Spurious Resonances Research Articles

Substrate integrated waveguide dual‐band filter with wide‐stopband performance

The first substrate integrated waveguide dual-band bandpass filter with wide-stopband performance is presented. This filter is synthesised and designed with fourth-order Chebyshev responses and identical fractional bandwidths for the two passbands centred at 12 and 16 GHz. Multiple spurious resonances have been intrinsically suppressed by introducing the harmonics-staggered technique and the centred coupling windows. Good agreements can be observed between the measured and simulated results, and better than 25-dB rejection level up to 2.05 f 1 has been successfully achieved.

Exact synthesis design theory of analogue broadband bandpass filter

In this article, an exact synthesis design procedure of broadband bandpass filter using step impedance resonator (SIR) and optimum distributed high frequency (ODHF) is presented. SIR provides a large degree-of-freedom owing to its uncomplicated implementation and broad frequency operations. It offers enormous possibilities for its practical applications as well. The filtering function in this work is extracted using the equivalent circuit model. Filtering parameters can be mapped onto Chebyshev type-I polynomials for a narrowband response. However, for broadband filter response this mapping of polynomials will not produce equiripple frequency response. Therefore, the filter polynomials are adjusted such that a required bandwidth with an equiripple response is achieved. The proposed filter structure provides compactness as well as suppression of spurious resonances at high frequencies. Moreover, for the verification purpose, the proposed filter synthesis is also applied to ODHF filter topology. To validate the proposed design procedures, a microstrip-based prototypes are realized. The simulated and measured results are found in good correlation.

Testing of Piezo-Actuated Glass Micro-Membranes by Optical Low-Coherence Reflectometry.

In this work, we have applied optical low-coherence reflectometry (OLCR), implemented with infra-red light propagating in fiberoptic paths, to perform static and dynamic analyses on piezo-actuated glass micro-membranes. The actuator was fabricated by means of thin-film piezoelectric MEMS technology and was employed for modifying the micro-membrane curvature, in view of its application in micro-optic devices, such as variable focus micro-lenses. We are here showing that OLCR incorporating a near-infrared superluminescent light emitting diode as the read-out source is suitable for measuring various parameters such as the micro-membrane optical path-length, the membrane displacement as a function of the applied voltage (yielding the piezo-actuator hysteresis) as well as the resonance curve of the fundamental vibration mode. The use of an optical source with short coherence-time allows performing interferometric measurements without spurious resonance effects due to multiple parallel interfaces of highly planar slabs, furthermore selecting the plane/layer to be monitored. We demonstrate that the same compact and flexible setup can be successfully employed to perform spot optical measurements for static and dynamic characterization of piezo-MEMS in real time.

Radiation pressure excitation of a low temperature atomic force/magnetic force microscope for imaging in 4-300 K temperature range.

We describe a novel radiation pressure based cantilever excitation method for imaging in dynamic mode atomic force microscopy (AFM) for the first time. Piezo-excitation is the most common method for cantilever excitation, however it may cause spurious resonance peaks. Therefore, the direct excitation of the cantilever plays a crucial role in AFM imaging. A fiber optic interferometer with a 1310 nm laser was used both for the excitation of the cantilever at the resonance and the deflection measurement of the cantilever in a commercial low temperature atomic force microscope/magnetic force microscope (AFM/MFM) from NanoMagnetics Instruments. The laser power was modulated at the cantilever's resonance frequency by a digital Phase Locked Loop (PLL). The laser beam is typically modulated by ∼500 μW, and ∼141.8 nmpp oscillation amplitude is obtained in moderate vacuum levels between 4 and 300 K. We have demonstrated the performance of the radiation pressure excitation in AFM/MFM by imaging atomic steps in graphite, magnetic domains in CoPt multilayers between 4 and 300 K and Abrikosov vortex lattice in BSCCO(2212) single crystal at 4 K for the first time.

Iterative averaging of spectra as a powerful way of suppressing spurious resonances in signal processing

