Use Of Notch Filters Research Articles

Sub-THz Raman response and soft phonon in tetragonal BaTiO3

ABSTRACT The sub-THz polarized Raman response was measured along the [100] direction in the tetragonal BaTiO3 single crystal. The soft phonon was detected as a resonance peak for the first time by Raman spectroscopy, thanks to the use of notch filters that suppressed elastic scattering. No relaxation peak was observed and we demonstrated that, contrary to the situation along the ferroelectric c-axis, the soft phonon is sufficient to describe the dielectric response of BaTiO3 along the a-axis, except in close vicinity of the tetragonal-cubic phase transition.

Analysis and Suppression of the Suspended Rotor Displacement Fluctuation Influence for Motor System

Suspended rotor displacement fluctuation would result in unbalanced magnetic pull and inaccurate speed measurement, which degrades the suspended rotor stability and motor performance. In order to reduce the blight, some research studies have been conducted. First, the influence on the motor magnetic field has been analyzed between motors with iron-cored and coreless stator structures. It is found that with the coreless stator, the air-gap magnetic flux density variation can be neglected. Second, the law of the speed fluctuation caused by the rotor runout has been studied. In addition, two methods, which are based on the use of notch filter and speed correction, have been proposed for suppressing the fluctuation. Third, the performances of the closed-loop systems with the proposed speed fluctuation suppression methods have been analyzed. Finally, experimental results are presented to demonstrate the correctness of the analysis and the validity of the proposed methods.

Esquemas de ordenamiento en sistemas celulares sobrepuestos CDMA

The CDMA overlay concept, has been proposed as one alternative to take advantage of the band width available in narrowband systems. In fact, the basic idea of the CDMA overlay is to allow to wideband CDMA wave forms, to share a common spectrum with narrowband conventional wave forms. In this work, we have focused in the analysis of the performance of the forward link of the CDMA and TDMA systems when they are over laid. In our model, in order to limit the interference into the CDMA layer caused by the TDMA system, the use of notch filters has been considered. However, one draw back of the filters is that it rejects only one part of the interference generated by the TDMA system. Therefore, we have proposed two new ideas of reduction of the interference which can not be eliminated by filters; ordered hunt and real location of the slots. Finally, we present an analytical evaluation of the forward link capacity of the systems involved in the over laid process, due to this is the limiting link and as a function of the outage probabilities. Practical considerations such as power requirements, power control, handoff, the offered load for different services and scenarios are also addressed.

High performance Raman spectroscopy with simple optical components

Several simple experimental setups for the observation of Raman scattering in liquids and gases are described. Typically these setups do not involve more than a small (portable) CCD-based spectrometer (without scanning), two lenses, and a portable laser. A few extensions include an inexpensive beam-splitter and a color filter. We avoid the use of notch filters in all of the setups. These systems represent some of the simplest but state-of-the-art Raman spectrometers for teaching/demonstration purposes and produce high quality data in a variety of situations; some of them traditionally considered challenging (for example, the simultaneous detection of Stokes/anti-Stokes spectra or Raman scattering from gases). We show examples of data obtained with these setups and highlight their value for understanding Raman spectroscopy. We also provide an intuitive and nonmathematical introduction to Raman spectroscopy to motivate the experimental findings.

CONTROLLING CHAOS IN A CHUA'S CIRCUIT USING NOTCH FILTERS

This paper explores the use of notch filters for the purpose of damping out chaotic oscillations. The design of the filter and the way it is interfaced to the system are investigated from a signal-processing point of view. A Chua's circuit, that has typical applications in synchronization and secure communications, is used to exemplify the suggested methodology where both theoretical and experimental results are provided. The power spectrum of the original system is analyzed to selectively damp-out portions of the power spectrum, thus truncating period-doubling, the original cause of chaos. Both single and double notch filters are explored to examine their effect on the performance of the modified system. Steady state analysis as well as issues regarding practical implementation are addressed and advantages and limitations of the proposed method are highlighted.

Auroral Contribution to Sky Brightness for Optical Astronomy on the Antarctic Plateau

AbstractThe Antarctic Plateau holds great promise for optical astronomy. One relatively unstudied feature of the polar night sky for optical astronomical observing is the potential contamination of observations by aurorae. In this study we analyse auroral measurements at South Pole Station and show that during an average winter season, the auroral contribution to the B band sky brightness is below 21.9 B mag arcsec−2 for 50% of the observing time. In V band, the median sky brightness contribution is 20.8 mag arcsec−2 during an average winter. South Pole Station is situated within the auroral zone and experiences strong and frequent auroral activity. The Antarctic locations of Dome C and Dome A are closer to the geomagnetic pole where auroral activity is greatly reduced compared with that of South Pole Station. Calculations based on satellite measurements of electron flux above the Antarctic Plateau are used to show that at Dome C, the contribution to sky background in the B and V bands is up to 3.1 mag less than that at the South Pole. The use of notch filters to reduce the contribution from the strongest auroral emission lines and bands is also discussed. The scientific potential of an extremely large telescope located at Dome C is discussed, with reference to the effect that auroral emissions would have on particular astronomical observations.

Resonant transmission of a chirped soliton in a long optical fiber with periodic amplification

Using narrow solitons is a natural way to increase the data-transmission rate in soliton-based optical communications lines. However, in the present work it is demonstrated that it does not make sense to employ ultrashort solitons whose dispersion lengths Z0 are much smaller than the amplification spacing Za: In this case, the interaction between the solitons gives rise to stable bound states in which the temporal separation between the solitons only increases with a decrease of the soliton width. This is the reason why, when Z0 and Za are close, the case is potentially the most promising. Also in this case, however, resonance effects are possible. In the present work, resonance excitation of the internal vibrations of a fundamental soliton by the periodic amplification is considered analytically. Both the fundamental and the second resonances are analyzed in detail by means of a variational approximation. The most salient feature of the resonant propagation of the soliton is that it is bistable. Interaction between vibrating solitons is also considered, and it is shown that this interaction can be suppressed by vibrations with fairly small amplitudes, preventing formation of bound states. These resonant features are beneficial for use in communication lines. Emission of radiation by the vibrating soliton, which is a detrimental effect, is considered too, and it is demonstrated that it can be suppressed in two different ways: by the straightforward use of notch filters, or, in a smarter way, by the vibrations being switched into a range in which the first vibrational harmonic does not radiate.

Digital hum filtering

Data may be overprinted by a steady-state cyclical noise (hum). Steady-state indicates that the noise is invariant with time; its attributes, frequency, amplitude, and phase, do not change with time. Hum recorded on seismic data usually is powerline noise and associated higher harmonics; leakage from full-waveform rectified cathodic protection devices that contain the odd higher harmonics of powerline frequencies; or vibrational noise from mechanical devices. The fundamental frequency of powerline hum may be removed during data acquisition with the use of notch filters. Unfortunately, notch filters do not discriminate signal and noise, attenuating both. They also distort adjacent frequencies by phase shifting. Finally, they attenuate only the fundamental mode of the powerline noise; higher harmonics and frequencies other than that of powerlines are not removed. Digital notch filters, applied during processing, have many of the same problems as analog filters applied in the field. The method described here removes hum of a particular frequency. Hum attributes are measured by discrete Fourier analysis, and the hum is canceled from the data by subtraction. Errors are slight and the result of the presence of (random) noise in the window or asynchrony of the hum and data sampling. Error is minimized by increasing window size or by resampling to a finer interval. Errors affect the degree of hum attenuation, not the signal. The residual is steady-state hum of the same frequency.