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A bandwidth-tunable multiband microwave photonic filter (MPF) using a strongly coupled microring resonator (MRR) with optical phase modulation is demonstrated theoretically and experimentally. Two notches of the MRR adjacent to the optical carrier break the intrinsic balance of the phase-modulated signal and then two sub-MPFs are formed thanks to the conversion from phase modulation to intensity modulation (PM-IM). The frequency responses of the two sub-MPFs are superimposed to form a passband with a fixed center frequency. Due to the periodicity of the MRR transmission spectrum, multiple passbands separated by a certain spacing appear in the frequency domain and combine to form a multiband MPF, whose bandwidth can be adjusted by tuning the wavelength of the carrier. The tunable bandwidth and shape factors ranging from 0.73 GHz to 2.73 GHz and 5.06 to 1.38 are experimentally performed. The number of passbands can be reconfigured. The proposed multiband MPF has the potential to be employed in modern multi-standard wireless communication systems.

Background and objective: The purpose of this study was to eliminate the interferences of electrical impedance tomography (EIT) on synchronous recording electroencephalography (EEG) for seizure detection.! Methods: The simulated EIT signal generated by COMSOL Multiphysics was superimposed on the clinical EEG signal obtained from the CHB-MIT Scalp EEG Database, and then the spectrum features of superimposed mixed signals were analyzed. According to the spectrum analysis, in addition to high-frequency interference at 51.2 kHz related to the drive current, there was also low-frequency interference caused by switching of electrode pairs, which were used to inject drive current. A low pass filter and a comb filter were used to suppress the high-frequency interference and low-frequency interference, respectively. Simulation results suggested the low-pass filter and comb filter working together effectively filtered out the interference of EIT on EEG in the process of synchronous monitoring. Results: As a result, the normal EEG and epileptic EEG could be recognized effectively. Pearson correlation analysis further confirmed the interference of EIT on EEG was effectively suppressed. Conclusions: This study provides a simple and effective interference suppression method for the synchronous monitoring of EIT and EEG, which could be served as a reference for the synchronous monitoring of EEG and other medical electromagnetic devices. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical background for design of comb decimator based on theorem of symmetric polynomials with roots on the unit circle. A simple multiplierless filter, called zero‐separation (ZS) filter, which separates doubled comb zeros, is derived. The separation of doubled comb zeros improves comb aliasing rejection. In order to get more benefits of the ZS filter, a two‐stage structure is considered. The classic comb filters are in both stages of the proposed structure. Additionally, in the second stage, a ZS filter is inserted to improve comb aliasing rejection. The passband droop is compensated by the compensator which works at low rate and is designed using particle swarm optimization (PSO). The method is illustrated with various examples. The comparisons with methods from literature prove the benefits of the proposed work. [ABSTRACT FROM AUTHOR]

Resonator structures with a multiwavelength filter are critical devices for the fabrication of stable output multiwavelength fiber lasers. In this study, we propose a spatially separated multiwavelength filter based on a 2D chirped fiber grating. The resonant fields of lasers with different wavelengths are spatially separated, reducing cross-gain modulation. In addition, the structure of the 2D chirped fiber grating is analyzed, and the spectral output characteristics of the device are investigated for different grating parameters, which provides theoretical guidance for designing such a novel optical comb filter. Furthermore, by fabricating the 2D chirped fiber grating onto a single-mode fiber, a multiwavelength filter with 17 wavelengths, a frequency interval of approximately 88 GHz, and a grating length of 4.8 cm is created. This device is characterized by its compact structure and simple fabrication method. [ABSTRACT FROM AUTHOR]

This paper proposes a nonadaptive error demodulation technique with which to track the amplitude, the phase and the frequency information of the grid voltage for single-phase applications. A nonadaptive comb filter, Lyapunov’s estimation law, and half-cycle moving average filters are exploited in order to reconstruct the fundamental orthogonal components. The proposed nonadaptive Lyapunov filter has good bandpass filtering characteristics, thus allowing the rapid rejection of the dc-offset and the harmonics. The proposed open-loop phase angle deviation algorithm is, moreover, a rescuer as regards estimating the fundamental frequency deviation, signifying that it correctly compensates the estimated amplitude and the phase angle information through the use of a mathematical regression approach under off-nominal frequency conditions. [ABSTRACT FROM AUTHOR]

