Explore the vast range of titles available.

Frequency modulated continuous wave laser ranging (FMCW LiDAR) enables distance mapping with simultaneous position and velocity information, is immune to stray light, can achieve long range, operate in the eye-safe region of 1550 nm and achieve high sensitivity. Despite its advantages, it is compounded by the simultaneous requirement of both narrow linewidth low noise lasers that can be precisely chirped. While integrated silicon-based lasers, compatible with wafer scale manufacturing in large volumes at low cost, have experienced major advances and are now employed on a commercial scale in data centers, and impressive progress has led to integrated lasers with (ultra) narrow sub-100 Hz-level intrinsic linewidth based on optical feedback from photonic circuits, these lasers presently lack fast nonthermal tuning, i.e. frequency agility as required for coherent ranging. Here, we demonstrate a hybrid photonic integrated laser that exhibits very narrow intrinsic linewidth of 25 Hz while offering linear, hysteresis-free, and mode-hop-free-tuning beyond 1 GHz with up to megahertz actuation bandwidth constituting 1.6 × 10 15 Hz/s tuning speed. Our approach uses foundry-based technologies - ultralow-loss (1 dB/m) Si 3 N 4 photonic microresonators, combined with aluminium nitride (AlN) or lead zirconium titanate (PZT) microelectromechanical systems (MEMS) based stress-optic actuation. Electrically driven low-phase-noise lasing is attained by self-injection locking of an Indium Phosphide (InP) laser chip and only limited by fundamental thermo-refractive noise at mid-range offsets. By utilizing difference-drive and apodization of the photonic chip to suppress mechanical vibrations of the chip, a flat actuation response up to 10 MHz is achieved. We leverage this capability to demonstrate a compact coherent LiDAR engine that can generate up to 800 kHz FMCW triangular optical chirp signals, requiring neither any active linearization nor predistortion compensation, and perform a 10 m optical ranging experiment, with a resolution of 12.5 cm. Our results constitute a photonic integrated laser system for scenarios where high compactness, fast frequency actuation, and high spectral purity are required. Stable and tunable integrated lasers are fundamental building blocks for applications from spectroscopy to imaging and communication. Here the authors present a narrow linewidth hybrid photonic integrated laser with low frequency noise and fast linear wavelength tuning. They then provide an efficient FMCW LIDAR demonstration.

Background Low-frequency noise may cause changes in cognitive function. However, there is no established consensus on the effect of low-frequency noise on cognitive function. Therefore, this systematic review and meta-analysis aimed to explore the relationship between low-frequency noise exposure and cognitive function. Methods We conducted a systematic review and identified original studies written in English on low-frequency noise and cognition published before December 2022 using the PsycINFO, PubMed, Medline, and Web of Science databases. The risk of bias was evaluated according to established guidelines. A random-effects meta-analysis was performed where appropriate. To explore the association between low-frequency noise exposure and cognitive function, we reviewed eight relevant studies. These studies covered cognitive functions grouped into four domains: attention, executive function, memory, and higher-order cognitive functions. The data extraction process was followed by a random-effects meta-analysis for each domain, which allowed us to quantify the overall effect. Results Our analysis of the selected studies suggested that interventions involving low-frequency noise only had a negative impact on higher-order cognitive functions (Z = 2.42, p  = 0.02), with a standardized mean difference of -0.37 (95% confidence interval: -0.67, -0.07). A moderate level of heterogeneity was observed among studies ( p  = 0.24, I 2  = 29%, Tau 2  = 0.03). Conclusions Our study findings suggest that low-frequency noise can negatively impact higher-order cognitive functions, such as logical reasoning, mathematical calculation, and data processing. Therefore, it becomes important to consider the potential negative consequences of low-frequency noise in everyday situations, and proactive measures should be taken to address this issue and mitigate the associated potential adverse outcomes.

To address low-frequency noise pollution in substations, this paper proposes a composite sound-absorbing structure based on melamine nano-modified materials. The composite structure incorporates a nanomodified melamine foam core with an aluminum fiberboard outer layer. Experimental studies and simulation calculations evaluate its sound absorption properties, while molecular analysis elucidates the modification mechanism of the nanomaterials. Results indicate that graphene oxide nanomodification increases the composite structure’s sound absorption coefficient from 0.56 to 0.78—a 39% improvement. At a graphene oxide content of 1.25%, the composite structure achieves a 66% higher sound absorption coefficient than conventional substation acoustic barriers (0.47). These findings provide an effective solution for mitigating boundary noise at substation facilities.

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/ f α dependence consistent with α  ~ 0.7, over 9 orders of magnitude in noise frequency. Spin-orbit coupling in gate-defined quantum dots in silicon metal-oxide semiconductors provides a promising route for electrical control of spin qubits. Here, the authors demonstrate that intervalley spin–orbit interaction enables fast singlet–triplet qubit rotations in this platform, at frequencies exceeding 200MHz.