The fast Padé transform (FPT) was applied to magnetic resonance spectroscopic (MRS) time signals encoded in vivo on a 1.5 T scanner from the parietal-temporal brain region of a pediatric patient who had suffered cerebral asphyxia. An iterative averaging procedure was implemented to the 9th iteration, whereby spurious structures on the total shape spectra were effectively suppressed. The parametric and non-parametric hbox {FPT}^{(pm )} were verified to reconstruct equivalent total shape spectra. Via the parametric FPT, the spectral region of interest was chosen to bypass the giant water resonance, automatically generating spectral envelopes without the need for windowing. The dense component spectra were reliably reconstructed by the hbox {FPT}^{(+)}, in the “usual” mode (mixture of absorption and dispersion components) and “ersatz” mode (reconstructed phases set to zero). Via the latter, interference effects were well-visualized for closely-overlapping and hidden resonances. The most stringent test was performed for the complex frequencies and associated complex amplitudes reconstructed by the hbox {FPT}^{(+)}. Exceedingly small variances were obtained for all four Padé-reconstructed parameters per genuine resonance, once convergence was achieved at the 7th to 9th iterated averages. This now fully-validated methodology can generate denoised spectra and accurate spectral parameters for in vivo MRS data encoded within neurodiagnostics. Such a multi-faceted Padé-based strategy for processing the dense spectra of the brain could vitally improve pediatric neurodiagnostics. A wider range of clinical applications becomes within reach, including areas of cancer diagnostics where the added value of in vivo MRS is urgently needed. The broad theoretical underpinnings of incorporating quantum mechanics into signal processing provide the basis for these innovative advances.

Electromechanical Measurements Of Gd-Doped Ceria Thin Films By Laser Interferometry

Highly sensitive laser interferometer was built to measure electromechanical coupling in Gd-doped ceria Ce<sub>0.9</sub>Gd<sub>0.1</sub>O<sub>2-x</sub> thin films in the frequency range up to 20 kHz. Spurious resonances due to substrate bending were avoided by the special mounting of the film in the center of substrate. Compact design allowed to reach high vertical resolution of about 0.2 pm. Electrostriction coefficient measured in 1 µm thick Ce<sub>0.9</sub>Gd<sub>0.1</sub>O<sub>2-x</sub> film was 4.3×10<sup>-21 </sup>m<sup>2</sup>/V<sup>2</sup> and slightly decreased with frequency till the extensional resonance of the substrate at about 20 kHz occurred. As expected, the displacement varied as a square of applied voltage without any sign of saturation.

A spin integral equation for electromagnetic and acoustic scattering

We present a new integral equation for solving the Maxwell scattering problem against a perfect conductor. The very same algorithm also applies to sound-soft as well as sound-hard Helmholtz scattering, and in fact the latter two can be solved in parallel in three dimensions. Our integral equation does not break down at interior spurious resonances, and uses spaces of functions without any algebraic or differential constraints. The operator to invert at the boundary involves a singular integral operator closely related to the three-dimensional Cauchy singular integral, and is bounded on natural function spaces and depend analytically on the wave number. Our operators act on functions with pairs of complex two-by-two matrices as values, using a spin representation of the fields.

Reconfigurable Planar Capacitive Coupling in Substrate-Integrated Coaxial-Cavity Filters

This paper expands our previous work on planar tunable capacitive coupling structures in substrate-integrated cavities using lumped components. We demonstrate both frequency and bandwidth tunable filters with adjustable transmission zeros (TZs). By the appropriate choice of the absolute and relative strength of magnetic and electric coupling coefficients, we demonstrate: 1) tunable bandwidth and the ability to maintain either a constant absolute bandwidth or a constant fractional bandwidth; 2) adjustable TZ location at a prescribed bandwidth; and 3) the ability to switch OFF the filter with high isolation. Filter design methodologies based on a dispersive coupling structure are presented using lumped circuit models, coupling matrix, and full-wave simulations. With this planar capacitive coupling, it is also convenient to realize cross-coupling in higher order filters to produce additional TZs for rejecting spurious resonances or interferes. Fabricated two-pole filters with one or two TZs and four-pole filters with three or four TZs validate the filter design. A two-pole filter with tunable center frequency and tunable bandwidth along with a four-pole filter with tunable center frequency and tunable TZs are also demonstrated.

Silicon on-chip 1D photonic crystal nanobeam bandstop filters for the parallel multiplexing of ultra-compact integrated sensor array.

