Simple Bandpass Filter Research Articles

Fabrication of MOD-derived YBCO films on [001]LaAlO/sub 3/ and their application to λ/4 CPW SIR BPFs

Chemically derived epitaxial thin films of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) are fabricated on [001]LaAlO/sub 3/ substrates by the metalorganic-deposition (MOD) process, which has advantages of high quality, nonvacuum, low-cost, and large-scale production of high-T/sub c/ superconducting films. The MOD-derived YBCO films have a sharp transition at the critical temperature (90.4 K) and a high-quality film with a surface resistance of 0.13 m/spl Omega/ (30 K, 9.98 GHz) is obtained. As a microwave application, simple and compact bandpass filters (BPFs) using /spl lambda//4 coplanar-waveguide. stepped-impedance resonators are demonstrated on the YBCO films. A two-stage Chebyshev BPF of center frequency of 5.731 GHz, bandwidth of 135 MHz, and insertion loss of 0.29 dB with little input power dependency in a power range less than 10 dBm is realized on the film.

Motion and Ballistocardiogram Artifact Removal for Interleaved Recording of EEG and EPs during MRI

Artifactsgenerated by motion (e.g., ballistocardiac) of the head inside a high magnetic field corrupt recordings of EEG and EPs. This paper introduces a method for motion artifact cancellation. This method is based on adaptive filtering and takes advantage of piezoelectric motion sensor information to estimate the motion artifact noise. This filter estimates the mapping between motion sensor and EEG space, subtracting the motion-related noise from the raw EEG signal. Due to possible subject motion and changes in electrode impedance, a time-varying mapping of the motion versus EEG is required. We show that this filter is capable of removing both ballistocardiogram and gross motion artifacts, restoring EEG alpha waves (8–13 Hz), and visual evoked potentials (VEPs). This adaptive filter outperforms the simple band-pass filter for alpha detection because it is also capable of reducing noise within the frequency band of interest. In addition, this filter also removes the transient responses normally visible in the EEG window after echo planar image acquisition, observed during interleaved EEG/fMRI recordings. Our adaptive filter approach can be implemented in real-time to allow for continuous monitoring of EEG and fMRI during clinical and cognitive studies.

Dual-mode elliptic-function bandpass filter usingone single patchresonator without coupling gaps

A novel dual-mode, compact, and simple elliptic-function bandpass filter structure without coupling gaps is proposed. This filter has insertion loss < 1.5 dB and return loss > 10 dB within 2.3–2.375 GHz. Without coupling gaps between the feed lines and the patch resonator, the new filter can provide a low insertion loss and reduce uncertainty in fabrication.

On decomposing speech into modulated components

We model a segment of filtered speech signal as a product of elementary signals as opposed to a sum of sinusoidal signals. Using this model, one can better appreciate the basic relationships between envelopes and phases or instantaneous frequencies (IFs) of signals. These relationships reveal some interesting properties of the signal's modulations. For instance, if the contribution due to a signal's envelope, specifically the Hilbert transform of its log-envelope, is removed from the signal's phase, then the resulting signal's IF is strictly positive. In addition, filtered speech signal having a bandwidth of B Hz can be essentially represented by the log-envelope and IF that have the same B Hz bandwidths. We extend the above ideas to decompose speech into modulated components. Specifically, a bank of data-adaptive filters (in a cross-coupled configuration) are used to decompose speech into its components; each adaptive filter is a simple single resonance bandpass filter (whose center-frequency or pole-location closely follows the desired formant frequency) supplemented by an adaptive all-zero filter (whose zero-locations sufficiently reduce unwanted leakage from neighboring formants). The filtered components are then represented by their respective log-envelopes and positive IFs; these small number of modulations closely approximate the speech signal.

