Multiple Bandpass Filters Research Articles

Miniaturized bandpass metamaterials filters using hybrid plasmonic waveguide and defected surface structures

In this paper, we present a novel approach for designing single-/multiple-band bandpass filters (BPFs) using a hybrid metamaterials approach, incorporating substrate integrated waveguide (SIW), spoof surface plasmon polariton (SSPP), and defected surface structures (DSSs) technologies. The substrate-integrated plasmonic waveguide (SIPW) is constructed by embedding a hybrid dual SSPP into a three-layer SIW. The SIPW demonstrates a reduced phase velocity and a lowered lower cutoff frequency, extracted from the slow-wave dispersion relationship. Initially, the SIPW-based single-band metamaterial BPF demonstrates miniaturized size and broadened bandwidth. Furthermore, by loading a pair of complementary electric-inductive capacitive (ELC) resonators consisting of DSSs and adjusting their symmetry properties and geometric parameters, multiple BPFs from 1 to 3 are realized. To validate the proposed designs, three prototypes are fabricated and measured. The results demonstrate good filtering performances of proposed metamaterial BPFs, featuring high reflection loss (S11 < −10.5 dB) and a high level of out-of-band rejection exceeding 25 dB between multiple passbands.

Weak beat frequency extraction method for photon Doppler signal with low signal-to-noise ratio

Abstract In the window function spectrum of the low signal-to-noise ratio photon Doppler signal after the short-time Fourier transform, the weak beat frequency cannot be obtained by extracting the maximum amplitude spectrum frequency of each window because the amplitude of the noise spectrum exceeds the weak beat frequency. In this article, the value of the beat frequency is first estimated by the Kalman filter. Then, a multiple analytical bandpass filter is constructed to refine the spectrum of the high noise signal with the value of the beat frequency estimate as the spectrum band center. This technique extracts only the beat frequencies from the narrowband refinement spectrum by removing the interference spectrum band range. We use this technique to process the photon Doppler signals from the tiny high-speed flying fragments explosion experiment. After data processing, the beat frequency value heavily affected by high-frequency noise can reduce the error by up to 64.9%. The beat frequency value of the low noise signal can be accurate to 106 Hz, equivalent to 0.775 m/s after velocity demodulation. This method fully considers the positioning and protection of the beat frequency characteristics. It makes weak beat frequencies more obvious in the refined narrowband spectrum without changing the signal amplitude. This article describes a method for extracting the weak beat frequency of the photon Doppler signal or a signal optimization algorithm for needing high-precision beat frequencies in a test environment.

Impedance-Edited Multiple Low-Frequency Harmonic Current Adaptive Suppression

In the two-stage inverter, a large amount of low-frequency harmonic current will emerge in the front-end dc-dc converter and input dc voltage source. The low-frequency harmonic current will reduce the service life of the dc source and decrease the efficiency of the system. Additionally, the main components of low-frequency harmonic current fluctuate with uncertainty. To address those issues, an adaptive current suppression method based on impedance editing of the source-stage dc-dc converter is proposed in this paper. Compared with the traditional active power filter (APF), the proposed adaptive low-frequency harmonic current suppression method does not require additional circuits, which will never decrease the system efficiency but reduce the cost. More importantly, when the amplitude of the main components of harmonic current fluctuates, adaptive multiple bandpass filters are proposed to adaptively suppress the main harmonic current, which never influences the dynamic performance. In addition, the virtual impedance is connected in parallel with the bus capacitor to reduce the bus-voltage overshoot. The key parameters design of the proposed control strategy is given and the dynamic response of the proposed control strategy is also discussed. Finally, a prototype of 900W was fabricated and tested.

A robust feedforward hybrid active noise control system with online secondary‐path modelling

In this study, a robust feedforward hybrid active noise control (ANC) system with online secondary-path modelling (SPM) is proposed that is capable of not only effectively suppressing the broadband and narrowband noise components but also tracking the secondary path (SP) variations. An finite impulse response online SPM subsystem as well as an efficient decoupling filter are included in the proposed feedforward hybrid ANC (HANC) system. The decoupling filter is a parallel-form bandpass filter bank that consists of multiple bandpass filters that are derived from the second-order infinite impulse response notch filters. It takes the residual noise as its input and separates the broadband component from the narrowband component, with the former used as not only a desired signal for the SPM but also as an error signal for updating the broadband sub-controller, whereas the latter adapted simultaneously to scale the auxiliary white Gaussian noise and to update the narrowband sub-controller. Extensive simulations are conducted with both the synthetic and real SPs as well as the synthetic and real noise signals that are generated by a large-scale factory cutting machine (strand-cutter) to demonstrate the advantages and effectiveness of the proposed feedforward HANC system. Comparisons are also demonstrated with the original HANC system as well as its directly extended version with an online SPM subsystem.

