Cutoff Frequency Fc Research Articles

Experimental Realization of Tunable Transmission Lines Based on Single-Layer SIWs Loaded by Embedded SRRs

Wave propagation in single layer substrate integrated waveguides (SIWs) loaded by embedded split-ring resonators (ESRRs) is discussed theoretically and experimentally. It is shown that the loaded SIW can support a backward-wave passband below the cutoff frequency (fc) of the host SIW or a stopband will appear above fc if the effective transversal permeability is negative. In addition, varactor-loaded ESSRs (VLESRRs) can show resonance frequency agility through a variable reverse bias voltage applied to the varactors. Next, VLESRRs are loaded in SIWs to realize transmission lines with either tunable passbands (stopbands) below (above) fc of the host SIWs. Both cases are considered in this paper. First, an SIW with fc=7 GHz is loaded by five VLESRRs showing a tunable passband below the cutoff from 1.5 to 4 GHz. Second, an SIW with fc=1.9 GHz and five VLESRRs is discussed where a tunable stopband is achieved above fc from 2 to 4 GHz. In both cases, the reverse-bias voltage applied to the varactors varies from 0 to 20 V. Finally, two fabricated prototypes are provided for each case to validate the analysis. The measured and simulated results are in good agreement.

Improved performance step impedance lowpass filter

Performances of the conventional Butterworth step impedance lowpass filters (LPF) are significantly improved by placing transmission zero either closer to the cut-off frequency (fc) or away from it. It is achieved by using transverse resonance width of the capacitive line sections. We report method of designing transverse resonance type LPF (TR-LPF) for 5 to 11-pole filters. At fc=2.5GHz, we obtained selectivity in the range 113.3–56.66dB/GHz and 20–60dB rejection BW in the range 9.61–7.29GHz. The TR-LPF can suppress the stopband signal by 60dB up to 5fc. Insertion loss in passband is within 0.72dB. Improved performance of TR-LPF can be designed for fc up to 7.5GHz.

Mode splitting transmission effect of surface wave excitation through a metal hole array

The resonant frequencies of the excited surface waves on a metal hole array with respect to the incident angle were studied in the terahertz region. The experimental and theoretical results demonstrate that the resonant peak of surface wave excitation splits into two when transmitted through a metal hole array off-normally. The high-order mode with resonant frequency above the cutoff frequency fc (plasma frequency effect) has a shorter attenuation length than that of the low-order mode whose resonant frequency is below fc. The reason is that the high-order mode is a coupled mode consisting of surface wave and hole modes, while the low-order mode is just an excited surface wave (which can be considered as the spoof surface plasmons). Our investigation may open a door to distinguish the spoof surface plasmons and the coupled modes of surface waves and hole modes. Changing the angle at which terahertz waves strike a hole-filled metal plate splits the radiation into two modes of different frequency. This is the finding of Lin Chen and co-workers from the University of Shanghai for Science and Technology in China, who studied the transmission of 0.1–0.5 THz terahertz radiation through a 250-µm-thick metal plate containing an array of 0.7-mm-diameter holes. They say that the observed mode splitting is due to the interaction between surface plasmon waves excited on the surface of the metal and the in-plane component of the incident terahertz wave. The researchers hope that such metal hole arrays could be useful for creating miniature components, such as filters and switches, for controlling terahertz radiation.

Effect of embedding nanoparticles on the lattice thermal conductivity of bulk semiconductor crystals

