Acoustic Transfer Characteristics Research Articles

Numerical simulation on acoustic streaming characteristics in boiler tube array

Strong sound can produce acoustic streaming around the tube, which can change the flow state around the tube, and then affect the heat exchange between the tube and the surrounding medium. In order to obtain the influence law of sound wave on the heat transfer characteristics in the tube array, firstly, we study the acoustic streaming and heat transfer characteristics around a single cylindrical tube by the scheme of theoretical derivation and simulation. On this basis, we study the acoustic streaming and heat transfer characteristics in the periodic tube array. The results show that the acoustic streaming structure outside the tube is axially symmetric, and the flow direction of the inner vortices and the outer vortices are opposite. When the frequency is constant, sound pressure level (SPL) only changes the acoustic streaming velocity, not the acoustic streaming distribution. As the frequency continues to increase, the velocity peak gradually shifts from the inner vortex to the outer vortex, so the outer vortex velocity gradually becomes the main body of flow. Low frequency and high intensity sound waves can form strong acoustic streaming movement and enhance heat transfer outside the tube. In the tube array, the acoustic streaming distribution should consider the effect of different incident directions on crystal plane spacing. For incident angle φ = 0°∼34°, the ratio of maximum velocity of outer vortex to the one of inner vortex an Nusselt number (Nu) are increasing with φ increasing. In this stage, the heat transfer effect changes greatly with the change of angle. For incident angle φ = 35°∼45°, the inner and outer vortex flow velocity and Nu increases together, but the scale of outer vortex decreases. In this stage, with the change of angle, the heat transfer effect changes less due to the reduction of the scale of outer vortex dominating heat transfer between tubes. In tube arrays, the optimal flow field incidence angle is φ = 34 °and the optimal heat transfer incidence angle is φ = 45°. The sound band gap and sound pressure level enhancement exist in the tube array, which affects the acoustic streaming distribution. The results are helpful to reveal the mechanism of acoustic streaming more clearly and provide a basis for the augmentation of heat transfer in tube arrays by acoustic waves.

Numerical Investigation of Influence of Entropy Wave on the Acoustic and Wall Heat Transfer Characteristics of a High-Pressure Turbine Guide Vane

As an indirect noise source generated in the combustion chamber, entropy waves are widely prevalent in modern gas turbines and aero-engines. In the present work, the influence of entropy waves on the downstream flow field of a turbine guide vane is investigated. The work is mainly based on a well-known experimental configuration called LS89. Two different turbulence models are used in the simulations which are the standard k-ω model and the scale-adaptive simulation (SAS) model. In order to handle the potential transition issue, Menter’s ð-Reθ transition model is coupled with both models. The baseline cases are first simulated with the two different turbulence models without any incoming perturbation. Then one forced case with an entropy wave train set at the turbine inlet at a given frequency and amplitude is simulated. Results show that the downstream maximum Mach number is rising from 0.98 to 1.16, because the entropy waves increase the local temperature of the flow field; also, the torque of the vane varies as the entropy waves go through, the magnitude of the oscillation is 7% of the unforced case. For the wall (both suction and pressure side of the vane) heat transfer, the entropy waves make the maximum heat transfer coefficient nearly twice as the large at the leading edge, while the minimum heat transfer coefficient stays at a low level. As for the averaged normalized heat transfer coefficient, a maximum difference of 30% appears between the baseline case and the forced case. Besides, during the transmission process of entropy waves, the local pressure fluctuates with the wake vortex shedding. The oscillation magnitude of the pressure wave at the throat is found to be enhanced due to the inlet entropy wave by applying the dynamic mode decomposition (DMD) method. Moreover, the transmission coefficient of the entropy waves, and the reflection and transmission coefficients of acoustic waves are calculated.

