Bandstop Filter Research Articles

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.

Planar Sensor for Noise Cancellation During Partial Discharge Detection in Open Substation

In compliance with next-generation high-voltage substations, ultra-high frequency (UHF) planar sensors are becoming more popular than ever for their online features in partial discharge (PD) diagnostics. However, PD signals mixing with different noises still exists as a major challenge for UHF sensors. Especially in open substations, telecommunication interferences become predominant noise sources to an external UHF sensor placed outside of the equipment chamber. Despite band-stop filters are additionally connected to UHF sensors for de-noising, the inherent noise cancellation mechanism is not yet found in any UHF sensor. With the best of our knowledge and survey, we are the first to introduce here a planar sensor that inherently eliminates telecommunication interferences during PD detection for open substations even without using any post-processing filters. To design our sensor, we have applied techniques of truncated partial ground plane for wideband characteristics and modified radiating patch for enhanced gain performance. A novel intermingled coupling resonator is designed to remove the GSM-900 band from within the sensor bandwidth. We have tested our prototype both for the free-space propagation and PD detection performances. The prototype has a compact physical size of 16×8 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and an operational bandwidth within 792-1414 MHz. For a surface discharge source, the prototype successfully detects the PD signals at the earliest stage. Our prototype minimizes the ambient noise-floor to 2.5 mV and improves the signal-to-noise ratio by more than 27.9 dB which is relatively higher than conventional UHF sensors. The proposed sensor also has potentials of classifying PD sources.

High-Q terahertz bandstop filter via cuboid frame structure

A terahertz (THZ) bandstop filter can be used to filter interference signals in a filter passband. The quality factor (Q) is the most important index in evaluating the transmission performance of the filter. Usually, a higher Q value, a narrow bandwidth and a larger stopband slope ensures good filtering accuracy and transmission response. However, the Q value taken from metamaterial structures designed on the plane is only ever in single digits, resulting in a less than satisfactory filtering performance. Herein, a high-Q THZ bandstop filter based on metamaterials was proposed. To fabricate this 3D metamaterial structure, a microtopographic substrate-guided method with feasible and high accuracy capacities was proposed. As a result, it is ascertained that the device is in the filtering state in the range 1.038–1.102 THz while it is stopped in the range 1.062–1.066 THz. The similarity between the experimental and simulated transmissions is up to 86.32%, indicating that the fabricating method possesses high accuracy. Accordingly, the Q value was calculated to be as high as 532. In future, the bandstop filter with this record Q value can be widely used in THZ detection, imaging and sensing. Meanwhile, the proposed fabrication method is effectively applied to a 3D metamaterial and a THZ device as well.

High-performance plasmonic band-pass / band-stop / cut-off filter using elliptical and rectangular ring resonators

A plasmonic filter including Metal-Insulator-Metal waveguides (MIM) with an elliptical ring resonator is proposed. Using the Finite Difference Time Domain (FDTD) method, we analyze the amount of transmittance in the structure. The results show the creation of five resonance modes with narrow FWHM and suitable transmittance at the resonance points of the spectrum. The resonance wavelength and transmittance at the resonance points are tuned by changing the device geometry. In this structure, preventing the transmittance of the spectrum creates a band-gap between the wavelengths 919 nm–1388 nm, which by changing the size of the structure, the band-gap width changes. This filter also cuts off the transmission of wavelengths greater than 1707 nm. By adding a rectangular ring resonator outside the elliptical ring resonator, the performance of the device was improved and the transmittance included very narrow resonance modes. Due to the number of resonance modes and their narrow FWHM, the introduced structures can be used as devices for filtering several wavelengths, which significantly reduces costs and enhances economic efficiency for the production of plasmonic band-pass filters. Also, this structure can be used as band-stop and cut-off filters. This multiplicity of functions makes it cost-effective to use the proposed device for making integrated optics devices.

Polarization-independent and reciprocity-unbroken multifunctional device with composite symmetrical structure.

