Comb Filter Research Articles

Cancelable palmprint: intelligent framework toward secure and privacy-aware recognition system

Cancelable template protection techniques are indispensable to provide essential security and privacy privileges in biometric systems. This paper introduces an efficient cancelable palmprint recognition technique based on multi-level transformations. Gabor filtering with feature remapping is introduced for extracting highly discriminative features. Histogram remapping is applied to nonlinearly transform the downsampled Gabor features to be normally distributed. This feature-remapping step is proposed to enhance the discriminatory power and alleviate the effect of feature variability and image artifacts. Comb filtering is applied to the mapped features as a first protection layer. To provide security guarantees against linkability attacks, index-based locality-sensitive hashing (LSH) is introduced as a second protection layer to transform the comb-filtered mapped real-valued features into maximum-ranked indices. Recognition is performed in the secured domain to accelerate matching and to preserve the user’s privacy. Results show that the proposed scheme provides a large re-issuance ability, protects templates from being inverted, and demonstrates strong unlinkability across different databases. In addition, favorable verification/identification accuracy is obtained and the system satisfies the needs for real-time applications. A global measure D↔sys\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${D}_{\\leftrightarrow }^{sys}$$\\end{document} value of 0.01 is obtained, and thus, correlation attacks are mitigated. The recognition results for the legitimate scenario are 100% identification accuracy and 0% EER. For the worst case (same token scenario), the corresponding results are 99.752% and 0.31%, respectively.

Design of an on-chip integrated multi-channel comb filter based on the Bragg grating structure.

We designed a multi-channel comb filter generation scheme with nearly consistent channel numbers and free spectral range (FSR) in standard 220-nm-thick silicon-on-insulator (SOI) technology. This scheme relies on the formation of optical microcavities using Bragg grating structures, which serve as reflectors. By precisely designing the optical path length of the microcavity, we can generate optical filters with a specific number of channels. Using this scheme, we developed and tested three devices to implement two-channel, three-channel, and four-channel comb filters, with FSRs of approximately 5.5 nm, 4 nm, and 3.3 nm, respectively. As an application, this three-channel filter can be used to implement a temperature sensor with a high temperature sensitivity of about 53 pm/K. The proposed multi-channel comb filter provides a novel, to the best of our knowledge, scheme to utilize Bragg gratings, offering a new perspective for future densely integrated silicon photonics.

Off-Axis Integral Cavity Carbon Dioxide Gas Sensor Based on Machine-Learning-Based Optimization.

Accurately detecting atmospheric carbon dioxide is a vital part of responding to the global greenhouse effect. Conventional off-axis integral cavity detection systems are computationally intensive and susceptible to environmental factors. This study deploys an Extreme Learning Machine model incorporating a cascaded integrator comb (CIC) filter into the off-axis integrating cavity. It is shown that appropriate parameters can effectively improve the performance of the instrument in terms of lower detection limit, accuracy, and root mean square deviation. The proposed method is incorporated successfully into a monitoring station situated near an industrial area for detecting atmospheric carbon dioxide (CO2) concentration daily.

Seasonality in synthetic average wind speed

There is a growing demand for computer-generated realistic high-fidelity wind speed data for various applications in the wind industry. Such data should capture the non-stationary dynamics of real-world wind time series, as well as be consistent with the statistical descriptors – the probability density function and power spectral density – of the observed wind speed. However, complying with the statistical descriptors is not a guarantee that the seasonality will be correctly reproduced in synthetic data. The seasonality, characterized by the average diurnal and seasonal variations, is driven by the periodicities embedded in diurnal and annual harmonic series respectively. Those periodicities are determined by the long-term orbital forcing components, which establish the insolation for a given latitude and longitude. We show that average diurnal and seasonal variations can be visualized as the output of comb filters, whose fundamental frequencies match the diurnal and annual fundamental frequency respectively. The aforementioned theoretical findings are readily reproduced in synthetic wind speed, generated by a non-parametric data-driven statistical model, based on the phase-randomized Fourier transform. The model, tested on both 10-min and 1-min resolution real-world datasets, yields average non-stationarities in synthetic wind speed with the accuracy close to the computing precision.

