Papers by Pedro Bertemes Filho
The aim of this study is to show how the modified Howland current source (MHCS) is affected by te... more The aim of this study is to show how the modified Howland current source (MHCS) is affected by temperature changes. The source has been tested in a temperature range from 20 to 70 °C and frequency range from 100 Hz to 1 MHz. Parameters like output current, output impedance, total harmonic distortion, and oscillation have been measured. The measurements were made inside a temperature controlled environment. It was showed that the MHCS is stable at temperatures below 70 °C. Operational amplifiers with a low temperature drift and matching resistor should be carefully considered in order to prevent oscillations at high temperatures.
development of wireless clinical devices for processing EEG, ECG and EMG signals. Over the last d... more development of wireless clinical devices for processing EEG, ECG and EMG signals. Over the last decade, he has been working with electrical impedance spectroscopy related to the characterization of tissue. He coordinates a project working with electrical cervical cancer diagnosis by using an impedance probe for taking the measurements of 500 women from 5 hospitals in the state of Santa Catarina (Brazil). He is an Associate Professor at the State University of Santa Catarina (UDESC) lecturing electrical instrumentation for undergraduate, Master and PhD students students in the Department of Electrical Engineering. Leader of the research group on Biomedical Engineering at UDESC and member of the University Ethic Committee. He has done postdoctoral studies at the University of São Paulo in 2003, working with the development of an Electrical
IEEE Latin America Transactions, 2012
The transfer impedance measured by a tetrapolar probe has been widely used to detect tumors locat... more The transfer impedance measured by a tetrapolar probe has been widely used to detect tumors located in the skin. The main drawback of this method is that its sensitivity is highly dependent on the electrode geometry probe. In this article, the impedance method is used to calculate the sensitivity for transfer impedance measurement by simulating two different medium: a sample
IEEE Latin America Transactions, 2009
Electrical impedance tomography (EIT) is a promising technique for imaging the conductivity distr... more Electrical impedance tomography (EIT) is a promising technique for imaging the conductivity distribution within the body from voltage surface measurements. The measuring precision is very important, where inaccuracies from the current source generate distortions in the images. These are particularly caused by stray capacitances which reduce the frequency response of the instrumentation. This paper investigates the performance of a bipolar current source attached to a multiplexer using an Automatic Gain Control (AGC) Amplifier circuit. Output current measurements were made in the frequency range 100 Hz to 1 MHz and also output impedance at 100 kHz, both with and without the AGC Amplifier circuit. The results showed a constant output current with a maximum error of ±2% when using the AGC Amplifier circuit whereas 300% not using it. Also, the output impedance was approximately 10.4 and 1.2 MΩ with and without using the AGC Amplifier circuit, respectively. It can be concluded that the AGC Amplifier circuit may increase significantly the precision of the current measurements and may improve the image quality in EIT systems.
Medical & Biological Engineering & Computing, 2009
The use of an amplitude/phase retrieval algorithm in electrical bioimpedance spectroscopy (EIS) t... more The use of an amplitude/phase retrieval algorithm in electrical bioimpedance spectroscopy (EIS) that allows a new technique to reconstruct the impedance spectrum in the frequency-domain is reported. To the authors' knowledge this is the first time the proposed algorithm has been used to calculate the modulus or phase of a bioimpedance in EIS from one of these two experimentally obtained parameters. The algorithmic technique is demonstrated in EIS, when wide-bandwidth amplifiers, phase-detectors, and high speed converters determine spectra over frequencies up to 500 kHz at isolated points in the frequency interval. Simulated data from bioimpedance models (Cole and 2R1C circuit impedance functions) and experimental data from a known electrical impedance are used to show the applicability and limitations of the technique with a phase retrieval and a modulus retrieval algorithm. Results comparing this technique with the Kramers-Kronig technique that retrieves the imaginary part of an impedance from its real part are also discussed.
