Upper Limit Of Frequency Research Articles

Estimating the high-frequency extent of binaural sensitivity to temporal fine structure across listeners

Füllgrabe et al. [2017, Int. J. Audiol. 56:926-35] developed a novel procedure to estimate the frequency dependence of listeners’ sensitivity to temporal fine structure in the form of interaural phase differences (IPD). Whereas traditional approaches fixed tone frequency and varied IPD, the new “TFS-AF” test fixed the IPD and varied frequencies adaptively so as to estimate the upper frequency limit (UFL) of IPD sensitivity, even in listeners who struggle with traditional tests. UFL estimates for young normal hearing listeners were consistently 1200–1400 Hz, with notable exceptions of lower UFL (e.g. 800–1000 Hz) in a small subset. The consistency of UFL and abrupt loss of IPD sensitivity above it remain among the most puzzling aspects of binaural hearing, unexplained by the (rather shallow) frequency dependence of audibility, neuronal phase locking, or internal noise in this region. Recently, our group adapted a version of the TFS-AF test to measure UFL as a function of sound level, comparing the resulting slope to predictions of candidate mechanisms. The limitation closely matches the upper edge of an auditory filter centered at ∼700 Hz, suggesting that IPD sensitivity is mediated exclusively by neurons tuned to that frequency or below. [Work supported by NIH R01DC014948, R01DC016643, and R01DC017924.]

Variation of the secondary acoustic paths from loudspeakers at the seat shoulder in an automobile cabin

The secondary path is essential in the design of adaptive active noise control systems, and it varies with several factors in practical implementation. In this paper, the acoustic responses from secondary loudspeakers installed at the shoulder of the front passenger seat to the error microphones at the passenger's ears in an automobile cabin are measured, when the factors including the passenger movement, the seat posture and the passenger number change. The upper limit frequency where the phase variation is within 90 deg. compared to the reference position is analyzed. The results show that the state of both the passenger head and the seat back determines the lowest upper limit frequency among all the factors under investigation. If multiple factors change at the same time, the upper limit frequency will be further reduced.

Active control of sound transmission through a floor-level slit.

The floor-level slit between the door and the floor is one weak point in building noise insulation. In this paper, an active noise control system is proposed to reduce the sound transmission through a floor-level slit with evenly distributed secondary sources on its top boundary. The system performance is first investigated based on the analytical and numerical models, and simulation results indicate a decrease in active control performance with increasing frequency. The upper limit frequency of 10 dB effective control increases with a higher number of secondary sources, and the corresponding wavelength of the upper limit frequency is approximately the interval between the secondary sources when a plane wave is incident normally. Although the upper limit frequency decreases with the slit height, it approaches a constant when the slit height becomes significantly smaller than the wavelength in the incident sound. The experimental results based on a typical floor-level door slit support the findings in the numerical simulations. For a slit with a width of 0.9 m and a height of 0.005 m, the upper limit frequency of 10 dB noise reduction can reach up to 2830 Hz when ten secondary sources are employed in the experiments.

Local active control of road noise with door loudspeakers in a car cabin

Active control of road noise in car cabins has received much attention in recent years and it has been well known that local quiet zones can be created with headrest loudspeakers. The local control performance achieved with door loudspeakers is investigated in this manuscript based on the measurements in a car cabin, and it is compared with that achieved with two headrest speakers. The noise reduction performance at error microphones, the upper limit frequency of effective control, as well as the size of the quiet zone are investigated in detail. The difficulties and challenges of using the door loudspeakers for local control are discussed.

