In ultrasonic spectroscopy, the propagation velocity and attenuation coefficient of an acoustic wave that propagates through a sample are measured as a function of frequency. From these parameters, other properties of the sample can be indirectly inferred, such as compressibility, elastic constants, concentration/composition, adulterations, etc. One acoustic method for measuring properties is the relative technique, in which a reference sample (usually distilled water, which has well-known properties) is first measured, and it is then replaced by the sample of interest. In the measurement of the acoustic parameters as a function of frequency, operations are carried out between the spectra of the signals from the reference sample and the sample of interest. In the calculation of the propagation velocity, a subtraction between the spectral phases is made, while the attenuation coefficient is calculated after a division between the magnitude spectra. A problem appears when the properties of the liquid of interest are very different from the properties of distilled water, producing small overlap between the respective spectra and large magnitude difference. This difference is not interesting from the point of view of data acquisition, because there will be more noise in the smaller amplitude signal, since the system works with the same scale/gain on the acquisition board for the different signals. One of the proposals of this work is to characterize other liquids that can be used as reference, such as glycerol, which is present in several industrial segments as raw material, is easy to prepare, stable and presents no risks of manipulation. From mixtures of water and glycerol, the sample attenuation can be controlled, and the velocity and attenuation of these samples will be measured as a function of temperature. Subsequently, water-glycerol mixtures will be used as reference samples to characterize samples of more attenuating liquids, such as castor oil. These results will be compared with measurements taken when distilled water is used as a reference. Using this procedure, different measuring bandwidths should be achieved. The keys advantages of the measuring cell that will be used are the eassy sample handling, the use of high frequencies and temperature control with variations smaller than 0.01°C. The student will also reformulate the instrumentation control, data acquisition and signal processing program in Matlab environment that is currently used in the system, in order to make it more intuitive and practical. In order to accomplish these tasks, the student will have to understand the concepts of acoustic and digital signal processing involved in calculating the parameters of interest, such as Fourier transform and digital filtering. The program's main functions consist of: initialization and control of the instruments (ultrasound dual pulser/receiver, data acquisition board and temperature control system); calibration with a reference liquid; measurement of the liquid of interest; calculation and visualization of intermediate and final results, in numerical and graphical form; storage of the data of interest. In the overall context of work, the student will be engaged with concepts of ultrasonic spectroscopy, electronic and virtual instrumentation, digital signal processing, complementing his skills in electrical engineering.
News published in Agência FAPESP Newsletter about the scholarship: