Internal Noise Level Research Articles

Incorporation of acoustic black hole stiffeners into composite airframes for reduction of noise radiation

Stiffened composite panels are commonly used in aerospace structures, because they are lightweight, while maintaining a high load-bearing ability. However, their high stiffness-to-mass ratio makes them efficient noise radiators. In rotorcraft cabins made with composite panels, for example, the internal noise levels can be quite high such that pilot and passenger communication and comfort are disrupted. This has led to a need for innovative noise reduction strategies for composite rotorcraft panels. A specialized stiffener, which incorporates the acoustic black hole (ABH) effect into the cross section, is proposed to improve the damping of stiffened composite panels. By incorporating the damping concept into the stiffeners, the panel’s radiated noise can be reduced while maintaining the weight advantages and panel strength. To determine the advantages and trade-offs of this concept, numerical models have been developed and incorporated into an optimization scheme. Computational studies reveal promising results from the optimized ABH stiffeners as compared to a baseline panel with traditional stiffeners.

Temporal integration for amplitude modulation in childhood: Interaction between internal noise and memory

It is still unclear whether the gradual improvement in amplitude-modulation (AM) sensitivity typically found in children up to 10 years of age reflects an improvement in “processing efficiency” (the central ability to use information extracted by sensory mechanisms). This hypothesis was tested by evaluating temporal integration for AM, a capacity relying on memory and decision factors. This was achieved by measuring the effect of increasing the number of AM cycles (2 vs 8) on AM-detection thresholds for three groups of children aged from 5 to 11 years and a group of young adults. AM-detection thresholds were measured using a forced-choice procedure and sinusoidal AM (4 or 32 Hz rate) applied to a 1024-Hz pure-tone carrier. All age groups demonstrated temporal integration for AM at both rates; that is, significant improvements in AM sensitivity with a higher number of AM cycles. However, an effect of age is observed as both 5–6 year olds and adults exhibited more temporal integration compared to 7–8 and 10–11 year olds at both rates. This difference is due to: (i) the 5–6 year olds displaying the worst thresholds with 2 AM cycles, but similar thresholds with 8 cycles compared to the 7–8 and 10–11 year olds, and, (ii) adults showing the best thresholds with 8 AM cycles but similar thresholds with 2 cycles compared to the 7–8 and 10–11 year olds. Computational modelling indicated that higher levels of internal noise combined with poorer short-term memory capacities in children accounted for the developmental trends. Improvement in processing efficiency may therefore account for the development of AM detection in childhood.

Double-pass consistency for amplitude- and frequency-modulation detection in normal-hearing listeners.

Amplitude modulation (AM) and frequency modulation (FM) provide crucial auditory information. If FM is encoded as AM, it should be possible to give a unified account of AM and FM perception both in terms of response consistency and performance. These two aspects of behavior were estimated for normal-hearing participants using a constant-stimuli, forced-choice detection task repeated twice with the same stimuli (double pass). Sinusoidal AM or FM with rates of 2 or 20 Hz were applied to a 500-Hz pure-tone carrier and presented at detection threshold. All stimuli were masked by a modulation noise. Percent agreement of responses across passes and percent-correct detection for the two passes were used to estimate consistency and performance, respectively. These data were simulated using a model implementing peripheral processes, a central modulation filterbank, an additive internal noise, and a template-matching device. Different levels of internal noise were required to reproduce AM and FM data, but a single level could account for the 2- and 20-Hz AM data. As for FM, two levels of internal noise were needed to account for detection at slow and fast rates. Finally, the level of internal noise yielding best predictions increased with the level of the modulation-noise masker. Overall, these results suggest that different sources of internal variability are involved for AM and FM detection at low audio frequencies.

Inter-individual variations in internal noise predict the effects of spatial attention

Individuals differ considerably in the degree to which they benefit from attention allocation. Thus far, such individual differences were attributed to post-perceptual factors such as working-memory capacity. This study examined whether a perceptual factor – the level of internal noise – also contributes to this inter-individual variability in attentional effects. To that end, we estimated individual levels of internal noise from behavioral variability in an orientation discrimination task (with tilted gratings) using the double-pass procedure and the perceptual-template model. We also measured the effects of spatial attention in an acuity task: the participants reported the side of a square on which a small aperture appeared. Central arrows were used to engage sustained attention and peripheral cues to engage transient attention. We found reliable correlations between individual levels of internal noise and the effects of both types of attention, albeit of opposite directions: positive correlation with sustained attention and negative correlation with transient attention. These findings demonstrate that internal noise – a fundamental characteristic of visual perception – can predict individual differences in the effects of spatial attention, highlighting the intricate relations between perception and attention.

