Noise Power Spectral Density Research Articles

Three-dimensional stacked filter: A non-linear filter for series images obtained using a transmission electron microscope

De-noising is an important issue in quantitative high-resolution transmission electron microscopy (HRTEM), and its roles become even more important in applications such as beam-sensitive materials and dynamic characterisations, where the attainable signal-to-noise ratio (SNR) of HRTEM images is frequently limited. In this study, we introduce a three-dimensional stacked filter (3DSF), a novel non-linear filter in which a series of HRTEM images is stacked into a 3D data cube and then treated with the Wiener filter in the 3D domain. In comparison to the traditional Wiener filter, which is widely used for individual images, this filter can accurately estimate the power spectral density of noise and filter images with a higher SNR, fewer artefacts and greater computation efficiency, which works particularly well for HRTEM images containing periodic information and feature similarities in successive micrographs, as demonstrated by simulated and experimental images of graphene and metal–organic framework (MOF). When applied to an ultra-low dose (∼8 e/Å2) HRTEM image stack of MOF MIL-101, the 3DSF could distinguish 40 consecutive frames, revealing the trajectory of subtle lattice shrinkage during the exposure.

Line shape of a delayed self-heterodyne varied with noise types and delays.

The delayed self-heterodyne and self-homodyne (DSH) method is widely used for measuring the line shapes of high coherent lasers. This method results in an autocorrelation of a laser line under the condition of a delay that is much larger than its coherent time. In practice, the delay is often not so long, especially for very narrow linewidth lasers, resulting in errors in rebuilding the laser's line shape from the DSH line. Many papers were devoted to the topic, but most of them are based on the formula for white noise. Analytical formulas of phase variance for 1/f noises are presented in this paper; the DSH line shapes for different noise types and different delay lengths are simulated based on the formulas. Some experimental data of the DSH line, combined with the power spectral density of frequency noise, are processed, showing good agreement with the theoretical analysis. It is indicated that the DSH line shape shows complicated behaviors varied with the delay, with noise types, and with the measurement duration. Such effects are to be compensated for in retrieving the laser's linewidth from the DSH data.

Enhanced statistical detection of random telegraph noise in frequency and time domain

In this work, a new statistical detection method of Random Telegraph Noise (RTN) in the frequency domain is presented. An algorithm for the automated detection of Lorentzian spectra in the noise power spectral density (PSD) of a device is proposed, which enables the processing of a large amount of experimental data. Using 40 nm Bulk CMOS technology as a test vehicle, we demonstrate that the detection of Lorentzian spectra in the noise PSD allows an easier, faster, and often more precise detection of RTN presence compared to the time domain detection.

Impact of the channel doping on the low-frequency noise of silicon vertical nanowire pFETs

In this work, the impact of the channel doping on the low-frequency noise of silicon Gate-All-Around (GAA) Vertical Nanowire (VNW) pMOSFETs on Silicon-on-Insulator (SOI) substrates will be described and discussed. It is demonstrated that the dominant fluctuation mechanism of the 1/f noise in weak inversion changes from mobility (Δμ) to number (Δn) fluctuations with increasing doping density of the silicon nanowires. At the same time, the lowest input-referred voltage noise Power Spectral Density is observed for an intermediate boron concentration of 5 × 1018 cm−3.

Dipolar Noise in Fluorinated Molecular Wires.

