Stealthy Voice Eavesdropping with Acoustic Metamaterials: Unraveling a New Privacy Threat

We present SuperEar, a novel privacy threat based on acoustic metamaterials. Unlike previous research, SuperEar can surreptitiously track and eavesdrop on the phone calls of a moving outdoor target from a safe distance. To design this attack, SuperEar overcomes the challenges faced by traditional acoustic metamaterials, including low low-frequency gain and audio distortion during reconstruction. It successfully magnifies the speech signal by approximately 20 times, allowing the sound to be captured from the earpiece of the target phone. In addition, SuperEar optimizes the trade-off between the number and size of acoustic metamaterials, improving the portability and concealability of the interceptor while ensuring effective interception performance. This makes it highly suitable for outdoor tracking and eavesdropping scenarios. Through extensive experimentation, we have evaluated SuperEar and our results show that it can achieve an eavesdropping accuracy of over 80% within a range of 4.5 meters in the aforementioned scenario, thus validating its great potential in real-world applications.