An experimental study on the upper limit frequency of global active noise control in car cabins

In this case study, the upper limit frequency for global noise control in car cabins is investigated with numerical simulations, and experimental results of global control are presented for the first time. To simulate the complicated noise field in a running car, a 1.90 m × 1.50 m × 1.10 m rectangular enclosure, which is approximately the size of a typical car is used with point monopoles evenly distributed near the boundaries generating the primary sound field. Besides verifying the fact that the upper limit frequency of effective control increases with the number of secondary sources, a formula is proposed in this paper to estimate the number of secondary sources required to achieve global control up to a certain frequency. The simulations are carried out in the time domain based on the transfer functions measured between the secondary loudspeakers and 40 evaluation points evenly distributed in a typical car, which show that the upper limit frequency of 3 dB global control is about 200 Hz while using 4 secondary sources and it can be improved to 315 Hz with 7 secondary sources. An active noise control system is realized with 16 accelerometers picking up vibration reference signals and 4 or 7 loudspeakers as secondary sources, and the real time test results in the car running at 50 km/h on a typical asphalt road demonstrated the validity of the findings in numerical simulations.

Study of dynamic biasing InGaAs/InAlAs avalanche photodiodes with different active areas.

In this work, by comparing and analyzing dynamic biasing InGaAs/InAlAs avalanche photodiodes(APDs) with different active areas, it is found that they have different noise suppression frequency ranges. The upper limit frequency(defined as the frequency at which the noise suppression effect begins to fail) of InGaAs/InAlAs APDs with active area diameter of 50 µm, 100 µm and 200 µm are 2400 MHz, 1990MHz and 1400 MHz respectively. In addition, for InGaAs/InAlAs APDs with an active area diameter of 50 µm, 100 µm and 200 µm, their optimal frequencies of dynamic biasing (defined as the frequency corresponding to the optimal SNR) are 1877MHz, 1670 MHz and 1075 MHz respectively. At last, applying dynamic biasing technology, it achieves a useful gain of 6698.1, which is much greater than that of DC bias (47.2), and this technology has the potential to be applied in high sensitivity laser radar receivers.

Decoding emotion from high-frequency steady state visual evoked potential (SSVEP)

BackgroundSteady-state visual evoked potential (SSVEP) by flickering sensory stimuli has been widely applied in the brain-machine interface (BMI). Yet, it remains largely unexplored whether affective information could be decoded from the signal of SSVEP, especially from the frequencies higher than the critical flicker frequency (an upper-frequency limit one can see the flicker). New MethodParticipants fixated on visual stimuli presented at 60 Hz above the critical flicker frequency. The stimuli were pictures with different affective valance (positive, neutral, negative) in distinctive semantic categories (human, animal, scene). SSVEP entrainment in the brain evoked by the flickering stimuli at 60 Hz was used to decode the affective and semantic information. ResultsDuring the presentation of stimuli (1 s), the affective valance could be decoded from the SSVEP signals at 60 Hz, while the semantic categories could not. In contrast, neither affective nor semantic information could be decoded from the brain signal one second before the onset of stimuli. Comparison with Existing Method(s)Previous studies focused mainly on EEG activity tagged at frequencies lower than the critical flickering frequency and investigated whether the affective valence of stimuli drew participants’ attention. The current study was the first to use SSVEP signals from high-frequency (60 Hz) above the critical flickering frequency to decode affective information from stimuli. The high-frequency flickering was invisible and thus substantially reduced the fatigue of participants. ConclusionsWe found that affective information could be decoded from high-frequency SSVEP and the current finding could be added to designing affective BMI in the future.

Ultrasonic vocalizations near 30 kHz may indicate excitement rather than distress in female Wistar rats

Rats emit ultrasonic vocalizations (USVs), sometimes referred to as 50-kHz vocalizations, during activities such as play and lower-frequency USVs, sometimes referred to as 22-kHz vocalizations, when experiencing distress. Definitions of 22-kHz vocalizations vary in terms of which frequencies should be included, with differing upper limits (e.g., 25 kHz, 30 kHz, or 33 kHz). In the current experiments, we examined the extent to which USVs near the upper frequency limit may represent milder anxiety than lower-frequency vocalizations. In Experiment 1, rats received both gentle tickling and simulated rough-and-tumble play with a human hand, while low-frequency (i.e.,18–33 kHz) and high-frequency (i.e., 34–90 kHz) USVs were recorded; rough-and-tumble play elicited significantly more low-frequency USVs (median 29.5 kHz), but also significantly more high-frequency USVs (median 50.7 kHz). In Experiment 2, rats were presented with 23-kHz, 32-kHz, and 52-kHz USVs while foraging in a T-maze. The 23-kHz USV elicited the most freezing, while the 32-kHz USV elicited significantly less freezing than either the 23- or the 52-kHz USV. Taken together, these results suggest that within the range of frequencies referred to as 22-kHz vocalizations, lower-frequency USVs may indicate a more negative affective state than higher-frequency ones. As USV production can serve as an indicator of rat welfare, an understanding of what frequencies represent positive versus negative affective states is crucial.

