IEEE CEIDP 2016 (Toronto, Canada)

Prof. Ruy Alberto Pisani Altafim from LMI and Prof. Ruy Alberto Corrêa Altafim from GAT-USP, presenting their collaborative work that was developed during Felipe Carvalho master thesis. The paper is about an improvement on the electric circuit that is normally used to simulate ferroelectrets with open tubular channels. 
During the conference Prof. Ruy A. P. Altafim also presented a work that was developed together with prof. Axel Mellinger from Central Michigan University, about the electrical discharges inside ferroelectrets with tubular channels and its relation with the polarization phenomena.

Presented Papers:
Electric circuit model for simulating ferroelectrets with open-tubular channels
Space charge build-in in tubular channel ferroelectrets

Book chapter by Prof. Ruy Alberto Pisani Altafim (13/10/2016)

Prof. Ruy Alberto Pisani Altafim from LMI, published a book chapter together with the german researcher Dmitry Rychkov. The is a collection of several topic in advanced materials and the specific chapter deals with ferroelectrets modeling.

Prof. Ruy Alberto Corrêa Altafim visiting LMI (11/10/2016)

Prof. Ruy Alberto Corrêa Altafim from the High-Voltage group from University of São Paulo giving a motivation lecture to the LMI students.

LMI - Group seminar (16/09/2016)

Last group meeting on friday, discussion about new projects and lab methodologies.

LMI - Group seminar (02/09/2016)

Last Friday (02/09/2016), we had the sixth group seminar where the new studend Kened provided a overview on solar and wind power generation for self-sustained houses. During his talk Prof. Dr. Camila was also present as our guest. After the first section the studend Janislley also gave a nice talk on embedded Operational System and Applications and to close the day Prof. Dr. mardson Freitas de Amorim provided an excellent lecture about measurements and instrumentation in biomedics.

LMI - Group seminar (12/08/2016)

The fifth group seminar was about main piezoelectret applications and its research evolution regarding the partnership between Prof. Ruy and the German group from Potsdam. After the presentation a new agenda of activities for the next semester was stablished. From the top left we had present: Jefferson (black t-shirt), Jordy, Leandro, Raul, Marília, Natália, Smith (in the back), Janislley, Luiz (with a gray hat), Renno, Ewerton, Prof. Ruy, Prof. Mardson and Caio (white t-shirt).    

International MeetUP: Latinamerika (Potsdam-Golm, Germany)

On July 12, University of Potsdam promoted an event named International MeetUP: Latinamerika to present and extent researches between Germany and South America countries. During the event Prof. Dr. Ruy Alberto Pisani Altafim from the Federal University of Paraíba (LMI), presented together with Dr. Dmitry Rychkov and Dipl.-Ing. Werner Wirges from the Applied Condensed Matter Physics a summary of the research that was developed between the two countries in the past 10 years of collaboration.

IEEE ICD 2016 (Montpellier, France)

Well-defined piezoelectrets fabricated with 3D printing technology

Three-dimensional (3D) printing is a feasible solution for fast prototyping with precision in micrometer range. On the other hand, piezoelectrets are polymeric films with internal cavities, which has been electrically charged, resulting in a material with piezoelectric behavior. In the present paper, both, technology and concept were combined to produce structures with well-defined cavities and electromechanical properties. 3D printing can be performed in large range of materials, however for piezoelectret production the polymer must be electrically stable as in electrets. For this study, acrylonitrile butadiene styrene (ABS) was chosen as the base structural material and different voided structures were prepared. Results from pressure dependence and temporal stability are here presented.

Heterogeneous polymers as capacitive sensors: Differences between foam cells and closed or open tubular channels

Polymer foams and polymer-film systems with internal cavities are highly compressible, at least in certain direction(s). Their Young’s moduli can be several orders of magnitude lower than those of the respective non-porous (essentially cavity-free) materials. Thus, polymer foams and polymer systems with cavities easily deform when the external pressure varies. The capacitance changes noticeably as a result of the sample deformation. Here, we study such heterogeneous polymers as capacitive sensors for applied external mechanical pressure or surrounding gas pressure. Both, cellular polypropylene (PP) foams and fluoroethylene propylene (FEP) film systems with tubular channels are investigated. While the former are closed-cell foams, the latter contain tubular channels that are either open or that have been closed via sealing at elevated temperatures. It is found that the sensor performance is strongly dependent on the material structure.

