Synthetic Aperture Focusing Applied to Imaging Using a Rotating Single Element Transducer

This paper applies the concept of virtual sources and mono-static synthetic aperture focusing (SAF) to 2-dimensional imaging with a single rotating mechanically focused concave element with the objective of improving lateral resolution and signal-to-noise ratio (SNR). The geometrical focal point of the concave element can be considered as a point source emitting a spherical wave in a limited angular region.

The SAF can be formulated as creating a high resolution line as a sum over low resolution tines (LRL). A LRL is the contribution from a single emission. Simulation in Field 11 is based on moving the concave element of radius 2.5 mm along a circle of radius 10 mm. Elements with different concave curvatures are used to obtain geometrical focusing depths at 10 rum, 15 rum, and 20 mm.

Point targets in the range from 5 mm to 65 mm. are used as image objects. The high resolution images (HRI) are shown and the radial and angular resolution are extracted at -6 dB and -40 dB. The performance of the setup with a VS at 20 mm is superior to the other setups. Due to the rotation, the synthesized aperture only experiences a moderate expansion, which is not sufficient to reduce the extent of the wide point spread function of a single emission.

The effect of SAF with focal depth at 20 mm is negligible, caused by the small number of LRL applied. The great profit of the SAF is the increase in SNR. For the setup with focal depth at 20 rum the SAF SNR gain is 11 dB. The SNR gain of a setup with a VS at radius 10 mm or 15 mm over conventional imaging with a VS at 20 mm, is also 11 dB.