Improvement in visual perception after high-frequency transcranial random noise stimulation (hf-tRNS) in those with migraine: An equivalent noise approach

Migraine is a common neurological disorder with strong links to vision. Interictal migraine is thought to be characterised by internal noise in the brain, possibly due to increased variability in neural firing, which can be estimated using equivalent noise tasks. High-frequency transcranial random noise stimulation (hf-tRNS) can be used to modulate levels of internal noise in the brain, and so presents a possible therapy to redress noise levels in the migraine brain. This is a case-control study using a 2-alternative forced choice (2AFC) design. Hf-tRNS and Sham control stimulation were used alongside a global motion direction discrimination task and visually based equivalent noise tasks. The migraine group demonstrated increased baseline internal noise levels compared to the control group. Internal noise levels, and sampling, were reduced using hf-tRNS but not Sham stimulation. However, there were no differences in terms of coherence thresholds, slopes, and lapse rate for global motion discrimination between the two groups. This is the first demonstration of the possibility of decreasing internal noise levels in migraine using hf-tRNS. Future work could explore the possibility of neurostimulation as a therapy for migraine.

Dual strategies in human confidence judgments.

Although confidence is commonly believed to be an essential element in decision-making, it remains unclear what gives rise to one's sense of confidence. Recent Bayesian theories propose that confidence is computed, in part, from the degree of uncertainty in sensory evidence. Alternatively, observers can use physical properties of the stimulus as a heuristic to confidence. In the current study, we developed ideal observer models for either hypothesis and compared their predictions against human data obtained from psychophysical experiments. Participants reported the orientation of a stimulus, and their confidence in this estimate, under varying levels of internal and external noise. As predicted by the Bayesian model, we found a consistent link between confidence and behavioral variability for a given stimulus orientation. Confidence was higher when orientation estimates were more precise, for both internal and external sources of noise. However, we observed the inverse pattern when comparing between stimulus orientations: although observers gave more precise orientation estimates for cardinal orientations (a phenomenon known as the oblique effect), they were more confident about oblique orientations. We show that these results are well explained by a strategy to confidence that is based on the perceived amount of noise in the stimulus. Altogether, our results suggest that confidence is not always computed from the degree of uncertainty in one's perceptual evidence but can instead be based on visual cues that function as simple Heuristics to confidence.

Сравнительный анализ методов построения интегральных перемножителей сигналов

This paper is devoted to the comparative analysis of modern integral variables. Today, a number of foreign companies, such as Texas Instruments and Analog Devices, produce analog signal multipliers (APS) in integrated design. Russian industry produces chips of the 525PS and 174HA series. Each manufacturer uses its own method of implementing the device. The main task of such devices is to calculate the current voltage, phase, exponential and transcendental functions. Wide applicability of APS in integrated design was found in devices for analog processing and conversion of signals of communication and radio equipment, in devices for automatic control of onboard and ground radio equipment. A very important characteristic of such equipment is the dynamic range. The dynamic range of the receiver is the range of input signal amplitudes that provide the required quality of reproduction of the received message. The lower limit of the dynamic range is determined by the level of internal noise or external interference in the device, and the upper limit is determined by the device's overload capacity. In this regard, manufacturers of multipliers are faced with the task of maximizing the voltage that can be applied to its inputs. The difficulty is that the upper limit of the dynamic range is set by non-linear distortions. The non-linearity of the multiplier is a component of the multiplication error and characterizes the limiting capabilities of the APS inputs. In this paper, a comparative analysis of the main types of integral multipliers offered on the market is carried out in order to identify the best construction method for achieving the value of the dynamic range of the multiplier in 90 dB with high multiplication accuracy, which will allow using such a multiplier in modern radio equipment.

Stress response capacity analysis during aging and possible new insights into aging studies.