The coherence of electron spin qubits in semiconductor quantum dots suffers mostly from low-frequency noise. During the past decade, efforts have been devoted to mitigate such noise by material engineering, leading to substantial enhancement of the spin dephasing time for an idling qubit. However, the role of the environmental noise during spin manipulation, which determines the control fidelity, is less understood. We demonstrate an electron spin qubit whose coherence in the driven evolution is limited by high-frequency charge noise rather than the quasistatic noise inherent to any semiconductor device. We employ a feedback-control technique to actively suppress the latter, demonstrating aπ-flip gate fidelity as high as99.04±0.23%in a gallium arsenide quantum dot. We show that the driven-evolution coherence is limited by the longitudinal noise at the Rabi frequency, whose spectrum resembles the1/fnoise observed in isotopically purified silicon qubits.

In order to effectively reduce the radiated transformer noise, high sound insulation membrane-type acoustic meta-materials is designed based on CAE method and the main noise reduction frequency is typical 100Hz to make the maximum noise reduction of transformer. After a scale-reduced 500kV transformer semi an-echoic room noise tests comparison, the results show that the membrane-type acoustic meta-materials effectively suppressed the tonal noise of the transformer, providing a solid application foundation for the noise reduction design of transformer in the future.

There is a large amount of medium and low frequency noise in the interior of a certain vehicle type under constant speed driving conditions. Through identifying the noise source, it is determined that it is mainly caused by road noise. The suspension rubber bushing, mounting inching stiffness, and vehicle body sheet metal are optimized, and the interior noise is reduced by 3 to 5 dB (A).

Low-frequency noise constantly affects human health. Traditional passive sound absorption materials or structures require considerable space. The shunt loudspeaker is emerging as a promising low-frequency noise control solution, where the acoustic impedance is adjusted by the shunt circuit without relying on a large back cavity. Compared with the analog shunt loudspeaker, the hybrid digital-analog shunt loudspeaker (HSL) offers greater stability, improved precision, and more convenient adjustment. However, the excellent low-frequency sound absorption capability of HSL is mainly around the tunable sound absorption peak, resulting in a narrow bandwidth. To broaden the sound absorption bandwidth in the low-frequency spectrum, this paper presents a novel low-frequency composite sound absorber with a perforated panel (PP) and a hybrid digital-analog shunt loudspeaker (PPHSL). The theoretical model is first established, and then a genetic algorithm is employed to optimize the parameters. Numerical simulations and experimental studies are carried out to verify the theoretical basis, confirming that the PPHSL can effectively attenuate low-frequency noise.

Low-frequency noise is a critical frequency band that affects people’s physical and mental health. Traditional sound absorption technology is limited in effectiveness at low frequencies due to spatial constraints. Shunt loudspeakers, which consist of a loudspeaker connected to a shunt circuit, have emerged as a rapidly developing solution for low-frequency noise control. However, most shunt circuits are implemented using analog circuits, resulting in poor stability and accuracy due to the presence of parasitic resistance. As a result of this situation, this paper proposes an adjustable low-frequency sound absorber based on digital shunt loudspeakers, where the shunt circuit is realized through digital synthetic impedance based on FPGA technology. Additionally, the acoustic impedance can be easily adjusted by the digital shunt circuit without relying on cavity depth adjustments. Experimental results validate that the proposed sound absorber offers excellent performance in adjustable low-frequency sound absorption, thus confirming its theoretical basis.

The link between jet-installation noise and the near-field flow features of the corresponding isolated jet is studied by means of lattice-Boltzmann numerical simulations. The computational set-up consists of a flat plate placed in proximity to a jet, replicating the interaction benchmark study carried out at NASA Glenn. Installation effects cause low-frequency noise increase with respect to the isolated case, mainly occurring in the direction normal to the plate and upstream of the jet’s exit plane. It is shown that the Helmholtz number, based on the wavelength of eddies in the mixing layer and their distance to the plate trailing edge, predicts the frequency range where installation noise occurs. Based on the isolated jet near field, scaling laws are also found for the far-field noise produced by different plate geometries. The linear hydrodynamic field of the isolated jet shows an exponential decay of pressure fluctuations in the radial direction; it is shown that the far-field spectrum follows the same trend when moving the plate in this direction. In the axial direction, spectral proper orthogonal decomposition is applied to filter out jet acoustic waves. The resultant hydrodynamic pressure fluctuations display a wavepacket behaviour, which can be fitted with a Gaussian envelope. It is found that installation noise for different plate lengths is proportional to the amplitude of the Gaussian curve at the position of the plate trailing edge. These analyses show that trends of jet-installation noise can be predicted by analysing the near field of the isolated case, reducing the need for extensive parametric investigations.