Band Filter Research Articles

Band offsets, electron affinities and optical dynamics at the CdBr2/SiO2 interfaces

Herein, the structural, optical, dielectric and optical conductivity parameters of the CdBr2/SiO2 interfaces are reported. Thin films of CdBr2 are coated with 50 nm thick SiO2 under a vacuum pressure of 10−5 mbar. The structural morphological and optical investigations have shown that CdBr2 exhibit hexagonal structure of lattice parameters of a=b=7.20Å and =13.86Å, energy band gap of 3.32 eV and Urbach energy of 0.84 eV. The interfacing of CdBr2 films with SiO2, shortened the lattice parameters, blue-shifted the energy band gap and decreased the Urbach energy value. The electron affinity of CdBr2 which is determined here is found to be 3.27 eV. The CdBr2/SiO2 interfaces displayed a conduction and a valence band offsets of 2.37 eV and 3.21 eV, respectively. In addition, the dielectric dispersion and optical conduction analyses using the Drude-Lorentz approach have shown that the drift mobility and plasmon frequency (Wpi) of the free charge carriers at the CdBr2/SiO2 interfaces varies in the range of 28.59–22.87 cm2/Vs and 0.41–6.47 GHz, respectively. The effectiveness of the plasmon frequency to limit signal propagation in the heterojunction devices is confirmed by the impedance spectroscopy technique which showed radiowave (RF) band filter characteristics at the targeted Wpi. The energy band offsets, the optical conductivity parameters and the RF filtering properties nominates the CdBr2/SiO2 heterojunctions for use in thin film transistor technology.

Asymmetric Diffraction in Plasmonic Meta-Gratings Using an IT-Shaped Nanoslit Array.

Diffraction is a fundamental phenomenon that reveals the wave nature of light. When a plane wave is transmitted or reflected from a grating or other periodic structures, diffracted light waves propagate at several angles that are specified by the period of the given structure. When the optical period is shorter than the wavelength, constructive interference of diffracted light rays from the subwavelength-scale grating forms a uniform plane wave. Many studies have shown that through the appropriate design of meta-atom geometry, metasurfaces can be used to control light properties. However, most semitransparent metasurfaces are designed to perform symmetric operation with regard to diffraction, meaning that light diffraction occurs identically for front- and back-side illumination. We propose a simple single-layer plasmonic metasurface that achieves asymmetric diffraction by optimizing the transmission phase from two types of nanoslits with I- and T-shaped structures. As the proposed structure is designed to have a different effective period for each observation side, it is either diffractive or nondiffractive depending on the direction of observation. The designed structure exhibits a diffraction angle of 54°, which can be further tuned by applying different period conditions. We expect the proposed asymmetric diffraction meta-grating to have great potential for the miniaturized optical diffraction control systems in the infrared band and compact optical diffraction filters for integrated optics.

Mid-infrared fluoroindate glass long-period fiber grating by femtosecond laser inscription

A long-period fiber grating (LPFG) was fabricated in a home-made fluoroindate fiber using a femtosecond laser, and attenuation peaks as strong as −17 dB, with sharp and predictable spectral resonances, were obtained over the transmission spectrum. A strain up to 2000 με applied on the LPFG yielded a resonant wavelength redshift of circa 8.46 nm. The strain sensitivity of this LPFG in fluoroindate fibers could pave the way for a new range of applications in the mid-infrared wavelength regions, such as tunable optical rejection band filters in fiber amplifiers and sensing devices.

