INFLUENCE OF SURFACE ROUGHNESS ON AXIAL ACOUSTIC ENERGY DISTRIBUTION IN A PARABOLIC REFLECTOR
Keywords:
Acoustics, parabolic reflectors, gain, impulse response, polar characteristicsAbstract
This paper analyzes the effect of surface roughness of an acoustic parabolic reflector on the scattering of acoustic energy outside the focal region. First, a formulation for calculating the gain of a parabolic reflector is presented as a function of its geometrical parameters, including the reflector depth H, aperture radius R, and focal position zF. The gain is then evaluated as a function of the acoustic wavelength λ for reflectors constructed in the courtyard of the Academy of Technical and Educational Applied Studies in Niš, Serbia. The reflecting surface of the reflector is not smooth but rough, which leads to a degradation of acoustic energy concentration E at the focus, i.e., to increased scattering of acoustic energy along the axial z-direction. In the second part of the paper, an experiment is described in which the spatial distribution of acoustic energy E(zi) is determined from measurements of acoustic impulse responses along the z-axis. Subsequently, by applying statistical parameters (the energy centroid zeff, standard deviation σ, position of the maximum zmax, full width at half maximum (FWHM), focusing efficiency η, and entropy H) the influence of surface roughness on the scattering of acoustic energy outside the focal region is quantified.
References
Cabrera, D., Lu, S., Holmes, J., & Yadav, M. (2023). The potential of focusing acoustic retroreflectors for architectural surface treatment. Applied Sciences, 13(3), 1547.
Cabrera, D., Lu, S., Holmes, J., Yadav, M., & Hutchison, O. (2023). Focusing acoustic retroreflectors for architectural applications. Applied Sciences, 13(3), 1547.
Chen, K., Irie, T, Iijima, T., & Morita, T. (2019). Double-parabolic-reflectors acoustic waveguides for high-power medical ultrasound. Scientific Reports, 9, 18493.
Chen, K., Irie, T., Iijima, T., & Morita, T. (2019). Acoustic focusing to the waveguides utilizing double parabolic reflectors. Applied Physics Letters, 114(7).
Coile, R. (1939). The parabolic sound concentrator, J. Acoust. Soc. Am. Vol. 11, 167.
Cremer, L. (1948). Die wissenschaftlichen Grundlagen der Raumakustik, Vol. 1, Geometrische Raumakustik, Zurich.
Hefler, M. (2009). Sound Source Localisation with Acoustic Mirrors, NAG/DAGA, pp. 1432-1453, Rotterdam.
Little, R. (1966). Acoustic properties of parabolic reflectors, J. Acoust. Soc. Am., Vol. 40, 919–920.
Milivojević, Z. (2018). Parabolični reflektor kao akustički pojačavač, Zbornik radova Visoke tehničke škole strukovnih studija u Nišu, 36 – 40.
Olson, H., & Wolff, I. (1930). Sound concentrator for microphones, J. Acoust. Soc. Am., Vol. 1, 410 - 417.
Rapp, M., Cabrera, D., & Lu, S. (2022). A polytrihedral dome for acoustic retroreflection and its applications. Applied Acoustics, 195, 108860.
Saka, B., & Kaderli, A. (1998). Direction of arrival estimation and adaptive nulling in array-fed reflectors, MELECON '98, 9th Mediterranean Electrotechnical Conference, 274 - 277, Tel-Aviv, Israel.
Stojanović, V., Milivojević, Z. (2024). The polar characteristic of an acoustic parabolic reflector, Facta Universitatis, Series: Working and Living Environmental Protection, 21(4), Special Issue, 293 – 303.
Wahlstrom, S. (1985) The parabolic reflector as an acoustical amplifier, J. Audio Eng. Soc., Vol. 33, 418–429.
Yi, T. Jinying, Z., & Haberman, M. (2013). Transient axial solution for plane and axisymmetric waves focused by a paraboloidal reflector, J. Acoust. Soc. Am. 133(4), 2025 - 2035.
Zhang, T., Geng, Y., Sun, J., & Chen Jiao, C. (2020). A unified speech enhancement system based on neural beamforming with parabolic reflector. Applied Sciences, 10(7), 2218.
Zhu, Y., Cao, L., Merkel, A., Fan, S.-W., Vincent, B., & Assouar, B. (2021). Janus acoustic metascreen with nonreciprocal and reconfigurable phase modulations. Nature Communications, 12, 7089.