This paper presents a proposed approach for cancelable biometric recognition related to speaker identification. Both comb and inverse comb filters are used to distort speech signals intentionally prior to and after feature extraction. The objective of this approach is to generate protected templates of speech signals representing speakers without subjecting the original speech signals or features to violations of attackers. Both comb and inverse comb filters are used for this purpose. In addition, a satisfactory performance represented in the speaker identification rate is retained. In case the database of speaker features is compromised, it is possible to change the comb or inverse comb filter orders to generate new features for the same speakers. Simulation results reveal the possibility to identify speakers from their deteriorated speech signals, which proves the robustness of the proposed cancelable speaker identification system. The reason of choosing the comb filter is that it is a multi-band filter with multiple nulls in its frequency response. Hence, its inversion is difficult due to the nulling effect. This characteristic can induce non-invertible distortion in speech signals. [ABSTRACT FROM AUTHOR]

This article presents a robust single-phase phase-locked loop (PLL)-less frequency, phase, and amplitude estimation technique. The proposed scheme, unlike PLL approaches, does not require a rigorous design and tuning process in order to attain a better stability margin. It is important to note that an improved discrete-time oscillator is obtained by involving a comb filter, which helps improve the dc-offset rejection capability and transient response time. Moreover, the notch-filter-like behavior and the introduction of imaginary zeros ensure better harmonic removal ability when compared to a known nonadaptive discrete-time oscillator. The proposed scheme relies on an open-loop frequency estimation technique that does not involve an inverse trigonometric function for the estimation of fundamental frequency deviation. The feedbackless architecture of the scheme and the avoidance of inverse trigonometric function, therefore, assist in reducing the real-time implementation complexity. However, under off-nominal grid frequency deviations, the amplitude and the phase of the output of the prefilter will suffer from errors. These errors are compensated by employing a mathematical regression approach. The results are experimentally validated and compared in order to prove the robustness and usefulness of the proposed scheme for single-phase applications. [ABSTRACT FROM AUTHOR]

Harmonic detection plays an important role in power quality for grid-tied inverters. Among the various methods, sliding discrete Fourier transform (SDFT) based algorithms have found wide and popular applications due to advantages like simplicity and excellent selectively filtering properties. However, SDFT suffers from disadvantages like slow dynamics and large memory occupation. In this paper, the discrete transfer function of SDFT harmonic extraction method is analyzed, and the SDFT transfer function is divided into three parts: comb filter, resonance controller, and adjustment factor. It is found that the comb filter determines the harmonic component that SDFT needs to detect and the dynamic performance of SDFT. Thus, the comb filter can be improved according to the characteristics of the load current, thereby achieving faster dynamic performance while reducing the digital storage space required for the implementation of the SDFT algorithm. Therefore, a general harmonics detection is proposed, which could detect harmonics by adjusting the comb filter of SDFT according to the characteristics of the load current. Finally, the correctness and effectiveness of the proposed general harmonics detection method are verified by relevant experiments.

To improve the performance of frequency-locked loops (FLLs) under distorted grid conditions, a series of pre-filtering techniques have been added to remove harmonics. One of them is the FLL-based comb filter (COMB-FLL), which offers a high disturbance rejection capability. However, it has some disadvantages, such as approximating a fractional delay and compensating an accumulated round-off error in the digital implementation of COMB-FLL. To alleviate these problems, this study proposes an active noise cancellation (ANC) FLL with a notch filter (NF), which incorporates an NF and an ANC to improve the frequency-locking ability. In this research, the structure of a comb filter is simplified into an NF, and an ANC is creatively introduced to eliminate harmonics from the frequency signal obtained by FLL. Furthermore, ANC has been improved to make it suitable for electricity-related applications. The proposed FLL features a unique cascade structure, which has excellent frequency-locking ability and dynamic characteristics under normal, abnormal, and harmonically distorted grid conditions. The simulations and experimental results verify the validity and reliability of the proposed FLL. [ABSTRACT FROM AUTHOR]