IFMBE Proceedings, 2015
ABSTRACT Constant current source is one of crucial components of every bioimpedance measurement d... more ABSTRACT Constant current source is one of crucial components of every bioimpedance measurement device. Here we present an analysis of a single supply current source based on a modified Howland circuit. The analysis of track to track capacitances has been performed by finite element numerical device simulation and compared to measurements on developed PCB without soldered elements. Capacitances of the order of 1 pF were simulated/measured the largest being the voltage source to ground capacitance (3 pF). The measured transconductance bandwith was about 3 MHz at 100 Ω load and 100 kHz at 100 kΩ. Circuit analysis with Spice resulted in larger bandwidths compared to the measured ones.
Over the last decade, the scientific advances in health care have increased the life expectancy o... more Over the last decade, the scientific advances in health care have increased the life expectancy of the world population. Although the number of research in this area has increased, there are still some question marks about the frailty in the elderly to be addressed. The objective of this work is to develop a biomedical instrumentation to measure and to assess the muscle strength by force measurements. In order to obtain the force curve, both handgrip strength and the quadriceps muscle strength are analyzed in the Maximum Voluntary Isometric Contraction (MVIC) from dominant body side. Muscle strength is measured by one load cell coupled into a home-made device. The signal is conditioned by a microcontroller and connected to a computer system for data visualization and storage. Both handgrip and quadriceps muscle strength are analyzed from two healthy volunteers. Preliminary results of this pilot study indicate that the developed device meets the objectives of this work and that it can be used to enhance the assessment in the elderly with the frailty syndrome.
A phantom is an object that mimics living tissues.
In this manuscript, the preliminary results of... more A phantom is an object that mimics living tissues.
In this manuscript, the preliminary results of gelatin’s characterization as a skin phantom for electrical impedance spectroscopy are presented. Skin and gelatin’s impedance modulus characteristic spectra are measured. Similarities between the impedance modulus spectra of skin and gelatin were found for different skin sites, showing that gelatin can be used as a skin phantom in electrical impedance spectroscopy, due to its spectral characteristics and flexibility of design.
The use of an amplitude/phase retrieval algorithm in electrical impedance spectroscopy(EIS) that ... more The use of an amplitude/phase retrieval algorithm in electrical impedance spectroscopy(EIS) that allows a new method to calculate the impedance spectrum in EIS systems from partial data information is described. To the authors’ knowledge, this is the first time such an algorithm has been used to calculate the magnitude/phase of an impedance in EIS from one of these two available parameters. The use of magnitude or phase retrieval circuits in EIS systems may become unnecessary with the proposed technique, reducing EIS systems cost and complexity. The algorithm is theoretically validated by using a reference impedance obtained from a simulated 2R1C function that represents a model for biological tissue whose parameters are readily obtainable from literature. Experimental validation is demonstrated by using a complete EIS system to obtain the values of a known impedance across a frequency interval from 100Hz up to 500kHz, where only phase is used as input data for the algorithm to calculate the impedance magnitude. Algorithm performance is studied when noise is added to typical bioimpedance simulated data. The algorithm shows robustness with typical bioimpedance noisy data and experimental results are shown to be consistent with simulation.
Medical & Biological Engineering & Computing, Oct 10, 2009
The use of an amplitude/phase retrieval algorithm in electrical bioimpedance spectroscopy (EIS) t... more The use of an amplitude/phase retrieval algorithm in electrical bioimpedance spectroscopy (EIS) that allows a new technique to reconstruct the impedance spectrum in the frequency-domain is reported. To the authors’ knowledge this is the first time the proposed algorithm has been used to calculate the modulus or phase of a bioimpedance in EIS from one of these two experimentally obtained parameters. The algorithmic technique is demonstrated in EIS, when wide-bandwidth amplifiers, phase-detectors, and high speed converters determine spectra over frequencies up to 500 kHz at isolated points in the frequency interval. Simulated data from bioimpedance models (Cole and 2R1C circuit impedance functions) and experimental data from a known electrical impedance are used to show the applicability and limitations of the technique with a phase retrieval and a modulus retrieval algorithm. Results comparing this technique with the Kramers–Kronig technique that retrieves the imaginary part of an impedance from its real part are also discussed.