Development and Detection Experiment of Scanning Stage for High-throughput Gene Sequencer

In order to meet the requirements of large stroke, high precision, and high acceleration step scanning imaging of the worktable of a high-throughput gene sequencer, a mechanical ultra-precision positioning platform is designed. The XY translation table has a significant impact on the fluxes and accuracy of gene sequencing detection. Using the finite element method to analyze the structural modal and obtain the first-order natural frequency; Then using the vibration test system and laser interferometer to test the first-order natural frequency and the repeat positioning accuracy of the XY translation table. The test results show that the first-order natural frequencies of the platform in X, y and Z directions are 175Hz, 111Hz and 191Hz respectively, which is much higher than the upper-frequency limit of 16.7Hz step scanning servo bandwidth. The two-way repeat positioning accuracy of XY translation table are ± 0.462 µ m and ± 0.429 µ m, meet ± 0.6 µm. So the scanning stage can meet the index requirements of a high-throughput gene sequencers under the specified working conditions, and the measured test data combined with the modal analysis model can provide a research basis for the optimal design of the subsequent platform.

Semi-anechoic chamber for electromagnetic compatibility tests of electric propulsion thrusters

The present work deals with electromagnetic compatibility (EMC) investigations in the field of electric propulsion (EP). A semi-anechoic chamber (SAC) was set up to perform EMC tests with thrusters under operating conditions. The facility includes a semi-anechoic room and a vacuum tank. The measurement electronics currently have an upper frequency limit at 18 GHz. Initial measurements were done operating a Pulsed Plasma Thruster (PPT) to familiarize with the electronic systems. The same device under test (DUT) was investigated in a reverberation chamber (RVC) to obtain comparative results which showed good agreement. Furthermore, the anechoic chamber shows satisfactory initial measurement characteristics, which will be further tested and improved in the future. Characteristics such as chamber pressure, base noise show realistic values. The next steps are to perform measurements on radio-frequency ion thrusters (RIT) including peripherals and cabling.

A parametric blueprint for optimum cochlear outer hair cell design.

The present work examines the hypothesis that cochlear outer hair cell (OHC) properties vary in precise proportions along the tonotopic map to optimize electromechanical power conversion. We tested this hypothesis using a very simple model of a single isolated OHC driving a mechanical load. Results identify three non-dimensional ratios that are predicted to optimize power conversion: the ratio of the resistive-capacitive (RC) corner to the characteristic frequency (CF), the ratio of nonlinear to linear capacitance and the ratio of OHC stiffness to cochlear load stiffness. Optimum efficiency requires all three ratios to be universal constants, independent of CF and species. The same ratios are cardinal control parameters that maximize power output by positioning the OHC operating point on the edge of a dynamic instability. Results support the hypothesis that OHC properties evolved to optimize electro-mechanical power conversion. Identification of the RC corner frequency as a control parameter reveals a powerful mechanism used by medial olivocochlear efferent system to control OHC power output. Results indicate the upper-frequency limit of OHC power output is not constrained by the speed of the motor itself but instead is probably limited by the size of the nucleus and membrane surface area available for ion-channel expression.

Comparing dusting and fragmenting efficiency using the new SuperPulsed thulium fiber laser versus a 120 W Holmium:YAG laser.