We propose a novel multiplexed ultra-compact high-sensitivity one-dimensional (1D) photonic crystal (PC) nanobeam cavity sensor array on a monolithic silicon chip, referred to as Parallel Integrated 1D PC Nanobeam Cavity Sensor Array (PI-1DPC-NCSA). The performance of the device is investigated numerically with three-dimensional finite-difference time-domain (3D-FDTD) technique. The PI-1DPC-NCSA consists of multiple parallel-connected channels of integrated 1D PC nanobeam cavities/waveguides with gap separations. On each channel, by connecting two additional 1D PC nanobeam bandstop filters (1DPC-NBFs) to a 1D PC nanobeam cavity sensor (1DPC-NCS) in series, a transmission spectrum with a single targeted resonance is achieved for the purpose of multiplexed sensing applications. While the other spurious resonances are filtered out by the stop-band of 1DPC-NBF, multiple 1DPC-NCSs at different resonances can be connected in parallel without spectrum overlap. Furthermore, in order for all 1DPC-NCSs to be integrated into microarrays and to be interrogated simultaneously with a single input/output port, all channels are then connected in parallel by using a 1 × n taper-type equal power splitter and a n × 1 S-type power combiner in the input port and output port, respectively (n is the channel number). The concept model of PI-1DPC-NCSA is displayed with a 3-parallel-channel 1DPC-NCSs array containing series-connected 1DPC-NBFs. The bulk refractive index sensitivities as high as 112.6nm/RIU, 121.7nm/RIU, and 148.5nm/RIU are obtained (RIU = Refractive Index Unit). In particular, the footprint of the 3-parallel-channel PI-1DPC-NCSA is 4.5μm × 50μm (width × length), decreased by more than three orders of magnitude compared to 2D PC integrated sensor arrays. Thus, this is a promising platform for realizing ultra-compact lab-on-a-chip applications with high integration density and high parallel-multiplexing capabilities.

Dual-Surface Electric Field Integral Equation Solution of Large Complex Problems

The integral equation analysis of large perfect electric conductor bodies is commonly formulated in terms of combined field integral equations (CFIE) that avoid spurious internal resonances. The dual-surface electric field integral equation (DSEFIE) is a less employed alternative approach; we discuss here how to cure its shortcomings and enhance its advantages over the CFIE for large bodies of nontrivial geometrical complexity. We study the convergence and accuracy of the DSEFIE also with respect to the current state of the art in the testing of the magnetic field integral equation. Examples of applications to large and realistic composite structures show the effectiveness of the proposed approach.

Fast Analysis of Electromagnetic Scattering From Conducting Objects Buried Under a Lossy Ground

Electromagnetic scattering from conducting objects is investigated for the applications of underground detection. The air–soil composite is modeled by a classical half space where the dyadic Green's function can be defined and formulated. The electric field integral equation (EFIE) is employed to guarantee the accuracy and robustness of the analysis for arbitrarily shaped scatterers. The internal resonance of EFIE is first studied under typical working conditions (frequencies, soil water contents, etc.). It is shown that this spurious resonance is much alleviated due to loss of the soil. Next, the unbounded and ill-posed spectrum of the EFIE operator is remedied by a novel localized half-space Calderon preconditioner by further exploring the lossy nature of the background. Such preconditioning is extremely useful for objects containing multiscale features. Finally, the half-space multilevel fast multipole algorithm based on real-image approximation is adopted to accelerate the computation for electrically large scatterers. Several examples in the applications of subsurface sensing are demonstrated to validate the efficiency and accuracy of this method.

Bandpass filter based on novel‐coupled half‐wavelength microstrip ring resonators

ABSTRACTA microstrip bandpass filter (BPF) based on centre‐coupled cylindrical microstrip ring resonator (MRR) for wireless application in ISM frequency band of applications is presented. The proposed is a combination of two identical bended half‐wavelength (λ/2) MRR, and centre‐coupled by an end‐coupled transmission feed line. The equivalent circuits of the MRR, the end‐coupled feed, and the effects of various spacing between them were investigated based on the even‐ and odd‐mode theory. The mechanism of resonant mode splitting is investigated with the possibility of enhancing the coupling effect, while suppressing spurious resonances in order to achieve sharp rejection skirts. Findings indicates that the proposed equivalent circuit are influenced by capacitances due to resonator – transmission feed line gap (d), the gap between each ring (g), the feed line gap (i), the radius of MRR (r), and the resonator head (m). The operation mechanism of the structure was investigated first theoretically to the intent of design a circuit model, then using numerical 3D EM based on finite integration technique (FIT) method, and finally, through 2D equivalent circuit modeller. The derived equivalent circuit model have been validated both by analytical formulae and numerical simulations. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:911–918, 2016

Modeling stepped U‐slot DGS microstrip line

ABSTRACTThis paper presents an equivalent circuit model for a stepped U‐slot defected ground structure (DGS). For a stepped U‐slot DGS, the defected structure is simply modeled using a short‐circuited stepped impedance coplanar waveguide (CPW) combined with a gap capacitor. The proposed circuit model is advantageous in its ability to accurately control the ratio (η = fs1/fr) of the fundamental resonance frequency (fr) to first spurious resonance frequency (fs1) by changing the impedance and the electrical length of the CPW in each step. By using this property, two types of resonators with normalized first spurious resonance frequencies (η = fs1/fr) of 4 and 2 were designed and fabricated. Good agreement between the EM simulations and the experimental results were achieved. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:583–587, 2016

