The age-related changes in the visco-elastic properties of the human lens are discussed with respect to presbyopia for a
long time. All known measurement techniques are based on extracted lenses or are damaging the tissue. Hence, in vivo
studies of lens hardness are not possible at the moment. To close this gap in lens diagnostics this project deals with an
approach for a non-contact laser-acoustic characterization technique. Laser-generated wave fronts are reflected by the
tissue interfaces and are also affected by the visco-elastic properties of the lens tissue. After propagating through the eye,
these waves are recorded as corneal vibrations by laser vibrometry. A systematic analysis of amplitude and phase of
these signals and the wave generation process shall give information about the interface locations and the tissues viscoelastic
properties. Our recent studies on extracted porcine eyes proved that laser-acoustic sources can be systematically
used for non-contacting generation and recording of ultrasound inside the human eye. Furthermore, a specific numerical
model provides important contributions to the understanding of the complex wave propagation process. Measurements of the acoustic sources support this approach. Future investigations are scheduled to answer the question, whether this novel technique can be directly used during a laser surgery for monitoring purposes and if a purely diagnostic approach, e.g. by excitation in the aqueous humor, is also possible. In both cases, this technique offers a promising approach for non-contact ultrasound based eye diagnostics.
The need for custom-designed sensor networks, tailored to the specific SHM task for practical application of guided
waves, is constantly growing. As a prerequisite for a successful development of different monitoring concepts the
transducers wave excitation and receiving properties have to be known. The more exactly they are understood the more
reliable monitoring concepts are possible. Nowadays different piezoelectric transducer concepts, with varying acting
principles having their specific advantages, are used in SHM applications. Strongly unequal properties concerning source
density and directivity patterns are revealed. Hence, a method is introduced by which different transducer types can be compared in respect to their efficiency in exciting and receiving guided waves. Furthermore a reciprocity-based model for the estimation of the maximum transducer to transducer distance is applied and discussed.
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