Liquid lens with adjustable focus for ultrasonic imaging

Abstract

An acoustic lens is an attractive device due to its superior ability to image and focus acoustic beams. Nevertheless, the limitation of such a solid-phase device is apparent in that once an acoustic lens is made, its focal length remains fixed. On the contrary, the liquid acoustic lens can not only flexibly tune the position of focus, but also avoid greater acoustic impedance. This paper presented a liquid acoustic convex lens with a tunable focus. The focal distance of the liquid acoustic lens is derived from the focal length formula of the optical lens group. The interface curvature of the lens and the dependent focus as a function of the infused liquid volume in the lens were studied theoretically and experimentally. Furthermore, the refraction index of the liquid can be accurately selected as needed by adjusting the concentrations of liquid. This also results in a modification of the lens focal length. The magnification ability of this acoustic lens in combination with a single element 6.8 MHz transducer was evaluated by imaging steel probes which were embedded at different position without performing mechanical axial scanning. The error caused by the difference of sound speed between the liquid in the lens and the host medium is corrected.