Design of a Low-Profile Dual-Polarized Stepped Slot Antenna Array for Base Station

In this letter, a microstrip-fed dual-polarized stepped-impedance (SI) slot antenna element with a low profile is first proposed. The antenna is composed of two pairs of SI slots excited by two orthogonal stepped microstrip feedlines. The broadband characteristic is achieved by combining the fundamental and spurious resonances of the SI slot resonators, while the good cross polarization is mainly due to the introduction of the shorting pins. Secondly, based on the proposed antenna, a four-element antenna array is designed, constructed, and measured for base-station applications. Measured results demonstrate the bandwidths (return loss ) of the antenna array are 46.9% (1.55-2.5 GHz) and 38.7% (1.69-2.5 GHz) for Port 1 and Port 2, respectively. The isolation between the two ports is greater than 35 dB, whereas the cross-polarization level maintains lower than -27 dB across the entire operating band. In addition, the antenna array prototype achieves average gains of 13.5 and 13.9 dBi for horizontal polarization and vertical polarization, respectively.

Quantification by the fast Padé transform of magnetic resonance spectroscopic data encoded at 1.5 T: implications for brain tumor diagnostics

Magnetic resonance spectroscopy (MRS) and spectroscopic imaging (MRSI) are widely applied in brain tumor diagnostics. Notwithstanding the important achievements, there are major problems in MRS and MRSI for neuro-oncology due to inadequate signal processing. In this proof-of-concept study, we apply the fast Pade transform (FPT) to MRS time signals of short signal length $$(N = 512)$$ encoded from a standard test phantom head on a 1.5 T MR scanner. The employed phantom head contains a number of major metabolites that are also detectable by way of MRS scans of in vivo human brain. Detailed parametric analysis is performed by which quantification is achieved with full reliability. The effectiveness of the FPT-based signal-noise separation is confirmed in handling these experimentally-encoded MRS time signals. The $$\hbox {FPT}^{(+)}$$ variant of the FPT shows particularly favorable capabilities for distinguishing the genuine from the numerous spurious resonances in the presence of the unavoidable noise, as is typical of data encoded at MR clinical scanners. Exhaustive examination of the convergence process is performed to confirm the stability of the reconstructed spectral parameters. Statistical analysis, as a procedure called “parameter averaging” demonstrates the accuracy and precision of the reconstructed complex-valued fundamental frequencies and amplitudes. This includes the dense regions of the spectrum, containing several very small and/or very closely overlapping resonances. Overall, the obtained results confirm that Pade-optimized MRS and MRSI can be directly used in our fully automated matlab program for in vivo encoded data with complete fidelity within neuro-oncology, with anticipated benefit for brain tumor diagnostics.

Impact of assimilation window length on diurnal features in a Mars atmospheric analysis

Effective simulation of diurnal variability is an important aspect of many geophysical data assimilation systems. For the Martian atmosphere, thermal tides are particularly prominent and contribute much to the Martian atmospheric circulation, dynamics and dust transport. To study the Mars diurnal variability and Mars thermal tides, the Geophysical Fluid Dynamics Laboratory Mars Global Climate Model with the 4D-local ensemble transform Kalman filter (4D-LETKF) is used to perform an analysis assimilating spacecraft temperature retrievals. We find that the use of a ‘traditional’ 6-hr assimilation cycle induces spurious forcing of a resonantly enhanced semi-diurnal Kelvin waves represented in both surface pressure and mid-level temperature by forming a wave 4 pattern in the diurnal averaged analysis increment that acts as a ‘topographic’ stationary forcing. Different assimilation window lengths in the 4D-LETKF are introduced to remove the artificially induced resonance. It is found that short assimilation window lengths not only remove the spurious resonance, but also push the migrating semi-diurnal temperature variation at 50 Pa closer to the estimated ‘true’ tides even in the absence of a radiatively active water ice cloud parameterisation. In order to compare the performance of different assimilation window lengths, short-term to mid-range forecasts based on the hour 00 and 12 assimilation are evaluated and compared. Results show that during Northern Hemisphere summer, it is not the assimilation window length, but the radiatively active water ice clouds that influence the model prediction. A ‘diurnal bias correction’ that includes bias correction fields dependent on the local time is shown to effectively reduce the forecast root mean square differences between forecasts and observations, compensate for the absence of water ice cloud parameterisation and enhance Martian atmosphere prediction. The implications of these results for data assimilation in the Earth's atmosphere are discussed.

