Low Acoustic Frequencies Research Articles

Acoustic stimulation of the human round window by laser-induced nonlinear optoacoustics.

The feasibility of low frequency pure tone generation in the inner ear by laser-induced nonlinear optoacoustic effect at the round window was demonstrated in three human cadaveric temporal bones (TB) using an integral pulse density modulation (IPDM). Nanosecond laser pulses with a wavelength in the near-infrared (NIR) region were delivered to the round window niche by an optical fiber with two spherical lenses glued to the end and a viscous gel at the site of the laser focus. Using IPDM, acoustic tones with frequencies between 20Hz and 1kHz were generated in the inner ear. The sound pressures in scala tympani and vestibuli were recorded and the intracochlear pressure difference (ICPD) was used to calculate the equivalent sound pressure level (eq. dB SPL) as an equivalent for perceived loudness. The results demonstrate that the optoacoustic effect produced sound pressure levels ranging from 140eq. dB SPL at low frequencies ≤ 200Hz to 90eq. dB SPL at 1kHz. Therefore, the produced sound pressure level is potentially sufficient for patients requiring acoustic low frequency stimulation. Hence, the presented method offers a potentially viable solution in the future to provide the acoustic stimulus component in combined electro-acoustic stimulation with a cochlear implant.

Low Acoustic Frequency Sensing Based on Ghost Mode of Small Angle Tilted Fiber Bragg Grating

Low Acoustic Frequency Sensing Based on Ghost Mode of Small Angle Tilted Fiber Bragg Grating

Ultralow Thermal Conductivity of a Chalcogenide System Pt3Bi4Q9 (Q = S, Se) Driven by the Hierarchy of Rigid [Pt6Q12]12- Clusters Embedded in Soft Bi-Q Sublattice.

Knowledge of structure-property relationships in solids with intrinsic low thermal conductivity is crucial for fields such as thermoelectrics, thermal barrier coatings, and refractories. Herein, we propose a new "rigidness in softness" structural scheme for intrinsic low lattice thermal conductivity (κL), which embeds rigid clusters into the soft matrix to induce large lattice anharmonicity, and accordingly discover a new series of chalcogenides Pt3Bi4Q9 (Q = S, Se). Pt3Bi4S9-xSex (x = 3, 6) achieved an intrinsic ultralow κL down to 0.39 W/(m K) at 773 K, which is considerably low among the Bi chalcogenide thermoelectric materials. Pt3Bi4Q9 contains the rigid cubic [Pt6Q12]12- clusters embedded in the soft Bi-Q sublattice, involving multiple bonding interactions and vibration hierarchy. The hierarchical structure yields a large lattice anharmonicity with high Grüneisen parameters (γ) 1.97 of Pt3Bi4Q9, as verified by the effective scatter of low-lying optical phonons toward heat-carrying acoustic phonons. Consequently, the rigid-soft coupling significantly inhibits heat propagation, exhibiting low acoustic phonon frequencies (∼25 cm-1) and Debye temperatures (ΘD = 170.4 K) in Pt3Bi4Se9. Owing to the suppressed κL and considerable power factor (PF), the ZT value of Pt3Bi4S6Se3 can reach 0.56 at 773 K without heavy carrier doping, which is competitive among the pristine Bi chalcogenides. Theoretical calculations predicted a large potential for performance improvement via proper doping, indicating the great potential of this structure type for promising thermoelectric materials.

Optimization of the acoustic influence for precipitation enhancing inside natural clouds with ground-based technique

Problem setting. The paper belongs to precipitation enhancement methods. The new option is proposed inside natural clouds by using low-frequency acoustics, 40–300 Hz, emitted from air sirens near ground. The purpose. The purpose of the article is to determine the necessary acoustic parameters, frequency and power, for effective collision of water droplet with their merge in natural clouds. Results. In this study convenient analytical formulas are derived for utilization during field experiments, and example calculations are provided for different environment. Increasing for acoustic intensity directly in atmosphere by diffraction is proposed. Practical significance. The paper indicates the optimal options and regimes for acoustics in natural clouds and ways to achieve this effect.

