Broadband Noise Research Articles

Low-frequency broadband acoustic metamaterial absorber based on nested resonator and synergistic coupled weak resonances

Utilizing absorbers with sub-wavelength thickness for low-frequency broadband noise control is a challenging problem, and rapid on-demand design of structures based on target noise frequency has received continuous attention. In this work, nested cavities are introduced into the typical neck-embedded Helmholtz resonator (NEHR) to obtain the nested neck-embedded Helmholtz resonator (NNEHR), which exhibits better cavity partitioning volume fraction and covers wider sound absorption band. Both theoretical analysis and simulations demonstrate that NNEHR possesses superior acoustic properties: generating an additional absorption peak, lowering the position of the first absorption peak by 11 %, and increasing the absorption coefficient by 4.7 %. Instantaneous velocity fields and thermal-viscous energy dissipation density illustrate that the efficient sound absorption of NNEHR originates from resonant dissipation in the neck and surrounding areas. Furthermore, by combining the theoretical model with genetic algorithms, three sets of NNEHR metasurfaces are optimized. The optimized structures achieve average absorption coefficients of 0.831, 0.913, and 0.885 in the range of 250–550 Hz, 400–1000 Hz, and 500–2000 Hz, with a thickness of only 50 mm, reflecting sub-wavelength, low-frequency broadband sound absorption characteristics. The excellent absorption stems from synergistic coupled weak resonances and higher-order absorption peaks of constituent units, and the overdamping characteristic ensures the realization of the optimal structure with minimal thickness. The contribution of weak resonant units to the total sound absorption performance can be measured by the surface admittance normalized by the total incident area, and the essence of the coupling effect is the strong interaction between units with adjacent absorbing frequencies. The proposed structure exhibits good sound absorption performance and great adjustability, while the genetic algorithm optimization based on the theoretical model demonstrates high efficiency and robustness, providing a methodology for the design and on-demand optimization of low-frequency broadband structures.

Segmentation of MHD modes using Fourier transform, wavelets and computer vision algorithms

Abstract Magnetohydrodynamic (MHD) activity in fusion devices is typically analyzed by examining time-frequency spectrograms obtained from various diagnostics. MHD modes often co-exist with various types of noise and complex patterns generated by other events like pellet injection or active diagnostics. Traditionally, identifying MHD modes has been a manual task, making it labor-intensive. To overcome this issue, this study proposes the use of computer vision (CV) algorithms for noise removal and automatic feature extraction. First, the automatic detection of straight-line patterns is achieved by applying the Hough transform. Then, the discrete wavelet transform is proposed to break down spectrograms into sub-images of different scales, removing broadband noise and pellet injection signatures. The multiscale decomposition is subsequently extended to multiple directions using either 2D Fourier transforms or curvelets, achieving a high signal-to-noise ratio in spectrograms and eliminating undesired frequency sweeps of toroidal Alfvén eigenmodes antenna. Once MHD activity is successfully enhanced, a pipeline of algorithms for ridge detection, thresholding and labeling perform a segmentation of the image, automatically labeling individual modes. This study demonstrates the effectiveness of CV algorithms for the identification of MHD modes. The use of such algorithms may potentially help in the analysis process and the creation of large databases of modes.

Optimizing the Shape of Space-Constrained Silencers Composed of Multiple Straight/Reverse Chambers Using the Simulated Annealing Method

Abstract To address the issue of hearing health problems caused by the broadband noise emitted from space-constrained marine diesel engines on a ship, an efficient silencer equipped at the engine's venting outlet is necessary. In consideration of the space-constrained situation that often occurs in ships, a reverse silencer with multiple chambers is introduced. A mathematical model of eigenfunction is adopted to consider the acoustic effect in high frequencies. An optimization of the silencer will be performed using the acoustic model of an eigenfunction together with the Simulated Annealing (SA) method under space-constrained conditions to achieve the best design. To pursue an efficient silencer design, two types of reverse silencers (Silencers A and B) are adopted to reduce the engine's venting noise. Acoustical models for straight chamber and reverse chamber silencers are checked before optimization. To assure the reliability of the SA scheme, a pure tone optimization at 250 Hz is exemplified. Results in silencers A and B show that the Sound Transmission Loss is approximately maximized at the desired frequency. Thereafter, a broadband noise elimination of engine noise using silencers A and B is performed. Simulated results show that overall noise abatement can be improved when the number of inverse chambers increases. The optimization of space-constrained reverse silencers with multiple chambers using eigenfunction in cooperation with Simulated Annealing (SA) has been accomplished. The overall silencer system's four-pole matrix is used to predict the silencer's acoustical performance of STL, which is achieved by multiplying individual four-pole matrices. With the introduction of the reverse silencer, the hearing health of workers can be protected, and noise pollution can be reduced in industrial settings.