LMI - Group seminar (27/05/2016)

In the fourth group presentation the computer engineering students Smith Lima and Jordy Allyson presented a remote system for irrigating plants. Later Prof. Dr. Mardson Amorim explained the use of a low level protocol to transmit small amount of information between microcontrollers. The last talk was given by the graduation student Raul Brito, who presented his initial research on piezoelectrets for energy harvesting.

LMI - Group seminar (15/04/2016)

On the last group meeting we had the student Luiz Henrique presenting his on-going study on Mechanisms for extreme event formation based on caotic electric circuits. The work is supervised by Prof. Hugo Cavalcante, who is a collaborator of our research group. The talk provided a nice discussion on the topic, and stimulated new ideas. In the following the student Renno Diniz presented his development on the project for a virtual goniometer. The group received the presence of Prof. Christian Azambuja Pagot, who was very interested in Luiz research.

LMI - Group seminar (01/04/2016)

Prof. Ruy open the group meeting giving some feedback about the implementation of the LMI website followed by the student presentations.  Ewerton provided a nice talk about his last contribution on measuring small pressure variations using piezoelectrets sensors. Afterwards Leandro presented his on-going research already with some prominent results on how to improve protection systems employed on power supplies using basic electronics. Closing the presentation sections, Jefferson demonstrated in details the evolution on the smart-home project, explaining how the group solve some problems and gave some informations about the project future steps.

Clovis Ferreira dos Reis during his master thesis defense entitled: Detection methods for impulsive sounds applied on a recognition fire-gun system

The urban violence growth in most cities has push authorities to seek for alternative tools to confront criminality. And the use of modern technologies can help policy to anticipate their decisions and guide them on how to expend their limited resources. In this context, the present work provides a description of a modular system based on computational tool that can assists in the firearm shot recognition. And as primordial part of the system, the work is focused on the detection of impulsive sounds, which are characteristics of firearm shots. For this, three impulsive detection algorithms were analyzed and comparative tests were performed in order to verify the most efficient on detecting gunshot. In order to distinguish impulsive sounds from those produced by firearms shots, different time and frequency domain techniques were investigated. Finally, it is presented implementations of the most relevant modules of the system.

Prof. Dr. Dmitry Rychkov gives lecture about artificial muscle, piezoelectric sensors and actuators

Dr. Dmitry Rychkov, reseacher at University of Potsdam (UP - Germany), during his talk about artificial muscle, piezoelectric sensors and actuators at the Informatics Center - UFPB. The seminar is part of the CAPES-PROBRAL collaboration project (USP-UFPB-UP) coordinated by professor Ruy Alberto Corrêa Altafim (USP) and prof. Reimund Gerhard (UP).

IEEE CEIDP 2015 (Ann Arbor, EUA)

Thermo-Formed Piezoelectrets with Open-Tubular Channels Produced from Water-Filled FEP Pads

In this work an alternative method for producing piezoelectrets with open-tubular channels is presented. The method consists of compressing two heated stamped metal plates over a water-filled pad prefabricated with fluoroethylenepropylene (FEP) films. During hot compression the heated water increases the pad internal pressure, helping to mold the FEP film over the metal stamped pattern. A corrugated pattern was used to create piezoelectrets with open-tubular channels similar to those previously reported in the literature, however, in this process instead of discarding a polytetrafluorethylene (PTFE) template water vapor is released. Some previous results obtained with these piezoelectrets regarding temporal stability, charging conditions and measurements performed under different pressures are also presented.

Unipolar Teflon-FEP ferroelectrets - Choice of Negative electret charge enhances stability

We investigate a layered ferroelectret that is based on the same layer sequence as a simple electret microphone. Only one electrically charged polymer film is employed instead of two as in previous tubular-channel ferroelectrets. The design has major advantages such as a reduced number of polymer films to be processed and a reduced amount of expensive electret material, as well as the possibility to choose the polarity of the charged layer for optimal stability. We demonstrate that the piezoelectricity in unipolar Teflon-fluoroethylenepropylene (FEP) ferroelectrets may be considerably more stable than in otherwise similar bipolar ferroelectrets if the most suitable polarity of the poling/charging voltage and thus also of the trapped electret charge is chosen.

