Electromagnetic Filter Research Articles

Electromagnetic bandgap filter with single-cell monolithic microwave integrated circuit-tuneable defect

A prototype tuneable planar electromagnetic bandgap filter has been developed for implementing a voltage-controlled bandwidth, intended for adaptive spectral control. A tuneable single-cell defect that allows tuning of the bandwidth is introduced into the structure using monolithic microwave integrated circuit technology. A combination of three-dimensional electromagnetic modelling of the planar structure and equivalent circuit modelling techniques is presented to validate this work. The simulation and measured results are in very close agreement.

Defect modes in one-dimensional anisotropic photonic crystal

We theoretically analyze the defect states in a single-defect photonic crystal composed of anisotropic dielectric materials. This structure can trap light of a given frequency range and filter only a certain frequency light. It is shown that the defect modes appear as peaks in the transmission spectrum. Their numbers, intensities, and frequency positions are extremely sensitive to the incidence angle and the orientation of the principal axes of layers constituting the superlattice and the layer defect. Our structure offers a great variety of possibilities for creating and controlling the number and transmitted intensities of defect modes. It can be a good candidate for realizing a selective electromagnetic filter.

Isotactic and syndiotactic polypropylene/multi-wall carbon nanotube composites: synthesis and properties

Isotactic polypropylene (iPP) and syndiotactic polypropylene (sPP) nanocomposites containing 0.1–3.5 wt.% multi-wall carbon nanotubes (MWCNTs) have been synthesized via in situ polymerization method with the use of C2- and Cs- symmetry zirconocenes activated by methylaluminoxane (MAO) in liquid propylene medium. Fracture morphology studies by SEM reveal different MWCNT dispersion efficiency in various polymer matrices, which arises from the catalytic peculiarities of the composite synthesis. Considerable Young’s modulus enhancement of iPP and sPP (25–66%) takes place even at low MWCNT loadings (below 0.5 wt.%). The obtained nanocomposites can find use as efficient electromagnetic shielding materials and microwave absorbing filters due to relatively low permittivity values and considerable dielectric losses in microwave range. Calorimetry data demonstrate that MWCNTs exert evident influence as nucleating agents causing the rise of iPP and sPP crystallization temperature. Considerable retardation effect on iPP thermal oxidative degradation has been observed: the temperature of maximal weight loss rate rises by ~52 °C upon incorporating only 1.4 wt.% MWCNTs.

Patterned indium tin oxide nanofiber films and their electrical and optical performance

We report on the preparation and characterization of indium tin oxide (ITO) nanofiberfilms with a patterned architecture that are transparent and conductive with a uniformfiber size. ITO nanofiber films with a crisscross pattern were prepared by theelectrospinning of a precursor solution containing ethanol, dimethyl formamide (DMF),indium chloride tetrahydrate, tin chloride pentahydrate and poly(vinyl pyrrolidone) (PVPK90) onto a metal mesh template, followed by calcinations after transfer to a glasssubstrate. The resulting ITO nanofibers had diameters of the order of 100 nmand were composed of single-crystalline nanoparticles that were pure in chemicalcomposition. The morphology, crystallinity and performance of the resulting nanofiberscould be controlled mainly by calcination. Optical and electrical investigationsdemonstrated that these nanofiber films are transparent conductors with an opticaltransmittance as high as 92%. The resulting patterned ITO nanofiber films would besuitable for applications such as solar cells, sensors and electromagnetic field filters.

Fabrication for multilayered composite thin films by dual-channel vacuum arc deposition

A flexible dual-channel curvilinear electromagnetic filter has been designed and constructed to fabricate multilayered composite films in vacuum arc ion plating. The filter possesses two guiding channels and one mixing unit. Multilayered TiN/AlN and TiAlN composite films can be produced by controlling the frequency or interval of the two cathodes. The x-ray photoelectron spectroscopy and low-angle x-ray diffraction results reveal the periodic Ti and Al structures in the TiN/AlN films. The TiAlN films exhibit a smooth surface morphology confirming effective filtering of macroparticles by the filter. High temperature oxidation conducted at 700 degrees C for an hour indicates that the weight increment in the TiAlN films produced by the dual filter is only half of that of the TiAlN films produced without a filter, thereby showing better resistance against surface oxidation.

