Complex Acoustic Emission Research Articles

STUDY ON ACOUSTIC BLACK HOLE EFFECT OF ACOUSTIC EMISSION SIGNALS IN PINUS SYLVESTRIS VAR. MONGOLICA LITV

The difference in density and wave velocity causes distinct wave impedance between air and wood, resulting in complex acoustic emission (AE) signals due to reflection on the wood's surface. This study explores the suppression of AE signal reflection by modifying the structure of thin wood panels, utilizing the theory of acoustic black holes (ABH). Initially, aone-dimensional ABH structure was created by forming a wedge structure on one side of thespecimen. Pencil-lead break (PLB) tests simulated sudden AE sources on the specimen's surface. AE signals were collected using three equidistant sensors on the upper surface, with asampling frequency of 2MHz. The AE signal was then segmented into frequency bands using the differential method and analyzed in both time and frequency domains. Comparisons were made to understand the impact of the one-dimensional ABH on AE signal propagation. Results demonstrated that the one-dimensional ABH effectively suppressed AE signal reflection on thewood's surface, reducing the high-frequency components by 18.31%, 20.83%, and 12.09% for each sensor, respectively. Furthermore, the experimental cut-off frequency of 0.98 kHz surpassed the theoretically calculated value of 0.39 kHz due to the disparity between the ABH structure's thickness and the theoretical prediction.

Emergent collective behaviors in a simplified model of dolphin echolocation and predation

A stochastic modeling framework for representing and simulating marine-mammal spatial distributions, collective motions, and vocalization occurrence times was previously developed [J. Acoust. Soc. Am. 101, 3197(A) (1997)]. Emergent behaviors in these models include clustered and polarized motions simulating collective motions of marine mammals. The present work explores the potential of these models for representing and simulating more complex acoustic emission and collective motion behaviors related to short-range echolocation and predation by dolphins. A simplified predation scenario is constructed by including predator, prey, and nonprey species in the collective motion model. Echolocation is simulated by a simplified, sonar equation-based representation of the backscattered acoustic energy, with different backscattering characteristics for predator, prey, and nonprey individuals. Parameters determining echolocation signal types and collective motion characteristics are then allowed to vary in a random search that favors parameter values leading to higher prey capture rates. Emergent collective behaviors, including echolocation signals and prey pursuit and capture, are then observed in computer-generated video animations. The potential of the models for representating sound generated by groups of marine mammals and for interpreting observed marine mammal collective behavior is discussed. [Work supported by ONR Base funding at NRL.]