Holmium:YAG laser lithotripsy requires high amperage power and has an upper limit of frequency and a minimal fiber size. The technology utilizing thulium-doped fiber offers low pulse energy settings and high pulse frequencies up to 2,400 Hz. We compared the novel SuperPulsed thulium fiber laser (SOLTIVE™; Olympus) to a commercially available 120 W Ho:YAG laser. Bench-top testing was conducted with 125 mm3 standardized BegoStones (Bego USA). Time to ablate the stone into particles <1 mm was recorded for efficiency calculations. Finite energy was delivered, and resulting particle sizes were measured to determine fragmentation (0.5 kJ) and dusting (2 kJ) efficiencies. Remaining mass or number of fragments were measured to compare efficacy. SOLTIVE™ was faster at ablating stones to particles <1 mm (2.23±0.22 mg/s, 0.6 J 30 Hz short pulse) compared to Ho:YAG laser (1.78±0.44 mg/s, 0.8 J 10 Hz short pulse) (p<0.001). Following 0.5 kJ of energy in fragmentation testing, fewer particles >2 mm remained using SOLTIVE™ than Ho:YAG laser (2.10 vs. 7.20 fragments). After delivering 2 kJ, dusting (1.05±0.08 mg/s) was faster using SOLTIVE™ (0.1 J 200 Hz short pulse) than 120 W 0.46±0.09 mg/s (0.3 J 70 Hz Moses) (p=0.005). SOLTIVE™ (0.1 J 200 Hz) produced more dust particles <0.5 mm (40%) compared to 24% produced by the P120 W laser at 0.3 J 70 Hz Moses and 14% at 0.3 J 70 Hz long pulse (p=0.015). The efficacy of SOLTIVE™ is superior to the 120 W Ho:YAG laser by producing smaller dust particles and fewer fragments. Further studies are warranted.

Audiograms and click spectra of seven novel and seldom-tested odontocetes

The use of auditory evoked potentials has been promoted as a means by which to collect audiometric information from odontocete cetaceans that are rarely encountered in stranding situations. This article presents the results of auditory evoked potential hearing tests collected from stranded odontocetes over nearly a decade. For six species, no audiograms previously existed – the dwarf sperm whale (Kogia sima), pygmy sperm whale (Kogia breviceps), northern right whale dolphin (Lissodelphis borealis), melon-headed whale (Peponocephala electra), long-beaked common dolphin (Delphinus capensis), and Atlantic spotted dolphin (Stenella frontalis). Additional hearing information was gathered for the pygmy killer whale (Feresa attenuata), a species for which only two prior audiograms had been collected. Audiograms for the delphinids demonstrated a typical dolphin-like form with upper-frequency limits of hearing &amp;gt; 149 kHz, except for the pygmy killer whales whose upper-frequency limit was between 103-107 kHz. The kogiid audiograms had a narrower region of increased sensitivity (80-128 kHz) closely aligned with their narrowband, high-frequency echolocation signals. Distinctions between kogiids and delphinids existed in the latencies of peaks of click-evoked auditory brainstem responses, with longer interwave intervals between P4 and N5 in the kogiids (mean of 0.60 ms vs. a mean of 0.37 ms in the delphinids). Modulation rate transfer functions collected in three of the species, suggested group-wide similarities in temporal processing capabilities.