Secure speaker identification in open and closed environments modeled with symmetric comb filters

Secure speaker identification in open and closed environments modeled with symmetric comb filters

A sampled-data feedforward programmable time-mode comb filter

In this work, a sampled-data feedforward comb filter suitable for time-mode signal processing (TMSP) is proposed. In the proposed system the input voltage is sampled and converted to a pulse-width (PWM); the pulse width is proportional to the input amplitude. The pulse width is the quantity which is being processed by the time-mode feedforward comb filter. Both input and output are synchronous with the sampling clock. The benefits of the proposed filter topology are (a) the modular and (b) hierarchical design which can be dealt with as a pure digital comb filter implementation counterpart. The frequency response of the proposed filter is digitally programmable. As a result, this filter can be used as building block for the implementation of higher-order time-mode systems. The comb filter was designed and verified through post-layout simulations in TSMC 65 nm technology process. The sampling rate was 5 MHz, the voltage supply was 1.2 V, consuming 540 μW for the use of 9-unit delay tap network and occupying a total area of 254 μm × 160 μm.

An acoustic comb filter by shunted electromechanical diaphragm

A noise with multiple tonal components is prevalent in practice, and these tones, contributing to noise annoyance, may even span several octaves and the frequencies of them always vary with working condition. Conventional broadband noise control structures with limited spaces are hard to address multiple-tonal noise due to sum rules in acoustics. Resonator arrays is feasible but their dependency on the geometrical and mechanical parameters challenges matching variable frequencies of tonal components. This work introduces a Shunt-Electromechanical Diaphragm (SEMD) to construct sound absorption and transmission spectra with multiple peaks, thereby creating an acoustic comb filter in deep-sub-wavelength scale to address multiple-tonal noise. The SEMD consists of a moving-coil loudspeaker integrated with a circuit housing multiple resonance branches, whose acoustic impedance is determined by circuit parameters. This allows the frequencies and number of sound absorption and transmission peaks to be arbitrarily reconfigured by adjusting circuit parameters. A comprehensive lumped parameter model is devised to elaborate on the electromechanical coupling of the SEMD and predicts its comb filter effect. Experiments in an impedance tube show that comb spectra with three peaks for sound absorption and transmission are successfully constructed and reconfigured by collocating circuit parameters, verifying the theoretical model. The three peaks of the sound absorption spectrum have values above 0.9 and are electrically tunable over more than three octaves. The method in this work blends electromechanical dynamics with specialized analog circuits for efficient tonal noise reduction across a broad bandwidth, which removes the geometrical and mechanical constrains and paves the way for digital reconfigurable acoustic devices. Moreover, the multiple peaks matching between noise source and sound absorption/transmission spectra via the electromechanical coupling mechanism of the SEMD bypasses the sum rules in acoustics, providing an alternative method for controlling noise over a much broader bandwidth.

Design and Implementation of Digital Down Converter for WiFi Network

This paper introduces a field-programmable gate array (FPGA)-based digital down converter (DDC) processing a sampling frequency of about 3.64 GHz to a down-converted frequency of 28.4375 MHz to match the IEEE 802.11ah Wi-Fi HaLow standard. The proposed DDC uses a polyphase mixer(PM) and a resampling filter. The PM adopts parallel coordinate rotation digital computer (CORDIC) processors and lowpass filter arrays to reduce high-speed data rates with minimum resource utilization. Again, the resampling filter employs a cascaded integrator comb (CIC) filter associated with a parallel prefixed adder (PPA) and a multi-channel systolic finite impulse response (FIR) filter implemented with canonical expression, attaining optimum hardware cost. Converting floating-point to fixed-point data types provides significant resource savings. Finally, the improved design is coded in the Xilinx Vivado synthesis tool and successfully tested on the FPGA Kintex-7 device. In contrast to other recent architectures, the proposed design substantially reduces area requirements and power utilization. The Matlab tool verifies the design to achieve an acceptable spurious-free dynamic range (SFDR) of 115 dB.

