Acoustic eavesdropping is a privacy risk, but existing attacks rarely work in real outdoor situations where people make phone calls on the move. We present SuperEar, the first portable system that uses acoustic metamaterials to reliably capture conversations in these scenarios. We show that the threat is real as a practical prototype can be implemented to enhance faint signals, cover the full range of speech with a compact design, and reduce noise and distortion to produce clear audio. We show that SuperEar can be implemented from low-cost 3D-printed parts and off-the-shelf hardware. Experimental results show that SuperEar can recover phone call audio with a success rate of over 80% at distances of up to 4.6 m - more than twice the range of previous approaches. Our findings highlight a new class of privacy threats enabled by metamaterial technology that requires attention.

翻译：声学窃听是一种隐私风险，但现有攻击方法在用户移动中进行手机通话的真实户外场景中鲜少有效。本文提出超耳系统，这是首个利用声学超材料在此类场景中可靠捕获对话的便携式系统。我们通过可实现的样机证明该威胁真实存在：系统能增强微弱信号，以紧凑设计覆盖全语音频段，并降低噪声与失真以生成清晰音频。超耳系统可由低成本3D打印部件与商用硬件实现。实验结果表明，在4.6米距离内，超耳系统恢复通话音频的成功率超过80%——这是现有方法有效距离的两倍以上。我们的研究揭示了由超材料技术赋能的新型隐私威胁，亟需引起关注。