Raimundo C. S. Freire

Hot-wire anemometer with temperature compensation using only one sensor

In conventional constant temperature hot-wire anemometers, the compensation for the fluid temperature is done by using two sensors. In this paper, the analysis of an anemometer circuit using only one sensor, operating alternately at two different temperatures is presented. The effect of the amplifier input offset voltage is taken into account, and its influence on the measurement of fluid velocity is quantified. Preliminary experimental results are also presented.

FPGA architecture for static background subtraction in real time

Background subtraction is a method typically used to segment moving regions in image sequences taken from a static camera by comparing each new frame to a model of the scene background. In this paper, we present an FPGA architecture for background subtraction, taking advantage of the data and logical parallel opportunities offered by a field programmable gate array (FPGA) architecture. At a clock rate of 40 MHz, the architecture can process 30 frames per second, where the image resolution is 240 x 120. The capability of the system is demonstrated for several tests and video sequences.

A hysteresis model for a vanadium dioxide transition-edge microbolometer

This paper presents the adaptation of the Preisach model, originally developed for magnetic hysteresis, to describe mathematically the hysteresis in the resistance-temperature characteristics of vanadium-dioxide (VO/sub 2/) thin film radiation sensors. The necessary and sufficient conditions for the applicability of the Preisach model to a VO/sub 2/ film sensor are experimentally verified. Experimentally measured characteristics are compared with those given by the model for minor and major loops.

Fast communication: Influence of low frequency noise in adaptive estimation using the LMS algorithm

Adaptive systems are employed in the cancelation of noises and estimation of periodic and quasiperiodic signals. Amongst these signals are the electrocardiogram (ECG), impedance cardiography (ZCG), brain evoked potentials and modulated signals in telecommunication applications. In this paper we study the behavior of the weights of the LMS algorithm when used to estimate the coefficients of the discrete Fourier transform (DFT) of a signal under influence of low frequencies. We show theoretically that low frequency noise affects the estimation of the weights at higher frequencies. The simulation results obtained are in agreement with theoretical results. Moreover, we exemplify the problem with impedance cardiography (ZCG) signals.

Dynamic response of thermoresistive sensors

Electronic circuit configurations for determining the dynamic response of thermoresistive sensors, using pulsed electrical excitation step and radiation step, are presented. Experimental results obtained with these circuits are included. The reduction in the response time of an instrument with these sensors in feedback structures is experimentally demonstrated. >

Designing a programmable analog signal conditioning circuit without loss of measurement range

Programmable analog signal conditioning circuits can be programmed in the field to permit their use in several applications with a variety of sensors with different output signal characteristics. The digital programming of the gain and dc level shift of a conditioning circuit can affect the measurement resolution and cause a reduction in the range of the measuring system in which it is employed. For a specified maximum acceptable loss in the measurement resolution, a procedure for defining and employing the programming values that guarantees the full measurement range is proposed. The proposed methodology takes into account practical implementation considerations and can be employed for designing either discrete or integrated circuits.

Applications of Thermoresistive Sensors Using the Electric Equivalence Principle

In this paper, a survey on the characteristics of thermoresistive sensors [positive temperature coefficient (PTC) and negative temperature coefficient (NTC)] and their applications to measurement structures that use the electric equivalence principle, in special radiometers and anemometers, is presented. The dynamic responses of the architectures and the influence of the operational amplifier offset voltage on the instrument performance are discussed. Alternative architectures employing pulsewidth modulation (PWM) and sigma-delta analog-to-digital (A/D) converters are also shown.

Fillet Weld Identification for Automatic Inspection of Spherical Tanks

In this article the development of a system for fillet weld identification is considered for automatic inspection of storage spheres. Distance sensors based on different physical principles are characterized and selected, thus getting, greater confidence of the acquired data. The data provided from the different types of sensors will be submitted to a fusing process, aiming at to increase the confidence and performance of the system.

Analysis of Multilayer Amplifier Structure by an Efficient Iterative Technique

A new compact microwave amplifier structure using an iterative technique based on the wave concept iterative procedure (WCIP) is presented. This new multilayer structure is composed of five planar interfaces of strip lines. The technique used to model this structure provides a mixed resolution in modal and spatial domain. By taking the best advantage of each resolution domain, a lower computing time is obtained. The purpose of this paper is to demonstrate that a near field amplification technique is achievable and the WCIP is suitable to electromagnetic analysis of this kind of structure. The numerical results show 13.4 dB gain at 5.6 GHz.

Electrostatic vibration energy harvester with piezoelectric start-up generator

The search for compact autonomous devices has been increasing in the microelectronics industry. These devices have the capacity to generate their own energy in order to be charged. One of the ways of harvesting environmental energy for charging such devices is by using mechanical vibrations through the use of variable capacitor. Taking this principle a basis, this work presents a behavioral analysis of a system model of harvesting vibratory energy for low power, made up of a circuit which includes a variable capacitor and a piezoelectric transducer. An architecture of a circuit which improves the ratio “amount of harvested energy - circuit area” comparing with conventional architectures is presented. The conventional circuit harvested a maximum power of 4.5µW whereas the circuit with the new architecture harvested a 6.25 µW power. The paper shows a use of a piezoelectric generator providing initial power and compensating the leakage losses in the capacitors.