Narrow-band Notch Filters Research Articles

Magnonic notch filter based on spin wave caustic beams

Here, we study a magnonic crystal made of low-damping yttrium iron garnet that utilizes pseudo-caustic spin wave beams generated from subwavelength square well features arranged in a two-dimensional array. The lattice symmetry and the angle between the caustic beam propagation direction and the applied magnetic field were tailored to optimize the interaction of spin waves with the engineered defects. A prominent, narrow 3 MHz feature with large rejection efficiency is observed in the spin wave transmission spectrum that could be useful as a narrowband notch filter, and time- and space-resolved Brillouin light scattering (BLS) measurements suggest that both caustic interference and edge effects may contribute to this notch feature. Furthermore, the BLS measurements show that caustics are generated efficiently at the laser ablated wells, and by tuning the frequency by 30 MHz, the caustic beam angles and, hence, the details of how the spin wave caustics hit the ablated wells change sufficiently to add and remove caustic beams, which can be used to create additional device functionality. The generation and conversion of caustic beams show promise for applications that require directional energy transport and for magnonic devices.

Development of the 174GHz collective Thomson scattering diagnostics at Wendelstein 7-X.

In this paper, we present the design and commissioning results of the upgraded collective Thomson scattering diagnostic at the Wendelstein 7-X stellarator. The diagnostic has a new radiometer designed to operate between the second and third harmonics of the electron cyclotron emission from the plasma at 171-177GHz, where the emission background has a minimum and is of order 10-100eV. It allows us to receive the scattered electromagnetic field with a significantly improved signal-to-noise ratio and extends the set of possible scattering geometries compared to the case of the original instrument operated at 140GHz. The elements of the diagnostic are a narrowband notch filter and a frequency stabilized probing gyrotron that will allow measuring scattered radiation spectra very close to the probing frequency. Here, we characterize the microwave components applied to the radiometer and demonstrate the performance of the complete system that was achieved during the latest experimental campaign, OP2.1.

Narrow-band notch filter and refractive index sensor based on rectangular-semi-annular cavity coupled with MIM waveguide structure

In this work, a symmetric structure based on a metal-insulator-metal (MIM) waveguide is proposed for narrow-band notch filters and refractive index sensors. The structure comprises a symmetrically intersecting rectangular-semi-annular cavity and a long straight waveguide. The transmission spectrum and magnetic field distribution of the notch filter are studied and analyzed by the finite element method (FEM) with scattering boundary conditions (SBC). Our analysis reveals that the band-stop filter exhibits a minimum transmittance of 0.35%, a bandwidth of 34 nm, and a quality factor (Q) of 35.16. These characteristics include low stop-band transmittance, a narrow bandwidth, and a high Q value. Furthermore, our structure allows for independent adjustment of the narrow band filtering range by varying geometric parameters such as H, d, R1, and d. Additionly, we conduct theoretical analysis to investigate the sensing properties of the structure. The refractive index sensitivity of the structure reaches a high value of 1222 nm RIU−1, accompanied by a figure of merit(FOM*) of up to 175.9. These results demonstrate the structure’s excellent filtering properties and high-sensitivity sensing characteristics.Consequently, it holds significant potential for application in high-density integrated circuits and nano-optics.

Design of feedback-structured IIR notch filter with transient suppression using gain variation

In many applications of notch filtering, short transient response and high quality factors are very important issues. Increasing Q factor, decreases the bandwidth and improves magnitude selectivity near the notch frequency, but unfortunately increases the transient duration of the response. Recently, time-variant methods using exponential or sigmoid functions are considered to enhance the notch filter performance. In this paper, conventional and feedback-structured notch filters (following a recent work by Pei et al) are investigated in details. Using feedback structure, anyone can obtain a good narrow-band notch filter by tuning the feedback gain. However, it suffers from a long transient duration. In order to improve the performance of the filter, a new simple time-variant method to control the pole-position is introduced. Proposed method can keep the pole radius in the minimum value to decrease the transient duration more efficiently than other recently-reported ones as Piskorowski, Li and Rana methods. Also, it drives the pole to approach the unit circle or final position rapidly, normally after a few samples, while attaining a narrow bandwidth. In this paper, the performance of the proposed filter is compared with Piskorowski, Li and Rana methods. Simulation results show that the proposed algorithm can improve the performance of the feedback-structured filter compared to other methods. The results demonstrate superior performance of the presented method not only in accordance with power line interference, but also in removing the distortion of the time-variant filters.