High‐frequency reflections in granite? Delineation of the weathering front in granodiorite at Piñon Flat, California

We analyze data from two orthogonal seismic lines 336 m in length collected at Piñon Flat, California, over weathered granodiorite bedrock. Each line was made up of 10 reversed segments 84 m in length. We analyzed the first arrivals from these data and found dramatic variations in velocity along the profiles. An upper layer (approximately 2-m thick) known from trenching to be composed of soil and sandy grus had measured velocities ranging from 400 to 700 m/s. Velocities inferred from refraction analysis of first arrivals of the reversed lines revealed a heterogeneous lower layer below the soil with measured velocities of 1600–2700 m/s by a depth of 15 m. We interpret these data to be measuring velocities of a deeply weathered unit characterized by granodiorite corestones embedded in a matrix of saprolite. The most remarkable feature of these data emerged from attempting to process the same data as reflection data. Simple bandpass filtering in the 250–400 Hz band revealed a bright, impulsive arrival with three characteristic properties: (1) irregular velocity moveout that is inconsistent with that expected from a layered earth model, (2) the arrival is at a nearly constant time‐depth on all data, and (3) the arrival tends to be followed by a ringing coda whose frequency varies from trace to trace. This arrival ties exactly with a velocity discontinuity measured in a borehole located on one of the profiles that we interpret as the base of the weathered layer. We suggest this arrival is a specular reflection from a weathering front that occurs along horizontal sheeting joints at a fixed depth below the surface. This surface acts as an effective mirror for high‐frequency seismic waves which are then channeled upward through an intact, high-Q path of unaltered blocks of granodiorite to define the observed signals at the surface.

Measuring gravitational waves from binary black hole coalescences. II. The waves’ information and its extraction, with and without templates

We discuss the extraction of information from detected binary black hole (BBH) coalescence gravitational waves by the ground-based interferometers LIGO and VIRGO, and by the space-based interferometer LISA. We focus on the merger phase that occurs after the gradual inspiral and before the ringdown. Our results are (i) if numerical relativity simulations have not produced template merger waveforms before BBH events are detected, one can study the merger waves using simple band-pass filters. For BBHs smaller than about ${40M}_{\ensuremath{\bigodot}}$ detected via their inspiral waves, the band-pass filtering signal-to-noise ratio indicates that the merger waves should typically be just barely visible in the noise for initial and advanced LIGO interferometers. (ii) We derive an optimized maximum-likelihood method for extracting a best-fit merger waveform from the noisy detector output; one ``perpendicularly projects'' this output onto a function space (specified using wavelets) that incorporates our (possibly sketchy) prior knowledge of the waveforms. An extension of the method allows one to extract the BBH's two independent waveforms from outputs of several interferometers. (iii) We propose a computational strategy for numerical relativists to pursue, if they successfully produce computer codes for generating merger waveforms, but if running the codes is too expensive to permit an extensive survey of the merger parameter space. In this case, for LIGO-VIRGO data analysis purposes, it would be advantageous to do a coarse survey of the parameter space aimed at exploring several qualitative issues and at determining the ranges of the several key parameters which we describe. (iv) A complete set of templates could be used to test the nonlinear dynamics of general relativity and to measure some of the binary's parameters via matched filtering. We estimate the number of bits of information obtainable from the merger waves (about 10--60 for LIGO-VIRGO, up to 200 for LISA), estimate the information loss due to template numerical errors or sparseness in the template grid, and infer approximate requirements on template accuracy and spacing.

An automated microwave measurements experience for undergraduates

Experiments in microwave measurements for an undergraduate laboratory course are described that bridge the gap between point-by-point manual measurements and automatic network analyzer measurements. In the sequence of 10 laboratory experiments, the basic parameters of frequency versus wavelength in a waveguide are explored, first in point-by-point measurements versus frequency. Swept frequency measurements are taken up next in the form of an open-ended design experiment investigating a simple two-pole band pass filter. Following this, scalar transmission and reflection measurements are made using a PC as a controller and data-acquisition unit. Lastly, the Hewlett-Packard 8510B Automatic Network Analyzer is used by the students to perform the measurements on the same device as a verification of the earlier results. This paper concentrates on the design of the computer-aided measurements experiment, describing the requirements for the experimental content as well as the peripheral content, such as the controller language (HP BASIC) and the interface (HPIB-HP Interface Bus). >

A note on pulse distortion by ionospheric reflection

An expression, suitable for a small desk-top computer, is presented to calculate the time domain envelope of a rectangular pulse reflected from a sech <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> model ionosphere and observed at the output of a simple receiver bandpass filter. Ionospheric, source pulse, and filter parameters can be varied to estimate distortion characteristics of the received pulse.

