Frequency Noise Research Articles

GHZ protocols enhance frequency metrology despite spontaneous decay.

The use of correlated states and measurements promises improvements in the accuracy of frequency metrology and the stability of atomic clocks. However, developing strategies robust against dominant noise processes remains challenging. We address the issue of decoherence due to spontaneous decay and show that Greenberger-Horne-Zeilinger (GHZ) states, in conjunction with a correlated measurement and nonlinear estimation strategy, achieve gains of up to 2.25 decibel, comparable to fundamental bounds for up to about 80 atoms in the presence of decoherence. This result is unexpected because GHZ states do not provide any enhancement under dephasing due to white frequency noise compared to the standard quantum limit of uncorrelated states. The gain arises from a veto signal, which allows for the detection and mitigation of errors caused by spontaneous emission events. Through comprehensive Monte Carlo simulations of atomic clocks, we demonstrate the robustness of the GHZ protocol.

Throughput improvement in ACO-OFDM-based VLC systems using noise cancellation and precoding techniques

One of the primary challenges faced by visible light communication (VLC) systems employing optical orthogonal frequency division multiplexing is the peak-to-average power ratio (PAPR). This study is dedicated to designing, simulating, and evaluating bit error rate (BER) and PAPR reduction methods tailored for the VLC broadcasting system. The asymmetric clipped optical orthogonal frequency division multiplexing (ACO-OFDM) scheme is highlighted in this work for its impressive performance. Therefore, the proposed PAPR mitigation methodologies applied to ACO-OFDM. The proposed PAPR reduction strategy involves 5 distinct precoding methodologies. The PAPR was mitigated by 3.485 dB after applying the DST precoding methodology. Still, the WHT precoding methodology can achieve PAPR reduction by 1.131 dB, without BER performance degradation, with respect to the conventional ACO-OFDM system. Furthermore, the work addresses another challenge in VLC systems: the bit error rate (BER). This is accomplished by introducing approaches to Time Domain Noise Cancelation and Frequency Domain Noise Cancelation (FDNC). The BER performance of these 2 receiver models is nearly the same. The simulation results indicate the system performance enhancement after applying noise cancellation approaches by 1.65 dB at the 4-QAM modulation scheme and 2.97 dB at the 1024-QAM modulation scheme. The 16-QAM modulation scheme, after applying DST and WHT methodologies alongside noise cancellation approaches, can enhance both PAPR by 20.83% and 6.76%, but the Eb/N0 performance enhancement by 10.10% and 14.64%, respectively. Additionally, the effectiveness and validity of the proposed schemes are verified by comparing them with relevant literature reviews on PAPR reduction techniques and selecting an optimal choice among them.

Harmonic analysis of phase-sensitive optical time-domain reflectometer

This study innovatively proposes a method of using harmonics to mitigate the influence of fading noise in Phase-Sensitive Optical Time-Domain Reflectometer (Φ-OTDR). Numerical modeling was conducted to investigate the behavior of the Φ-OTDR. A section optical fiber is coiled around a PZT (piezoelectric transducer). By applying a signal to the PZT, it emulates an external vibration. The response of the simulated vibration was extracted using phase demodulation algorithm. In the response spectrum of the vibration, the fundamental frequency may be submerged because of the fading noise, causing the useful information to be obscured. However, the region impacted by fading noise in the fundamental frequency is unaffected in certain harmonic components. Thus, information from the harmonics can be used to compensate for the missing information in the fundamental frequency. By analyzing multiple harmonic components, the accuracy of vibration detection and localization can be improved. Experiment was performed to corroborate the findings, and the results demonstrated good consistency with the simulated data. Both the simulation and the experiment proved that considering harmonics can enhance the measurement accuracy of Φ-OTDR. This discovery provides new insights and methods for the application of Φ-OTDR.

