Fernandez Grande, Efren

Akustisk nærfeltsholografi (kendt under forkortelsen NAH) er en effektiv metode til identifikation af lydkilder som gør det muligt at rekonstruere lydfelter i alle detaljer ud fra målinger på en overflade nær en sammensat, kompliceret støjkilde. Kortlægning af delkilder er en vigtigt del af mange akustiske undersøgelser. Dette PhD-projekt har undersøgt en række forskellige målemetoder baseret på kombinationer af forskellige akustiske tranducere (trykmikrofoner og partikelhastighedstransducere). En af konklusionerne er at der er store fordele ved at kombinere sådanne transducere; bl.a. bliver det muligt at skelne mellem bidrag til lydfeltet fra kilden og refleksioner fra rummet som kommer fra den modsatte side af måleoverfladen. Projektet har også undersøgt forskellige holografiske rekonstruktionsprincipper. Endvidere er der også foretaget en undersøgelse af "sfærisk holografi", en metode baseret på mikrofoner placeret på overfladen af en hård kugle; bl.a. er der udviklet en metode der gør det mulig at kompensere for spredningen af lyd som skyldes kuglen og rekonstruere det uforstyrrede såkaldte indfaldende lydfelt. Endelig er der udført en grundig teoretisk og eksperimentel undersøgelse af begrebet “supersonic intensity", en vigtig størrelse der siger noget om en lydkildes udstråling til fjernfeltet.Near-field acoustic holography (NAH) is a powerful sound source identification technique that makes it possible to reconstruct and extract all the information of the sound field radiated by a source in a very efficient manner, readily providing a complete representation of the acoustic field under examination. This is crucial in many areas of acoustics where such a thorough insight into the sound radiated by a source can be essential. This study examines novel acoustic array technology in near-field acoustic holography and sound source identification. The study focuses on three aspects, namely the use of particle velocity measurements and combined pressure-velocity measurements in NAH, the relation between the near-field and the far-field radiation from sound sources via the supersonic acoustic intensity, and finally, the reconstruction of sound fields using rigid spherical microphone arrays. Measurement of the particle velocity has notable potential in NAH, and furthermore, combined measurement of sound pressure and particle velocity opens a new range of possibilities that are examined in this study. On this basis, sound field separation methods have been studied, and a new measurement principle based on double layer measurements of the particle velocity has been proposed. Also, the relation between near-field and far-field radiation from sound sources has been examined using the concept of the supersonic intensity. The calculation of this quantity has been extended to other holographic methods, and studied under the light of different measurement principles. A direct formulation in space domain has been proposed, and the experimental validity of the quantity has been demonstrated. Additionally, the use of rigid spherical microphone arrays in near-field acoustic holography has been examined, and a method has been proposed that can reconstruct the incident sound field and compensate for the scattering introduced by the rigid sphere. It is the purpose of this dissertation to present the relevant findings, discuss the contribution of the PhD study, and frame it in the context of the existing body of knowledge

Online Research Database In Technology

Near-field acoustic holography with sound pressure and particle velocity measurements

http://orbit.dtu.dk/ws/files/51822040/PhD_Thesis_Efren_Fernandez_Grande.PDF

Near-field acoustic holography with sound pressure and particle velocity measurements

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Online Research Database In Technology