Synthesis and Properties of Polypropylene/Multiwall Carbon Nanotube Composites

Isotactic polypropylene and elastomeric stereoblock polypropylene nanocomposites containing 0.1−3.5 wt % multiwall carbon nanotubes (MWCNTs) have been synthesized via the in situ polymerization approach using MAO-activated C2- and C1-symmetry ansa-zirconocenes, a technique that has not been previously reported in literature. Fracture morphology examination of the nanocomposites revealed very efficient distribution of the MWCNTs within the isotactic polypropylene matrix, yet interfacial adhesion level and the reinforcement efficiency were dependent on the nanotube loadings. The elastomeric stereoblock polypropylene/MWCNT and the isotactic polypropylene-based nanocomposites exhibited different morphologies depending on the synthesis peculiarities. For isotactic polypropylene, Youngʼs modulus increased by ∼22% even at 0.1 wt % MWCNT loading, and further modulus growth was observed at higher filler contents. Relatively low permittivity values and considerable dielectric losses in microwave range infer that the obtained nanocomposites can find use as efficient electromagnetic shielding materials and microwave absorbing filters. Outstanding improvement of thermal stability (∼60 °C at maximum weight loss rate temperature) has been achieved for isotactic polypropylene upon incorporating only 3.5 wt % of carbon nanotubes.

Polymer Nanocomposite Thin Film Mirror for the Infrared Region

Thin film metal oxide coatings have been used commercially as electromagnetic filters from the UV to infrared regions for over half a century. Deposition onto a substrate has typically been accomplished using vapor deposition techniques [1‐3] and more recently sol‐gel methods. [4‐7] These coatings provide very good optical and mechanical performance when applied to substrates with similar thermal and mechanical properties. When conventional metal oxide coatings are applied to flexible, relatively soft substrates such as polymers, mismatches in mechanical properties can reduce interfacial adhesion or accelerate mechanical failures. [8,9] Theauthorsrecentlyshowedthatathinfilmpolymer nanocomposite can be applied to a polymer substrate and maintain adhesion even under high strains. [10] This paper describes the first time demonstration of an IR mirror using a relatively inexpensive method to apply complicated thin film dielectric stacks to a polymer substrate that can function effectively in high strain systems. Ultrathin layers of polymer nanocomposites can be used to develop electromagnetic filters, with improved mechanical performance, on compliant substrates such as polymers. Self-assembled polymer nanocomposite thin film layers composed of UV-cured acrylates and metal oxide nanoparticles were developed as antireflective coatings for ophthalmic lenses. [11,12] The primary failure mode in this application is associated with intrinsic stresses introduced during processing and thermal cycling of the plastic. Nanocomposite coatings outperform ceramic coatings on plastic substrates because the primary failures are ductile, limiting secondary cracks propagating from abrasions and thereby reducing haze. [10] Ceramic thin films in similar studies exhibited brittle fracture, which led to secondary cracks and higher haze measurements. [8,9] The use of nanoparticles at high packing densities,