We demonstrate a strategy to directly map and quantify the effects of dipole formation on electrical transports and noises in the self-assembled monolayers (SAMs) of molecular wires. In this method, the SAM patterns of fluorinated molecules with dipole moments were prepared on conducting substrates, and a conducting probe in contact-mode atomic force microscopy was utilized to map currents and noises through the probe on the molecular patterns. The maps were analyzed to extract the characteristic parameters of dipolar noises in SAMs, and the results were compared with those of hydrogenated molecular patterns without dipole moments. At rather low bias conditions, the fluorinated molecular junctions exhibited a tunneling conduction and a resistance value comparable to that of the hydrogenated molecules with a six-times-longer length, which was attributed to stronger dipoles formation in fluorinated molecules. Interestingly, conductance (G) in different regions of fluorinated molecular patterns exhibited a strong correlation with a noise power spectral density of SI/I2 like SI/I2 ∝ G−2, which can be explained by enhanced barrier fluctuations produced by the dipoles of fluorinated molecules. Furthermore, we observed that the noise power spectral density of fluorinated molecules showed an anomalous frequency (f) dependence like SI/I2 ∝ 1/f1.7, possibly due to the slowing down of the tunneling of carriers from increased barrier fluctuations. In rather high bias conditions, conductions in both hydrogenated and fluorinated molecules showed a transition from tunneling to thermionic charge transports. Our results provide important insights into the effects of dipoles on mesoscopic transport and resistance-fluctuation in molecules and could have a significant impact on the fundamental understanding and applications in this area.

Analysis and Suppression of Aliased Noises in Time-Division-Multiplexing Interferometric Fiber-Optic Sensor Array

Aliased noises elevate the ultimate noise level of a pulse-triggered time-division-multiplexing (TDM) interferometric fiber-optic sensor array. Here we for the first time present an analytical model of the aliasing factor based on noise power spectral density analysis of the interferometric fiber sensor array. In contrast to the previous reports, the aliasing factor is found not only dependent on the pulse width and the repetition frequency, but also on the rising time of the pulse when matched filters are applied to suppress the noise components out of the main lobe. The model also indicates the explicit scaling rule between the aliasing factor and the number of TDM channels. The model are experimentally validated by measuring the noise floors under different combinations of pulse parameters. Based on the model, an ultra-low noise floor of -114 dB ref rad/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sqrt{\mathbf {Hz}}$</tex-math></inline-formula> (i.e. 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\boldsymbol{\mu}$</tex-math></inline-formula> rad/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sqrt{\mathbf {Hz}}$</tex-math></inline-formula> ) is achieved and up to 6 interferometric sensors can be multiplexed, which, to the best of knowledge, represents the lowest noise level to date for the TDM interferometric fiber-optic sensor array. Our results reveal the prominent influence of the pulse rising time on the aliased noises and provides a practical approach to suppress noise floor of TDM sensor array.

Expansion of the seismological monitoring network on the Kola Peninsula

In July 2021, the seismological monitoring network of the Kola Branch of the Geophysical Survey of the Russia Academy of Sciences was expanded by installing a new seismic station. It is installed in the southern part of the Kola Peninsula in the village of Umba (station code UMBA). The expansion of the seismological network to the south has improved the monitoring detail of the Kandalaksha earthquake source zone. According to modern concepts, the Kolvitsky and Kandalaksha grabens are potentially the most seismically hazardous object in the eastern part of the Baltic Shield. To select the location of the new seismic station, reconnaissance work was carried out. This work included an assessment of the level of background seismic noise. The article presents an analysis of noise power spectral density for seismic station UMBA. A low level of background noise is shown in comparison with the NHNM and NLNM models. The following equipment is used at the seismic station: Guralp 6T analog seismometer (registration range 30 s - 50 Hz) and seismic signal recorder “Ermak-5”. Seismic data is transmitted in near real time to the Kola Regional Processing Center via mobile Internet channels. The ability to register weak seismic events with a local magnitude of less than 2 in the area of the Kandalaksha seismic zone and accurately determine the coordinates of their epicenters is shown by the example of a weak earthquake.

