Elnatan Chagas Ferreira

A Fiber Bragg Grating RMS Current Transducer Based on the Magnetostriction Effect Using a Terfenol-D Toroidal-Shaped Modulator

A new approach to the fabrication of robust and low-cost fiber Bragg gratings optical current transducers using a Terfenol-D magnetostrictive material is presented. Electro-erosion is used to manufacture a magnetic core in a toroidal shape, which results in a single piece robust mechanical design. By applying mechanical compression to the toroidal sensor and making its response very close to a quadratic function, it is possible to calculate the rms value of the current directly from the output of the sensor and eliminate the dc biasing magnetic field used in all previous techniques. A new electronic interrogation circuit technique, which allows for the measurement of ac signals and keeps the dc operation point of the fiber Bragg grating, is developed and successfully used in the prototype. Experimental results measured in the developed optical current transducer show that an error of ±0.6% is achieved for currents over the 320-900 A range. When tested over the temperature range of 25°C -45°C, a maximum error of ±2% is observed. The developed system presents a fast transient response, and needs only 34 ms to reach the steady state after a 150% amplitude step increase is applied to current being measured.

An 8-bit Folding A/D Converter with a New Interpolation Technique

This paper proposes a new interpolation technique for application in a folding A/D converter with interpolation. However, there is not a specific interpolation circuit because this interpolation technique is applied to the folding encoder circuit and to the master latches of the A/D converter. This interpolation technique adds some transistors in the folding encoder circuit, and it adds only three transistors to some master latches. An 8-bit A/D converter has been designed and implemented in a 0.8 μm BiCMOS process, at FT of 12 GHz to evaluate the proposed interpolation technique.

A Closed-Loop Interrogation Technique for Multi-Point Temperature Measurement Using Fiber Bragg Gratings

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.

Precision analog demodulation technique for open-loop Sagnac fiber optic gyroscopes

This paper presents an analog technique for the demodulation of interferometric fiber optic gyroscopes signals, based on the calculation of the mean value of the negative cycles of the measured photodetector signal from sinusoidally modulated Sagnac gyroscopes. The developed signal processing circuit was implemented and tested in a laboratory, and it was possible to detect signals as low as 5 microrad. Experimental results measured in a 890 m fiber optic coil gyroscope equipped with the developed circuit showed that the proposed circuit, when compared to the widely used and mature lock-in amplifier technique, presented a 5.1 dB higher signal-to-noise ratio. The circuit is also very stable with the temperature, since a very low drift of 0.04 degrees /h degrees C was measured in a complete gyroscope system. The Brazilian research sounding rocket VSB-30 is currently being equipped with the developed demodulator circuit.

Experimental Investigation on the Load Signature Parameters for Non-Intrusive Load Monitoring

One of the most important design decisions in Non-Intrusive Load Monitoring (NILM) systems is choosing which electrical parameters will be used to define load signatures. In this paper, we present an experimental study where several electrical quantities of common home appliances were measured, in order to identify the most adequate to perform load disaggregation. It was found that active power, reactive power, rms voltage, and the first five odd harmonics of the current and voltage signals comprises the best set of parameters to define the signatures of residential loads. Streszczenie. W artykule zaprezentowano eksperymentalne studium w ktorym zmierzono parametry typowych urządzen elektrycznych w celu określenia i zestawienia obciązen. Stwierdzono ze moc czynna, moc bierna, napiecie skuteczne i pierwsze piec nieparzystych harmonicznych prądu mogą stanowic podstawe do prognozowania obciązen. Badania parametrow urządzen dla nieinwazyjnego monitorowania obciązen.

A Temperature-Independent Interrogation Technique for FBG Sensors Using Monolithic Multilayer Piezoelectric Actuators

In this paper, a temperature-independent technique for measurements of ac signals, such as voltage and electrical current, with fiber Bragg grating (FBG) sensors is presented. This technique is based on a twin-grating scheme, in which the measured quantity is obtained from the optical power of convolution between a sensing FBG and a tunable FBG. The proposed interrogator employs a low-voltage monolithic multilayer piezoelectric actuator (MMPA) to sweep the tunable FBG over the wavelength range of the sensing FBG, in order to obtain the convolution function accurately. A dedicated microcontrolled optoelectronic system with a firmware-based tracking routine is responsible for keeping the tunable FBG following the sensing FBG over temperature-induced wavelength shifts with subpicometric resolution, while the dc level of convolution is controlled precisely at the highest sensitivity point of operation. The MMPA employed allows the tracking of the tunable FBG after the sensing FBG over a maximum temperature difference that ranges from -29 °C to +90 °C. The proposed interrogator presents lower cost compared with the systems that employ frequency-scanning devices, such as high-speed Fabry-Perot tunable filters.

Technique for suppressing the electronic offset drift of interferometric open-loop fiber optic gyroscopes

A technique to eliminate the offset drift in the demodulator circuitry of open-loop interferometric fiber optic gyroscopes is presented. This technique employs a demodulation scheme that uses the area of the negative half-cycles of the output signal of a sinusoidally modulated gyroscope to obtain the angular velocity. We propose an electronic circuitry that periodically reverses the demodulator input, allowing for the acquisition of two samples of the gyroscope signal with the same magnitude and opposite polarities. The angular velocity is obtained from the subtraction of these two samples, suppressing the electronic offset. Experiments showed that the proposed method reduces the demodulator offset drift from 4.4 μV/°C to about 14 nV/°C, which is equivalent to a reduction, from 0.2 deg/h/°C to about 0.0006 deg/h/°C in the tested gyroscope. The proposed technique improved the bias stability of the tested gyroscope from 0.0162 to 0.0071 deg/h.

A Low-Cost Technique for Simulation and Characterization of Fibre Bragg Grating Sensors in Undergraduate Instructional Laboratories

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.

Minimum detectable signal and optimal operating point in intensity noise-limited fiber optic gyroscopes

The relative intensity noise in sinusoidally modulated fiber optics gyroscopes is analyzed in order to determine which is the value of the minimum detectable signal by the demodulator electronics circuits. The analysis is conducted for both the well known lock-in amplifier demodulator and the mean value demodulator (MVD). Numerical results show that, in intensity noise-limited fiber optics gyroscopes, the MVD allows for the demodulation of smaller signals when compared to the lock-in amplifier.

A synchronous frequency discriminator using 'injected-locking'

A technique for synchronous frequency discrimination is described. It is based on the principle of injected-locking. Its feasibility and usefulness for broadcasting or TV IF is discussed. This technique provides good performance with regard to the principal characteristics in FM systems: low distortion, good AM rejection, and high signal-to-noise ratio.<<ETX>>