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A scale model experimental study is conducted addressing howl occurring during engine tests in the Propulsion Systems Laboratory (PSL) of NASA Glenn Research Center. The aim is to understand the sources of the howling noise and find possible remedies. It is shown that a jet discharged into the model of the PSL entrance duct gives rise to high levels of low frequency noise. This occurs apparently due to duct acoustic modes randomly excited by the jet. Wire-mesh screens of various mesh size and configuration as well as tabs, placed at the end of the model duct, are shown to affect the noise. Comparative effects of these configurations are studied, and some are found to alleviate the low-frequency noise significantly. Based on these results, the equivalent of a 4-mesh screen is recommended as the end treatment for the duct of the PSL facility. [ABSTRACT FROM AUTHOR]

The audio codecs in conventional active noise control systems can only use a high-speed single sampling rate, so the modeling filters and adaptive filters in the system require a longer filter length and the time reserved for iterations is very short, which leads to high computational complexity and difficulty in real-time online computation. To address these problems, a multi-sampling rate system is firstly proposed, which uses extraction and interpolation methods to provide lower sampling rates for active noise control system, reducing the computational complexity while increasing the time available for iterative computation. Based on the minimum mean square algorithm, the secondary sound channel is modeled and a multi-sampling rate double-channel feedback active noise control system is modeled too. Finally, an experimental platform based on seat headrest and digital signal processor is built to experimentally verify the effectiveness of the double-channel active noise feedback control system with multi-sampling rates. The experimental results show that for low frequency noise, the noise reduction system can achieve a noise reduction of about 15 dB in the corresponding frequency band, and the noise reduction is obvious. [ABSTRACT FROM AUTHOR]

In the article, we have proposed to use microwave-fluctuation meters resistant to external intense electromagnetic noise in order to measure the low-frequency (LF) noise of microwave transistors working under these conditions. The transistor located on the board is excited by a low-noise microwave generator, the oscillation amplitude of which, being modulated by the LF noise of the transistor, is measured by a microwave spectrum analyzer. The proposed method was tested on GaN/AlGaN heterotransistors, in whose channels the electron density was formed by spontaneous and piezoelectric polarization. In addition to experimental testing, a theoretical justification for the method is presented. We obtained conditions in which the normalized spectra of oscillation amplitude fluctuations were similar to the normalized LF noise of the transistor current.

This paper presents an extensive characterization of the low-frequency noise (LFN) at room temperature (RT) and cryogenic temperature (4.2K) of 40-nm bulk-CMOS transistors. The noise is measured over a wide range of bias conditions and geometries to generate a comprehensive overview of LFN in this technology. While the RT results are in-line with the literature and the foundry models, the cryogenic behavior diverges in many aspects. These deviations include changes with respect to RT in magnitude and bias dependence that are conditional on transistor type and geometry, and even an additional systematic Lorentzian feature that is common among individual devices. Furthermore, we find the scaling of the average LFN with the area and its variability to be similar between RT and 4.2K, with the cryogenic scaling reported systematically for the first time. The findings suggest that, as no consistent decrease of LFN at lower temperatures is observed while the white noise is reduced, the impact of LFN for precision analog design at cryogenic temperatures gains a more predominant role.

The impacts of retrograde counter doping (RCD) profiles on low frequency noise (LFN) of buried channel (BC) PMOSFETs were investigated. RCD profiles were formed using heavy ion implantation. The RCD profile reduced LFN by more than 50%. The origin of LFN reduction in the RCD device was investigated using TCAD simulation. It was found that both RCD profile itself and the polarity of Si surface contributed to the deeper channel position and larger energy barrier between Si surface and channel position.

The compatibility of the advanced BSIM-CMG to the low frequency noise (LFN) simulation in amorphous IZO TFTs is evaluated over subthreshold and linear regions. Two kinds of devices with SiO2-SiNx and Al2O3 gate insulators are studied. In these devices, the 1/f noise is confirmed as the main component of LFN. Then the dominated origin of the 1/f noise is explained by the $\Delta \text{N}$ model in devices with SiO2-SiNx layers, and by the $\Delta \text{N}$ - $\Delta \mu $ model in devices with Al2O3 layers, respectively. Based on these models, the interficial traps density and the Hooge’s parameters are further calculated, and then applied to the extraction of noise parameters (NOIAeff, NOIB and NOIC) in BSIM-CMG. Compared to the measured data, the simulated results indicate that the noise can be well simulated by the improved BSIM-CMG both in the subthreshold and linear regions of IZO TFTs. It provides a comprehensive evaluation on the suitability of the BSIM-CMG for 1/f noise modelling in amorphous metal oxide TFTs.