Design of compact signal source with reduced phase noise for airborne pulse Doppler RF sensor

Abstract In this article, a low phase noise signal source to be used as local oscillator in pulse Doppler radio frequency (PDRF) sensor is proposed. Innovative design techniques for realization of the low phase noise frequency source using phase-locked loop (PLL) and dielectric resonator (DR) are presented. Qualitative investigations have been carried out on the effect of phase noise in PDRF sensor performance. An X-band vibration resistant PLL-based frequency source with phase noise better than −95 dBc at 1 kHz frequency offset has been designed here. It also presents the design of a 7.6 GHz low phase noise, vibration resistant DR oscillator. Systematic analysis of the key design aspects, their thermal-vibrational stability, and ease of integration with hybrid microwave integrated circuits have been disclosed. A prototype board is fabricated, assembled in a compact mechanical enclosure of dimension 55 × 55 × 15 mm3. Finally, developed module is experimentally validated under 7.6 g rms magnitude random vibration test in three axes and compared results with other state of-the-art similar works. The comparison clearly shows the merit of present research work over other similar existing works.

Frequency noise suppression of the high-power pumping laser in the SERF atomic magnetometer

Abstract A high-sensitivity SERF atomic magnetometer based on a noise-suppressed master oscillator power amplifier (MOPA) system is demonstrated. The spectrum and frequency noise of the laser are measured and it is proved that the frequency noise in the MOPA system is affected by the amplified spontaneous emission (ASE) stimulated from the power amplifier. The frequency noise of the MOPA system is decreased by filtering out the ASE background in the spectrum through a bandpass filter. The sensitivity of the SERF atomic magnetometer is improved by using the frequency noise-suppressed MOPA system as a pumping laser. This method can also be applied to other precision measurement fields based on the MOPA systems that have high requirement for frequency noise of laser.

Transient flow and noise characteristics of vortex-turbulence-noise interaction in centrifugal pump

Centrifugal pump operation noise is an avoidable common phenomenon in engineering practices, and its characteristics are closely influenced by the flow characteristics of the fluid. In this paper, a numerical simulation of centrifugal pump operation with different flow rates is carried out using the detached eddy simulation turbulence model and compared with the experimental results. Then the noise source and far-field radiated noise characteristics of the centrifugal pump are investigated using Lighthill’s analogy. The results show that the noise of centrifugal pump is closely related to the flow characteristics of impeller, especially the generation and development of vortex. The relationship between turbulent kinetic energy (TKE) and vortex is complex, involving the generation, development and shedding of vortex. The influence of flow rate variation on vortex structure in impeller is studied by vortex transport equation. It is found that the relative vortex stretching (RVS) term is the main driving force of vortex distribution. The distribution of the Coriolis force (CORF) term is mainly concentrated in the inlet and outlet areas of the flow channel, which is related to the rotational motion of the impeller and the dynamic characteristic of the fluid. The power spectral density inside the impeller is mainly concentrated in the low frequency region, indicating that the low frequency noise component is dominant in energy. The directivity curve of far-field noise pressure level is influenced by hydrodynamic effect, impeller rotation direction and pump design structure, and will have a certain deviation. The spectral curve analysis of velocity, vorticity, pressure and sound pressure level shows that these physical quantities have strong correlation on the spectrum, in which the low frequency component is large, and the high frequency component is complex and volatile.

Analysis of Low-Frequency Sound Absorption Performance and Optimization of Structural Parameters for Acoustic Metamaterials for Spatial Double Helix Resonators

Low-frequency noise absorbers often require large structural dimensions, constraining their development in practical applications. In order to improve space utilization, an acoustic metamaterial with a spatial double helix, called a spatial double helix resonator (SDHR), is proposed in this paper. An analytical model of the spatial double-helix resonator is established and verified by numerical simulations and impedance tube experiments. By comparing the acoustic absorption coefficients of the spatial double-helix resonator, it is shown that the results of the analytical model, the numerical model, and the experiments are in good agreement, proving the accuracy of the theoretical model. The effects of different structural parameters on the peak sound absorption coefficient and resonance frequency are quantitatively revealed. The impedance variation law of the model is obtained, and the resistance and reactance distributions at the resonance frequency are analyzed. In the optimization model, the Back Propagation (BP) network is used to construct the mapping between the structural parameters and the resonance frequency and sound absorption coefficient, and this is used as the constraints of the equation, which is combined with Wild Horse Optimization (WHO) to establish the BP-WHO optimization model to minimize the volume of the spatial double helix resonator. The results show that, for a given noise frequency, the optimized structural parameters enhance the space utilization without affecting the performance of the space double helix resonator.

