Free-field reciprocity calibration of low-frequency ultrasonic transducers

2012 ◽  
Vol 132 (3) ◽  
pp. 1956-1956
Author(s):  
M. R. Serbyn
Keyword(s):  
Free Field ◽  
Low Frequency ◽  
Ultrasonic Transducers ◽  
Reciprocity Calibration

Sensitivity to Interaural Temporal Disparities of Low- and High-Frequency Neurons in the Superior Olivary Complex. I. Heterogeneity of Responses

1997 ◽  
Vol 78 (3) ◽  
pp. 1222-1236 ◽  
Author(s):  
Ranjan Batra ◽  
Shigeyuki Kuwada ◽  
Douglas C. Fitzpatrick
Keyword(s):  
Fine Structure ◽  
High Frequency ◽  
Complex I ◽  
General Trend ◽  
Free Field ◽  
Low Frequency ◽  
Superior Olivary Complex ◽  
Field Range ◽  
Multiple Units ◽  
Additional Phase

Batra, Ranjan, Shigeyuki Kuwada, and Douglas C. Fitzpatrick. Sensitivity to interaural temporal disparities of low- and high-frequency neurons in the superior olivary complex. I. Heterogeneity of responses. J. Neurophysiol. 78: 1222–1236, 1997. Interaural temporal disparities (ITDs) are a cue for localization of sounds along the azimuth. Listeners can detect ITDs in the fine structure of low-frequency sounds and also in the envelopes of high-frequency sounds. Sensitivity to ITDs originates in the main nuclei of the superior olivary complex (SOC), the medial and lateral superior olives (MSO and LSO, respectively). This sensitivity is believed to arise from bilateral excitation converging on neurons of the MSO and ipsilateral excitation converging with contralateral inhibition on neurons of the LSO. Here we investigate whether the sensitivity of neurons in the SOC to ITDs can be adequately explained by one of these two mechanisms. Single and multiple units ( n = 124) were studied extracellularly in the SOC of unanesthetized rabbits. We found units that were sensitive to ITDs in the fine structure of low-frequency (<2 kHz) tones and also units that were sensitive to ITDs in the envelopes of sinusoidally amplitude-modulated high-frequency tones. For both categories there were “peak-type” units that discharged maximally at a particular ITD across frequencies or modulation frequencies. These units were consistent with an MSO-type mechanism. There were also “trough-type” units that discharged minimally at a particular ITD. These units were consistent with an LSO-type mechanism. There was a general trend for peak-type units to be located in the vicinity of the MSO and for trough-type units to be located in the vicinity of the LSO. Units of both types appeared to encode ITDs within the estimated free-field range of the rabbit (±300 μs). Many units had varying degrees of irregularities in their responses, which manifested themselves in one of two ways. First, for some units there was no ITD at which the response was consistently maximal or minimal across frequencies. Instead there was an ITD at which the unit consistently responded at some intermediate level. Second, a unit could display considerable jitter from frequency to frequency in the ITD at which it responded maximally or minimally. Units with irregular responses had properties that were continuous with those of other units. They therefore appeared to be variants of peak- and trough-type units. The irregular responses could be modeled by assuming additional phase-locked inputs to a neuron in the MSO or LSO. The function of irregularities may be to shift the ITD sensitivity of a neuron without requiring changes in the anatomic delays of its inputs.

scholarly journals Development of Low Frequency High Temperature Ultrasonic Transducers for In-service Monitoring of Pipework in Power Plants

2016 ◽  
Vol 168 ◽  
pp. 983-986 ◽  
Author(s):  
A. Dhutti ◽  
S.A. Tumin ◽  
A. Mohimi ◽  
M. Kostan ◽  
T.H. Gan ◽  
...  
Keyword(s):  
High Temperature ◽  
Power Plants ◽  
Low Frequency ◽  
Ultrasonic Transducers ◽  
Service Monitoring

scholarly journals Variations between Foundation-Level and Free-Field Earthquake Ground Motions

2000 ◽  
Vol 16 (2) ◽  
pp. 511-532 ◽  
Author(s):  
Jonathan P. Stewart
Keyword(s):  
Free Field ◽  
Low Frequency ◽  
Strong Motion ◽  
Dimensionless Frequency ◽  
Spectral Acceleration ◽  
Ground Acceleration ◽  
Attenuation Relations ◽  
Ground Motion Selection ◽  
Motion Data ◽  
Embedded Foundations

