Background Vibration Research Articles

Microcontrolled pyro-electric instrument for measuring X-ray intensity in mammography

A novel instrument for measurement of X-ray intensity from mammography consists of a sensitive pyro-electric detector, a high-sensitivity, low-noise current-to-voltage converter, a microcontroller and a digital display. The heart of this device, and what makes it unique is the pyro-electric detector, which measures radiation by converting heat from absorbed incident X-rays into an electric current. This current is then converted to a voltage and digitised. The detector consists of a ferro-electric crystal; two types were tested: lithium tantalate and lithium niobate. X-ray measurement in mammography is challenging because of its relatively low photon energy range, from 11 keV to 15 keV equivalent mean energy, corresponding to a peak tube potential from 22 to 36 kV. Consequently, energy fluence rate or intensity is low compared with that of common diagnostic X-ray. The instrument is capable of measuring intensities as low as 0.25 mW m(-2) with precision greater than 99%. Not only was the instrument capable of performing in the clinical environment, with high background electromagnetic interference and vibration, but its performance was not degraded after being subjected to 140 roentgen (3.6 x 10(-2) C kg(-2) air) as measured by piezo-electric (d33) or pyro-electric coefficients.

Selection of wavelet packet basis for rotating machinery fault diagnosis

Wavelet packets provide a library of orthonormal bases and can therefore represent a signal in many different ways. This paper presents a method to select the orthonormal basis to represent vibration signals for rotating machinery fault diagnosis. The selected basis is formed by two sets of basis functions for representation of the transients excited by localized faults and other signal components of interest, respectively. This method overcomes the limitation of the widely used Coifman and Wickerhauser's best basis algorithm in detection of transients hidden in large background vibration and is more effective in rotating machinery fault diagnosis especially in the early stage of fault development. In addition, differing from some existing studies, this method does not need training samples and is relatively easy to implement in practice. Applications in the analysis of gearbox and bearing vibration signals show that the proposed method performs better than the best basis algorithm.

Development of thrust stand for low impulse measurement from microthrusters

A thrust stand has been developed to accurately measure thrust produced by two types of microthrusters—a liquid propellant pulsed plasma thruster (LP-PPT) and a diode laser ablation microthruster. The impulse of LP-PPT ranged from 20 to 80 μNs. The diode laser microthruster, which is a new type of microthruster, produces much lower impulse range of 1–10 μNs for about 1 s. The mechanical noise induced from the background vibrations becomes a crucial problem for precise estimate of thrust particularly in low impulse measurements. A data analysis method to reduce the effect of mechanical noise is proposed by introducing an additional term in a fitting function. It was verified that the analysis method used in our experimental conditions reduced variance caused by noise down to one-third that of a normal fitting method. The accuracy of the thrust stand is 2.1 μNs in the case of the LP-PPT and 0.7 μNs in the case of the diode laser microthruster.

Application of the acousto-optic effect to pressure measurements in ultrasound fields in water using a laser vibrometer

A non-intrusive measuring technique, applied to sensing and measuring acoustic waves at ultrasonic frequencies is considered. The method is optically based and so does not interfere with the ultrasound field. The measurement procedure relies on the acousto-optic effect, that is the change in refractive index which occurs with changing pressure in the ultrasound field. This change in refractive index is detected through the change in the path length of a laser beam propagating through the region of interest. Typically these changes are small corresponding to a physical change of the order of 10−6 m. Fourier analysis is used to separate the component of the signal corresponding to the pressure variation from background noise and vibrations which can be dominant. Application of the technique is illustrated for an underwater ultrasound transducer. Measurements are made using the optical technique and compared to measurements taken with a hydrophone. The effectiveness of the optical measuring technique is discussed. It is shown that the laser vibrometer produces a good estimation of the mean beam pressure provided an estimation of the beam width is available, a restriction which is often satisfied; and the acoustic field can be assumed to be approximately constant across the beam.

Surface following scanning in a scanning microwave microscope

In this Note we provide the basic principle of obtaining topological data with a scanning microwave microscope. When samples are sufficiently “metallic,” the resonant frequencies as a function of the gap between the sample surface and the tip all fall on a universal curve despite differences in sheet resistance. Based on this result, we have built a surface-following feedback circuit and succeeded in measuring the topological images of many metallic surfaces. To date, the best topological resolution was 50 nm. However, we believe it can be further improved by reducing the background vibration and using electronics with lower noise.

