Reference Noise Source Research Articles

캐비테이션 소음의 위치 규명을 위한 추진기 상부 선체 표면 수중 음향센서 배치에 대한 실험적 연구

To localize cavitation noise using the beam forming method, sensors are mounted above the propeller on the hull surface of a model-scale ship. Beam forming results are highly dependent on the number and arrangement of sensors; thus, an array with a large number of sensors for a wide range will have good performance. However, it is difficult for such a system to be applied to a model scale, or to a full-scale ship in practical applications. A model-scale experiment was thus conducted at the cavitation tunnel of KRISO using various on-board sensor arrangements. The performance of each arrangement was verified from the experiment using the reference noise source, and it was confirmed that the location of the noise source could be estimated. Additionally, a feasibility study was carried out for a model ship with a single screw propeller, and it was confirmed that the location of the cavitation noise at the 12 o’clock position of the propeller was well represented.

High Directivity Reference RF Source and its Radiated Emission Model for Site Correlation

This article presents a configurable high directivity radio frequency reference noise source and its radiated emission (RE) simulation model. This noise source is a representative of actual programmable logic controller (PLC) and input output (IO) products with a high-speed gigabit backplane. It is designed to produce a reference noise signature from 30 MHz to 6 GHz with RE levels close to the class A electromagnetic radiation disturbance limits of CISPR 11 and CISPR 22. An RE model f this noise source was established to investigate the design factors. Multiple emissions' scans were performed in two separate semianechoic chambers located in different facilities in order to test the repeatability of this noise source. The measurement results indicated that the noise source has very good repeatability and that it can serve as a reference noise source. The results were also used to evaluate the maturity of the simulation technology as well as to quantify the difference between chambers.

A two adaptive filters-based method for reducing effects of acoustic feedback in single-channel feedforward ANC systems

In most of the existing approaches for neutralizing the effects of acoustic feedback in feed-forward active noise control (FF-ANC) systems, three adaptive filters have been employed. Besides the noise control and feedback neutralization filters (FBNF), a third disturbance removal filter has been exploited to obtain suitable signals for (apposite) adaptation of the other two (adaptive filters). In this paper, we develop an effective acoustic feedback neutralization method which does not require any supplementary third adaptive filter. The proposed method incorporates a probe signal with a time-varying gain and a novel variable step-size strategy for adaptation of the FBNF. During the transient state, the FBNF is excited by a large variance probe signal and a large valued step-size. This enhances the convergence rate of the FBNF. As the FF-ANC system converges, the level of probe noise is decreased to achieve good residual error attenuation performance (at steady-state). Furthermore, the step-size is also reduced to a small value to improve the steady-state performance of the acoustic FBNF. Simulations results show that the proposed two adaptive filters-based method outperforms the existing methods for broad-band reference noise sources and yields better steady-state residual error attenuation performance for narrow-band noise signals.

Total Power Radiometer for Medical Sensor Applications Using Matched and Mismatched Noise Sources.

This paper presents a simple total power radiometer to noninvasively measure the temperature of the human body. The proposed 3-GHz radiometer consists of an antenna collecting the noise power generated by a target, a low-noise and high-gain receiver amplifying the noise power, and a detector converting the noise power to voltage. A single-pole-triple-throw (SP3T) switch is placed between the antenna and the receiver, while a personal computer is used to control the SP3T switch, collect and process the data such as detector output voltages and physical temperatures of the reference noise sources and the target. The fabricated radiometer shows a good performance agreement with a thermometer in the temperature measurement of water from 25.0 to 43.1 °C. For the accurate prediction of the target temperature, the radiometer is calibrated adaptively to the environment and radiometer variations. For this purpose, two reference noise sources (hot and cold) are proposed using matched and mismatched resistors at room temperature. These resistor-based noise sources offer a reliable performance without complex temperature control systems. Furthermore, they can be easily calibrated in real time by periodically measuring the physical temperatures of the resistors. In addition, the logarithmic detector with wide dynamic range is adopted and logarithmically-fitted based on the measurement results instead of linear approximation, which reduces the error caused by the limited dynamic range of resistor-based noise sources. In order to further increase the accuracy, the performance imbalances between ports in the SP3T switch are also taken into account by employing offsets in the radiometer output voltages.