Seismic signal analysis for the characterisation of elephant movements in a forest environment

Monitoring of pachyderm movements in the neighbourhood of a forest is an important area of research for mitigation of human-wildlife conflict issues. This paper reports the feasibility study for the detection of elephants using seismic sensors inside a forest environment and further characterisation of the seismic signals. Seismic signals generated during elephant locomotion are analysed for various distances. Frequency analysis of these signals shows an average dominant frequency of 15.80 Hz (±1.03 s.d.) and 16.52 Hz (±1.20 s.d.) in the range of 0 m to ~20 m and 20 m to ~40 m respectively. Based on frequency information of the seismic signal, different filter bands were incorporated and the highest accuracy of detection was achieved corresponding to the filter band of 10–20 Hz. The paper also illustrates the statistical analysis of three signal detection algorithms; short and long time averaging (STA/LTA), amplitude spectrum of Fourier transform (ASFT) and continuous wavelet transform (CWT) as a function of the distance from the sensor and elephant group size. Comparative analysis of the preliminary dataset was carried out where CWT based detection approach shows F1-score improvement of ~28% and ~14% in comparison with STA/LTA and ASFT respectively for a radial distance 0– 20 m whereas, ~2% for a radial distance 20– 40 m from the sensor. Furthermore, CWT outperforms with a detection accuracy of ~90% on the preliminary dataset.

Design of Microstrip Dual-Mode Wideband Bandpass Filter with Controlled Center Frequency and Bandwidth Using Bandstop Filter Topology

ABSTRACT This paper discusses a new method for designing a microstrip dual-mode, sharp skirt, wideband bandpass filter with controlled center frequency and bandwidth from bandstop filter topology. A meander closed loop resonator with directly connected orthogonal feed lines provides a Bandstop filter (BSF) with reduced size. A pair of L-shaped open stubs introduced along the diagonal axis D-D1 realizes a wide passband within the rejection band (0.93–4.13 GHz) of the bandstop filter with sharp stopbands on either side of the passband. Furthermore, the effect of L-shaped open stubs susceptance on passband edges is demonstrated. A quarter wavelength stepped impedance shunt stub (SISS) connected at is proposed to achieve additional transmission zeros in the upper and lower rejection bands to improve the sharpness of filter response. Both center frequency and bandwidth of the proposed filter are controlled by the impedance ratio (R) of the SISS element. The proposed filter is simulated using ADS, fabricated and measured using Vector Network Analyzer (VNA). A good agreement is achieved between simulated and measured results.

A novel survey for young substellar objects with the W-band filter III: Searching for very low-mass brown dwarfs in Serpens South and Serpens Core

ABSTRACT We present CFHT photometry and IRTF spectroscopy of low-mass candidate members of Serpens South and Serpens Core (∼430 pc, ∼0.5 Myr), identified using a novel combination of photometric filters, known as the W-band method. We report SC182952+011618, SS182959-020335, and SS183032-021028 as young, low-mass Serpens candidate members, with spectral types in the range M7-M8, M5-L0, and M5-M6.5, respectively. Best-fitting effective temperatures and luminosities imply masses of < 0.12M⊙ for all three candidate cluster members. We also present Hubble Space Telescope imaging data (F127M, F139M, and F850LP) for six targets in Serpens South. We report the discovery of the binary system SS183044-020918AB. The binary components are separated by ≈45 AU, with spectral types of M7-M8 and M8-M9, and masses of 0.08–0.1 and 0.05–0.07 M⊙. We discuss the effects of high dust attenuation on the reliability of our analysis, as well as the presence of reddened background stars in our photometric sample.

The processing of resonances excited by gear faults using continuous wavelet transform with adaptive complex Morlet wavelet and sparsity measurement