Calculation of peripheral capillary oxygen saturation (SpO 2) levels in humans is often made with a pulse oximeter, using photoplethysmography (PPG) waveforms. However, measurements of PPG waveforms are susceptible to motion noise due to subject and sensor movements. In this study, we compare two SpO 2 -level calculation techniques, and measure the effect of pre-filtering by a heart-rate tuned comb peak filter on their performance. These techniques are: (1) "Red over Infrared," calculating the ratios of AC and DC components of the red and infrared PPG signals, (A C / D C) red (A C / D C) infrared , followed by the use of a calibration curve to determine the SpO 2 level Webster (in: Design of pulse oximeters, CRC Press, Boca Raton, 1997); and (2) a motion-resistant algorithm which uses the Discrete Saturation Transform (DST) (Goldman in J Clin Monit Comput 16:475–83, 2000). The DST algorithm isolates individual "saturation components" in the optical pathway, which allows separation of components corresponding to the SpO 2 level from components corresponding to noise and interference, including motion artifacts. The comparison we provide here (employing the two techniques with and without pre-filtering) addresses two aspects: (1) accuracy of the SpO 2 calculations; and (2) computational complexity. We used both synthetic data and experimental data collected from human subjects. The human subjects were tested at rest and while exercising; while exercising, their measurements were subject to the impacts of motion. Our main conclusion is that if an uninterrupted high-quality heart rate measurement is available, then the "Red over Infrared" approach preceded by a heart-rate tuned comb filter provides the preferred trade-off between SpO 2 -level accuracy and computational complexity. A modest improvement in SpO 2 estimate accuracy at very low SNR environments may be achieved by switching to the pre-filtered DST-based algorithm (up to 6% improvement in SpO 2 level accuracy at −10 dB over unfiltered DST algorithm and the filtered "Red over Infrared" approach). However, this improvement comes at a significant computational cost. [ABSTRACT FROM AUTHOR]

We present an in-depth analysis of the sources of variance in state-of-the-art unbiased volumetric transmittance estimators, and propose several new methods for improving their efficiency. These combine to produce a single estimator that is universally optimal relative to prior work, with up to several orders of magnitude lower variance at the same cost, and has zero variance for any ray with non-varying extinction. We first reduce the variance of truncated power-series estimators using a novel efficient application of U-statistics. We then greatly reduce the average expansion order of the power series and redistribute density evaluations to filter the optical depth estimates with an equidistant sampling comb. Combined with the use of an online control variate built from a sampled mean density estimate, the resulting estimator effectively performs ray marching most of the time while using rarely-sampled higher-order terms to correct the bias. [ABSTRACT FROM AUTHOR]

We demonstrate a switchable and flexible comb filter/interleaver based on ring-resonator (RR) in which the directional couplers are replaced by tunable couplers. The tunable coupler is composed of an even-arm-length Mach-Zehnder interferometer (MZI) with a micro-heater embedded in one of the arms. For the sake of discussion, we convert the heating power of the micro-heater into a pure phase shift value independent of the waveguide material and size. By changing the phase shift value, the filter can be switched between comb filter and interleaver. Meanwhile, the insertion loss (IL), full width at half maximum (FWHM), extinction ratio (ER), and the shape of the response spectrum can also be reconfigured. The switchable and flexible comb filter/interleaver may provide a potential application in dense wavelength division multiplexing (DWDM) optical communication systems. [ABSTRACT FROM AUTHOR]

This work deals with electromyography (EMG) signal processing for the diagnosis and therapy of different muscles. Because the correct muscle activity measurement of strongly noised EMG signals is the major hurdle in medical applications, a raw measured EMG signal should be cleaned of different factors like power network interference and ECG heartbeat. Unfortunately, there are no completed studies showing full multistage signal processing of EMG recordings. In this article, the authors propose an original algorithm to perform muscle activity measurements based on raw measurements. The effectiveness of the proposed algorithm for EMG signal measurement was validated by a portable EMG system developed as a part of the EU research project and EMG raw measurement sets. Examples of removing the parasitic interferences are presented for each stage of signal processing. Finally, it is shown that the proposed processing of EMG signals enables cleaning of the EMG signal with minimal loss of the diagnostic content. [ABSTRACT FROM AUTHOR]