X-Ray Spectral and Temporal Properties of LMXB 4U 1608-52—Observed with AstroSat and NICER

We report results from a detailed study of the neutron star X-ray binary, 4U 1608-52, using observations with AstroSat (Large Area X-ray Proportional Counter/Soft X-ray Telescope) and the Neutron Star Interior Composition Explorer during its 2016 and 2020 outbursts. The 0.7–20.0 keV spectra could be well described with the disk blackbody and thermal Comptonization model. The best-fitting inner disk temperature is ∼1 keV and radius ∼ 22.17−2.38+2.57 –27.19 −1.85+2.03 km and no significant evolution was observed in the disk radius after performing flux and time-resolved spectroscopy. We used a multi-Lorentzian approach to fit the power density spectra and obtained broadband noise variability. We estimated the energy-dependent fractional rms and time lag of the broadband noise, and these variations are quantitatively modeled as being due to the coherent variation of the disk emission and the coronal heating rate. Thus, the rapid temporal modeling is consistent with the longer-term spectral evolution where the inner disk radius does not vary, and instead, the variations can be attributed to accretion rate variations that change the inner disk temperature and the coronal heating rate.

Heterogeneous spatial tuning in the auditory pathway of the Mongolian Gerbil (Meriones unguiculatus).

Sound-source localization is based on spatial cues arising due to interactions of sound waves with the torso, head and ears. Here, we evaluated neural responses to free-field sound sources in the central nucleus of the inferior colliculus (CIC), the medial geniculate body (MGB) and the primary auditory cortex (A1) of Mongolian gerbils. Using silicon probes we recorded from anaesthetized gerbils positioned in the centre of a sound-attenuating, anechoic chamber. We measured rate-azimuth functions (RAFs) with broad-band noise of varying levels presented from loudspeakers spanning 210° in azimuth and characterized RAFs by calculating spatial centroids, Equivalent Rectangular Receptive Fields (ERRFs), steepest slope locations and spatial-separation thresholds. To compare neuronal responses with behavioural discrimination thresholds from the literature we performed a neurometric analysis based on signal-detection theory. All structures demonstrated heterogeneous spatial tuning with a clear dominance of contralateral tuning. However, the relative amount of contralateral tuning decreased from the CIC to A1. In all three structures spatial tuning broadened with increasing sound-level. This effect was strongest in CIC and weakest in A1. Neurometric spatial-separation thresholds compared well with behavioural discrimination thresholds for locations directly in front of the animal. Our findings contrast with those reported for another rodent, the rat, which exhibits homogenous and sharply delimited contralateral spatial tuning. Spatial tuning in gerbils resembles more closely the tuning reported in A1 of cats, ferrets and non-human primates. Interestingly, gerbils, in contrast to rats, share good low-frequency hearing with carnivores and non-human primates, which may account for the observed spatial tuning properties.

Aerodynamic and aeroacoustic design of electric ducted fans

This paper describes the aerodynamic and aeroacoustic design of an electric ducted fan (EDF). A prototype EDF was designed and built with three different rotor-stator sets to operate at design flow coefficients ϕd=[0.60,0.75,0.90]. Computational Fluid Dynamics (CFD) simulations show that changing the design flow coefficient changes the proportions of endwall and blade profile loss, with the ϕd=0.75 design providing the optimum balance. CFD predictions of aerodynamic performance are compared with experimental measurements and show good agreement. Data collected from full annulus Unsteady Reynolds-Averaged Navier Stokes (URANS) CFD simulations is used to predict tonal noise radiation using a numerical solution to Farassat's Formulation 1A, and compare favourably to acoustic measurements in an anechoic chamber. All three EDF iterations show similar levels of broadband noise radiation, although tonal noise radiation decreases with increasing design flow coefficient and results in more favourable Sound Quality Metrics performance. Design flow coefficient is shown to have a first-order impact on both the aerodynamic and aeroacoustic behaviour of the EDF, and it is proposed that an optimal design, encompassing both aerodynamic performance and reduced acoustic impact, can be achieved at design flow coefficients between ϕd=0.75 and ϕd=0.90.