Strong motion data from sites having both an instrumented structure and free-field accelerograph are compiled to evaluate the conditions for which foundation recordings provide a reasonably unbiased estimate of free-field motion with minimal uncertainty. Variations between foundation and free-field spectral acceleration are found to correlate well with dimensionless parameters that strongly influence kinematic and inertial soil-structure interaction phenomena such as embedement ratio, dimensionless frequency (i.e., product of radial frequency and foundation radius normalized by soil shear wave velocity), and ratio of structure-to-soil stiffness. Low frequency components of spectral acceleration recorded on shallowly embedded foundations are found to provide good estimates of free-field motion. In contrast, foundation-level peak ground acceleration (both horizontal and vertical) and maximum horizontal velocity, are found to be de-amplified. Implications for ground motion selection procedures employed in attenuation relations are discussed, and specific recommendations are made as to how these procedures could be improved.

Acoustic Barriers Based on Sonic Crystals

2007 ◽  
Author(s):  
V. Romero-Garci´a ◽  
E. Fuster-Garcia ◽  
L. M. Garci´a-Raffi ◽  
J. V. Sa´nchez-Pe´rez
Keyword(s):  
Geometric Distribution ◽  
Free Field ◽  
Low Frequency ◽  
Optimization Methods ◽  
Band Gaps ◽  
High Symmetry ◽  
Low Frequencies ◽  
Periodic Arrays ◽  
Sonic Crystals ◽  
High Sound

Environmental noise problems become an standard topic across the years. Acoustic barriers have been purposed as a possible solution because they can act creating an acoustic attenuation zone which depends on the sound frequency, reducing the sound transmission through it. It was demonstrated that at high sound frequencies the effect of the barriers is more pronounced than at low frequencies, due to the diffraction in their edges. Sonic Crystals (SCs) are periodic arrays of scatterers embedded in a host material with strong modulation of its physical properties, that produces band gaps attenuation in frequencies related with their geometry. These frequencies are explained by the well known Bragg’s diffraction inside the crystal. SCs present different high symmetry directions, where the Bragg’s peaks appears in different frequencies ranges due to the variation of the geometry in each direction. Recently, some authors have studied the possibility to use SCs to reduce noise in free-field condition. Also, it was showed that SCs built by trees are acoustic systems that present acoustic band gaps in low frequency range due to the geometric distribution of the trees. These results led us think that these structures are a suitable device to reduce noise, this means SCs could be use as acoustic barriers. Nevertheless the technological application of these devices for controlling the noise present some problems. First, the angular dependence of the frequencies attenuated when the sound impinges over the SC. Second, the fact that the necessary space to put the SC is bigger than in the case of the traditional acoustic barriers. Finally, the necessity of some robust and long-lasting materials to use them outdoors. In this paper we show the possibility to use different materials (rigid, mixed or soft) to make scatterers, explaining their advantages or disadvantages. These materials in conjunction with some optimization methods will allow us find some solutions to the problems mentioned above. We will relate both acoustic systems, acoustic barriers and SCs, making a comparison of the main properties of each one and then, we will present the technological possibilities to design acoustic barriers based on SCs.

scholarly journals Bimodal Cochlear Implant Listeners’ Ability to Perceive Minimal Audible Angle Differences

2019 ◽  
Vol 30 (08) ◽  
pp. 659-671 ◽  
Author(s):  
Ashley Zaleski-King ◽  
Matthew J. Goupell ◽  
Dragana Barac-Cikoja ◽  
Matthew Bakke
Keyword(s):  
Cochlear Implant ◽  
Sound Localization ◽  
Repeated Measures ◽  
Free Field ◽  
Low Frequency ◽  
Spatial Location ◽  
Speech Understanding ◽  
Repeated Measures Design ◽  
Acoustic Environments ◽  
The Right

