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We demonstrate optical frequency division of an octave-spanning large repetition rate microcomb to an electronically-detectable frequency in an all-silicon nitride dual microcomb platform

Frequency microcombs, alternative to mode-locked laser and fiber combs, enable miniature rulers of light for applications including precision metrology, molecular fingerprinting and exoplanet discoveries. To enable frequency ruling functions, microcombs must be stabilized by locking their carrier-envelope offset frequency. So far, the microcomb stabilization remains compounded by the elaborate optics external to the chip, thus evading its scaling benefit. To address this challenge, here we demonstrate a nanophotonic chip solution based on aluminum nitride thin films, which simultaneously offer optical Kerr nonlinearity for generating octave soliton combs and quadratic nonlinearity for enabling heterodyne detection of the offset frequency. The agile dispersion control of crystalline aluminum nitride photonics permits high-fidelity generation of solitons with features including 1.5-octave spectral span, dual dispersive waves, and sub-terahertz repetition rates down to 220 gigahertz. These attractive characteristics, aided by on-chip phase-matched aluminum nitride waveguides, allow the full determination of the offset frequency. Our proof-of-principle demonstration represents an important milestone towards fully integrated self-locked microcombs for portable optical atomic clocks and frequency synthesizers., Though octave soliton microcombs are attractive for on-chip metrology and optical clocks, limitations in existing materials lead to increased chip integration complexity. Here, the authors report access to octave soliton microcombs and self-referencing using aluminium nitride nanophotonic chips.

We have developed a broadband and high-precision THz frequency counter based on a semiconductor-superlattice harmonic mixer. Its comprehensive characterization showed a measurement uncertainty of less than 1×10−16 over a four-octave range from 120GHz to 2.8THz. This compact and easy-to-handle THz counter operating at room temperature is suitable for many THz applications requiring a wide measurement range without a bulky cryogenic apparatus.

Recent progress on supercontinuum generation of OAM modes in optical fiber is reviewed. Two-octave SC generation of up to OAM17,1 mode spanning from 1560 to 6250 nm in the high-index ring fiber will be discussed.

The work is devoted to the development of the acoustic direction of creation of means of detection of unmanned aerial vehicles (UAVs). The work of these tools is based on the principles of noise direction finding with the use of such variable characteristics of the acoustic field as: sound intensity, frequency spectrum and spatial spectrum. The architecture of UAV detection devices on the acoustic field corresponds to the algorithms of reproduction in separate paths of the device of ideology of registration and control of dynamics of change of characteristic of an acoustic field which defines the specified change as the fact of detection. The technical implementation of the above detection devices is to create a path of parallel octave, ½ octave and ⅓ octave filters, a path of narrowband filtering and a path of detection by power (intensity). The ideology of construction of detection devices is based on variability and physical manifestations of changes in such characteristics of acoustic noise as: sound intensity in the space - time interval of observation, broadband filtering, narrowband filtering, correlation characteristics. To ensure the detection of acoustic power (or intensity) with subsequent measurement of the level, the counter-inclusion (by switching or using operational amplifiers) of the elements of the cross-shaped group is used. An important and new feature is that one of the linear discrete acoustic antennas with an enlarged base additionally has two more pressure receivers symmetrically relative to the phase center. For broadband filtration, a comb of ⅓ octave band and semi-octave filters is used. In turn, the path of the narrowband spectrum is an octave band filter and a unit for calculating the fast Fourier transform. The path of the correlation direction-finding method implements the determination of changes in the autocorrelation coefficient and the corresponding electrical parameter (say the current through the display circuit) in the processing path in situations of fixing the direction to the target. Therefore, the proposed system for detecting useful noise signals should contain four paths, the physical implementation of detection in which is performed by software implementation of detection algorithms and, threshold processing and indication of results In order to improve and increase the reliability of detection, the direction finder is supplemented by the path of detection on the mutual spectrum and the path of the correlation method of direction finding. The processing of input acoustic information of the type of specific noise-like signal is carried out by using the instrumental laboratory software package Lab View and Math Lab. We will add that the article contains theoretical and practical results of measurements of noise loading and range of action of a noise direction finder. Experimental studies in terms of detection and measurement of the main characteristics of the device were conducted in laboratory and field conditions. At the same time, the present demonstrates the rapid development of the UAV fleet, which determines the urgency of the work and the development of the device as a means of counteracting small aircraft of various recognitions is its goal.

We demonstrate ultra-rapid electro-optic sampling (EOS) of octave-spanning mid-infrared pulses centered at 9 μm, implemented by mechanically scanning a mirror with a sonotrode resonating at 19 kHz (forward and backward acquisition at 38 kHz). The instrument records the infrared waveform with a spectral intensity dynamic range of 1.6 × 105 for a single scan over a 1.6-ps delay range, acquired within 26 μs. The purely reflective nature of the delay scanning technique is compatible with broad optical bandwidths, short pulse durations (16 fs, centered at 1030 nm) and high average powers (Watt-level). Interferometric tracking of the sonotrode motion in combination with a predictor-corrector algorithm allows for delay-axis determination with down to single-digit attosecond precision. Ultra-rapid mid-infrared EOS will advance applications such as molecular fingerprinting of static samples as well as tracking of biological processes and chemical reactions and is likely to find new fields of application such as infrared-spectroscopic flow cytometry.