Data Center Air-cooled Chiller Broadband and Tonal Noise Control

Data centers require vast amounts of cooling using large farms of air-cooled chillers as the primary equipment of choice. The amount and nature of noise generated by these chiller farms to the surrounding area can create complaints and the noise control solutions require an understanding and knowledge of both broadband and tonal noise. The dominant noise sources on air-cooled chillers are compressors and condenser fans, each of which produce both broadband and tonal noise spectrums. Therefore, noise control solutions should address both the broadband and tonal aspects of the source. A common noise control solution for chillers serving data centers is a sound barrier wall and while effective at providing overall broadband noise control, does little in targeting tonal issues. However, a sound barrier wall can be supplemented to address these tonal issues by applying source treatments to the chiller, such as a sound cover treatment for the compressors and associated refrigerant piping and sound stacks and intakes for the condenser fans. In addition, barrier walls an create a "pit" application impeding chiller condenser fan discharge air resulting in recirulation and nuisance trips. Using a sound stack source treatment with a barrier wall can help mitigate this issue while providing attenuation.

Broadband Aircraft Noise Attenuation Across Low and High Frequencies Using Structured Materials

Controlling broadband noise throughout the spectrum, from low to high frequencies, is a significant challenge for the aerospace, transportation, and construction industries. Although recent research has focused on low-frequency noise control solutions using acoustic metamaterial designs, the narrow-band resonances of these materials remain a limitation. This paper presents a structured material system which addresses this limitation by proposing a parallel assembly of structured materials, enabling broadening of the resonance frequency band from low to high frequencies. The study involves an arrangement of structured metamaterials and Helmholtz Resonators embedded in a layer of glass wool. By meticulously grouping individual resonant frequencies, the proposed assembly effectively attenuates noise over the frequency range of interest. The present research contributes to the development of lasting solutions for aircraft noise across a broad frequency spectrum, showing promising potential for significant noise reduction within practical constraints.

Standard models of spatial vision mispredict edge sensitivity at low spatial frequencies

One well-established characteristic of early visual processing is the contrast sensitivity function (CSF) which describes how sensitivity varies with the spatial frequency (SF) content of the visual input. The CSF prompted the development of a now standard model of spatial vision. It represents the visual input by activity in orientation- and SF selective channels which are nonlinearly recombined to predict a perceptual decision. The standard spatial vision model has been extensively tested with sinusoidal gratings at low contrast because their narrow SF spectra isolate the underlying SF selective mechanisms. It is less studied how well these mechanisms account for sensitivity to more behaviourally relevant stimuli such as sharp edges at high contrast (i.e. object boundaries) which abound in the natural environment and have broader SF spectra. Here, we probe sensitivity to edges (2-AFC, edge localization) in the presence of broadband and narrowband noises. We use Cornsweet luminance profiles with peak frequencies at 0.5, 3 and 9 cpd as edge stimuli. To test how well mechanisms underlying sinusoidal contrast sensitivity can account for edge sensitivity, we implement a single- and a multi-scale model building upon standard spatial vision model components. Both models account for most of the data but also systematically deviate in their predictions, particularly in the presence of pink noise and for the lowest SF edge. These deviations might indicate a transition from contrast- to luminance-based detection at low SFs. Alternatively, they might point to a missing component in current spatial vision models.

Analytic Prediction of Rotor Broadband Noise with Serrated Trailing Edges with Applications to Urban Air Mobility Aircraft

Theoretical predictions for broadband noise generated by rotors with serrated trailing edges are presented. This study extends Lyu and Ayton’s model for serrated trailing-edge noise to account for factors such as finite span length, the accurate acoustic attenuation rate of trailing-edge noise, modified spanwise wavenumber, and the proper scattering factor. This new model is implemented in the rotorcraft broadband noise tool, UCD‐QuietFly. The validation results demonstrate a satisfactory level of agreement with the experimental data for serrated trailing‐edge noise of a wing section, a hovering rotor, and a forward‐flight rotor. Next, the effects of serration parameters, such as the number of serrations, serrations starting radial location, serration geometry, and serration height, on rotor broadband noise are investigated. For example, it is observed that sine-wave, chopped peak, or sawtooth serration shapes provide the most significant noise reduction among the various shapes considered. Finally, broadband noise reduction through serrations is applied to two urban air mobility aircraft scenarios: a six‐passenger quadrotor and a quiet helicopter. For the quadrotor, serrated trailing edges show a noise reduction potential of over 9 dB, with higher reductions observed at higher tip speeds and fewer blades. A quiet helicopter equipped with serrated blades in forward flight achieves a maximum noise reduction of over 10 dB in the forward direction.