SMART submarine cable technology can facilitate acoustics on the global scale

The submarine cable industry is beginning to share their infrastructure for ocean observing. Science Monitoring And Reliable Telecommunications (SMART) Subsea Cables is working to integrate temperature, pressure, and seismic acceleration sensors into commercial cables (∼70 km spacing) to support climate monitoring and disaster risk reduction on the global scale. The seismic and pressure sensors are expected to have sensitivity at low acoustic frequencies, (e.g., <50 Hz and <5 Hz, respectively); future systems could include hydrophones and other sensors. Further, telecom rated branching cables supporting multipurpose “nodes” are becoming a reality (per existing dedicated science cable systems). These can support low frequency transceivers and autonomous undersea vehicles (AUVs). With cabled power, these would be part of the fixed/mobile acoustic tomography system measuring ocean heat content and more generally for transporting energy, data, and acquiring multidisciplinary data throughout a large volume of the ocean. A 3700 km SMART ring system in Portugal will be ready in 2026 and one connecting Vanuatu and New Caledonia is starting. Others in planning stages that could include these concepts are: Far North Fiber connecting Norway/Finland/Ireland with Japan, the NSF proposed SMART cable connecting New Zealand with Antarctica, New Zealand-Chatham Islands, and Lisbon-Egypt through the Mediterranean.

Thermoelectricity in Ag/Cu-based complex crystal structure minerals with inherent low thermal conductivity

Abstract Inherently poor lattice thermal conductivity (κL) is highly desired for applications like thermoelectricity, thermal management in electronics, thermal barrier coatings and refractories. Recently, complex crystalline materials have drawn serious scientific attention because of various interesting underlying physical phenomena which explain the unique thermal properties. In this review, we have discussed various interesting concepts and their consequences leading to ultralow κL in complex bulk chalcogenide minerals having multiple scattering channels for heat-carrying phonons. The primary focus of this review is on the Ag- and Cu-based large unit cell structures with low heat capacity and liquid-like superionic conduction of cations. The Ag/Cu sublattice of these materials that followed the phonon-liquid electron-crystal concept strongly reduces the transportation of phonons and enhances the scattering process. The presence of a large number of atoms in the unit cell results in low acoustic phonons cut-off frequency, robust acoustic–optical phonons scattering, poor sound velocity and strong crystal anharmonicity inside the crystalline lattice.

On a Novel Algorithmic Determination of Acoustic Low Frequency Coefficients for Arbitrary Impenetrable Scatterers

The calculation of low frequency expansions for acoustic wave scattering has been under thorough investigation for many decades due to their utility in technological applications. In the present work, we revisit the acoustic Low Frequency Scattering theory, and we provide the theoretical framework of a new algorithmic procedure for deriving the scattering coefficients of the total pressure field, produced by a plane wave excitation of an arbitrary, convex impenetrable scatterer. The proposed semi-analytical procedure reduces the demands for computation time and errors significantly since it includes mainly algebraic and linear integral operators. Based on the Atkinson–Wilcox theorem, any order low frequency scattering coefficient can be calculated, in finite steps, through algebraic operators at all steps, except for the last one, where a regular Fredholm integral equation with a continuous and separable integral kernel is needed to be solved. Explicit, ready to use formulae are provided for the first three low frequency scattering coefficients, demonstrating the applicability of the algorithm. The validation of the obtained formulae is demonstrated through recovering of the well-known analytical results for the case of a radially symmetric scatterer.

Acoustic frequency-dependent physical mechanism of sub-MHz ultrasound neurostimulation

Ultrasound allows non-invasive and reversible modulation of neural circuit activity with high spatial resolution. Despite growing interest in clinical applications, the safe and effective use of ultrasound neuromodulation has been limited by a lack of understanding of the physical mechanisms underlying its effects. Here, we demonstrate acoustic frequency-dependent physical effects that underlie ultrasound neuromodulation, where cavitation and radiation forces are the dominant sources of low- and high-frequency stimulation, respectively. We used 39.5 and 500 kHz acoustic frequencies to stimulate cultured neural and glial cells to study acoustic frequency-dependent neural responses. We demonstrate increased evoked responses due to increased cavitation activity at the 39.5 kHz acoustic frequency. In contrast, notable cavitation activity was not detected at 500 kHz despite detection of evoked responses. Our work highlights the dependence of ultrasound neuromodulation on acoustic frequencies, with different physical effects underlying cell responses to low and high sub-MHz acoustic frequency ranges.