Array of pPZTpyroelectric thick-film sensors for contactless measurement of XY position

This paper presents the design, fabrication, and experimental characterization of a pyroelectric sensor array made by 8×8 pixels of PZT screen printed on alumina substrate. The electrodes are configured as eight columns and eight rows evenly spaced, whose respective crossings form the 64 pixels of the array. When an amplitude-modulated light emitting diode (LED) is placed in front of the array and moved in the XY plane parallel to the array surface, the array and the LED, respectively, work as the reference element and the contactless cursor of a biaxial position sensor. By means of a proper method of readout and processing of the pyroelectric signals, a continuous and linear dependence of the output voltages on XY-position of the LED can be obtained. The system intrinsically rejects background vibrations and microphonics. The configuration can be easily scaled to a larger number of pixels, and migrated to other manufacturing technologies.

Elimination of background disturbances from measurement spectra

Performing measurements (as for instance vibration measurements) in harshindustrial environments can be a tough task. In contrast to controlled laboratoryconditions, important disturbing background vibrations can be present. Sincethese disturbances are often very high in amplitude, the measurements can beuseless, even if the frequency of the disturbance is separated from the actualfrequency band of interest of the structure under investigation. Indeed, because ofspectral leakage a single-frequency component can spread out its energy over alarge frequency range. In this paper, a technique is proposed to eliminatebackground disturbances from measurements (although vibration measurementsare considered in the paper the technique also works for general signals). Thetechnique developed uses two periods of a periodic signal as the excitationsignal. The odd frequency lines of the discrete Fourier transform of twoperiods are used to estimate a parametric model of the disturbance. Thismodel is then used to correct the measurement. The proposed technique isvalidated on both simulations and vibration measurements of a car door.

A broadband tactile array on the fingertip.

A stimulator array is described which can deliver a wide range of displacement waveforms from each contactor, allowing vibratory stimuli to be targeted towards different populations of mechanoreceptors in the skin. The array has a working bandwidth of 20-400 Hz and 100 moving contactors covering an area of 1 cm2 on the fingertip. The array was validated with two experiments on the perception of moving vibratory targets within a uniform background vibration. In the first experiment, with target and background at the same frequency, equivalent discrimination of target movement was obtained at higher values of target/background amplitude ratio for 40-Hz stimuli than for 320-Hz stimuli. In the second experiment, discrimination of target movement within a different-frequency background (320-Hz target and 40-Hz background, or vice versa) was found to be much easier than within a same-frequency background. These results suggest that tactile spatial acuity is better at 320 Hz than 40 Hz and that it is possible to target different receptor populations in the skin by using these frequencies. However, there are problems with this interpretation: on the basis of characterization of touch receptors in previous studies, spatial acuity is expected to be worse at 320 Hz than at 40 Hz.

Talking Back: Sending Soil Vibration Signals to Lekking Prairie Mole Cricket Males1

SYNOPSIS. The male prairie mole cricket, Gryllotalpa major, native of the tallgrass prairie of the south central U.S., constructs a specialized acoustical burrow in the spring in the prairie soil from which he generates an airborne calling song that attracts flying females for mating. Males do not phonorespond to manipulations involving playbacks of airborne sounds. At the same time, vibrations with the same temporal scale and pattern as the airborne signal are produced in the substrate through an unknown mechanism. These ground vibrations can be distinguished from background vibrations in the soil at distances up to 3 m depending on soil conditions and conditions that control the background vibration environment (e.g., wind, highway traffic). We hypothesize that males use the vibration component of the call as information for spacing as they form display arenas, or leks. We used modified field recordings of soil vibrations from singing males with an electromechanical vibration exciter to simulate the vibration component of a calling song in playback experiments. Airborne sounds of males were monitored for two minutes before and two minutes after the introduction of the ground vibration stimulus with a tape recorder microphone placed 20 cm from the burrow opening. Males did respond to the manipulation experiment; although, we observed individual variation in the level of response.

