Speaker
Description
(2) Material and Methods
At Fraunhofer IKTS, several cost-effective fabrication technologies are available each enabling a specific range of structure dimensions and therefore specific frequency range of ultrasonic transducers. For high frequency ultrasonic transducers which can be operated well above 15MHz the soft mold process offers the appropriate technology. Structured PZT thick films can be prepared by screen printing with thicknesses between 20μm and 150μm on planar substrates. However, the frequency is limited to about 4MHz. Polysulphone spinning has been developed and is applied for shaping green ceramic fibres of PZT. For transducer manufacturing, the sintered piezoceramic fibres are aligned and embedded into a polymer matrix, and shaped after curing.
(3) Results
PZT Fibres with a diameter of 460 μm fabricated by polysylphone spinning have been processed to single-fibre transducer arrays for ultrasound tomography. Array thicknesses between 0.4 and 2.1 mm have been investigated, having resonance frequencies between 3 MHz and 500 kHz accordingly. The fibres are arranged in a specific pattern and individually contacted in order to work as a single element transducer each. They exhibit superior and homogenous electromechanical properties. However, the coupling factor decreases slightly with increasing frequency due to lateral clamping.
(4) Discussion and Conclusion
Piezocomposites based on single PZT fibers are investigated as promising cost effective alternative to dice-and-fill transducers allowing for improved 3D-USCT systems. 3D designs are feasible within the framework of fibre arrangement and CNC processing possibilities. The minimum composite thickness achievable by machining and the minimum fibre diameter limit the maximum frequency of fibre composite transducers to about 10 MHz.