Evaluation of a damping coefficient influence made by notch filters on efficiency of ECG signals processing

Introduction. The aim of this study is to evaluate the effectof damping coefficient ξ provided by narrow-band notch filterson the quality indicators of the ECG signal processing accompaniedby development of a special software package forexperimental testing of the cascade filtering system of naturalelectrical noise and its harmonics.Materials and Methods. For the formation of additive componentsof signal and noise, test ECG signals from the MassachusettsInstitute of Technology were selected as a model, andelectrical noise was synthesized taking into account their harmonicnature. The transfer function of the notch filtering systemwas tuned and calculated. Quantitative quality metrics was usedto determine the processing efficiency at the input and output ofthe signal filtering system. To assess the effect of damping coefficientsmade on the ECG signal processing system, the method ofthe linear regression analysis was applied. Methods of structuraland procedural programming were used to create a softwarepackage for processing a full-scale noisy signal recording.Results. An increase in the efficiency of the ECG signal processingsystem was revealed when calculating quantitative indicatorscharacterizing the quality solution to the signal filteringproblem. It has been found that at values of the dampingcoefficient ξ = 0.1, the efficiency of the analysis of ECG signalprocessing in terms of accuracy and noise resistance increases,and the filtering error decreases due to the improvement ofthe selectivity of the notch filter at the resonant frequency. Theeffect of the damping coefficient on the quality indicators ofECG signal processing was established, and regression equationswere obtained to characterize the adequacy of the designedmodel for the confidence interval (P = 0.99) at p <0.01.The performance of the developed software package has beendemonstrated, which combines a cascade filtering system witha damping coefficient ξ = 0.1, to eliminate the natural electricalinterference of the ECG signal and its harmonics.Conclusion. The evidence data obtained in our work, both calculated(theoretical) and practical (experimental) data, confirmthe efficiency of the proposed processing approach to the selectionof informative components ECG signal under the influenceof high-frequency electrical interference and its harmonics.The sequential incorporation of two narrow-band notchfilters with a damping coefficient ξ = 0.1 to suppress interferenceat a frequency of 50 Hz and its harmonics at a frequencyof 100 Hz opens up new possibilities for processing ECG signals.

Development of fast-ion collective Thomson scattering diagnostics for the GDT experiment

In this paper, we describe hardware developed for the collective Thomson scattering (CTS) diagnostic for the large open magnetic trap GDT (Budker Institute, Russia) used in fusion researches. The diagnostic utilizes 400 kW/54.5 GHz gyrotron as a source of probe radiation and is aimed at the reconstruction of fast ion distributions over transverse and longitudinal velocities driven by high-power neutral beam injection. Formation and manipulation of the probe beam and collection of the scattered microwave radiation are done with large-aperture quasi-optical mirror systems. The receiving complex consists of two identical channels for simultaneous detection of scattering in two complement geometries. Each channel includes a highly sensitive radiometer/spectrum analyzer with the band of 54.470 ± 0.550 GHz, the noise temperature of 0.35 eV, the sensitivity less than 0.025 eV, the frequency/time resolution of 5–50 MHz/10 μs, and narrow-band notch filter providing at least -40 dB rejection in the band of 25 MHz with a central frequency tunable in 54.470 ± 0.050 GHz for protection of the input RF circuit from a backlight of powerful gyrotron radiation.

Development of the ion cyclotron emission diagnostic for the W7-X stellarator.