Improvements of the pulsed-wire method to measure undulators

We present the Pulsed-Wire Method (PWM) for undulator measurements used for the first crossed overlapped electromagnetic undulator OPHeLIE. This method gives directly the first integral of the magnetic field using a short current pulse and the second integral using a step current pulse through the wire. We characterized OPHeLIE using the second integral mode to optimize the beam trajectory in the respect of specifications. There was a good correlation between these results and those obtained from the on-beam test. We were therefore encouraged to further develop this method to determine optical performances of undulators. In order to validate this approach we compared the spectrum determined by the pulsed-wire technique and Hall probe scans, used as reference, applied both to the OPHeLIE prototype, which is a shorter planar version. For the PWM, we used the short current pulse according to the undulator's period (the first integral mode). Digital data processing techniques have been used to improve the signal-to-noise ratio, to minimize the effect of the background vibrations and to characterize the wire response.

Study of fluxless soldering using formic acid vapor

This paper presents a systematic study of the use of formic acid vapor fluxless soldering with eutectic Pb/Sn solder. The study focused on the solder joint self-aligning process and the final alignment accuracy. The main effect considered was the formic acid vapor concentration. In addition, other effects of solder joint height and background vibration were studied. The self-alignment characteristics of the fluxless soldering process was as good as those using liquid flux at 220/spl deg/C. 2 /spl mu/m alignment accuracy could be achieved within 10 s. The most important parameter was the formic acid vapor concentration in the reflow chamber. The effective concentration window was found to be greater than 0.7% in volume.

Leaf Vibrations and Air Movements in a Leafminer–Parasitoid System

Abstract This paper analyzes the vibratory environment of the leafminerPhyllonorycter malella(Ger.) (Lep. Gracillariidae) and its parasitoidSympiesis sericeicornisNees (Hym. Eulophidae). Previous studies established that both the host and the parasitoid not only produce but also use leaf vibrations: the former in order to escape ovipositor stings, the latter as a physical cue in the foraging process. First we characterize vibration patterns produced by simulated wind and rain and discuss the influence of these background vibrations on the host–parasitoid interaction. Second, we present a method of producing leaf vibration patterns of high repeatability. This technique allows us to characterize the influence of the leaf as modifier of vibratory signals. We discuss howS. sericeicorniscould use such spatially variable vibratory information for between-mine foraging. Finally, a combined laser Doppler vibrometry–laser Doppler anemometry study revealed that leaf vibrations induce air movements in their immediate surroundings with characteristic temporal and spatial structures. We discuss if and how host-related information contained in the air particle displacement can be used by parasitoids.

Performance degradation of a Michelson interferometer when its misalignment angle is a rapidly varying, random time series

When subjected to random background vibrations, a standard, circular-aperture Michelson interferometer with a dynamic alignment servo system has a misalignment angle that is a random function of time. Here we derive formulas for the loss in performance when the misalignment angle is modeled as a stationary stochastic time series and show how these formulas are simplified when the power spectrum is band-limited white noise.

Effects of 1-Hz and 2-Hz transient vertical vibration on discomfort

The discomfort caused by 1-Hz and 2-Hz vertical sinusoidal vibration has been studied with 20 seated subjects, using the method of magnitude estimation. The sinusoidal transients were superimposed on an 80-s background vibration which consisted of a 1-oct band of random vibration, centered on 1 Hz, with a magnitude of 0.63 m s−2 rms. The transients were added at five magnitudes (0.63–1.6 m s−2 rms) and seven durations (1–60 s). Male and female subjects produced comparable results and similar discomfort was produced by the two frequencies of vibration. Discomfort increased when the magnitudes or the durations of the transients were increased. Of alternative methods of predicting the discomfort, the overall vibration dose values gave the highest correlations with subject estimates, followed by the overall root-mean-square accelerations. A lower correlation was found with peak acceleration and the lowest correlation was with a running rms measurement, using a 1-s window.

