Piezoelectric micromachined ultrasonic transducers (PMUTs) are widely used for ultrasound imaging and sensing applications that require broad bandwidth. A single PMUT is normally smaller than its ...wavelength and, therefore has small acoustic impedance and bandwidth. To make PMUTs broadband and desirable for advanced applications, this paper demonstrates equivalent circuit and finite element method (FEM) modeling results of mutual acoustic impedance impact on the frequency and bandwidth of an element including a group of PMUTs in parallel connection. The equivalent circuit analysis was shown to be a computing-efficient method with good agreement with FEM simulation results. To maximize bandwidth, various PMUT elements with different diaphragm numbers and pitches were designed, fabricated, characterized, and optimized to be 3×3 and 82 μm, respectively. The PMUT element with a center frequency of 6.5 MHz and a −6 dB fractional bandwidth of 107.6 % was demonstrated, compared to 6 MHz center frequency and 32.5 % fractional bandwidth for 1×1 and 7.8 MHz center frequency and 60.7 % fractional bandwidth for 8×8. Meanwhile, the optimized PMUT element shows a high transmitting performance of 195 Pa/V at 2 cm away from the element.
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•This paper demonstrates equivalent circuit and finite element method simulation results of mutual acoustic impedance impact on PMUT elements’ bandwidth and frequency with good agreement.•To maximize bandwidth, various membrane numbers and pitches of PMUT elements were studied and optimized to be 3×3 and 82 μm, respectively, via a computing-efficient method which was verified by FEM simulation and measurement results.•Based on systemic studies of mutual acoustic radiation effect, the optimized PMUT element with a center frequency of 6.5 MHz was fabricated and characterized, showing the transmitting performance of 195 Pa/V at 2 cm away and the fractional bandwidth of 107.6 % with a small footprint of 0.0557 mm2, which makes it ideal for miniature 2D phased array applications.
•The effect of Rint and aK on the thermal conductivity (k) of the oxide-composite is investigated.•The Rint between the SBTO and LSMO phases does not reduce k of the composite for particle size ...greater than aK.•A significant reduction in k of composite, lower than km is observed for particle size of LSMO smaller than aK.
We present a novel approach to reduce the thermal conductivity (k) in thermoelectric composite materials using acoustic impedance mismatch and the Debye model. Also, the correlation between interface thermal resistance (Rint) and the particle size of the dispersed phase on the k of the composite is discussed. In particular, the k of an oxide composite, which consists of a natural superlattice Aurivillius phase (SrBi4Ti4O15) as a matrix and perovskite (La0.7Sr0.3MnO3) as a dispersed phase, is investigated. A significant reduction in k of composite, even lower than the k of the matrix when the particle size of La0.7Sr0.3MnO3 is smaller than the Kapitza radius (aK) is observed, depicting that Rint dominates for particle size lower than aK due to increased surface to volume ratio. The obtained results have the potential to provide new directions for engineering composite thermoelectric systems with desired thermal conductivity and promising in the field of energy harvesting.
U.S. national wideband absorbance (WBA) data for 17,446 ears included in the National Health and Nutrition Examination Surveys for 2015-2016 and 2017-2020 were analyzed to develop and apply normative ...reference intervals (RIs).
Analyses used distribution-free medians and cumulative distribution functions (CDFs). Notable differences between medians were defined as those with non-overlapping 95% confidence intervals, and differences between CDFs were evaluated using Cohen's
effect size. Strict inclusion criteria identified "healthy ears" with 1,240 ears meeting all the inclusion criteria for the reference group. RIs, WBA values corresponding to the 2.5th and 97.5th percentiles for the reference group, were established. The established RIs were then applied to the full unscreened data set to determine the prevalence of WBA values outside the RIs.
WBA RIs were established for all 6- to 19-year-olds and for 20- to 69-year-olds separated into three groups: females, males, and non-Hispanic Asians. The differences among the CDFs underlying these RIs corresponded to small effect sizes. When a single RI, 0.40 < average WBA < 0.75, was applied to the full data set, about 6%-13% of ears fell outside the derived RIs. Logistic regression analyses found abnormal tympanometric results to be responsible for the extreme WBA values among the general population. Abnormal tympanometric results increased the odds of having WBA values outside the RI by ≥ 300%.
U.S. population data for healthy ears were used to establish RIs for WBA of about 0.40-0.75. About 6%-13% of Americans, 6-80+ years of age, had WBA values outside these RI limits.
https://doi.org/10.23641/asha.24185745.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, OILJ, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK, VSZLJ
A novel method for simultaneous measurement of temperature and acoustic impedance based on forward Brillouin scattering (FBS) in a thin polyimide-coated G657 single-mode optical fiber is proposed. By ...measuring the changes of frequency shift and linewidth of the FBS spectrum corresponding to a certain transverse acoustic mode, temperature and acoustic impedance sensing can be realized with high sensitivity, high mechanical strength and relatively high accuracy. The linewidth-temperature, frequency shift-acoustic impedance and linewidth-acoustic impedance coefficients of the polyimide-coated fiber are 19.5, 5.5 and 5.9 times of those of the bare LEAF, respectively. In a proof-of-concept experiment, the thin polyimide-coated G657 is used as the sensing fiber, and the temperature and acoustic impedance measurement errors are 0.17 °C and 0.007 MRayl, respectively. The proposed FBS based sensor is expected to become a simple, accurate fiber sensor with potential advantages of durable and stable for simultaneously measuring temperature and acoustic impedance, which has great potential in many practical applications.
