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Laser Eavesdropping

Contact Information

     University:Huazhong University of Science and Technology (HUST - China)

     Team Members (with year of graduation): Cheng Li(2015), Xiaofei Deng(2015), Qian Zhang(2015)

     Faculty Advisers: Ying Wang


     Submission Language: English

Project Information

     Title: Laser Eavesdropping

     Description: Laser Eavesdropping Device.With this device, we can achieve remote

eavesdropping by simply pointing the laser beam at the window. It can also adjust its

position automatically in order to receive the reflected beam and get the target sounds.


NI-USB6353, LabVIEW2012, 650nm 100mW Semiconductor Laser, PIN diode and Ultrasonic distance measuring Module.

The Challenge:

The traditional way of eavesdropping is to fix a detectaphone at somewhere secrete. However, this method requires people to get into the place and fix devices beforehand, which is not always feasible. We want to obtain the sounds at a distance without the constraint of a cable. Here, we use laser beam to capture the information of sounds. When people speak in a room, the sounds carry energy to force the glass windows into sympathetic vibration. When a laser beam points at the vibrating window, the vibrations will modulate on it and result in a small back and forth displacement of the beam synced with the window oscillations. We receive the modulated beam and optimize the receiving process by adjusting the actuator automatically. Then the complex signals is demodulated and turned back into intelligible sounds with LabVIEW Demodulation Tool Kit. By doing this, we can eavesdrop with a laser.


The Solution:

The laser beam is delivered by a 650nm, 100mW semiconductor laser and received by a PIN photodiode, where the intensity variation due to the back and forth displacement of the beam are turned into electrical signals. These signals are then amplified, filtered and changed back into sounds. We use NI-USB6353 to capture these sounds and utilize LabVIEW for further processing. The sounds are then stored in files for future playback.


Because of the coherence properties of laser, the beam reflects at the surface of the window and changes its direction widely when it has a small angle of incidence. Then the receiver will be too far away from the transmitter. For the purpose of system integration, the laser beam are expected to be incident on the window nearly at right angle, which is convenient for receiving. We use NI-USB6353 to control the rotation of two actuators on the three-dimensional PTZ. NI-USB6553 collects real-time data from the ultrasonic ranging module and sends them to LabVIEW. The software analyzes the data and then determine the rotation of actuators. So the NI-USB6353 adjust the device to the right angle.

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