This paper summarizes the currently available knowledge on the impact of infrasound (IS) and low frequency noise (LFN) on human health and well-being. This narrative review of the literature data was based on the selected, mostly, peer-reviewed research papers, review articles, and meta-analyses that were published in 1971–2022. It has been focused on the results of epidemiological studies concerning the annoyance related to infrasound and low frequency noise, as well as their impact on the cardiovascular system and sleep disorders. Particular attention was also paid to the latest research results and specific sources of IS and LFN, i.e., wind turbines. Med Pr Work Health Saf. 2023;74(5):409–23.

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We have investigated the effect of Au nanoparticles on the low frequency noise and current-voltage of Au/Cu doped ZnO nanoparticles (Nps) based photodetectors (PDs). Besides, 1/f noise of Cu doped ZnO is studied with and without Au Nps conditions and varied bias voltages. The Au/Cu codoped ZnO Nps showed much lower 1/f noise and higher normalized photocurrent to the dark current ratio (NPDR) than Cu doped ZnO Nps and undoped ZnO Nps. This enhancement may be attributed to the effect of localized surface Plasmon resonances (LSPR). Furthermore, the noise equivalent power represents the minimum optical power that a photodetector can distinguish from the noise and the detectivity (D*) is an important parameter in evaluating the ability of a photodetector to detect a weak signal. These parameters were determined using low frequency noise measurements. The observed low frequency noise performances could be used for Au/Cu codoped ZnO Nps based UV photodetectors. [ABSTRACT FROM AUTHOR]

Exposure to high intensity, low frequency noise (HI-LFN) causes vibroacoustic disease (VAD), with memory deficit as a primary non-auditory symptomatic effect of VAD. However, the underlying mechanism of the memory deficit is unknown. This study aimed to characterize potential mechanisms involving morphological changes of neurons and nerve fibers in the hippocampus, after exposure to HI-LFN. Adult wild-type and transient receptor potential vanilloid subtype 4 knockout (TRPV4 -/- ) mice were used for construction of the HI-LFN injury model. The new object recognition task and the Morris water maze test were used to measure the memory of these animals. Hemoxylin and eosin and immunofluorescence staining were used to examine morphological changes of the hippocampus after exposure to HI-LFN. The expression of TRPV4 was significantly upregulated in the hippocampus after HI-LFN exposure. Furthermore, memory deficits correlated with lower densities of neurons and neurofilament-positive nerve fibers in the cornu ammonis 1 (CA1) and dentate gyrus (DG) hippocampal areas in wild-type mice. However, TRPV4-/- mice showed better performance in memory tests and more integrated neurofilament-positive nerve fibers in the CA1 and DG areas after HI-LFN exposure. TRPV4 up-regulation induced neurofilament positive nerve fiber injury in the hippocampus, which was a possible mechanism for memory impairment and cognitive decline resulting from HI-LFN exposure. Together, these results identified a promising therapeutic target for treating cognitive dysfunction in VAD patients. [ABSTRACT FROM AUTHOR]

In this work, we report on the results of the low-frequency ($1/ {f}$ noise) measurements in vertical Channel-All-Around (CAA) InGaZnO field effect transistors, and the investigation of the $1/\text{f}$ noise was performed for different temperatures, bias, and channel width. A physics-based model for the $1/\text{f}$ noise is also developed. It was found that a unified fluctuation model modified by hopping transport can describe the $1/\text{f}$ noise in InGaZnO FETs. More remarkable, by fitting the $1/ {f}$ measurements data based on this model, the thermal-activated mobility was obtained, and the scattering coefficient between the oxide trapped carrier and channel carriers is extracted for the CAA InGaZnO transistor for the first time. [ABSTRACT FROM AUTHOR]

In this paper, we present metrology and control methods and techniques for electromagnetically actuated microcantilevers. The electromagnetically actuated cantilevers belong to the micro electro mechanical systems (MEMS), which can be used in high resolution force and mass change investigations. In the described experiments, silicon cantilevers with an integrated Lorentz current loop were investigated. The electromagnetically actuated cantilevers were characterized using a modified optical beam deflection (OBD) system, whose architecture was optimized in order to increase its resolution. The sensitivity of the OBD system was calibrated using a reference cantilever, whose spring constant was determined through thermomechanical noise analysis registered interferometrically. The optimized and calibrated OBD system was used to observe the resonance and bidirectional static deflection of the electromagnetically deflected cantilevers. After theoretical analysis and further experiments, it was possible to obtain setup sensitivity equal to 5.28 mV/nm.