Frequency-tunable sound insulation via a reconfigurable and ventilated acoustic metamaterial

In acoustic engineering, sound-proofing ventilation barriers find wide applications in diverse situations. However, most of the structures only have responses with fixed frequencies and a very narrow frequency range, especially for low frequency acoustics. Here we show a subwavelength acoustic metamaterial based on labyrinthine structures, which possesses tunable sound insulation and ventilation properties. The Fano-like asymmetric transmission dips is formed by the interference between the resonant scattering of discrete states and the background scattering of continuous states. By adjusting the spacing between these two half zigzag molds, the sound insulation dip frequency can shift from 360 Hz to 575 Hz while the free ventilation area ratio is kept to over 36.3% and the total thickness is only about 0.06λ. Moreover, the noise peak frequency can be detected by a microphone detection and adaptive adjustment of the spacing with a small stepping motor is demonstrated, the results agree well with numerical simulations. We anticipate our design may find potential applications in acoustic air vents, soundproofing window and duct noise control.

Observations of Noise due to Nonlinear Internal Waves in the ASIAEX Experiment in the South China Sea

Large, transient increases in underwater noise intensity (noise bursts) were repeatedly observed during the ASIAEX experiment on a 48-hydrophone array consisting of vertical and horizontal line arrays. The arrays were located in the South China Sea in the area known for exceptionally strong nonlinear internal waves (NIWs). The ASIAEX experiment was intended to study sound propagation in the presence of NIWs and featured extensive, concurrent acoustic and oceanographic observations. The NIWs propagating past the acoustic array site were characterized using water temperature measurements with a nearby thermistor chain. Remarkable correlation is found between noise intensity increases on the vertical array hydrophones and the NIW presence. Intensity of the noise bursts strongly depends on the hydrophone depth. The low acoustic frequencies below 30–40 Hz are primarily responsible for the noise enhancement during the NIW passage. Analysis of the spectral properties and the depth dependence of the noise intensity suggests the flow noise due to NIW-induced currents as the physical mechanism of the noise bursts in the South China Sea. [Work was supported, part, by ISF award 946/20.]

Phonotactics of Gender in Mandarin Given Names: Patterns and Constraints

In this paper, we investigate the phonotactic patterns that correlate with gender in given names for Mandarin Chinese, a language that is phonotactically quite different from English. We find that many of the phonological predictors for gender in English trend in the same direction for Mandarin. We also compare the phonotactic grammars of Mandarin female and male given names obtained from Maximum-Entropy phonotactic learning models, and find that certain low acoustic frequency sounds that imply largeness according to the Frequency-Code Hypothesis are penalized for female names, while higher acoustic frequency sounds that imply smallness according to the Frequency-Code Hypothesis are not marked in the grammar for male names.

Effects of tonotopic matching and spatial cues on segregation of competing speech in simulations of bilateral cochlear implants.

In the clinical fitting of cochlear implants (CIs), the lowest input acoustic frequency is typically much lower than the characteristic frequency associated with the most apical electrode position, due to the limited electrode insertion depth. For bilateral CI users, electrode positions may differ across ears. However, the same acoustic-to-electrode frequency allocation table (FAT) is typically assigned to both ears. As such, bilateral CI users may experience both intra-aural frequency mismatch within each ear and inter-aural mismatch across ears. This inter-aural mismatch may limit the ability of bilateral CI users to take advantage of spatial cues when attempting to segregate competing speech. Adjusting the FAT to tonotopically match the electrode position in each ear (i.e., increasing the low acoustic input frequency) is theorized to reduce this inter-aural mismatch. Unfortunately, this approach may also introduce the loss of acoustic information below the modified input acoustic frequency. The present study explored the trade-off between reduced inter-aural frequency mismatch and low-frequency information loss for segregation of competing speech. Normal-hearing participants were tested while listening to acoustic simulations of bilateral CIs. Speech reception thresholds (SRTs) were measured for target sentences produced by a male talker in the presence of two different male talkers. Masker speech was either co-located with or spatially separated from the target speech. The bilateral CI simulations were produced by 16-channel sinewave vocoders; the simulated insertion depth was fixed in one ear and varied in the other ear, resulting in an inter-aural mismatch of 0, 2, or 6 mm in terms of cochlear place. Two FAT conditions were compared: 1) clinical (200–8000 Hz in both ears), or 2) matched to the simulated insertion depth in each ear. Results showed that SRTs were significantly lower with the matched than with the clinical FAT, regardless of the insertion depth or spatial configuration of the masker speech. The largest improvement in SRTs with the matched FAT was observed when the inter-aural mismatch was largest (6 mm). These results suggest that minimizing inter-aural mismatch with tonotopically matched FATs may benefit bilateral CI users’ ability to segregate competing speech despite substantial low-frequency information loss in ears with shallow insertion depths.