Coupling Matrix Design of Compact Multiband Cascaded Trisection Bandpass Filters

In this brief, a universal coupled topology to design cascaded multiple passbands bandpass filters (BPFs) with numerous in-band poles and out-band transmission zeros (TZs) is presented. Based on the proposed topology, the coupling matrices are constructed to design multiband bandpass filters (MBPFs) with cascaded trisection (CT) BPFs’ filtering responses. To validate the theory and topologies, a quad-band CT BPFs with TZs located in each lower sub-band is successfully synthesized firstly. Then, a dual-band and tri-band CT BPF with TZs generated in the upper side of each passband are theoretically investigated by employing the coupling matrix. Finally, the proposed dual- and tri-band examples are implemented in compact planar multi-coupled lines structures. In all individual passbands, measured insertion losses (ILs) and measured return losses (RLs) are better than 2.82 dB and 15.9 dB, respectively. Good matching level between the simulated and experimental results have been achieved.

Epileptic Spike Detection Using Neural Networks With Linear-Phase Convolutions

To cope with the lack of highly skilled professionals, machine learning with proper signal processing is key for establishing automated diagnostic-aid technologies with which to conduct epileptic electroencephalogram (EEG) testing. In particular, frequency filtering with the appropriate passbands is essential for enhancing the biomarkers-such as epileptic spike waves-that are noted in the EEG. This paper introduces a novel class of neural networks (NNs) that have a bank of linear-phase finite impulse response filters at the first layer as a preprocessor that can behave as bandpass filters that extract biomarkers without destroying waveforms because of a linear-phase condition. Besides, the parameters of the filters are also data-driven. The proposed NNs were trained with a large amount of clinical EEG data, including 15833 epileptic spike waveforms recorded from 50 patients, and their labels were annotated by specialists. In the experiments, we compared three scenarios for the first layer: no preprocessing, discrete wavelet transform, and the proposed data-driven filters. The experimental results show that the trained data-driven filter bank with supervised learning behaves like multiple bandpass filters. In particular, the trained filter passed a frequency band of approximately 10-30 Hz. Moreover, the proposed method detected epileptic spikes, with the area under the receiver operating characteristic curve of 0.967 in the mean of 50 intersubject validations.

Monolithically-integrated 3D printed coaxial bandpass filters and RF diplexers: single-band and dual-band

AbstractThe manuscript reports on additively-manufactured (AM) coaxial-resonator-based bandpass filters (BPFs) and RF diplexers. A monolithic integration concept using stereolithography apparatus (SLA) is proposed and discussed in detail. Coupled-resonator-based synthesis alongside full-electromagnetic-based design methods is used for the design of the monolithic filters and RF diplexers. In particular, the paper discusses a new external coupling mechanism for dual-band BPFs that allow to independently control the coupling in each of the BPF passbands. Furthermore, a novel coaxial transmission line-type T-junction is proposed for the design of single- and dual-band RF diplexers. For practical validation purposes, multiple BPF and RF diplexer prototypes were designed, manufactured and tested at S- and C-band demonstrating the applicability of the proposed concept to low-cost, low-loss and low-weight RF components with complex geometrical features.

Design of extensible superconducting multiplexer with modular structure to overcome the limit of wafer size

In this paper, a new compact superconducting multiplexer with an extensible modular structure is proposed. The multiplexer consists of a common input feeder and multiple bandpass filters. The common feeder is realized by a transmission line with a characteristic impedance of 50 ohms. Compared with the conventional multiplexer, the proposed length of the common feeder is extensible, making it feasible to design a multiplexer consisting of arbitrary number of channels. In addition, the interaction between channel filters can be compensated for by adjusting the parameters of the channel filters. Therefore, no additional compensation circuit will be needed for the proposed multiplexer, leading to a lower volume or smaller size than conventional multiplexers. A six-channel multiplexer is designed and fabricated. Moreover, since there are open circuit points in the common input feeder of the proposed multiplexer, it is possible to divide the whole multiplexer into several individual components along these points. As a result, each component can be fabricated individually before being assembled by bonding gold wires at those open circuit points. Electromagnetic simulation results show that the performance of the proposed wire-bonded multiplexer only changes slightly, when compared to multiplexers that are fabricated on a single HTS wafer. Measurement results show that the proposed method is efficient in designing multiplexers. Therefore, a multiplexer with a large number of channels can be created to overcome the limit of wafer size by assembling individual components that are fabricated on different superconducting substrates.

