Small Frequency Band Research Articles

Towards full-resolution inline electron holography

With the availability of fast computers, inline electron holography, a technique for reconstructing both amplitude and phase of the electron wave function as scattered by the sample from a set of differently aberrated transmission electron microscopy images, is becoming increasingly quantitative. While focal series reconstruction from transmission electron microscopy images has already been practiced for at least 3 decades, existing approaches can only recover a relatively small band of spatial frequencies. Here I present a reconstruction scheme which is capable of reconstructing the electron wave function for a very large range of spatial frequencies, demonstrating its performance using simulated as well as experimental data.

The Dividing Frequency Bands Prediction Method Based on Bornitz Model for Train-Induced Environmental Vibration and its Application

The frequency component of ground vibration induced by train is complex. The propagating attenuation characteristics of ground vibration are dependent on frequency. A new prediction method based on Bornitz model for predicting the train-induced ground vibration is presented in this paper. This approach divides the frequency component into many small frequency bands according to one-third-octave. Then it predicts the vibration acceleration level VAL of each frequency bands based on Bornitz model respectively. Finally, the predicted value of Z-vibration level VLZis computed by the predicted value of VAL and the corresponding frequency-weighting value C. The traininduced ground vibration was measured and predicted in Chengdu-Dujiangyan railway. The results of comparing the predicted value of VLZ with the measured value show that the prediction value of VLZ is 3.8dB less than the measured value in the prediction point of 25m away from the railway, where the vibration strength occur rebound. In other five prediction points the ground vibration predicted value are 1.3~3.1dB more than measured value. This study shows that using the prediction method presented in this paper for predicting train-induced ground vibration has good accuracy on the whole.

Bounding the Polynomial Approximation Errors of Frequency Response Functions

Frequency response function (FRF) measurements take a central place in the instrumentation and measurement field because many measurement problems boil down to the characterization of a linear dynamic behavior. The major problems to be faced are leakage and noise errors. The local polynomial method (LPM) was recently presented as a superior method to reduce the leakage errors with several orders of magnitude while the noise sensitivity remained the same as that of the classical windowing methods. The kernel idea of the LPM is a local polynomial approximation of the FRF and the leakage errors in a small-frequency band around the frequency where the FRF is estimated. Polynomial approximation of FRFs is also present in other measurement and design problems. For that reason, it is important to have a good understanding of the factors that influence the polynomial approximation errors. This article presents a full analysis of this problem and delivers a rule of thumb that can be easily applied in practice to deliver an upper bound on the approximation error of FRFs. It is shown that the approximation error for lowly damped systems is bounded by ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LPM</sub> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3dB</sub> ) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R + 2</sup> with <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LPM</sub> the local bandwidth of the LPM, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> the degree of the local polynomial that is selected to be even (user choices), and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dB</i> the 3 dB bandwidth of the resonance, which is a system property.

Elastic properties of nanocrystalline aluminum substituted nickel ferrites prepared by co-precipitation method

NiAlxFe2−xO4 (x=0.0–1.0 in the step of 0.2) spinel ferrite system was prepared by the co-precipitation method. The elemental compositional stoichiometry, microstructure, infrared spectral and elastic properties have been carried out by means of energy dispersive analysis of X-ray (EDAX), scanning electron microscopy (SEM) and infrared spectroscopic (IR) measurements. Infrared spectra were carried out at room temperature in the wavenumber range of 300–800cm−1. The IR spectra show three major absorption bands. High frequency bands ‘ν1’ is assigned to the tetrahedral and low frequency bands ‘ν2’ is assigned to the octahedral complex. Small frequency bands ‘ν3’ is assigned to Al3+O−2 complexes. Force constant for the tetrahedral and octahedral site was determined by using IR data. Force constant used to calculate the stiffness constants (C11 and C12). Using the values of stiffness constants; elastic moduli such as Young’s modulus, bulk modulus, modulus of rigidity, Poisson ratio and Debye temperature were calculated.

Different Zoom Approaches for Improving Spectral Resolution with Applications in Radar Signal Processing

Different approaches for a high-resolution analysis of narrow-band spectra are reviewed and compared. Partial-band algorithms are proved to be zoom-FFT's. In this contribution, three new modifications of the (Subband-FFT) SB-FFT are presented. In the first modification the chirp z-transform substitutes the small FFT which calculates the band of interest. In the second modification, the idea of zero-padding the input signal is applied to the SB-FFT with pruning at both input and output. Lastly zooming a small band of frequencies using a method of transforming by parts is applied for a narrow-band signal using the adaptive SB-FFT. A newly introduced version of the subband technique is included also in this work. In this version the subband decomposition technique is combined with the linear prediction method for higher spectrum resolution. Application of the SB-FFT and its modified versions and the new version in measuring the Doppler-frequency directly and indirectly for the purpose of vehicle-speed measurements is introduced in this paper. Comparison between all methods in terms of complexity and resolution is given. A new idea of channel test is included to keep the real-time successive measurements of Doppler frequency stable and consistent as well as simple.