The soliton crystal (SC) was recently discovered as an extraordinary Kerr soliton state with regularly distributed soliton pulses and enhanced comb line power spaced by multiples of the cavity free spectral ranges (FSRs), which will significantly extend the application potential of microcombs in optical clock, signal processing, and terahertz wave systems. However, the reported SC spectra are generally narrow. In this Letter, we demonstrate the generation of a breathing SC in an aluminum nitride (AlN) microresonator (FSR ∼ 374 G H z ), featuring a near-octave-spanning (1150–2200 nm) spectral range and a terahertz repetition rate of ∼ 1.87 T H z . The measured 60 fs short pulses and low intensity–noise characteristics confirm the high coherence of the breathing SC. Broadband microcombs with various repetition rates of ∼ 0.75 , ∼ 1.12 , and ∼ 1.5 T H z were also realized in different microresonators of the same size. The proposed scheme shows a reliable design strategy for broadband soliton generation with versatile dynamic control over the comb line spacing.

The ice-free sea areas are increased continually in the past 20 years in Arctic, however, it’s of great significance to study the ocean ambient noise at ice-free sea area. From September 9 to October 24, 2017 (local time), the Chukchi Plateau was ice-free, and the ocean ambient noise data were recorded by an underwater signal recorder (USR) at 519.5 m depth for 3 min every 2 h. The correlation coefficients of noise spectrum level and sea surface wind speed are greater than 0.5 in frequencies from 31.5 Hz to 5 kHz. Especially, it is greater than 0.73 when the frequency is above 80 Hz. The variation law of noise spectrum levels with time is basically the same as that of wind speed. It suggests that the ocean ambient noise is significantly affected by sea surface wind and the wind-driven noise should be the main noise source during ice-free periods. The empirical probability densities and percentile distribution of noise spectrum levels from 20 Hz to 5 kHz have been given in this paper. The distribution of noise spectrum levels is relatively concentration below 160 Hz and discrete above 160 Hz. According to wind speed, different sea states are divided. The mean values of noise spectrum levels of different frequencies under different sea states are given and compared with the Knudsen’s curves. In the frequency band between 800 Hz and 5 kHz, the wind-driven noise spectrum levels decrease about 4.65 dB/octave with increasing frequency, which is slightly less than that of Wenz’s result of about 5 dB/octave.

While evaluating Ship-radiated noise with operational transfer path analysis (OTPA), a question arises that the input of OTPA cannot meet the linear system requirement, which results in a large estimated error in several frequencies. Therefore, to reduce the estimated error, in this paper a method based on OTPA optimized by operation clustering is proposed. First, a complete clustering feature matrix is constructed and weighted principal component analysis (W-PCA) used for feature extraction. Then, several classes of operating mode(OM) are clustered by K-means based on the feature, and the classified OMs are taken as the input of OTPA, which can meet the linear system requirement of OTPA. Experiments with cabin in Thousand Islet Lake show that the statistical probability of the line spectrum with an estimated error less than 3 dB is more than 95%, which is an improvement of 16.7% compared to the error before optimization, and the maximum estimated error of the line spectrum is reduced by 11.3 dB. The estimated error of 1/3 Octave is less than 2 dB in all frequencies, which can be reduced by approximately 7 dB. The results verify the feasibility of OTPA optimized by operation clustering.

Microalgae biomass production rate in short light-path photobioreactors potentially can be improved by mixing-induced flashing light regimes. A cascade photobioreactor features a thin liquid layer flowing down a sloping, wavy-bottomed surface where liquid flow exhibits peculiar local recirculation hydrodynamics, potentially conducive to an ordered flashing light regime. This article presents a model-based analysis of the frequency distribution of perceived irradiance in said wavy-bottomed photobioreactor. The model combines a Lagrangian description of the motion of individual cells, in turn derived from the hydrodynamic parameters of the photobioreactor extracted from an experimentally validated Computational Fluid Dynamic model, with a simplified description of the irradiance field across the culture thickness, down to the spectral analysis of perceived irradiance. The main finding of the work is that the wavy bottomed photobioreactor provides a ‘robust’ spectral excitation to the circulating microalgae up to 3 Hz frequency, while in flat panels and bubble columns excitation decays evenly at a 24 db/octave rate. This analysis paves the way to improving the light flashing performance of the wavy-bottomed photobioreactor with respect to geometry (cavity size and installation inclination) and operation (flow rate).

Microcombs have exhibited outstanding potential in the fields of optical frequency synthesizer, atomic clock, lidar, etc. To achieve a fully stabilized optical frequency comb, the microcombs should simultaneously have a nearly octave spectrum for self-referenced locking and a relatively small comb line spacing so that the beating frequency can be located in a comfortable photodetection bandwidth, e.g., 10 GHz. Unfortunately, it is still challenging for microcombs based on integrated microresonators, mainly due to the limitation on waveguide loss and dispersion control. Moreover, it is also highly desired that the microcombs can be stabilized in a simple way rather than complicated control.

Passive optical resonators are widely used for power enhancement, high harmonic generation and sensitive absorption spectroscopy [1] - [4] . The usual way of "filling" such a resonator with light is to couple in through a slightly transparent mirror, via constructive interference. We demonstrate an alternative method by using a thin wedged plate in the cavity, at an angle of incidence (AOI) close to Brewster’s angle. By adjusting the AOI on the plate, the cavity can be operated at different values of finesse without changing components. The main advantage, however, is the possibility of using low-dispersion mirrors, e.g., gold mirrors for the cavity, allowing for ultrabroadband resonant enhancement. We note that related ways of input coupling have been previously demonstrated. A parallel plate, one side of which was antireflection coated [5] and a plate with a slight wedge angle have been applied for input coupling [6] . However, both of these experiments were strongly limited in bandwidth and were conducted with continuous-wave lasers.