Resonator structures with a multiwavelength filter are critical devices for the fabrication of stable output multiwavelength fiber lasers. In this study, we propose a spatially separated multiwavelength filter based on a 2D chirped fiber grating. The resonant fields of lasers with different wavelengths are spatially separated, reducing cross-gain modulation. In addition, the structure of the 2D chirped fiber grating is analyzed, and the spectral output characteristics of the device are investigated for different grating parameters, which provides theoretical guidance for designing such a novel optical comb filter. Furthermore, by fabricating the 2D chirped fiber grating onto a single-mode fiber, a multiwavelength filter with 17 wavelengths, a frequency interval of approximately 88 GHz, and a grating length of 4.8 cm is created. This device is characterized by its compact structure and simple fabrication method.

In this paper, we present a numerical analysis of a novel comb filter in a double-pass Mach–Zehnder interferometer and a Sagnac interferometer (DP-MZI–SI) configuration and verify it by partial experimental demonstration. The proposed filter comprises an in-line fibre polarisation controller (PC), positioned in one arm of the Mach–Zehnder interferometer, and a polarisation-maintaining fibre (PMF) with a three-component fibre-coil PC in the Sagnac loop. The transmission of the DP-MZI–SI filter was determined using the Jones matrix of each component. This filter allows control of the free spectral range (Δλ) via two alternative modes of operation: by changing the length of the PMF or by increasing the arm length of the filter. In addition, the contrast of the interference fringes and their position can be controlled by adjusting the PCs. The possibility to generate stable patterns with narrow fringe separation was also demonstrated. Simulation results for the DP-MZI–SI filter were validated through experimental measurements. The experimental and numerical results agreed closely in terms of both Δλ and fringe visibility. The proposed DP-MZI–SI filter has characteristics suitable for application to tunable multi-wavelength and switchable fibre laser development, as well as to optical sensors, communication systems, and microwave generation.

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., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Author(s).)

This letter presents a new filter to suppress radio frequency interference (RFI) in microwave remote sensing instruments, particularly a wideband autocorrelation radiometer (WiBAR). RFI increases the noise floor and results in a decreased signal-to-noise ratio (SNR) of the WiBAR delay peak. The proposed filter operates like a Fabry–Perot interferometer (FPI) in optics and has the frequency response of a comb filter with many evenly spaced alternating pass and stop bands. The frequencies of these bands are varied with an electrically adjustable phase shifter. The design of a comb filter with an airy finesse value of 20 has been verified by simulation and measurement. [ABSTRACT FROM AUTHOR]

Here, by harnessing a composite combination of wave retarders, we propose and experimentally demonstrate a first-order narrowband fiber comb filter capable of continuously tuning its wavelength, of which the filter structure is on the fundamental basis of a polarization–diversity loop structure. The demonstrated comb filter consists of a polarizing beam splitter (PBS), two high birefringence fiber (HBF) segments of the same length, an ordered wave retarder combination (WRC) of a quarter-wave retarder (QWR) and a half-wave retarder (HWR) before the first HBF segment, and an ordered WRC of an HWR and a QWR before the second HBF segment. The second HBF segment is butt-coupled to one port of the PBS so that its principal axis should be 22.5° away from the horizontal axis of the PBS. Taking the filter transmittance obtained by Jones calculus into consideration, we found the azimuth orientation angle (AOA) sets of the four wave retarders, which could allow extra phase shifts (ψ's) ranging from 0° to 360° to be induced in the narrowband transmittance function. From filter transmission spectra calculated according to the AOA sets found above, it is confirmed that the first-order narrowband comb spectrum can be continuously tuned by properly controlling the AOA's, clearly indicating the continuous wavelength tunability based on a composite combination of ordered wave retarders. This theoretical prediction was verified by actually constructing the proposed filter. Then, it is concluded that our filter employing the composite combination of wave retarders can be continuously frequency-tuned by properly controlling the AOA's of the wave retarders. [ABSTRACT FROM AUTHOR]