Modeling perceived externalization of a static, lateral sound image

Perceived externalization is a relevant feature to create an immersive acoustic environment with headphone reproduction. In the present study, listener-specific acoustic transfer characteristics for an azimuth angle of 90° were modified to investigate the role of monaural spectral cues, interaural level differences (ILDs), and temporal fluctuations of ILDs on perceived externalization in anechoic and reverberant environments. Listeners’ ratings suggested that each acoustic cue was important for perceived externalization. If only one correct acoustic cue remained in the ear signals, the sound image could not be perceived as fully externalized. Reverberation did reduce but not eliminate the influences of monaural spectral and ILD cues on perceived externalization. Additionally, the spectral details of the ipsilateral ear signal were more important for perceived externalization than those in the contralateral ear signal. A computational model was proposed to quantify those relationships and predict externalization ratings by comparing the acoustic cues extracted from the target (modified) and template (non-processed) binaural signals after several auditory processing steps. The accuracy of predicted externalization ratings was higher than 90% under all experimental conditions.

Evaluation of fetal exposure to external loud noise using a sheep model: quantification of in utero acoustic transmission across the human audio range

There is mounting evidence that neural memory traces are formed by auditory learning in utero and that premature newborns are particularly sensitive to the intense, sustained noises or impulses sounds associated with the use of intensive care equipment. One area of critical importance is the determination of sound level exposure in utero associated with maternal occupation. The attenuation factors provided by the abdomen and tissue as well as the routes by which the inner ear receives stimulation need careful consideration and investigation to provide prenatal protection from external sound levels and frequencies that may cause harm. To measure how sound from external sound sources is transmitted to the fetus inside the uterus of a pregnant sheep in 6 Hz frequency steps between 100 Hz and 20 kHz (ie, across most of the human audio range). We measured acoustic transfer characteristics invivo in 6 time-mated singleton pregnant Romney ewes (gestational age, 103-130 days, weight, 54-74 kg). Under general anesthesia and at hysterotomy, a calibrated hydrophone was attached to the occiput of the fetal head within the amniotic sac. Two calibrated microphones were positioned in the operating theater, close to the head and to the body of each ewe. Initial experiments were carried out on 3 pregnant ewes 3 days after transport recovery to inform the data acquisition protocol. This was followed by detailed data acquisition of 3 pregnant ewes under general anesthesia, using external white noise signals. Voltage signals were acquired with 2 calibrated microphones, located near the head and the body of each ewe and with a calibrated hydrophone located in the amniotic fluid. Measurement of acoustic transmission through the maternal abdominal and uterine walls indicates that frequency contents above 10 kHz are transmitted into the amniotic sac and that some frequencies are attenuated by as little as 3 dB. This study provides new data about in utero sound transmission of external noise sources beyond physiological noise (cardiovascular, respiratory, and intestinal sounds), which help quantity the potential for fetal physiological damage resulting from exposure to high levels of noise during pregnancy. Fine-frequency acoustic attenuation characteristics are essential to inform standards and clinical recommendations on exposure of pregnant women to noise. Such transfer functions may also inform the design of filters to produce an optimal acoustic setting for maternal occupational noise exposure, use of magnetic resonance imaging during pregnancy, and for neonatal incubators.

Sound intensity transfer path analysis and its application to analyze the acoustics in vehicle interior

A new technology based on conventional transfer path analysis (TPA) called sound intensity TPA (SITPA) is proposed and applied to analyze the acoustic field in a vehicle interior excited by a pair of front speakers. First, we introduce an analogy of a mass-spring-damper system for our intuitive understanding of sound intensity. On the basis of the analogy, we determined that the active and reactive components of sound intensity represent energy transmission and storage in the acoustic field, respectively. Next, formulation of SITPA, which extends the capability of conventional TPA, is introduced and demonstrates how SITPA expresses the sound intensity at the receiver by using the sum of partial sound intensities transferred from multiple sound sources. Application of SITPA shows that the active and reactive components of partial sound intensities generated by the interference of front-left and front-right speakers can be changed by modifying not only acoustic transfer characteristics of the vehicle interior but also phase-lag of input signals for speakers. The effect of modifying the phase-lag on the sound intensity is experimentally examined under the scheme for minimizing and maximizing reactive sound intensity.

