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

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Near-field acoustic holography with sound pressure and particle velocity
measurements
Fernandez Grande, Efren
Publication date:
2012
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Citation (APA):
Fernandez Grande, E. (2012). Near-field acoustic holography with sound pressure and particle velocity
measurements. Technical University of Denmark, Department of Electrical Engineering.

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Efren Fernandez Grande

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

PhD thesis, June 2012
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Near-field acoustic holography
with sound pressure and
particle velocity measurements
PhD thesis by
Efren Fernandez Grande
Technical University of Denmark
2012
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ThisthesisissubmittedtotheTechnicalUniversityofDenmark(DTU)aspartialfulfill-
mentoftherequirementsforthedegreeofDoctorofPhilosophy(Ph.D.)inElectronics
and Communication. The work presented in this thesis was completed between Jan-
uary15,2009andFebruary23,2012atAcousticTechnology,DepartmentofElectrical
Engineering, DTU, under the supervision of Associate Professor Finn Jacobsen. The
projectwasfundedbyDTUElektro.
Title
Near-field Acoustic Holography with Sound Pressure and Particle Velocity Measure-
ments
Author
EfrenFernandezGrande
Supervisor
FinnJacobsen
DepartmentofElectricalEngineering
TechnicalUniversityofDenmark
ISBN978-87-92465-82-5 DK-2800KONGENSLYNGBY,Denmark
PrintedinDenmarkbyRosendahls-SchultzGrafiska/s
c 2012EfrenFernandezGrande
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Coverillustration: RadiationKernelbyEfrenFernandezGrande
No part of this publication may be reproduced or transmitted in any form or by any
means, electronic or mechanical, including photocopy, recording, or any information
storageandretrievalsystem,withoutpermissioninwritingfromtheauthor.
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Amispadres,aDavid,
καiστην Iωα´ννα
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Abstract
Near-field acoustic holography (NAH) is a powerful sound source identification tech-
niquethatmakesitpossibletoreconstructandextractalltheinformationofthesound
fieldradiatedbyasourceinaveryefficientmanner,readilyprovidingacompleterepre-
sentationoftheacousticfieldunderexamination.Thisiscrucialinmanyareasofacous-
ticswheresuchathoroughinsightintothesoundradiatedbyasourcecanbeessential.
Thisstudyexaminesnovelacousticarraytechnologyinnear-fieldacousticholography
andsoundsourceidentification. Thestudyfocusesonthreeaspects,namelytheuseof
particlevelocitymeasurementsandcombinedpressure-velocitymeasurementsinNAH,
therelationbetweenthenear-fieldandthefar-fieldradiationfromsoundsourcesviathe
supersonicacousticintensity,andfinally,thereconstructionofsoundfieldsusingrigid
sphericalmicrophonearrays.
Measurement of the particle velocity has notable potential in NAH, and further-
more, 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 sep-
arationmethodshavebeenstudied,andanewmeasurementprinciplebasedondouble
layer measurements of the particle velocity has been proposed. Also, the relation be-
tweennear-fieldandfar-fieldradiationfromsoundsourceshasbeenexaminedusingthe
conceptofthesupersonicintensity. Thecalculationofthisquantityhasbeenextended
to other holographic methods, and studied under the light of different measurement
principles. A direct formulation in space domain has been proposed, and the exper-
imental validity of the quantity has been demonstrated. Additionally, the use of rigid
sphericalmicrophonearraysinnear-fieldacousticholographyhasbeenexamined,anda
methodhasbeenproposedthatcanreconstructtheincidentsoundfieldandcompensate
forthescatteringintroducedbytherigidsphere. Itisthepurposeofthisdissertationto
presenttherelevantfindings,discussthecontributionofthePhDstudy,andframeitin
thecontextoftheexistingbodyofknowledge.
Keywords: Near-field acoustic holography, NAH, particle velocity transducers, su-
personic intensity, sound radiation, sound source identification, sound visualization,
sphericalmicrophonearrays.
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Resumé
Akustisk nærfeltsholografi (kendt under forkortelsen NAH) er en effektiv metode til
identifikationaflydkildersomgørdetmuligtatrekonstruerelydfelterialledetaljerud
fra målinger på en overflade nær en sammensat, kompliceret støjkilde. Kortlægning
afdelkildererenvigtigtdelafmangeakustiskeundersøgelser. DettePhD-projekthar
undersøgt en række forskellige målemetoder baseret på kombinationer af forskellige
akustisketranducere(trykmikrofonerogpartikelhastighedstransducere). Enafkonklu-
sionerne 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
forskelligeholografiskerekonstruktionsprincipper. Endvidereerderogsåforetageten
undersøgelseaf"sfæriskholografi",enmetodebaseretpåmikrofonerplaceretpåover-
fladenafenhårdkugle;bl.a.erderudvikletenmetodedergørdetmuligatkompensere
for spredningen af lyd som skyldes kuglen og rekonstruere det uforstyrrede såkaldte
indfaldende lydfelt. Endelig er der udført en grundig teoretisk og eksperimentel un-
dersøgelseafbegrebet“supersonicintensity",envigtigstørrelsedersigernogetomen
lydkildesudstrålingtilfjernfeltet.
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