Design of a Sigma-Delta Analog-to-Digital Converter Cascade Decimation Filter

As the current mainstream high-precision ADC architecture, sigma-delta ADC is extensively employed in a wide range of domains and applications. This paper presents the design of a highly efficient cascaded digital decimation filter for sigma-delta ADCs, emphasizing the suppression of high folding band noise and the achievement of a flat passband. Additionally, this study addresses the critical balance between filter performance and power consumption. An inserting zero (IZ) filter is incorporated into a cascaded integrator comb (CIC) filter to enhance aliasing suppression. The IZ filter and compensation filter are optimized using the particle swarm optimization (PSO) algorithm to achieve greater noise attenuation and smaller passband ripple. The designed filter achieves a noise attenuation of 93.4 dB in the folding band and exhibits an overall passband ripple of 0.0477 dB within a bandwidth of 20 KHz. To decrease the power consumption in the filter design, polyphase decomposition has been applied. The filter structure is implemented on an FPGA, processing a 5-bit stream from a 64-times oversampling rate and third-order sigma-delta modulator. The signal-to-noise ratio (SNR) of the output signal reaches 91.7 dB. For ASIC design, the filter utilizes 180 nm CMOS technology with a power consumption of 0.217 mW and occupies a layout area of 0.72 mm2. The post-layout simulation result indicates that the SNR remains at 91.7 dB.

Integrated optical ring resonator based comb filter in silicon-on-insulator with through-to-add port feedback path showing larger free spectral range

Integrated optical ring resonator based comb filter in silicon-on-insulator with through-to-add port feedback path showing larger free spectral range

MCSA-based fault diagnosis for rotary parts in servo motion system: Approach and experimental study

Motor current signature analysis (MCSA), as a non-invasive diagnostic method, is robust to environmental noise and of less sensor cost than vibration-based monitoring. Although large amount of progress has been achieved, little attention is paid to the MCSA-based diagnosis task in the Servo motion systems (SMS). An approach using Park vector demodulation, comb filtering and the ensemble empirical mode decomposition (EEMD) is proposed for cyclic fault event detection in this paper. Experiment studies reveal that the MCSA approach could extract the fault signature under extremely low-speed or noisy working condition, which has potential in the scenarios where the accelerometers placement is limited or affected by interferences.

Time-varying Comb Filters to Improve SpeechPerception in Sensorineural Hearing LossSubjects

Time-varying Comb Filters to Improve SpeechPerception in Sensorineural Hearing LossSubjects

Vernier effect based on cascading two Mach–Zehnder interferometers for selectable comb filter and saturable absorber applications in erbium-doped fiber laser

We present the applications of a Vernier effect based on cascading two Mach–Zehnder interferometers (MZIs) as a selectable comb filter and saturable absorber (SA) in an erbium-doped fiber laser (EDFL).Each MZI is composed of bi-tapered polarization-maintaining fibers (PMFs) constructed by fusion splicing between two single-mode fibers (SMFs), which are then connected in series to produce the Vernier effect. The first tapered MZI (called MZI-1) acted as a comb filter to providea larger free spectral range (FSR). The second MZI (MZI-2) based comb filter has a smaller FSR. The combination of these two filters forms an envelope structure on the comb-like spectrum. In this work, the first implementation of the comb filterbased onthe Vernier effectwas used as a wavelength-selectable filter. Through the adjustment of the polarization controller (PC1) and (PC2) inside the cavity, the FSR of the envelope can be varied, thereby switchable and adjustable multiwavelength was achieved. The second implementation uses a graphene nanoparticle (G-Nps)/polymer composite deposited onto the MZI-1 comb filter to act as an SA. At the 80 mW pump threshold, stable Q-switching EDFL operation was successfully activated at 1560.8 nm. The shortest pulse width of 2.89 μs at a 85.91 kHz repetition rate was achieved at 330 mA (180 mW) pump power. The proposed Vernier effect based on cascading two tapered MZIs configuration can find potential applications in the fields of advancedmultiwavelength fiber lasers and short pulse generation.