An ion cyclotron emission (ICE) diagnostic is prepared for installation into the W7-X stellarator, with the aim to be operated in the 2022 experimental campaign. The design is based on the successful ICE diagnostic on the ASDEX Upgrade tokamak. The new diagnostic consists of four B-dot probes, mounted about 72° toroidally away (one module) from the neutral beam injector, with an unobstructed plasma view. Two of the B-dot probes are oriented parallel to the local magnetic field, aimed to detect fast magnetosonic waves. The remaining two probes are oriented poloidally, with the aim to detect slow waves. The radio frequency (RF) signals picked up by the probes are transferred via 50 Ω vacuum-compatible coaxial cables to RF detectors. Narrow band notch filters are used to protect the detectors from possible RF waves launched by the W7-X antenna. The signal will be sampled with a four-channel fast analog-to-digital converter with 14 bit depth and 1 GSample/s sampling rate. The diagnostic's phase-frequency characteristic is properly measured in order to allow measuring the wave vectors of the picked up waves.

Adaptive Complex Filtering for Narrowband Jamming Mitigation in Resource-Constrained Wireless Networks

Jamming attacks present a major challenge for the physical layer security of wireless communication systems. Among the large number of existing methods for jamming mitigation, filtering is a simple but promisingly effective solution that can be applied in resource-constrained and low-power wireless networks. In this article, a first-order adaptive complex narrowband notch filter is proposed for use against high-power narrowband jamming attacks. The central frequency of the filter is adaptively adjustable to match the interfering frequency. This enables the proposed solution to perform effectively in the presence of a jammer whose frequency varies in fixed or random time periods. The simulation results demonstrate the filter's behavior and the efficiency of the proposed technique.

Tunable hybrid spectral filter and time-division multiplexing of second-order fluorescence controlled by phonon and dressing on Pr3+:YSO

Atom-like nonlinear responses of rare earth doped crystal Pr3+:Y2SiO5 (Pr3+: YSO) exhibit unique features compared with other nonlinear crystals. The responses become more interesting, while Pr3+: YSO is modulated simultaneously by temperature and multi-parameters related to dressed state. The generations of Stokes and fluorescence (FL) signals are demonstrated in both time and spectral domains. Here, we are presenting a new controlling strategy by interaction between dressing and phonon on Pr3+: YSO to manipulate the intensity of Stokes and FL signals. Interaction between dressing and phonon leads to more stable nonlinear response of the YSO crystal, which is very important for integrated quantum photonic device stability and multi-functionality. Also, we have realized tunable hybrid spectral filter (narrow-band pass notch filter (NBPNF), narrow-band stop notch filter (NBSNF)) and time-division multiplexing router on Pr3+: YSO by controlling the interaction between dressing and phonons. Tunable hybrid spectral filter and pure NBPNF are realized from dressing dip of Autler-Townes (AT) splitting and spectral intensity Stokes emission peak. Also, time-division multiplexing router is realized by time-domain adiabatic expansion. Furthermore, optical switch between tunable hybrid spectral filter to pure NBPNF is realized from dressing dip (AT splitting) to spectral intensity Stokes emission peak. Our experimental results suggests advanced technique for realizing tunable hybrid spectral filter with a contrast of about 98%, and optical time-division multiplexing router with channel equalization is about 85%.

CSRR Embedded CPW Band-Stop Filter

This paper proposes topologies for narrowband and broadband notch filters using complementary split ring resonators (CSRR) in coplanar waveguide (CPW) technology. Simple analysis justifies these topologies. Strong coupling between the resonator and the signal line in these topologies can reduce the radiation loss in the stop-bands. Characteristics of these filters realized from electromagnetic simulations match closely with those from measurements on prototypes.

