Implementation of a Virtual Microphone Array to Obtain High Resolution Acoustic Images

Using arrays with digital MEMS (Micro-Electro-Mechanical System) microphones and FPGA-based (Field Programmable Gate Array) acquisition/processing systems allows building systems with hundreds of sensors at a reduced cost. The problem arises when systems with thousands of sensors are needed. This work analyzes the implementation and performance of a virtual array with 6400 (80 x 80) MEMS microphones. This virtual array is implemented by changing the position of a physical array of 64 (8 x 8) microphones in a grid with 10 x 10 positions, using a 2D positioning system. This virtual array obtains an array spatial aperture of 1 x 1 m(2). Based on the SODAR (SOund Detection And Ranging) principle, the measured beampattern and the focusing capacity of the virtual array have been analyzed, since beamforming algorithms assume to be working with spherical waves, due to the large dimensions of the array in comparison with the distance between the target (a mannequin) and the array. Finally, the acoustic images of the mannequin, obtained for different frequency and range values, have been obtained, showing high angular resolutions and the possibility to identify different parts of the body of the mannequin.