High-power mid-IR supercontinuum generation has attracted significant interest in the past decade due to the potential diverse applications in this spectra region ranging from molecular finger printing [1] , absorption spectroscopy, non-invasive imaging [2] and atmospheric LIDAR [3] . Despite many reports of SC generation in the mid-infrared using various fibers made of different materials, there are still important aspects to address for generating sources in the mid-infrared with performance similar to that of supercontinuum in the visible-near infrared, and in particular in terms of power spectral density. The main limitation typically arises from the soft-glasses used and whose damage threshold is much lower than that of silica. Among the different glasses used for supercontinuum generation in the mid-infrared, tellurite glasses exhibit transmission band comparable with that of fluoride while offering lower intrinsic losses than chalcogenide, making them an excellent candidate for supercontinuum generation in the mid-infrared [4] . Recently, the use of multimode graded-index (GRIN) fibers in supercontinuum generation has been demonstrated, allowing to generate ultrabroadband spectra with very high power spectral density while preserving a near single-mode spatial beam profile due to nonlinear self-beam cleaning dynamics [5] . All demonstrations of supercontinuum generation in GRIN fibers have been so far limited to silica fibers.

The technique of intra-pulse difference frequency generation (IDFG) is highly sought after for delivering broadband mid-infrared (MIR) radiation (2.5-20 µm) in a robust single-beam geometry [1] . Featuring intrinsic carrier-envelope phase stabilization, the few-cycle output pulses can be directly used for numerous emerging time-domain and frequency comb applications [2] , [3] . However, a complex chain of amplification, pulse compression and parametric conversion stages is typically required to drive IDFG in an efficient manner. Here, we report a novel and powerful directly diode-pumped Cr:ZnS oscillator to generate a multi-octave-spanning MIR spectrum.

Tunable biphotons are highly important for a wide range of quantum applications. For some applications, especially interesting are cases where two photons of a pair are far apart in frequency. Here, we report a tunable biphoton source based on a xenon-filled hollow-core photonic crystal fiber. Tunability is achieved by adjusting the pressure of the gas inside the fiber. This allows us to tailor the dispersion landscape of the fiber, overcoming the principal limitations of solid-core fiber-based biphoton sources. We report a maximum tunability of 120 THz for a pressure range of 4 bar with a continuous shift of 30 THz/bar. At 21 bar, the photons of a pair are separated by more than one octave. Despite the large separation, both photons have large bandwidths. At 17 bar, they form a very broad (110 THz) band around the frequency of the pump., 5 pages, 4 figures

Since microcavity Kerr soliton combs have spectrum which can exceed one octave, high repetition rate and potential for on-chip integration, the dissipative Kerr soliton generation in microresonators has been widely studied in recent years. Although microcavity soliton combs have been demonstrated in microcavities of different materials and shapes, it is still challenging for soliton generation due to positive thermal effects. In this paper, a sol-gel processed SiO2-CaF2 hybrid toroid microresonator is numerically investigated. Based on the calculation and simulation model we developed, this CaF2 coated SiO2 microresonator may avoid thermal effects and thermo-mechanical oscillations. Compared to organic coatings for thermal compensation in previous studies, it is a more promising platform for soliton generation.

Heating ventilating and air-conditioning systems which equip our buildings/rooms represent noise sources unfavorable affecting the people decent living and working conditions. Usually, silencers are used to reduce the annoying sound from these systems. They are lined with different materials and they have various geometries in order to satisfy the consumer needs, in terms of acoustic comfort. Sound absorption and sound transmission loss characterize the materials acoustic properties, but it is not mandatory that a good absorbent material to be also an efficient one from transmission loss (attenuation) point of view. Our paper is focused on an acoustic study of different materials lining three commercial silencers of same geometry and size. We have recorded the sound data according to standards: ISO 10534-1:1998 for the sound absorption coefficient and ISO 7235:2009 for the transmission loss rating. Third octave analysis with LabView soft is used to process the sound information and then the two parameters values are calculated. The acoustic characteristics of the tested materials are discussed and features that recommend them to be used as lining materials for silencers are highlighted.

Recent policy changes to the United States radar S-band allocation requires that radar transmitters share the 3.45 to 3.7 GHz range with fifth-generation (5G) wireless communication systems. As more radar spectrum is designated for sharing, reconfigurable high-power radar transmitters are needed that can maintain performance while quickly adjusting operating frequency. At the heart of a frequency-agile radar transmitter is a reconfigurable matching network, placed between the power amplifier and the antenna, that can maintain optimal range performance in real time by adaptively matching the antenna to the amplifier. Our impedance tuner consists of laser diodes illuminating semiconductor-plasma switches to selectively expose six microstrip stubs and has an octave tuning range from 2–4 GHz. Using an advanced tuning algorithm, the tuner can optimize output power in approximately 260 µs under control of a software-defined radio platform, an improvement of three orders of magnitude over presently available high-power tuning technologies.

A millimeter(mm)-wave widely-tunable mixer-first noise-cancelling receiver is demonstrated in 130 nm BiCMOS where an HBT LNTA loaded by a quadrature mixer is protected by an HBT-based N-path filter with linear-periodically-time-varying feedback for impedance transparency providing bandpass filtering. 20–40 GHz tunable, dual-resonant LO buffers use inductance to resonate out the mixer capacitance but still generate 25% duty-cycle LO pulses to reduce overlap-induced loss. The receiver simultaneously achieves +8.9 dBm OOB B1dB and 8.55 dB NF while functioning across an octave in the mm-wave band.