Hydroacoustic analysis of a full-scale marine vessel: Prediction of the cavitation-induced underwater radiated noise using large eddy simulations

This numerical study provides insight into the mechanism of noise generation by a cavitating flow in the wake of a marine propeller under realistic operating conditions, which poses a significant threat to marine ecosystems. We examined a full-scale vessel with an entire hull and an isolated model-scale marine propeller (INSEAN E779A) with a maneuverable rudder under various highly turbulent inflow conditions that strongly affect the spectral characteristics of the radiated noise. Insight into the acoustic behavior was gained by employing a combination of the large eddy simulation (LES) treatment of turbulence and the Schnerr–Sauer volume of fluid cavitation model. The hydrodynamic solution was coupled with the Ffowcs Williams-Hawkings (FW-H) strategy for noise and vibration identification. We focused on the interactions between the characteristic cavitation patterns of marine propellers (sheet, tip, and hub cavities) and the dominant structures of the turbulent wake (tip, root, trailing edge, and hub vortices, as well as the distributed small-scale vorticity). The small-scale topological structures in the swirling wake of a propeller directly manifest in the radiated sound level and affect the intensity of multiple frequency ranges. Quantitative analysis of thrust, pressure fluctuations, and sound pressure levels (SPLs) demonstrates significant effects of blade loading, wake distribution, and cavitation development. The peak and average SPL distributions obtained through LES show lower dominant and higher average frequencies compared to those obtained by the FW-H method. The overall SPL obtained by LES were higher than those calculated using the FW-H acoustic analogy at all microphone locations. The overall noise was dominated by the low-frequency broadband noise, attributed to energetic helical vortices, and narrow-band peaks in the medium-high frequency range that originated from other sources, like cavitation structures.

Autonomous design of noise-mitigating structures using deep reinforcement learning.

This paper explores the application of deep reinforcement learning for autonomously designing noise-mitigating structures. Specifically, deep Q- and double deep Q-networks are employed to find material distributions that result in broadband noise mitigation for reflection and transmission problems. Unlike conventional deep learning approaches which require prior knowledge for data labeling, the double deep Q-network algorithm learns configurations that result in broadband noise mitigations without prior knowledge by utilizing pixel-based inputs. By employing unified hyperparameters and network architectures for transmission and reflection problems, the capability of the algorithms to generalize over different environments is demonstrated. In addition, a comparison with a genetic algorithm highlights the potential for generalized design in complex environments, despite the algorithms tending to predict local maxima. Furthermore, we examine the impact of hyperparameters and environment types on agent performance. The autonomous design approach offers generalized learning while avoiding restrictions to specific shapes or prior knowledge of the task.

A study on multi-channel active sound profiling algorithm for hybrid control of broadband and narrowband noise inside vehicles

The vehicle interior noise consists of both broadband road noise and narrowband engine order noise. Currently, the road noise control (RNC) system and engine noise control (EOC) system operate independently in engineering applications. This paper introduces a novel multi-channel hybrid broadband and narrowband active noise control (HBNANC) algorithm, designed to simultaneously attenuate road noise and engine order noise inside vehicles. On this basis, by integrating an error signal design (ESD) subsystem and a sinusoidal error separation (SES) subsystem, a multi-channel hybrid broadband and narrowband active sound profiling (HBNASP) algorithm is further proposed, enabling specific attenuation or amplification of individual narrowband components to meet subjective acoustic comfort requirements. The paper validates the algorithms’ effectiveness and robustness through simulations, and real vehicle experimental measurements under various conditions. The research offers a comprehensive approach to enhancing the auditory experience inside vehicles, contributing to the advancement of active noise control technology.

Tranylcypromine upregulates Sestrin 2 expression to ameliorate NLRP3-related noise-induced hearing loss.