Electronics Letters, 2000
... Lett., 1995, 31, pp. 5-6 VACCARO, S., TORRES, l?, MOSIO, JR, SHAH, A., ZORCHER, JLP., SKRIVER... more ... Lett., 1995, 31, pp. 5-6 VACCARO, S., TORRES, l?, MOSIO, JR, SHAH, A., ZORCHER, JLP., SKRIVERVIK, AK, CAKDIOL, F., DE MAAGT, P., and GERLACH, L.: 'Integrated solar panel antennas', Electron. Lett., 2000, 36, (3, pp. ... BH Brown, AJ Wilson and P. Bertemes-Filho ...
Physiological Measurement, 2003
Tetrapolar probes have been widely used for measuring the impedance spectra of tissues. However, ... more Tetrapolar probes have been widely used for measuring the impedance spectra of tissues. However, the non-uniform sensitivity distribution of these probes limits the ability to identify conductivity changes in tissue. This paper presents a novel method for improving the sensitivity distribution beneath a tetrapolar probe. The method consists of placing a hydrogel layer between the probe and the tissue in order to make the sensitivity positive everywhere within the tissue. Theoretical and measured sensitivity distributions are compared. A good agreement between theoretical and measured data from an electrolytic tank was obtained with a maximum error of 1.3%. In vivo forearm measurements showed that the use of a conductive layer does enable tissue conductivity spectra to be determined. A smaller variation between subjects was obtained when using the stand-off. It was not possible to assess the absolute accuracy of the method due to the absence of a 'gold standard' for the measurement of tissue conductivity spectra.
Physiological Measurement, 2000
Multi-frequency electrical impedance tomography (EIT) systems require stable voltage controlled c... more Multi-frequency electrical impedance tomography (EIT) systems require stable voltage controlled current generators that will work over a wide frequency range and with a large variation in load impedance. In this paper we compare the performance of two commonly used designs: the first is a modified Howland circuit whilst the second is based on a current mirror. The output current and the output impedance of both circuits were determined through PSPICE simulation and through measurement. Both circuits were stable over the frequency ranges 1 kHz to 1 MHz. The maximum variation of output current with frequency for the modified Howland circuit was 2.0% and for the circuit based on a current mirror 1.6%. The output impedance for both circuits was greater than 100 k for frequencies up to 100 kHz. However, neither circuit achieved this output impedance at 1 MHz. Comparing the results from the two circuits suggests that there is little to choose between them in terms of a practical implementation.
Howland circuits have been widely used as powerful source for exciting tissue over a wide frequen... more Howland circuits have been widely used as powerful source for exciting tissue over a wide frequency range. When a Howland source is designed, the components are chosen so that the designed source has the desired characteristics. However, the operational amplifier limitations and resistor tolerances cause undesired behaviors. This work proposes to take into account the influence of the random distribution of the resistors in the modified Howland circuit over the frequency range of 10 Hz to 10 MHz. Both output current and impedance of the circuit are deduced either considering or the operational amplifiers parameters. The probability density function due to small changes in the resistors of the circuit was calculated by using the analytical modeling. Results showed that both output current and impedance are very sensitive to the resistors variations. In order to get higher output impedances, high operational amplifier gains are required. The operational amplifier open-loop gain increases as increasing the sensitivity of the output impedance. The analysis done in this work can be used as a powerful co-adjuvant tool when projecting this type of circuit in Spice simulators. This might improve the implementations of practical current sources used in electrical bioimpedance.
