Micromachined water-immersible micro scanning mirrors with torsional and bending hinges

This paper reports a new two-axis water-immersible micro scanning mirror (WIMSM) using torsional and bending BoPET (biaxially-oriented polyethylene terephthalate) hinges. A micromachining-based fabrication process is developed to enable high patterning resolution and alignment accuracy and to reduce the amount of manual assembly. With a torsional hinge, the fast axis has a resonance frequency of ~300 Hz in air and ~200 Hz in water. With a bending hinge, the slow axis has a resonance frequency of 60~70 Hz in air and 20~40 Hz in water. 2D B-scan and 3D volumetric ultrasound microscopy are demonstrated by using the hybrid-hinge scanning mirror. The ability of scanning the slow axis at DC or very low frequencies allows a dense raster scanning pattern to be formed for improving both the imaging resolution and field of view.