Here we theoretically and experimentally demonstrated the arbitrary phase modulation of a general transmittance function (GTF) of the first-order optical comb filter based on a polarization-diversity loop structure, which employed two ordered waveplate sets (OWS's) of a quarter-wave plate (QWP) and a half-wave plate (HWP). The proposed comb filter is composed of a polarization beam splitter (PBS), two equal-length polarization-maintaining fiber (PMF) segments, and two OWS's of a QWP and an HWP with each set located before each PMF segment. The second PMF segment is butt-coupled to one port of the PBS so that its principal axis should be 22.5° away from the horizontal axis of the PBS. First, we explained a scheme to find four waveplate orientation angles (WOA's) allowing the phase of a GTF to be arbitrarily modulated, using the way each component of the filter, such as a waveplate or PMF segment, affects its input or output polarization. Then, with the WOA finding method, we derived WOA sets of the four waveplates, which could give arbitrary phase retardations ϕ's from 0° to 360° to a GTF chosen here arbitrarily. Finally, we showed phase-modulated GTF's calculated at eight selected WOA sets allowing ϕ's to be 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°, and then the predicted results were verified by experimentally measured results. It is concluded from the theoretical and experimental demonstrations that the GTF of our filter based on the OWS of a QWP and an HWP can be arbitrarily phase-modulated by properly controlling the WOA's of the four waveplates. [ABSTRACT FROM AUTHOR]

This paper presents a novel scheme for cancelable iris recognition based on comb filtering. This scheme begins with a coarse-to-fine iris localization stage. After that, Gabor filtering is applied for feature extraction. The two-dimensional phase pattern of features generated with the LogGabor filter is distorted through comb filtering. The objective of this distortion process is to generate a cancelable feature pattern that represents the iris. The ability to reinitiate a new cancelable pattern is guaranteed through the variation of the comb filter order. The proposed scheme is compared with a cancelable random projection scheme for iris recognition. Experimental results are conducted on CASIA-IrisV3-Interval database for both random projection and comb filtering schemes. Moreover, evaluation metrics are estimated for different comb filter orders of 6, 8, 10, and 12 in addition to the case of original iris features. Hamming distance and Receiver Operating Characteristic (ROC) curve are estimated for both random projection and comb filtering schemes to check robustness and stability. The experimental results show a significant gain in both privacy and performance. Also, the comb filtering scheme achieves a superior performance for all orders compared to the random projection scheme. The proposed comb filtering scheme achieves the highest accuracy of 99.75% for order 6 and a promising Equal Error Rate (EER) of 0.36% for order 10. [ABSTRACT FROM AUTHOR]

A novel electronically tunable shadow comb filter with N notches is presented. The proposed filter is built around the commercially available current-feedback operational-amplifier (CFOA). The bandwidth of each notch can be independently controlled, without disturbing the gain of the comb filter and the notch frequency, by adjusting the gain of an external voltage amplifier built around a CFOA. The gain of this CFOAbased voltage amplifier is controlled by adjusting a variable grounded resistance. This grounded resistance can be implemented, if desired, using an operational transconductance amplifier (OTA) configured as a grounded resistance. The proposed shadow comb filter enjoys the attractive feature of low output impedance. This would facilitate cascading of comb filters to obtain any number of notch frequencies. Experimental results obtained from a shadow comb filter with 4 notch frequencies using the AD844 CFOA are presented. These results confirm the functionality of the proposed comb filter both for low as well as high notch frequencies. [ABSTRACT FROM AUTHOR]

Batch measurement of sheet-like product quantity is very common in manufacturing and commercial areas. Particularly, to satisfy the growing requirement of automatic and nondestructive detection, a machine vision system for stacked substrates counting is proposed in this paper. With a brief description of the system architecture and imaging module, the challenges for real data analysis are investigated. Our main contribution is to develop a robust stripe detection algorithm by combining the merits of local template matching and global frequency domain filtering. Besides the peak-valley feature across the stack profile, the collinear prior shape along the substrates is also utilized in a morphological scheme to purify the obtained ridge-line or stripe images, which, finally, benefits the statistical counting output. It is verified in experiments using a diversity of substrate media that our developed system can achieve a high counting accuracy with the detection error not more than 0.01% as the sample thickness varies between 0.05 mm and 0.5 mm. Moreover, the proposed algorithm performs much robustly with various kinds of abnormalities and interferences like irregular piling, media distortion, and foreign contamination. [ABSTRACT FROM AUTHOR]

