José A. Siqueira Dias

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.

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.

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.

A CMOS fast transient response low-dropout regulator with a compact NMOS output driver

We present a CMOS low-dropout voltage regulator with a high-speed NMOS compact driver suitable for supplying on-chip voltages for the digital core of a SoC. The LDO is part of a power management controller hardblock integrated within a microcontroller. The die area of the circuit implemented in a 90nm CMOS process is only 0.054mm^2. Experimental results show that the developed LDO can supply up to 15mA and it presents a very fast transient response, with a settling time of approximately 30ns and a voltage drop of 200mV when the load current changes from 100nA to 9mA.

The Berimbot: A Robotic Musical Instrument as an Outreach Tool for the Popularization of Science and Technology

The purpose of this article is to describe an outreach program based on the engineering design of a robotic musical instrument aimed to the segment of the population not served by traditional academic initiatives or outreach programs. It aims to contribute to develop the interest among children and youngsters in pursuing scientific and technology careers and also mitigating science illiteracy among the general public. The program consists in a keynote showing the various phases undertaken, people involved and the knowledge and skills needed to build the robotic musical instrument. The concepts of teamwork, consulting and multidisciplinarity are also examined. The presentation includes a musical performance.

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.

Variations of high-level injection knee voltage in lateral p-n-p transistors

Abstract The variation of the high-level injection knee voltage Vkwith the base width of lateral p-n-p transistors is discussed. A simple model that includes the compensation of the epitaxial layer in the base region is used to explain the changes in the onset of the high-level injection mechanism. The calculated values agree well with the measured data.