This paper explores an improved technique for detection and characterisation of excited resonances by gear faults using the redundant information of continuous wavelet transforms (CWT) and sparsity measurement (SM) as a criterion for selecting the optimal parameters. The proposed method is conducted in two steps. First, the CWT is calculated with a scale vector that covers the medium and high frequency range of the inspected signal, with 0.1 increments. The wavelet coefficients at the resonance scale have the form of a pulse train with the same resonance characteristics and large amplitude. Away from the scales resonance value, the resemblance with the pulse train decreases continuously until it becomes noise. Thus, the scales of the excited resonances with higher signal-to-noise ratio are revealed clearly by sparsity measurement maximisation (SMM). The proposed SM-based scale selection method allows to select more than one or two resonance frequency bands. Second, the signal is band-pass filtered around each located resonance in order to detect the fault-contained frequency band. The bandwidths are obtained by adjusting the shape factor values of the Complex Morlet Wavelet. The optimal band where the SNR is the highest can be deduced using the SMM. This technique makes it possible to locate accurately all scales of resonances present in a signal, including those with low energies, and the optimal filter band of each resonance. The effectiveness of the proposed method has been verified by numerical simulations and by fault vibration signals from a gear with three types of local faults: broken tooth, hunting tooth defect and flaking defect tooth. The results show that the proposed method allows an accurate identification and location of a single or even multiple defects.

Research on extracting weak repetitive transients of fault rolling element bearing

The selection of the filter band for demodulation is crucial to extract the weak repetitive transients of fault rolling element bearing (REB). However, when the signal to noise is low, traditional methods for finding a suitable filter band are susceptible to the cyclostationary (CS) interference and the abnormal shock. In order to solve this problem, a new extraction method with reweighted singular value decomposition and improved Fast_kurtogram, namely RWSVD_IFK, is proposed. Firstly, by combining the new weight factors with singular components, a novel denoised strategy is presented to preprocess the original signal for reducing the CS interference. Secondly, considering that the kurtosis index is sensitive to the abnormal shock, the proposed method introduces the autocorrelation function into Fast_kurtogram to weaken the interference of the abnormal shock. And then, the squared envelope is applied to extract the weak repetitive transients from the optimal filtered signal. The simulated data and measured data of the fault REB are used to verify the validity of the proposed RWSVD_IFK. The results show that the proposed method can overcome the CS interference and the abnormal shock in finding the optimal filter band and effectively extract the weak repetitive transients of fault REB.

A spatial-frequency-temporal 3D convolutional neural network for motor imagery EEG signal classification

Motor imagery (MI) EEG signal classification is a critical issue for brain–computer interface (BCI) systems. In traditional MI EEG machine learning algorithms, feature extraction and classification often have different objective functions, thus resulting in information loss. To solve this problem, a novel spatial-frequency-temporal (SFT) 3D CNN model is proposed. Specifically, the energies of EEG signals located in multiple local SFT ranges are extracted to obtain a novel 3D MI EEG feature representation, and a novel 3D CNN model is designed to simultaneously learn the complex MI EEG features in the entire SFT domains and carry out classification. An extensive experimental study is implemented on two public EEG datasets to evaluate the effectiveness of our method. For BCI Competition III Dataset IVa, the average accuracy rate of five subjects obtained by the proposed method reaches 86.6% and yields 4.1% improvement over the state-of-the-art filter band common spatial pattern (FBCSP) method. For BCI Competition III dataset IIIa, by achieving an average accuracy rate of 91.85%, the proposed method outperforms the state-of-the-art dictionary pair learning (DPL) method by 4.44%.

Tunable dual-band mid-infrared absorber based on the coupling of a graphene surface plasmon polariton and Tamm phonon-polariton.

We propose and demonstrate a tunable dual-band mid-infrared absorber structure based on the coupling effect of a surface plasmon polariton (SPP) and Tamm phonon-polariton (TPhP). The structure is composed of the distributed Bragg reflector (DBR), air layer, SiC and graphene ribbons. In the air layer, the graphene ribbons are embedded to realize the localized SPP (LSPP), which makes the structure support both the graphene LSPP (GLSPP) and TPhP. The absorption properties of the structure are investigated theoretically and numerically. It is found that strong coupling of the GLSPP and TPhP can be realized by choosing reasonable parameters, which causes a dual-frequency perfect absorption and makes the maximum Rabi splitting of the coupled mode reach 5.76 meV. Furthermore, the mode coupling and absorption intensity can be tuned by adjusting the thickness of the air layer and the Fermi level of the graphene ribbons. This work might provide new possibilities for the development of mid-infrared band sensors, filters and emitters based on the coupling of multiple modes.