Multiscale Characterizations of Surface Anisotropies.

Anisotropy can influence surface function and can be an indication of processing. These influences and indications include friction, wetting, and microwear. This article studies two methods for multiscale quantification and visualization of anisotropy. One uses multiscale curvature tensor analysis and shows anisotropy in horizontal coordinates i.e., topocentric. The other uses multiple bandpass filters (also known as sliding bandpass filters) applied prior to calculating anisotropy parameters, texture aspect ratios (Str) and texture directions (Std), showing anisotropy in horizontal directions only. Topographies were studied on two milled steel surfaces, one convex with an evident large scale, cylindrical form anisotropy, the other nominally flat with smaller scale anisotropies; a µEDMed surface, an example of an isotropic surface; and an additively manufactured surface with pillar-like features. Curvature tensors contain the two principal curvatures, i.e., maximum and minimum curvatures, which are orthogonal, and their directions, at each location. Principal directions are plotted for each calculated location on each surface, at each scale considered. Histograms in horizontal coordinates show altitude and azimuth angles of principal curvatures, elucidating dominant texture directions at each scale. Str and Std do not show vertical components, i.e., altitudes, of anisotropy. Changes of anisotropy with scale categorically failed to be detected by traditional characterization methods used conventionally. These multiscale methods show clearly in several representations that anisotropy changes with scale on actual surface measurements with markedly different anisotropies.

NESTED CIRCULAR ELLIPTICAL SHAPED MIXED LOOP RESONATOR BASED BANDPASS FILTER FOR MICROWAVE APPLICATIONS / PENAPIS JALUR BERASASKAN CAMPURAN GEGELUNG PENYALUN BERBENTUK SARANG BULAT UNTUK APLIKASI GELOMBANG MIKRO

An elliptical thumb printed nested circular mixed loop resonator (MLR) is introduced in this article to design a multiple bandpass filter for microwave applications. The proposed structure is composed of a series of loop resonators on a Rogers RT-5880 dielectric substrate, where the overall system is developed into a 377Ω framework. Similar structure is designed on both sides of the substrate and an investigation is made on scattering parameters, relative permittivity, permeability, refractive index and current distributions. The 12 ´ 14 mm2 structure is designed and evaluated by a simulation software CST microwave studio and the metamaterial characteristics have been classified by Nicolson-Ross-Weir method at the filtering frequencies. The proposed filter shows resonances at 2.65 GHz, 5.85 GHz, 7.12 GHz, and 8.59 GHz, and the measured results are compared with the simulated ones. With a favorable design and double-negative characteristics, this design is suitable for multiple bandpass filter particularly for S, C, and X-band applications.

Multimodal Multispectral Imaging System for Small UAVs

Multispectral imaging is an attractive sensing modality for small unmanned aerial vehicles (UAVs) in numerous applications. The most compact spectral camera architecture is based on spectral filters in the focal plane. Vehicle movement can be used to scan the scene using multiple bandpass filters arranged perpendicular to the flight direction. With known camera trajectory and scene structure, it is possible to assemble a spectral image in software. In this letter, we demonstrate the feasibility of a novel concept for low-cost wide area multispectral imaging with integrated spectral consistency testing. Six bandpass filters are arranged in a periodically repeating pattern. Since different bands are recorded at different times and in different viewing directions, there is a risk of obtaining spectral artifacts in the image. We exploit the repeated sampling of bands to enable spectral consistency testing, which leads to significantly improved spectral integrity. In addition, an unfiltered region permits conventional 2D video imaging that can be used for image-based navigation and 3D reconstruction. The proposed multimodal imaging system was tested on a UAV in a realistic experiment. The results demonstrate that spectral reconstruction and consistency testing can be performed by image processing alone, based on visual simultaneous localization and mapping (VSLAM).