Watt-level single-frequency optical parametric oscillator around 2 µm.

A single-frequency optical parametric oscillator (OPO) operating in the wavelength range around 2 µm is reported. The OPO comprises a periodically poled LiNbO3 (PPLN) crystal for quasi-phase matching and a four-mirror ring-cavity resonant to the signal. The OPO signal and idler are tuned from 1.89 to 2.05 µm and from 2.21 to 2.42 µm, respectively, by changing the crystal temperature. Output powers in excess of 2 W are demonstrated at a pump power of 9 W for both the signal and idler over all of the respective tuning ranges. A detailed characterization of the intensity and frequency noise is presented. The OPO exhibits an integrated intensity noise below 0.1% and a linewidth of ∼58 kHz for an observation time of 1 ms. The reported performance makes this source an ideal candidate for the generation of squeezed light around 2 µm via cascaded second-harmonic generation (SHG) and parametric downconversion (PDC).

Modeling and characterization of low frequency noise in self-aligned top-gate coplanar IGZO thin-film transistors

Abstract A modified low-frequency noise (LFN) model was proposed to accurately estimate the quality of the gate dielectric in self-aligned top-gate (SA TG) coplanar structure indium–gallium–zinc oxide (IGZO) thin-film transistors (TFTs). The proposed LFN model was derived by modifying the conventional carrier number with correlated mobility fluctuation model considering the peculiar characteristics of SA TG coplanar IGZO TFTs such as the channel length reduction due to the diffusion of hydrogen atoms or oxygen vacancies from the source/drain to the channel, as well as the relatively large source/drain parasitic resistance. The proposed model was validated by demonstrating that the measured LFN values were in good agreement with the predicted values from the proposed model for all SA TG coplanar IGZO TFTs with SiO2 gate dielectrics deposited under different plasma-enhanced chemical vapor deposition (PECVD) power densities. The near-interface gate dielectric trap densities extracted from each TFT using the proposed LFN model revealed a clear increase as the PECVD power increased, which is considered a major cause of poor positive-bias-temperature-stress stability of the SA TG coplanar IGZO TFT with SiO2 gate dielectric deposited under high PECVD power conditions.

Study of cosmic rays with energies above 5 EeV using radio method

At the Yakutsk array in 1986 regular measurements of radio emission produced by relativistic air shower particles were started. After monitoring of background noise in the array area frequency of 30–35 MHz was chosen, since noise level is minimal in this frequency range. During this time, air showers with highest energies of 100 EeV were registered. By using hybrid measurements of charged particles, Cherenkov light and radio emission it was shown that signal amplitude proportional to air shower energy and shape of lateral distribution at sea level correlates with the depth of maximum development. Using the obtained characteristics, atomic weight of primary particles that generated air shower was estimated within QGSjetII-04 framework simulation.

Characterization of heterodyne optical phase locking for relative laser frequency noise suppression in differential measurement

Characterization of heterodyne optical phase locking for relative laser frequency noise suppression in differential measurement

Aeroacoustic analysis of fixed- and variable-pitch controlled multirotors and noise reduction via rotor phase control

This research conducts a comparative analysis of the aerodynamic and aeroacoustic characteristics of fixed-pitch and variable-pitch controlled multirotors (i.e., revolution per minute and collective pitch control). The study encompasses hovering and forward flight conditions, considering wind gust effects. Specifically, high-resolution time-frequency analysis is conducted to investigate the interference and modulation effects of multirotor noise. The analysis reveals significant variations in spectral characteristics depending on the control method. Notably, the frequencies of tonal noise from variable-pitch controlled multirotor do not exhibit short-periodic modulation, in contrast to those of fixed-pitch controlled multirotor. Considering the distinctive spectral characteristics of variable-pitch controlled multirotor, this study explores the effectiveness of noise reduction in variable-pitch controlled multirotor by implementing rotor phase control methods. To validate the noise reduction in time series simulations, a deep learning model is employed to determine the dynamically optimized rotor phases. A multilayer perceptron neural network was trained to derive the optimal rotor phase angles over time, considering the target observer points and flight conditions. The results demonstrate a substantial reduction in noise at the target observer points.

