Analysis Of Noise Spectra Research Articles

Characteristics of Flow Through Throttling Valve Undergoing a Steep Pressure Gradient

AbstractThis paper presents predictions and measurements of the structures of cavitation flow inside the throttling valve. The three-dimensional Navier-Stokes equations in a moving reference frame are solved on tetrahedral meshes. A sliding mesh technique is utilized to characterize unsteady interactions. The accuracy of the predicted flow fields is evaluated by comparison to measurement results taken with a high-speed camera. Results show that the pressure distribution inside the throttling groove is sensitive to the valve port configuration and flow direction. Bubbles form near the side wall of the groove on the throttling edge where, in the case of flow into the throttling groove, the pressure is at a minimum. With the increase of the pressure gradient bubbles saturate the flow. Noise spectrum analysis indicates that the noise level induced by cavitation is determined by the number and size of the bubbles passing through the valve grooves.

Cavitation and noise characteristics of high-speed gap flow

To study the cavitation mechanics and its relation- ship with noise characteristics of the valve-port high-speed flow, high-speed photography and noise spectrum analysis are applied to investigate the flow area and the related phenomenon inside the throttling area of valves. The observation is taken under macroshot-model and the frame rate of high-speed camera can reach 120 000 frames/s. Both the experimental and the nume- rical results reveal that the cavitation inception and flow separation have close relationship with the pressure distribution in the valve. As the secondary influencing factor, the change of inlet-pressure also affects the characteristics of cavitation and noise. To deep orifice, the position of cavitation inception is invariably near the sharp-edged area, where the throttling-edge crosses the side-wall of the orifice, and the inception position slightly changes with the change of valve opening. Spectrum analysis indicates that the size and shape of cavitations are also the most important factors which affect the noise.

Location and quantification of noise sources on a wind turbine

Acoustic field measurements were carried out on a three-bladed wind turbine with a rotor diameter of 58 m, in order to characterize the noise sources and to verify whether trailing edge noise from the blades was dominant. To assess the effect of blade roughness, one blade was cleaned, one blade was tripped, and one blade remained untreated. A large horizontal microphone array, positioned about one rotor diameter upwind from the turbine, was used to measure the distribution of the noise sources in the rotor plane and on the individual blades. The operation parameters of the turbine were recorded in parallel to the acoustic tests. In total more than 100 measurements were performed at wind speeds between 6 and 10 m/s. The array results reveal that besides a minor source at the rotor hub, practically all noise (emitted to the ground) is produced during the downward movement of the blades. This strongly asymmetric source pattern can be explained by convective amplification and trailing edge noise directivity. The blade noise is produced at the outer part of the blades (but not at the very tip), and the level scales with the fifth power of the local flow speed. Comparison of the noise from the individual blades shows that the tripped blade is significantly noisier than the other two. Narrowband analysis of the de-dopplerized blade noise spectra indicates that trailing edge bluntness noise is not important. All in all, the test results convincingly show that broadband trailing edge noise is the dominant noise source for this wind turbine.

Development of microelectromechanical systems capacitive microphone for high-frequency applications

In this paper the development is described of a new high-frequency capacitive microphone based on the Knowles SiSonic MEMS microphone technology. The intended application for these microphones is aero-acoustic testing, which requires a transducer bandwidth of 80–100 kHz and the ability to measure sound pressures to 150 dB SPL without excessive distortion. The MEMS microphone structure was modified to meet these requirements and still be manufactured using the Knowles SiSonic production process. In addition, the microphone package was modified to eliminate the front port resonance, at approximately 12 kHz, associated with the standard SiSonic device. Specifically, the microphone package was modified with a lid that has lower acoustic inertance, thereby increasing the resonance frequency of the Helmholtz resonator formed by the front port and the microphone interior cavity. Details of the design process and the theoretical behavior of the microphones are presented, and it is shown that a microphone sensitivity of 0.5–1 mV/Pa can be achieved for a 100-kHz bandwidth. Preliminary results from fabricated microphones indicate a sensitivity around 0.5 mV/Pa and an A-weighted noise level of approximately 61.5-dB SPL. A more detailed analysis of the microphone noise spectrum and frequency response is presented.

Measurement of the working parameters of an air-post vertical-cavity surface-emitting laser

We present a complete experimental evaluation of the effective parameters necessary to describe the dynamical behavior of an air-post vertical-cavity surface-emitting lasers, on the basis of theoretical equations which are also derived in this paper. The experimental investigation is composed of several steps, including power versus current measurement, noise spectrum analysis, linewidth evaluation. The complete set of parameters derived, in particular the linewidth-enhancement factor and the spontaneous emission factor, is particularly important for accurate comparisons of theoretical models on the laser dynamics with experiments.

