Ultrasonic Phased Array Device for Acoustic Imaging in Air

An ultrasonic phased array device is developed to provide mobility aid for visually impaired people. To perform acoustic imaging, two different linear transducer arrays are composed using commercially available transducers for ranging applications. The transmitter and receiver arrays are formed with six and four transducer elements, respectively. Individual transducer elements are discrete components with a radius of 1.9 wavelengths and a half-power beamwidth of 43± at 40.8 kHz center frequency. The transmitter array is formed by aligning the transducers with minimum spacing between the elements. Even this placement leads to the occurrence of unwanted grating lobes in the array response and decreases the Field of View to 30±. To eliminate these grating lobes, the elements of the receiver array are placed with a different spacing. Forming the receiver and transmitter arrays with non-identical element spacing causes the grating lobes to appear at different places. Since the response of the overall system is the product of the directivity patterns of receiver and transmitter arrays, the grating lobes diminish for the overall system and the Field of View increases.