The causes and consequences of aging have always been a concern. In recent studies, changes in the stress response capacity of cells during aging were quantitatively analyzed. It was found that aging was accompanied by a decline in response capacity. When the response capacity decreased to a critical value, which we assumed was the internal noise level, the cell soon died. To survive, the response capacity should be, at minimum, sufficiently strong to resist intracellular noise. Here, we discuss the role of stress response capacity in aging and conjecture that lifespan might be extended by enhancing stress response capacity.

Internal Electrical Noises of BioFET Sensors Based on Various Architectures

The results of a comparative literature analysis of internal electrical noises and signal-to-noise ratio for nanoscale BioFET (biological field-effect transistor) and DNA (deoxyribonucleic acid) sensors based on different architectures MIS (metal-insulator-semiconductor), EIS (electrolyte-insulator-semi-conductor) and ISFET (ion-selective field-effect transistor) are presented. Main types, models and mechanisms of internal noises of bio- & chemical field-effect based sensors are analyzed, summarized and presented. For the first time, corresponding detail electrical equivalent circuits were built to calculate the spectral densities of noises generated in the active part of a solid (semiconductor, dielectric) and in an aqueous solution for MIS, EIS and ISFET structures based sensors. Complete expressions are obtained for the rms (root mean square) value of the noise current (or voltage), as well as the noise spectral densities for the architectures under study. The miniaturization of biosensors leads to a decrease in the level of the useful signal-current. For successful operation of the sensor, it is necessary to ensure a high value of the SNR (signal-to-noise ratio). In case of weak useful signals, it is necessary to reduce the level of internal electrical noise. This work is devoted to a detailed study of the types and mechanisms of internal electrical noises in specific biosensor architectures.

A crew of listeners with no more than “slight” hearing loss who exhibit binaural deficits also exhibit higher levels of stimulus-independent internal noise

Listeners having, at most, "slight" hearing loss may exhibit deficits in binaural detection which appear to stem from increased levels of stimulus-dependent, additive internal noise [Bernstein and Trahiotis, J. Acoust. Soc. Am. 140, 3540-3548 (2016); J. Acoust. Soc. Am. 144, 292-307 (2018)]. This study reports that a small crew of such listeners also exhibits increased levels of low-level, stimulus-independent, additive internal noise. Detection thresholds were measured in: (1) the NoSπ configuration as a function of masker level; (2) the NρSπ configuration as a function of masker interaural correlation (ρ); (3) "the quiet" for So and Sπ tonal signals. Those measures were combined suitably to yield estimates of stimulus-independent, additive internal noise, separately, at center frequencies of 250, 500, and 4000 Hz. Derived levels of internal noise were found to be elevated, by about 5 dB at 250 and 500 Hz, and by about 9 dB at 4 kHz, for the group of listeners having no more than slight hearing loss and who exhibited deficits in binaural detection. The new findings, taken together with earlier investigations by the authors (which included data obtained from dozens of listeners), provide evidence that such listeners have greater levels of both stimulus-dependent and stimulus-independent, additive internal noise.

Features of sanitary and hygienic characteristics of silvinite complexes

Currently, medical technologies based on natural factors are widely used in practical health care, including the effect of the medicinal properties of the mineral silvinite (natural potassium salts of the Verkhnekamsk Deposit) on the patient’s body. However, there is no regulatory framework for sanitary control of such devices. The aim of the study was to develop methodological approaches to the hygienic assessment of silvinite complexes. The analysis of the current regulations used in carrying out hygienic supervision and preventive measures in the salt structures that are part of the silvinite complexes is carried out. Based on long-term hygienic studies of silvinite structures by the salt treatment Center of Perm medical University. academician E. A. Wagner together with LLC NPK «Medical climate» (Tchaikovsky) developed and implemented sanitary and hygienic requirements for the created salt complexes. It is a complex of structural divisions, including the place of stay and treatment of patients, as well as the salt device. All units must meet the requirements of current sanitary rules and regulations. It is necessary to conduct a thorough survey of the location of the future salt complex. Optimal conditions of the internal environment in silvinite structures are determined by a special air preparation system consisting of air conditioning and cleaning of the external air using a filter-saturator. The special hygienic requirements of the sylvinite furniture in the room, the decoration of walls, ceilings and floors. The room must be equipped with radio equipment and a video camera for monitoring patients. Full expanded hygienic control of the parameters of the medical environment of silvinite premises should be carried out at least once a year according to the following indicators: microclimate parameters, content of multicomponent fine salt aerosol, aeroionic composition of the air environment, radiation background, microbial contamination of the internal environment, noise and light levels. Thus, increasing the use of salt therapy requires further research to improve the sanitary and hygienic control of silvinite complexes.

