform microwave frequency selection. The central frequency of the microwave filter is a function of the optical wavelength and the chromatic dispersion of the dispersive element, therefore, the oscillation frequency can be simply tuned by tuning the wavelength of the laser source or the chromatic dispersion of the dispersive element. A theoretical analysis is provided, which is verified by experiments. The phase noise performance and the frequency tunability are both experimentally investigated.

Approaches to Spectral Imaging Hardware

Instruments used for spectral, multispectral, and hyperspectral imaging in the biosciences have evolved significantly over the last 15 years. However, very few are calibrated and have had their performance validated. Now that spectral imaging systems are appearing in clinics and pathology laboratories, there is a growing need for calibration and validation according to universal standards. In addition, some systems produce spectral artifacts that, at the very least, challenge data integrity if left unrecognized. This unit includes a comparison of the band-pass and light-transmission characteristics of electronic tunable filters, interferometers, and wavelength-dispersive spectral imaging instruments, as well as a description of how they work. Methods are described to test wavelength accuracy and perform radiometric calibration. A real-life example of spectral artifacts is dissected in detail in order to show how to detect, diagnose, verify, and work around their presence when they cannot be eliminated.

Time and amplitude reconstruction from sampling measurements of the PHOS signal profile in the ALICE project

This paper presents the analysis of procedures dedicated for time and amplitude reconstruction from sampling measurements of the ALICE electromagnetic spectrometer PHOS signal profile. The proposed approach is based on the least squares method to fit the profile measured in discrete number of points to the known impulse response function of electronic filter. Assuming semi-Gaussian shape of this function one can reduce the problem of simultaneous determination of signal time mark t0 and amplitude A to the solution of algebraic equation of the nth power, where n is the order of used electronic filter. The proper analytical formulae to define parameters A and t0 as well as their uncertainties σA and σt are proposed. This approach allows one to reduced substantially the processing time for effective estimation of A and t0 with simplification of the used software. The application of obtained formulae to the analysis of beam test data from the prototype of electromagnetic spectrometer PHOS equipped with the ALTRO electronics are considered together with corresponding Monte-Carlo simulation.

Design considerations to overcome cross talk in a photon counting silicon strip detector for computed tomography

This article presents a Monte Carlo simulation of the detector energy response in the presence of pileup in a segmented silicon microstrip detector designed for high flux spectral computed tomography with sub-millimeter pixel size. Currents induced on the collection electrode of a pixel segment are explicitly modeled and signals emanating from events in neighboring pixels are superimposed together with electronic noise before the entire pulse train is processed by a model of the readout electronics to obtain the detector energy response function.The article shows how the lower threshold and the time constant of the electronic filters need to be set in order to minimize the detrimental influence of cross talk from neighboring pixel segments, an issue that is aggravated by the sub-millimeter pixel size and the proposed segmented detector design.

Computer-assisted experiments with oscillatory circuits

A basic setup for data acquisition and analysis from an oscillatory circuit is described, with focus on its application as either low-pass, high-pass, band-pass or band-reject frequency filter. A homemade board containing the RLC elements allows for the interchange of some of them, in particular, for the easy change of the R value, and this makes apparent for the student its influence on the damping factor. The function generator operates in the swap frequency mode over a suitable frequency range and all the circuit parameters are chosen to provide a reasonable set of data for all the electronic filters studied. The output data are acquired through a commercially available DAQ board and data analysis is performed using a graphing and fitting workspace. The main objective is to develop a methodology of teaching the laboratory material through a computer-based environment devised to help students to appreciate how the governing equations work and to visualize their practical applications.

Data Analysis of Translocation Events in Nanopore Experiments

Nanopores have become important tools for single molecule experiments, where information about the properties of DNA/RNA or proteins is inferred from current pulses elicited by individual molecules as they traverse a single pore. However, because of necessary electronic filters employed in the measurement technique, the extraction of meaningful information from short pulses is limited. This restricts the use of nanopores for the investigation of small molecules which cross the pore rapidly. Here we present a method which significantly improves the accuracy of the analysis of noise-filtered current pulses. We introduce improved criteria to measure the pulse width and propose a method to evaluate the pulse height from the falling edge of the pulse, which renders the identification of a pulse plateau unnecessary. The new methods are compared to conventional routines and validated by analyzing representative current pulses as well as experimental protein translocation data. It is demonstrated that the pulse properties can be recovered with satisfying accuracy beyond the usual limitations of Bessel filters, i.e., from pulses featuring a width of merely 0.3f(c)(-1) (f(c) being the filter cutoff frequency).