Ambient seismic noise in Cuba: analysis of broadband seismic stations in the Cuban Seismic Network

This paper analyses seismic noise from broadband seismic stations within the Cuban National Seismic Service, focusing on location sites, soil or rock quality at installation sites and the impact of various factors on the noise signature of these seismic stations. A brief technical description of deployed equipment is provided and the methodology for data selection and analysis is presented.The study provides annual performance assessment for each station, considering specific details for each particular case. Likewise, the effect of diurnal/nocturnal and seasonal variations on noise power spectral density (PSD) is analyzed. In addition, plotted graphs show the relationship between the occurrence of extreme weather events, such as hurricanes and cold fronts through Cuban eastern and western regions, respectively, and the increase of noise level, specifically for marine microseisms period band. Finally, the influence of instrumental variations in noise level of seismic stations is characterized.

Noise behavior and reliability analysis of non-uniform body tunnel FET with dual material source

In this paper the noise analysis of Non-Uniform Body TFET with Dual Material Source is performed incepting both the absence and presence of different types of trap charges when the device undergoes various changes in source material (like Si, Ge, and both Si + Ge), and temperature (200 K–400 K) etc. In this study it has been found that the value of drain current noise power spectral density (Sid) for the device is 9.92 × 10−23 A2/Hz and for entire source region having Si and Ge materials the Sid values are estimated as 3.3 × 10−24 A2/Hz and 1.7 × 10−19 A2/Hz, respectively. In the device noise degradation effect is admissible when different performance parameters are accounted as compared to the cases when source material is completely made of Si or Ge. The aforesaid fact has been validated by normalized Sid (Sid/Ids2) vs. Drain current (Id) and Sid (Sid/Ids2) vs. Subthreshold Swing (SS) plot analysis, which clearly indicates the less effect of noise and superior electrostatic coupling in the device. Furthermore, the systematic study for effect of different types of noise under various trap charge distributions is also reported which showed that the device is negligibly effected by donor trap charges. Lastly to explore the reliability part of the device the temperature analysis including the absence and presence of trap charges for the noise behavior illustrated that the effect of increase in noise due to presence of trap charges is more at low temperatures and low gate to source voltages (Vgs) and the dominating noise component is found to be G-R noise.

Dark current and noise analysis for Long-wavelength infrared HgCdTe avalanche photodiodes

In this paper, the temperature-dependent current–voltage (I-V) characteristics (30∼100 K) of planar (n+/n-/p) long-wavelength infrared (LWIR, cutoff-wavelength λc = 11.5 μm at 80 K) HgCdTe avalanche photodiodes (APDs) device were measured and numerical simulated. The parameters in the Okuto-Crowell model were obtained as a function of bandgap and operation temperature, and the results showed that our theoretical model fit well with the experiment. Considering the difficulty of evaluating excess noise factor F at high gains due to the rapid increase in band-to-band tunneling (BBT) current, the effects of BBT on the F measurements were discussed, by means of noise power spectral density (PSD) and noise figure meter. We obtained a low F = 1–1.27@gain (M) = 6 at −2 V and extended the F to a higher gain (M = 23 at −3 V). The bias-dependent dark noise was further studied, and we supposed that the BBT component might partially undergo avalanche multiplication in our LWIR devices. Therefore, suppressing the BBT current by an appropriate annealing process was one possibility to reduce dark current and noise in devices. The method in this paper can provide a reference for performance evaluation in HgCdTe APDs, as well as guidance for designing or optimizing the structure.

Coherent fibre link for synchronization of delocalized atomic clocks.