A 6-31 GHz reflection-mode N-path filter is implemented in 45 nm SOI technology. The filter is comprised of an on-chip hybrid coupler with through and coupled ports terminated with four-phase passive mixers. Each mixer provides a high impedance in-band and a 50-ohm impedance out-of-band, enabling reflection-mode bandpass filtering of the signal, with the center frequency set by the local-oscillator frequency. To increase selectivity, an active baseband load with adjustable bandwidth can be enabled to increase the roll-off to 12 dB/octave. The baseband loads between the two N-path mixers are shared to reduce size and power with the added benefit of creating a non-reciprocal filter response. Measurements show the filter can be tuned across 6–31 GHz with insertion loss 10 dB, noise figure exceeding insertion loss by 1 dB at 6 GHz and 10 dB at 31 GHz, and in-band IIP3 of 1.4-6.3 dBm.

Temporary hearing threshold shifts (TTSs) were investigated in two adult female harbor seals after exposure for 60 min to a continuous one-sixth-octave noise band centered at 16 kHz (the fatiguing sound) at sound pressure levels of 128–149 dB re 1 μPa, resulting in sound exposure levels (SELs) of 164–185 dB re 1 μPa2s. TTSs were quantified at the center frequency of the fatiguing sound (16 kHz) and at half an octave above that frequency (22.4 kHz) by means of a psychoacoustic hearing test method. Susceptibility to TTS was similar in both animals when measured 8–12 and 12–16 min after cessation of the fatiguing sound. TTS increased with increasing SEL at both frequencies, but above an SEL of 174 dB re 1 μPa2s, TTS was greater at 22.4 kHz than at 16 kHz for the same SELs. Recovery was rapid: the greatest TTS, measured at 22.4 kHz 1–4 min after cessation of the sound, was 17 dB, but dropped to 3 dB in 1 h, and hearing recovered fully within 2 h. The affected hearing frequency should be considered when estimating ecological impacts of anthropogenic sound on seals. Between 2.5 and 16 kHz the species appears equally susceptible to TTS.Temporary hearing threshold shifts (TTSs) were investigated in two adult female harbor seals after exposure for 60 min to a continuous one-sixth-octave noise band centered at 16 kHz (the fatiguing sound) at sound pressure levels of 128–149 dB re 1 μPa, resulting in sound exposure levels (SELs) of 164–185 dB re 1 μPa2s. TTSs were quantified at the center frequency of the fatiguing sound (16 kHz) and at half an octave above that frequency (22.4 kHz) by means of a psychoacoustic hearing test method. Susceptibility to TTS was similar in both animals when measured 8–12 and 12–16 min after cessation of the fatiguing sound. TTS increased with increasing SEL at both frequencies, but above an SEL of 174 dB re 1 μPa2s, TTS was greater at 22.4 kHz than at 16 kHz for the same SELs. Recovery was rapid: the greatest TTS, measured at 22.4 kHz 1–4 min after cessation of the sound, was 17 dB, but dropped to 3 dB in 1 h, and hearing recovered fully within 2 h. The affected hearing frequency should be considered when estima...

Temporary hearing threshold shift (TTS) caused by fatiguing sounds in the 1.5 to 16 kHz range has been documented in harbor porpoises (Phocoena phocoena). To assess impacts of anthropogenic noise on porpoise hearing, TTS needs to be investigated for other frequencies, as susceptibility appears to depend on the frequency of the fatiguing sound. TTS was quantified after two porpoises (Porpoises F05 and M06) were exposed for 1 hour to a continuous one-sixth-octave noise band centered at 32 kHz, at average received sound pressure levels of 118 to 148 dB re 1 µPa, and at a sound exposure level (SEL) range of 154 to 184 dB re 1 µPa2s. Hearing thresholds for 32, 44.8, and 63 kHz tonal signals were determined before and after exposure to quantify initial TTS and recovery. Porpoise M06’s hearing was tested 1 to 4 min after exposure. At 32 kHz, the lowest SEL that resulted in significant TTS1-4 (3.4 dB) was 166 dB re 1 µPa2s. At 44.8 kHz, the lowest SEL that resulted in significant TTS1-4 (5.2 dB) was 178 dB re 1 µPa2s. The highest TTS1-4 (18.3 dB) occurred at 44.8 kHz after exposure to 184 dB SEL. Porpoise F05’s hearing was tested 12 to 16 min after exposure. At 32 kHz, the lowest SEL that resulted in significant TTS12-16 (3.5 dB) was 184 dB re 1 µPa2s. At 44.8 kHz, the lowest SEL that resulted in significant TTS12-16 (1.2 dB) was 178 dB re 1 µPa2s. The highest TTS12-16 (8.2 dB) occurred in Porpoise F05 at 44.8 kHz after exposure to 184 dB SEL. At 63 kHz, no TTS could be elicited in either animal. Considering that Porpoise F05 had more time than Porpoise M06 for recovery, the susceptibility of the two porpoises to TTS after exposure to sounds of 32 kHz was similar. In the range investigated so far (1.5 to 32 kHz), susceptibility to TTS appears to increase with increasing frequency below ~6.5 kHz, and to decrease with increasing frequency above ~6.5 kHz.

This paper presents a novel method to widely tune high-quality factor evanescent-mode cavity resonators and filters using contactless tuners. The proposed method resolves multiple challenges facing reliable manufacturing and operation of these filters by avoiding the attachment of the flexible tuner to the cavity and replacing it with capacitive contactless tuners. This paper discusses the design consideration and tradeoffs as well as demonstrates the performance of the proposed concept using the substrate-integrated-waveguide technology. The resonators demonstrate more than octave tuning range (TR), quality factor up to 650, and power handling exceeding 100 W. In addition, the second-order bandpass filters are demonstrated, along with the long-term measurements, showing better than 1.17% frequency error after a 15-h stability test, and less than 1.47% frequency error after a 450 cycles repeatability test over an octave TR from 1.8 to 3.6 GHz.