Temperature compensated, high permittivity dielectric resonators for millimeter wave systems

The properties of selected low loss, temperature compensated high permittivity microwave and millimetre wave dielectrics are summarised and experimental convenience suggests that planar hybrid microstrip is the preferred circuit technology for the initial studies of dielectric resonators at the millimetre wavelengths. Data are presented for temperature stabilised oscillators and some simple band pass filters are discussed.

A Study of the Filter Properties of Single and Parallel-Coupled Dielectric-Waveguide Gratings

Our work with gratings in dielectric image guide shows that it is distinctly advantageous to place the grating notches on the sides of the guide, or on the top of the guide, depending on the mode used. Means are discussed for modeling gratings using an equal-line-length transmission-line equivalent circuit. Excellent agreement between computed and measured bandstop frequency responses of gratings are obtained. Design relations for gratings are presented, and equations for analysis and design of parallel-coupled grating structures are derived. It is shown that a simple bandpass filter can be made from properly designed parallel-coupled gratings with distributed loads at one end. It is also shown that by use of combinations of parallel-coupled and direct-coupled gratings, multiresonator filters with Chebyshev or other characteristics can be obtained. Experimental results in agreement with computed responses are demonstrated.

Preprocessing of electrocardiograms by digital techniques

A simple but powerful digital band-pass filter is proposed for the preprocessing of ECG signals. It consists of two parallel triangular filters implemented recursively. The application of this filter to noisy ECG signals shows that baseline variations are removed, the powerline component and its higher harmonics are suppressed quite successfully and artefacts are considerably attenuated. This filtering is necessary as preprocessing when extracting features for automated classification of arrythmia.

Equivalent circuits for high-frequency sonar transducers

The equivalent circuits for high-frequency transducers with quarter-wave matching layers, such as are used in sonar and ultrasonic applications, are discussed in terms of simple lumped bandpass filter circuits. Expressions for the matching criteria are given for half-section and full-section filters.

Active inductances using current conveyors and their application in a simple bandpass filter realisation

An active grounded inductance using a single second generation current conveyor (CC II) as the active element and three passive components is proposed. The inductance is seen to be suitable for moderate-Q applications. For high-Q with independent Q-controlled inductances suitable circuit techniques pertaining to the introduction of a second CC II as a voltage follower are also presented.

A new high-Qactive band-pass filter with low-gain stages

The paper describes a simple high-Q insensitive active band-pass filter having relatively few passive components and active elements with low closed-loop gains, using positive feedback Q enhancement scheme. The proposed filter has minimum dependence on the bandwidth of the operational amplifiers and is capable of operating over a wide frequency range with relatively stable Q and resonant frequency.

A simple hybrid thick-film band pass filter : D. P. Heywood. IERE Conf. Hybrid Microelectronics, Loughborough p. 43. 9–11 Sept. 1975

A simple hybrid thick-film band pass filter : D. P. Heywood. IERE Conf. Hybrid Microelectronics, Loughborough p. 43. 9–11 Sept. 1975

A Bandpass Filter System for Far-Infrared Radiation Measurements

A simple bandpass filter system that is suitable to resolve the radiation emitted by far-infrared (4–0.1 mm wavelength) source that has a relatively flat emission spectrum is described. This system, which has a resolving power of 2, an insertion loss of 3 dB, and an acceptance angle of 7°, was used in conjunction with a cooled InSb detector to measure the temperature vs wavelength characteristics of a mercury arc lamp from 4 to 0.3 mm.

Proposed Ultraviolet Bandpass Filters

The ultraviolet transmission characteristics of selected alkali alloys are presented, and a scheme for constructing simple ultraviolet bandpass filters is described.

Atomic Absorption Studies with a Bandpass Filter

Atomic absorption studies were performed with a simple bandpass filter. Results of these studies for lithium indicated that the sensitivity and detectability obtained were comparable to existing atomic absorption techniques that employ a monochromator to isolate a waveband. The main advantages of using a bandpass filter in place of a monochromator are the relatively low cost of the filter and the ease of operation.