Acoustic transfer characteristics study through the fingers vibrations using wrist vibrator

In these days, people are exposed in many kind of noise, such as machinery, aircraft, construction site, or road traffic. The noise is situated in one part of the modern life of human. In this study, we confirmed that the characteristics of acoustic transmission through the finger in noisy environment. To investigate the function of the sound transfer to ear, we measure the vibration from the wrist actuator fingertips to figure out the mechanisms of transmission. And we using the bone-conduction equivalent circuit for compensation with normal hearing and estimate the acoustic characteristics. The experiment of propose mechanism, set the noise environment with monitor speakers in semi-anechoic room and check the acoustic transfer performance.

Type 1 Tympanoplasty by Cartilage Palisade and Temporalis Fascia Technique: A Comparison.

(1) To compare graft take up of type-1 tympanoplasty with cartilage palisade technique with those of type-1 tympanoplasty using autotemporalis fascia. (2) To compare hearing results of type 1 tympanoplasty with cartilage palisade technique with those of type-1 tympanoplasty using autotemporalis fascia. A prospective clinical study. It consisted of 60 patients divided into two groups of 30 patients each. After randomization 30 patients underwent type 1 tympanoplasty using cartilage palisade technique and 30 underwent type 1 tympanoplasty using autotemporalis fascia. In follow up, pure tone audiogram were carried out at 2nd, 4th and 6th month. Clinical assessment was done at 2nd 4th and 6th month. The graft uptake rate between the group 1 and group 2 are 93.33 and 90% respectively. As p value was greater than 0.05 so statistically there is no significant difference between the two group. The post operative air bone gap of the two groups were compared using student t test. The pre op mean of group 1 was 32.5db and pre op mean of group 2 was 30.66db. The post op mean of group 1 was 21.33, with standard deviation of 3.6984 and standard error of 0.67523. The post op mean of group 2 was 21.09 with standard deviation of 3.29 and standard error of 0.58261. t value was 0.1357. Analysis was done using student t test and p value was found to be greater than 0.05. p value is greater than 0.05 which shows that there is no statistical difference between the two groups. This study establishes the fact that hearing results after performing type 1 tympanoplasty by autotemporalis fascia when compared with type 1 tympanoplasty performed by cartilage palisade technique showed similar hearing gain and post operatively graft take up rate was also similar in two groups. The disadvantage of reducing the mechanical vibration of the tympanic membrane was overcome by the palisade reconstruction of the tympanic membrane. This study definitely emphasizes upon usage of new grafting materials in reconstruction of tympanic membrane, with similar, if not better functional results, without compromising the acoustic transfer characteristics.

Comparative acoustic performance and mechanical properties of silk membranes for the repair of chronic tympanic membrane perforations

The acoustic and mechanical properties of silk membranes of different thicknesses were tested to determine their suitability as a repair material for tympanic membrane perforations. Membranes of different thickness (10–100μm) were tested to determine their frequency response and their resistance to pressure loads in a simulated ear canal model. Their mechanical rigidity to pressure loads was confirmed by tensile testing. These membranes were tested alongside animal cartilage, currently the strongest available myringoplasty graft as well as paper, which is commonly used for simpler procedures. Silk membranes showed resonant frequencies within the human hearing range and a higher vibrational amplitude than cartilage, suggesting that silk may offer good acoustic energy transfer characteristics. Silk membranes were also highly resistant to simulated pressure changes in the middle ear, suggesting they can resist retraction, a common cause of graft failure resulting from chronic negative pressures in the middle ear. Part of this strength can be explained by the substantially higher modulus of silk films compared with cartilage. This allows for the production of films that are much thinner than cartilage, with superior acoustic properties, but that still provide the same level of mechanical support as thicker cartilage. Together, these in vitro results suggest that silk membranes may provide good hearing outcomes while offering similar levels of mechanical support to the reconstructed middle ear.