Miniaturized integrated spectrometer using a silicon ring-grating design.

We introduce and experimentally demonstrate a miniaturized integrated spectrometer operating over a broad bandwidth in the short-wavelength infrared (SWIR) spectrum that combines an add-drop ring resonator narrow band filter with a distributed Bragg reflector (DBR) based broadband filter realized in a silicon photonic platform. The contra-directional coupling DBR filter in this design consists of a pair of waveguide sidewall gratings that act as a broadband filter (i.e., 3.9 nm). The re-directed beam is then fed into the ring resonator which functions as a narrowband filter (i.e., 0.121 nm). In this scheme the free spectral range (FSR) limitation of the ring resonator is overcome by using the DBR as a filter to isolate a single ring resonance line. The overall design of the spectrometer is further simplified by simultaneously tuning both components through the thermo-optic effect. Moreover, several ring-grating spectrometer cells with different central wavelengths can be stacked in cascade in order to cover a broader spectrum bandwidth. This can be done by centering each unit cell on a different center wavelength such that the maximum range of one-unit cell corresponds to the minimum range of the next unit cell. This configuration enables high spectral resolution over a large spectral bandwidth and high extinction ratio (ER), making it suitable for a wide variety of applications.

Practical Study and Implementation of an Isolated Word Speech Recognition System.(Dept.E)

The art and science of speech recognition have been advanced to the state where it is now possible to communicate reliably with a machine by speaking to it in a disciplined manner using a vocabulary of moderate size. It is the purpose of this paper to present a hardware implementation of a simple real time speech recognition system for isolated words. The system determines the energy of the spoken word through a bank of four channels band pass filters. The output from each filter is passed through a rectifier followed by a low pass filter to provide an average level which is proportional to the total signal energy within the particular filter band. The energy measurements from each channel is then passed to a personal computer where a recognition algorithm program is then executed. The program detects the starting and ending points of each spoken word. compares the energy features with the reference stored in the library, and chooses the most close pattern that matches the pattern of the spoken word. Results from experiments conducted by simulation and by the hardware prototype using Arabic speech show that the system provides recognition score between 76 % and 94%.

CMOS Realization of Fully Electronically Tunable Single Resistance Control Mixed Mode Biquad Filter Employing Single VDTA at ± 0.6V

This paper presents a single VDTA based Mixed Mode type Biquad filter. The proposed Transadmittance Mode (TAM) type Biquad filter configuration employed single voltage differencing transconductance amplifier (VDTA) as an active building block, three passive element namely one grounded resistor, one grounded capacitor and one floating capacitor. The proposed transadmittance Mode multifunction Biquad filter configuration is presenting transadmittance mode type four basic standard filter functions low pass, high pass, band pass, band reject or band stop or band eliminate filter responses. These four type filter responses are realizing simultaneously with the selection of single input voltage signal. The proposed Transadmittance Mode multifunction Biquad filter configuration has more advantageous features such as low active and passive sensitivities, low power supply voltage, low power consumption, low quality factor, very low power consumption, more electronic tunability, higher linearity and required small area of the chip. The performance of the proposed configuration has been verified through PSPICE simulation using 0.18μm CMOS Technology process parameters.

Efficiency enhancement of an updated solar-driven intermediate band thermoradiative device

A novel model of the solar-driven intermediate band thermoradiative device consisting of a solar concentrator, an absorber, an intermediate band thermoradiative cell and an optical filter is proposed. The formulas of the power output density and efficiency are derived analytically. The device performances are optimized and the parametric selection criteria are provided. The maximum efficiency of the device operating in the optimal state reaches 23.1% and increases of 25.5% if compared with that of a thermoradiative solar cell without the intermediate band. It means that the intermediate band has a great effect on the systemic performance improvement. It is very significant to find that the proposed device can attain a large efficiency under a low concentration factor and the performance of the device is much better than that of the normal thermoradiative solar cell without the intermediate band and optical filter. Solar-driven intermediate band thermoradiative devices are worthy of research and development.