A Method for the Routine Testing of Digital X-Ray Units

A method for the routine monitoring of digital X-ray diagnostic systems is presented, with assessment of the performance of the X-ray unit and the digital detector by medical staff before the patient arrives. The operability (inoperability) of one part or another is determined from results obtained by indirect assessment of anode voltage, the quantity of electricity, and the gain and the level of internal noise in the X-ray receiver. The time required for testing is generally no more than 5 min.

The internal noise of the visual system and cognitive functions in schizophrenia

Abstract In this study, we report the existence of correlation between the ability of the object perception in the presence of the external noise and the cognitive functioning in schizophrenia. The level of the internal noise of the visual system have been measured for the 41 healthy volunteers and for the 68 schizophrenia patients in the task of distinguishing the location of the rupture of the Landolt ring, under the conditions of external interference. The collected evidence demonstrated an increase in the level of internal noise of the visual system in the patients with schizophrenia.

Optical and psychophysical studies of the visual system of cosmonauts before and after long orbital flights

The changes in the spatial and frequency characteristics of the visual system, visual acuity, and the morphological structures of the macular zone of the retina in cosmonauts and pilots as a result of various gravitational loads were studied. We found that, after long space missions, cosmonauts exhibit a slight but statistically significant decrease in distance visual acuity, a significant decrease in contrast sensitivity mainly in the middle and low spatial frequencies, a decrease in the light sensitivity of the macular zone, a decrease in the optical density of the macular retinal pigment, and thickening of the chorioretinal layer. A pronounced decrease in contrast sensitivity in the low- and medium-spatial-frequency regions but an insignificant one in the high-spatial-frequency region and accordingly a small decrease in visual acuity indicate a disruption of the operation of the nerve structures of the visual analyzer, probably resulting from an increase in the level of internal noise. This increase in the level of internal noise in cosmonauts is associated with a prolonged exposure to microgravity, which causes a disruption of normal blood circulation.

Investigation and improvement of vehicle A/C system compressor noise by 6sigma approach

Recent developments on the vehicle engine noise show that tonal sounds such as a compressor noise is audible if its sound is 7-9dB higher than level of masking noise. Therefore, the acoustic performance of air-condition (A/C) compressors becomes more important for passenger comfort during engine idling and run up. The air conditioning system compressor noise is transmitted to interior cabin in both air-borne paths and structure-borne paths of the compressor pipes. The compressor is driven by the engine and it has also a high interaction with the other components of the system such as Expansion Valve (TXV), Electric cooling fan, Condenser and Evaporator. Therefore, to make a proper NVH design of the air conditioning system in terms of customer satisfaction, it is necessary to consider all these interactions when determining the type of compressor. In this study, the noise problem induced by the A/C system compressor was investigated by Six Sigma approach to determine solution alternatives. The air conditioning system was examined in detail as a cooling process in order to determine individual factors of each system components affecting the compressor noise issue. The most important factors are defined by Cause and Effect matrix to simplify the working model. The effect of each factor/input on internal noise level was measured with the microphones and accelerometers based on the pressure increase in the A/C system. A correlation analysis is performed between these factors/inputs and interior noise level to define high correlated factors of each system component. Besides, a regression analysis is performed to identify the compressor noise generation model (equation describing the noise model) based on these highly correlated factors. A series of experiments is designed (DOE) on these regression model to find out the optimum solution to improve compressor noise problem perceived in the vehicle cabin.