Acoustic and heat transfer characteristics of an impinging elliptical synthetic jet generated by acoustic actuator

Abstract The acoustic aspects and average heat transfer characteristics of an elliptic synthetic jet impinging on a heated flat plate were experimentally investigated and compared with circular, rectangular and square orifices having same equivalent diameter. The aim of the study is to investigate the effect of orifice shape, aspect ratio and operating parameters of the synthetic jet at which optimum acoustic and heat transfer performance is obtained. It is found that irrespective of the shape of the orifice, the synthetic jet generates the minimum sound pressure level when operated at its resonance frequency, which is equal to the diaphragm frequency in the present case. The maximum heat transfer enhancement is obtained at the resonance frequency for elliptical orifice of aspect ratio 1.4 at the jet to plate spacing (z/de) of 3, where z is the axial distance and de is the equivalent diameter of the orifice. The aspect ratio of an orifice is a sensitive parameter as with increase in the aspect ratio, reduction in the Nusselt number is observed. For low jet to plate spacing ratios (z/de

A New Modality Using Breath Sound Analysis to Evaluate the Control Level of Asthma

Reliable symptom assessment is essential in asthma management. We developed new technology for analyzing breath sounds and assessed its clinical usefulness for monitoring asthmatic children. Eighty asthmatic children and 59 non-asthmatic children underwent breath sound analysis in an asymptomatic state. Their asthma control was assessed by the Asthma Control TestTM or Childhood ACTTM scores and divided into two groups, namely, well-controlled (perfect) (n = 19) and not well-controlled (not perfect) (n = 61). Breath sounds were recorded using two sensors, located on the right anterior chest and trachea. We calculated the acoustic transfer characteristics between the two points, which indicated the relationship between frequencies and attenuation during breath sound propagation. Two indices of sound parameters, the chest wall sound index (CWI) and the tracheal sound index (TRI), were calculated from the transfer characteristics and tracheal sounds. We also developed a new parameter, the breath sound index (BSI), on a 2-dimensional diagram of CWI and TRI and tried to determine whether BSI may clarify asthma control better than CWI or TRI alone. There was a significant difference in TRI and BSI between asthmatic and non-asthmatic children (p = 0.007, p < 0.001). There was a significant difference in CWI and TRI between the well-controlled and not-wellcontrolled groups (p < 0.001). BSI discriminated between the two groups accurately (p < 0.001). The sensitivity and specificity of BSI for asthma control were 83.6% and 84.2%, respectively. Asthma control could be evaluated using a new index calculated from breath sound analysis.

New Total Ossicular Replacement Prostheses With a Resilient Joint

New flexible total ossicular prostheses with an integrated microjoint can compensate for large static displacements in the reconstructed ossicular chain. When properly designed, they can mimic the function of the joints of the intact chain and ensure good vibration transfer in both straight and bent conditions. Prosthesis dislocations and extrusions are frequently observed after middle ear surgery. They are mainly related to the altered distance between the coupling points because of large static eardrum displacements. The new prostheses consist of 2 titanium shafts, which are incorporated into a silicone body. The sound transfer function and stapes footplate displacement at static loads were evaluated in human temporal bones after ossicular reconstruction using prostheses with 2 different silicones with different hardness values. The stiffness and bending characteristics of the prostheses were investigated with a quasi-static load. The sound transfer properties of the middle ears with the prostheses inserted under uncompressed conditions were comparable with those of ears with intact ossicular chains. The implant with the soft silicone had improved acoustic transfer characteristics over the implant with the hard silicone in a compressed state. In the quasi-static experiments, the minimum medial footplate displacement was found with the same implant. The bending characteristics depended on the silicone stiffness and correlated closely with the point and angle of the load incidence. The titanium prostheses with a resilient joint that were investigated in this study had good sound transfer characteristics under optimal conditions as well as in a compressed state. As a result of joint bending, the implants compensate for the small changes in length of the ossicular chain that occur under varying middle ear pressure. The implants require a stable support at the stapes footplate to function properly.