In this paper, switchable multi-wavelength erbium-doped fiber lasers (MW-EDFLs) are proposed and experimentally demonstrated. An in-fiber Mach–Zehnder interferometer (IFMZI) composed of asymmetric biconical fiber taper (ABFT) pairs is integrated into the all-fiber ring cavity for multi-wavelength filtering. This laser can stably emit single-, dual-, or triple-wavelength outputs by fine-tuning the polarization controller. A high optical signal to noise ratio of 58.5 dB is obtained for the output spectra. The maximum wavelength shift is 0.08 nm and the power fluctuation in all laser emissions is recorded at 1.64 dB. • Multi-wavelength erbium-doped fiber laser generating single-, dual-, and triple-wavelength emissions is demonstrated. • An in-fiber Mach–Zehnder interferometer composed of asymmetric biconical fiber taper pairs is exploited as the comb filter. • A maximal optical signal to noise ratio of 58.5 dB is obtained. • Favorable temporal stability with the maximum wavelength shift of 0.08 nm and power fluctuation of 1.64 dB is presented. [ABSTRACT FROM AUTHOR]

This work deals with electromyography (EMG) signal processing for the diagnosis and therapy of different muscles. Because the correct muscle activity measurement of strongly noised EMG signals is the major hurdle in medical applications, a raw measured EMG signal should be cleaned of different factors like power network interference and ECG heartbeat. Unfortunately, there are no completed studies showing full multistage signal processing of EMG recordings. In this article, the authors propose an original algorithm to perform muscle activity measurements based on raw measurements. The effectiveness of the proposed algorithm for EMG signal measurement was validated by a portable EMG system developed as a part of the EU research project and EMG raw measurement sets. Examples of removing the parasitic interferences are presented for each stage of signal processing. Finally, it is shown that the proposed processing of EMG signals enables cleaning of the EMG signal with minimal loss of the diagnostic content.

In view of problems of bad accuracy and real-time existed in harmonic and inter-harmonic detection algorithm, a harmonic and inter-harmonic detection algorithm based on comb filter and subgroup idea was proposed, and a harmonic monitoring device based on the algorithm was designed. Firstly, the device uses the comb filter to separate harmonic and inter-harmonics from original signal effectively. Then, the device uses inter-harmonic subgroup algorithm to calculate inter-harmonic component of the separated signal, and uses original signal component to minus the inter-harmonic component to reconstruct of sampled sequences. Finally, the device adopts harmonic subgroup algorithm to calculate the harmonic component, so as to realize high precision detection of harmonic. Test results verify that the device has high detection accuracy.

Brain-Computer Interface (BCI) systems are widely based on steady-state visual evoked potentials (SSVEP) detection using electroencephalography (EEG) signals. SSVEP-based BCIs are becoming attractive due to their higher signal-to-noise ratio (SNR) as well as faster information transfer rate (ITR). However, their performances are largely affected by the interference coming from the spontaneous EEG activities which intrinsically restrict their efficiency in distinguishing between SSVEPs and background EEG activities. In this paper, we introduce a new approach for the detection of SSVEP based on bispectral analysis to palliate the frequency-dependent bias. A COMB filter associated with a wavelet denoising filter is firstly used to minimize the noise while improving the SNR of phase signals. Next, the complementary orthogonal projections and the principle component analysis (PCA) are used to decompose the components related to SSVEPs and components related to brain activities. Finally, the bispectrum, a powerful tool for the analysis and the characterization of nonlinear properties of stochastic signals, is used to extract the features of the EEG signal benefiting from the information about the phase coupling of the signal components. The results of experiments, using two databases on five (or ten) subjects, show that the proposed approach significantly outperformed the standard CCA approach in distinguishing the target frequency and in average information transfer rate. [ABSTRACT FROM AUTHOR]

Aiming at the high passband drop in cascaded integrator comb (CIC) filters, this paper proposes an improved integer programming for the design of CIC compensator. By separating minimum fraction part from the representation of the sum of powers of two, a one-to-one correspondence is established between the set of coefficients of CIC compensator and an integer set, so that coefficients of CIC compensator can be optimized by integer variable. Particle swarm optimization is applied to avoid truncation error in branch and bound algorithm. Simulation results indicate that the compensated CIC filter by the proposed method can achieve absolute passband deviation less than 0.03 dB. [ABSTRACT FROM AUTHOR]

