With the development of digital devices, the recording process has become increasingly easier to conduct. However, the portability of the recording devices has also made recording difficult to monitor. If private conversations are illegally recorded, it will cause serious secret-leakage events. Therefore, it is imperative to prevent unauthorized recordings. Recent works have demonstrated that the nonlinearity effect of microphones can be leveraged to interfere with microphone recording using ultrasounds. However, an ultrasonic array has a limited jamming area. The design of an anti-recording system composed of multiple ultrasonic arrays remains to be addressed. In this paper, a jamming system, JamSys, is presented to prevent eavesdropping in a given region. We propose a new scheme composed of the angle coverage model and the modified harmony search algorithm (MHSA) to optimize the deployment of ultrasonic arrays, which achieves the maximum jamming area with the given number of arrays. In the simulation and experiments, three different optimization algorithms, the MHSA, the genetic algorithm (GA), and the regular coverage algorithm (RCA) are compared. The MHSA is demonstrated to provide the best results.INDEX TERMS Privacy protection, anti-recording, microphones, ultrasounds, optimization algorithms.
I. INTRODUCTIONElectronic eavesdropping is a means of stealing important information. Recording is a typical type of eavesdropping. Due to the small size of recording devices, attackers can easily record secret information in confidential meetings and private conversations. Therefore, protecting confidential and private activities from illegal recording is very important for personal communication secrets, commercial trade, and even national security.The current protection methods can be categorized into two broad categories: detection and jamming techniques. The detection techniques rely on metal detectors or X-ray scanners to detect electronic devices. However, such techniques are unreasonable if electronic devices are not allowed in some situations, such as cinemas. Some electronic devices, such as laptops, cannot be blocked from being carried because they may be used in meetings. The above drawbacks limit the use of detection techniques.The associate editor coordinating the review of this manuscript and approving it for publication was Cristina Rottondi.
