Ultrasonic phased array device for acoustic imaging in air
Harput, Sevan (2007) Ultrasonic phased array device for acoustic imaging in air. [Thesis]
The acoustic imaging technology is widely used for medical purposes and underwater imaging. In this work, an ultrasonic phased array device is developed by using piezoelectric transducers to provide autonomous navigation for robots and mobility aid for visually impaired people. To perform acoustic imaging, two different linear transducer arrays are composed with phase-delay focusing phenomenon in order to detect proximate objects with no mechanical scanning. The requirement of half wavelength spacing can not be satisfied between elements, because of using general purpose transducers. The transmitter array is formed by aligning the transducers with minimum spacing between them, which is 2.11 times of the wavelength. This placement strategy leads to the occurrence of unwanted grating lobes in the array response. To eliminate these grating lobes, the receiver array is formed with a different spacing between each transducer. By forming the receiver array and the transmitter array non-identical, the directivity pattern for both arrays become different. The off-alignment between two arrays causes the grating lobes to appear at different places. Since the overall gain of the system is the product of receiver gain and transmitter gain, the grating lobes diminish for the overall system. The developed phased array device can transmit/receive ultrasonic waves to/from the arbitrary front directions using electronic sector scanning circuits. A detailed scan can be performed to detect the presence of an object or distinguish different objects.
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