An analog topology is proposed to implement a comb filter for removal of power-line interference from various low-amplitude biomedical signals. In this proposed methodology, an n-number of all-pass filters (APFs) and an adder circuit are used to suppress n-number of frequencies. All the APFs as well as the adder circuit are designed using a current conveyor to utilize the various properties of the current-mode circuits. The active and passive components used to design the comb filter include second-generation current conveyor (CCII±), resistor, and capacitor. The circuit is designed for n = 4 to remove the power-line frequency of 50 Hz, and its three odd harmonics such as 150 Hz, 250 Hz, and 350 Hz. A PSPICE simulation is done to verify the performance of the proposed circuit. In simulation, all CCII± are designed using macro model of commercially-available current feedback operational amplifier integrated circuit (IC) AD844 as well as dynamic threshold voltage metal oxide semiconductor technology. The proposed circuit is also implemented also using commercially available IC AD844 on breadboard for n = 3. The output result on digital storage oscilloscope confirm the effectiveness of the proposed comb filter circuit in removing the power line interference i.e. the power-line frequency and its odd harmonics. [ABSTRACT FROM AUTHOR]

Here, by harnessing a composite combination of wave retarders, we propose and experimentally demonstrate a first-order narrowband fiber comb filter capable of continuously tuning its wavelength, of which the filter structure is on the fundamental basis of a polarization–diversity loop structure. The demonstrated comb filter consists of a polarizing beam splitter (PBS), two high birefringence fiber (HBF) segments of the same length, an ordered wave retarder combination (WRC) of a quarter-wave retarder (QWR) and a half-wave retarder (HWR) before the first HBF segment, and an ordered WRC of an HWR and a QWR before the second HBF segment. The second HBF segment is butt-coupled to one port of the PBS so that its principal axis should be 22.5° away from the horizontal axis of the PBS. Taking the filter transmittance obtained by Jones calculus into consideration, we found the azimuth orientation angle (AOA) sets of the four wave retarders, which could allow extra phase shifts (ψ’s) ranging from 0° to 360° to be induced in the narrowband transmittance function. From filter transmission spectra calculated according to the AOA sets found above, it is confirmed that the first-order narrowband comb spectrum can be continuously tuned by properly controlling the AOA’s, clearly indicating the continuous wavelength tunability based on a composite combination of ordered wave retarders. This theoretical prediction was verified by actually constructing the proposed filter. Then, it is concluded that our filter employing the composite combination of wave retarders can be continuously frequency-tuned by properly controlling the AOA’s of the wave retarders.

Here we theoretically and experimentally demonstrated the arbitrary phase modulation of a general transmittance function (GTF) of the first-order optical comb filter based on a polarization-diversity loop structure, which employed two ordered waveplate sets (OWS’s) of a quarter-wave plate (QWP) and a half-wave plate (HWP). The proposed comb filter is composed of a polarization beam splitter (PBS), two equal-length polarization-maintaining fiber (PMF) segments, and two OWS’s of a QWP and an HWP with each set located before each PMF segment. The second PMF segment is butt-coupled to one port of the PBS so that its principal axis should be 22.5° away from the horizontal axis of the PBS. First, we explained a scheme to find four waveplate orientation angles (WOA’s) allowing the phase of a GTF to be arbitrarily modulated, using the way each component of the filter, such as a waveplate or PMF segment, affects its input or output polarization. Then, with the WOA finding method, we derived WOA sets of the four waveplates, which could give arbitrary phase retardations ϕ’s from 0° to 360° to a GTF chosen here arbitrarily. Finally, we showed phase-modulated GTF’s calculated at eight selected WOA sets allowing ϕ’s to be 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°, and then the predicted results were verified by experimentally measured results. It is concluded from the theoretical and experimental demonstrations that the GTF of our filter based on the OWS of a QWP and an HWP can be arbitrarily phase-modulated by properly controlling the WOA’s of the four waveplates.