Individual Fit Testing of Hearing Protection Devices Based on Microphone in Real Ear.

BackgroundLabeled noise reduction (NR) data presented by manufacturers are considered one of the main challenging issues for occupational experts in employing hearing protection devices (HPDs). This study aimed to determine the actual NR data of typical HPDs using the objective fit testing method with a microphone in real ear (MIRE) method.MethodsFive available commercially earmuff protectors were investigated in 30 workers exposed to reference noise source according to the standard method, ISO 11904-1. Personal attenuation rating (PAR) of the earmuffs was measured based on the MIRE method using a noise dosimeter (SVANTEK, model SV 102).ResultsThe results showed that means of PAR of the earmuffs are from 49% to 86% of the nominal NR rating. The PAR values of earmuffs when a typical eyewear was worn differed statistically (p < 0.05). It is revealed that a typical safety eyewear can reduce the mean of the PAR value by approximately 2.5 dB. The results also showed that measurements based on the MIRE method resulted in low variability. The variability in NR values between individuals, within individuals, and within earmuffs was not the statistically significant (p > 0.05).ConclusionThis study could provide local individual fit data. Ergonomic aspects of the earmuffs and different levels of users experience and awareness can be considered the main factors affecting individual fitting compared with the laboratory condition for acquiring the labeled NR data. Based on the obtained fit testing results, the field application of MIRE can be employed for complementary studies in real workstations while workers perform their regular work duties.

폐쇄형 시험부에서 케블라 덮개가 장착된 마이크로폰 어레이의 주파수 특성에 대한 실험적 연구

An experimental study on frequency characteristics of the microphone array covered with Kevlar sheet was conducted in the closed test section. Microphones that were flush-mounted in the wall of wind tunnel were subjected to very high flow noise resulting from the turbulence in the wall boundary layer. This noise interference by the boundary layer was referred as 'a microphone self-noise' and various approaches were studied to reduce this interference. Recessed microphone array with high tensioned cover was one of the good approaches to reduce this self-noise. But, the array cover could cause an unexpected interference to the measuring results. In this paper the frequency characteristics of the microphone array with Kevlar cover was experimentally studied. The white noise was used as a reference noise source. Three kinds of tensions for the Kevlar cover were tested and those results were compared with the test results without the Kevlar cover. The gap effect between the cover and microphone head was also tested to find out the proper position of microphone in the array module. Test results show that the mid-tension and 10mm gap was the best choice in the tested cases.

Optimum-setting and calibration procedures for heterodyne measurements of amplitude and phase noise in high-frequency amplifiers

An overview of several calibration stages has been studied and developed to obtain an optimum setting for phase and amplitude noise measurements through heterodyne techniques, which allows to measure white and flicker noise from amplifiers in the presence of a carrier signal. A technique to obtain a reliable calibration of phase and gain conversion of the measuring blocks is also presented, where the calibration of conversion factors and null conditions, using amplitude and phase modulators for each, phase and amplitude noise levels, have been fully characterized to suppress uncertainties in the measuring process. Furthermore, we introduce a procedure to measure noise of amplifiers in the presence of carrier signal based on a reference noise source and a known lossy line, which allows to determine the noise delivered from the source generator, and the contribution of the setup required for the measurement. We have found a good correlation of the measurements in small signal in comparison with the Y-factor. White noise of matched passive components was measured with the technique presented, obtaining an error of ±0.15 dB. Measurements of an SiGe-HBT amplifier designed for low phase noise are also reported. The technique has also been applied for flicker noise measurements.

