Surface preparation of 1-3 piezocomposite material for microfabrication of high frequency transducer arrays

A key issue in the development of ultrasound imaging arrays to operate at frequencies above 30 MHz is the need for photolithographic patterning of array electrodes. To achieve this directly on a 1-3 piezocomposite requires planar, parallel and smooth surfaces. This paper reports an investigation of the surface finishing of 1-3 piezocomposite material by mechanical lapping and/polishing that has demonstrated that excellent surface flatness can be obtained. Subsequently, high frequency array elements have been fabricated on these surfaces using a low temperature lift-off photolithography process. A 50 MHz linear array with 30 pm element pitch has been patterned on the lapped and polished surface of a low frequency 1-3 piezocomposite. Good electrode edge definition and electrical contact to the composite were obtained. Additionally, patterning has been demonstrated on a fine-scale composite, itself suitable for operation above 30 MHz.</p

Dynamics of levitated objects in acoustic vortex fields

Acoustic levitation in gaseous media provides a tool to process solid and liquid materials without the presence of surfaces such as container walls and hence has been used widely in chemical analysis, high-temperature processing, drop dynamics and bioreactors. To date high-density objects can only be acoustically levitated in simple standing-wave fields. Here we demonstrate the ability of a small number of peripherally placed sources to generate acoustic vortex fields and stably levitate a wide range of liquid and solid objects. The forces exerted by these acoustic vortex fields on a levitated water droplet are observed to cause a controllable deformation of the droplet and/or oscillation along the vortex axis. Orbital angular momentum transfer is also shown to rotate a levitated object rapidly and the rate of rotation can be controlled by the source amplitude. We expect this research can increase the diversity of acoustic levitation and expand the application of acoustic vortices