Acoustic Attenuation Performance of Two-Pass Perforated Hybrid Mufflers with Mean Flow

The one-dimensional (1-D) analytical approach is developed to predict and analyze the acoustic attenuation performance of two-pass perforated hybrid mufflers in the presence of mean flow. The expressions of complex acoustic wavenumber and impedance of long fiber glass wool are presented by using the impedance tube measurement and curve fitting. The 1-D approaches as well as the fitting expressions are validated by comparing the predicted and measured transmission loss of two-pass perforated hybrid mufflers with a different Mach number. Results illustrate that the 1-D predictions agree well with measurements below the plane wave cut-off frequency and deviate in higher frequency range. The influences of geometric parameters including the lengths of extended tubes, perforations on the right bulkhead and the outlet tube, and mean flow on the acoustic attenuation behavior of the hybrid mufflers are examined.

On the recovering of acoustic attenuation in 2D acoustic tomography

The inverse problem of recovering the acoustic attenuation in the inclusions inside the human tissue is considered. The coefficient inverse problem is formulated for the first-order system of PDE. We reduce the inverse problem to the optimization of the cost functional by gradient method. The gradient of the functional is determined by solving a direct and conjugate problem. Numerical results are presented.

Influence of surgical and N95 face masks on speech perception and listening effort in noise

Daily-life conversation relies on speech perception in quiet and noise. Because of the COVID-19 pandemic, face masks have become mandatory in many situations. Acoustic attenuation of sound pressure by the mask tissue reduces speech perception ability, especially in noisy situations. Masks also can impede the process of speech comprehension by concealing the movements of the mouth, interfering with lip reading. In this prospective observational, cross-sectional study including 17 participants with normal hearing, we measured the influence of acoustic attenuation caused by medical face masks (mouth and nose protection) according to EN 14683 and of N95 masks according to EN 1149 (EN 14683) on the speech recognition threshold and listening effort in various types of background noise. Averaged over all noise signals, a surgical mask significantly reduced the speech perception threshold in noise was by 1.6 dB (95% confidence interval [CI], 1.0, 2.1) and an N95 mask reduced it significantly by 2.7 dB (95% CI, 2.2, 3.2). Use of a surgical mask did not significantly increase the 50% listening effort signal-to-noise ratio (increase of 0.58 dB; 95% CI, 0.4, 1.5), but use of an N95 mask did so significantly, by 2.2 dB (95% CI, 1.2, 3.1). In acoustic measures, mask tissue reduced amplitudes by up to 8 dB at frequencies above 1 kHz, whereas no reduction was observed below 1 kHz. We conclude that face masks reduce speech perception and increase listening effort in different noise signals. Together with additional interference because of impeded lip reading, the compound effect of face masks could have a relevant impact on daily life communication even in those with normal hearing.

An investigation of the use of transmission ultrasound to guide minimally invasive thermal therapy

Minimally Invasive Thermal Therapy (MITT) is an effective way for the treatment of localized cancer and could replace surgery, chemotherapy or radiation. During MITT, high temperatures in the range of 55-95 °C are produced locally in the target tissue or tumour, resulting in localized protein coagulation. A real-time imaging method is required to guide the procedure of thermal therapy. Ideally, this imaging modality should be noninvasive, inexpensive and easily used and interpreted. It is known that acoustic attenuation is sensitive to both the tissue temperature and the structural changes due to protein coagulation (the endpoint of any thermal therapy treatment) during thermal therapy. Transmission ultrasound imaging is a real-time imaging modality which measures the attenuation property of ultrasound. The goal of this work is to demonstrate the potential of ultrasound attenuation imaging during MITT to quantitatively monitor lesion formation dynamics. An important finding of the present study is that the temporal changes in acoustic attenuation during MITT follow a reproducible pattern in albumen phantoms and bovine liver tissue within the range of thermal therapy temperatures. After heating, the measured attenuation remains higher than the initial amount, suggesting that this irreversible increase is a result of the structural change due to protein coagulation.

An investigation of the use of transmission ultrasound to guide minimally invasive thermal therapy

Minimally Invasive Thermal Therapy (MITT) is an effective way for the treatment of localized cancer and could replace surgery, chemotherapy or radiation. During MITT, high temperatures in the range of 55-95 °C are produced locally in the target tissue or tumour, resulting in localized protein coagulation. A real-time imaging method is required to guide the procedure of thermal therapy. Ideally, this imaging modality should be noninvasive, inexpensive and easily used and interpreted. It is known that acoustic attenuation is sensitive to both the tissue temperature and the structural changes due to protein coagulation (the endpoint of any thermal therapy treatment) during thermal therapy. Transmission ultrasound imaging is a real-time imaging modality which measures the attenuation property of ultrasound. The goal of this work is to demonstrate the potential of ultrasound attenuation imaging during MITT to quantitatively monitor lesion formation dynamics. An important finding of the present study is that the temporal changes in acoustic attenuation during MITT follow a reproducible pattern in albumen phantoms and bovine liver tissue within the range of thermal therapy temperatures. After heating, the measured attenuation remains higher than the initial amount, suggesting that this irreversible increase is a result of the structural change due to protein coagulation.