Excessive Noise Levels Research Articles

White noise study of JFET's on a new mixed rad-hard technology

A new technology, called DMILL and based on re-epitaxied SIMOX structures, is being developped, with which both logic (CMOS) and analogic (JFET and BICMOS) devices are available. A good radiation hardness and a complete isolation between components is achieved. Isolation between analog and digital parts of a circuit corresponds to the trends for future low-noise mixed circuit applications. JFET's are used as input stage because of their high input impedance and low l/f excess noise. An excess white noise level in or near saturation, depending on channel doping and gate length is observed and studied. Precise measurements are used to compare several theoretical explanations.

Low noise, high efficiency GaAs IMPATT diodes at 30 GHz

Low noise, very high efficiency IMPATT diodes provide an attractive alternative to Gunn diodes for many millimetre-wave applications. In the Letter, GaAs Hi–Lo single-drift IMPATT diodes are demonstrated. The diodes are fabricated using molecular beam epitaxy and (at ~30 GHz) exhibit exceptional efficiencies (>20%), very low FM noise (–88 dBc/Hz at 100 kHz off-carrier) and simultaneous CW power levels in excess of 300 mW.

Modal study of the role of excess noise in x-ray lasers.

Current x-ray laser designs rely on amplifying spontaneous emission in a high-temperature plasma. A central problem in the study of x-ray lasers is determining and optimizing the degree of transverse spatial coherence for holographic applications. The inherent non-power-orthogonal character of the normal modes in a general amplifying medium necessarily results in excess noise and cross-correlation effects that can significantly affect the predicted coherence and intensity profiles of an x-ray laser. In particular, loosely bound discrete transverse eigenstates of the paraxial wave equation have previously been found to dominate the intensity and coherence in the low-amplification regime if the continuum eigenstates are omitted from the spectrum (London, Strauss, and Rosen, Phys. Rev. Lett. 65, 563 (1990)). A detailed analysis of the role of excess noise on steady-state laser intensity and coherence is presented for the simple case of a transverse square gain and density profile in a finite geometry. The inclusion of the continuum portion of the spectrum is found to substantially reduce the level of excess noise and to alter the coherence predictions for low and intermediate gain-length products.

Noise and hearing conservation: Young adults’ habits, knowledge, and attitudes.

According to the National Institutes of Health (NIH), approximately 28 million individuals in the United States suffer from significant hearing loss. More than one-third of those losses are attributable to noise exposure [Lankford, Hearing Instruments 41(10), 6 (1990)]. Between 1971 and 1985, the number of persons aged 35–44 years suffering from hearing loss increased from approximately 55 to 85 per thousand−a larger increase than for the 45–54 or 65 year old and older age group. Two hundred young adults, ages 14 to 38 years, were surveyed via a 20-item questionnaire concerning their habits pertaining to, knowledge of, and attitudes toward noise and hearing conservation. Results indicated that the majority of young adults participated in activities exposing them to excessive noise levels at least twice a week and for several hours in duration for each activity. Further, the large majority reported at least one incident of having symptoms (e.g., tinnitus) of overexposure to noise resulting from those activities. Although the large majority demonstrated basic knowledge about the effects of noise on hearing, most had deficiencies in their knowledge of the effectiveness of hearing protection devices (HPDs) and would feel self-conscious in using them or taking other measures to circumvent noise-induced hearing loss.

Progress in noise control of mining equipment

With the advent of mechanization in the mining industry, one of the by‐products has been the generation of excessive noise levels. In order to protect miners from these excessive noise levels, the Mine Safety and Health Administration has promulgated various noise regulations over the years, starting with the Coal Mine Safety and Health Act of 1969. One method used to reduce these excessive noise levels has been with the utilization of engineering noise controls. The progress in noise control of mining equipment has essentially followed three avenues of approach. These involve retrofit noise control, machine redesign, and advanced technology. One example of each of these approaches is (1) cut and fit application of acoustical materials to mobile equipment cabs, (2) redesign of cutting heads for underground continuous miners, and (3) electronic noise cancellation. This presentation will involve a general discussion of the progress made in noise control of mining equipment. In addition to the three examples previously mentioned, other examples of noise control will also be discussed.

Leakage currents and 1/fnoise in buried InGaAsP/InP heterostructure lasers

An investigation was made of the relationship between the excess 1f 1/f noise and electrical characteristics of InGaAsP heterojunction lasers. The excess noise level was found to be governed by the nonradiative current in these lasers. Degradation of these laser diodes resulted in an increase in the 1/f noise.