PHOCUS radiometer

Abstract. PHOCUS – Particles, Hydrogen and Oxygen Chemistry in the Upper Summer Mesosphere is a Swedish sounding rocket experiment, launched in July 2011, with the main goal of investigating the upper atmosphere in the altitude range 50–110 km. This paper describes the SondRad instrument in the PHOCUS payload, a radiometer comprising two frequency channels (183 GHz and 557 GHz) aimed at exploring the water vapour concentration distribution in connection with the appearance of noctilucent (night shining) clouds. The design of the radiometer system has been done in a collaboration between Omnisys Instruments AB and the Group for Advanced Receiver Development (GARD) at Chalmers University of Technology where Omnisys was responsible for the overall design, implementation, and verification of the radiometers and backend, whereas GARD was responsible for the radiometer optics and calibration systems. The SondRad instrument covers the water absorption lines at 183 GHz and 557 GHz. The 183 GHz channel is a side-looking radiometer, while the 557 GHz radiometer is placed along the rocket axis looking in the forward direction. Both channels employ sub-harmonically pumped Schottky mixers and Fast Fourier Transform Spectrometers (FFTS) backends with 67 kHz resolution. The radiometers include novel calibration systems specifically adjusted for use with each frequency channel. The 183 GHz channel employs a continuous wave CW pilot signal calibrating the entire receiving chain, while the intermediate frequency chain (the IF-chain) of the 557 GHz channel is calibrated by injecting a signal from a reference noise source through a directional coupler. The instrument collected complete spectra for both the 183 GHz and the 557 GHz with 300 Hz data rate for the 183 GHz channel and 10 Hz data rate for the 557 GHz channel for about 60 s reaching the apogee of the flight trajectory and 100 s after that. With lossless data compression using variable resolution over the spectrum, the data set was reduced to 2 × 12 MByte. The first results indicate that the instrument successfully performed measurements of the mesospheric water profile as planned. However, the temperature environment for the instruments showed more extreme behaviour than expected and accounted for. Consequently, the results of the calibration and the final data reduction will need careful treatment. Further, simulations through finite element method (FEM), modelling and direct measurements of the simulated thermal environment and its impact on the instrument performance are described, as well as suggestions for improvements in the design for future flights.

Auxiliary-Transmission-Line Method for Calibrating Noise Temperature of a Microwave Thermal Noise Source

We have proposed and discussed a method to calibrate the effective noise temperature (ENT) of a noise source by using an auxiliary transmission line (ATL). A cryogenic 7-mm coaxial noise source was developed for verifying the ATL method. The ENT is determined from the parameters evaluated by a radiometer and the available power ratio of the transmission line measured by a vector network analyzer. The calibrated ENT by this method was 139.8 K-143.6 K with an expanded uncertainty of 4.0 K-4.6 K (k = 2) in the frequency range of 8-12 GHz. We also performed a comparison of the ENT using two different methods: an ordinary radiometer measurement using two reference noise sources and a theoretical calculation method analyzing temperature and loss distribution along the transmission line. The experimental results show the validity of the ATL method for determining the ENT.

Novel instrumentation for measurement of relative intensity noise

Laser diode relative intensity noise (RIN) metrology capabilities have been developed and demonstrated, providing significantly improved sensitivity and accuracy compared with existing methods. The novel use of the demonstrated reference noise source has shown significant advantages, achieving improved sensitivity, reducing measurement accuracy as low as ±1 dB and simplifying the system calibration methodology, thus improving flexibility. Laser RINs of between 10 and 14 dB below the shot RIN have been shown (typically −170 dBm/Hz), which is a direct result of the improved system sensitivity. A neodinium yag 1319-nm ring laser provided a ‘cold’ reference source, in a similar manner to that used in RF electrical metrology. Application of the ‘flat’ low noise optical RF noise source from 10 MHz to 20 GHz has been demonstrated for the first time in optical RF metrology, providing a calculable reference traceable via the incident optical power received. Because of the simplistic nature of this approach, system calibration can be performed for each RIN measurement that is carried out, reducing measurement uncertainty associated with RF mismatch, system linearity and loss. High specification components have been assessed individually and in the combined system indicating an overall system noise figure of 2–3 dB over the 10 MHz to 20 GHz frequency range (−171 to −172 dBm), some 4–5 dB better than previously reported.