Broadband architecture for galvanically accessible superconducting microwave resonators

In many hybrid quantum systems, a superconducting circuit is required, which combines DC-control with a coplanar waveguide (CPW) microwave resonator. The strategy thus far for applying a DC voltage or current bias to microwave resonators has been to apply the bias through a symmetry point in such a way that it appears as an open circuit for certain frequencies. Here, we introduce a microwave coupler for superconducting CPW cavities in the form of a large shunt capacitance to ground. Such a coupler acts as a broadband mirror for microwaves while providing galvanic connection to the center conductor of the resonator. We demonstrate this approach with a two-port λ/4-transmission resonator with linewidths in the MHz regime (Q∼103) that shows no spurious resonances and apply a voltage bias up to 80 V without affecting the quality factor of the resonator. This resonator coupling architecture, which is simple to engineer, fabricate, and analyse, could have many potential applications in experiments involving superconducting hybrid circuits.

Novel Frequency-Agile Bandpass Filter With Wide Tuning Range and Spurious Suppression

A new frequency-agile scheme for the loaded stepped-impedance resonator (SIR) is introduced, which can be employed for designing a wideband tunable bandpass filter (BPF). Two identical capacitors are added to the two open ends, and a capacitor is added to the center of the SIR. By properly controlling their respective values, the even-mode resonant frequency $(f_\mathrm{even})$ can be bidirectionally tuned, resulting in a wideband tuning range (approximately double those of the traditional tunable resonators). However, in such frequency range, the odd-mode resonant frequency $(f_\mathrm{odd})$ functions as a spurious resonance would appear. To overcome this, the feed line is attached to the center of the SIR where it is always short-circuited for $f_\mathrm{odd}$ and its odd-order harmonics, which cannot be excited accordingly. Thus, the wideband tuning range of the passband $(f_\mathrm{even})$ in the proposed BPF is validated to be meaningful, and the selectivity of the passband is improved due to the suppression of odd-mode spurious near the passband. For demonstration, a wideband tunable BPF is designed, and the simulated and measured results are presented, showing good agreement. The results showcase that the tuning range of passband reaches 84.4%, i.e., from 0.77 to 1.42 GHz with insertion loss from 3.1 to 1 dB.

Design of Compact Wideband Manifold-Coupled Multiplexers

The design of manifold-coupled multiplexers for wideband applications is considered in this paper. A systematic procedure, based on the sequential connection of filters to the manifold and subsequent adjustment of the interconnection elements, is presented. The filters are attached to the manifold without using stubs in order to minimize the effect of spurious resonances. The interconnection elements, the manifold, and the remaining filters are considered as the first inverter of each new filter that is attached. This technique has been applied to several practical examples. The obtained results validate the proposed design methodology.

How the fast Padé transform handles noise for MRS data from the ovary: importance for ovarian cancer diagnostics

Advanced signal processing through the fast Pade transform (FPT) can enhance resolution and generates quantitative metabolic information for magnetic resonance spectroscopy (MRS). Herein, we apply both \(\hbox {FPT}^{(\pm )}\) variants to in vitro MRS data as encoded from benign and malignant ovarian cyst fluid and perform detailed analysis with several noise levels. In the presence of higher background noise, all genuine metabolites were unambiguously identified and their concentrations precisely computed, using small fractions of the total signal length by both FPT variants. In the \(\hbox {FPT}^{(-)}\), signal–noise separation was accomplished with the help of the “Stability test”, whereby the non-physical information is binned and denoised spectra are generated. In the \(\hbox {FPT}^{(+)}\) even more stringent signal–noise separation was achieved: the spurious resonances reside exclusively in the negative imaginary frequency domain, whereas the genuine content is all in the positive imaginary frequency region. Pole-zero coincidence of spurious resonance remained complete in the \(\hbox {FPT}^{(+)}\) even at higher noise levels. Via the \(\hbox {FPT}^{(+)}\), a denoised spectrum is generated automatically, without the need for the “Stability test”. The two variants \(\hbox {FPT}^{(\pm )}\) provide self-contained cross-validation of the reconstructed spectral parameters, from which the metabolite concentrations of benign and malignant ovarian cyst fluid are reliably computed. These results are particularly promising for more effective ovarian cancer diagnostics, overcoming the major obstacles that have hindered MRS from becoming the method of choice for non-invasive assessment of ovarian lesions.