MSR acoustic vibrations due to the HP and LP tube bundle and cavity interactions using a bond graph model

Excessive noise levels are sometimes observed in Moisture Separator Reheaters (MSRs) at various nuclear power stations. The transverse vibrations of the tube due to buffeting/vortex shedding phenomena constitutes the main acoustic source in MSRs. The noise can be amplified by the acoustic resonance due to locking in of tube vibration frequency with one of the natural frequencies of the cavity. The mathematical modelling of the tube bundle as an acoustic source is quite complicated. This is further complicated by the interactions between the HP (high pressure) and LP (low pressure) tube bundles and their cavities. A simple bond graph model incorporating the interaction between HP and LP tube bundles is developed, which showed the cause of high noise levels in a particular MSR to be the matching of the HP tube bundle forcing frequency with the LP cavity natural frequency. This model showed excellent agreement with measured values of noise levels and their frequency content from an actual MSR. The bond graph model is simple, quick and provides a basic understanding of the complex acoustic phenomenon. It is also very flexible and versatile for incorporation of any future research results or better measurements when available.

Noise characteristics of lattice-matched InGaAs/InAlAs heterostructure p-i-n photodiodes

The authors report the experimental characterization of a set of three InGaAs/InAlAs heterostructure p-i-n photodiodes. Current-voltage, capacitance-voltage, S-parameter, and noise data were collected at room temperature over a wide range of bias current and voltage and a function of incident light intensity. The first device consisted of 360 alternating, undoped, lattice-matched In/sub 0.53/Ga/sub 0.47/As and In/sub 0.52/Al/sub 0.48/As layers 30 AA wide, sandwiched between an n/sup +/ and a p/sup +/ absorption layer of In/sub 0.53/Ga/sub 0.47/As. In the second and third device the number of layers and the layer width were respectively 200 and 90 AA and 50 and 500 AA. The capacitance-voltage data indicate that, in the dark, the heterostructure photodiodes are depleted gradually when the reverse bias is increased, i.e. one quantum well at a time. As a result, two high-field depleted regions at the contacts and a low-field undepleted region in the center are formed. Upon illumination by a light-emitting diode (1350 nm), the p-i-n photodiodes show large excess noise levels up to 500 MHz. Beyond this frequency the 30-AA devices show full short noise at field strengths E where impact ionization and Zener tunneling are absent, 0<E<220 kV/cm. The 90- and 500-AA devices, however, show distinctive subshot noise levels in the same field and frequency region. This difference in device operation can be understood in terms of the properties of the quantum-well structures located in the i-region of the device.

Study of the effects of simultaneous exposure to noise and carbon disulfide on workers' hearing.

The aim of this study was to explore the effects of simultaneous exposure to noise and carbon disulfide on workers' hearing and balance. The study was conducted by interviews and by audiometric and balance tests on workers in a rayon factory in the city of São Paulo, Brazil (n = 258). The workers studied had a history of exposure both to excessive noise levels (86-89 dBA) and to excessive levels of carbon disulfide (89.92 mg/m3). The percentage of hearing loss found was much higher than expected for this occupational activity, which reinforced the possible connection between the exposure to noise and carbon disulfide.

A propeller model for studying trace velocity effects on interior noise

There is concern that advanced turboprop (ATP) engines currently being developed as an alternative to turbofan engines may produce excessive aircraft cabin noise levels. This concern has stimulated renewed interest in developing aircraft interior noise reduction methods that do not significantly increase takeoff weight. Both syncrophasing and active control of interior noise have been proposed as solutions, but neither has been perfected, mostly from lack of physical understanding of the sound transmission mechanism. This paper exploits an existing analytical model for noise transmission into aircraft cabins to investigate the behavior of an improved propeller source model for use in aircraft interior noise studies. The new source model, a virtually rotating dipole, is shown to adequately match measured fuselage sound pressure distributions, including the correct phase relationships, for published data. As an example of its application, the virtually rotating dipole is used to study the sensitivity of synchrophasing effectiveness to the fuselage sound pressure trace velocity distribution. Results of calculations reveal the importance of correctly modeling the surface pressure phase relations in synchrophasing and other aircraft interior noise studies.

Increased received power and decreased modal noise by preferential excitation of low-order modes in multimode optical-fiber transmission systems

The dependence of the performance of a simple multi-mode optical-fiber transmission system on launch conditions is evaluated. Current methods of aligning lensed multimode fiber pigtails to injection lasers are shown to generate excessive levels of attenuation and modal noise. By altering these launch conditions, we are able to achieve an increase in the received power level of as much as 1.4 dB, and a decrease of the relative modal noise level of as much as 2.8 dB. Some of these improvements should be readily achievable in multimode optical-fiber systems.

