Wide Frequency Span Research Articles

Model for plasma transport due to drift waves based on mappings including finite Larmor radius

Abstract Turbulence in plasmas is modeled by fluctuating electric fields that determine particle motion through the E × B drift velocity which can lead to chaotic behavior. When applied to an ensemble of plasma particles in the chaotic regime their transport is studied: the anomalous plasma transport. The fluctuations are modeled by a spectrum of traveling waves with a wide frequency span which converts the equations of motion into an iterative mapping. The statistical properties of transport are derived. When the waves amplitude is small the particle orbits are regular, but as it is increased the behavior becomes increasingly chaotic. The effect of finite Larmor radius and the presence of a background plasma flow is also studied. We show that when a thermal population of particles is considered, the transport becomes non-local, as evidenced by a non-Gaussian particle distribution function (PDF). We have analyzed two different kinds of sheared flows: (1) a monotonic velocity shear and (2) a non-monotonic shear. The presence of transport barriers associated with the sheared velocity is also studied. We also present the application of the same techniques to study the transport of energetic particles that are born with a monoenergetic distribution.

Phase-amplitude coupling-based adaptive filters for neural signal decoding.

Bandpass filters play a core role in ECoG signal processing. Commonly used frequency bands such as alpha, beta, and gamma bands can reflect the normal rhythm of the brain. However, the universally predefined bands might not be optimal for a specific task. Especially the gamma band usually covers a wide frequency span (i.e., 30-200 Hz) which can be too coarse to capture features that appear in narrow bands. An ideal option is to find the optimal frequency bands for specific tasks in real-time and dynamically. To tackle this problem, we propose an adaptive band filter that selects the useful frequency band in a data-driven way. Specifically, we leverage the phase-amplitude coupling (PAC) of the coupled working mechanism of synchronizing neuron and pyramidal neurons in neuronal oscillations, in which the phase of slower oscillations modulates the amplitude of faster ones, to help locate the fine frequency bands from the gamma range, in a task-specific and individual-specific way. Thus, the information can be more precisely extracted from ECoG signals to improve neural decoding performance. Based on this, an end-to-end decoder (PACNet) is proposed to construct a neural decoding application with adaptive filter banks in a uniform framework. Experiments show that PACNet can improve neural decoding performance universally with different tasks.

New Modified Voltage Differencing Voltage Transconductance Amplifier (MVDVTA) based Meminductor Emulator and its Applications

This paper presents a new modified voltage differencing voltage transconductance amplifier (MVDVTA) basedmeminductor emulator circuit. The proposed emulator circuit is memristor-less, uses only a single active building block(ABB) and has simple circuitry. The MVDVTA based emulator design consists of only two capacitors and a single resistor.The performance of the proposed design has been verified over a wide frequency span. For simulation purpose LTSpice toolis used with 0.18μm CMOS technology. The proposed emulator has also been employed in chaotic oscillator and adaptivelearning application circuit to verify its workability. The proposed design gives satisfactory performance for both theapplications, hence confirming its functionality in practical environment.

Realizing an Entanglement-Based Multiuser Quantum Network with Integrated Photonics

Quantum network facilitates the secure transmission of information between different users. Establishing communication links among multiple users in a scalable and efficient way is important for realizing a large-scale quantum network. Here we develop an energy-time entanglement-based dense wavelength division multiplexed network based on an integrated silicon nitride micro-ring resonator, which offers a wide frequency span (covering at least the entire C-band) and narrow bandwidth modes (~ 650MHz). Six pairs of photons are selected to form a fully and simultaneously connected four-user quantum network. The observed quantum interference visibilities are well above the classical limits among all users. Each pair of users perform the BBM92 protocol for quantum key distribution. Our results pave the way for realizing large-scale quantum networks with integrated photonic architecture.

A Fast Tracking and Wide Swing CMOS Peak Detector for On-Chip Q-Factor Measurement

In this paper, a CMOS peak detector is proposed in order to satisfy the requirement of an on-chip time-domain quality factor (Q-factor) measurement. Unlike a conventional peak detector in which an Operational Trans-conductance Amplifier (OTA) is used as the core circuit, a high-speed comparator is deployed as the core circuit within the proposed peak detector. As a result, the proposed peak detector can offer a fast peak tracking with a high dynamic range and over a large voltage swing while still covering a wide frequency span with an excellent linearity and accuracy, which are key features required by on-chip Q-factor measurement. The proposed circuit was implemented in a CMOS 0.35μm technology under 5V. The experimental results have shown an output swing almost 4Vpp for an input signal amplitude ranging from 0.02V to 1.9V with a maximum signal dynamic ratio of 50 (Vmax/Vmin), an excellent linearity with a relative error <0.2%, a peak tracking accuracy less than 0.7% for 1MHz and a fast peak tracking with only one period delay in the worst case. The experimental results show that the operating frequency spans from 100 kHz to 5MHz and power consumption is around 9mW within this frequency range.

