Applied Acoustics 

About: Applied Acoustics is an academic journal. The journal publishes majorly in the area(s): Noise & Sound pressure. It has an ISSN identifier of 0003-682X. Over the lifetime, 6270 publication(s) have been published receiving 90748 citation(s).

Acoustical properties of fibrous absorbent materials

Abstract: Results are presented of an investigation into the acoustical properties of a range of fibrous absorbent materials. Measured values of characteristic impedance and propagation coefficient are shown to normalise as a function of frequency divided by flow-resistance and can be represented by simple power-law functions. Absorption coefficients of thin layers of material over a range of flow-resistance values are also shown. Supplementary data provide a basis for estimating the flow-resistance of a material from its bulk density.

Materials for high temperature acoustic and vibration sensors: A review

Abstract: The industrial and scientific communities have expressed a real need for the capability of pressure, acoustic, and vibration sensing at elevated temperatures. This review compares the various commercial methods and materials for acoustic transduction, identifying their advantages and limitations. Techniques and devices include simple piezoelectric sensors, accelerometers, strain gauges, proximity sensors, fiber optics and buffer rods. Sensors with operating temperatures in excess of 650°C are readily available from commercial sources. Of the mechanisms investigated, the piezoelectric approach offers several advantages, including design cost and simplicity. Therefore, the bulk of this review concentrates on piezoelectric materials, both those that are already available commercially, and those that are presently under development. The new materials include perovskite layer structure ferroelectric ceramics, which possess the highest known Curie temperatures, and thin film AlN, which has been reported to be piezoactive at 1150°C.

Application of empirical mode decomposition and artificial neural network for automatic bearing fault diagnosis based on vibration signals

Abstract: Condition monitoring and fault diagnosis of rolling element bearings (REBs) are at present very important to ensure the steadiness of industrial and domestic machinery. According to the non-stationary and non-linear characteristics of REB vibration signals, feature extraction method is based on empirical mode decomposition (EMD) energy entropy in this paper. A mathematical analysis to select the most significant intrinsic mode functions (IMFs) is presented. Therefore, the chosen features are used to train an artificial neural network (ANN) to classify bearings defects. Experimental results indicated that the proposed method based on run-to-failure vibration signals can reliably categorize bearing defects. Using a proposed health index (HI), REB degradations are perfectly detected with different defect types and severities. Experimental results consist in continuously evaluating the condition of the monitored bearing and thereby detect online the severity of the defect successfully. This paper shows potential application of ANN as effective tool for automatic bearing performance degradation assessment without human intervention.

Fundamentals of Binaural Technology

Abstract: This article reviews the fundamental ideas of the binaural recording technique. A model is given that describes the sound transmission from a source in a free field, through the external ear to the eardrum. It is shown that sound pressures recorded at any point in the ear canals—possibly even a few millimeters outside and even with a blocked ear canal—can be used for binaural recordings, since they include the full spatial information given to the ear. The sound transmission from a headphone is also described. It is shown how the correct total transmission in a binaural system can be guaranteed by means of an electronic equalizing filter between the recording head and the headphone. The advantage of an open headphone is stated. It is shown that a certain degree of loudspeaker compatibility can be achieved, if the equalizer is divided into a recording side and a playback side. A method for true reproduction of binaural signals through loudspeakers is also described. A number of topical and prospected applications of binaural technology are mentioned. Some of these utilize computer synthesis of binaural signals, a technique which is also described.

Vibration characteristics of functionally graded cylindrical shells under various boundary conditions

Abstract: In the recent years, functionally gradient materials (FGMs) have gained considerable attention in the high temperature environment applications. In the present work, study of the vibration of a functionally graded cylindrical shell made up of stainless steel and zirconia is presented. Material properties are graded in the thickness direction of the shell according to volume fraction power law distribution. Effects of boundary conditions and volume fractions (power law exponent) on the natural frequencies of the FG cylindrical shell are studied. Frequency characteristics of the FG shell are found to be similar to those of isotropic cylindrical shells. Further, natural frequencies of these shells are observed to be dependent on the constituent volume fractions and boundary conditions. Strain displacement relations from Love's shell theory are employed. Rayleigh method is used to derive the governing equations. Further, analytical results are validated with those reported in the literature.