We propose an In-Memory Computing (IMC) scheme to implement Fast Fourier Transform (FFT) for noise signal processing using flash memory. By taking advantage of the algorithms of complex number calculation and butterfly operation in FFT, the analyses of low-frequency noise (LFN) and random telegraphy noise (RTN) signals using flash-based IMC were demonstrated successfully, showing the frequency properties of 1/ ${f}$ and 1/ ${f}$ 2, respectively, and matching well with the Matlab numerical calculation. An energy efficiency of 2.7 TOPS/W has been achieved with a dynamic power of 27.7 mW. Our proposed IMC scheme provides an efficient way to enable FFT using a hardware solution and is extendable for other important applications such as image processing and voice recognition. [ABSTRACT FROM AUTHOR]

Total-ionizing-dose (TID) effects are investigated in a highly-scaled gate-all-around (GAA) FET technology using Si nanowire channels with a diameter of 8 nm. n- and p-FETs are irradiated up to 300 Mrad(SiO2) and annealed at room temperature. TID effects are negligible up to 10 Mrad(SiO2). At ultrahigh doses, the TID degradation depends on the irradiation bias condition, with more severe effects observed in longer channel devices. The worst case irradiation condition is when positive bias is applied to the gate. Threshold-voltage shifts are caused by H+-driven generation of interface traps at the oxide/channel interface. In contrast, FETs irradiated under negative gate bias are dominated by transconductance loss and increases of low-frequency noise, suggesting the activation of border traps. Enhanced off-leakage current is observed in n-FETs due to charge trapping in shallow-trench isolation, and in p-FETs due to trap-assisted recombination at STI sidewalls and/or spacer dielectrics at drain/bulk junctions. [ABSTRACT FROM AUTHOR]

New results are presented for the low frequency noise (LFN) characterization of N-MOS and P-MOS from a standard CMOS technology node. The impact of n + and p + polysilicon gate doping on the LFN for N-MOS and P-MOS devices has been investigated. The results demonstrate that the higher p + poly doping of the P-MOS improves the noise performance up to a factor of six. The N-MOS device with higher n + poly doping shows no significant change in the LFN level. It is interesting to note that the effective Coulomb scattering prefactor Ω increased for both devices. [ABSTRACT FROM AUTHOR]

In this letter, degradation of InSnZnO thin-film transistors (TFTs) under positive bias stress (PBS) is evaluated by low frequency noise (LFN) measurement for the first time. With PBS time, the LFN level and trap state density first decrease and then increase, and meanwhile, the dominant fluctuation model changes from carrier number fluctuation model toward to bulk carrier mobility fluctuation model. By considering the interactions of oxygen vacancies, hydrogens and electrons, a degradation model based on the effect of vertical electrical field and water ionization is tentatively proposed and discussed. [ABSTRACT FROM AUTHOR]

Field-effect transistors (FETs) employing two-dimensional (2D) materials have attracted significant attention as a potential alternative to silicon FETs. Among these materials, multilayer rhenium disulfide (ReS 2) has emerged as a focal point of interest owing to its distinctive direct bandgap properties. While there is extensive research on the electrical characteristics and doping, studies on the changes in electrical properties during scale-down for practical applications are insufficient. In this study, we investigated the mobility reduction of ReS 2 FETs at high drain bias of ReS 2 FETs by comparing the different channel lengths of 0.24 μm and 1.5 μm. A reduction in mobility was observed for the shorter channel length, attributed to the enhanced scattering factor at high electric field. To assess the impact of scattering degradation, we conducted a low-frequency noise analysis at drain-source voltage (V DS) = 0.4 V and V DS = 3.0 V for the 0.24 μm length FET. The decrease of the Hooge parameter (α H) at high V DS was observed, which was attributed to an augmentation in Coulomb scattering. This study observed mobility degradation under high electrical fields during scale-down and identified the cause of mobility degradation through low-frequency noise analysis. This contributes to scaling down for practical applications of 2D FETs. • Observation of the mobility reduction in short channel of ReS 2 (TMD) FETs at high drain-source voltage. • Correlation of the smaller Hooge parameter in 1/f noise spectra with the reduced mobility. • Explanation on the mobility degradation by enhanced coulomb scattering at high electric field. [ABSTRACT FROM AUTHOR]