A design method for a dynamically tunable multifunctional device, which is insensitive to polarization while maintaining unbroken reciprocity, is proposed. The device utilizes a multilayer composite symmetrical structure incorporating vanadium dioxide (VO2). This design enables dynamic switching among the functions of linear polarization conversion, filtering, and absorption. In the polarization conversion state, the device achieves orthogonal deflection of incident waves at any polarization angle, with a polarization conversion ratio (PCR) exceeding 95%. When switched to the filtering function, a band-stop filter with a -20 dB bandwidth of 0.56 THz is obtained. In the absorption function, the device exhibits a peak absorption efficiency of up to 99%. Furthermore, the paper discusses the potential for a dual-band device based on the proposed structure. The device maintains reciprocity in all functions and effectively handles incident waves from both positive and negative directions. This adaptability and flexibility make it suitable for various applications, including switches, sensors, and modulators.

Microwave Common-Frequency Absorption/Transmission Mode Conversion Based on Active Components

To overcome the limitations of traditional frequency selective surfaces in flexible state switching at the same frequency, this paper proposes a novel active frequency selective surface (AFSS) that simultaneously exhibits conversion between absorption and transmission modes at the same frequency band. By welding PIN diodes on the bottom structure of the AFSS, the conversion between band-pass (transmission) and band-stop (absorption) filters can be controlled electronically. In the common-frequency switch between absorption and transmission modes, the impedance matching of the AFSS is attained by altering the capacitance value of the varactors embedded on the top structure of the AFSS. The functionalities of the proposed AFSS design are investigated by full-wave simulations (in HFSS software) at 11.4 GHz. Furthermore, the operating principle is analyzed using an equivalent circuit model (in AWR software). To verify the concept, a prototype is manufactured, and the responses of mode switching are measured by adjusting the bias voltage. The measurement result is consistent with the simulation analysis. Owing to the tunability of the varactors, the structural asymmetry is compensated to achieve 80% absorptivity and transmissivity within a field of view of ±35°. The developed AFSS structure is highly valuable to be used in scenarios such as antenna domes, etc.

Impact of ligands on the performance of band-stop and bandpass optical filter of cobalt sodium zinc borate glass

Impact of ligands on the performance of band-stop and bandpass optical filter of cobalt sodium zinc borate glass

Tunable bandstop filter using spoof surface plasmon polaritons for terahertz applications

This paper presents the design and analysis of a spoof surface plasmon polaritons (SSPP)-based bandwidth tunable bandstop filter (BSF) operating at 0.26 THz frequency. The proposed filter is comprised of SSPP T-shape resonators which are coupled to the spoof transmission line. Odd and even mode analysis is carried out for the proposed design, and using Co-EM simulation, it is shown that the designed band stop filter is capable of offering tunable bandwidth at THz frequency using a variable capacitor. In order to experimentally validate the proposed approach, design studies are carried out at microwave frequencies and the BSF is developed on a Rogers R4003C substrate of thickness 1.524 mm. The proposed filter designs have a 3 dB bandwidth tunability of 3 GHz (0.038–0.041 THz) and 50 MHz (0.55–0.60 GHz) in the THz and microwave frequency regimes, respectively. The proposed terahertz filter has the potential to be used as an ultra-compact BSF in future applications of photonic integrated circuits in terahertz imaging.

Compact Microstrip Bandstop Filter for UWB Application

In this paper, a novel Ultra-Wideband (UWB) Bandstop Filter (BSF) with five Transmission Zeros (TZ) and three Transmission Poles (TP) is presented. This filter is designed with a new type of resonator. Validation of the proposed filter with the lumped model is also investigated. Further, the transmission line circuit model of the filter is proposed, and consequently even and odd mode impedance is calculated analytically. Furthermore, a compact size of 16.8 mm × 14.98 mm (0.2λg × 0.18λg) is achieved by employing folded stubs. The proposed filter offers an Ultra-wide bandwidth of 7.5 GHz (2.9 –10.4 GHz) with a rejection depth of greater than 20 dB over the entire stopband. Moreover, the upper and lower skirt factors of 70 dB per GHz are achieved. A prototype of the proposed UWB BSF is fabricated and measured. Simulated and measured results are in good agreement, which validates the proposed design.