We analyze the effect of embedding semiconductor nanoparticles as extrinsic phonon scattering centers on the steady-state κ(0) and dynamical κ(Ω) behaviors of the lattice thermal conductivity of bulk semiconductor (SC) alloy crystals. As an example, we consider the case of Ge nanoparticles embedded in a Si0.7Ge0.3 alloy crystal host matrix. The analysis includes the study of the effect of changing the size and concentration of the nanoparticles in combination with changing the ambient temperature while all other intrinsic properties of the SC alloy crystal host matrix are kept constant. Our calculations confirm the existence of an optimal nanoparticles size that minimizes κ(0). Depending on the ambient temperature, the optimal size either increases or decreases as a function of the nanoparticles concentration. Our calculations show also the cut-off frequency fC of κ(Ω) to be very sensitive to the size and concentration of the embedded nanoparticles. For a fixed ambient temperature and nanoparticles concentration, fC manifests a very interesting behavior as a function of the nanoparticles size. While embedding nanoparticles in SC alloy matrices reduces the steady-state κ(0), it however tends to increase fC of the dynamical κ(Ω) in comparison with intrinsic SC alloys. The study sheds light also on the fundamental role that normal processes have in treating phonon heat transfer phenomenon.

Scaled behavior of interface waves at an imperfect solid-solid interface

Laser ultrasonic techniques allow the remote analysis of adhesion mechanisms at imperfect interfaces up to GHz frequencies. However, the sensitivity of interface waves to the properties of the contact is not very well known. In the present work, the mechanical boundary conditions are described considering that the contacting solid half-spaces are connected by tangential and normal springs. Such a modeling implies a discontinuity of the displacement field across the interface. To identify the relative amplitudes of the different types of interface waves—skimming, leaky Rayleigh (LR) and Stoneley (St) waves—a semi-analytical time domain model describing the thermoelastic laser generation is derived. The results illustrate the influence of the boundary conditions on the attenuation of the LR wave and on the existence of the St wave. In addition, a single compact and elegant dispersion equation is presented to investigate the behaviour of the interface waves propagating along a generalized imperfect boundary. Such analysis reveals the existence of a cutoff frequency fc close to which the St wave behaves like a skimming transverse wave. A scaled analysis demonstrates that two master curves suffice to describe the dispersion of LR and St waves and that fc is inversely proportional to the tangential interfacial spring constant.

High-performance short channel organic transistors using densely aligned carbon nanotube array electrodes

We report high-performance short channel pentacene field effect transistor (FET) using carbon nanotube aligned array electrodes. The devices show field effect mobility of up to 0.65 cm2/Vs and current on-off ratio of up to 1.7 × 106, which is the best for sub-micron pentacene FETs. The calculated cutoff frequency (fc) of the devices is up to 211 MHz which is among the best reported fc for organic transistors. The high performance of our short channel FET is attributed to improved charge injections from the aligned array carbon nanotube electrodes into the pentacene.

DGS embedded transformed radial stub for ultra-wide stopband lowpass filter

A novel lowpass filter (LPF) with a wide stopband by using defected ground structures (DGSs) and a transformed radial stub (TRS) in combination is proposed. The characteristics of DGS cells are investigated and the DGS embedded TRS LPFs are designed and verified by experiment. The designed DGS embedded TRS LPF demonstrates a passband insertion loss of less than 1dB, a cutoff frequency (fc) of 2.5GHz, a wide stopband with more than 16dB rejection up to 14fc, a passband return loss of better than 18dB and a compact size of 0.26λg×0.167λg (λg is the guided wavelength at the cutoff frequency).

Ultra-wide rejection band lowpass cell

A novel lowpass cell with ultra-wide band rejection and compact size by using proposed radial loaded transformed radial stubs is proposed. The implemented lowpass filter with 1dB cutoff frequency fc of 3.2 GHz demonstrates stopband rejection up to 11.8 fc, i.e. 38 GHz. The measured passband insertion loss, including the connector loss, is less than 1.0 dB. The effective size of the unit cell lowpass filter is only about 310×170mil, i.e. 0.12 λg × 0.063 λg (λg is the guide wavelength at cutoff frequency) without using any lumped elements.