Selective noise control by adaptive bandpass filter and secondary aural cartilage source

When a transducer is put on an aural cartilage, the transmitted vibration generates sound in the external auditory canal (i.e., cartilage conduction). Different from conventional earphones, the cartilage conduction technology enables the use of earphones without occluding the canal. However, the opening ears allow both desired sounds (e.g., speech) and unwanted noises to reach the eardrums. To minimize only the noise selectively, our study introduced filtered-x least means square algorithm combined with adaptive bandpass filter (ABF-FxLMS). The ABF-FxLMS stored the narrowband noise separating from a speech and transferred it to the FxLMX as a secondary sound source produced via the cartilage conduction. The adaptive bandpass filter actively adjusted to changes in the center frequency of noise, and the ABF-FxLMS ensured effective noise reduction permitting the passing of speech. Our simulations demonstrated achieving approximately 19 dB reduction in the noise while keeping the speech quality. A coming cartilage conduction device will enable conversations in noisy environments.

Numerical study of acoustic metamaterial made of Helmholtz resonators with complex necks for low frequencies noise attenuation

In this paper, an acoustic metamaterial consisting of Helmholtz resonators with complex necks is proposed for low frequency noise reduction. The resonators are made of a cavity and a complex neck, which is a periodic succession of necks with small and large diameters. The acoustic attenuation performance of the proposed metamaterial design is demonstrated using finite element method. For such a shaped neck, the sound absorption coefficient presents multiple peaks. With a succession of N small and (N - 1) large neck diameters, N peaks in the sound absorption coefficient are obtained. By increasing the number of successions, the number of peaks increases. At the peaks, the surface acoustic impedance of the metamaterial nearly matches with the characteristic impedance of the air. This makes the sound absorption coefficient being nearly 100%. Keeping the same cavity volume, we increase the number of sound absorption peaks by the complex shape of the neck, while the classic Helmholtz resonator presents only one peak.

Noise modeling of UAM around the urban vertiport

The present study aims to investigate the noise distribution around urban vertiport caused by UAM(Multicopter) and helicopter. Noise modelings were carried out using SoundPLAN software at the some vertiports in Seoul, Korea. Sound source model of UAM and helicopter were used as a form of hemisphere. Noise predictions were undertaken with three different operations including depart, level flight and landing. In order to evaluate the noise impact on the buildings around the vertiport, noise levels at the outer wall of nearby buildings were calculated as the three noise units including Leq, Lmax and Lden. Also, noise maps were drawn around the vertiport. As a result, it was found that average noise level of UAM is approximately 12 dB lower than the helicopter noise levels. Regarding the noise frequency distribution, most high noises are made at the mid-frequencies during landing hours while low frequency noise level around 63 Hz was dominant at take-off time.

Effect of scatterer shape, opening angle and periodicity on sound attenuation by local resonating sonic crystal

Noise Control has become critical and demanding task for acoustic engineers due to continuous Technological developments in construction, transportation, and industries. These developments have raised the level of low frequency noise in densely populated areas. Unfortunately, there cannot be sufficient noise reduction with traditional acoustic materials. However, new research has shown that the manipulation of sound waves and drastic reduction in sound transmission can be possible using periodic structure known as Sonic Crystals (SnC). This study describes the eigenfrequency analysis to investigate the effect of different shapes, periodicities, and opening angles of scatterers in a Local resonating Sonic Crystal (LRSnC). The Block-Floquet boundary condition is applied to the unit cell of the LRSnC, using the Finite Element Method to study the complex acoustic wave interactions throughout the structure. An acoustic module has been applied to find the band gap and to simulate transmission loss spectra in COMSOL Multiphysics. Results show that shape, opening angle and periodicity effect the band gap and transmission loss significantly. Based on these results, it is possible to develop advanced SnC with a wider band gap and higher sound attenuation in the lower sound frequency range by carefully considering these factors.