Spectrum analysis of voltage noise of moving vortex lattice and dynamic phase transition

Using Langevin molecular dynamics method, we have studied the voltage noise spectrum generated by current-driven vortices as a function of the magnetic field an d current. It is found that the broad band noise (BBN) at low frequencies decrea ses with increasing magnetic field, it decreases at the magnetic field near th e vortex dynamic transition field FP， and the Lorentze narrow ba nd noise (NBN) at high frequencies appears. As the magnetic field increases near the melt ing field Fm, the NBN peak goes up and shifts towards higher freq uencies. In the elastic motion region of vortices with strong driving currents, NBN exhib its the washboard-like shape. This behavior arises from the periodic modulation of the translational velocity of vortices, suggesting that there is a Bragg gla ss phase with the translation order in the vortex lattices of the layered superc onductors.

The Okinawa study: an estimation of noise-induced hearing loss on the basis of the records of aircraft noise exposure around Kadena Air Base

Aircraft noise measurements were recorded at the residential areas in the vicinity of Kadena Air Base, Okinawa in 1968 and 1972 at the time of the Vietnam war. The estimated equivalent continuous A-weighted sound pressure level L Aeq for 24 h was 85 dB.The time history of sound level during 24 h was estimated from the measurement conducted in 1968, and the sound level was converted into the spectrum level at the centre frequency of the critical band of temporary threshold shift (TTS) using the results of spectrum analysis of aircraft noise operated at the airfield. With the information of spectrum level and its time history, TTS was calculated as a function of time and level change. The permanent threshold shift was also calculated by means of Robinson's method and ISO's method. The results indicate the noise exposure around Kadena Air Base was hazardous to hearing and is likely to have caused hearing loss to people living in its vicinity.

Live recordings of sound levels during the use of powered instruments in ENT surgery.

Otolaryngology is one of the surgical specialities employing high-powered instruments and this study was designed in order to establish whether sound levels at work conform to HSE guidelines. No study to date has measured intra-operative noise levels in ENT operation theatres. A prospective observational study was therefore performed. Sound levels were measured during the use of bone drills for mastoid surgery and microdebriders for endoscopic sinus surgery. A SLM/IS Acos Class I sound level meter calibrated to BS 1259 was employed. A spectrum analysis of drill-generated noise was measured using a calibrated B and K precision sound level meter. Sound levels emitted varied as follows: Large burrs- 72.4 dB (A), medium size; 71.2 dB (A), small sized burrs- 68.8 dB (A) (all values for cutting burrs) and 60.8 dB (A) for diamond burs. With microdebriders, the average sound level was 60.1 dBA. Spectrum analysis revealed that the maximum intensity was at 3.15 kHz, followed by 4 kHz, while the least sound was produced at 40 kHz and 31.5 kHz. Essentially sound produced by drills was between 1.6 kHz and 6.3 kHz. Powered instruments used in ENT surgery are safe and pose no occupational hazard.

소형 선박의 소음 특성에 관한 연구

FRP 소형 선박의 선내소음의 원인을 규명하고 이들에 대한 합리적인 허용기준 설정 및 저소음화 설계를 위해 FRP 4~11톤급 신조 소형 선박을 대상으로 시운전시에 선내소음을 측정하여 소형 선박의 선내 소음특성 및 소음과 진동과의 상관관계를 검토, 분석하고, 이들에 대해 IMO와 DNV의 허용기준상의 적합도를 비교한 결과를 요약하면 다음과 같다. 소형 선박의 선내 소음 최대 레벨 범위는 79~115<TEX>$dB$</TEX>(A)로 나타났다. 또한, IMO 및 DNV 규제치와 비교에서 주기관실 소음은 비슷하게 나타났으며, 상부, 하부 거주실의 소음은 각각 5~19<TEX>$dB$</TEX>(A), 18~22<TEX>$dB$</TEX>(A) 높고, 조타실의 소음은 14<TEX>$dB$</TEX>(A) 높았으며, 동형선 E와 G선의 소음비교에서 선박의 크기, 마력이 비슷함에도 불구하고 E선 주기관이 G선의 주기관보다 진동 및 소음이 제작당시부터 높은 것으로 판단되었다. 한편 소음원 규명을 위한 진동과의 상관관계에서 주기관실, 상부 거주실, 하부 거주실, 조타실, 연통상부 모두 3차수가 우세하게 나타났으며, 3차수가 각 선내소음을 일으키는 주원인으로 판단된다. Most of the vibration and noise generating in small boats come from shipboard machinery such as main engine, generator and auxiliary machinery etc. In order to build up the comfortable environment for the crew and to reduce the ambient noise, and provide basic materials for reasoning selection application, the design under allowable vibration & noise conditions and the examination of vibration condition of the new ships, this paper researches the frequency spectrum and order analysis of vibration and noise. The obtained results are summarized as follows : Through comparing the small boat internal noise with the regulation of IMO and DNV, it revealed that the noise level of main engine room accords with the standard, and the noise of other places are beyond the values. In this paper, two boats are analyzed, which are same type, same size and power, but the main engines noise of them is different. In order to search the noise source, the noise of main engine room and relative parts are measured. The third order of measured points is dominant in frequency domain by the order analysis.