In this paper, a mesa-type 256 × 8 long-wavelength infrared detector is prepared by using InAs/GaSb type-II superlattice (T2SL) material with double barrier structure. The area of each pixel is 25 × 25 μm2. The cut-off wavelength and dark current density of the detector at −0.05 V bias with liquid nitrogen temperature are 11.5 μm and 4.1 × 10–4 A/cm2, respectively. The power spectral densities of low-frequency noise under different temperatures have also been fitted through the Hooge model, and the correlations with dark current are extracted subsequently. The results shown that the 1/f noise of the detector is mainly caused by the generation-recombination current at a low reverse bias, however, when the reverse bias is high, the 1/f noise should be expressed by the sum of Igr noise and Ibtb noise which was ignored in the previous research. The 1/f noise-current correlation assessed in this work can provide insight into the low frequency noise characteristics of InAs/GaSb T2SL long-wavelength detectors, and allow us to understand the main source of low-frequency noise better. [ABSTRACT FROM AUTHOR]

The control of noise propagating along ventilation system ducts has always been an important issue in the building and vehicle sectors. This problem is generally tackled by selecting noise-reducing components with a suitable transmission loss, possibly verifying their effectiveness at a later time. The aim of this article is to characterize the nature of the problem and propose a design approach focusing directly on the perceived effect, that is, on the sound pressure level downstream of the outlet. Because the nature of the noise emission depends on various generation mechanisms, different methods can be applied. Usually, it is more difficult to realize good attenuations at low frequencies because of the limits of sound absorbing materials in such frequency range. For this reason, the ability of reactive components to attenuate the noise below the cut-on frequency will be investigated. This goal is reached by applying the transfer matrix approach to a duct system, with the implementation of the transfer matrices of each single element, and then assembling a system capable of acoustically describing the source and the duct structure. The coupling between the duct system with source and receiver impedances allows one to predict the sound pressure level at a given distance from the outlet. The proposed methodology is implemented in a user-friendly calculation tool with possible academic and professional application. Predictive capability, usability, and intuitiveness of the proposed design procedure are validated against experimental results by real potential users, who express positive feedback. [ABSTRACT FROM AUTHOR]

The expansion of renewable energy usage is one of the major social tasks in Europe and therefore requires acceptance and support from the population. In the case of onshore wind turbines, the complaints of local residents are often interpreted as infrasound disturbances conceivably caused by wind turbine operation. To improve the acceptance for wind energy projects, national standards and regulations need to incorporate such low frequency effects. This contribution presents long-term acoustic measurement data of low frequency noise recorded directly near wind turbines (emission) and inside of residential buildings (immission) with the objectives to identify the signal characteristics and main influential parameters. Different locations (wind farm and individual turbine), wind conditions, and time ranges are evaluated. It is shown that various frequency content below 150 Hz (harmonics of blade passing frequency, etc.) is connected to the rotation of the rotor blade and the operation of the generator. Furthermore, stable atmospheric conditions are determined to be of high importance for the transmission of the characteristic signals. For future research, this work also serves as an example for low frequency sound pressure data during operation and shutdown of wind turbines.

This paper concerns measurements and calculations of low frequency noise for semiconductor layers with four-probe electrodes. The measurements setup for the voltage noise cross-correlation method is described. The gain calculations for local resistance noise are performed to evaluate the contribution to total noise from different areas of the layer. It was shown, through numerical calculations and noise measurements, that in four-point probe specimens, with separated current and voltage terminals, the non-resistance noise of the contact and the resistance noise of the layer can be identified. The four-point probe method is used to find the low frequency resistance noise of the GaSb layer with a different doping type. For n-type and p-type GaSb layers with low carrier concentrations, the measured noise is dominated by the non-resistance noise contributions from contacts. Low frequency resistance noise was identified in high-doped GaSb layers (both types). At room temperature, such resistance noise in an n-type GaSb layer is significantly larger than for p-type GaSb with comparable doping concentration.