Target setting and practical Improvement for sound quality of electric vehicles

For electric vehicles, because there is no masking effect of combustion engine noise, the middle frequency and high frequency noise of electric components become distinct and annoying. Electric driven unit, electric compressor, electric pump, and motors of seat adjusting device are always major noise sources for electric vehicles. Some of those noise signals are steady, some are transient and some are time-variable. So only SPL is hard to reflect human's true perception. Psychoacoustic metrics, such as loudness, roughness, sharpness, and tonality, is hard to evaluate all complicated NVH phenomenon of electric vehicles using one metrics. In this paper, the author tested different operation noises of above-mentioned electric components of several popular EVs, and finalized proper psychoacoustic metrics for different operations based on loudness, modulation, tonality and objective evaluation. Furthermore, the author studied target setting for dedicated metrics, and effective improving methods for sound quality of EVs from the point of source and path. For example, effective designing for acoustic encapsulation of EDU and electric compressor, and good insulation performance designing for dash inner and trunk floor trim. Keywords: Sound quality, Psychoacoustic metrics, electric vehicle, objective evaluation, target setting

Expanding road noise cancellation to higher frequencies

Active vehicle Road Noise Cancellation (RNC) systems effectively reduce persistent vehicle rumble and booming noise which is very difficult to control with traditional NVH measures, particularly at low frequencies. Therefore, more and more vehicles are adapting RNC systems in their production applications. Most current RNC systems cancel low frequency structure-born noise, which is typically below 400 Hz. Although it provides appreciable noise attenuation, remaining high frequency noise contents still requires mitigation for a premium cabin experience. This study targets a next generation RNC system development which extends noise cancellation frequency range up to 1 kHz. High frequency RNC system (HF-RNC) development begins with analyzing limiting factors of the current RNC systems. Theoretical and practical limitations of the current system are discussed. Then, new technology and enablers to overcome those limitations are introduced. New enablers investigated herein in includes feedforward microphones, low latency system, headrest speakers and microphones, and head tracking system. HF-RNC system architecture is defined to comprise extended features and enablers. Low latency software is ported into a development platform which is based on a commercial DSP. The new HF-RNC system demonstrates noise cancellation up to 1 kHz when applied to an electric vehicle.

Impact noise from roof terrace - elastic ceiling in Sylomer hangers and free ceiling

Modern houses and apartments are built with flat roof and often the upper apartments contain a roof terrace. Impact noise has been measured from a roof terrace with floating floor on mineral wool, a good wooden construction with 2 layers of gypsum stiff fastened in the ceiling. This measurement shows L'n,w of 55 dB, and make it necessary with better solution for ceiling to achieve L'n,w 53 dB or better. Two measurements for improved situation in different buildings are done with ceiling in Sylomer hangers and with free ceiling. These two situations show L'n,w of 50 and 46 dB. The measurement of solution with free ceiling shows the lowest value of L'n,w for these two elastic solutions and also has the lowest levels in the low frequency range. This paper will show that for roof terrace the need for elastic or free ceiling is important. Concerning annoyance and low frequency noise, solution with free ceiling is to be preferred in future projects. There has been no complaining about impact noise from roof terrace, for the situation with free ceiling. For the situation with Sylomer hangers people living there hear some noise, but they have not complained about that.

Centrifugal pump impeller wheel inspired acoustic metamaterial for low frequency sound absorption

Addressing low-frequency noise is a significant concern within the realm of acoustics and noise management. Labyrinthine channel based acoustic metamaterials have been proved to control low frequency noise using local resonance effect and thermoviscous dissipations. Drawing inspiration from centrifugal pump impeller wheel, an acoustic metamaterial absorber has been devised. The design incorporates impeller vanes to create a channel with variable widths and a micro-perforate panel through which sound wave propagates to the channels. Numerical simulations using COMSOL Multiphysics and experimental analysis are conducted employing Two microphone impedance tube method. Acoustic pressure and acoustic particle velocity distribution plots from numerical simulation study are used to comprehend the sound absorption mechanism. Sound absorption coefficient results reveal that this design offers a tunable sound absorption peak in low frequency regime. Furthermore, this paper discusses the influence of various geometric parameters such as, number of vanes, panel thickness and micro-hole diameter. The subwavelength dimensions of the design contribute to noise control in machineries with space constraints.