Graduate Aerospace Laboratories, and Applied Physics, California Institute of Technology, Pasadena, CA 91125, USA.
Proc Natl Acad Sci U S A. 2010 Apr 20;107(16):7230-4. doi: 10.1073/pnas.1001514107. Epub 2010 Apr 5.
Acoustic lenses are employed in a variety of applications, from biomedical imaging and surgery to defense systems and damage detection in materials. Focused acoustic signals, for example, enable ultrasonic transducers to image the interior of the human body. Currently however the performance of acoustic devices is limited by their linear operational envelope, which implies relatively inaccurate focusing and low focal power. Here we show a dramatic focusing effect and the generation of compact acoustic pulses (sound bullets) in solid and fluid media, with energies orders of magnitude greater than previously achievable. This focusing is made possible by a tunable, nonlinear acoustic lens, which consists of ordered arrays of granular chains. The amplitude, size, and location of the sound bullets can be controlled by varying the static precompression of the chains. Theory and numerical simulations demonstrate the focusing effect, and photoelasticity experiments corroborate it. Our nonlinear lens permits a qualitatively new way of generating high-energy acoustic pulses, which may improve imaging capabilities through increased accuracy and signal-to-noise ratios and may lead to more effective nonintrusive scalpels, for example, for cancer treatment.
声透镜在各种应用中得到了广泛应用，从生物医学成像和手术到防御系统以及材料中的损伤检测。例如，聚焦声信号使超声换能器能够对人体内部进行成像。然而，目前声设备的性能受到其线性工作范围的限制，这意味着相对不准确的聚焦和低焦点功率。在这里，我们展示了在固体和流体介质中产生的剧烈聚焦效应和紧凑声脉冲（声弹）的产生，其能量比以前可实现的能量大几个数量级。这种聚焦是通过由有序的颗粒链组成的可调谐非线性声透镜实现的。通过改变链的静态预压缩，可以控制声弹的幅度、大小和位置。理论和数值模拟证明了这种聚焦效应，光弹性实验也证实了这一点。我们的非线性透镜允许以一种全新的方式产生高能声脉冲，这可能通过提高准确性和信噪比来提高成像能力，并可能导致更有效的非侵入性手术刀，例如用于癌症治疗。