Effect of Prefiltering Cutoff Frequency and Scatter and Attenuation Corrections During Normal Database Creation for Statistical Imaging Analysis of the Brain

The present study aimed to quantify which image reconstruction conditions for normal databases and patients affect statistical brain function image analysis using an easy z score imaging system (eZIS) and 3-dimensional stereotactic surface projections (3D-SSP). We constructed normal databases based on cerebral perfusion SPECT images obtained from 15 healthy individuals. Each normal database was created with the following unique conditions: a variable Butterworth filter cutoff frequency (fc) with and without scatter and attenuation corrections. To simulate patient data, we selected 1 dataset from among those created from the 15 healthy individuals. The simulated patient data were designed to include hypoperfused regions with prespecified volumes. Using 3D-SSP and eZIS, we compared how the above processing conditions affect the distribution of SD in normal database images and the accuracy of detecting specific regions. The SD for the SPECT images increased with the fc of the Butterworth filter. The z score decreased by 30% for 3D-SSP and by 14% for eZIS, indicating that the prefilter significantly affected z scores. The accuracy of detecting the hypoperfused regions was significantly influenced by the fc; 3D-SSP decreased by 7.51%, and eZIS decreased by 55.34%. The detection accuracy with eZIS, which involves a smoothing process, was significantly decreased. The error of the area of hypoperfused regions was minimized when normal database and patient data were both corrected for scatter and attenuation. When the reconstruction conditions (fc, scatter correction, and attenuation correction) at normal database creation differed from those at patient data processing, the z scores widely underestimated the analytic results because the SD varied according to the reconstruction conditions. The accuracy of brain function image analysis can be improved by considering the reconstruction conditions and correcting for scatter and attenuation on both normal databases and patient data.

New Ultra-Wide Stopband Low-Pass Filter Using Transformed Radial Stubs

A new type of low-pass filter (LPF) with ultra-wide band rejection and compact size by using a proposed transformed radial stubs (TRSs) is introduced and investigated. The operating mechanism of the filter is investigated based on proposed equivalent-circuit model. The implemented LPF with 1-dB cutoff frequency fc of 3 GHz demonstrates stopband rejection up to 8 fc i.e., 24 GHz. The skirt selectivity is achieved up to -144 dB per octave through multiple-zero generation using TRSs. The measured passband insertion loss is less than 1.5 dB. I/O loading cells are used to further extend the deep stopband to more than 13 fc i.e., above 40 GHz. The size of the four-cell LPF is only 0.31 λg × 0.24 λg, (λg is the guide wavelength at center cutoff frequency) without using any lumped elements.

Compact Metamaterial Microstrip Low-Pass Filter

Complimentary hexagonal-omega structures are used to design compact, low insertion loss (IL), low pass filter with sharp cut-off. It has been designed for improvement of roll-off performance based on both μ and ε negative property of the complimentary hex-omega structure while maintaining the filter pass-band performance. By properly designing and loading the hexagonal-omega structure in the ground of microstrip line not only improve the roll-off of the low pass filter, but also reduced the filter size. The simulated results indicate that the proposed filter achieves a flat pass band with no ripples as well as selectivity of 19.68 dB/GHz, corresponding to 5-unit cells hex-omega structures. This significantly exceeds the 5.6 dB/GHz selectivity of the conventional low pass filter design, due to sub-lambda dimensions of the hex-omega structure. A prototype filter implementing area is: 0.712λg x 0.263λg, λg being the guided wavelength at 3-dB cut-off frequency (fc). The proposed filter has a size smaller by 36.2%.

High-performance low-pass filter using complementary square split ring resonators defected ground structure

In this study, a complementary square split ring resonator (CSSRR) using defected ground structure in microstrip line form is introduced. The CSSRR unit has interesting filtering characteristics, such as a very high attenuation rate, couple of the dimension-dependent finite attenuation poles and a very low-passband ripple level. Cascading CSSRR units with different dimensions has been used to design a high-performance low-pass filter (LPF) with a cutoff frequency (fc) of 1.80 GHz through a simple, straightforward design procedure. The designed LPF exhibits an attenuation rate of 300 dB/GHz and passband ripples of less than 0.30 dB. Moreover, it has a wide 20-dB stopband at up to 4.5 times fc with an attenuation of more than 30 dB in most of the stopband. To the authors knowledge, the overall performance of the LPF, particularly the attenuation rate, is the best among published reports to date. The designed filter has been fabricated and validated by measurements.