Challenging experiments for tests in fundamental physics require highly coherent optical frequency references with suppressed phase noise from hundreds of kHz down to μHz of Fourier frequencies. It can be achieved by remote synchronization of many frequency references interconnected by stabilized optical fibre links. Here we describe the path to realize a delocalized optical frequency reference for spectroscopy of the isomeric state of the nucleus of Thorium-229 atom. This is a prerequisite for the realization of the next generation of an optical clock - the nuclear clock. We present the established 235 km long phase-coherent stabilized cross-border fibre link connecting two delocalized metrology laboratories in Brno and Vienna operating highly-coherent lasers disciplined by active Hydrogen masers through optical frequency combs. A significant part (up to tens of km) of the optical fibre is passing urban combined collectors with a non-negligible level of acoustic interference and temperature changes, which results in a power spectral density of phase noise over 105 rad2· Hz-1. Therefore, we deploy a digital signal processing technique to suppress the fibre phase noise over a wide dynamic range of phase fluctuations. To demonstrate the functionality of the link, we measured the phase noise power spectral density of a remote beat note between two independent lasers, locked to high-finesse stable resonators. Using optical frequency combs at both ends of the link, a long-term fractional frequency stability in the order of 10-15 between local active Hydrogen masers was measured as well. Thanks to this technique, we have achieved reliable operation of the phase-coherent fibre link with fractional stability of 7 × 10-18 in 103 s.

A silicon singlet–triplet qubit driven by spin-valley coupling

Spin–orbit effects, inherent to electrons confined in quantum dots at a silicon heterointerface, provide a means to control electron spin qubits without the added complexity of on-chip, nanofabricated micromagnets or nearby coplanar striplines. Here, we demonstrate a singlet–triplet qubit operating mode that can drive qubit evolution at frequencies in excess of 200 MHz. This approach offers a means to electrically turn on and off fast control, while providing high logic gate orthogonality and long qubit dephasing times. We utilize this operational mode for dynamical decoupling experiments to probe the charge noise power spectrum in a silicon metal-oxide-semiconductor double quantum dot. In addition, we assess qubit frequency drift over longer timescales to capture low-frequency noise. We present the charge noise power spectral density up to 3 MHz, which exhibits a 1/fα dependence consistent with α ~ 0.7, over 9 orders of magnitude in noise frequency.

Multi-sensory sound source enhancement for unmanned aerial vehicle recordings

A method to effectively perform sound source enhancement from an unmanned aerial vehicle (UAV)-mounted audio recording system is proposed. The objective of this study is to utilise audio recordings and non-acoustical UAV rotor characteristics to improve rotor noise power spectral density (PSD) estimation accuracy and robustness. The improved rotor noise PSD estimate in turn improves the effectiveness of the rotor noise postfilter, leading to improvement in source enhancement performance. The performance of the proposed source enhancement algorithm is evaluated via experiments, with recordings made in an outdoor environment with an in-flight UAV. Experiment results show PSD estimation accuracy to within 1.5 dB log spectral distortion regardless of the given input conditions, such as the presence of surrounding sound sources. The method also achieves a consistent ∼20–25 dB improvement in source enhancement performance, where the effects of rotor noise from the noisy microphone recordings are significantly reduced. The proposed method also outperforms existing state-of-the-art such as the beamformer with postfilter and speech distortion weighted multichannel Wiener filter frameworks.

Construction strategy of quantum air communication network of imitation goose swarm array

Quantum satellite communication is a research hotspot in the field of quantum communication, which has the characteristics of wide coverage, high communication efficiency and strong security. The construction strategy of the quantum communication network is an essential part of quantum communication. However, the construction strategy of quantum air communication network has not been studied yet so far. In this paper, according to the characteristics of flying goose array and principle of bionics, a simulated wild goose group Λ quantum air communication network topology is proposed, which can be divided into single-head node Λ type and multi-head node Λ type. Based on Greenberger-Horne-Zeilinger (GHZ) state particles, a certifiable QSDC inter-network communication system and a GHZ-EPR quantum teleportation communication system are established. The bit error rate, energy consumption, throughput, and other parameters are studied. After theoretical analysis and experimental measurement, for the single-head node Λ network structure in the environment where the average power spectral density of noise is 2 dB/m, when the communication distance between the head node and the child node is less than 400 m, the bit error rate is less than 0.094; if the communication distance increases from 400 m to 1000 m, the bit error rate increases rapidly, reaching 0.585; when the number of child nodes on one side increases from 2 to 7, the throughput decreases from 110.6 kb/s to 46.45 kb/s. For example, when the total number of nodes is 21, the single-head node Λ network structure saves 32.6% energy but reduces the throughput to 23.9 kb/s. By comparison, the multi-head node Λ network structure with 21 nodes saves 29.3% energy and achieves throughput of 163.4 kb/s. The above studies show that the quantum air network with the structure of imitation goose group array has good network scalability, excellent information security and flexible network structure.