The previous cilia MEMS vector hydrophone were mainly aimed at monitoring the noises of remote ships due to the limitation of frequency band. Moreover, the methods of adding appendants to cilia were usually used to improve the sensitivity, which increased the difficulty of fabrication, secondary integration and the consistency of production. In this paper, based on the bionic principle of multiple cilia on fishes’ sense cells, a cilia cluster MEMS vector hydrophone(CCVH) is designed. This micro-structure not only improves the sensitivity of hydrophone without adding appendants to cilia, but also designs a suitable frequency band to monitor ships and some valuable marine species. Firstly, a mathematical model is established for theoretical analysis. Then, simulation analysis is carried out to verify the correctness of theoretical analysis, and the optimal size of cilia is found simultaneously. Secondly, the fabrication of cilia cluster MEMS vector hydrophone is more simpler because the cilia have the same properties and integrated process. Finally, test results show that the sensitivity of hydrophone has been increased by 9.6 dB, which can reach up to -183.3 dB@1600 Hz(0 dB ref.1 V/uPa) with the frequency band in the range of 20 Hz-1 kHz. Besides, the sensitivity is increased by 6 dB per octave. Concave point depth of 8-shaped directivity is beyond 30 dB, which indicates that CCVH is promising in underwater application.

This article presents a hybrid acoustic technique applied to an acoustic shutter. It uses active noise control (ANC) at frequencies below 1000 Hz and acoustic foam, glued at the shutter walls, to attenuate frequencies above 1000 Hz. The use of the active noise control applied to acoustic shutters to increase the performance of noise attenuation in low frequencies. The control system was the Feedforward Filtered-x Least Mean Square (FxLMS) scheme and the influence of the actuator speaker position. It was implemented a low-cost active noise control using ARDUINO DUE. At low frequencies, without active noise control, the average insertion loss of the acoustic shutter is approximately 7 dB. Up to cutoff frequency (565 Hz) of the acoustic shutter, the highest attenuation due to active noise control was approximately 14 dB in 125 Hz discrete frequency and 17 dB in 400 Hz 1/3 octave band. The results between 500 and 1000 Hz were interesting since the active noise control was not expected to be efficient above the cutoff frequency of the acoustic chamber. The highest attenuation was 17.5 dB at the frequency of 710 Hz. From 100 to 8000 Hz an average attenuation of 13 dB (1/3 octave bands) was observed using the semi-active apparatus presented in this article.

Noise is one of the key issues in the operation of high-speed railways, with sound source localisation and its transfer path as the two major aspects. This study investigates both the exterior and interior sound source distribution of a high-speed train and presents a method for performing the contribution analysis of airborne sound with regard to the interior noise. First, both exterior and interior sound source locations of the high-speed train are identified through in-situ measurements. Second, the sound source contribution for different regions of the train and the relationships between the exterior and interior noises are analysed. Third, a method for conducting the contribution analysis of airborne sound with regard to the interior noise of the high-speed train is described. Lastly, a case study on the sidewall area is carried out, and the contribution of airborne sound to the interior noise of this area is obtained. The results show that, when the high-speed train runs at 310 km/h, dominant exterior sound sources are located in the bogie and pantograph regions, while main interior sound sources are located at the sidewall and roof. The interior noise, the bogie area noise and the sound source at the middle of the coach exhibit very similar rates of increase with increasing train speed. For the selected sidewall area, structure-borne sound dominates in most of the 1/3 octave bands.

This article discusses the requirements for a window function in applications aiming at efficient spectral resolution along with high harmonic suppression. A brief review of potential windows that tend to meet these requirements is presented, and it is noted that polynomial windows are best suited for such applications. A design procedure is described to synthesize a polynomial window with a 24-dB/octave sidelobe decay and minimal main-lobe width.

BACKGROUND: The evaluation of how air rarefaction can affect a loudspeaker performance at altitude implies the need for characterization of earphones during hypobaric conditions. The aim of this study was phonometric analysis at different altitudes of the acoustic output of a widely used earphone model, along with its consequences on audiological investigations conducted under such environmental conditions.METHODS: The transfer function of a TDH-39P earphone was analyzed with an artificial ear under nine different altitude levels, from sea level up to 35,000 ft, inside a hypobaric chamber. A specific phonometric system not sensitive to environmental pressure changes was used. Other potentially confounding factors, such as environmental temperature and humidity, were continuously monitored.RESULTS: No relevant temperature or humidity changes were detected. The sound pressure level generated by the earphone under hypobaric conditions was found considerably affected by air density changes. These data produced a correction table aiming at recalibrating the earphone's output at each audiometric octave test frequency within the 250-8000 Hz range. Quite different characteristics of response were observed at different audiometric frequencies. Such findings were particularly evident for altitudes exceeding 12,000 ft.DISCUSSION: The development of a frequency-selective and altitude-related correction factor for acoustic stimuli is an essential aspect when hearing threshold measurements in hypobaric environments are performed.Lucertini M, Botti T, Sanjust F, Cerini L, Autore A, Lucertini L, Sisto R. High altitude performance of loudspeakers and potential impact on audiometric findings. Aerosp Med Hum Perform. 2019; 90(7):655-659.