Examination of Single-phase Partial Discharge Monitoring Device for Partial Discharge Diagnosis on Three-phase GIS

This paper deals with partial discharge induced electromagnetic wave investigation on three-phase GIS using UHF method and the application of single-phase partial discharge monitoring device (PDM) on three-phase gas insulated switchgear (GIS). The PD source is a protrusion at different positions on the conductor or on the tank. Frequency and phase spectrums of EMW signals emitted by PD at different positions were observed. The most dominant frequency of EMW signal in three-phase GIS was estimated from the cutoff frequency (fc) formula for single-phase GIS. The main difference in frequency spectrum between three-phase and single-phase GIS was found to be the shift of fc to the lower value for three-phase GIS. The presence of three conductors can be considered as increase in an equivalent radius of three-phase conductor by a factor of 1.6 for this GIS model. The phase of PD phase pattern in the phase spectrum depended on the particle position. The PD sources on three-phase GIS were diagnosed by single-phase PDM device. The success rate of diagnosis results is low. The error is predicted to be caused by error in phase recognition of PD pattern. The change in phase shift setting of PD phase pattern in PDM device based on the phase angle of applied voltage at maximum electric field gave better diagnosis results. Index Terms: three-phase, GIS, PDM device, phase shift setting, success rate

Simulation of an EAS Implant with a Hybrid Vocoder

Although EAS electrode arrays are shorter, they have the same number of electrodes as conventional implant arrays. The possibility of channel interaction already exists with a standard length electrode array. As electrodes on an EAS array are closer together, the likelihood of channel interaction is even greater. To compensate for this, we proposed to deactivate several channels on the electrode array, on the premise that the reduction in speech intelligibility due to fewer channels would be offset by the low frequency residual hearing. Recent studies have demonstrated that low frequency residual hearing provides significant benefit for speech understanding (Dorman et al., 2005; Turner et al., 2004). This study aims to determine the number of channels necessary to provide good speech understanding according to the degree of low frequency residual hearing, particularly the boundary or cutoff frequency (Fc) between acoustic and electrical stimulation. This study utilized an acoustic simulation of an EAS device in normal-hearing subjects.

An integrated compact coplanar waveguide high‐pass filter implemented on high resistivity silicon substrate

AbstractIn this article, the fabrication of a compact and high performance semi‐lumped coplanar waveguide high‐pass filter (CPW‐HPF) implemented on high resistivity silicon (HRS) substrate is proposed.The design procedure and the equivalent circuit of the proposed semi‐lumped CPW‐HPF is discussed. The filter structure is simple, and the performances are fairly good. This designed filter at cutoff frequency fc of 21.6 GHz has very good measured characteristics including a balance passband of S21 of −0.5 ± 0.3 dB and a sharp band edge rejection. Experimental results of the fabricated filter show a good agreement with the predicted results. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1150–1153, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25116

Traveling-Wave Amplifiers in Transferred Substrate InP-HBT Technology

Promising transistor results of an InP transferred substrate (TS) technology are presented. ft and fmax are reported as high as 420 and 450 GHz, respectively. Processing has been developed to a full monolithic microwave integrated circuit compatible technology with metal-insulator-metal capacitors, NiCr resistors, and a multilevel wiring scheme. As an example, traveling-wave amplifiers (TWAs) have been designed and realized in a microstrip environment. Simulations of the environment have been done, and are presented in this paper. They have then been used as a design kit to perform circuit simulations. The TWAs demonstrate a gain of 12.8 dB and a 3-dB cutoff frequency fc of 70 GHz. To the authors' knowledge, this is the highest proven bandwidth of a broadband amplifier in TS technology.

