Theoretical analysis of the difference – frequency generation in nonlinear Rayleigh seattering of acoustic beams

Detalhes bibliográficos
Ano de defesa: 2011
Autor(a) principal: Melo, Anderson Bandeira de
Orientador(a): Não Informado pela instituição
Banca de defesa: Não Informado pela instituição
Tipo de documento: Dissertação
Tipo de acesso: Acesso aberto
Idioma: por
Instituição de defesa: Universidade Federal de Alagoas
Brasil
Programa de Pós-Graduação em Física
UFAL
Programa de Pós-Graduação: Não Informado pela instituição
Departamento: Não Informado pela instituição
País: Não Informado pela instituição
Palavras-chave em Português:
Link de acesso: http://www.repositorio.ufal.br/handle/riufal/4748
Resumo: In this work, the difference-frequency (DF) generation in the scattering of two acoustic waves by a sphere in the Rayleigh limit is theoretically analyzed. A multipole series is derived for the DF scattered pressure at the farfield by applying the method of successive approximation and the Green’s function technique to the Westervelt’s nonlinear wave equation. In the Rayleigh limit, this series has only the monopole, dipole, and quadrupole moments. These moments depend on the nonlinear interaction of the primary incident and scattered waves. Theoretical results are obtained for the case of two intersecting plane waves localized within a spherical spatial region. The radius of the interaction region is assumed to be much smaller than the distance from the scatterer to observation point (radial distance). A similar configuration is found in vibro-acoustography imaging system. The directive patterns of the DF scattered field are illustrated for plane waves intersecting at 0º; 45º; 90º; and 180º. The center- and differece-frequencies of the waves are 1:5MHz and 50 kHz, respectively, while the spherical scatterer radius is 0:125mm. These frequencies are typically used in vibro-acoustography. The behavior of the DF scattered pressure is also analyzed for two colinear plane waves with varying radial distance from the scatterer, center- and the difference-frequency. Results indicate that the interaction of the primary scattered waves is the main process behind difference-frequency generation for most parameter combinations chosen here. Based on this conclusion, we will also discuss the DF generation process in vibro-acoustography.