Voice monitoring system using laser beam

Abstract

An infrared laser beam (B,) is irradiated from a transmitter (,) toward a window pane (,) of a building (,), and a reflected laser beam (B2) is received by a receiver (,). A laser spot (Q) picked up by a CCD camera is displayed on respective target display units (,). Within the receiver, there are provided a photo-cell for outputting an electric signal corresponding to light energy of the reflected beam, and a knife edge for shielding a portion of the reflected beam. Vibrational component of the window pane caused by voice in the room is detected as a positional change of the reflected beam. In determining an installation place of the receiver, a beam detector (,) comprised of a large number of light receiving elements is used to detect the reflected beam. The transmitter scans an object with the laser beam (B,) modulated by an audible frequency so that the reflected beam (B,) is easily detected. When the reflected beam hits the beam detector, the detector beeps vibratorily with the audible frequency. The XY coordinates showing an actual scanning position are transmitted from the transmitter to the receiver, and shown on a coordinate display unit (,).