The Origin of Mercury’s Internal Magnetic Field

Mariner 10 measurements proved the existence of a large-scale internal magnetic field on Mercury. The observed field amplitude, however, is too weak to be compatible with typical convective planetary dynamos. The Lorentz force based on an extrapolation of Mariner 10 data to the dynamo region is 10−4 times smaller than the Coriolis force. This is at odds with the idea that planetary dynamos are thought to work in the so-called magnetostrophic regime, where Coriolis force and Lorentz force should be of comparable magnitude. Recent convective dynamo simulations reviewed here seem to resolve this caveat. We show that the available convective power indeed suffices to drive a magnetostrophic dynamo even when the heat flow though Mercury’s core–mantle boundary is subadiabatic, as suggested by thermal evolution models. Two possible causes are analyzed that could explain why the observations do not reflect a stronger internal field. First, toroidal magnetic fields can be strong but are confined to the conductive core, and second, the observations do not resolve potentially strong small-scale contributions. We review different dynamo simulations that promote either or both effects by (1) strongly driving convection, (2) assuming a particularly small inner core, or (3) assuming a very large inner core. These models still fall somewhat short of explaining the low amplitude of Mariner 10 observations, but the incorporation of an additional effect helps to reach this goal: The subadiabatic heat flow through Mercury’s core–mantle boundary may cause the outer part of the core to be stably stratified, which would largely exclude convective motions in this region. The magnetic field, which is small scale, strong, and very time dependent in the lower convective part of the core, must diffuse through the stagnant layer. Here, the electromagnetic skin effect filters out the more rapidly varying high-order contributions and mainly leaves behind the weaker and slower varying dipole and quadrupole components (Christensen in Nature 444:1056–1058, 2006). Messenger and BepiColombo data will allow us to discriminate between the various models in terms of the magnetic fields spatial structure, its degree of axisymmetry, and its secular variation.

A flexible curvilinear electromagnetic filter for direct current cathodic arc source

Widespread applications of direct current (dc) cathodic arc deposition are hampered by macroparticle (MP) contamination, although a cathodic arc offers many unique merits such as high ionization rate, high deposition rate, etc. In this work, a flexible curvilinear electromagnetic filter is described to eliminate MPs from a dc cathodic arc source. The filter which has a relatively large size with a minor radius of about 85 mm is suitable for large cathodes. The filter is open and so the MPs do not rebound inside the filter. The flexible design allows the ions to be transported from the cathode to the sample surface optimally. Our measurements with a saturated ion current probe show that the efficiency of this flexible filter reaches about 2.0% (aluminum cathode) when the filter current is about 250 A. The MP density measured from TiN films deposited using this filter is two to three orders of magnitude less than that from films deposited with a 90 degrees duct magnetic filter and three to four orders of magnitude smaller than those deposited without a filter. Furthermore, our experiments reveal that the potential of the filter coil and the magnetic field on the surface of the cathode are two important factors affecting the efficacy of the filter. Different biasing potentials can enhance the efficiency to up to 12-fold, and a magnetic field at about 4.0 mT can improve it by a factor of 2 compared to 5.4 mT.

Scattering Characteristics of Stratified Double Negative Stacks Using the Frequency Dispersive Cold Plasma Medium

We present the wave propagation through stratified double negative stacks to illustrate the scattering characteristics of their structure. The double negative stacks are modeled by using the hypothetical non-dispersive and the frequency dispersive cold plasma media. The stacks are embedded between two double positive media and the incident electric field is assumed a plane electromagnetic wave with any arbitrary polarization. By imposing the boundary conditions, the relations between the fields inside and outside the stacks can be written in a matrix form. Using this transfer matrix, the incident, reflected, and transmitted powers are derived. The variations of the powers for the stratified double negative stacks using the frequency dispersive cold plasma medium have not been investigated yet, in detail. Thus, their characteristics for the perpendicular polarization is computed and presented in numerical results with the emphasis on the plasma frequencies. It is seen from the numerical results that the stratified double negative stacks can be used as electromagnetic filters at some frequency bands.

Microfabricated electromagnetic filters for millikelvin experiments

In this article we report on the design, fabrication, and tests of microfabricated broadband filters suitable for proper electromagnetic thermalization of electrical lines connected to sensitive quantum electronics experiments performed at dilution fridge temperatures. Compared to previous such miniature filters, the new design improves on performance and reliability. These filters can be packed in space-saving cases with either single or multicontact connector. Measured performance in the accessible range compares well to simulations. We use these simulations to discuss the effectiveness of these filters for electromagnetic thermalization at 30mK.