A Calibration Method for RF and Microwave Noise Sources

Uncertainties in noise-figure and noise-parameter measurements depend to a large degree on the accuracy with which noise sources are calibrated. In some cases, the uncertainties are similar to measured quantities. This paper discusses a method for calibration of RF and microwave noise sources against a reference noise source. This method takes into account noise parameters of the receiver used for noise power measurements and includes temperature corrections to account for both drifts in the ambient temperature and heat transfer between the receiver and noise sources. Experimental results demonstrate the feasibility of the proposed method. As estimated with a Monte Carlo analysis, a uncertainty of 0.046 dB for a 5-dB excess-noise-ratio (ENR) noise source is obtained with the proposed method. This uncertainty is approximately one third of ENR uncertainties reported for commercial noise sources.

Inter Laboratory Comparison of Environmental Noise Measurement

Results of an inter laboratory comparison for environmental noise measurements are presented in this article. 18 laboratories took part in this study. A purpose of individual measurement was to quantify environmental noise levels, calculate noise descriptors and compare them with community noise regulations. Measurements and calculations were performed according to standards ISO 1996-1:2005, ISO 1996-2:2007 and national legislation. A loudspeaker was used as a reference noise source. It was mounted at the top of the hayloft just below the roof. The loudspeaker emitted a pink noise, representing a constant broadband noise source. The noise source was operating from 8:00 in the morning to 16:00 at the afternoon, each day for 4 weeks. During this time, laboratories performed all required measurements. Each laboratory performed measurements independently from other laboratories and according to its own procedures. Measurement results of equivalent noise level L Aeq , percentile values L 1 , and calculation of noise descriptors L d and L den were compared. An estimation of measurement uncertainty for a given environmental conditions and measurement setup conditions is given.

A New Microwave Radiometer Simultaneously Receiving Dual-Polarized Radiation

A new cost-effective microwave radiometer has been designed for simultaneously receiving both vertically and horizontally polarized thermal radiation, which are important signals for improving the capability of passive remote observations of geophysical phenomena. It is basically a Dicke-switched superheterodyne receiver whose both polarization channels share a single set of a reference noise source, a low-noise microwave amplifier, and a mixer with a local oscillator by adopting a scheme that both channels are slightly spaced in receiving frequency. A 15-GHz band radiometer has been built and tested for the verification of this scheme.

A Noise Temperature Measurement System for Mismatched Noise Sources

A measurement system is described which allows us to determine the noise temperature of mismatched noise sources with unknown reflection coefficients. The system consists of a null-balancing radiometer extended by a circuit to compensate for the reduced noise power emitted by the mismatched one-port. In this circuit, no passive nonreciprocal components are necessary. Special consideration is given to measurement errors that are caused by the correlation of the input and output noise waves of the radiometer preamplifiers. Several methods to eliminate these errors are described. Furthermore, a circuit is given by which the measurement range is extended down to 0 K without the use of cold reference noise sources. Finally, a practical setup, operating in the 20-40-MHz range, is described together with corresponding measurement results.

The computer-controlled solar radio spectrometer ?IKARUS?

The radiospectrometer IKARUS is a fully computer-controlled instrument covering the frequency band 0.11 to 1 GHz in steps of 1 MHz. It can automatically detect solar radio bursts and then write, on magnetic tape, 2000 measurements per second of intensity and circular polarization. The frequencies to be measured can be readily programmed in the band, compromising between frequency and time resolution. Reference noise sources are switched in automatically by the computer to calibrate the receiver at each frequency. The dynamic range is about 50 dB, recorded logarithmically with 8 bit resolution. The novelty of the instrument is its ability to measure broadband calibrated spectra (flux and degree of polarization) in the very interesting region of the lower corona.