ON SMALL-SIGNAL AMPLIFICATION IN A GYRO-TWT

The corrected dispersion relation governing the linear interaction of a TE mode in a circular cylindrical wave guide with an annular beam of gyrating electrons in a gyro-TWT conflguration is derived. The derivation of the correct dispersion relation no longer involves any integration with respect to the radial coordinate ro of the electron guiding center as the relevant equilibrium distribution function turns out to be independent of ro. When the cyclotron resonance condition is satisfled by the TE mode for a positive s-number, the small-signal theory is shown to predict an initial exponential growth of the mode with interaction length over a small but flnite band of frequencies around the design frequency.

Performance evaluation of fault-branch detection in TDM passive optical networks by spectral analysis of interferometric signals

A new fault-branch detection scheme is proposed to troubleshoot the breaks of any distribution fibers in a time-division multiplexing (TDM) passive optical network. We employ a continuous optical frequency sweeper at the optical line terminal (OLT) and an interferometric (IF) device at each optical network unit (ONU). By analyzing the spectrum of the returned combined signals at the OLT, we can obtain the status of all branches. This detection method not only uses a small optical frequency band for surveillance monitoring, but is also simple to operate. Furthermore, a modified architecture is proposed to relax the specifications of IF devices. The tolerance of the IF device length was analyzed using the Monte---Carlo simulation method.

The intermuscular 3–7 Hz drive is not affected by distal proprioceptive input in myoclonus-dystonia

In dystonia, both sensory malfunctioning and an abnormal intermuscular low-frequency drive of 3–7 Hz have been found, although cause and effect are unknown. It is hypothesized that sensory processing is primarily disturbed and induces this drive. Accordingly, experimenter-controlled sensory input should be able to influence the frequency of the drive. In six genetically confirmed myoclonus-dystonia (MD) patients and six matched controls, the low-frequency drive was studied with intermuscular coherence analysis. External perturbations were applied mechanically to the wrist joint in small frequency bands (0–4, 4–8 and 8–12 Hz; ‘angle protocol) and at single frequencies (1, 5, 7 and 9 Hz; ‘torque’ protocol). The low-frequency drive was found in the neck muscles of 4 MD patients. In these patients, its frequency did not shift due to the perturbation. In the torque protocol, the externally applied frequencies could be detected in all controls and in the two patients without the common drive. The common low-frequency drive was not be affected by external perturbations in MD patients. Furthermore, the torque protocol did not induce intermuscular coherences at the applied frequencies in these patients, as was the case in healthy controls and in patients without the drive. This suggests that the dystonic 3–7 Hz drive is caused by a sensory-independent motor drive and sensory malfunctioning in MD might rather be a consequence than a cause of dystonia.

Structural health monitoring in changing operational conditions using tranmissibility measurements

This article uses frequency domain transmissibility functions for detecting and locating damage in operational con- ditions. In recent articles numerical and experimental examples were presented and the possibility to use the transmissibility concept for damage detection seemed quite promising. In the work discussed so far, it was assumed that the operational conditions were constant, the structure was excited by a single input in a fixed location. Transmissibility functions, defined as a simple ratio between two measured responses, do depend on the amplitudes or locations of the operational forces. The current techniques fail in the case of changing operational conditions. A suitable operational damage detection method should however be able to detect damage in a very early stage even in the case of changing operational conditions. It will be demonstrated in this paper that, by using only a small frequency band around the resonance frequencies of the structure, the existing methods can still be used in a more robust way. The idea is based on the specific property that the transmissibility functions become independent of the loading condition in the system poles. A numerical and experimental validation will be given.

Structural Health Monitoring in Changing Operational Conditions Using Tranmissibility Measurements

This article uses frequency domain transmissibility functions for detecting and locating damage in operational conditions. In recent articles numerical and experimental examples were presented and the possibility to use the transmissibility concept for damage detection seemed quite promising. In the work discussed so far, it was assumed that the operational conditions were constant, the structure was excited by a single input in a fixed location. Transmissibility functions, defined as a simple ratio between two measured responses, do depend on the amplitudes or locations of the operational forces. The current techniques fail in the case of changing operational conditions. A suitable operational damage detection method should however be able to detect damage in a very early stage even in the case of changing operational conditions. It will be demonstrated in this paper that, by using only a small frequency band around the resonance frequencies of the structure, the existing methods can still be used in a more robust way. The idea is based on the specific property that the transmissibility functions become independent of the loading condition in the system poles. A numerical and experimental validation will be given.

