Author: Chien-I Liao
Standing: 4th Place Grand Award
Reconstructing Acoustic Image through Ultrasonic Wave Interference
Instead of optic wave, we are interested in a subject: if the image of the test object can be reconstructed by the same physical process in hologram through acoustic wave interference?
We carried out time retardation and dual slit experiments to verify that the acoustic wave presents phase coherence and interference. Then an ultrasonic transducer (f=40KHz) is set up so sound would pass through an aperture with a specific shape. At the same time, a fixed-phased electrical signal is connected directly to the oscilloscope as the reference wave, mixed with the wave from the aperture, which simulates the reflected wave of the test object. Through moving the sonic sensor in a plane, the intensity of each picture element (pixel) is recorded and a 2-D holography is also formed.
To reconstruct the acoustic image, a computer program was designed to simulate the formal reference wave passing through the holography and forming another interference pattern. Thus we generated the 2-D acoustic image by calculating the intensity of each pixel in a plane with a specific distance.
We also performed the experiments to study image resolution about two factors, which are related to (a) in-axis or off-axis (b) pixels per unit area. The results showed that resolution could be improved by either off-axis or increasing of pixel density. Finally, by choosing different distance from the holography to the simulated plane while reconstructing, a profile of each cross-section can be separated, which means the possibility of 3-D image reconstructing is mentioned.
National Taiwan Science Education Center
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