All-Dielectric Metasurface for Highly Tunable, Narrowband Notch Filtering

A novel scheme of an all-dielectric metasurface with double-layer patch array is proposed to achieve the highly tunable, narrowband notch filtering across visible and near-infrared range. The all-dielectric metasurface presents efficient blocking (transmittance 0.01–0.0001) at targeted wavelength and high (>93%) transmission across the visible and near-infrared light range outside the targeted wavelength band. The bandwidth of the notch filter could be greatly compressed with this all-dielectric metasurface, compared with those typical interference notch filters for distinctive wavelengths. The effect of the geometrical parameters on the spectral filtering of this metasurface is studied to provide a distinct relationship to design the desired narrowband notch filter conveniently. And the antireflection effect of the top silicon dioxide layer is verified with similar bandwidth, lower transmission at notch filtering wavelength and higher transmission at other wavelengths. In addition, the optical Fano resonance excited by the all-dielectric metasurface is responsible for the spectral filtering feature including the deep blocking feature at the specific wavelength and high transmission at other wavelengths.

Brillouin-Assisted Notch Filtering Based All-Optical Image Rejection Mixer

A novel approach for realizing a microwave photonic image rejection mixer is presented in this paper. It is based on using a widely tunable narrow-band optical notch filter implemented by stimulated Brillouin scattering (SBS) to remove the image signal. The image rejection mixer has a simple structure as it only requires a single integrated dual-polarization modulator for both frequency conversion and pump wave generation for the SBS process. The absence of electrical components enables the image rejection mixer to be operated over a wide frequency range with a high image rejection ratio. A technique is also proposed to suppress the noise generated by the SBS process in the image rejection mixer. Experimental results demonstrate a high and constant image rejection ratio of over 32 dB for the image rejection mixer operating over an RF signal frequency range of 11.8–19.6 GHz, and around −5 dB conversion efficiency.

Multiplex CARS imaging with spectral notch shaped laser pulses delivered by optical fibers.

We present an experimental demonstration of single-pulse coherent anti-Stokes Raman spectroscopy (CARS) using a spectrally shaped broadband laser that is delivered by an optical fiber to a sample at its distal end. The optical fiber consists of a fiber Bragg grating component to serve as a narrowband notch filter and a combined large-mode-area fiber to transmit such shaped ultrashort laser pulses without spectral distortion in a long distance. Experimentally, our implementation showed a capability to measure CARS spectra of various samples with molecular vibrations in the fingerprint region. Furthermore, CARS imaging of poly(methyl methacrylate) bead samples was carried out successfully under epi-CARS geometry in which backward-scattered CARS signals were collected into a multimode optical fiber. A compatibility of single-pulse CARS scheme with fiber optics, verified in this study, implies a potential for future realization of compact all-fiber CARS spectroscopic imaging systems.

Elimination on power line interference from ECG signal using combined bidirectional narrow-band notch filter

The aim of current research was to find negative effects caused by eliminating power line interference in ECG signal with narrow-band recursive notch filter and to search for a filtering method that will solve a problem of signal distortion. During the study the method of ECG filtering with narrow-band recursive filter was described. The main negative attribute of this filter is transient noise, also called “ringing” effect, as the reaction to a single impulse visible as R waves on the ECG signals. Also discovered, that “ringing” effect appears after the impulse during forward filtering and before the impulse during backward filtering. Based on this effect we proposed method, the main idea of which was to build the finite signal with regions without transients.

Narrowband Notch Filters with Composite Nanostructure Layers on a GaN-Based Light Emitting Diode

In this paper, novel active narrowband notch filters with triple-layer composite nanostructures on a GaN-based LED are obtained by mainly adjusting the grating period and duty cycle. The three layers consist of two dielectric thin layers and one metallic / dielectric grating layer. The grating layer composes of subwavelength period and thickness rectangular stripes, which lies between a transition layer and a protecting layer. Line-width and attenuation peak properties of the resonance filters are calculated and investigated by using a full vector implementation of Rigorous Coupled Wave Analysis (RCWA) algorithm. It is shown that the grating period can significantly change the filter peak wavelength, and the grating duty cycle heavily changes the filter line-width. The filter attenuation peak has a red shift with 23.3nm as the grating period increases 18nm. The FWHM (Full Width at Half Maximum) of the filter reduces from 1.9nm to 0.28nm as the duty cycle changes from 0.55 to 0.3, which compressed more than six times. Moreover, thickness of each composite nanostructure layer can also affect the narrowband width and peak wavelength of the filter. The results provide guidance in designing, optimizing and fabricating such an active narrowband filter with highly integrated photonic devices.

