A.A. de Carvalho

Optical microphone for photoacoustic spectroscopy

An optical microphone configuration is experimentally demonstrated. It is based on the deflection of a He‐Ne laser beam from a thin reflective pellicle bound on one edge over the duct of a conventional photoacoustic cell. Possible applications of this kind of photoacoustic detection are discussed.

Microcontrolled pyro-electric instrument for measuring X-ray intensity in mammography

A novel instrument for measurement of X-ray intensity from mammography consists of a sensitive pyro-electric detector, a high-sensitivity, low-noise current-to-voltage converter, a microcontroller and a digital display. The heart of this device, and what makes it unique is the pyro-electric detector, which measures radiation by converting heat from absorbed incident X-rays into an electric current. This current is then converted to a voltage and digitised. The detector consists of a ferro-electric crystal; two types were tested; lithium tantalate and lithium niobate. X-ray measurement in mammography is challenging because of its relatively low photon energy range, from 11 keV to 15 keV equivalent mean energy, corresponding to a peak tube potential from 22 to 36 kV. Consequently, energy fluence rate or intensity is low compared with that of common diagnostic X-ray. The instrument is capable of measuring intensities as low as 0.25 mWm−2 with precision greater than 99%. Not only was the instrument capable of performing in the clinical environment, with high background electromagnetic interference and vibration, but its performance was not degraded after being subjected to 140 roentgen (3.6×10−2 C kg−2 air) as measured by piezo-electric (d33) or pyro-electric coefficients.

Ferroelectric ceramic/polymer composite for measuring X-ray intensity in the ortovoltage range

Pyroelectric sensors work as a thermal transducer converting the non-quantified thermal flux into the output measurable quantity of electrical charge, voltage or current. Ferroelectric ceramics and ferroelectric polymers have been extensively used as thermal detectors. More recently the research in the field of pyroelectricity has been concentrated on discovering materials with higher figures of merit (FOM), which means better sensing materials. Composite materials obtained with ferroelectric ceramics embedded in polymer host have received great attention because of their formability, mechanical resistance and the possibility to change their dielectric property varying the volume fraction of ceramic particles. In this work composite films made of modified lead titanate (PZ34) and poly(ether-ether-ketone) (PEEK) were characterized and used as sensing element to measure X-ray intensity in the ortovoltage range (120 -300 kVp). The sensor response varies from 2.70 V to 0.80 V in the energy fluency range of 6.30 to 37.20 W/m2. Furthermore the absorbed energy was analyzed as a function of the ionizing energy. The results indicate that the PZ34/PEEK composite with 60/40 vol.% can be useful to monitor X-ray radiation therapy.

Electrical stimulation tracking control for paraplegic patients using T–S fuzzy models

Abstract This paper presents the design and simulation results considering the use of functional electrical stimulation to control the leg position of paraplegic patients. The plant is described by a nonlinear system using Takagi–Sugeno fuzzy models and a closed-loop control is presented. A transfer function represents the mathematical model related to the muscle torque and the electrical stimulation pulse width. Considering that, during the operation, the leg position is between 0° and 60°, then two fuzzy regulators were designed, assuming that the state vector is available or using an observer when only the output is available. This design was based on the Lyapunov stability theory and Linear Matrix Inequalities (LMIs). The simulation results show that the proposed procedures are efficient and offer good results for this control problem. Finally, new conditions regarding the design of the output tracking control, using a suitable nonlinear transformation for the description of the plant in an adequate form, is presented.

High sensitivity low cost capacitive strain gage

This paper describes a high sensitivity low cost capacitive strain gage sensor. The theory, design and sensor construction details are presented. It consists of eight capacitive sensors connected in two full bridges. The capacitive strain gage sensor structure was designed in order to produce high sensitivity and low dependence with temperature. By using a simple signal conditioning circuit constituted by a differential amplifier, a band-pass filter, and a precision rectifier the device can measure forces with resolution of 0.009 N and precision of 98.7%. It is rugged, presents linear response, and good repeatability. It presents sensitivity of 8.7 V/N and fall time of 12 ms.

Plataforma para Medição de Forças na Região Plantar de Pacientes Normais e Hemiplégicos

This work describes an electronic system implementation with two force plates, 24 load cells with strain gages, signal conditioning circuit, interfacing circuit and data acquisition system, designed for measuring plantar force distribution in patients. The system presented linear response, low hysteresis, with determination coefficient of 0.9997, precision better than 0,84% and resolution less than 0.5 N. The Measurements are presented on a computer screen and easier visualization to specialists, mainly physicians, physiotherapists and occupational therapists. Using the system, the distribution of weight in the plantar region of 100 normal subjects and 10 hemiplegic patients was investigated. There were determined the relationship between weight distribution on the right and left forefoot, hemiplegic patients and normal patients, with the implemented system.

Common architecture for discrete wavelet transform analysis and synthesis with sequential and constant processing elements

This paper addresses the problem on processing biological data such as cardiac beats, audio and ultrasonic range, calculating wavelet coefficients in real time, with processor clock running at frequency of present ASICs and FPGA. The parallel filter architecture for DWT has been improved, calculating wavelength coefficients in real time with hardware reduced to 60%. The new architecture, which also processes IDWT, is implemented with the Radix-2 or the Booth-Wallace constant multipliers. Including series memory register banks, one integrated circuit signal analyzer, ultrasonic range, is presented.