Low‐Frequency Noise in AlGaN/GaN High Electron Mobility Transistors Irradiated by γ‐Ray Quanta

Room temperature current–voltage and noise measurements have been made before and after gamma irradiation on AlGaN/GaN high electron mobility transistors (HEMTs) grown on sapphire. The saturation current due to radiation-induced defects shows a nonlinear dependence on radiation dose. The deviation of the device parameters does not exceed 20% at highest radiation dose 109 Rad and the devices with larger gate lengths demonstrate a higher radiation hardness to the 60Co gamma rays. The noise spectra of devices after gamma irradiation follow the flicker noise (1/fγ) dependence with the exponent γ close to one. The Hooge parameter estimated for the HEMTs after gamma irradiation dose does not show a gate-bias dependence and increases by approximately three to five times at radiation dose 2 × 108 Rad. The analysis of noise spectra allowed to identify the major sources of noise generation in the investigated HEMT heterostructures.

Dumbbell-shaped fibers for gravitational wave detectors

Fused silica fibers with a dumbbell-shaped diameter profile are proposed to simultaneously achieve low thermal noise and low vertical bounce frequency in an interferometric gravitational wave detector. We present a theoretical analysis of achievable noise spectra. We also survey the sources of dissipation in fused silica fibers. Finally, we apply the model to analyze the influence of welded end pins on Q's of suspensions.

Analysis of turbulent noise spectra of electrochemical reactions in different experimental conditions

The Ershler–Randles impedance model is used to analyze the physical foundations of potentiostatic and galvanostatic spectra of turbulent noise of electrochemical redox reactions as a function of the frequency range of measurements and the electrode potential. On the whole, the theoretically calculated and experimentally measured spectra are in satisfactory agreement. A computer simulation of the dependence of characteristic frequencies on the electrode potential, reaction parameters, and experimental conditions is realized. The approach allows one to tentatively estimate the in-principle possibility of experimental realization of spectrum sections, which are located in different frequency ranges and contain information on the characteristic frequencies and kinetic parameters of the reaction under study, and to formulate conditions required for performing an experiment and extracting data on the process kinetics.

Noise spectrum analysis in perpendicular magnetic recording of double-layered media

Noise spectrum properties of double-layered perpendicular magnetic recording media were studied for two dominant medium noises, a transition jitter noise and a reversed domain noise. It was found that the transition jitter noise spectrum was delivered from the derivative of the transition shape, while the reversed domain noise spectrum was derived from a simple model of the impulsive reversed domain. The noise enhancement in a low-frequency region with increasing the recording density was found to be attributed to the relative increase in the jitter noise. The noise spectra for both sources were theoretically whitened when the transition width and the reversed domain size became negligibly small against reproducing resolution.

Evaluation of MP tape packing homogeneity through depth-probing

The particle packing of MP tape media is explored by means of a new measurement technique. Utilizing a narrow gap length record head, the tape is evaluated throughout its thickness with the use of an incremental DC erase measurement. A quantitative analysis of the medium noise spectra at different erase currents allows for the packing fluctuations at different depths into the tape to be proportioned. The technique provides a method for evaluating the interface between the magnetic recording layer and non-magnetic underlayer in dual-layer tape, and measurements indicate that interfacial roughness at the magnetic coating backside in some dual-layer media is a major source of medium noise.

Quantifying advanced tape medium noise

An investigation of the tape medium noise mechanism analyzed the magnetization fluctuation produced by an incremental dc erase process in a variety of modern metal-particle tape media. It examined the wavelength characteristics of the noise and compared the integrated noise during the reverse dc erase process with in situ remanent hysteresis curves. The integrated noise power followed the square of the first field derivative of the remanent hysteresis curve, (dM/dH)/sup 2/, showing that spatial fluctuation of the recording field inside the medium is a major source of the tape medium noise. It excluded spatial fluctuation of the medium coercivity as a possible noise source by comparing results from recording heads with two very different gap lengths. A quantitative analysis of the medium noise spectra at different erase currents indicated that interfacial roughness at the magnetic coating backside in some dual-layer media is a major source of medium noise. The conclusion: The main mechanism of the medium noise in advanced tape media is the head medium spacing fluctuation due to surface roughness.