The distributed fibre sensing technology based on backward stimulated Brillouin scattering (BSBS) is experiencing a rapid development. However, all reported implementations of distributed Brillouin ...fibre sensors until today are restricted to detecting physical parameters inside the fibre core. On the contrary, forward stimulated Brillouin scattering (FSBS), due to its resonating transverse acoustic waves, is being studied recently to facilitate innovative detections in the fibre surroundings, opening sensing domains that are impossible with BSBS. Nevertheless, due to the co-propagating behaviour of the pump and scattered lights, it is a challenge to position-resolve FSBS information along a fibre. Here we show a distributed FSBS analysis based on recovering the FSBS induced phase change of the propagating light waves. A spatial resolution of 15 m is achieved over a length of 730 m and the local acoustic impedances of water and ethanol in a 30 m-long uncoated fibre segment are measured, agreeing well with the standard values.
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•We propose a hybrid composite meta-porous structure.•Spatial fluctuation and slow wave effect exist.•Balance between inner losses and the leakage of the acoustic energy.•A detailed ...discussion on the effect of geometric parameters.•Acoustic impedance tube test are conducted.
In order to improve and broaden the sound absorption performance of porous materials with low flow resistance, this study proposes the composite meta-porous structure embedded multiple lateral plates of different lengths, and investigates the corresponding sound absorption coefficients with the fixed and periodic boundary. Characteristics of spatial fluctuation and slow wave effect are embodied in acoustic pressure distributions. Further, the hybrid composite meta-porous structure with periodic boundary could achieve high sound absorption in range of 0–6.4 kHz. The Theoretical model using transfer matrix method suitable for these models is proposed, and verify the FEM results. Normalized surface impedance, phase and trajectory of the complex reflective coefficient illustrates the loss of acoustic energy inside the structure and leakage to the outside. By detailed discussion on the relationship between the geometric parameters and the corresponding sound absorption coefficients, the three boundaries would have different effects on sound absorption performance. Sound absorption test results by acoustic impedance tube confirm the rationality of the composite meta-porous structure with fixed boundary in range of 0.2–5.716 kHz and its practical application in the noise reduction.
In this Letter, we theoretically propose and experimentally demonstrate a three-dimensional soundproof acoustic cage structure, hereby denoted as an acoustic metacage. The metacage is composed of six ...acoustic metamaterial slabs with open holes and hidden bypass space coiling tunnels connected to the holes. Band structure analysis reveals a novel physical mechanism to open a low-frequency broad partial band gap via the band folding in other directions, which can also be interpreted by an effective medium with indefinite effective mass density and negative effective modulus. Transmission loss in simulations and in the acoustic impedance tube are administered. Strikingly, we prove that the soundproofing effect of the metacage is robust against the airflow perturbation induced by a fan. Our work paves a road for low-frequency airborne soundproof structures in the presence of ventilation.
Ultrasound-triggered drug delivery has been widely researched for its potential to improve the therapeutic efficacy of drugs. This paper presents drug release using hydrogel microbeads with release ...enhancer for efficient ultrasound-triggered drug delivery. By using a centrifuge-based microfluidic device, drug-model-encapsulating calcium alginate hydrogel microbeads containing tungsten particles with high acoustic impedance were fabricated. Because the tungsten particles work as release enhancer, the hydrogel microbeads become to have high sensitivity to ultrasound with localized variation in acoustic impedance so that the release rate of drug models improves. By applying ultrasound at 20 kHz to the hydrogel microbeads, the release of fluorescent silica nanoparticles that are a drug model for virus vectors, micelles, and proteins was tested. Importantly, the proposed hydrogel microbeads released the drug model even under a cavitation-suppressed environment. Furthermore, the additional coating on the hydrogel microbeads with poly-l-lysine enabled us to adjust the release rate of the drug model. The proposed ultrasound-triggered drug release system using release enhancer is expected to be an effective approach for expanding the varieties of applicable treatments using on-demand drug delivery systems.
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•Calcium alginate hydrogel beads containing silica drug models and tungsten particles were fabricated by cetrifuge-based method.•Tungsten particles made localized acoustic impedance changes in the microbeads to increase their sensitivity to ultrasound.•3% tungsten particles improved the release rate of silica nanoparticles by 1.5 times from the beads by ultrasound stimuli.•The base leakage of silica nanoparticles from the hydrogel microbeads was controlled by poly-l-lysine coating.•Ultrasound-triggered controlled release of silica nanoparticles and bovine serum albumin was demonstrated for 96 h.
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