Wideband, Bandpass, and Versatile Hybrid Filter Bank A/D Conversion for Software Radio

This paper deals with analog-to-digital (A/D) conversion for future software/cognitive radio systems. For these applications, A/D converters should convert wideband signals and offer high resolutions. In order to achieve this and to overcome technological limitations, the A/D conversion systems should be versatile, i.e., it should be possible to adapt the conversion characteristics (resolution and bandwidth) by software. This work studies and adapts hybrid filter banks (HFBs) in this context. First, HFBs, which can provide a large conversion bandwidth, are extended to bandpass sampling, thus minimizing the sampling frequency. Then, we provide efficient ways of improving the HFB resolution in a smaller frequency band, only by reprogramming the digital part. Moreover, this paper takes into account the main drawback of HFBs which is their very high sensitivity to analog imperfections. Simulation results are presented to demonstrate the performance of HFBs.

One Tooth, Two Tooth, Green Tooth, Bluetooth, Part I

One Tooth, Two Tooth, Green Tooth, Bluetooth, Part I

Electromagnetically induced negative refraction in an atomic system with spontaneously generated coherence

We propose a new scheme for realizing left-handed electromagnetic properties in a coherently driven four-level system. At the presence of spontaneously generated coherence and the local field effect, both dielectric permittivity and magnetic permeability may have negative real parts of the same order in a small frequency band. Thus, one can achieve the negative refractive index and then manipulate it by modulating the coherent field or changing the atomic density. With incoherent pumping applied to have more remarkable spontaneously generated coherence, one can further obtain a wider frequency band of negative refraction and simultaneously reduce the accompanied absorption.

Cochlear Nerve Stimulation With Optical Radiation

Problem Neural prosthetic devices are artificial extensions to the body that restore or supplement nervous system function that was lost during disease or injury. The devices stimulate remaining neural tissue with electric current, providing some input to the nervous system. Hereby, the challenge for neural prostheses is to stimulate remaining neurons selectively. However, electrical current spread does not easily allow stimulation of small neuron populations. In neural prostheses developments, particular success has been realized in the cochlear prostheses development. The devices bypass damaged hair cells in the auditory system by direct electrical stimulation of the auditory nerve. Stimulating discrete spiral ganglion cell populations in cochlear implant users’ ears is similar to the encoding of small acoustic frequency bands in a normal-hearing person's ear. In contemporary cochlear implants, however, the injected electric current is spread widely along the scala tympani and across turns. Consequently, stimulation of spatially discrete spiral ganglion cell populations is difficult. Methods Spiral ganglion cells in guinea pigs were stimulated with laser pulses from an Aculight Capella infrared laser. Results With our experiments we demonstrate that extreme spatially selective stimulation is possible using light. Conclusion Our long-term goal is to develop and build an optical cochlear implant prosthesis to stimulate small populations of spiral ganglion cells. Significance Our long-term goal is to develop and build an optical cochlear implant prosthesis to stimulate small populations of spiral ganglion cells. Support This project has been funded with federal funds from the National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Department of Health and Human Services, under Contract No. HHSN260-2006-00006-C / NIH No. N01-DC-6-0.

Tissue resistivities determine the current flow in the cochlea

In individuals with severe to profound hearing loss, cochlear implants bypass normal inner ear function by applying electrical current directly into the cochlea, thereby stimulating cochlear nerve fibers. Stimulating discrete populations of spiral ganglion cells in cochlear implant users' ears is similar to the encoding of small acoustic frequency bands in a normal-hearing person's ear. Thus, spiral ganglion cells stimulated by an electrode convey the information contained by a small acoustic frequency band. Problems that refer to the current spread and subsequent nonselective stimulation of spiral ganglion cells in the cochlea are reviewed. Cochlear anatomy and tissue properties determine the current path in the cochlea. Current spreads largely via scala tympani and across turns. While most of the current leaves the cochlea via the modiolus, the facial canal and the round window constitute additional natural escape paths for the current from the cochlea. Moreover, degenerative processes change tissue resistivities and thus may affect current spread in the cochlea. Electrode design and coding strategies may result in more spatial stimulation of spiral ganglion cells, resulting in a better performance of the electrode-tissue interface.

Non-resonant vibration conversion

The development of distributed wireless sensor systems for automotive, medical or industrial monitoring applications is one of the aims for MEMS technology. For applications where environmental vibrations are present, the harvesting of this kinetic energy is an opportunity to power remote sensor nodes. For the conversion, typically resonant spring–mass–damper systems are considered. In this paper, a novel non-resonant conversion mechanism is presented. Depending on the geometry of the harvester and the vibration, this conversion mechanism shows a few advantages: low frequencies can be converted, higher or lower modes of vibration will be converted instantaneously, the transducer has 2 DOF for energy conversion and the generation of energy is not limited to a small frequency band. Based on a vibration amplitude of 100 µm, the behavior of a fine-mechanical generator and a MEMS generator has been simulated. The results of the fine-mechanical generator were verified by measurements of a prototype with 1.5 cm3 volume. So far the transducer is capable of producing 0.4–3 mW for vibration frequencies ranging from 30 to 80 Hz.

