Development of high frequency medical ultrasound arrays

Recent progress in the development of high frequency linear and phased arrays has resulted in a number of devices that operate at and above 20 MHz. The highest frequency commercial arrays that are presently available rely on mechanical dicing and operate at a maximum frequency of 20 MHz. For higher frequencies novel approaches are required. Several researchers have fabricated fine-scale 2-2 composites using methods such as interdigital pair bonding, stacking-and-bonding, and tape casting. For mass production and ultra-fine feature size, sol gel and sputtered piezoelectrics hold great promise, even though their electromechanical performance is often sub-optimal. Both laser micromachining and chemical etching have been used to define the array elements in these materials. Polymer arrays take advantage of the mechanical flexibility and low acoustic impedance of PVDF and P(VDF-TrFE). As an alternative to traditional piezoelectric devices, optical techniques have been demonstrated at frequencies above 50 MHz. The technology, advantages, and limitations of each of these approaches are reviewed, as is the status of several devices currently under development.