Hybrid vibro-acoustic energy harvesting using electromagnetic transduction for autonomous condition monitoring system

Condition monitoring systems (CMS) play a significant role in enhancing performance and lowering failure losses in any industrial setup. Appropriate wireless sensor nodes (WSNs) used in CMS will permit the user to check the live status of machines, however, these WSNs are facing the periodic replacement and recharging problems of batteries. Energy harvesters, used to scavenge ambient energy, are viable alternatives to batteries for achieving the self-sustained long-term operation of WSNs. Ambient vibration and acoustic energies are abundantly available in the industrial environment. The currently available energy harvesters are utilizing only vibration or acoustic energy, however, research on harvesters using both vibration and acoustic sources is missing. We present a new hybrid vibro-acoustic energy harvester (HVA-EH) using electromagnetic transduction, where the power to the WSNs can be harvested from both vibration and acoustic sources simultaneously. The architecture, working principle, fabrication, and experimentation of the HVA-EH are discussed. The HVA-EH was operated at a low vibration and acoustic frequencies and low acceleration and sound pressure levels (SPL). At matching impedance, the maximum power generated by the HVA-EH under vibration energy at zero SPL is 372 μW at acceleration level of 0.3 g and under acoustic energy at zero acceleration level is 271 μW under SPL of 130 dB. While, under a hybrid environment, the HVA-EH generates maximum power of 153 μW, 361 μW, and 656 μW at vibration levels of 0.1 g, 0.2 g, and 0.3 g respectively, under SPL of 130 dB at 2nd acoustic mode (495 Hz). The results are promising and the ability of harvesting low-frequency sound and vibration simultaneously makes the HVA-EH an energy efficient system. Furthermore, this study demonstrates the possibility of new solutions to the problems of WSNs utilizing both sound and vibration energy resources.

Hydro-acoustic signals from the Panarea shallow hydrothermal field: new inferences of a direct link with Stromboli

Abstract We present the results from a mid-term monitoring activity carried out at the submarine hydrothermal system located off Panarea Island (Aeolian Islands, Italy). The collected data concern multiparametric information from a self-operating seafloor station (acoustics and chemical–physical parameters) acquiring data at regular intervals and transmitting it twice a day in near real-time. The acoustic records were analysed with the principal aim of investigating bubbling variations related to gas flow rate. Several anomalies have been documented, in the bubbling activity detected at high frequencies (100–2000 Hz), as well as in very low acoustic frequencies, related to fluids dynamic along cracks. An astonishing correlation between soil CO 2 flux emissions recorded at Stromboli craters and the acoustic signals in the 1–30 Hz range has been identified, suggesting how this tectonic link could act as an escape route for fluids characterized by a shared source.

Photoacoustic characteristics of carbon-based infrared absorbers

We present an experimental comparison of photoacoustic responsivities of common highly absorbing carbon-based materials. The comparison was carried out with parameters relevant for photoacoustic power detectors and Fourier-transform infrared (FTIR) spectroscopy: we covered a broad wavelength range from the visible red to far infrared (633 nm to 25 μm) and the regime of low acoustic frequencies (< 1 kHz). The investigated materials include a candle soot-based coating, a black paint coating and two different carbon nanotube coatings. Of these, the low-cost soot absorber produced clearly the highest photoacoustic response over the entire measurement range.

Exploring the Acoustic and Dynamic Characteristics of Phase-Change Droplets.

