Sensor Array Optimization for Multiple Harmonic Sound Source Separation and DOA

INTRODUCTION In the last years a lot of researches about source separation have been realized, like extraction of a signal of interest (vocal recognition application), identification of which source gives which sound (motor engine applications) or noise source characterization (environmental application). Most of these techniques for sound source estimation use the signal-subspace approach, where the number of emitting sources is determined by the multiplicity of the lowest eigenvalue of the correlation matrix. The problems arise when the number of microphones is equal to the number of sources radiating, hence the noise subspace could not exist. This Master Thesis investigates how to realize a Goniometer Antenna to record communications, as well as the implementation of an algorithm to optimize the location of the sensors with the intend of separating the different sound sources in the at-worst case(number of sources equal number of sensors). It has been achieve using the eigenvalues of the correlation matrix of the received signals and the delay between microphones. Finally, measurements in the anechoic chamber verified the proposed approach. METHODS An acoustic goniometer is a system that measures the angle between a source and a receptor using the phase delay, thereby obtaining the source direction. The design dwell on two sensors (microphones) collocated in the 2D space in a concrete geometry. The implementation of each algorithm was done in Matlab based on two parts: the time delay estimation used in source localization by computing the azimuth in [2], and also an adaptation of the MPE block carried out in [4]. Likewise different methods based on the properties of the correlation matrix have been studied for delay estimating like in [3]. Apart from that, in [1] is explored the relation between sensor array geometry and eigenvalues to obtain the optimal sound sources separation and detection. This theory has been put into practice in programming in Matlab: minimization of the distance between microphones such that accomplish the condition of sources separation or sources detection. The optimization procedure has been done using two different SQP Methods: Active Set and Interior Point. Moreover, an optimization approach is presented for a system composed by two sensors and three sound sources. Several options based on mathematical theory has been considered for solving the problem. Eventually, taking advantage of the procedure followed in [1] and combined with the circumcenter calculation, the optimal distance for the microphones can be found. RESULTS Afterwards all this work, different simulations with the code in Matlab were tested reaching successful results. Then, a process of validation is required in the anechoic chamber for more realistic measurements. CONCLUSIONS In conclusion is demonstrated by theoretical calculation at first and then by experimental measurements that the optimal array geometry could help to improve the sound source separation approach. Forthcoming works will consist in extending this work for larger bandwidth and much more sound sources. Also, taking into consideration a more realistic model with reflections, interfering signals or noise corrupted

Analysis of the different signal acquisition schemes of an optical feedback based laser diode interferometer

The optical feedback interferometry phenomenon occurs when a portion of the output optical power is back-scattered from a remote target and coupled into the laser cavity to vary the laser’s emission properties (frequency and power mostly). Thus, this scheme results in a compact, self-aligned and contact-less interferometric sensor. Recent applications of optical feedback interferometer in the domains of microfluidics or acoustics have shown promising results and open new fields of researches. However in these applications, the amplitude of the sensing signal is extremely small due to the weakness of the backscattered power changes that are measured. In this thesis, an analytical model that describes the laser injection current and temperature dependence of the optical feedback interferometry signal strength for a single-mode laser diode has been derived from the Lang and Kobayashi rate equations. The model has been developed for all the known signal acquisition methods of the optical feedback interferometry scheme: from the package included monitoring photodiode, by collection of the laser power with an external photodetector and by amplification of the variations in the laser junction voltage. The model shows that both the photodiodes and the voltage signals strengths are related to the laser slope efficiency, which itself is a function of the laser injection current and of the temperature. Moreover, the model predicts different behaviors of the photodiodes and the voltage signal strengths with the change of the laser injection current and the temperature; an important result that has been proven by conducting measurements on all three signals for a wide range of injection current and temperature. Therefore, this simple model provides important insights into the radically different biasing strategies required to achieve optimal sensor sensitivity for the different interferometric signal acquisition schemes. In addition, the phase and amplitude relationships between the external and the in-package photodiode signals have been investigated theoretically and experimentally demonstrating unexpected results. Based on our model and on experimental observations, a critical study has been performed on the impact of the combination of the three signals in the signal processing strategy in order to improve the sensor sensibility to low amplitude optical feedback