Biomechanical Modeling and Design Optimization of Cartilage Myringoplasty Using Finite Element Analysis

The purpose of this study was to determine the acoustic transfer characteristics of cartilage for optimal cartilage myringoplasty. In order to do so, we developed a cartilage plate/tympanic membrane-coupled model using finite element analysis. Cartilage specimens of the tragus were obtained from fresh human cadavers, and the parameters of the tragus were determined by curve fitting and cross-calibration. A cartilage plate was used to repair an eardrum perforation, and the new coupled tympanic membrane-cartilage complex was loaded into our 3-dimensional biomechanical model of the middle ear for analysis. Our results show that first the β-damping value of the cartilage plate depends on frequency. The value of β damping was close to 3 × 10^–4 s at lower frequencies and 5 × 10^–6 s at higher frequencies. Secondly, reducing cartilage thickness leads to an improvement of its acoustic transfer qualities. From an acoustics point of view, the 0.1- to 0.2-mm cartilage plate seems to be most preferable with regard to tympanic membrane vibration. Furthermore, thicknesses of 0.2 mm at lower frequencies and 0.1 mm at higher frequencies were regarded as good compromises between sufficient mechanical stability and low acoustic transfer loss.

Method of positioning sound image with distance adjustment

A sound apparatus is constructed for directing a sound image of a virtual sound source at a designated source point to a listener in a virtual sound field. In the sound apparatus, a database provisionally memorizes acoustic transfer characteristics of the virtual sound field in correspondence to reference source points distributed radially around a center point of the listener. Left and right filters respectively filter audio signals of left and right channels according to the acoustic transfer characteristics loaded from the database. A processor computes a leftward acoustic direction from the designated source point to a left ear of the listener, and computes a rightward acoustic direction from the designated source point to a right ear of the listener. A controller specifies a leftward reference source point coincident with the leftward acoustic direction to load an effective acoustic transfer characteristic corresponding to the leftward reference source point from the database into the left filter, and specifies a rightward reference source point coincident with the rightward acoustic direction to load another effective acoustic transfer characteristic corresponding to the rightward reference source point from the database into the right filter. A feeder feeds an audio signal of the left channel to the left filter and feeds another audio signal of the right channel to the right filter to thereby direct the sound image of the virtual sound source located at the source point to the listener positioned at the center point.

Acoustic properties of different cartilage reconstruction techniques of the tympanic membrane.

The use of cartilage in reconstruction of the tympanic membrane has been established especially in cases such as tubal dysfunction and adhesive processes. Cartilage offers the advantage of higher mechanical stability compared with membranous transplants but may alter the acoustic transfer characteristics of the graft. Apart from material properties, it can be assumed that, also, the microsurgical reconstruction technique might influence the sound transmission properties of the reconstructed tympanic membrane. The purpose of the study was to investigate the acoustic transfer characteristics of different cartilage transplants being typically used in different reconstruction techniques of the tympanic membrane. Cartilage plates of different thicknesses (1.0, 0.7, 0.5, and 0.3 mm), cartilage palisades, and cartilage island transplants of varying size were investigated by means of an ear canal-tympanic membrane model. In contrast to former single-point measurements, sound-induced vibrational amplitudes of the entire transplant were measured by scanning laser Doppler vibrometry (measuring points, n = 133) (PSV-200, Polytec, Waldbronn, Germany). Frequency response functions (displacement vs. sound pressure) of all measured points were determined in the frequency range of 200 Hz to 4 kHz for the different transplants. Cutting thick cartilage transplants into thin plates or palisades decreased the first resonance frequency and increased its amplitude, reflecting improved sound transmission properties of the transplant. From an acoustical point of view, the 0.5-mm cartilage plate seems preferable compared with the palisade technique. Cartilage island techniques showed vibration characteristics superior to plate or palisade techniques. Apart from material characteristics, the sound transmission properties of the reconstructed tympanic membrane are strongly influenced by the reconstruction technique. The choice of the surgical technique should consider requirements based on mechanical stability and acoustic transfer characteristics of the transplant.