Conduction characteristics and low frequency noises in ITO-stabilized ZnO thin film transistors (TFTs) with constant channel width (W=50 μm) and different channel lengths (L=5, 10, 25, 50 and 100 μm) are measured and analysis. Firstly, dependences of threshold voltage and field effect mobility on channel length are examined. With decreasing channel length, the threshold voltage shifts to the negative direction which may attribute to carrier diffusion from source/drain to the intrinsic device channel. In addition, significant degradation of field effect mobility is observed in short channel device which are induced by the presence of series contact resistance. The value of contact resistance has also been extracted. Secondly, the drain current noise power spectral densities (SID) are measured at varied effective gate voltages. The measured noises follow a 1/fγ and y is about -1.1. Moreover, the normalized noises (SID/Ids) are dependent linearly on the inverse of channel length and the slope is about -0.75. Finally, the dominant mechanism of low frequency noise in ITO-stabilized ZnO thin film transistor are examined. The slope of normalized noise against effective gate voltage are extracted, which are varied from -1.03 to -1.84 with decreasing channel length and thus it indicates that ITO-stabilized ZnO TFTs varied from bulk dominated devices to interface dominated devices. By using of ΔN-Δμ model, the normalized noises are simulated by considering of contact resistance. Several noise parameters (flat-band voltage noise spectral density, etc) are extracted and analysis.

Fast and stable switching between states is one of the key factors for the success resistive random access memory (RRAM) development. In an array, wide reset efficiency variation in RRAM cells is found to link to the characteristics of its low frequency noise (LFN) in bit-cell current. Through Monte Carlo simulation on randomly placing conductive filaments (CF), LFN characteristics correspond to the densities of the CF in the RRAM film. Further correlations between LFN features and the reset efficiency are found. In addition, CF topography are found to change after long term cycling tests. A trimming process is proposed to minimize the impacts of stochastic CF generation, leading to increase reset speed.

The negative bias temperature instability (NBTI) mechanisms for Core and input/output (I/O) devices from a 130 nm partially-depleted silicon on insulator (PDSOI) technology are investigated. The I/O device degrades more than the Core device under the same stress electric field due to the different gate oxide processes in these two types of devices. Both the oxide trap charge and interface trap lead to the transfer characteristics degradations of the device after NBTI. While the near interfacial traps result in the increase of low frequency noise (LFN). The trap densities near the silicon/gate oxide interface introduced by stress are extracted using the LFN method. NBTI-induced gate current increase is observed for Core device, but not for I/O device. It is result from the enhanced tunneling process, which is induced by the increase of electric field in the gate oxide after charge trapping at or near the channel interface. The gate width and length dependences of NBTI are observed. The enhanced NBTI degradation observed in short channel and narrow channel device is result from the enhanced NBTI effect at channel edge regions. The larger hole concentration is a main cause of the more serious NBTI degradation at the channel edge regions, including the nearby region of STI sidewall along the channel width direction and the gate edge region along the channel length direction. This conclusion is also verified by the TCAD simulations.

In this paper, we present metrology and control methods and techniques for electromagnetically actuated microcantilevers. The electromagnetically actuated cantilevers belong to the micro electro mechanical systems (MEMS), which can be used in high resolution force and mass change investigations. In the described experiments, silicon cantilevers with an integrated Lorentz current loop were investigated. The electromagnetically actuated cantilevers were characterized using a modified optical beam deflection (OBD) system, whose architecture was optimized in order to increase its resolution. The sensitivity of the OBD system was calibrated using a reference cantilever, whose spring constant was determined through thermomechanical noise analysis registered interferometrically. The optimized and calibrated OBD system was used to observe the resonance and bidirectional static deflection of the electromagnetically deflected cantilevers. After theoretical analysis and further experiments, it was possible to obtain setup sensitivity equal to 5.28 mV/nm. [ABSTRACT FROM AUTHOR]

A comparative combined stress-induced reliability issues between Auger hot carrier and ionizing radiation in double polysilicon bipolar transistor is investigated. The observed differences in the low-frequency noise spectra of devices with different stressing conditions could be interpreted as the differences in the defects-related noise contributions. Low-frequency noise and electrical performance degradation results show that Auger hot carriers greatly induce the atomic hydrogen depassivating the dangling bonds in grain boundaries of emitter polysilicon. However, ionizing radiation damage occurs both at SiO2/Si interfaces and in the oxide layer. 1/f noise characteristics indicate that these two damages have different time dependences. [ABSTRACT FROM AUTHOR]