Statistical analyses on multi-scale features of monitoring data from health monitoring system in long cable supported bridges

Strain-time histories and other data acquired from a structural health monitoring system (SHMS) installed on a bridge reflect the real-time structural response of the bridge under actual service and environmental loading. It is necessary to understand the inherent features of the data if we want to have confidence in using them to assess the health state or detect potential damage in the structure. This paper aims at exploring the inherent features of strain-time histories data from SHMS in order to find out their behavior in multiple temporal scales and to obtain reliable, clean and normalized data at the dominant scale of stresses inducing fatigue. Firstly, the strain history data from SHMS installed on Runyang Yangtze Bridges (RYB) were analyzed within three typical temporal scales to explore their different characteristics and their own cut-off frequency which span different orders of magnitude. Then, based on the description of the multi-scale features of the monitored data, a further investigation of the dominant scale controlling fatigue failures was carried out. The result shows that, the strain data corresponding to the typical temporal scales of 106, 103 and 100 sec are caused by temperature change, with cut-off frequency fc,1 in the 10−2 Hz range, by train load, with fc,2 in the 10−1 Hz range and by truck load, with fc,3 in the 100 Hz range. Noise shows significant coupling effect when coarse scale strain data are used for the evaluation, which may lead to significant error even it is in small level acceptable in engineering analyses.

Study on the Frequency Dependence of Lateral Energy Leakage in RF Bulk Acoustic Wave Device by Fast-Scanning Laser Probe System

This paper describes the application of the developed fast-scanning laser probe system to the diagnosis of frequency dependence of lateral energy leakage occurring in RF bulk acoustic wave (BAW) devices. According to wavenumber domain analyses, dispersion relation for the device under test is derived, the leakage behaviors at different frequencies are shown as images, and energy of each lateral mode is evaluated quantitatively. The cause of the lateral energy leakage and its frequency dependence are discussed. It is shown that the cause of lateral energy leakage is the higher order transverse modes which are not excited at frequency higher than a cut-off frequency ( fc) for the longitudinal extension mode. It is demonstrated that by using this laser probe system, the lateral energy leakage variation upon frequency can be seen intuitively, and the underlying mechanism for the leakage can be analyzed and explained clearly.

Synthesis Design of Ultra-Wideband Bandpass Filters With Composite Series and Shunt Stubs

This paper presents a direct synthesis procedure for efficient design of a class of ultra-wideband bandpass filters with composite series and shunt transmission-line stubs. The proposed single-stage bandpass prototype is formed by cascading two sets of series open-ended and shunt short-ended stubs through a multisection nonuniform transmission line. All the stubs are set with an identical electrical length, i.e., thetasc , at lower cutoff frequency fc and the middle connecting line is composed of stepped-impedance transmission line with i sections, and each section has an electrical length thetasc. The proposed filter topology aims to construct an ultra-wide bandpass filter with Chebyshev equal-ripple responses and (i + 3) in-band transmission poles. Based on the derivation of the transfer function, a synthesis approach is established and systematically described to design this type of filters according to the specifications such as lower/upper cutoff frequencies. Next, a multistage bandpass filter prototype is proposed and the synthesis design procedure is also presented. The implementation is achieved by using hybrid microstrip line and slotline sections. Compared with traditional stub filters, the proposed filters achieve higher order transmission zeros and thus provide higher selectivity. As design examples, two single-stage and one three-stage bandpass filters are designed and fabricated to confirm the theoretical predictions.

A novel compact low‐pass filter using defected ground structure

AbstractIn this article, a novel gradual change defected ground structure (DGS) for low‐pass filter (LPF) design is presented and analyzed. The proposed DGS combined with open stubs is presented to enhance the out‐band suppression. The equivalent circuit model and simulated results for the DGS are used to determine the dimension parameters. Based on gradual change structure, the LPF with cutoff frequency fc of 3.1 GHz has presented good measured characteristics, including low insertion loss of 0.325 dB and wide stopband from 3.4 to 10 GHz below −35 dB. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 792–795, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24139