Recent Advances on Sub-Nyquist Sampling-Based Wideband Spectrum Sensing

Cognitive radio (CR) is a promising technology enabling efficient utilization of the spectrum resource for future wireless systems. As future CR networks are envisioned to operate over a wide frequency range, advanced wideband spectrum sensing (WBSS) capable of quickly and reliably detecting idle spectrum bands across a wide frequency span is essential. In this article, we provide an overview of recent advances on sub-Nyquist sampling-based WBSS techniques, including compressed sensing-based methods and compressive covariance sensing-based methods. An elaborate discussion of the pros and cons of each approach is presented, along with some challenging issues for future research. A comparative study suggests that the compressive covariance sensing-based approach offers a more competitive solution for reliable real-time WBSS.

A Widely Tunable Bandpass CMOS Filter Based on a Low-Voltage Active Inductor

A Chebyshev bandpass filter for digital TV (DTV) tuner ICs, as an RF tracking filter, based on a low-voltage tunable active inductor (TAI) is presented. The new filter has a tuning range of 200–800[Formula: see text]MHz. Independent tuning of the inductance and central frequency of the filter are very important in this wide frequency span. Adjusting the inductance for tuning of the filter should not vary its quality factor and consequently performance of the filter. Use of a feedback resistor in the active inductor makes the inductance and quality factor tuning-independent. Moreover, the feedback resistor increases the quality factor of the active inductor. Biasing the bulk terminals of the devices to a positive voltage, we achieve low threshold devices and consequently low voltage TAI. The proposed filter has IIP3 and noise figure of [Formula: see text]0.8 to 9.5[Formula: see text]dBm and 19.1 to 20.9[Formula: see text]dB, respectively. Besides, the power consumption varies from 9.6 to 25.5[Formula: see text]mW in the tuning range of 200–800[Formula: see text]MHz.

Thermal-Piezoresistive SOI-MEMS Oscillators Based on a Fully Differential Mechanically Coupled Resonator Array for Mass Sensing Applications

A mechanically coupled array technique to enable a fully differential operation of single-crystal silicon thermal-piezoresistive resonators (TPRs) has been demonstrated to alleviate resistive feedthrough issues often seen in TPRs, therefore, featuring clear resonance behavior with decent signal-to-feedthrough ratio. The proposed thermal-piezoresistive dual-II-BARs exhibits feedthrough reduction of more than 67 dB, and no spurious mode, is found within a wide frequency span. The resonator array together with board-level sustaining circuitry also works as a thermal-piezoresistive oscillator (TPO) and demonstrated its performances for real-time mass sensing. Finally, the proposed TPO mass sensor possesses several key features, including real-time monitoring, fast response time, and most importantly, excellent mass resolution of only 83 fg extracted from the measured TPO’s Allan deviation. [2017-0085]

Ultra wideband channel coefficient measurements for detecting methane gas in a multipath environment

In this paper, an investigation was carried out into the effect of a non-explosive methane gas mixture on various ultra wide band channel coefficients. Using simplified apparatus consisting of a rubberised tube (6 mm diameter) connected for significant periods to either a (pressurised) source of mixed methane and nitrogen or alternatively to a nitrogen only source. The tube containing either gas feed was wrapped using two complete turns around a 160 mm diameter PVC pipe. Several flows of the mixed gas, containing 2.57% methane, were introduced and flowed through the pipe before being sealed in the tube. Removal of any methane in the tube was achieved by flushing it with the pure nitrogen source, initially and in-between samples of the mixed source. A Vector Network Analyser was connected using two identical directional antennas with the wrapped section of tubing placed between the two antennas and the wireless channel coefficients were measured over the ultra wide band frequency span of 0.3–8 GHz. Magnitude differences were taken between the baseline condition (tube flushed out with nitrogen) and alternatively containing the methane mixture. It was found that consistent and repeatable experiments produced the same trend of differences over the same frequency span. This system based on this approach could thus be used as a simple sensor to detect the accumulation of methane gas in an environment well before it becomes explosive at around a concentration of 5%.

High Rejection, Self-Packaged Low-Pass Filter Using Multilayer Liquid Crystal Polymer Technology

A compact low-pass filter based on the principle of destructive interference is proposed and analyzed, followed by an improved design demonstrating very high rejection levels better than 40 dB over a wide frequency span. Both filters, fabricated using liquid crystal polymer (LCP) multilayer techniques, are self-packaged, with small footprint and profile, and also very lightweight. Simulation and measured results are presented, showing good agreement.

Process Variation Aware Wide Tuning Band Pass Filter for Steep Roll-Off High Rejection

A wide tuning band pass filter (BPF) with steep roll-off high rejection and low noise figure is presented. The design feature of steep roll-off high stopband rejection (>20 dB) and low noise figure (<6 dB) provides a wide tuning frequency span (1–2.04 GHz) to accept desirable signals and reject close interfering signals. The process variation aware design approach demonstrates robustness of the BPF after calibration from process variations, operating in 1.04 GHz tuning frequency span: almost zero deviation on center frequency, an average maximum deviation 1.16 dB on a nominal pass band gain of 55.6 dB, and an average maximum deviation 1.06 MHz on a nominal bandwidth of 12.3 MHz.