Design of a tracking correlation receiver with feedback for radio astronomical interferometry

A tracking correlation receiver being developed as part of a flux-density measurement programme for 12·5 MHz radio sources will employ three type-one negative feedback loops. An amplitude insensitive phase loop will control an internal phase shifter to track radio sources through an interferometer aerial pattern. Simultaneously, this loop will keep the inputs to an amplitude multiplier in phase or antiphase. Relative phase read-out will provide for detection of possible phase scintillation.An amplitude loop will use the integrated output from an amplitude multiplier to control a variable reference noise source whose output is added directly to the aerial inputs. This loop will keep the time-averaged multiplier output nulled, such that the output level setting of the controlled reference source is, at all times, indicative of the signal power received by the aerials.A third loop will control an independent noise source whose output is added to one receiver channel. This loop will provide an output of the total noise power received and will keep the operating points of all receiver elements equal in the two channels. The proposed receiver combines principles developed by the authors with those of several other workers. The overall receiver scheme is expected to provide exceptional accuracy and stability, independent of channel gain, phase, and bandwidth. Frequent recalibration will be unnecessary. This paper describes the operation of the proposed receiver scheme and provides test results and data regarding an analogue simulation study of the multiple feedback loop schemes to be used in the receiver.

Chemical diffusion in CoO

We have developed a new active control algorithm based on discrete wavelet transform (DWT) for both stationary and non-stationary noise control. First, the Mallat pyramidal algorithm is introduced to implement the DWT, which can decompose the reference signal into several sub-bands with multi-resolution and provides a perfect reconstruction (PR) procedure. To reduce the extra computational complexity introduced by DWT, an efficient strategy is proposed that updates the adaptive filter coefficients in the frequency domainDeepthi B.B using a fast Fourier transform (FFT). Based on the reference noise source, a ‘Haar’ wavelet is employed and by decomposing the noise signal into two sub-band (3-band), the proposed DWT-FFT-based FXLMS (DWT-FFT-FXLMS) algorithm has greatly reduced complexity and a better convergence performance compared to a time domain filtered-x least mean square (TD-FXLMS) algorithm. As a result of the outstanding time-frequency characteristics of wavelet analysis, the proposed DWT-FFT-FXLMS algorithm can effectively cancel both stationary and non-stationary noise, whereas the frequency domain FXLMS (FD-FXLMS) algorithm cannot approach this point.

New riometer developed

A compact, all solid state riometer has been developed at the University of California, San Diego, in connection with a research program to study ionospheric absorption at high latitudes. The unit is particularly suitable for unmanned ground stations where reliability must be high and power consumption low.In the new units the thermionic diodes, which have been used traditionally as a reference noise source, have been replaced by low power planar silicon transistors. These have a good linear response and do not require any special power supplies. A regular sequence of calibrations has been arranged using logic circuitry so that the stability of the riometer can be monitored easily. A crystal clock is an integral part of the unit to maintain accurate timing. The system time constant has been set as low as 0.2 sec in order that rapidly changing details of absorption events can be studied with the instrument.

Upper-Hybrid Resonance Absorption, Emission, and Heating of an Afterglow Plasma Column

Microwave absorption and emission and electron temperatures of a nonuniform axially magnetized afterglow plasma column in a waveguide geometry have been investigated experimentally. Frequency ω and magnetic field ωc are chosen to satisfy the upper-hybrid resonance condition ω2=ωc2+ωp2(r), where ωp(r) is the local electron plasma frequency. Nearly perfect absorption is observed in the range of upper-hybrid frequencies, while at other frequencies the absorption coefficient is essentially zero. The sharp absorption onset at the maximum upper-hybrid frequency yields an accurate measure for the peak electron density. Density decay and profile in the plasma column are observed—the latter using a new technique. In the range of high absorption the noise emission approaches the blackbody limit. The electron temperature is measured with a radiometer and a reference noise source in a new technique yielding both spatial and time dependence without perturbing the plasma. The time resolution is obtained by a sampling technique. The spatial resolution results from the fact that upper-hybrid resonance absorption and emission are confined to a narrow resonant layer. This property is also used to heat the electrons locally and observe the thermalization process.

Noise Spectrum Measurements from 10 Hz to 1 MHz using a Tunable Switching Radiometer. I. Instrumentation

The first application of a switching (Dicke) radiometer to high-precision, noise spectrum measurements from 10 Hz to 1 MHz is described. The solution of the instrumentation problems unique to this frequency range are discussed in detail. The advantage of this radiometer is that it can be employed in a null mode so that it is direct reading and the measurement precision at all frequencies is limited fundamentally by the bandwidth and averaging time or by the calibration of the reference noise source and its attenuator.