The sound pressure level (SPL) of environmental noise inside a dwelling is usually calculated by subtracting the outdoor-indoor level difference (DL) of the facade from the outdoor SPL. However, there is very little DL data available below 50 Hz. The purpose of our study was to determine the sound reduction index (SRI) within 50–5000 Hz according to ISO 16283-3 and the DL within 5–200 Hz for a broad range of different vertical facade constructions. The statistical distributions of SRI and DL were determined. Thirteen residential buildings involving twenty-six facade constructions were measured. A special infrasound loudspeaker was built to provide sufficient SPL within 5–20 Hz. The indoor SPL was measured in four corner and five central positions in the receiving room. The inter-facade differences of SRI within 50–5000 Hz were 17–36 dB. The differences for DL were smaller within 5–200 Hz: 12–30 dB in corner positions and 14–30 dB in central zone positions. The DL values measured in corner positions were significantly lower than the DL values measured in central zone positions within 40–200 Hz. Our DL results in corners were in agreement with three previous Danish studies only at a few one-third octave bands within 8–50 Hz. Our values were, in general, larger below 50 Hz. This study is unique because we were able to measure DL values down to 5 Hz using loudspeaker excitation. The statistical estimates can be used to assess the SPL of environmental noise indoors when the SPL outdoors is known.

For characteristic analysis of the 24 KHz audio, the 10-ms, 18-band quasi-ANSI filter bank has been proposed and designed for advanced hearing aids. To greatly reduce the computation complexity, several time-domain multirate signal processing techniques, such as the up- and down-sampling rate conversions and the interpolated finite impulse response (IFIR) filters, were investigated. However, it is well known that using fast Fourier transform (FFT) to perform the linear convolution can dramatically reduce the computational complexity. Taking both advantages, in this brief we investigated the FFT-based multirate signal-processing technique and explored their efficient architecture. To demonstrate the success of the proposed architecture, we implemented a real-valued FFT-based 10.7-ms, 18-band quasi-ANSI 1/3-octave filter bank using TSMC 90-nm CMOS high-VT technology. We found that, for each input sample, the proposed FFT-based quasi-ANSI 1/3-octave filter bank used approximately 77% fewer multiplications than the previous time-domain design. The proposed FFT-based quasi-ANSI filter bank was operated at 13 MHz to process the 24-KHz audio in real time, and it consumed only $14~ \mu \text{W}$ (@0.9V) of dynamic power.

Here we describe a new program, written in Octave version 4.2.1, freely available to run in both Linux and Windows systems, called ZTR.m. ZTR.m is one of a series designed to exclusively mimic and model quasielastic neutron scattering (QENS) data on water, ranging from that confined in nano-pores to bulk water. This program promptly allows for visualising initial fitting results, including modelling of the experimental spectra and evolution of the diffusion coefficients vs scattering vector, Q. As example, QENS spectra obtained using the time of flight spectrometer PELICAN at ANSTO from a clay that has been stored over a saturated solution has been used to demonstrated how ZTR.m correctly describes the dynamics of water in confinement.

Gabions - metal-wired cages filled up with stones - are increasingly becoming popular as decorative elements and land property boundaries. It has been shown before that such structures can be used as road traffic noise barriers as well. However, the types of stones used in gabions have not been experimentally studied so far. Exploratory measurements at full scale in a semi-anechoic room were performed to study the effect of both porous and rigid stones on their noise reducing potential. At the 1/3 octave bands below 1 kHz, low-height gabions (with depths of 20 cm and 30 cm) hardly provide any sound pressure level reduction. At higher sound frequencies, in contrast, the shielding rapidly increases. Porous lava stones were found to significantly increase the shielding compared to rigid stones. Reflections on such nondeep low-height barriers towards the source side were found to be of minor importance when considering a standardized A-weighted road traffic noise spectrum. (C) 2018 Elsevier Ltd. All rights reserved.

Source level and frequency are important in determining how far an acoustic signal can travel. However, in some species these sound characteristics have been found to be biomechanically linked, and therefore cannot be modified independently to achieve optimal transmission. This study investigates the variability in source levels and their relationship with frequency in the songs of humpback whales (Megaptera novaeangliae). Songs were recorded off eastern Australia using a fixed hydrophone array deployed on the whales' migratory corridor. Singing whales were acoustically tracked. An empirical, frequency-dependent model was used to estimate transmission loss. Source levels and frequency were measured for 2408 song units from 19 singers. Source levels varied from 138 to 187 dB re 1 μPa at 1 m (root mean squared), while peak frequency ranged between 52 and 3877 Hz. Much of the variability in source levels was accounted for by differences between the unit types, with mean source levels for each unit type varying by up to 17 dB. Source levels were negatively correlated with peak frequency and decreased by 2.3 dB per octave. The negative correlation between source levels and frequency is consistent with the presence of an air-filled resonator in the whales' sound production system.

We demonstrate a high-Q (>5 × 106) swept-frequency membrane mechanical resonator achieving resonance tuning over more than one octave via a simple integrated electrical heater. Throughout this tuni...

Psychophysical experiments on listeners with normal hearing were conducted to discriminate the rippled spectra of an acoustic signal against maskers with different positions of the spectral band relative to the signal band. As the signal level changed from 50 to 80 dB SPL, the on-frequency masker level changed by 29 dB, whereas the low-frequency masker level (the position of the center of the spectral band was from –1.25 to –1 octave relative to the signal) changed by 8.7–9.8 dB. These results are interpreted as 0.3 dB/dB compression of responses to the signal and no compression of the effect of low-frequency maskers. If the spectral bands of the signal and masker partially overlap, discrimination of the spectral structure occurs predominantly in the part of the spectrum that does not overlap the masker spectrum and is subjected to low-frequency masking that is not compressed.