Acoustic droplet vaporization (ADV) provides the on-demand production of bubbles for use in ultrasound (US)-based diagnostic and therapeutic applications. The droplet-to-bubble transition process has been shown to involve localized internal gas nucleation, followed by a volume expansion of threefold to fivefold and inertial bubble oscillation, all of which take place within a few microseconds. Monitoring these ADV processes is important in gauging the mechanical effects of phase-change droplets in a biological environment, but this is difficult to achieve using regular optical observations. In this study, we utilized acoustic characterization [i.e., simultaneous passive cavitation detection (PCD) and active cavitation detection (ACD)] to investigate the acoustic signatures emitted from phase-change droplets ADV and determined their correlations with the physical behaviors observed using high-speed optical imaging. The experimental results showed that activation with three-cycle 5-MHz US pulse resulted in the droplets (diameter: 3.0- [Formula: see text]) overexpanding and undergoing damped oscillation before settling to bubbles with a final diameter. Meanwhile, a broadband shock wave was observed at the beginning of the PCD signal. The intense fluctuations of the ACD signal revealed that the shock wave arose from the inertial cavitation of nucleated small gas pockets in the droplets. It was particularly interesting that another shock-wave signal with a much lower acoustic frequency (< 2 MHz) was observed at about [Formula: see text] after the first half signal. This signal coincided with the reduction of the ACD signal amplitude that indicated the rebound of the transforming bubble. Since internal gas nucleation is a crucial process of ADV, the first half signal may indicate the occurrence of an ADV event, and the second half signal may further reveal the degrees of expansion and oscillation of the bubble. These acoustic signatures provide opportunities for monitoring ADV dynamics based on the detection of acoustic signals.

Low-Power Sensor Interface with a Switched Inductor Frequency Selective Envelope Detector

With the growing need to understand our surroundings and improved means of sensor manufacturing, the concept of Internet of Things (IoT) is becoming more interesting. To enable continuous monitoring and event detection by IoT, the development of low power sensors and interfaces is required. In this work we present a novel, switched inductor based acoustic sensor interface featuring a bandpass filter and envelope detector, perform a sensitivity, frequency selectivity, and power consumption analysis of the circuit, and present its design parameters and their qualitative influence on circuit characteristics. We develop a prototype and present experimental characterization of the interface and its operation with input signals up to 20 mV peak-to-peak, at low acoustic frequencies from 100 Hz to 1 kHz. The prototype achieves a sensitivity of approximately 2 mV/mV in the passband, a four times lower sensitivity in the stopband, and a power consumption of approximately 3.31 µW. We compare the prototype interface to an interface consisting of an active bandpass filter and a passive voltage doubler using a prerecorded speedboat signal.

The impact of chemical modelling on turbulent premixed flame acoustics

Abstract

Underwater low acoustic frequency detection based on in-line Mach–Zehnder interferometer

We propose and demonstrate an in-line Mach–Zehnder interferometer (IMZI) as an optical hydrophone. The IMZI is fabricated by creating two tapers in the single-mode fiber (SMF), and the two tapered sections are separated by a small section of untapered SMF. To achieve higher sensitivity, this IMZI is attached to a circular natural rubber (NR) diaphragm. The sensing mechanism is based on the acoustic pressure-induced wavelength shift of the IMZI transmission spectrum. The proposed hydrophone is tested underwater with acoustic signals of different frequencies in the range of 15–250 Hz. For a specific IMZI structure, the hydrophone shows a sensitivity of 27.93 nm/Pa and a noise-limited minimum detectable pressure of 5.53 m P a / √ H z . One can tailor the acoustic sensitivity of the proposed hydrophone by changing different parameters of diaphragm and IMZI. The excellent underwater performance of the NR diaphragm makes the proposed hydrophone an efficient and economical system for underwater low-frequency acoustic signal detection.

Recovering piecewise constant refractive indices by a single far-field pattern

We are concerned with the inverse scattering problem of recovering an inhomogeneous medium by the associated acoustic wave measurement. We prove that under certain assumptions, a single far-field pattern determines the values of a perturbation to the refractive index on the corners of its support. These assumptions are satisfied, for example, in the low acoustic frequency regime. As a consequence if the perturbation is piecewise constant with either a polyhedral nest geometry or a known polyhedral cell geometry, such as a pixel or voxel array, we establish the injectivity of the perturbation to far-field map given a fixed incident wave. This is the first unique determinancy result of its type in the literature, and all of the existing results essentially make use of infinitely many measurements.