Thin Teflon-FEP capacitors with open-tubular channels employed on low-pressure measurements for smart-grid monitoring systems

In order to improve quality and efficiency in electrical energy distribution, power supply companies have sought for better ways to monitor their equipment, stimulating research in smart-grid projects. Equipment subjected to constant monitoring are power and distribution transformers, in which severe faults can be avoided through preventive maintenance, such as, detecting partial discharges in early stages, conducting oil chemical analysis or monitoring transformer internal pressure. In the present contribution we discuss the use of thin voided capacitors made of fluoroethylenepropylene (FEP) films to measure pressure changes in sealed chambers, as in distribution transformers. Voided film structures are very sensitive to pressure variations due to their low mechanical resistance in the thickness direction. Here voided capacitors were fabricated using the same thermal lamination process reported to produce piezoelectrets with open tubular channels. In order to measure pressure disturbance an electrical circuit was specifically designed for detecting variations in capacitance and results correlating these changes with pressure increase are presented.

Electronics Letters 2015

In a collaborative work with University of São Paulo (USP-São Carlos), professor from LMI developed a new technique for producing piezoelectric sensors based on 3D printing and piezoelectrets devices. The work has been recently accepted for publication in Electronics Letters.

Piezoelectrets with well-defined cavities produced from 3D-printed ABS structures

Abstract: A novel piezoelectret with well defined cavities produced by threedimensional (3D) printing technology is reported. This prototyping tool allows many samples to be prepared in a single printing step and gives the possibility to design voided structures with control of the cavity geometric parameters, such as height, diameter and shape. In the present work, Acrylonitrile Butadiene Styrene (ABS) piezoelectrets were fabricated through this method and measurements regarding their electrical response as a function of time, temperature and pressure are presented. The samples show average piezoelectric coefficient d33 around 100 pC/N and 70of this piezoelectricity remain after they were exposed to temperatures up to 85 oC.

Electric Power Systems Research 2015-2016

Professor from LMI has paper accepted for publication in Electric Power System Research. This research results from a collaboration between three other institutions: USP-São Carlos, USP-Poly and UNESP-Bauru.

One-port Nonlinear Electric Circuit for simulating Grounding Systems under Impulse Current.produced from 3D-printed ABS structures

Abstract: An one-port nonlinear electric circuit to simulate grounding systems behaviors under high impulse currents is presented. The circuit is based on Loboda's and Pochanke's equations, which describe nonlinear behaviors of soil ionization phenomena. One of the major features of this nonlinear circuit is the possibility to simulate both ionization regions (linear and nonlinear) as a complete grounding system, in commercial simulation software such as Pspice, WorkBench, ATP or EMTP. In order to determine the linear and nonlinear circuit parameters, two known impulse current curves i(t) were applied on scale models and the corresponding impulse voltages U (t) was measured. From these circuit parameters, the U(t) x i(t) experimental curves were compared with one port simulated results and the similarities, evaluated using the Area Under Curve (AUC) method, varied in the range 92% - 99%. In order to compare simulations with experimental data, a field circuit was elaborated to test three experimental scale models using single rods of different lengths.

IEEE CEIDP 2015 (Ann Arbor, USA)

Professors and student from LMI has three paper accepted for publication in IEEE-Conference on Electrical Insulation and Dielectric Phenomena (CEIDP 2015 - Ann Arbor, USA).

  • Paper I: Thin Teflon-FEP capacitors with open-tubular channels employed on low-pressure measurements for smart-grid monitoring systems;

  • Paper II: Thermo-formed piezoelectrets with open-tubular channels produced from water-filled FEP pads (Em parceria com a USP-São Carlos);

  • Paper III: Unipolar Teflon-FEP ferroelectrets: Choice of negative electret charge enhances stability (Em parceria com a Universidade de Potsdam (Alemanha)

Measurement Science and Technology 2015

The work Piezoelectret-based hydrophone: an alternative device for vibro-acoustography published in Measurement Science and Technology is the result of a partnership between professors from LMI and University of São Paulo (USP-São Carlos and USP-Ribeirão Preto).

