论文总字数：33793字

摘 要

窃听与防窃听作为一个古老又重要安全问题一直都被研究人员们密切关注着，在现代通信技术的不断进步的同时，窃听的方式也有了新的发展，利用智能手机的录音功能进行的窃听就是其中之一。智能手机等移动终端的普及带来了方便，也带来了新的安全问题。随着它们的硬件不断更新迭代，它们体积越来越小，录音功能越来越强。使用智能手机录音十分隐蔽，成本也相当低廉。在法院、律师事务所、证券交易所等机构中，由于工作的特殊性，从业者十分忌讳在他们不知情的情况下被录音，而近年来，窃听者使用随身携带的智能手机偷录对话的例子屡见不鲜，让人防不胜防。现有的防录音方案常使用大功率的背景噪声覆盖录音，或是用电磁波干扰录音设备，但是前者会影响正常的对话，后者的干扰效果又十分有限。针对上述问题，需要一种解决方案可以干扰智能手机的录音，同时不影响正常的对话。

本文设计了一种利用超声波干扰智能手机等移动终端的系统。在基于单片机的声源信号生成模块中，该系统可以生成原始高频超声波，再通过功率放大模块放大其功率，最后通过压电陶瓷超声波换能器将电信号转换为声音信号发射出去。在本系统的干扰范围内，智能手机的录音功能将受到严重干扰，录下的音频终将会有强烈的杂音信号，完全掩盖住人的声音信息，窃听者将不能从录音音频中还原出正常的对话内容。另一方面，由于本系统的干扰利用的是超声波，干扰对人耳来说是不可听的，所以不会影响到人们的正常对话。

本文基于所用到的“声学的非线性”理论，设计了整套超声波干扰系统，并对该方案的可行性进行了理论分析与仿真验证。同时，为了实现预期的干扰效果，本文还利用 “扩频调制”和 “BASK调制”处理信号，探讨了它们的原理与应用方式，并进行了仿真验证。根据理论研究与仿真分析，本文搭建整个系统并对其进行了测试。测试的结果证明了本系统可以对多种型号的智能手机的录音功能进行干扰，其录音音频中的人类语音信息不能被正常分辨。

关键词：防录音窃听 超声波 声学非线性

ABSTRACT

As an ancient and important security issue, wiretapping and anti-wiretapping have always been closely followed by researchers. With the continuous progress of modern communication technology, the method of wiretapping also has a new development. Wiretapping with the recording function of smart phones is one of them. The popularity of mobile terminals such as smart phones not only brings convenience to people but also brings new security problems. As their hardware iterates, they get smaller and better at recording. Recording with a smartphone is both covert and cheap. In courts, law firms, stock exchanges and other relevant institutions, due to the particularity of their work, practitioners are very afraid to be recorded without their permission. In recent years, people's use of portable smart phones to secretly record conversations is becoming more and more common, making it hard to prevent. Existing anti-recording schemes often use high-power background noise to cover the human voice, or use electromagnetic wave to interfere with the recording equipment, but the former will affect the normal dialogue, the latter interference effect is very limited. In order to deal with this kind of eavesdropping, a solution is needed that can interfere with the recording of smart phones without affecting normal conversations.

This paper designs a system which uses ultrasonic wave to interfere with mobile terminal such as smart phone. In the sound source signal generation module based on single chip microcomputer, the system can generate the original high-frequency ultrasonic wave, and then amplify its power through the power amplifier module. Finally, the electrical signal is converted into sound signal through the piezoelectric ceramic ultrasonic transducer. Within the interference range of this system, the recording function of smart phones will be seriously disturbed, and the recorded audio will eventually have a strong noise signal, completely covering the human voice, and the eavesdropper will not be able to restore the normal conversation content from the recorded audio. On the other hand, because this system uses ultrasound to disturb the recording, it is not audible to the human ear, so it will not affect people's normal conversation.

In this paper, based on the theory of "acoustic nonlinearity", a whole set of ultrasonic interference system is designed, and the feasibility of the scheme is analyzed theoretically and verified by simulation. At the same time, in order to achieve the expected interference effect, this paper also uses "spread spectrum modulation" and "BASK modulation" to process signals, discusses their principle and application mode, and conducts simulation verification. Based on theoretical research and simulation analysis, this paper builds the whole system and tests it. The test results prove that the system can interfere with the recording function of many types of smart phones, and the human voice information in the recorded audio can not be distinguished normally.

Keywords: anti-wiretapping, ultrasonic, acoustic nonlinear

目 录

摘 要 I

ABSTRACT II

第一章 绪 论 1

1.1 课题研究背景 1

1.2研究现状及发展 1

1.2.1 防窃听技术发展及现状 1

1.2.2 移动终端的声音传感器相关安全研究现状 2

1.2.3 基于超声波的安全研究现状 3

1.3 论文研究内容及意义 3

1.4论文章节安排 5

第二章 理论基础 6

2.1声学的非线性特性 6

2.2超声波干扰的原理 7

2.2.1 双频干扰理论模型 7

2.2.2 多频干扰理论模型 9

2.3 扩频和BASK调制方案 11

2.3.1 直接序列扩频 11

2.3.2 BASK调制 16

2.3.3 扩频和BASK调制方案的仿真验证 19

2.4 本章小结 20

第三章 超声波干扰系统的设计 21

3.1 超声波录音干扰系统结构组成 21

3.2 信号处理平台的硬件设计 21

3.2.1 单片机核心板 22

3.2.2 片外模块硬件设计 23

3.3 信号处理平台的软件设计 25

3.3.1 片内模块的软件设计 25

3.3.2 片外模块的软件设计 28

3.4 功率放大模块的设计 30

3.4.1 三极管电路与变压器电路 30

3.4.2 TDA2030功放电路 31

3.5 超声波阵列的设计 32

3.6 本章小结 35

第四章 超声波干扰系统的测试与分析 36

4.1 实验测试总体方案设计 36

4.2 声源与干扰设备在一处 37

4.3 声源与录音设备在一处 39

4.4 其他影响因素 40

4.4.1 麦克风摆放方向 40

4.4.2 干扰信号角度范围 41

4.4.3 对话音源声音强度 42

4.5 本章小结 43

第五章 总结与展望 44

5.1 全文总结 44

5.2 工作展望 44

参考文献 46

致 谢 49

第一章 绪 论

1.1 课题研究背景

随着现代通信技术的不断发展，移动终端的功能越来越强大。移动终端从诞生以来已有几十年的历史，但是其真正开始发生突飞猛进式的进步是从2007年开始的。移动终端很快成为了新型媒体，电子商务等新兴产业的接入口；其硬件设备与通信技术的革新也成全球ICT行业研究的重点。而移动终端的定义在如今的大部分情况下也慢慢变成智能手机或者便携式的平板电脑。

移动终端中使用的硬件设备一直在快速的更迭换代，比如智能手机中的传感器，它们的功能正变得越来越强大。智能手机中有着种类繁杂，数量众多的传感器，比如光强传感器、温度传感器、湿度传感器、方向传感器、运动传感器等。随着用户需求的不断提升，这些传感器被设计制造得越来越精密，这在给人们带来方便的同时，也带来了一些安全方面的隐患。

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