Large converse magnetoelectric effect in Metglas FeCoBSi and 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 laminated composite

Converse magnetoelectric (CME) effect is investigated in a FeCoBSi/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 laminated composite by using induction method within different frequencies. A large CME coefficient of 3.05 G/V is observed at the resonance frequency of 76.5 kHz under a low bias magnetic field of 50 Oe. The CME coefficient of the heterostructure is almost constant and exhibits a relatively high value in a wide frequency span of 1–64 kHz. The origin of large CME effect and the advantages of Metglas acting as ferromagnetic layer are discussed in the present paper.

FTS Opacity Measurements of the South Pole Submillimeter Sky

AbstractA sub-millimeter Fourier Transform Spectrometer (FTS) was used at the South Pole to acquire wide frequency span (300 GHz < v < 2 THz) measurements of the atmospheric opacity, T(V). Comparisons were made with other ongoing measurements to allow inference of typical wintertime observing statistics.

Generation of frequency-tunable light and frequency reference grids using diode lasers for one-petahertz optical frequency sweep generator

Generation of frequency-tunable light and frequency reference grids in a wide frequency span for a diode laser based optical frequency sweep generator has been performed. Frequency tuning and noise characteristics in nonlinear frequency conversions have been discussed. By using AlGaAs, InGaAsP lasers and their frequency conversions in the type II angle phase-matching KTP crystal, highly coherent frequency-tunable outputs have been obtained from 600 THz (0.5 /spl mu/m) to 170 THz (1.7 /spl mu/m). Use of the DFB lasers ensures the continuous tuning with a frequency range as wide as 1 THz. Atomic potassium and molecular iodine absorption resonances have been employed as frequency references for stabilizing the frequencies of lasers and the generated light with the frequency stability of 10/sup -9/-10/sup -10/. Optical frequency COMB94 generation has been realized at the 0.8 /spl mu/m wavelength with a two-sided sidebands span of 4 THz. We have also proposed and demonstrated specific frequency-tunable systems based on sum and difference-generations of diode lasers. >

Inversion of broad frequency band geomagnetic response data.

Electromagnetic response data for the Earth covering a wide frequency span are analysed using linearised inverse theory. The response measure adopted is the natural logarithm of the complex apparent resistivity. Model finding and interpretation takes place in plane geometry, a simple transformation converts the solutions to spherical geometry for global problems. Thus the methods will apply to local problems, where the combination of AMT and MT data provides several decades of frequency, and to global problems of which this paper is an example. The global data used here are drawn from four sources and cover more than 6 decades in frequency (3.5×10-9 to 8.7×10-3Hz).

Precordial-intracardiac phonocardiographic correlative study of ventricular septal defect.

Precordial and intracardiac phonocardiographic correlation was investigated in 28 cases with ventricular septal defect (VSD) to confirm the diagnostic value of intracardiac phonocardiography and to clarify the clinical as well as physiological significance of the point of maximum intensity (PMI) of the regurgitant systolic murmur of VSD. At the same time, the teleological use of catheterization was documented and the recent concept of the auscultatory was modified.(1) The regurgitant systolic murmur of VSD was localized within the right ventricle (RV) or partially transmitted toward the pulmonary artery (PA) and had the PMI somewhere in the RV. The murmur was pansystolic in timing and had a wide frequency span. A few exceptional cases were described, but the murmur of these cases became typical following the administration of methoxamine. The findings due to the associated anomalies were documented. The fact that the presence of regurgitant systolic murmur within the RV is the most sensitive diagnostic clue of VSD was confirmed.(2) The PMI of the regurgitant systolic murmur within the RV was so localized that it was easy to locate the site of the septal defect in almost all cases.(3) The localized PMI within the RV was the best site for the sampling of any measurements. The oxygen content was significantly high at this point when compared to those of randam sampling. This fact enables us to utilize teleologically the catheterization to detect the shunt. Methoxamine administration made the oxygenation of the sample conclusive in doubtful cases.(4) In a dorsoventral projection to the chest wall, intracardiac PMI of the regurgitant systolic murmur coincided with the precordial PMI in all cases. Therefore, the sampling at the site immediately beneath the precordial PMI was also recommended instead of the intracardiac PMI whenever the intracardiac phonocardiography was not available. Moreover, the site of septal defect could be anticipated in many cases with a reasonable accuracy based on this topographical correspondence of both PMIs.(5) The correspondence of the 2 (intracardiac and precordial) PMIs suggests that there is a direct transmission of the murmur from the origin to the chest wall. In this regard, the present authors made a minor modification to the revised auscultatory areas for the sake of the regurgitant systolic murmur of VSD and reserved a name of interventricular septal area to the precordial PMI.