A pumped storage power plant produces significant noise such that adjacent areas were deemed uninhabitable for the local population. In recent years, the population in the area has increased, and the noise levels are now causing significant distress to the local population. The company operating the power plant and a citizens’ initiative have both commissioned noise measurements. The measurements showed that the continuous pump noise was audible over many kilometers. The A-weighted sound-pressure level of 50 dBA at the next residential area underestimates the perceived noise, given the clear tonal nature in the low frequency range. Interviews of the exposed population, together with detailed “annoyance diaries” by a sample of the residents, proved their high level of annoyance. Their reported observations on distress and sleep disturbances coincide with the time course of the pumping operation. The pumping noise leads to annoyance in a large area, and to considerable nuisance in a smaller one. For the most exposed homes, long-term exposure might be considered a health hazard due to stress and disturbances in sleep quality. Therefore, the operator committed to developing a technical noise control plan. This case shows that a scientific approach within a complex environmental noise problem can foster an agreement about noise protection measures. However, this can only be successful if all involved parties participate in the process. Pilot studies are underway to test the impact of damping material layers on the pipes, the housing of the pipes, and the kind of air vessel solutions between the pumps and the pipes. Int J Occup Med Environ Health. 2019;32(3):401–11

In this letter, strong low frequency noise (LFN) reduction is observed when the buried oxide (BOX)/silicon interface of a Schottky junction gated silicon nanowire field-effect transistor (SJGFET) is depleted by a substrate bias. Such LFN reduction is mainly attributed to the dramatic reduction in Coulomb scattering when carriers are pushed away from the interface. The BOX/silicon interface depletion can also be achieved by sidewall Schottky junction gates in a narrow channel SJGFET, leading to an optimal LFN performance without the need of any substrate bias.

Scaling down effects on conduction and low frequency noise characteristics are investigated in a set of p-type polycrystalline silicon thin-film transistors (poly-Si TFTs) with fixed channel width ( $W=8 \mu$ m) and different channel lengths ( $L=2, 4, 8, 12, ~\text{and}~ 20 \mu$ m). First, short channel effects on threshold voltage, field effect mobility, and sub-threshold swing are examined, while the presence of contact may induce to the degradation of field effect mobility in the short channel devices. Subsequently, the drain current noise power spectral densities are measured at varied effective gate voltages and drain currents. The slopes of normalized noise against effective gate voltage are varied from −1.1 to −2 with decreasing channel length, which indicates that poly-Si TFTs varied from bulk dominated devices to interface dominated devices. Based on $\Delta N-\Delta \mu$ model, the flat-band voltage noise spectral density and coulomb scattering coefficient are extracted. Therefore, measured normalized noises are simulated by considering of contact resistance. Finally, short channel effects on some noise parameters (such as Hooge’s parameter, etc.) are studied and discussed.

Objective: To observe the destructive effects of low frequency noise on periodontium with special emphasis on the alveolar bone. Study Design: Laboratory based randomized control study. Place and Duration of Study: The study was conducted at Anatomy department of Army Medical College, Rawalpindi, in collaboration with animal house of National Institute of Health, Islamabad. The study continued for one year, from Sep 2012 to Aug 2013. Material and Methods: Thirty adult BALB mice were divided into three equal groups. The animals from group A (Control) were exposed to routine outside environment of animal house with normal daily activity going on. The animals from experimental group B were kept in an environment having complete silence with no exposure to external environment. The animals from group C (Experimental) were exposed to low frequency noise of 200 Hz continuously for a period of three months. This sound was generated by an analogue frequency generator having uninterrupted power supply (UPS). At the end of the study, animals were sacrificed and histomorphological changes were observed on the alveolar bone. The data was collected at the end of study and analyzed using SPSS version 21. The results with p-value

Low frequency noises are predominant in neonatal intensive care units (NICUs). Some studies affirm that neonates can perceive noises from 113 Hz, and can therefore be affected by sound sources with high spectral content at low frequencies (e.g., incubator engine, air fan). Other studies suggest that reverberation amplifies noise within incubators. In this paper, the reverberation time (T, T30) within an incubator with standard dimensions was measured in one-third octave bands. To get reliable results, the T was measured in 15 positions at the neonate's ear height, in a room with low T values (to reduce the influence of the room in the results), using an impulsive sound method. Results show a heterogeneous T distribution at the neonate's ear height, with maximum average T differences between positions of 1.07 s. The highest average T of all microphone positions is 2.27 s at 125 Hz, an extremely high mean value for such a small space. As the frequency of electrical devices in America is 60 Hz, some harmonics lay within the one-third octave band of 125 Hz, and therefore may create a very reverberant and inappropriate acoustic environment within the audible spectrum of neonates. As the acoustic environment of the incubator and the room are coupled, it is expected that the results are higher in the NICUs than in the room where the measurements were conducted, as NICUs are more reverberant. Therefore, it is recommended that the T will be limited in the international standards, and that incubator designers take it into account.