Heterodyne Method for Time Resolved Spectral Analysis of Fast Laser Wavelength Switching

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> We present a highly sensitive heterodyne method for time resolved optical spectrum analysis of fast laser wavelength switching. The method achieves signal-to-noise ratios in excess of 50 dB and allows, for the first time, the direct measurement of the dynamic sidemode suppression ratio during fast laser channel transitions. Wavelength range and accuracy are determined by the reference external cavity laser, while temporal and wavelength resolution are set by electronic filtering. </para>

Space partitioning in piecewise metamodeling: a graphical approach

This paper presents a graphically-based space-partitioning methodology for piecewise metamodel building. The method is based on using data displays—in particular, the so-called ordinal plots—leading to a metamodel with acceptable prediction accuracy on a piece-by-piece basis, not just on average. The proposed methodology is general and can be applied to various metamodel types. A one-dimensional example is first used to demonstrate the approach, then the methodology is tested on a number of analytical examples in higher dimensions, one of which corresponds to an electronic filter.

Measurement unit for tunable low frequency vibration detection with MEMS force coupled oscillators

This paper reports on the measurement unit of a micromechanical sensor–actuator system for adjustable frequency selective vibration detection in the frequency range below 1 kHz. The sensitivity of the micro-electro-mechanical system (MEMS) is tunable and can reach values up to 400 mV/m s −2. Its spectral resolution without any electronic filtering is 105 Hz. The MEMS itself consists of two force coupled oscillators, which are operated at standard pressure. The superheterodyne principle, well known from information technologies, is then applied to the mechanical domain by the two oscillators. The intelligent silicon system is therefore used to detect the low frequency vibration, transform the vibration signal into a higher frequency range and perform amplification and filtering at a specific, tunable frequency. The analog circuitry is used to pick-off the sensor output signal and demodulate it to the baseband.

On optimal design of low-pass electronic filter using Chebyshev polynomial response

On optimal design of low-pass electronic filter using Chebyshev polynomial response

A Frequency-Doubling Optoelectronic Oscillator Using a Polarization Modulator

A novel realization of a frequency-doubling optoelectronic oscillator (OEO) using a polarization modulator (PolM) is proposed and experimentally demonstrated. In the proposed system, the PolM in combination with two optical polarizers connected via two polarization controllers (PCs) is operating as a two-output intensity modulator. One output of the intensity modulator is connected to the radio-frequency port of the PolM, to form an optoelectronic loop for the generation of a microwave signal with the fundamental frequency determined by the center frequency of a narrowband electronic filter. The other output of the intensity modulator provides a fundamental or frequency-doubled optically modulated microwave signal depending on the static phase term introduced by the PC before the polarizer. The proposed OEO is experimentally demonstrated. A fundamental microwave signal at 10 GHz or a frequency-doubled microwave signal at 20 GHz is generated. The phase noise performance of the generated microwave signal is also investigated.

Multi-focus excitation coherent anti-Stokes Raman scattering (CARS) microscopy and its applications for real-time imaging

We developed a multi-focus excitation coherent anti-Stokes Raman scattering (CARS) microscope using a microlens array scanner for real-time molecular imaging. Parallel exposure of a specimen with light from two highly controlled picosecond mode-locked lasers (jitter of 30 fs through an electronic low-pass filter with 150 Hz bandwidth, point-by-point wavelength scan within 300 ms) and parallel detection with an image sensor enabled real-time imaging. We demonstrated real-time CARS imaging of polystyrene beads (frame rate of 30 fps), a giant multi-lamellar vesicle of dipalmitoylphosphatidylcholine (frame rate of 10 fps), and living HeLa cells (frame rate of 10 fps).