Experimental Investigation Of Noise Research Articles

Experimental Investigation of Noise and Vibration in a Multi-three Phase Unit Interior Permanent Magnet Synchronous Machine with Open-circuit Fault conditions

Experimental Investigation of Noise and Vibration in a Multi-three Phase Unit Interior Permanent Magnet Synchronous Machine with Open-circuit Fault conditions

Light activation of noise at microwave frequencies: a study on scaled gallium arsenide HEMT's

This study is focused on the experimental investigation of noise at microwave frequencies for scaled gallium arsenide high-electron-mobility transistor's (HEMT's). The light activation of noise has been achieved by laser exposure in the visible range. The devices have 0.25 μm gate length and 100-200-300 μm gate widths. Their DC characteristics, linear scattering and noise parameters were measured both in dark condition and under continuous wave light exposure in the 2-18 GHz frequency range. Previous results had shown a remarkable influence on all the above-measured parameters under illumination, with a special concern for the noise performance. Therefore, the authors investigated the origin of this light-activated noise in terms of the intrinsic noise sources, by extracting a noise temperature circuit model for each HEMT.In addition, the noise model formulation based on the P, R and C as well as the K g , K r and K c coefficients is used to enlighten the key aspects of the optically activated noise on the device performance. It is observed that the degradation of the minimum noise figure can be attributed to the noise coefficient R, related to the gate noise source that is strongly affected by the charge generation related to light exposure.

Experimental investigation of noise generated by submerged circular cylinder

The characteristics of flow-induced noise generated around a circular cylinder have been well established theoretically and experimentally, regardless of the medium. However, the predicted results have not been proven for submerged cylinders; thus, the acoustic characteristics are unknown. In this experimental study, a flow-induced noise due to vortex shedding, which is classified as a singing noise, is recorded at several velocities by placing a cylinder in a cavitation tunnel. The results helped confirm the validity of the theoretical predictions for underwater applications. An equation is developed to predict the flow-induced noise generated by the submerged cylinder.

English

English

Experimental Investigation of Noise and Flow Characteristics of Supersonic Underexpanded Jet Interaction with a Coannular Tube

Experimental Investigation of Noise and Flow Characteristics of Supersonic Underexpanded Jet Interaction with a Coannular Tube

Experimental investigation of noise in 4H–SiC p+–n–n+ junctions

The excess 1/f low-frequency noise in 4H–SiC p+–n–n+ junctions has been investigated experimentally at room temperature. The main noise sources observed in these junctions were attributed to carrier recombination at the sidewall surface of the mesa structure for forward currents below 5 × 10−7 A and to mobility fluctuations in the depletion region of the junction for higher currents. From analysis of the noise data, the density of surface states and the Hooge factor, characterization of the surface and the bulk quality of the diode, respectively, was determined.

Mathematical analysis and experimental investigation of noise in quantitative magnetic resonance imaging applied in polymer gel dosimetry

In polymer gel dosimetry, the spin–spin relaxation rate R2=1/ T2, is related to the absorbed dose that is delivered to a gel phantom by high-energy radiation beams. In a two-points method, R2 is calculated from two differently T2-weighted images. In the many-points method, R2 is calculated by fitting the pixel intensities of a set of differently exponentially T2-weighted images. An analysis of the influence of noise on the resulting R2 image may contribute considerably to the enhancement of the accuracy of the dose map. The relation between the noise level in the differently T2-weighted images and the noise level in the R2 image is derived mathematically. This relation is dependent on the actual R2, on the choice of the echo times in the sequences used, and the fitting algorithm. Both a least square fit to the semi-logarithmic T2-relaxation plot and a maximum-likelihood estimation on the T2-relaxation plot were investigated. It was found that dose images obtained from R2 images through calibration will contain noise that originates from the noise in the R2 image and from the probability distribution of the coefficients of the calibration curve. We present a method for optimizing the echo times in order to maximize the signal-to-noise ratio (SNR) in the resulting R2 image for both methods and for both fitting algorithms. The mathematical considerations on the SNR as presented, can also be applied on other data sets which display a mono-exponential behavior (e.g. diffusion measurements, T1 relaxation).

Experimental investigation of noise generated by large turbulent diffusion flames

The sound power of combustion noise emitted by a natural gas fired experimental burner (1–3 MW) was measured under free-field conditions and compared with the noise emitted inside a refractory furnace. Measurements under free-field conditions show that the noise power output is proportional to the average gas velocity to the 2.8 power and to the burner throat diameter to the 5.6 power. The peak frequency of the combustion noise ranges between 125 Hz and 300 Hz depending on the swirl number but not on the firing rate. Measurements inside the furnace show the predominance of resonance phenomena at low frequencies. The actual combustion noise could be evaluated by the sound pressure level measured in the 250 Hz or 500 Hz octave band. The increase of combustion noise with firing rate is greater than under free-field conditions, which can be attributed to an increase of the flame turbulence rather than to an increase of the gas temperature. Preheating the combustion air greatly increases the sound power output as well as the peak frequency. A study of noise emitted by three industrial burners inside the furnace confirmed these results, notwithstanding the very different flame shapes obtained. Oil flames were found to be less noisy than natural gas flames when the combustion air was not preheated, whereas this difference disappeared on preheating the combustion air or using a pregasification burner.

Computers in NMR. II. experimental investigation of noise and dynamic range in the fourier transform process

the noise generated in the Fourier transform process has been examined experimentally using specially prepared programs. The dynamic range observable following a Fourier transform has been found to be proportional to the computer's word length and inversely proportional to the number of transformed words and the number of memory locations full at the outset of the transform. Dynamic range can thus be affected by judicious selection of the rf carrier position relative to the large solvent peak and by use of quadrature detection NMR. Block averaging cannot reduce the coherent noise generated by the transform process.

Experimental investigation of noise associated with modulated pulses

The theory of noise associated with pulses is considered from the point of view of application to the study of noise in pulse communication. The process of slicing and its effect on the signal to noise ratio are also considered. Experimental arrangement to verify the theoretical deductions and also the optimum slicing level formula are given. The results are fully discussed.