Long-term reliability of amorphous alloy wound core distribution transformers

In order to verify long-term reliability of amorphous alloy wound core distribution transformers, accelerated aging tests and field trials used on actual transformers were practised. As for accelerated aging tests, short-circuit tests were added to imitate mechanical stress in operation on a utility's distribution system. As a result, even after the equivalent of 30 years, which was the normal expected transformer's life, the magnetic characteristic was unchanged, so these transformers could be operated. Additionally, two hundred transformers of four kinds were installed on a utility's distribution system to study no-load characteristics. They were equipped with a mechanism to measure load current, background vibration and lightning surge current, so their influence on magnetic characteristic could be inspected. As a result, no remarkable change was seen even after six months.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Statistical analysis of field data of railway noise and vibration collected in an urban area

The effects of various factors on railway noise and vibration were studied through multiple regression analysis of the field data at 79 sites along 8 railway lines in an urban area. The results show that peak and sound exposure levels of railway noise can be explained fairly well by distance from track, railway structure, train speed, train length and so on. Because of the close relationship between peak and sound exposure levels, the main factors such as distance from track and railway structure give similar contributions to both noise levels. Train speed gives a greater contribution to peak level than to sound exposure level, while train length gives less. Regarding the vibration level, it was found that the contribution of background vibration is greater than that of railway structure and train speed. The results were applied to predict railway noise and vibration, and were also compared with the results of the Shinkansen Super Express railway which have already been reported.

Afferent bursting activity of ruff lateral line induced by background noise stimulation

Single unit resting activities were recorded from fibres innervating a neuromast of the supra-orbital canal of the lateral line system of the ruff (Acerina cernua). The interval histogram of 1 of the 4 types of resting activity had a bimodal distribution (‘bursting’ activity). The resting activity of these fibres was compared with the measured vibration of the experimental table. The conclusion that the ‘bursting’ activity is not spontaneous but is caused by small background vibrations of the table was supported by recording of extracellular hair cell responses.

A theory of estimating the whole from the partial information on the probability distribution of amplitude fluctuation and its application to noise environment

AbstractActual environmental noise and vibration exhibit arbitrary probability distribution forms due to the diversified causes of the fluctuation. Furthermore, the objective signal usually is contaminated by background noise or vibration, and often is effected by the dynamical range of the measuring meter. Therefore, it happens that the reliable observation data are only the partial information confined to a finite amplitude interval.This paper proposes a practical test to estimate the whole probability distribution (connected with the evaluation quantities: Leq and Lx) of the objective signal by using only the partial stochastic information with the influence of the background noise or vibration and of the forementioned dynamical range.More explicitly, the probability distribution of the objective signal is given first in a generalized series expansion form of probability expression. Next, we estimate the expansion coefficients in this expression by using four methods from different viewpoints. Finally, the effectiveness of the proposed theory is confirmed by applying it to the observed data of actual road traffic noise.

Experimental facility for fluid/structure interaction research

The boundary layer research facility (BLRF) at Penn State is being modified so that experimental research on the interaction between fluid boundary layers and vibration response of underlying structures can be conducted. Because the BLRF is a closed‐loop glycerine tunnel, the boundary layer is thick, which provides space for detailed measurements required for research in fluid/structure interaction. In addition, laminar, transition, or turbulent flow can be generated and maintained. Modifications to the BLRF for fluid/structure interaction research include: (1) the introduction of an elastic and exchangeable structure in contact with the flow, (2) the reduction of background vibration to remove interference of structural response measurements by background vibrations, and (3) an increase in the measurement accessibility to the boundary layer. A description of the modified BLRF is presented along with technical support for several of the key design elements. Measurements to characterize and define the capa...

A search for impact origin using the vibration intensity method.

In approaches to finding noise and vibration control of machinery, measurement of the vibration energy flow in the structure can give useful information about vibration properties and noise generation mechanisms. This energy flow within the structure is denoted by the vibration intensity vector. By tracing back in the direction of this flow, it is possible to clarify the transmission path of the vibration energy and the location of the exciting source which most affects the response at each point of the structure. In this paper, the vibration energy flow delivered by the impulsive excitation excitation force is measured for a response necessary for a rectanguler plate in the presence of background vibration. The conditions of signal processing of the response necessary for accurate measurement of the vibration intensity vector are also discussed. The direction of the vibration intensity vector is then detected at some points in an operating diesel engine structure and was demonstrated in a valve-sheeting impact.