Effects of interaural delay, center frequency, and no more than ”slight” hearing loss on binaural processing: Behavioral data and quantitative analyses

Recent neurophysiological studies concerning “hidden hearing loss” have motivated investigators to attempt to uncover behaviorally-measured auditory deficits that might exist in human listeners who would be categorized via standard audiometry as having normal hearing or, at most, “slight” hearing loss. We hypothesized that behavioral measures of binaural auditory performance could reveal the presence of deficits that may not be discoverable via standard audiometric testing or via measures of monaural processing. That hypothesis was based on the notion that monaural (perhaps, peripheral) deficits would be effectively multiplied via binaural interaction. Groups of listeners, all having no greater than “slight” hearing loss were tested. Binaural detection thresholds were elevated across a wide range of center frequencies for listeners whose absolute thresholds at 4 kHz exceed 7.5 dB HL. Quantitative predictions made via an interaural correlation-based model of binaural processing suggest that the elevated binaural detection thresholds observed for listeners having slightly elevated absolute thresholds stem solely from their having elevated levels of internal noise. They appear to stem neither from reduced sensitivity to signal-dependent changes in information derived from the stimuli as processed internally nor from increased noise along the listener’s putative internal delay line.

A new approach for an FE-model optimization of a MEMS piezoelectric accelerometer for implantable hearing devices

Totally implantable hearing devices have been proposed as a solution to mitigate the constraints related to the presence of external elements in traditional hearing devices. This work reports on a novel approach for the development of a MEMS piezoelectric accelerometer as an implantable sensor for hearing devices. Traditionally these sensors are designed for maximum sensitivity; however, the primary bottleneck for this type of transducer is the internal noise level. Two differential evolution optimization routines were developed. The first used sensitivity maximization whereas the second seeks minimization of the equivalent input noise (EIN). Both methods were applied to different designs of Lead Zirconate Titanate (PZT) MEMS piezoelectric accelerometer in the frequency range of 250 Hz to 8 kHz with layer thickness varying from 0.1 μm to 1 μm. In the latter approach, the sensor's acceleration noise was estimated analytically, considering capacitance and charge response acquired through finite element mode...

Noise level in neonatal incubators: A comparative study of three models

BackgroundPreterm infants usually have to spend a long time in an incubator, excessive noise in which can have adverse physiological and psychological effects on neonates. In fact, incubator noise levels typically range from 45 to 70 dB but differences in this respect depend largely on the noise measuring method used. The primary aim of this work was to assess the extent to which noise in an incubator comes from its own fan and how efficiently the incubator can isolate external noise. MethodsThree different incubator models were characterized for acoustic performance by measuring their internal noise levels in an anechoic chamber, and also for noise isolation efficiency by using a pink noise source in combination with an internal and an external microphone that were connected to an SVAN958 noise analyzer. ResultsThe incubators studied produced continuous equivalent noise levels of 53.5–58 dB and reduced external noise by 5.2–10.4 dB. ConclusionsA preterm infant in an incubator is exposed to noise levels clearly exceeding international recommendations even though such levels usually comply with the limit set in the standard IEC60601-2-19: 2009 (60 dBA) under normal conditions of use.

Simulation of sound transmission through the porous material, determining the parameters of acoustic absorption and sound reduction

Currently, the quality of structural design of a railway coach is evaluated by so called acoustic comfort, which is characterized by achieved levels of internal noise. Therefore, acoustic parameters of car body are being developed purposely. The paper presents the results of the computer simulation of noise transmission through the wagon walls and the use of noise tests from the train running. The acoustic properties of the original and new materials in the care body are compared.

Study of architectural design & acoustic conditions of primary schools in Singapore

Urban noise problems are a growing concern in rapidly urbanizing cities such as Singapore. Studies have revealed that children are particularly susceptible to the harmful effects of noise. Children in Singapore schools are particularly susceptible considering the long hours spent in naturally ventilated classrooms. This study aims to assess the architectural design and planning of schools in Singapore based on their acoustic qualities. External ambient noise, façade sound insulation, and reverberation time were measured in three schools about the architectural design to characterize their acoustic environments and seek areas for improvements. It is revealed that all the classrooms studied experience internal noise levels above the guideline values recommended by the World Health Organization (WHO) of 35 dB, suggesting poor acoustic conditions and harmful effects on children’s’ health, behavior, and learning abilities. Reverberation time standards were only met by the classrooms in one school out of three, implying that speech intelligibility and learning performance are hindered elsewhere. Two overseas case studies are explored to demonstrate how better acoustic environments can be achieved through planning and design in unbuilt schools and abatement strategies for built schools. Architects and planners can adapt and incorporate them into the design of primary schools in Singapore.