The proposed engineering method of calculation of sound insulation of multilayer intercommunication pen-indoor. The calculation takes into account the effect on the sound insulation of cylindrical stiffness and surface density of inertial elements, as well as the stiffness of sound-proof gasket materials, which allows for rational design of the overlap. The calculation is reduced to the calculation of the frequency response of the impact noise reduction due to the multilayer structure of the floor and to the comparison of the calculated value of the index of the reduced level of impact noise with the standard. The list of necessary initial data and the validity of the calculation are given. Formulas are given to determine the boundaries of the natural oscillation frequencies within which the value of the reduced level of shock noise is calculated. The sequence of constructing the dependence of the natural oscillation frequencies of the system and reducing the level of shock noise by multi-layer inter-floor overlap is described. It is shown that above the second resonance frequency of the eigenfrequencies of the multilayer floor, the improvement of the shock noise isolation (relative to the single-layer overlap) is 24 dB per octave in the low frequency region and 12 dB per octave in the medium and high frequency region. Comparison of the calculated and measured frequency characteristics of the impact noise reduction showed a good agreement of the results obtained by the engineering calculation method with experimental studies.

In this paper, we propose the octave deep plane-sweeping network (OctDPSNet). OctDPSNet is a novel learning-based plane-sweeping stereo, which drastically reduces the required GPU memory and computation time while achieving a state-of-the-art depth estimation accuracy. Inspired by octave convolution, we divide image features into high and low spatial frequency features, and two cost volumes are generated from these using our proposed plane-sweeping module. To reduce spatial redundancy, the resolution of the cost volume from the low spatial frequency features is set to half that of the high spatial frequency features, which enables the memory consumption and computational cost to be reduced. After refinement, the two cost volumes are integrated into a final cost volume through our proposed pixel-wise “squeeze-and-excitation” based attention mechanism, and the depth maps are estimated from the final cost volume. We evaluate the proposed model on five datasets: SUN3D, RGB-D SLAM, MVS, Scenes11, and ETH3D. Our model outperforms previous methods on five datasets while drastically reducing the memory consumption and computational cost. Our source code is available at https://github.com/matsuren/octDPSNet.

Mid-infrared (MIR) optical frequency combs (OFCs) are ideal light sources for precision metrology and can find extensive applications, especially in molecular spectroscopy and gas detection. Here the generation of mode-locked MIR frequency comb in a LiNbO3 microring through optimized slot-waveguide design is proposed. Such microcomb can span over four-fifths of an octave (ranging from ~2810 nm to ~4630 nm) with pump power as low as 50 mW, which can be applied to the 2f-3f self-referencing for fully stabilization and helpful to monolithic integration of the whole system. Further investigations on complex dynamical processes for the microcomb generation suggest that the intracavity soliton drifting caused by the third-order dispersion could be compensated by the self-steepening effect as introducing an additional drift through proper dispersion tailoring. This work could facilitate the low-threshold broadband MIR frequency comb generation technique, as well as provide a way to realize more delicate control of soliton microcombs in both temporal and spectral domain.

We developed a simple device to teach the concept of pH to visually impaired people through an experimental approach. An interface between a glass electrode and an open-source electronics platform based on easy-to-use hardware and software (Arduino Uno) was designed using an operational amplifier of ultralow input current. A headphone connected to digital output from Arduino Uno was employed to convert the electrical signals from pH to sound frequency. Using an audio file that emits sound frequencies, visually impaired students were trained to associate specific frequencies with pH values. There is a direct relationship between the logarithm of sound frequency from a given musical note and a pH value, which can be used to train students with low vision who would otherwise have difficulty observing pH values from visual indications. Sound frequency signals of 131–659 Hz that correspond to the piano musical scale of C3, which is one octave below middle C (small octave or the “Do” note in solfege), to E5, on...

This paper provides a survey of various experimental data available on the value of the propagation path loss of radio waves in a cellular wireless environment. It is shown starting with the Okumura et al. ’s paper on propagation measurements and other available published experimental data that they all exhibit that the electric field varies as $\rho ^{-1.5}$ within a cellular radius of a few kilometers, where $\rho $ is the radial distance of the receiving antenna from the transmitting one. This decay in the fields is equivalent to a propagation loss of −9 dB/octave or −30 dB for a decade of the distance. This value is independent of the nature of the ground, whether it be composed of rural, urban, suburban, or water. This is the first time it is stated that the propagation path loss due to the presence of ground generates a path loss of 90 dB when the signals travel a distance of 1 km. This value is rather large when compared to a loss of 30–50 dB produced by buildings, trees, and similar artifacts. Therefore, the experimental data indicate that the effect of trees and buildings have a secondary influence on the decay of the electric field with distance, the dominant one is the propagation loss over an imperfect ground. Contemporary propagation models do not acknowledge this fact. Outside the cellular radius of a few kilometers, the path loss appears to be 12 dB/octave or 40 dB/decade of distance. In a companion paper, it will be demonstrated that the values for the path loss can be explained from an analytical standpoint without taking recourse to statistics which involves a lot of assumptions on the functional variation of the variables of interest.

We develop an optimization model to linearize analog photonic links (APLs) with substantially enhanced multi-octave spurious-free dynamic range (SFDR). By quantifying the power weighting factor and polarization incident angle, the link linearity is maximized at the optimal point.

International audience; We report supercontinuum generation from an all-normal dispersion SiGe-on-Si waveguide pumped with 205 fs pulses at 4 μm. The supercontinua are spanning over an octave for both orthogonal polarizations of the fundamental mode.