JOURNAL/nrgr/04.03/01300535-202505000-00030/figure1/v/2024-07-28T173839Z/r/image-tiff Noise-induced hearing loss is the primary non-genetic factor contributing to auditory dysfunction. However, there are currently no effective pharmacological interventions for patients with noise-induced hearing loss. Here, we present evidence suggesting that the lysine-specific demethylase 1 inhibitor-tranylcypromine is an otoprotective agent that could be used to treat noise-induced hearing loss, and elucidate its underlying regulatory mechanisms. We established a mouse model of permanent threshold shift hearing loss by exposing the mice to white broadband noise at a sound pressure level of 120 dB for 4 hours. We found that tranylcypromine treatment led to the upregulation of Sestrin2 (SESN2) and activation of the autophagy markers light chain 3B and lysosome-associated membrane glycoprotein 1 in the cochleae of mice treated with tranylcypromine. The noise exposure group treated with tranylcypromine showed significantly lower average auditory brainstem response hearing thresholds at click, 4, 8, and 16 kHz frequencies compared with the noise exposure group treated with saline. These findings indicate that tranylcypromine treatment resulted in increased SESN2, light chain 3B, and lysosome-associated membrane glycoprotein 1 expression after noise exposure, leading to a reduction in levels of 4-hydroxynonenal and cleaved caspase-3, thereby reducing noise-induced hair cell loss. Additionally, immunoblot analysis demonstrated that treatment with tranylcypromine upregulated SESN2 expression via the autophagy pathway. Tranylcypromine treatment also reduced the production of NOD-like receptor family pyrin domain-containing 3 (NLRP3) production. In conclusion, our results showed that tranylcypromine treatment ameliorated cochlear inflammation by promoting the expression of SESN2, which induced autophagy, thereby restricting NLRP3-related inflammasome signaling, alleviating cochlear hair cell loss, and protecting hearing function. These findings suggest that inhibiting lysine-specific demethylase 1 is a potential therapeutic strategy for preventing hair cell loss and noise-induced hearing loss.

Passive laser power stabilization in a broadband noise spectrum via a second-harmonic generator.

An extremely conspicuous passive power noise stabilization is the first, to the best of our knowledge, discovered in a cavity-enhanced second-harmonic generation (SHG) process. Differing from the SHG as a buffer reservoir, the stronger strength of the nonlinear interaction pushes the power noise suppression level to a higher value and exhibits a broadband noise reduction performance due to the mechanism of dynamic pump suppression in the SHG process. The noise is suppressed to near shot noise limit (SNL) among the kHz to MHz frequency range, accompanied by a maximum noise reduction of 35 dB. A comprehensive demonstration indicates that the nonlinear interaction has no function on the phase noise of fundamental and harmonic waves. A theoretical model is also established that is consistent well with the experimental results. The methodology is beneficial to multiple optical metrology experiments.

Enhancing active noise control through stacked autoencoders: Training strategies, comparative analysis, and evaluation with practical setup

This work is motivated by the imperative to overcome the limitations of conventional active noise control (ANC) techniques. These limitations are rooted in linear systems like the least mean square algorithm when faced with nonlinear distortions in the acoustic environment and system electronics, such as loudspeakers. This work addresses the nonlinear ANC problem by conceptualizing ANC as a deep learning problem. A novel stacked autoencoder (SAE) model is proposed, which is trained to estimate the noise that should be played at a loudspeaker so that the noise received at an error microphone may be attenuated. ANC experiments are initially set up in an anechoic room to study the fundamental performance characteristics of the architecture without extraneous considerations of room impulse response. This is followed by performance analysis in a normal reflective room. Actual noise, comprising broadband and tonal noise, is recorded in both an anechoic room and a normal reflective room. The importance of these experiments in the design process lies in their ability to account for nonlinear effects in actual setups, surpassing the limitations of relying solely on models. Experiment outcomes demonstrate that the proposed SAE model yields a noise reduction (NR) of up to 26.44 dB for wideband noise and up to 35.74 dB for tonal noise types. Additionally, there is an improvement in the extent of the quiet zone provided by the proposed SAE for tonal noise cases as compared to the traditional filtered-x least mean square (FxLMS) technique.