Multi-wavelength UV imaging detection system applied for varying environmental conditions: Detection of SO2 as an example

We demonstrate a multi-wavelength ultraviolet (UV) imaging detection system for gaseous pollutants with absorption characteristics in the UV band. As a proof of concept, the detection of sulfur dioxide (SO2) was used as an example to develop a method based on UV imaging. The critical component of the system is a highly sensitive CCD array (1024 × 1024 pixels) UV camera with high quantum efficiency (QE) in the UV range (>30% transmission at 200–240 nm, >50% transmission at 240–400 nm), multiple different wavelength bandpass filters (270 nm, 280 nm, 300 nm, and 310 nm for SO2), environmental condition controller (temperature range 278–318 K, relative humidity range 35–85%), and a compact and robust design (362 mL of the gas absorption cell with a 4.2 m optical path length). The advantages of this system are convenient, fast, and can realize visualization. The system was applied for detecting SO2 in various conditions (different concentrations, temperatures, and humidity). After optimization, the detection limit for SO2 detection is 4 ppb, and the uncertainty of concentration measurement is only about 2.7%.

Multilayer triple band bandpass filter with a floating U-shaped SIR and split ring resonator

A multiple band bandpass filter (BPF) is designed using multilayer arrangement. The bandpass filter has three passbands having centre frequencies at 2.45 GHz, 4 GHz and 5 GHz. First a single band BPF is designed which includes a pair of coupled resonator and a split ring resonator in a multilayer arrangement. This geometry of the filter structure is studied and validated by fabrication and measurement. The initial single band filter structure is further improved to provide triple band BPF. All these bands are realized by a stub loaded U-shaped step impedance resonator (SLU-SIR). However, to improve the response of the second and third band a modified split ring resonator and a pair of open stubs are used. Each passband can be controlled individually. A mathematical analysis is done to study the proposed SLU-SIR using transmission line model. The proposed filter provides compactness and low insertion loss. A prototype is measured using vector network analyser (VNA) and shows a good matching with the simulated result.

Approximate analytical HVSR curve using multiple band-pass filters and potential applications

The Nakamura method, which utilizes the Horizontal to Vertical Spectral Ratio (HVSR) analysis, is widely used for seismic microzonation studies. The HVSR is an easy tool for estimation of site response resonances based on recorded ambient noise; however, it gives amplifications at resonant frequencies that are poorly correlated to the actual amplifications during strong ground motion.Generally, the site response, including any resonant effects, depends on the amplitude, frequency and duration of ground motion. An approach was proposed previously by McGuire [1], in which the transfer function of the soil response was approximated as a Single Degree of Freedom (SDOF) oscillator with one resonant frequency, obtained from the maximum in HVSR. A new approach is developed here, in which the entire HVSR curve is approximated by a manageable set of parallel band-pass resonators. Each individual oscillator is defined by three parameters: center frequency, gain, and steepness (Q factor). This approximation allows for the development and use of an analytical model of the HVSR curve.The application of the new approach is demonstrated on data recorded by the stations of the Southern Ontario Seismic Network (SOSN/Polaris), which have well studied characteristics and site response [2,3]. Data collected at each site consists of noise recordings to obtain the HVSR, as well as earthquake records. The analytical HVSR curves for each station are used to remove the site effect component from the recorded seismograms.

Alkalis atomic emission spectroscopy and flame temperature measurement of diesel impinging flames in an opposed multi-burner gasifier

Atomic emission spectroscopy can well characterize atom release properties and flame temperature. This work aims to investigate the spectroscopic characteristics of alkalis atoms and measurement method of flame temperature in diesel impinging flames, based on a bench-scale opposed multi-burner (OMB) gasifier. A fiber-optic spectrometer and a CCD camera coupled with multiple bandpass filters are used to obtain the spectral emission lines and two-dimensional emission distributions of Na∗ and K∗, respectively. The results indicate that alkalis atoms can be released and excited in impinging region and four jet regions. The emission intensities of Na∗ and K∗ under different O/C are the strongest in the impinging region, suggesting that the atom release concentration and flame temperature are the highest. Moreover, the thermal excitation degree is related to the type of atom, and Na atom is much easier to be excited than K atom. It is confirmed that alkalis atom content and flame temperature were the two main influence factors on the emission intensity, and emission intensity can be used to qualitatively characterize flame temperature under the same O/C. In addition, atomic emission spectroscopy (AES) was given to quantitatively calculate the flame temperature. It is verified that the AES method is and feasible to derive diesel flame temperature and monitor the temperature changes of OMB gasifiers in real time.

Photonic analog-to-digital conversion using a red frequency chirp in a semiconductor optical amplifier.

A photonic analog-to-digital conversion (PADC) based on intensity-to-frequency conversion using a frequency chirp in a semiconductor optical amplifier (SOA) is proposed. The presented PADC has a simple scheme whereby optical quantization is achieved using a single SOA with multiple rectangular bandpass filters placed in parallel. In this Letter, we successfully achieve 10 GSamples/s, eight-level optical quantization using a quantum-dot SOA. The PADC also has much lower input signal pulse power requirements for optical quantization, compared with conventional PADCs.