In the safe driving of driverless vehicles, vehicle acoustic identification is one of the most important parts in driverless applications. During the process of driving the vehicle, there are many external interference factors, among them the vehicle acoustic signal is a complex multi-source signal, which is difficult to extract effective feature values. In this paper, an improved algorithm for extracting eigenvalues of vehicle acoustic signals is proposed to achieve a higher correct identification rate for different types of vehicles. Traditional frequency division method is improved by analyzing the characteristics of the 1/3 octave and the human ear Bark domain frequency sensing method. The algorithm extracts the effective energy feature values of different frequency ranges from the vehicle acoustic signals, and uses a probabilistic neural network for vehicle identification. Experimental results show that the recognition rate of trucks reaches 100%, the recognition rate of small vehicles, medium-sized vehicles and Buses reaches 90%, and the recognition rate of motorcycles is 85%. It indicates that the algorithm is feasible in vehicle type recognition and has a good recognition rate, and can be a reference for related vehicle identification researches.

Implementing optical-frequency combs with integrated photonics will enable wider use of precision timing signals.Here, we explore the generation of an octave-span, Kerr-microresonator frequency comb, using hybrid integration ofan InP distributed-feedback laser and a SiN photonic-integrated circuit. We demonstrate electrically pumped and fiber-packaged prototype systems, enabled by self-injection locking. This direct integration of a laser and a microresonatorcircuit without previously used intervening elements, like optical modulators and isolators, necessitates understand-ing self-injection-locking dynamics with octave-span Kerr solitons. In particular, system architectures must adjust tothe strong coupling of microresonator back-scattering and laser-microresonator frequency detuning that we uncoverhere. Our work illustrates critical considerations towards realizing a self-referenced frequency comb with integratedphotonics., 9 pages, 4 figures. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in APL Photonics 6, 026102 (2021) and may be found at https://doi.org/10.1063/5.0035452

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

Author(s): Taheri, Hossein | Abstract: In this invited article, we report the experimental demonstration of the simultaneous coherent locking of two independent lasers with arbitrary multi-FSR (free spectral range) frequency separation to a Kerr microcomb soliton, resulting in the creation of synthetic microcomb soliton crystals. Each of the two pumps is self-injection-locked to its neighboring microcavity mode and acts as an arbiter linking the microcomb to the cavity. We show that the beating of the two pumps creates a manifest discrete symmetry and that certain microcomb states generated in this pumping scheme spontaneously break this symmetry, thereby realizing \emph{dissipative} discrete time crystals. Apart from introducing a powerful platform leveraging advanced photonics for the creation and scientific exploration of various types of dissipative time crystals and their properties, our results constitute a decisive step towards the two-point locking of Kerr microcombs with moderate bandwidths much smaller than an octave which cannot be self-referenced through standard approaches such as the f-2f technique.

We report what we believe to be the first octave-spanning supercontinuum generation from all-normal dispersion waveguide on a silicon-based chip in the mid-infrared. Here we use 205 fs pulses at 4 μm coupled to low loss, 5.0 μm x 2.7 μm cross-section, silicon germanium-on-silicon waveguide operating in tha all-normal dispersion regime. Generated supercontinuum spans more than an octave between 2.8 and 5.7 μm. Besides, simulations show a high degree of coherence across the entire -30 dB spectrum. Such supercontinuum provides an ideal light probe for broadband mid-infrared molecular absorption spectroscopy.

Photonic chip frequency comb generation based on Kerr-mediated nonlinear optical processes in microresonators is promising for a number of applications in time and frequency metrology, spectroscopy, sensing, and communications. In this talk, I will discuss our work in developing soliton microresonator frequency combs whose spectral bandwidths exceed an octave, so that when self-referenced, they can be used as core components of optical frequency synthesizers and optical atomic clocks. I will present recent efforts to create even broader bandwidth microcombs and to access visible wavelengths, which is a particular challenge due to the large dispersion of the constituent materials. Finally, I will discuss some of the outstanding design and simulation challenges associated with the development of these microcombs.

Although lightning discharge is not the only source or only physical phenomenon that affects the Schumann resonances, they have the highest contribution to the Schumann resonances oscillating between the ground the ionosphere. Schumann resonances are predicted through several different numerical models such as the transmission-line matrix model or partially uniform knee model. This contribution reports a different prediction method for Schumann resonances derived from the first principle of fundamental physics combining both particle radiation patterns and the mathematical concept of the Golden ratio. This prediction allows the physical understanding of where Schumann resonances originate from radiation emitted by a particle that involves many frequencies that are not related to Schumann resonances. In addition, this method allows predicting the wave propagation direction of each frequency value in the Schumann frequency spectrum. Particles accelerated by lightning leader tip electric fields are capable of contributing most of the Schumann resonances. The radiation pattern of a single particle consists of many frequencies. There are only specific ones within this pattern that contribute to the Schumann radiation. The vast majority of Schumann resonances distribute quite nicely obeying the Golden ratio interval. This property, used in conjunction with the full single-particle radiation patterns, also revealed that high-frequency forward-backward peaking radiation patterns, as well as low-frequency radiation patterns, can contribute to Schumann resonances. This method allows to locate them on the full radiation pattern. A theoretical analysis using the Golden ratio spiral, predict that there are more Schumann resonances in the high-frequency forward-backward peaking radiation pattern of a relativistic particle than low-frequency dipole radiation pattern. Extending the idea to an octave that identifies the identical sounding notes with different frequencies in standing waves. By knowing the value of the initial Schumann resonant frequency, this method allows us to predict the magnitude of other Schumann resonances on the radiation pattern of a single accelerated charged particle conveniently. In addition, it also allows us to find and match Schumann resonances that are on the same radiation lobe, which is named electromagnetic Schumann octaves. Furthermore, it is important to find Schumann octaves as they propagate in the same direction and have a higher likelihood of wave interference.