Experimental Assessment of the Flow Recirculation Effect on the Noise Measurement of a Free-Flying Multi-rotor UAS in a Closed Anechoic Chamber

AbstractThe flow recirculation effect on the noise measurement of a multi-rotor unmanned aircraft system (UAS) hovering in a closed anechoic chamber is experimentally characterized in this work. The measured acoustic spectrogram reveals that the recirculation forms around 30 s after the UAS’s take-off, manifested as prominent fluctuations in blade passage frequency and its harmonics. However, the instantaneous overall sound pressure level shows no obvious increase with the development of the recirculation. The result indicates that the recirculation effect does not significantly change the total acoustic energy but increases the uncertainties in the spectral distribution, which can be quantified by spectral entropy. The quantitative analysis of different noise components shows that the recirculation has a minimal effect on the tonal noise levels but slightly increases the broadband noise level out of the rotors’ plane. The results from parametric tests suggest that this broadband noise increment has a positive correlation with the UAS’s hover height but a negative correlation with the UAS’s gross mass. The comparison with existing studies highlights the difference in the recirculation effect on the noise of isolated rotor(s) and free-flying multi-rotor UAS in confined spaces.

Midbrain sensitivity to auditory motion studied with dichotic sweeps of broadband noise

Many neurons in the central nucleus of the inferior colliculus (IC) show sensitivity to interaural time differences (ITDs), which is thought to be relayed from the brainstem. However, studies with interaural phase modulation of pure tones showed that IC neurons have a sensitivity to changes in ITD that is not present at the level of the brainstem. This sensitivity has been interpreted as a form of sensitivity to motion.A new type of stimulus is used here to study the sensitivity of IC neurons to dynamic changes in ITD, in which broad- or narrowband stimuli are swept through a range of ITDs with arbitrary start-ITD, end-ITD, speed, and direction. Extracellular recordings were obtained under barbiturate anesthesia in the cat. We applied the same analyses as previously introduced for the study of responses to tones.We find effects of motion which are similar to those described in response to interaural phase modulation of tones. The size of the effects strongly depended on the motion parameters but was overall smaller than reported for tones. We found that the effects of motion could largely be explained by the temporal response pattern of the neuron such as adaptation and build-up. Our data add to previous evidence questioning true coding of motion at the level of the IC.

Data Reduction Technologies in Prediction of Propeller Noise

High-fidelity computations are often used in predicting the tonal and broadband noise of propellers and rotors associated with Advanced Air Mobility Vehicles (AAMVs). But LES is both CPU and storage intensive. We present here an investigation of the feasibility of reduction methods such as Proper Orthogonal Decomposition as well as Dynamic Mode Decomposition for reduction of data obtained via LES to be used further to obtain additional parameters. Specifically, we investigate how accurate reduced models of the high-fidelity computations can be used to predict the far-field noise. It is found that POD is capable of accurately reconstructing the parameters of interest with 15–40% of the total mode energies, whereas the DMD can only reconstruct primitive parameters such as velocity and pressure loosely. A rank truncation convergence criterion > 99.8% is needed for better performance of the DMD algorithm. In the far-field spectra, DMD can only predict the tonal contents in the lower and mid frequencies, while the POD can reproduce all frequencies of interest.

Accurate determination of impact ionization coefficient ratio and temperature dependence of InGaAs/InP avalanche photodiodes

We propose a broadband noise test method (10 Hz–1 MHz) using a direct power method to measure the excess noise of InGaAs/InP avalanche photodiodes (APDs) with a separate absorption, grading, charge, and multiplication structure. By this means, the impact ionization coefficient ratio (the k value) can be accurately determined. Compared with previous studies, this method can distinguish between low-frequency noise and excess noise, so for an appropriate high frequency spectral range, the excess noise can be analyzed without mixing in other noise information. Three different APDs fabricated in-house with different diameters (12, 25, and 60 µm) were investigated using the above-mentioned method under temperatures varying from −10 to −40 °C. Our findings showed that the k value of the APDs decreased as the temperature decreased. When the temperature decreased to −40 °C, the k value of the 12, 25, and 60 µm diameter diodes was as low as 0.1, 0.3, and 0.2, respectively. The measurement results are consistent with our device design and not only provide useful information for the future selection of device materials and structures but also demonstrate the feasibility of the broadband noise measurement method in the accurate determination of the k value. It indicates that low excess noise can be achieved by utilizing the temperature dependence of k.