Search Results (2)

With the development of acoustic simulation methods in recent decades, it has become feasible to simulate the sound pressure distribution of loudspeakers before actually setting physical speakers and measuring the sound field. The parametric array loudspeaker (PAL) has attracted attention due to its sharp directivity and unique applications. However, the sound reproduced by PALs is generated by the nonlinear interactions of ultrasound in the air, which makes it difficult to simulate the reproduced sound of a PAL with low computational load. Focusing on the sharp directivity of ultrasound, we extended conventional acoustic ray-tracing methods to consider the self-demodulation phenomenon of PALs. In this study, we developed a visualization method for the demodulated sound of a PAL. Specifically, the demodulated sound pressure distribution can be simulated to estimate and visualize the area covered by the reproduced sound of PAL before setting a real PAL. In the proposed method, acoustic rays were generated sequentially to express the generation of demodulated sound. Therefore, the proposed method is expected to simulate the demodulated sound of a PAL with acceptable accuracy and low calculation complexity. Quantitative evaluation between simulation results and practical measurement has been carried out, and the results demonstrate the effectiveness of the proposed method. Full article

With the development of fiber optical technologies, fiber Bragg grating (FBG) sensors are frequently utilized in structural health monitoring due to their considerable advantages, including fast response, electrical passivity, corrosion resistance, multi-point sensing capability and low-cost production, as well as high accuracy and resolution over a long period. These characteristics allow FBG to be a proper alternative sensing element for displacement measurements. In this article, the recent sensing advances and principles of detection of FBG-based displacement sensors are illustrated. Specifically, the latest FBG-based displacement technologies are examined from three principles of detection, i.e., wavelength, intensity and phase signal demodulation. Regarding wavelength detection methods, the problem related to the cross-sensitivity can significantly be reduced depending on the new type of cantilever–FBG-based sensing developed. Vice versa, only the packaging method of FBG prestressed between two fixed ends can still avoid the chirp phenomenon in the reflection spectrum. Moreover, to attenuate the influence of temperature variations on the accuracy of FBG displacement sensors, specific temperature self-compensation structures were successfully designed according to the concepts of phase signal demodulation. In future investigations, different elastic structures and gratings manufactured through special fibers and new methodologies for temperature compensation will still highly refine the efficiency of FBG-based displacement sensors. Full article