Excess thermal noise and low-frequency oscillations during capillary flow of aqueous solutions of poly(ethylene oxide)

The excess thermal noise generated in polymer solutions through narrow capillaries is studied in detail for aqueous solutions of poly(ethylene oxide),\((\bar M_w \approx 4 \cdot 10^6 )\), of varying concentration. With increasing flow rate, the excess noise level increases, the noise spectrum assuming a 1/fα-form with α ≈ 1.5. Within a critical flow range, distinct peaks appear in the spectrum, their frequencies being multiples of a fundamental frequency. The latter frequency (f0) is found to increase with the flow rate; this variation, as well as that brought about by varying concentration and capillary dimensions, can be accommodated in a single curve correlatingf0 with the shear rate at the capillary wall. No such correlation was found for the total noise level. The value off0 appeared to be determined by transversal oscillations of the liquid stream entering the capillary. Addition of small amounts of silica particles (Aerosil) led to the disappearance of the peaks in the spectrum.

Excess noise level in MOS structures without straight-through macrodefects in the dielectric

Excess noise level in MOS structures without straight-through macrodefects in the dielectric

Reduced Control Effort for Self-Tuning Regulators via an Input Window

Self-tuning regulators (STRs) have proven themselves to be well suited to many process control environments, especially in the case of unknown or slowly time varying parameters. However, for processes containing moderate to excessive noise levels the basic minimum variance type STRs may prove inadequate as the resulting control action may be excessive and costly. This paper presents a method of limiting the control action via an input window without unnecessarily exceeding output variance limitations.

Interior noise levels in passive solar residences

Typical single family dwellings with passive solar heating systems involve large open plan areas. Multilevel designs often incorporate open plans within and between levels. Current design practice for passive solar residences commonly utilizes hard interior surface treatments and furnishings—primarily wood, metal, glass, or masonry. The combination of open plan design and acoustically hard surfaces can result in unacceptable interior noise levels. The results of a detailed noise survey conducted in a typical passive solar home are presented. The data reveal that household appliances, HVAC equipment, and home entertainment equipment can all cause excessive interior noise levels. Sound levels in excess of 80 dBA and NC values greater than 60 were observed in living areas of the home. These results indicate that boundary absorption is as important in open plan residential design as it is known to be in open plan commercial and institutional design. [Work supported by the Agriculture and Home Economics Experiment Station and the Engineering Research Institute.]

Use of glass fiber materials in industrial and commercial buildings

Many types of glass fiber products, composites, and systems can be effectively employed to reduce excessive noise levels in industrial and commercial buildings. New and expanded acoustical data are presented on the best utilization of glass fiber materials in ceilings, interior and exterior walls or roofs, air distribution systems, pipe quieting, source and receiver enclosures, and related acoustical treatments.

A study of the application of ear defenders and audiometry in the machine tool industry

Many machine tool applications are known to generate real ear noise levels in excess of ear damage thresholds. Yet there are no practicable engineering means of controlling noise exposure levels in many cases. Thus ear defenders are a necessary part of an ongoing hearing conservation programme. It follows therefore that much contemporary concern is given by industry to the application of semi clinical audiometric testing in manufacturing environments. Further, much thought is being given to the use of acoustically satisfactory ear defenders offering adequate “real ear” attenuation. This paper outlines the more important parameters of audiometry in a typical machine tool industry and gives details of audiometric results obtained against quoted noise exposure levels.

Excess thermal noise and low-frequency oscillations in capillary flow of non-Newtonian aqueous polymer solutions exhibiting elasticity

Results of thermal noise measurements (frequency range 0.01–1000 Hz) on aqueous solutions of poly(ethylene oxide) and maltose/poly(acrylamide) during capillary flow are reported. The flow of these solutions, both being of the pseudoplastic (shear thinning) type, gave rise to an excess thermal noise exhibiting a 1/fα-frequency distribution. The excess noise level increased with the flow rate. At a critical value of this rate, the noise showed a pulsating character. The corresponding frequency spectra contained a number of sharp peaks, all being multiples of a fundamental frequency of the order of 1 Hz. Increasing the flow rate still higher caused the pulsations to disappear, the excess noise regaining its 1/fα character. The pulsations appear to be associated with the elasticity of the solutions used. Solutions with comparable shear thinning properties but lacking elasticity did not produce such effects. No excess thermal noise was observed with Newtonian solutions of comparable viscosity.

Valve noise suppression by fluid recirculation

First Page

Glass fiber products for industrial noise control

A wide range of glass fiber products may be employed to reduce excessive industrial noise levels. Descriptions of these products, specific examples of their use as ceiling and sidewall absorbers, within sound attenuation barriers, air‐duct attenuation, pipe quieting, etc., and their acoustical values will be presented.