Simulation of high frame rate spread-spectrum color Doppler imaging of pulsatile flow

Spread-spectrum Doppler, a method introduced by our lab, preserves the maximum unaliased velocity of ultrafast Doppler while retaining some of the image quality benefits of compounding plane waves transmitted at different angles. The technique employs a sequence of pulses transmitted at M angles that are repeated L times in different random orders. Shuffling the slow-time samples so the angles repeat in the ascending order concentrates echoes from stationary off-focus targets in M harmonic frequency bins while spreading the in-focus signal across all frequencies. Off-focus echoes are suppressed, without compounding, by applying a notching comb filter, while the portion of the in-focus signal spread to the other (L − 1)M bins is retained for velocity estimation. Field II simulations were used to assess the method’s ability to track pulsatile velocity fluctuations in a straight vessel. The angle-corrected peak velocity was accurate to within ±10% of the true value when imaging at a Doppler frame rate of approximately 115 frames per cardiac cycle. Further improvement of the method will require a filter to attenuate off-focus echoes from non-stationary tissue.

Wavelength continuously tunable and wavelength spacing variable comb filter based on a High-Birefringence fiber loop mirror

We demonstrated an all-fiber comb filter that can continuously tune the wavelength for four switchable wavelength spacings. The comb filter consists of a fiber loop mirror (FLM) that is inserted with three polarization maintaining fibers (PMFs) and three polarization controllers (PCs). The transmission characteristics of the comb filter was theoretically analyzed. The output characteristics of the comb filters shows a dependence of the orientation angles of the PCs. With the angles being optimally set, the comb filter with four different wavelength spacings can be achieved. The wavelength continuously tunable and wavelength spacing variable mechanisms are elaborated. The three PCs are employed to enable the tunable and switchable functions. The two PCs between the PMFs serve as a polarization rotator to align the birefringent axes of the PMFs for varying the wavelength spacing while the PC adjacent to the optical coupler can be used for wavelength tuning function. When the two quarter-waveplates (QWPs) of the PC are optimally set at π/4 and - π/4, the half-waveplate (HWP) acts as a wavelength tuning element, and when the QWPs are set at zero degrees, the HWP serves as an amplitude tuning element. The center wavelength of the comb filter could be linearly tuned with the rotation angle of the HWP, and a π/2 change in the rotation angle leads to a wavelength change in one free-spectral-range (FSR). A π/4 change in the rotation angle could bring the normalized peak transmission from its maximum at 1 to minimum at 0. The proposed tunable technique has been verified by our experimental results. We experimentally demonstrated the comb filters can switch among FSRs of 0.75 nm, 1.01 nm, 1.51 nm, and 3.1 nm with tunable functions.

Design method for VDCC-based analog comb filter for power line interference cancellation

An analog comb filter is implemented by linking multiple VDCC-based notch filters in a cascading fashion (N in total), eliminating N different pole frequencies. This study focuses on suppressing a fundamental frequency of power-line interference of 50 Hz and its consecutive three odd harmonics at 150 Hz, 250 Hz, and 350 Hz. One significant advantage of this comb filter is the independent control over filters' parameters like quality factor and pole frequency. Additionally, these filters can be electronically tuned by adjusting the transconductance gain of VDCC. The suggested notch filter configuration involves 2 capacitors, 2 resistors, and 1 VDCC element. Extensive simulations were conducted using PSPICE simulator software to validate the effectiveness of these filters. The basic building block, VDCC, is designed and implemented in the simulation using integrated circuits MAX435 and AD844.•Design uses a VDCC-based high Q notch filter as the active building block.•The filter employs fewer active and passive components.•Simulated results using commercially available ICs, MAX435 and AD844, confirm the filter's practical utility.

Enhancing speaker identification through reverberation modeling and cancelable techniques using ANNs.