Extraction of Trap Characteristics from Excess Noise in GaN Devices

ABSTRACTCharacteristics of traps are extracted from excess noise spectra of the doped-and undoped-channel GaN/AlGaN heterostructure field-effect transistors. The two types of excess noise that have been analyzed include flicker, e.g. 1/fγ noise, and generation-recombination noise. The average trap density determined for the undoped and doped devices is 1.1 × 1016 cm−3 and 7.1 × 1017 cm−3, respectively. Two distinct trap time constants τ determined for doped devices were 16 μsec and 0.1 msec. The trap characteristics obtained from the analysis of the excess noise spectra are in agreement with data provided by other techniques.

Software Reviews : Sound Forge Version 4.0b Publisher: Sonic Foundry Inc., 100 South Baldwin, Suite 204, Madison, WI 53703-8062; telephone: 608-256-7300; fax: 608-256-7300 Version reviewed: 4.0b, with noise reduction plug-in, spectrum analysis, and batch converter options Minimum System Requirements: Windows 95, NT 3.51 or later, 486SX processor (Pentium recommended), 10 MB hard drive space (with 300 MB temporary additional space

Software Reviews : Sound Forge Version 4.0b Publisher: Sonic Foundry Inc., 100 South Baldwin, Suite 204, Madison, WI 53703-8062; telephone: 608-256-7300; fax: 608-256-7300 Version reviewed: 4.0b, with noise reduction plug-in, spectrum analysis, and batch converter options Minimum System Requirements: Windows 95, NT 3.51 or later, 486SX processor (Pentium recommended), 10 MB hard drive space (with 300 MB temporary additional space

A precision noise measurement and analysis method used to estimate reliability of semiconductor devices

In this paper, some problems with previous ultra-low noise measurement methods have been discussed, then a double-channel preamplifier cross-spectrum measurement method has been adopted, different from the previous cross-correlation method [A. van der Ziel, Noise: Sources, Characterization, Measurement, p. 54. Prentice-Hall, Englewood Cliffs, NJ (1970), L. Stor, Experimental techniques in noise measurement with special emphasis on precision measurement, Proc. 10th Int. Conf. on Noise in Physical Systems, pp. 551–560. Budapest, Hungary (1989)] in that an average periodogram using a windowing procedure has been performed. The theoretical analysis shows that the expected value of the cross-spectrum is incoherent with background noise and zero-drift from the preamplifier and power supply system, the average periodogram can decrease the variance of the periodogram and the additional bias of the cross-spectrum periodogram. Experimental results demonstrate that if the equivalent input noise of measuremental set-up is two orders of magnitude lower than the noise of each preamplifier, then an ultra-low noise spectrum can be measured accurately, the low limit is about 0.1 nV/√Hz at 1 kHz, which is 20 dB lower than the noise of each preamplifier. The thermal noise of a small resistance and the shot noise of a diode under forward conditions have been measured, the experimental results are in good agreement with the theoretical value, this means that this method is feasible and accurate for an ultra-low noise spectrum measurement. Finally, the noise spectrum analysis procedure based on the curve fitting method has been presented, which ensures that we obtain an accuracy value of three noise components in the semiconductor, i.e. 1 φ noise, white noise and g-r noise. This noise spectrum analysis method is a useful tool for investigation of noise mechanism, the diagnosis of defects in semiconductors and reliability estimation.

Power spectrum analysis of the timing noise in 18 southern pulsars

Power spectra of the timing noise observed in 18 southern pulsars have been derived using a novel technique, based on the CLEAN algorithm. Most of the spectra are well described by a single- or double-component power-law model. Some of these spectra can be interpreted in the context of one or more of the current timing noise models. The results combined with those obtained from the time-domain analyses of the timing activity in these pulsars are used to assess the viability of the various theoretical models of pulsar timing noise.

Frequency Doubling of CW And Pulsed CO2 Lasers Using Diffusionbonded, Quasi-Phase-Matched Gaas Stacks

AbstractWe describe the fabrication, characterization and frequency doubling properties of first order stacks of diffusion bonded 2″ diameter GaAs wafers. Near IR imaging through the stacks indicated that excellent bonding was obtained over 40%–70% of the central area of the wafers. A power spectrum analysis of the spectral noise (due to interface reflections) appearing in the transmission data is shown to be a quantitative diagnostic tool useful for determining interface quality and for accurately estimating the thickness of the bonded layers in a stack. The conversion efficiency for a four layer stack at 10.6 microns was found to be 0.03% or 3 mJ for a 10 mJ pulse with a 100 nanosecond pulse length. The corresponding efficiency for cw SHG was found to be 0.0002%.