Wireless medical devices have been widely used inside hospitals, medical centers, ambulances and ... more Wireless medical devices have been widely used inside hospitals, medical centers, ambulances and patients home. The wireless connectivity enable remote monitoring of patients' vital signs and improved care providers' ability to deliver timely treatment, leading to a better health care system. ZigBee is one of the technologies which have been widely used for wireless monitoring bioelectrical signals from patient freely moving. The objective of this work is to develop a wireless monitoring system for acquiring, monitoring and processing blood oxygenation, heart rate and body temperature. It is also presented a graphical interface for controlling and managing the ZigBee network devices. The ZigBee network was implemented by using the MC13213-EVK kit from Freescale Semiconductor and data were measured by the MED-SPO2 development kit. Additionally, the body temperature circuit was developed by using a negative temperature coefficient resistor. Data were recorded from 3 healthy volunteers of 25, 28 and 65 years old and recorded to a host computer. Comparisons were made by using commercial standard devices. The maximum error was found to be approximately 3.2% for the heart rate whereas a maximum of 1% for the others measured data. The network communication link between the sensors and the host computer was approximately 13 meters inside a room with walls but without using router devices. It can be concluded that the use of a wireless ZigBee system for monitoring and transmitting bioelectrical signals is feasible and it can be adjusted according to the patient needs. This might give to patient greater mobility for their daily activities during the day and it may also assist hospitals and medical centers with a great tool for monitoring and post-processing patients' vital signs.
The electrical bioimpedance spectroscopy is used as powerful technique for characterizing biologi... more The electrical bioimpedance spectroscopy is used as powerful technique for characterizing biological materials and detecting tissue anomalies. Commercial impedance analyzers can make impedance measurements of biological materials in a wide frequency range. However, they are expensive and have not been manufactured for measuring in vivo biological materials due to safety concerns. This work presents the performance of first bioimpedance system of the State University of Santa Catarina (BIATRON I). It is based on a FPGA which generates the signals and processes the data to be visualized in the computer via an USB interface. It contains an isolated front-end measuring system, guard electrodes for compensating cable capacitances and an impedance probe which can be fully sterilized in autoclaves. Measurements were taken from five saline solutions in order to perform the system frequency response. Data were converted into impedance by using a novel PSO algorithm. Results have shown that the developed system is reliable for measuring impedance spectra of saline solutions. Future measurements from biological tissues are going to be done for a fully characterization.
Thesis Chapters by Pedro Bertemes Filho
Electrical Impedance Spectroscopy (EIS) involves the injection of a constant current into tissue ... more Electrical Impedance Spectroscopy (EIS) involves the injection of a constant current into tissue at different frequencies and measurement of the resultant voltages. The transfer impedance is then calculated, fitted to an appropriate model and parameters are extracted to describe the electrical properties of the tissue. This technique has been used for characterising oesophageal and cervical tissue. However, electrode/tissue interface impedance and tissue inhomogeneities limit the consistency of the technique. The objective of this research is to optimise the ability of a tetrapolar impedance probe to characterise tissue in terms of electrical impedance spectra.
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Papers by Pedro Bertemes Filho
In this manuscript, the preliminary results of gelatin’s characterization as a skin phantom for electrical impedance spectroscopy are presented. Skin and gelatin’s impedance modulus characteristic spectra are measured. Similarities between the impedance modulus spectra of skin and gelatin were found for different skin sites, showing that gelatin can be used as a skin phantom in electrical impedance spectroscopy, due to its spectral characteristics and flexibility of design.
Thesis Chapters by Pedro Bertemes Filho
In this manuscript, the preliminary results of gelatin’s characterization as a skin phantom for electrical impedance spectroscopy are presented. Skin and gelatin’s impedance modulus characteristic spectra are measured. Similarities between the impedance modulus spectra of skin and gelatin were found for different skin sites, showing that gelatin can be used as a skin phantom in electrical impedance spectroscopy, due to its spectral characteristics and flexibility of design.