Three-phase electromagnetic filter for zero-sequence harmonics

This paper proposes a shunt electromagnetic filter to attenuate zero-sequence harmonic injection into three-phase star-grounded supplies. The device is built on the basis of zigzag windings and a three-leg core-type magnetic arrangement. Physical considerations as well as mathematical modeling and computer implementation are fully described. The paper reports on computational investigations to verify the filter performance under balanced and unbalanced supply voltages and on laboratory validation of a prototype device. Both the modeling and the laboratory results are in close agreement and demonstrate the capacity of the equipment to filter the components of the zero-sequence currents. The product performance in a real system is also included in the analysis. The theoretical and practical studies show that the level of zero-sequence harmonic injected into the mains can be reduced by 80% or more, depending on the control of filter leakage inductance. This method also leads to cheaper, simpler, and more robust equipment

Magnetic MEMS Reconfigurable Frequency-Selective Surfaces

A reconfigurable frequency-selective electromagnetic filter implemented by integrating hard magnetic materials with microelectromechanical systems (MEMS) provides a new variation of reconfigurable frequency-selective surfaces (FSS). By incorporating magnetically actuated dipole elements that are capable of being tilted away from the supporting surface, we can tune the FSSs operating frequency without having to physically alter the dimensions of the dipole elements. The 25/spl times/25 array of microactuators used in this work each consist of a 896/spl times/168/spl times/30 /spl mu/m/sup 3/ ferromagnetic plate made of 40Co-60Ni, layered with a 1-/spl mu/m-thick conductor (Au), attached to a pair of 400/spl times/10/spl times/1 /spl mu/m/sup 3/ polysilicon torsion beams, suspended just above the supporting substrate. The high remanent magnetization of the ferromagnetic material allows for relatively small magnetic fields (/spl sim/2.1 kA/m) to induce significant angular deflections (/spl sim/45/spl deg/). This innovative reconfigurable FSS design has successfully demonstrated electromagnetic-signal diplexing and tuning its resonant frequency over a bandwidth of 2.7 GHz at a frequency of 85 GHz.

Tapered dual-plane compact electromagnetic bandgap microstrip filter structures

In this paper, the designs of two novel tapered dual-plane compact electromagnetic bandgap (C-EBG) microstrip filter structures are presented. With the dual-plane configuration, the proposed structure displays an ultrawide stopband with high attenuation within a small circuit area. Chebyshev distribution is adopted to eliminate ripples in the passband caused by the periodicity of the EBG structure. This gives rise to a compact EBG structure that exhibits excellent transmission and rejection characteristics in the passband and the stopband, respectively. The proposed structures are implemented and the measurement results are found to be in good agreement with the simulation results, verifying the excellent stopband and passband performance obtained using the proposed configuration. These novel structures are easy to fabricate and are promising structures that have wide applications for compact and high performance circuit component designs in microwave circuits.

Reliability of electromagnetic filters of cardiac pacemakers tested by cellular telephone ringing

State-of-the art cardiac pacemakers are protected against radiofrequency signals. Although there have been earlier clinical and in vitro reports of cellular phone interference with implantable devices, only a few studies have been performed in recent years. The ringing phase of digital GSM or PCS cellular phones includes a brief period of peak radiated power. This study tested the protection offered by electromagnetic filters of cardiac pacemakers against cellular phone ringing. We performed 330 consecutive tests in 158 patients at the time of routine examination in our pacemaker follow-up clinic. The programmed parameters remained unchanged before testing. During electrocardiographic monitoring, 2 single-band digital cellular phones consecutively placed over the pacemaker pocket each received a call. The phone systems tested were 1) GSM at a maximal power output of 2 W, operating on a 900 MHz carrier frequency, and 2) PCS at a maximal output of 1 W, operating on a 1800 MHz carrier frequency. Interference was noted in only 5 tests, due to interaction by the GSM system with 4 unprotected pacemaker models. The GSM test was negative in 12 other tests of identical pulse generator models. The overall incidence of interference was 1.5% of tests. Interference by cellular phone ringing occurred only with unprotected pacemaker models. Standard programming of these unprotected models was associated with a low incidence of interference.

