Abstract

Abstract
Feasibility of High Repetition Rate Laser Generated Ultrasound with Composite Comprising Candle Soot Nanoparticles and PDMS on Glass
Mahta Nazemi
Ultrasound is widely used in biomedical imaging and non-destructive testing. Recently, Laser Generated Ultrasound (LGU) with high frequencies, large bandwidths have been introduced. LGU transducer typically consists of a light absorber layer and a thermal expansion layer. In this thesis, we concentrate on Candle Soot Nanoparticles (CSNPs) as the light absorption layer and Polydimethylsiloxane (PDMS) as an acoustic transfer medium. There is a lot of work done on LGU composites, however, most of these are experimental. Not much has been done to understand the theory behind LGU composites. On the other hand, almost all the works in the literature utilize high power lasers for the experiments. We aspire to work on high repetition rate LGUs, as they are extensively used in industry and the costs are competitive. Should the feasibility study for high repetition rate LGU needs to be performed, fundamental physics behind LGU need be understood. To this effect, 2D simulation was performed on CSNP/PDMS composite LGU with COMSOL Multiphysics. The material properties of the composite were taken from the literature. The input parameters were selected from literature and the pressure output was extracted from the model. The results from the model for generated acoustic pressure was measured as 5MPa, which compared well with the experiments in literature that measured 4.8MPa under similar conditions. The robustness of the model was further validated using experimental studies for different composites with different thicknesses under different laser fluence. Excellent agreement/trend was found between the results of the model vs results from experiments. Further, high repetition rate laser was examined to study the feasibility of pressure generation. To this effect, composites were fabricated. Damage threshold and absorption coefficient were measured and input into the model for accurate simulation. It was concluded that LGU was feasible under repetition rates of up to 10kHz without damaging the CSNP/PDMS composite. The developed model provides valuable data on how to improve the performance of laser generated ultrasound by tailoring the effective parameters. In this thesis, the study has been successfully carried out to understand the feasibility of using a high repetition rate laser for ultrasound generation using composite (CSNP/PDMS) transducer.