AbstractBilateral inputs should ideally improve sound localization and speech understanding in noise. However, for many bimodal listeners [i.e., individuals using a cochlear implant (CI) with a contralateral hearing aid (HA)], such bilateral benefits are at best, inconsistent. The degree to which clinically available HA and CI devices can function together to preserve interaural time and level differences (ITDs and ILDs, respectively) enough to support the localization of sound sources is a question with important ramifications for speech understanding in complex acoustic environments.To determine if bimodal listeners are sensitive to changes in spatial location in a minimum audible angle (MAA) task.Repeated-measures design.Seven adult bimodal CI users (28–62 years). All listeners reported regular use of digital HA technology in the nonimplanted ear.Seven bimodal listeners were asked to balance the loudness of prerecorded single syllable utterances. The loudness-balanced stimuli were then presented via direct audio inputs of the two devices with an ITD applied. The task of the listener was to determine the perceived difference in processing delay (the interdevice delay [IDD]) between the CI and HA devices. Finally, virtual free-field MAA performance was measured for different spatial locations both with and without inclusion of the IDD correction, which was added with the intent to perceptually synchronize the devices.During the loudness-balancing task, all listeners required increased acoustic input to the HA relative to the CI most comfortable level to achieve equal interaural loudness. During the ITD task, three listeners could perceive changes in intracranial position by distinguishing sounds coming from the left or from the right hemifield; when the CI was delayed by 0.73, 0.67, or 1.7 msec, the signal lateralized from one side to the other. When MAA localization performance was assessed, only three of the seven listeners consistently achieved above-chance performance, even when an IDD correction was included. It is not clear whether the listeners who were able to consistently complete the MAA task did so via binaural comparison or by extracting monaural loudness cues. Four listeners could not perform the MAA task, even though they could have used a monaural loudness cue strategy.These data suggest that sound localization is extremely difficult for most bimodal listeners. This difficulty does not seem to be caused by large loudness imbalances and IDDs. Sound localization is best when performed via a binaural comparison, where frequency-matched inputs convey ITD and ILD information. Although low-frequency acoustic amplification with a HA when combined with a CI may produce an overlapping region of frequency-matched inputs and thus provide an opportunity for binaural comparisons for some bimodal listeners, our study showed that this may not be beneficial or useful for spatial location discrimination tasks. The inability of our listeners to use monaural-level cues to perform the MAA task highlights the difficulty of using a HA and CI together to glean information on the direction of a sound source.

Central and peripheral contributions to coding of acoustic space by neurons in inferior colliculus of cat

1986 ◽  
Vol 55 (3) ◽  
pp. 587-603 ◽  
Author(s):  
M. B. Calford ◽  
D. R. Moore ◽  
M. E. Hutchings
Keyword(s):  
Inferior Colliculus ◽  
Single Unit ◽  
Arrival Time ◽  
Interaural Time Difference ◽  
Free Field ◽  
Low Frequency ◽  
Intensity Function ◽  
Central Nucleus ◽  
Stimulus Position ◽  
Acoustic Space

Recordings of response to free-field stimuli at best frequency were made from single units in the central nucleus of the inferior colliculus of anesthetized cats. Stimulus position was varied in azimuth, and the responses of units were compared with variation in the intensity and arrival time of the sound at each ear, derived from cochlear microphonic (CM) recordings. CM recordings were made at each frequency and at every point in space for which single-unit data were collected. Interaural time difference (delay) increased monotonically, but not linearly, as the stimulus was moved away from the midline. However, a given delay did not represent a single azimuth across frequency. Low-frequency interaural intensity differences (IIDs) were monotonic across azimuth and peaked at, or near, the poles. Higher-frequency IIDs were nonmonotonic and peaked relatively close to the midline, decreasing toward the poles. Units that showed little variation in discharge across azimuth formed 28% of the sample and were classified as omnidirectional. For other units, the spike-count intensity function and the variation of the CM with azimuth were combined to form a derived monaural azimuth function. For 29% of those units showing azimuthal sensitivity, the derived monaural azimuth function matched the actual azimuth function. This suggested that these units received input from only one ear. The largest group of azimuthally sensitive units (47%) was formed from those units inferred to be IID sensitive. At higher frequencies these units displayed a peaked azimuth function paralleling the nonmonotonic relation of IID to azimuth. The proportion of inferred IID-sensitive units was close to that found in dichotic studies.

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