Characterization and absolute calibration of an AERONET-OC radiometer.

The Ocean Color component of the global Aerosol Robotic Network (AERONET-OC) utilizes CE-318 sun photometers modified for above-water radiometry from fixed structures such as oil rigs, lighthouses, and service platforms. Primarily, AERONET-OC measurements allow determination of the water-leaving radiance required for the validation of ocean color satellite data products. One instrument from the AERONET-OC network, identified as AERONET #080, was studied in this work. A laser-illuminated integrating sphere of known radiance enabled determination of the linearity with flux and absolute radiance responsivity at multiple wavelengths within seven of the AERONET #080 filter bands. We compared the results to calibrations from the AERONET facility at the Goddard Space Flight Center of the National Aeronautics and Space Administration and from the Joint Research Centre of the European Commission. These results agree within the estimated mean comparison uncertainty of 1.88 % (k=2). We also assessed these results using calibrated lamp-illuminated integrating spheres and observed a spectral dependence to the comparison results that is unexplained.

Experimental investigation of turbulent coherent structures interacting with a porous airfoil

The flow field on solid and porous airfoils subjected to turbulence shed by an upstream cylindrical rod and the corresponding far-field noise radiations are studied through particle image velocimetry (PIV) and microphone measurements, respectively. Three different Reynolds numbers based on the rod diameter are considered in a range between $${2.7\times 10^4}$$ and $${5.4\times 10^4}$$ , and two porous airfoil models are tested to analyze the influence of the design elements of the permeable treatment. A standard proper orthogonal decomposition (POD) algorithm is employed to band filter the different length scales that characterize the turbulent flow, making it feasible to determine which turbulence scales are affected by porosity. The aeroacoustic results indicate that the porous treatment of the wing profile leads to a noise reduction at low frequencies and a noise regeneration at high frequencies due to surface roughness. The investigation on the flow field shows that the main effect of porosity is to mitigate the turbulent kinetic energy in the stagnation region, attenuating the distortion of turbulence interacting with the airfoil surface. The application of the POD algorithm indicates that this effect acts mainly on the largest scales of turbulence.

A planar CPW fed UWB antenna with dual rectangular notch band characteristics incorporating U‐slot, SRRs , and EBGs

In this article, a planar ultra-wideband (UWB) antenna with dual rectangular notchband characteristics (ie, 5.94-7.50 GHz and 8.02-10.46 GHz) is presented. The two-notch bands are chosen based on various wireless applications operating in C-band and X-band. The size of the antenna is very compact (25 × 25 × 1.6 mm3) and is designed on a low-cost FR4 substrate. Co-planar waveguide (CPW) feed and beveling techniques are utilized for achieving the UWB operation. In order to yield the first rectangular notch, a U-slot and a pair of split-ring resonators are embedded into the radiating patch and the backside of the design, respectively. The coupling between these two structures is adjusted so as to achieve a rectangular band-notch operation. The second rectangular notch has been achieved by introducing the two mushroom type electromagnetic band-gap structures on the opposite side of the CPW feed. The parametric analysis for controlling band notches, time-domain analysis, and filter synthesis is also presented. Finally, simulated as well as measured results of S11, gain, radiation pattern, group delay, and total efficiency are demonstrated to show the suitability of this design for UWB systems.