Characterization of copper metallization for interconnect by 90°-bend electromagnetic filtered vacuum arc

The cathodic arc evaporation plasma generated the highest plasma density compared with other physical vapor deposition systems, but is known to be contaminated with macro-particles. In order to produce high quality particle-free copper films, a 90°-bend magnetic filter is suitable for ultra-large scale integrated circuit interconnects metallization application.Macro-particle contamination has been alleviated by electromagnetic filter; the copper ions in the fully ionized copper plasma were accelerated and deposited on the wafer with a negative pulsed bias voltage. The fully ionized copper plasma stream was highly directionally deposited on the patterned and blank wafers. Electron backscattered diffraction spectra showed the textures distribution of the grain growth. The result of this process as made, by mechanical pull-up tests, showed that substrate applied with −100V pulsed bias can effectively enhance the adhesion strength of copper film on a-TaN layer. The roughness measured by atomic force microscope increased as the negative bias voltage applied to the substrate increased. The filling of trench/via as narrow as 0.2μm, with an aspect ratio as high as 5, field emission scanning electron microscope images showed excellent gap-filling ability.

Use of electromagnetic band‐gap materials for RCS reduction

AbstractMost applications of electromagnetic band gap (EBG) concern antenna radiation or electromagnetic filters. In this paper, a metallic EBG structure is designed for stealth applications. We show how this structure allows us to reduce the radar cross section (RCS) of targets. An application of this kind of MEBG is the design of a radome allowing the reduction of antenna RCS. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 546–550, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20693

Electromagnetic periodic structure bandpass filter (EPS‐BPF) with two transmission zeros

AbstractIn this paper, an improved electromagnetic periodic structure bandpass filter (EPS‐BPF) is designed and analyzed, and its equivalent circuit is also presented. The proposed structure achieves two transmission zeros on both sides of passband, while a good rolling skirt is obtained as well. The measured results show that the filter has a fractional 3‐dB bandwidth of 16%, and its insertion and return losses are −2 and −27 dB at the 5‐GHz center frequency, respectively. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 265–267, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20273

Frequency selective surfaces as near-infrared electromagnetic filters for thermophotovoltaic spectral control

Frequency selective surfaces (FSSs) effectively filter electromagnetic radiation in the microwave band (1 mm to 100 mm). Interest exists in extending this technology to the near infrared (1 μm to 10 μm) for use as a filter of thermal radiation in thermophotovoltaic (TPV) direct energy conversion. This article assesses the ability of FSSs to meet the strict spectral performance requirements of a TPV system. Inherent parasitic absorption, which is the result of the induced currents in the FSS metallization, is identified as a significant obstacle to achieving high spectral performance.

Ohmic loss in frequency-selective surfaces

The present study was undertaken in order to quantify absorption effects due to ohmic loss in frequency-selective surfaces (FSS) at infrared frequencies. The structures considered in this work act as electromagnetic filters, and as such, are of interest for use as thermophotovoltaic spectral control devices. For this application, absorption is of primary concern since it leads to reduced filter efficiency. This work focuses on the behavior of single-layer, free-standing FSS arrays comprised of circular apertures (holes) and circular loop apertures (rings). Numerical calculations of the transmission, reflection, and absorption characteristics of various arrays were carried out for wavelengths between 1 and 15 μm using a commercial finite-element software package. Absorption effects were included using measured optical properties as input parameters to a surface impedance boundary condition. Analytical techniques were then employed to determine the absorption behavior in the static limit. An interesting result of this analysis is the fact that absorption at 15 μm is predicted by the finite-element calculations to increase versus aperture radius (for fixed aperture separation), while in the static limit absorption was found (through the use of analytical techniques) to decrease. The results of the finite-element calculations were confirmed using another numerical method based on the periodic moment method. We are thus led to the conclusion that the qualitative relationship for absorption versus aperture radius must reverse for some frequency regime yet to be investigated.