Mechanical & Manufacturing Engineering

Ollscoil Chaithair Bhaile Atha Cliath Dublin City University

Photoacoustic Cell

Laser Transmitter

Laser Receiver Unit

Potentiometer Volume Control

“Surface Displacement Amplitude”

BNC Connector Signal Output

Reflected Laser Beam

2. WINDOW STIMULATOR: A piece of glass is attached to the centre of the speaker cone mimicking a real world vibrating window surface.

4. LASER RECEIVER CIRCUIT: Amplitude modulation of the laser beam

deflection caused by the displacement of the vibrating glass surface of the photoacoustic

chamber is deciphered and amplified into an audible audio signal.

Real World Application

Designed Laser Microphone using the “angular grazing method” for photoacoustic signal detection.

DESIGN OF A LASER MICROPHONE FOR PHOTOACOUSTIC SIGNAL DETECTION ABIOLA OGUNDE

1. LASER TRANSMITTER: Class II 1mW laser diode (650 nm wavelength) used as the light source. Laser beam is bounced off a vibrating glass surface.

LASER MICROPHONE OPERATION: Detects displacement-amplitudes (vibrations) on a reflective glass surface with a laser beam and converts the deflected motion of the beam into a digital signal using a laser receiver unit.

3. PHOTOACOUSTIC CHAMBER: A sound source (speaker) is enclosed in a photoacoustic cell and sealed with a glass on the top. This is will result in the displacement-amplitude of the

glass surface.

PROJECT OBJECTIVE! Non-destructive

method of photoacoustic signal detection USING A

LASER MICROPHONE.

PA Detection Results

Blue waveform: 2Hz Sine Wave sound frequency sent to the speaker in the PA chamber speaker. Black waveform: Detected 2Hz frequency sound signal with noise.