Random trapping and detrapping of charged carriers in the vicinity of gate oxide/Si interface has for long been considered as the dominant noise source in Si nanowire (SiNW) FET-based biochemical sensors. Here we extend our previous work presenting a Schottky junction tri-gate SiNWFETs (SJGFET) fabricated on a bonded silicon-on-insulator (SOI) substrate, aiming for ultra-low device noise generation. The SJGFET exhibits near-ideal gate coupling efficiency with a subthreshold swing of ~66 mV/dec. Its gate-referred voltage noise, Svg, are 1.2 × 10−10 and 1.1 × 10−11 V2 μm2/Hz at 1 and 10 Hz, respectively. These Svg values are significantly lower than that of previously reported FET-based sensors. More importantly, Svg of the SJGFET are below the reported voltage noise generated by the oxide/electrolyte sensing interface. Using our SJGFET as the signal transducer can greatly relieve the concern of the adverse effect from the intrinsic device noise in biochemical sensing applications. [ABSTRACT FROM AUTHOR]

In this paper, the forward bias conduction and low frequency noise (LFN) characteristics of GaN Schottky barrier diodes (SBDs) have been measured and studied in the temperature range from 300 K to 450 K. Based on I–V measured results, the temperature dependence of ideality factor and zero bias Schottky barrier height reveals the inhomogeneities of Schottky barriers at the metal-semiconductor (MS) interface. Further study of the LFN measured results shows that the flicker noise (1 / f noise) is the main component of LFN in GaN SBDs. The current dependence of LFN indicates the influences of the Schottky barrier and the series resistance on 1 / f noise, and the temperature dependence of LFN is analyzed according to Luo's model and the barrier inhomogeneities model. [ABSTRACT FROM AUTHOR]

The control of noise propagating along ventilation system ducts has always been an important issue in the building and vehicle sectors. This problem is generally tackled by selecting noise-reducing components with a suitable transmission loss, possibly verifying their effectiveness at a later time. The aim of this article is to characterize the nature of the problem and propose a design approach focusing directly on the perceived effect, that is, on the sound pressure level downstream of the outlet. Because the nature of the noise emission depends on various generation mechanisms, different methods can be applied. Usually, it is more difficult to realize good attenuations at low frequencies because of the limits of sound absorbing materials in such frequency range. For this reason, the ability of reactive components to attenuate the noise below the cut-on frequency will be investigated. This goal is reached by applying the transfer matrix approach to a duct system, with the implementation of the transfer matrices of each single element, and then assembling a system capable of acoustically describing the source and the duct structure. The coupling between the duct system with source and receiver impedances allows one to predict the sound pressure level at a given distance from the outlet. The proposed methodology is implemented in a user-friendly calculation tool with possible academic and professional application. Predictive capability, usability, and intuitiveness of the proposed design procedure are validated against experimental results by real potential users, who express positive feedback.

A new approach for modeling low frequency noise is presented to enable the predictions of noise behavior from negative bias temperature instability (NBTI). The noise model is based on a capture-emission energy (CEE) map describing the probability density function of widely distributed defect capture-emission activation energies. To enlarge the capture-emission energy window and to perform the accurate estimation of the recoverable component of CEE, the Gaussian mixture model (GMM) is applied to the CEE map. This approach provides an efficient identification of noise sources and an in-depth noise analysis under both stationary and cyclo-stationary conditions. [ABSTRACT FROM AUTHOR]

The neonatal intensive care unit (NICU) is a very noisy place as compared to the intrauterine environment. To protect the neonate's health, international guidelines suggest avoiding noise levels above 45 dB in NICUs, but this recommendation is not normally met. The incubator acoustic isolation and the acoustic features of the NICU play important roles in determining the noise measured inside the incubator. In this study, the influence of two types of rooms, one with sound-absorbent covering and the other with reverberant surfaces, on the acoustic isolation of a neonatal incubator was evaluated using three acoustic isolation indexes: the level difference, the apparent sound reduction index, and the standardized level difference. Results show that the acoustic isolation of the incubator is very poor, with a level difference below 11 dBA at all frequencies. At 62.5 Hz, the level difference measured in both rooms exhibits a negative value, indicating that the incubator amplifies the noise coming from the NICU. Isolation of the incubator is poor, and the reverberation time (RT) of the containing room influences RT of the incubator, which is consequently higher when the containing room is reverberant; for example, the incubator RT in the reverberant NICU is 0.72 s higher at 500 Hz than that in a room with sound-absorbent covering.