Image Denoising Based Improved Curvelet Threshold

Although wavelets are powerful as a tool in image processing it has three serious drawbacks: shift sensitivity, poor directionality and lack of phase information. Wavelets suitable for dealing with objects with point singularities; it can only capture limited directional information due to its poor orientation selectivity. Through decomposing the image into a series of high-pass and low-pass filter bands, the wavelet transform extracts directional information that capture vertical, horizontal, and diagonal activity. However, in noisy images, these three linear directions are limiting and might not capture enough directional information, like medical CT scans, which do not have strong vertical, horizontal, or diagonal directional elements. Ridgelet transform improves Multiresolution Analysis MRA segmentation; however, they capture structural information of an image based on multiple radial directions in the frequency domain. Line singularities in ridgelet transform provides better edge detection than its wavelet counterpart. One limitation to use ridgelet in image segmentation is that ridgelet is most effective in detecting linear radial structures, which are not dominant in images. The curvelet transform is a recent extension of ridgelet transform that overcome ridgelet weaknesses. Curvelet is proven to be particularly effective at detecting image activity along curves instead of radial directions which are the most comprising objects of images. However, the fact that at sufficiently fine scales, a curved edge is almost straight, and so to capture curved edges, one ought to be able to deploy ridgelets in a localized manner, at sufficiently fine scales. In this paper, a new method is used combining the Window Shrink threshold and Bayes Shrink threshold based on Curvelet transform to enhance removing Additive Weight Gaussian Noise AWGN noise from image. It has better PSNR than the traditional Curvelet that uses each threshold alone, and the images gotten by this method is better and outperform that of the traditional curvelet and wavelet methods and the results reported here are promising

Increasing the noise immunity of radio receiving paths with automatic sensitivity control

The relevance of the study of automatic sensitivity control systems (ASC) is determined by their demand for the creation and modernization of radio receiving paths (RRP) with increased noise immunity for radar systems, radio navigation and radio communication. The article analyzes typical attenuating ASCs, which are traditionally widely used to match the dynamic range (DR) of the RRP with the DR of a group radio signal, determined by the current state of the electromagnetic environment at the receiving system location. The fundamental possibility of increasing the noise immunity of RRPs with attenuating ASCs is shown on the basis of the current analysis of the resulting output signal in the IF main filter band. At the same time, it was found that the procedure for determining the optimal value of the attenuator transmission coefficient is characterized by low response speed. In addition, an increase in noise immunity in a RRP with such ASC leads to a significant loss of sensitivity. To overcome the disadvantages of attenuating ASCs, structures that implement the exchange of the transmission coefficient of the RRP to DR and linearity are proposed. Studies of various possible ASC structures have shown that with a proportional exchange of the transmission coefficient for the DR, an improvement in the noise immunity of the RRP is provided while maintaining a high sensitivity of the system. An original ASC system is proposed, which is invariant to the sampling step of the transmission coefficients of controlled elements with increased performance. The considered structural solutions and algorithms make it possible to optimize the technical appearance of RRPs for radar, radio navigation and radio communication with increased noise immunity and to adapt their characteristics to the conditions of nonstationary electromagnetic environment.

Differential Mode Noise Estimation and Filter Design for Interleaved Boost Power Factor Correction Converters

Interleaved power factor correction (PFC) is widely used circuit topology due to good efficiency and power density for single-switch boost PFC. As the differential mode (DM) electromagnetic interference (EMI) noise magnitude depends upon the input current ripple, this research details a comprehensive study of DM EMI filter design for interleaved boost PFC with the aim of minimizing the component size. It is also demonstrated that the different numbers of interleaved stages and switching frequency influence the filter attenuation requirement and, thus, the EMI filter size. First, an analytical model is derived on the basis of the Norton equivalent circuit model for the differential mode noises of interleaved boost PFC within the frequency range of 9–500 kHz. The derived model can help identify the proper phase shifting among the interleaved boost converters in order to minimize the considered differential mode noises at the filter design frequency. So, a novel phase-shift method is developed to get a minimized attenuation required by a filter in Band B. Further, a volume optimization of the required DM filter was introduced based on the calculated filter attenuation and volumetric component parameters. Based on the obtained results, unconventional and conventional phase shifts have demonstrated a good performance in decreasing the EMI filter volume in Band B and Band A, respectively. A 2-kW interleaved PFC case study is presented to verify the theoretical analyses and the impact of phase-shifting on EMI filter size.