Pressure-shear wave conversions on free boundaries or interfaces of solids are peculiar and unavoidable wave phenomena in two-dimensional (2D) elasticity, compared with electromagnetic and acoustic wave systems. However, flexibly tailoring their conversions in a reversible and programmable manner to meet a predefined conversion efficiency and spatial distributions of converted wave fields has never been touched before. In this letter, we introduce a programmable meta-boundary with deep subwavelength thickness that is composed of an array of piezoelectric sensing-and-actuating units controlled by electrical circuits such that pressure to shear wave conversions are able to be electrically reconfigured. Through numerical simulations, we show the meta-boundary can nearly totally convert an incident pressure wave to a reflected shear wave even for normal incidences. Thanks to the programmability of electrical control circuits, incident waves can span a large range of angles, from negative to positive values, and reflected shear waves converted from pressure waves are also able to be steered to different directions. The design could find potential applications in protection of underwater structures, acoustic cloaks, ultrasonic imaging and new types of shear-wave-transducer devices.

与电磁波和声波系统相比，二维（2D）弹性中的固体自由边界或界面上的压力-剪切波转换是特殊且不可避免的波现象。但是，以前从未涉及过以可逆和可编程的方式灵活地调整其转换以满足预定的转换效率和转换波场的空间分布。在这封信中，我们介绍了具有深亚波长厚度的可编程元边界，该边界由由电路控制的压电传感和致动单元的阵列组成，从而可以对电波到剪切波的转换进行电重构。通过数值模拟 我们显示，即使对于垂直入射，超边界也几乎可以将入射压力波完全转换为反射剪切波。由于电气控制电路的可编程性，入射波可以跨大角度范围，从负值到正值，并且从压力波转换而来的反射剪切波也可以转向不同的方向。该设计可以在水下结构，声学隐身衣，超声成像和新型剪切波换能器的保护中找到潜在的应用。