Distance localization using nonindividualized head-related transfer functions

Past research has suggested that virtual auditory displays are most accurate when implemented using individualized head-related transfer functions (HRTFs). Directional localization accuracy, for example, is often substantially degraded when nonindividualized HRTFs are used, due to the resulting distortion of spectral cues to sound source direction. Although equally important for accurate spatial representation, little is known about distance localization accuracy in virtual auditory displays, and specifically, whether individualized HRTFs are necessary for accurate distance localization. Here, distance localization accuracy was assessed for six listeners, using both individualized and nonindividualized HRTFs in separate blocks of trials. The virtual sound sources were produced from special HRTF measurements (source distance ranging from 0.3 to 13.8 m) that also contained the acoustic transfer characteristics of a semireverberant room environment. This provided listeners with additional acoustic cues to source distance, including the ratio of direct-to-reverberant sound energy. Since no significant differences were observed in listener’s judgments of apparent sound source distance in the two stimulus conditions, it is concluded that distance localization accuracy, and degree of sound source externalization, do not depend on the use of individualized HRTFs when natural reverberation is available to the listener. [Work supported by NIH-NIDCD, NASA, and NIH-NEI.]

Experimental investigations of the use of cartilage in tympanic membrane reconstruction.

Temporalis fascia, perichondrium, and cartilage are commonly used for reconstruction of the tympanic membrane in middle ear surgery. Cartilage grafts offer the advantage of higher mechanical stability, particularly in cases of chronic tubal dysfunction, adhesive processes, or total defects of the tympanic membrane, in contrast to fascia and perichondrium, which presumably offer better acoustic quality. The purpose of this study was to determine the acoustic transfer characteristics of cartilage of varying thickness and its mechanical deformation when exposed to fluctuations in atmospheric pressure. Ten pairs of cartilage specimens from the cavum conchae and the tragus were obtained from fresh human cadavers. Young's modulus was determined by mechanical tension tests and statistically evaluated using the t test. The acoustic transfer characteristics of an additional 10 specimens were measured by a laser Doppler Interferometer after stimulation with white noise in an external auditory canal--tympanic membrane model. Mechanical stability was determined by measuring displacement of the cartilage using static pressure loads of < or = 4 kPa. Young's modulus determinations for conchal and tragal cartilage were 3.4 N/mm2 and 2.8 N/mm2, respectively, but the difference was not significant. Acoustic testing showed a 5-dB higher vibration amplitude in the midfrequency range for conchal compared with tragal cartilage, but the difference was not significant. Reducing cartilage thickness led to an improvement of its acoustic transfer qualities, with a thickness < or = 500 microm resulting in an acceptable acoustic transfer loss compared with the tympanic membrane. Both conchal and tragal cartilage are useful for reconstruction of the tympanic membrane from the perspective of their acoustic properties. The acoustic transfer loss of cartilage can be reduced by decreasing its thickness. A thickness of 500 microm is regarded as a good compromise between sufficient mechanical stability and low acoustic transfer loss.

Apparatus for controlling acoustical transfer characteristics

An apparatus for controlling acoustical transfer characteristics having an input section (2) for inputting data on acoustical transfer decision factors determining the acoustical transfer characteristics of an audio reproduction output signal (7), an arithmetic section (3, 4) for calculating a value of control of the acoustic transfer characteristics of the audio reproduction output signal (7) by fuzzy inference based on the decision factors, and an operational section (6) for changing the acoustical transfer characteristics. The factors for compensating for auditory sensation characteristics vary depending upon the sound volume level. Acoustic transfer characteristics suitable for the auditory sensitivity characteristics of the listener with changes in the sound volume can be obtained by a simple operation.

Acoustic transfer characteristics in human middle ears studied by a SQUID magnetometer method.

The middle-ear transfer characteristics for sound in 14 human temporal bones were determined using a SQUID magnetometer method. With this method, the cochlea and middle ear remain intact. Postmortem changes were studied using a guinea pig. The mass-loading effects of the applied magnets were determined and were found to be negligible. The mean umbo displacement was equal to the mean of six other studies. Lever ratios varied between the individual temporal bones and as a function of frequency.