Theoretical analysis of adaptive harmonic window and its application in frequency extraction of vibration signal

The goal of this paper is to find an excellent adaptive window function for extracting the weak vibration signal and high frequency vibration signal under strong noise. The relationship between windowing transform and filtering is analyzed first in the paper. The advantage of adjustable time-frequency window of wavelet transform is introduced. Secondly the relationship between harmonic wavelet and multiple analytic band-pass filter is analyzed. The coherence of the multiple analytic band-pass filter and harmonic wavelet base function is discussed, and the characteristic that multiple analytic band-pass filter included in the harmonic wavelet transform is founded. Thirdly, by extending the harmonic wavelet transform, the concept of the adaptive harmonic window and its theoretical equation without decomposition are put forward in this paper. Then comparing with the Hanning window, the good performance of restraining side-lobe leakage possessed by adaptive harmonic window is shown, and the adaptive characteristics of window width changing and analytical center moving of the adaptive harmonic window are presented. Finally, the proposed adaptive harmonic window is applied to weak signal extraction and high frequency orbit extraction of high speed rotor under strong noise, and the satisfactory results are achieved. The application results show that the adaptive harmonic window function can be successfully applied to the actual engineering signal processing.

Investigations of CH∗ chemiluminescence and blackbody radiation in opposed impinging coal-water slurry flames based on an entrained-flow gasifier

The characteristics of excited CH radical (CH∗) chemiluminescence and blackbody radiation in opposed impinging coal-water slurry (CWS) flames were investigated in this paper based on a bench-scale opposed multi-burner (OMB) gasifier. CH∗ chemiluminescence is a significant radical species in flame spectral diagnostics, and blackbody radiation can reflect the spatial distribution of solid particles produced in flame. A fiber-optic spectrometer and a CCD camera coupled with multiple bandpass filters are used to obtain the spectral emission lines and two-dimensional spectral distributions, respectively. The results show that CH∗ emission peak at 431 nm and continuous blackbody radiation can be detected in CWS flames. The differences of spectral distributions between diesel and CWS impinging flame are analyzed. Impinging zone is the core chemical reaction region, and solid particles are also concentrated in impinging zone, indicating that four-burner impinging can well restrict the reactants and flames in the impinging zone, thereby greatly reduce the damage to the refractory walls. Moreover, according to the time-averaged distributions, the intensity and area of CH∗ emission and blackbody radiation are enhanced with the increase of oxygen and carbon molar ratio (O/C), demonstrating that improving O2 velocity promotes the chemical reactions, and flame temperature plays more dominant role than solid particle quantity in blackbody radiation. The time-dependent blackbody radiation evolution presents periodical change. Besides, it is found that O/C or syngas concentration can be feasibly estimated using CH∗ chemiluminescence in OMB gasifier.

定常状態視覚誘発電位に基づく人間の状態識別

This paper presents a signal processing technique to recognize human mental states from steady state visual evoked potentials. In this method, multiple band pass filter is applied to the electroencephalographic signals in order to extract feature points. A neural network classifier is used to recognize the type of LED stimulus the user is gazing at in real-time. An experiment is conducted on three participants to evaluate the classification performance of the proposed method. In this experiment, each participants gazes at three types of LEDs flashing at different frequencies. Another experiment is also conducted to evaluate the efficiency of information transfer based on recognition time. Experiment results show that the proposed method can achieve a mean recognition accuracy of 80%. Furthermore, the average time taken to recognize the target LED stimulus is 4.74 seconds.

A robust SEM auto-focus algorithm using multiple band-pass filters

An auto-focus algorithm using multiple band-pass filters for a scanning electron microscope (SEM) is proposed. To acquire sharp images of various kinds of defects by SEM defect observation in semiconductor manufacturing, the auto-focus process must be robust. A method for designing a band-pass filter for calculating the ‘focus measure’ (a key parameter of the auto-focus process) is proposed. To achieve an optimal specific frequency response for various images, multiple band-pass filters are introduced. As for the proposed method, two series of focus measures are calculated by using multiple band-pass filters independently, and it is selected according to reliability of the series of focus measures. The signal-to-noise ratio of an image for acceptable auto-focus precision is determined by simulation using pseudo images. In an experiment using the proposed method with real images, the success rate of auto focus is improved from 79.4% to 95.6%.