Photonic crystals slow light for better sensing

Photonic-crystal (PC) structures offer an important platform for optofluidic devices, photonic circuits, and dispersionengineered metamaterials. These devices promise lab-on-a-chip capabilities with considerable flexibility for managing light. They are also likely to reduce the cost of integrated optical circuits and devices. PC circuits have primarily been defined by their periodicity and the architecture of the holes or columns fabricated in the transparent material. This has encouraged the development of stamping and printing technologies that can produce prototypes quickly and make large quantities of sensors inexpensively. In addition to being manufacturable, PC platforms have two attractive attributes for sensing applications. First, a gas or liquid analyte can flow directly through the nanoscopic holes within the photonic structure. Second, ’slow light’ can boost the device’s sensitivity. Optical sensors that exploit spectroscopic analysis—such as surface-enhanced Raman phenomena—are already theoretically capable of molecular sensitivity: PC sensors using slow light could increase even this sensitivity. Because controlling the speed of light has a host of important applications, engineers have learned to manage the dispersion characteristics of a material to control it or, more specifically, to control the group velocity of light. In an isotropic linear medium, the velocity of light is the same in all directions and is defined by the angular frequency (ω) divided by the wavenumber (k). The plot of ω versus k provides the phase velocity of the light. An optical pulse—which one can consider as the envelope or constructive interference arising from a number of frequencies— has a group velocity that is the derivative of ω with respect to k. If this derivative is zero, then at that frequency and for the small band of frequencies in its neighborhood, a pulse has a group velocity that is close to zero. This interests us because slow-light pulse propagation can enhance the energy density of the electromagnetic field within Figure 1. A carefully designed periodic stack with sub-wavelength features can slow certain wavelengths to a crawl and increase the resonant field intensity. The form-birefringent structure in the photo is made of Fullcure 720, a UV-cured material with a refractive index of 1.9 at 8GHz.

Frequency-domain method based on the singular value decomposition for frequency-selective NMR spectroscopy

In several applications of NMR spectroscopy the user is interested only in the components lying in a small frequency band of the spectrum. A frequency selective analysis deals precisely with this kind of NMR spectroscopy: parameter estimation of only those spectroscopic components that lie in a preselected frequency band of the NMR data spectrum, with as little interference as possible from the out-of-band components and in a computationally efficient way. In this paper we introduce a frequency-domain singular value decomposition (SVD)-based method for frequency selective spectroscopy that is computationally simple, statistically accurate, and which has a firm theoretical basis. To illustrate the good performance of the proposed method we present a number of numerical examples for both simulated and in vitro NMR data.

Left-handed metamaterial and its experimental verifications

The artificial metamaterial simultaneously possessing negative permittivity and permeability has many fantastic properties, and has attracted a lot of attention in the field of physics and electromagnetism. In this paper, we fabricated this kind metamaterial and performed refraction and beam shifting experiments using triangular-shaped and parallelogram-shaped sample respectively. The experimental results demonstrate that, the metamaterial we fabricated may have negative permittivity and permeability simultaneously in a specific small frequency band.

The Coding of Spatial Location by Single Units in the Lateral Superior Olive of the Cat. II. The Determinants of Spatial Receptive Fields in Azimuth

The lateral superior olive (LSO) is one of the most peripheral nuclei in the auditory pathway to receive inputs from both ears, and its cells are sensitive to interaural level disparities (ILDs) when stimulated by sounds presented over earphones. It has, accordingly, long been hypothesized that the functional role of the LSO is to encode a correlate of ILDs, one of the acoustical cues to the spatial location of sound. In the companion paper, we used the virtual space (VS) technique to present over earphones stimuli containing all the acoustical cues to the location of broadband stimuli and measured the spatial receptive fields (SRFs) in azimuth of single LSO cells. The shapes of the SRFs were generally consistent with the ILD sensitivity of the cells (Tollin and Yin, 2002), but because the only variable under our control was azimuth, and not ILD directly, the precise cues responsible for the SRFs could not be unambiguously determined. Here, we test more directly the hypothesis that ILDs are the primary determinants of the SRFs in azimuth of LSO cells by digitally manipulating the head-related transfer functions used to create the VS stimuli by independently varying (or holding constant) in azimuth each of the primary localization cues in isolation while holding constant (or varying) the others. Our results support the classical view of the LSO that the form of the SRFs of the cells in azimuth is determined primarily by the ILDs in a small band of frequencies around the characteristic frequencies of the cells.