Chemiresistive graphene sensors are promising for chemical sensing applications due to their simple device structure, high sensitivity, potential for miniaturization, low-cost, and fast response. In this work, we investigate the effect of (1) ZnO nanoparticle functionalization and (2) engineered defects onto graphene sensing channel on device resistance and low frequency electrical noise. The engineered defects of interest include 2D patterns of squares, stars, and circles and 1D patterns of slots parallel and transverse to the applied electric potential. The goal of this work is to determine which devices are best suited for chemical sensing applications. We find that, relative to pristine graphene devices, nanoparticle functionalization leads to reduced contact resistance but increased sheet resistance. In addition, functionalization lowers 1/f current noise on all but the uniform mesa device and the two devices with graphene strips parallel to carrier transport. The strongest correlations between noise and engineering defects, where normalized noise amplitude as a function of frequency f is described by a model of AN/fγ, are that γ increases with graphene area and contact area but decreases with device total perimeter, including internal features. We did not find evidence of a correlation between the scalar amplitude, AN, and the device channel geometries. In general, for a given device area, the least noise was observed on the least-etched device. These results will lead to an understanding of what features are needed to obtain the optimal device resistance and how to reduce the 1/f noise which will lead to improved sensor performance.

Low-frequency noise (LFN) is investigated in a set of indium-zinc-oxide thin-film transistors (IZO TFTs) with fixed channel width (W = 10 μm) and different channel lengths (L = 10, 20, 30, and 40 μm) from sub-threshold, linear to saturation regions. The drain current noise power spectral density is measured as a function of effective gate voltage and drain current. The variation slopes of normalized noise with effective gate voltage are in the range of -1.27 and -1.48, which are close to the prediction of the mobility fluctuation mechanism. According to the ΔN - Δμ model, the flat-band voltage noise spectral density and Coulomb scattering coefficient are extracted. Subsequently, variations of noise with the drain current in the above threshold region are analyzed by considering the band-gap distribution of the tail states. Finally, the BSIM model is also used to model 1/f noise in the IZO TFTs. The noise parameter NOIB is extracted which is inversely proportional to the effective gate voltage. Good agreements are achieved between the simulated and measured results in the linear region.

Hysteresis is a frequently observed phenomenon in the transfer characteristics of thin film transistors. Charge trapping/de-trapping processes of gate oxide and gate-channel interface are commonly known to be the origin of hysteresis and correlated to low frequency noise (LFN) properties of the devices. In this letter, a rapid four-point sweeping method (RFSM) is proposed to reveal the dependence of hysteresis, as well as the distribution of effective trap density on sweeping rate and gate bias range. Based on the RFSM, the hysteresis properties of four-layer MoS2 FETs are studied in detail. The experimental results demonstrate that the hysteresis and trap density at different frequencies and gate voltages, which could further roughly map the traps with different time constants and energy depths, can be obtained by the simple RFSM. Trap density estimated by RFSM shows a comparable range with that extracted from LFN, indicating that the traps inducing the hysteresis may also cause LFN. [ABSTRACT FROM AUTHOR]

In this study, we investigate low frequency noise under the reverse body bias conditions from sub-threshold to moderate inversion regime, in order to experimentally extract the impact of depletion capacitance with the reverse body bias. From 1/ ${f}$ noise measurement for small-area conventional ${n}$ MOSFETs, the reverse body bias is not influenced on the coulomb scattering process, even though the depletion capacitance was influenced by body bias. Furthermore, small gate-to-bulk coupling with smaller depletion capacitance caused by reverse body bias reduced Random Telegraph Noise as well as flat-band fluctuations of gate voltage noise spectral density. These results suggest that reverse body bias is applicable to the low power and high signal-to-noise ratio for low current operation. [ABSTRACT FROM AUTHOR]