|ALBERTINI DAVIDE||Cycle: XXXV |
Tutor: CESANA MATTEO
Advisor: SARTI AUGUSTO Major Research topic
:Signal Processing Methodologies for Acoustic Characterization of Structures and EnviromentsAbstract:
Semiconductor technology has driven the development of low-cost transducers, due to large scale production, in a large number of research and technological applications. Those transducers are delivering performances comparable to traditional sensors but can be massively deployed due to their reduced cost and dimensions. Moreover, recent advancements in digital signal processing techniques allow filling the gap between high-class sensors and semiconductor transducers in terms of sensibility, dynamic range, frequency response, and resolution. In particular, MEMS microphones are being used as a low-cost replacement in acoustic applications such as sound field acquisition in both Wave Field Synthesis and Ambisonics frameworks. They are even being employed in Differential Microphone Arrays to suppress noise, locate and separate sound sources, by means of digital signal processing algorithms. Inferior cost and small dimensions, however, come with some drawbacks in the frequency range of operation. In particular, MEMS microphones are less sensitive to low frequencies, and conversely, show a resonant peak above 10kHz due to the Helmholtz resonance of the air cavity. Moreover, sensitivity is frequency-dependent. Those deficiencies can be compensated through signal processing techniques, exploiting the fact that most MEMS microphones have a direct digital output that can be directly processed in real-time. Digital filtering, artificial intelligence, and super-resolution techniques could address those issues and give a flat response over frequency and dynamic range of interest. Moreover, due to the advancements in digital emulation of analog circuits, a large range of nonlinearities in those devices could be linearized through digital filtering and nonlinear inversion, instead of using the standard approach of an electronic conditioning network.
The same growing trend of MEMS microphones usage in consumer and professional electronic equipment could potentially become a reality for MEMS speakers. It is of interest the investigation in Wave Field Synthesis to recreate a specific soundscape by using multiple Piezo MEMS speakers. The main limitations are the inability to reach frequencies below a few hundred Hertz, and the impairment in moving significant air mass, due to the reduced dimensions. Considering the current state of the art in acoustic applications for semiconductor transducers and possible developments, my Ph.D. thesis explores algorithms to obtain high-quality measures using a combination of semiconductor transducers, (MEMS, PMUT, and Piezo) with the objective of demonstrating how far this technology can go beyond current high-level sensors and actuators. The limitation of those devices is going to be addressed through digital signal processing techniques, to obtain virtual, higher quality measurements.