Improved Speech Enhancement Considering Speech PSD Uncertainty

Speech enhancement based on statistical models has been studied for several decades. Recently, the speech enhancement adopting a speech power spectral density (PSD) uncertainty model has been proposed. This approach distinguishes the true speech PSD from its estimate and considers both as random variables. It incorporates a prior distribution of speech spectra and speech PSD estimators to derive the PSD uncertainty-aware counterpart to conventional clean speech estimators, which results in performance improvement. However, the speech PSD uncertainty model has not yet been adopted for parameter estimations such as <inline-formula><tex-math notation="LaTeX"><?TeX $\mathit{a posteriori}$?></tex-math></inline-formula> speech presence probability, noise PSD, and speech power spectra estimations in the speech enhancement framework. In this paper, we incorporate the speech PSD uncertainty model to all the components of the statistical model-based speech enhancement framework by deriving PSD uncertainty-aware counterparts to conventional parameter estimators. Specifically, we derive the <inline-formula><tex-math notation="LaTeX"><?TeX $\mathit{a posteriori}$?></tex-math></inline-formula> speech presence probability (SPP) where the likelihood function for each hypothesis is based on the speech PSD uncertainty. With this <inline-formula><tex-math notation="LaTeX"><?TeX $\mathit{a posteriori}$?></tex-math></inline-formula> SPP, a novel SPP-based noise PSD estimator is derived. Also, we derive the minimum mean-square error (MMSE) estimator for the power spectrum of the clean speech in the current frame under speech PSD uncertainty which is exploited to refine the speech PSD estimator. Finally, the refined speech PSD estimator is incorporated into the spectral gain function based on the speech PSD uncertainty model. The proposed approach showed improved noise PSD estimation performance in terms of the averaged logarithmic error distance, and improved speech enhancement performance in terms of the noise reduction, segmental signal-to-noise ratio, perceptual evaluation of speech quality (PESQ) scores and short-time objective intelligibility in our experiments. It also exhibited comparable performance with a real-time deep learning-based speech enhancement system in terms of the PESQ scores and composite measures for the VoiceBank-DEMAND dataset.

МОДЕРНИЗАЦИЯ СИНТЕЗАТОРОВ ЧАСТОТ РАДИОСТАНЦИИ УКВ РАДИОСВЯЗИ

Trends and prospects for the development of modern systems and complexes of radio communication, features of the use of frequency synthesizers based on the pulse-phase-locked loop in modern radio communications are analyzed. The results of the MF modernization on an integrated circuit HMC704 for transceivers of VHF radio stations are presented. The modeling of the upgraded midrange main units was carried out in the TI PLLatinumSim program. The LPF elements values and power spectral density of the output MF signal phase noise on LMX2594 IC are calculated. Due to the possibility of using a high comparison frequency in a frequency-phase detector, it was possible to improve the weight and size indicators, increase the speed and purity of the output signal spectrum of upgraded MF, which was confirmed by the results of modeling and experimental studies of the current synthesizer layout.

Frequency Noise Characterization of Diode Lasers for Vapor-Cell Clock Applications

The knowledge of the frequency noise spectrum of a diode laser is of interest in several high-resolution experiments. Specifically, in laser-pumped vapor cell clocks, it is well established that the laser frequency noise plays a role in affecting clock performances. It is then relevant to characterize the frequency noise of a diode laser since such measurements are rarely found in the literature and hardly ever provided by vendors. In this paper, we describe a technique based on a frequency-to-voltage converter that transforms the laser frequency fluctuations into voltage fluctuations. In this way, it is possible to characterize the laser frequency noise power spectral density in a wide range of Fourier frequencies, as required in cell clock applications.

