All Optical Fiber Ultrasonic Sources for Non Destructive Testing and Clinical Diagnosis

Conclusion

The innovative feature of our photoacoustic source consists in the double function of the optical fibre that acts both as optical waveguide and as mechanical constraint for the elastic wave generated in the liquid.

It was experimentally demonstrated that the bandwidth and the maximum frequency of the ultrasonic signal can be controlled by the laser pulse duration. Consequently, high frequency ultrasonic transducer with high bandwidth can be realized with good miniaturization.

A peculiar characteristic of the proposed source is the high value of the generated ultrasonic intensity with respect to ultrasonic piezoelectric transducers. In fact, the acoustic intensity emitted from the photoacoustic source is indipendent from the frequency while the piezoelectric transducer intensity strongly decreases when the frequency rises in value. Afterwards the metallized fiber appears to be a source with high efficiency for frequency higher then several MHz, even if it is not competitive in the kHz range.

As mentioned above, the proposed all-optical fibre transducers are characterized by high thermo-acoustic efficiency, but the enhancement of opto-thermal conversion is ignored in this work and further efforts are still need. An array of the U-bent transducers fed by the same optical pulse was demostrated to be a praticable way to solve the efficiency problem.