This paper introduces a method aiming at enhancing the efficacy of speaker identification systems within challenging acoustic environments characterized by noise and reverberation. The methodology encompasses the utilization of diverse feature extraction techniques, including Mel-Frequency Cepstral Coefficients (MFCCs) and discrete transforms, such as Discrete Cosine Transform (DCT), Discrete Sine Transform (DST), and Discrete Wavelet Transform (DWT). Additionally, an Artificial Neural Network (ANN) serves as the classifier for this method. Reverberation is modeled using varying-length comb filters, and its impact on pitch frequency estimation is explored via the Auto Correlation Function (ACF). This paper also contributes to the field of cancelable speaker identification in both open and reverberation environments. The proposed method depends on comb filtering at the feature level, deliberately distorting MFCCs. This distortion, incorporated within a cancelable framework, serves to obscure speaker identities, rendering the system resilient to potential intruders. Three systems are presented in this work; a reverberation-affected speaker identification system, a system depending on cancelable features through comb filtering, and a novel cancelable speaker identification system within reverbration environments. The findings revealed that, in both scenarios with and without reverberation effects, the DWT-based features exhibited superior performance within the speaker identification system. Conversely, within the cancelable speaker identification system, the DCT-based features represent the top-performing choice.

The application and innovation of erhu music in modern popular music

Abstract This study introduces a sophisticated music recognition classification system designed to preprocess musical samples from various instruments and extract cepstrum coefficients. These coefficients are subsequently utilized to train the tuning parameters of a deep confidence network. Once trained, the model is employed to predict the types of instruments used in test samples. Additionally, this paper explores the innovative application of a digital sound effector to process audio from the erhu and popular music, aiming to achieve a harmonious integration of frequency and pitch, thereby facilitating both reference and innovation of the erhu within the realm of popular music. The analysis delineates that within the digital sound effector, the pitch accumulation plugin and the stirring effect plugin exert a more pronounced influence on the fusion of erhu sounds with pop music compared to the comb filter plugin. The integration of frequencies is predominantly observed in two key segments of the composition. The first segment, spanning from 1’30” to 3’25”, showcases the fusion within bars 21-85 of the erhu piece “Chu Song”. The second segment, occurring from 4’68” to 7’49”, employs equalizer and delay effects to blend electronic music elements with the erhu, enhancing the piece’s contemporary relevance and appeal. This innovative approach underscores the potential of digital effects in bridging traditional Chinese musical instruments with modern music genres.

Generation of cylindrical vector beam pulses by using multi-wavelength EDFL with two-mode fiber filter

A multi-wavelength erbium-doped fiber laser (MW-EDFL) operating in the L-band with cylindrical vector beam outputs is proposed and experimentally investigated. The multi-wavelength lasing is realized by exploiting a two-mode fiber filter (TMFF) as the comb filter and a single-mode fiber spool with 2-km in length to suppress the mode competition. The multi-wavelength combs with channel spacing of 0.36 nm, 0.58 nm, and 1.12 nm are achieved by regulating the interference length of the TMFF, and up to 18 lasing channels are obtained with a wavelength spacing of 0.36 nm. Good long-term stability is manifested within a 100-minute duration, as the maximum peak power fluctuation of 1.96 dB and the maximum wavelength shift of 0.03 nm are measured. By adjusting the polarization controller associated with the two-mode long-period grating as a high-efficiency mode converter, radially and azimuthally polarized cylindrical vector beams of high purity are thus generated.

Enhanced Position Estimation Based on Frequency Adaptive Generalized Comb Filter for Interior Permanent Magnet Synchronous Motor Drives

Accurate rotor position estimation is critical to ensure the high-performance operation of position sensorless interior permanent magnet synchronous motor (IPMSM) drives. However, the back electromotive force (BEMF) estimated by the model-based observers is usually nonideal, which may further degrade the position estimation accuracy. In this paper, a frequency adaptive generalized comb filter (FAGCF) with a quadrature phase-locked loop (PLL) is adopted to suppress the rotor position estimation errors by filtering out the dominant distortions in the BEMF, including the (6k±1)th harmonics caused by inverter nonlinearity and flux spatial harmonics, as well as the DC offset from the inaccurate current measurements. This proposed filter is constructed by multiple digital delay blocks and therefore has the advantage of easy implementation with less online parameters tuning effort. Meanwhile, a linearized model is derived for PLL parameter design, with which the stability of the FAGCF-PLL position estimation system can also be analyzed theoretically. The effectiveness of the proposed sensorless control strategy has been validated with the experimental results on a 1.5-kW IPMSM drive.