Influence of Analog-To-Digital Conversion and Decimation Parameters on the Signal-To-Noise Ratio in the Radar Path

Introduction. The digital representation of received radar signals has provided a wide range of opportunities for their processing. However, the used hardware and software impose some limits on the number of bits and sampling rate of the signal at all conversion and processing stages. These limitations lead to a decrease in the signal-to-interference ratio due to quantization noise introduced by powerful components comprising the received signal (interfering reflections; active noise interference), as well as the attenuation of a low-power reflected signal represented by a limited number of bits. In practice, the amplitude of interfering reflections can exceed that of the signal reflected from the target by a factor of thousands.Aim. In this connection, it is essential to take into account the effect of quantization noise on the signal-tointerference ratio.Materials and methods. The article presents expressions for calculating the power and power spectral density (PSD) of quantization noise, which take into account the value of the least significant bit of an analog-to-digital converter (ADC) and the signal sampling rate. These expressions are verified by simulating 4-, 8- and 16-bit ADCs in the Mathcad environment.Results. Expressions are derived for calculating the quantization noise PSD of interfering reflections, which allows the PSD to be taken into account in the signal-to-interference ratio at the output of the processing chain. In addition, a comparison of decimation options (by discarding and averaging samples) is performed drawing on the estimates of the noise PSD and the signal-to-noise ratio.Conclusion. Recommendations regarding the ADC bit depth and sampling rate for the radar receiver are presented.

Assessment of Fuel Cells’ State of Health by Low-Frequency Noise Measurements

We proposed applying low-frequency (flicker) noise in proton-exchange membrane fuel cells under selected loads to assess their state of health. The measurement set-up comprised a precise data acquisition board and was able to record the DC voltage and its random component at the output. The set-up estimated the voltage noise power spectral density at frequencies up to a few hundred mHz. We observed the evolution of the electrical parameters of selected cells of different qualities. We confirmed that flicker noise intensity varied the most (more than 10 times) and preceded changes in the impedance or a drop in the output DC voltage (less than 2 times). The data were observed for current loads (from 0.5 to 32 A) far from the permissible load. We deduce that the method can be utilised in industrial conditions to monitor the state of health of the selected cells by noise analysis. The method can be used in real-time when the flicker noise is measured within the range of a few Hz and requires a reasonable amount of averaging time to estimate its power spectral density. The presented method of flicker noise measurement has considerable potential for use in innovative ways of fuel cell quality monitoring.

A Novel Signal Design and Performance Analysis in NavCom Based on LEO Constellation.

The mega-launch of low Earth orbit satellites (LEOs) represents a critical opportunity to integrate navigation and communication (NavCom), but first, challenges related to signal design must be overcome. This article proposes a novel signal scheme named CE-OFDM-PM. Via research on the in-band or adjacent band, it was found that the proposed signal scheme was suitable for S-band and had a wide normalized power spectrum density (PSD), high peak-to-side lobe ratio (PSR), and multiple peaks in autocorrelation. In an analysis of the simulation performance evaluation in navigation and communication, it is found that the proposed signal scheme has the potential for high accuracy, a code tracking accuracy of up to 0.85 m, a small mutual influence between the proposed signal scheme and other schemes, excellent anti-interference properties, and a better performance at both short and long distances in terms of its anti-multipath capability. Furthermore, the proposed signal scheme shows the ability to communicate between satellites and the ground and is outstanding in terms of its bit error rate (BER), CNR, and energy per bit to noise power spectral density ratio (Eb/N0). From the technical, theoretical, and application perspectives, our proposed signal scheme has potential as an alternative scheme in future BDS, PNTs, and even 5G/B5G.