Dynamic achromatic ultrasound imaging with a stretchable flexible metalens

Ultrasound imaging is widely used in both engineering and medicine due to its advantages of deep penetration and no ionizing radiation. Focusing techniques can improve image resolution, but conventional methods often suffer from chromatic aberration. This blurring effect arises from the inherent dispersion of focusing lenses and significantly reduces image quality. We present an approach to ultrasound imaging that overcomes this challenge, which utilizes a stretchable and flexible metalens to experimentally achieve dynamic reconfigurable achromatic imaging. By carefully stretching and releasing the metalens, we can focus ultrasound of different frequencies at the same depth. This method features remarkable focusing resolutions of 0.6\ensuremath{\lambda} in the radial direction and 2.3\ensuremath{\lambda} in the axial direction. Notably, the high-resolution focusing is maintained throughout the entire modulation process, where a 13% deformation of the metalens enables effective compensation for chromatic aberration of ultrasound from 0.81 to 1 MHz. Furthermore, we demonstrate the dynamic achromatic imaging of microstructures, showcasing its ability to capture high-resolution ultrasound images. This flexible reconfigurable metalens for dynamic ultrasound achromatic imaging holds great promise for various applications, including ultrasound sensing, nondestructive testing, and improved medical diagnosis.