Performance analysis and enhancement of a PVDF-based P-P sound intensity probe

This study investigates the feasibility of a laminated polyvinylidene fluoride (PVDF) structure for realising a pressure–pressure (P-P) intensity probe, as well as the effects of various backing materials on the performance of the probe. The PVDF structure consists of two parallel PVDF films that serve roles as pressure sensors, and each of them is laminated between stiff plates. The sensitivity and directivity of these pressure sensors are examined numerically and experimentally. The physical properties and configuration of the PVDF sensing structure are optimised for the best sensing performance. For frequencies below 15 kHz, the averaged voltage outputs of the two PVDF films are proportional to the sound pressure of the incident plane sound wave. It has a flat frequency response and omni-directional directivity pattern. The difference between the outputs is proportional to the particle velocity of the incident sound, featured by a dipole directivity pattern and almost-linear dependence upon frequency. Such under-covered properties of the pressure- and velocity-generated voltages for the integrated sensing structure demonstrate its suitability for intensity estimation in the aforementioned frequency range. This study shows that the probe can determine the intensity of a plane wave field below an upper-frequency limit with pre-determined probe gains. The upper limit is determined by the finite-difference approximation error introduced by the pressure gradient method. Small errors exist in narrow frequency bands around resonances and are sensitive to the pressure-intensity index, which is the ratio of the mean square pressure to the sound intensity. These errors are caused by variations of probe gains due to the resonances and can be reduced by careful calibration around the resonance frequencies.

Improved Locating Method for Local Defects in XLPE Cable Based on Broadband Impedance Spectrum

The crosslinked polyethylene (XLPE) cable safety is affected by environmental factors and artificial defects during operation. This work proposes an improved locating method based on broadband impedance spectrum (BIS) to locate local defects in XLPE cables. The calculation process of the algorithm has been analyzed. The selection of the incident Gaussian signal and the peak recognition method have been discussed, where the pulse width of the Gaussian signal was found to be determined primarily by the upper limit frequency of the traveling wave transmitting in the cable. The centroid and function fitting methods were established to reduce the peak recognition error caused by the test sampling rate. This work verified the accuracy of the algorithm through experiments. A vector network analyzer (VNA) was used to test the BIS of the cable. A 20 m-long cable containing abrasion and an inserted nail with different depths was measured in the BIS test. It was found that the abrasion and the nail could be located. The locating deviation of abrasion was within ±1%, and the centroid and function fitting methods could effectively reduce the locating deviation. The locating deviation was within ±1% when the depth of the nail inserted into the cable accounted for less than 50% of the insulation thickness. When the depth exceeded 75% of the insulation thickness, the deviation of each method was more significant, and the maximum absolute value of the deviation was 4%.

A study on coherence between virtual signal and physical signals in remote acoustic sensing.

Remote acoustic sensing can be used to estimate the error signals in human ears without placing any physical microphones there. In this paper, the coherence between the signals picked up by physical microphones over a sphere surface and the signal obtained at the sphere center is investigated. Based on the multiple channel coherence formulas in the time domain and frequency domain, the relationship between the coherence and the placement of physical microphones is analyzed by numerical simulations first, then the experimental results obtained in a reverberation chamber and a car cabin are presented to verify the simulation results. Finally, a placement of physical microphones for active control of road noise in car cabins is discussed. Both the numerical and experimental results show that an upper limit frequency exists for accurate sound pressure estimation at the center of a sphere with the sound pressure on the sphere surface. For a sufficiently complex sound field such as that in a reverberation room or in a car, half the wavelength of the upper limit frequency is about the average distance among the physical microphones.

A Novel System for Quasi-Continuous THz Signal Transmission and Reception.

This paper presents a novel system for generating and receiving quasi-continuous (QC) TeraHertz (THz) waves. A system design and theoretical foundation for QC-THz signal generation are presented. The proposed QC-THz system consists of commercially available photo-conductive antennas used for transmission and reception of THz waves and a custom-designed QC optical signal generator, which is based on a fast optical frequency sweep of a single telecom distributed-feedback laser diode and unbalanced optical fiber Michelson interferometer used for a high-frequency modulation. The theoretical model for the proposed system is presented and experimentally evaluated. The experimental results were compared to the state-of-the-art continuous-wave THz system. The comparison between the continuous-wave THz system and the proposed QC-THz system showed the ability to transmit and receive QC-THz waves up to 300 GHz. The upper-frequency limit is bounded by the length of the used Michelson interferometer. The presented design of THz signal generation has a potential for industrial application because it is cost-efficient and can be built using commercially available components.

A reinterpretation of critical flicker-frequency (CFF) data reveals key details about light adaptation and normal and abnormal visual processing.