Convex-Programming Design of Linear and Nonlinear Phase Wideband Blocking Filters

Blocking filters are commonly used in array processing to excise targets from data when suitable target-free training data is not available. A drawback is the reduction of the effective size of the array by the order of the filter, motivating a search for the smallest filter that meets the design specifications. Common linear-phase approaches lead to convex optimization and efficient global solutions, but can be inefficient when the phase of the blocking filter is unimportant. Although direct magnitude-response optimization is nonconvex in general, for narrowband linear arrays optimal-magnitude blocking filters can be found using constrained optimization followed by spectral factorization. This approach cannot be directly applied to wideband arrays, as finite-support spectral factors do not generally exist in higher dimensions. Instead, a procedure is presented in which an approximate multidimensional spectral factor of an optimized spectral density is used as a target response in a second optimization stage. Linear and nonlinear-phase solutions are found and compared for both narrowband and wideband notch filters, with the nonlinear phase outperforming the linear phase in both notch width and passband error. The various optimizations are performed using second-order cone programming, an efficient class of convex optimization.

Unbalance compensation using generalized notch filters in the multivariable feedback of magnetic bearings

Unbalance of magnetically levitated rotors causes undesirable synchronous vibrations which may lead to saturation of the magnetic actuator. To avoid this problem we propose a generalized narrow-band notch filter which is inserted into the multivariable feedback without destabilizing the closed loop. The parameters of the generalized notch filter strongly depend on the inverse sensitivity matrix evaluated at rotational speed. This matrix is easily measured a priori and stored in a look-up table. It is shown that a decentralized notch is feasible for weakly gyroscopic rotors. The proposed notch filter approach has advantages in terms of run-time complexity and analytical verification of closed-loop stability. Results from the implementation of the proposed unbalance compensation in industrial magnetic bearing systems are included.

DESIGN PROCEDURE FOR TUNABLE NARROW-BAND DIGITAL FILTERS

A new design technique is presented for narrow-band digital notch filters .The transversal filters have linear phase and their design is based on minimization of the integrated error energy over designated approximation bands. The optimal design is formulated as a constrained quadratic programming problem. A closed-from expression for the filter coefficients is presented. The notch frequency and null depth are the tunable parameters and the tuning process is described. It is shown that tuning the filter requires a relatively minimal number of operations, a matrix-vector multiply is required to change the filter coefficients. Several examples are included which show the effectiveness of the proposed design technique.

New digital notch filter structures with low coefficient sensitivity

For narrow-band digital notch filters, poles are near the unit circle. Also, when the sampling rate is increased, the poles approach the point Z = + 1 . The usual realizations of digital notch filters are highly sensitive to coefficient quantization. Three new digital notch filter structures are proposed, and their coefficient sensitivities are derived.

Low-transient high-pass filters

A new and simple method is given for transforming a low-pass filter (LPF) to a high-pass filter (HPF) whose impulse and step-function responses have the same quality (in terms of overshoot, delay, settling time, transition time, etc.) as that of the LPF. The transfer functions, impulse, and step responses of these two filters are related by H_h (s) = 1 - H_l (s), h_h (t) = \delta(t) - h_l (t) , and s_h (A) = 1 - s_l (t) , respectively. This immediately enables us to define new classes of low-transient HPFs having little or no overshoot. One new class is obtained by transforming all-pole Bessel filters, but other low-pass families can be transformed to obtain similar results. It is also shown that if the quality of an all-pole LPF transient response is to be retained by the HPF, then the maximum attenuation rate of the HPF magnitude response near \omega = 0 is 6 dB/octave. These results are additionally beneficial for designing low-transient narrow-band notch filters.