Wideband quasi-reflectionless bandstop filters using open/shorted coupled lines

AbstractTwo wideband bandstop filters (BSFs) for single and dual-band are proposed and then extended to reflectionless BSFs based on the analysis from input impedance/admittance perspective. Also, topologies of higher-number-stopband input-reflectionless BSF are provided to broaden the design scope. Open/shorted coupled lines are adopted to obtain multi transmission zeros and desired stopband bandwidth by adjusting the even-/odd-mode impedance of coupled lines. Resistor-loaded coupled lines are connected with Port 1 to absorb unwanted signals and obtain input-reflectionless behavior. For validation of the proposed theory analysis, BSFs with corresponding absorptive prototypes are constructed and measured.

Tunable Fano resonance analysis in plasmonic waveguide side-coupled multiple Taiji resonators

In this paper, we first propose and analyze tunable Fano resonance based on indirect interaction between two Taiji resonators which both side-couple with a MIM (metal–insulator–metal) waveguide. An S-shaped branch waveguide embedded in the Taiji ring can tailor the propagating modes and then varying the number of whispering-gallery (WG) modes in the Taiji resonator, leading to the convenient tuning of Fano resonance lineshape. By covering monolayer graphene on the waveguide, Fano resonance lineshape can be all-optically tuned with relatively low pump intensity because of the optical Kerr effect of graphene; by coating UV-glue on the proposed structure, temperature sensing with high sensitivity of −0.23 nm/°C is obtained because of large negative thermo-optic coefficient of UV-glue. Furthermore, up to 16 Taiji resonators are designed and coupled with a common MIM waveguide to observe and analyze Fano lineshape variation, finally realizing the optical band-stop filter with maximal bandwidth of 49.5 nm and optical band-pass filter with maximal bandwidth of 45.3 nm. This ultra-compact micro-structure of plasmonic waveguide coupling multiple Taiji resonators demonstrates good potential applications in the nonlinear optics, optical modulation, and high-sensitivity biochemical sensors.

Coplanar Stripline Single Pole Single Throw Switch

Coplanar stripline (CPS) series-connected spurline resonators are terminated with diodes, which can have a voltage applied to them, creating either a short circuit or open circuit. By connecting two spurline resonators in series separated by a quarter-wavelength transmission line, and when the diodes are reverse biased, the total circuit passes the RF power unimpeded. When the diodes are forward-biased, the circuit is a bandstop filter. This creates a CPS RF series switch with an insertion loss of 0.1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm$</tex-math> </inline-formula> 0.1 dB, a reflection coefficient of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 30 dB, and an isolation of 20 dB. The switch was simulated, fabricated, and measured for both single-element and two-element configurations.

Micromachined Tunable Magnetostatic Forward Volume Wave Bandstop Filter

We have successfully designed, fabricated, and characterized a planar monolithic yttrium iron garnet (YIG) Chebyshev bandstop filter on gadolinium gallium garnet (GGG) substrate with tunable frequency, low insertion loss (IL), and high rejection. This filter is created in YIG micromachining technology that allows direct placement of metal transducers on YIG for strong spin-wave coupling. With an out-of-plane 3900-Oe bias field, the bandstop filter exhibits 55-dB maximum stopband rejection at a center frequency of 6 GHz, with 2-dB passband IL and 37.8-dBm passband <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ \mathrm{IIP_3} $</tex-math> </inline-formula> . By applying different bias fields, the stopband center frequency is tuned from 4 to 8 GHz while maintaining more than 30-dB rejection. Incorporated with proper design of tunable compact electromagnet, this new filter design can provide attenuation of spurs appearing across the fifth generation (5G) and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$X$</tex-math> </inline-formula> -band spectrum.