Our ability to see flicker has an upper frequency limit above which flicker is invisible, known as the "critical flicker frequency" (CFF), that typically grows with light intensity (I). The relation between CFF and I, the focus of nearly 200 years of research, is roughly logarithmic, i.e., CFF∝log(I)-a relation called the Ferry-Porter law. However, why this law should occur, and how it relates to the underlying physiology, have never been adequately explained. Over the past two decades we have measured CFF in normal observers and in patients with retinal gene defects. Here, we reanalyse and model our data and historical CFF data. Remarkably, CFF-versus-I functions measured under a wide range of conditions in patients and in normal observers all have broadly similar shapes when plotted in double-logarithmic coordinates, i.e., log (CFF)-versus-log(I). Thus, the entire dataset can be characterised by horizontal and vertical logarithmic shifts of a fixed-shape template. Shape invariance can be predicted by a simple model of visual processing built from a sequence of low-pass filters, subtractive feedforward stages and gain adjustment (Rider, Henning & Stockman, 2019). It depends primarily on the numbers of visual processing stages that approach their power-law region at a given intensity and a frequency-independent gain reduction at higher light levels. Counter-intuitively, the CFF-versus-I relation depends primarily on the gain of the visual response rather than its speed-a conclusion that changes our understanding and interpretation of human flicker perception. The Ferry-Porter "law" is merely an approximation of the shape-invariant template.

On the Robustness and Efficiency of the Plane-Wave-Enriched FEM with Variable q-Approach on the 2D Room Acoustics Problem

Partition of unity finite element method with plane wave enrichment (PW-FEM) uses a shape function with a set of plane waves propagating in various directions. For room acoustic simulations in a frequency domain, PW-FEM can be an efficient wave-based prediction method, but its practical applications and especially its robustness must be studied further. This study elucidates PW-FEM robustness via 2D real-scale office room problems including rib-type acoustic diffusers. We also demonstrate PW-FEM performance using a sparse direct solver and a high-order Gauss–Legendre rule with a recently developed rule for ascertaining the number of integration points against the classical linear and quadratic FEMs. Numerical experiments investigating mesh size and room geometrical complexity effects on the robustness of PW-FEM demonstrated that PW-FEM becomes more robust at wide bands when using a mesh in which the maximum element size maintains a comparable value to the wavelength of the upper-limit frequency. Moreover, PW-FEM becomes unstable with lower spatial resolution mesh, especially for rooms with complex shape. Comparisons of accuracies and computational costs of linear and quadratic FEM revealed that PW-FEM requires twice the computational time of the quadratic FEM with a mesh having spatial resolution of six elements per wavelength, but it is highly accurate at wide bands with lower memory and with markedly fewer degrees of freedom. As an additional benefit of PW-FEM, the impulse response waveform of quadratic FEM in a time domain was found to deteriorate over time, but the PW-FEM waveform can maintain accurate waveforms over a long time.

An Efficiency-Enhanced 0.5-THz BWO Using Double-Slot Embedded Electron Beams to Drive a Grating Loaded Rectangular Waveguide

The backward wave oscillator (BWO) is one of the best choices for generating high-power radiation waves in the terahertz (THz) region. In order to improve the efficiency of beam&#x2013;wave interaction and output power, a novel THz BWO scheme is proposed in this article, which uses double-slot embedded electron beams (DSEEB) to drive a grating loaded rectangular waveguide (GLRW) slow wave structure (SWS). The dispersion relation and the coupling impedance of the proposed SWS are derived by using an eigenfunction method (EFM) and solved with a numerical method. The results show that the upper limit frequency and the coupling impedances are remarkably improved, which are greater than those of traditional grating SWS. Based on this scheme, a BWO operating at the frequency of 0.5 THz is designed. The particle-in-cell simulations show that the output power reaches 8.86 W with an efficiency of 0.9&#x0025;, which is 2.5 times the electronic efficiency of the conventional BWO. Thus, the proposed scheme provides a promising aim to develop the high-power THz source, which may be used in THz biomedical and material studies, and so on.