Felipe Walter Dafico Pfrimer

A small Brazilian speech corpus was created for educational purposes to study a state-of-the-art speaker recognition system. The system uses the Gaussian Mixture Model (GMM) as a statistical model for speakers and employs the Mel-frequency cepstral coefficients (MFCC) as acoustic features. The results using clean and noisy speech are compatible with the expected results, showing that the bigger the mismatch between training and test conditions, the worse the results. The results also improve with the increase in the utterance length. Finally, the obtained results can be used as baselines to compare with other speaker statistical models created with different acoustic features in different acoustic conditions.

An acoustic emitter based on electrical–mechanical transduction is designed to have a projected emission pattern. However, due to constructive features, design flaws, and different material qualities, the final device does not match project specifications which may cause, among other things, the reduction of performance, loss of emission power, and undesirable noise. In this work, an apparatus for acoustic characterization comprising a turntable and an arc is developed to estimate the emission power of acoustic emitters. The time-stretched pulse method is used as a test signal to obtain the emission power for each emitter's azimuth and elevation angles. Processing the acquired signals gives an estimated radiation pattern in the three-dimensional space, which visually allows the analysis of the emission characteristics of the acoustic source.

In many countries, water quality monitoring is limited due to the high cost of logistics and professional equipment such as multiparametric probes. However, low-cost sensors integrated with the Internet of Things can enable real-time environmental monitoring networks, providing valuable water quality information to the public. To facilitate the widespread adoption of these sensors, it is crucial to identify which sensors can accurately measure key water quality parameters, their manufacturers, and their reliability in different environments. Although there is an increasing body of work utilizing low-cost water quality sensors, many questions remain unanswered. To address this issue, a systematic literature review was conducted to determine which low-cost sensors are being used for remote water quality monitoring. The results show that there are three primary vendors for the sensors used in the selected papers. Most sensors range in price from US$6.9 to US$169.00 but can cost up to US$500.00. While many papers suggest that low-cost sensors are suitable for water quality monitoring, few compare low-cost sensors to reference devices. Therefore, further research is necessary to determine the reliability and accuracy of low-cost sensors compared to professional devices.

In this paper a closed-loop interrogation technique for multi-point temperature measurement using fiber Bragg gratings (FBG) is presented. The technique uses a broadband light source and n tunable FBGs to interrogate an array of n FBGs sensors placed along the optical fiber. Each center wavelength of the tunable FBGs is matched with the center wavelength of one FBG sensor placed in the array. The light source directly illuminates the sensor array, so that all the light reflected from the FBGs enters in the optical circuit through an optical circulator and the reflected spectrum of each sensing FBG illuminates a matched tunable FBG. Because the current generated by the photodiode is proportional to the convolution between the two FBGs profiles (the sensor FBG and the tunable FBG), by controlling the value of the convolution at a fixed value, the center wavelengths of the two FBGs are kept spaced by a constant value. Therefore, the temperature of the FBG sensor can be associated with the temperature of the tunable FBG. A two channel prototype was constructed to validate the technique and a very high resolution of ±0.001 ^°C was obtained.

Fibre optic sensors are becoming so important in engineering that it is important to introduce this new subject in Electrical Engineering courses. This work describes the construction of a simple, low-cost fibre Bragg grating (FBG) electronic interrogation system that uses LabVIEW as a tool for simulation, measurement interface and parameter extraction of the FBGs. Although the system is relatively slow (a precise FBG characterization takes 10 minutes to be performed), the students can observe, while performing the assigned tasks, all the signals in the interrogator circuit, resulting in an extremely useful didactic tool. The measurements obtained with the system are in very good agreement with results measured on expensive Optical Spectrum Analysers when obtaining a full FBG profile. The system can also be used to measure and characterize FBGs submitted to external strains (e.g., temperature and force) demonstrating the Bragg shift caused by these strains on FBG sensors.