Multioctave Interference Detectors With Sub-Microsecond Response

High-power interferers are one of the main hurdles in wideband communication channels. To that end, this article presents a wideband interferer detection method. The presented technique operates by sampling the incoming signal as an input, and produces the frequency and the power readings of the detected interferer. The detection method relies on driving an open circuit stub, where the voltage is proportional to the power of the interferer, and the standing wave pattern is an indicator of its frequency. This approach is feasible over multioctave bandwidth with a wide power dynamic range. The concept is analyzed for design and optimization, and a prototype is built for a proof-of-concept. The measured results demonstrate the ability to detect an interferer within the 1–16 GHz frequency range, with a power dynamic range between <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 20 and 20 dBm. The detection concept is also fit with different types of tunable bandstop filters (BSFs) for automatic detection and suppression of the interferer if its power exceeds a programmable threshold. With a measured response time of 500 ns, the presented method is a technology enabler for wideband receivers.

A quantitative model of the cerebral windkessel and its relevance to disorders of intracranial dynamics.

Traditional models of intracranial dynamics fail to capture several important features of the intracranial pressure (ICP) pulse. Experiments show that, at a local amplitude minimum, the ICP pulse normally precedes the arterial blood pressure (ABP) pulse, and the cranium is a band-stop filter centered at the heart rate for the ICP pulse with respect to the ABP pulse, which is the cerebral windkessel mechanism. These observations are inconsistent with existing pressure-volume models. To explore these issues, the authors modeled the ABP and ICP pulses by using a simple electrical tank circuit, and they compared the dynamics of the circuit to physiological data from dogs by using autoregressive with exogenous inputs (ARX) modeling. The authors' ARX analysis showed close agreement between the circuit and pulse suppression in the canine cranium, and they used the analogy between the circuit and the cranium to examine the dynamics that underlie this pulse suppression. This correspondence between physiological data and circuit dynamics suggests that the cerebral windkessel consists of the rhythmic motion of the brain parenchyma and CSF that continuously opposes systolic and diastolic blood flow. Such motion has been documented with flow-sensitive MRI. In thermodynamic terms, the direct current (DC) power of cerebral arterial perfusion drives smooth capillary flow and alternating current (AC) power shunts pulsatile energy through the CSF to the veins. This suggests that hydrocephalus and related disorders are disorders of CSF path impedance. Obstructive hydrocephalus is the consequence of high CSF path impedance due to high resistance. Normal pressure hydrocephalus (NPH) is the consequence of high CSF path impedance due to low inertance and high compliance. Low-pressure hydrocephalus is the consequence of high CSF path impedance due to high resistance and high compliance. Ventriculomegaly is an adaptive physiological response that increases CSF path volume and thereby reduces CSF path resistance and impedance. Pseudotumor cerebri is the consequence of high DC power with normal CSF path impedance. CSF diversion by shunting is an accessory windkessel-it drains energy (and thereby lowers ICP) and lowers CSF path resistance and impedance. Cushing's reflex is an accessory windkessel in extremis-it maintains DC power (arterial hypertension) and reduces AC power (bradycardia). The windkessel theory is a thermodynamic approach to the study of energy flow through the cranium, and it points to a new understanding of hydrocephalus and related disorders.

Compact Dual-Band MIMO Antenna With Shared Decoupling Structure for 5G Mobile Terminals

In this letter, a compact dual-band MIMO antenna, consisting of four antenna pairs, is presented for 5G mobile terminal applications. Each pair includes two tightly-arranged monopoles. By folding the L-shaped monopoles into U-shaped structures, both the 3.5 GHz band and 4.9 GHz band can share the same decoupling inductor. By adding stop-band filter on the monopole, dual-band operation can be provided by a single branch. The size of the dual-band antenna pair is merely 19×4 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The measured -6 dB bandwidth can cover 3.4-3.6 GHz and 4.8-5.0 GHz, with port isolation higher than 12 dB. The measured radiation efficiency varies from 41% to 59% in the lower band, and varies from 38% to 62% in the upper band.

A monostatic RCS reduction study for an antenna in structural mode at X band

ABSTRACT In this paper, a radar cross-section (RCS) reduction of a microstrip antenna is investigated both experimentally and numerically. A traditional metal ground plane antenna and a bandstop frequency selective surface (FSS) filter are designed at 5.4 GHz. In order to reduce RCS and reflectivity of the reference antenna, the bandstop filter structure is set up instead of the full metal ground plane. The study observed a wide frequency range between 3 GHz and 14 GHz. The maximum RCS reductions between the reference antenna and the low RCS antenna in-band and out of band are obtained at 9.2 dBsm and 28 dBsm, respectively. The antennas are analysed under different θ – and φ – polarised incidence conditions. Low RCS antenna shows satisfactory results especially at X band in terms of reflectivity and RCS under these angular conditions.

Band-stop-filter-based repetitive control of fast tool servos for diamond turning of micro-structured functional surfaces

Fast tool servo (FTS) is a promising technique for the high-speed diamond turning of micro-structured functional surfaces due to its fast response capacity. However, the inherent actuator non-linearity, the lightly damped vibration mode and the external disturbance of the FTS would degrade its tracking performance severely and thus restrict its machining ability. To overcome this limitation, a band-stop-filter-based repetitive control (BSF-RC) scheme is proposed in this article to improve the operating performance of the FTS. Firstly, the spectra of the FTS tool paths (FTS-TPs) for machining typical micro-structured functional surfaces with the cylindrical coordinate machining method are analyzed in detail. The results reveal that the frequency components concentrate on the tiny neighborhoods of the rotational frequency of the spindle and its harmonic frequencies. Afterwards, the comb-like band-stop filter used by the BSF-RC is elaborately designed via the cascade of three comb-like notch filters to generate a comb-like band-stop loop shape for covering main spectral components of the FTS-TPs. The analytical expression of the comb-like band-stop filter amplitude as well as the stability condition of the closed-loop control system are derived to provide effective criteria for the parameter selection of the BSF-RC. The experimental validation of the developed BSF-RC scheme is conducted on a five-axis ultra-precision lathe equipped with a self-developed FTS via the diamond turning of three typical micro-structured functional surfaces. The experimental results show that good surface qualities with the maximal form error of a few hundred nanometers and the surface roughness of a several nanometers are achieved for all the obtained micro-structured surfaces by using the BSF-RC scheme under a high spindle speed.

A robust motion correction technique for infrared thermography during awake craniotomy

PurposeIntraoperative infrared thermography is an emerging technique for image-guided neurosurgery, whereby physiological and pathological processes result in temperature changes over space and time. However, motion during data collection leads to downstream artifacts in thermography analyses. We develop a fast, robust technique for motion estimation and correction as a preprocessing step for brain surface thermography recordings.MethodsA motion correction technique for thermography was developed which approximates the deformation field associated with motion as a grid of two-dimensional bilinear splines (Bispline registration), and a regularization function was designed to constrain motion to biomechanically feasible solutions. The performance of the proposed Bispline registration technique was compared to phase correlation, a band-stop filter, demons registration, and the Horn–Schunck and Lucas–Kanade optical flow techniques.ResultsAll methods were analyzed using thermography data from ten patients undergoing awake craniotomy for brain tumor resection, and performance was compared using image quality metrics. The proposed method had the lowest mean-squared error and the highest peak-signal-to-noise ratio of all methods tested and performed slightly worse than phase correlation and Demons registration on the structural similarity index metric (p < 0.01, Wilcoxon signed-rank test). Band-stop filtering and the Lucas–Kanade method were not strong attenuators of motion, while the Horn–Schunck method was well-performing initially but weakened over time.ConclusionBispline registration had the most consistently strong performance out of all the techniques tested. It is relatively fast for a nonrigid motion correction technique, capable of processing ten frames per second, and could be a viable option for real-time use. Constraining the deformation cost function through regularization and interpolation appears sufficient for fast, monomodal motion correction of thermal data during awake craniotomy.

Design of a dual-band filter with high selectivity and wide stopband

ABSTRACT This paper proposes a design of dual-band bandpass filter with a high selectivity and a wide stopband, by using two ring type hairpin resonators. The equivalent circuit of the used resonator is analyzed through the analysis of odd and even modes. The designed filter can achieve dual passbands at 2.4 GHz and 3.65 GHz for wireless local area network (WLAN) and 5 G communication systems, with transmission zeros at 2.9 GHz and 5.1 GHz, realizing high selectivity. With a wideband bandstop filter on the input port, a wide stopband from 4.6 GHz to 17.3 GHz is realized.