Abstract:Piezoelectric polymers are highly desirable for ultrasound applications since their low acoustic impedance is much closer to the impedances of air and water than those of traditional piezoceramics. However, the piezoelectric effect observed in these poled polymers is limited to a few dozen picocoulombs per newton and requires very low-noise amplification. A different class of polymeric material known as piezoelectrets, presents piezoelectric effect in the same order of magnitude as those found on piezoceramics. This new class of materials has been explored in a wide range of applications such as flexible keyboards and airborne ultrasound transducers. Based on these polymers, we present here a new transducer for vibroacoustography (VA), which is an ultrasonic image technique employed in medical diagnosis or material analysis based on ultrasound scattered by a target object. A calibration was carried out using a standard hydrophone, which is normally employed in VA. The average sensitivity of the transducer in the continuous wave mode was 1.712 mV Pa−1(−182.7 dB re 1 V μPa−1 with a maximum sensitivity of 18.25 mV Pa−1 (−154.8 dB re 1 V μPa−1) at its resonance frequency around 40 kHz. Subsequently, measurements in the burst mode and of directional sensitivity were taken and are presented here together with VA images obtained from a chicken bone and a metal sphere.

PAECI Prize 2015

Students from LMI are encourager to compete for the PAECI prize promoted by the Informatics Center from Federal University of Paraíba (https://sites.google.com/a/ci.ufpb.br/premio-paeci/).

Intel Competition on Embedded Systems 2015

Project from LMI based on acoustic detection of fire-gun shots with piezoelectrets is selected for the competition.


LMI project on Smart-home for light controlling was presented at the EXPOTEC 2015, which happened in João Pessoa - PB.


Research Project between professors from LMI, USP and University of Potsdam was approved by CAPES and DAAD. The project entitle Optimization of piezoelectret sensors for non-invasive measurements in high-voltage equipment, coordinated by professor Ruy Alberto Corrêa Altafim (USP) and Professor Reimund Gerhard (Potsdam) was approved for a two years collaboration. (see result

IEEE CEIDP 2014 (Des Moines, EUA)

Acoustic detection of single and multiple air-gap partial discharges with piezoelectrets transducers
Electrical equipment installed in power transmission and distribution lines are usually subjected to abnormal conditions and intense electric fields, which eventually lead, among others phenomena, to partial discharges (PD). These, have been pointed as one of the main causes of equipment failures and premature aging. Therefore, detect PD became an important issue in the prospect of efficient and reliable electric energy. Concerning PD detection there are several sensors that can be employed e.g. optical, magnetic or acoustic, and each of them presenting particular advantages and limitations. One of the drawback of such sensors are their elevated costs for transmission lines equipments, which has restrict the PD monitoring to power transformers. Although, if the intention is only to detect the PD occurrence a new class of acoustic sensors implemented with piezoelectrets may be a feasible economic alternative. Therefore, in this work we have investigated the acoustic behavior of such transducers exposed to different PD conditions, for instance, the piezoelectret sensor was employed on the detection of PD produced by a single or multiple point-to-point electrode setup with different air gaps driven by high AC voltages. The recorded signals amplitudes were than correlated with the gap distance and voltage amplitude.

Unipolar ferroelectrets – Following the example of the electret microphone more closely
We report first investigations on a ferroelectret transducer material that is based on the same layer sequence as a simple electret microphone. Only one electrically charged polymer film is employed instead of two as in previous tubular-channel ferroelectrets. The new materials design has major advantages such as a reduced number of polymer films to be processed and a reduced amount of expensive electret material, as well as the possibility to choose the polarity of the charged layer for optimal stability. A drawback seems to be a lower piezoelectric coefficient, since the values obtained in our preliminary experiments amount to roughly half of those found on bipolar ferroelectrets made from two polymer-electret films. Nevertheless, the d33 values observed on our samples are still twice as high as those of polyvinylidene fluoride (PVDF) and can be further improved, e.g. through modifications of the ferroelectret geometry, the layer sequence and the electret properties or via multi-layer stacking as already demonstrated for polypropylene piezoelectrets.

XXIV CBEB 2014 (Uberlândia, Brasil)

Relative humidity in neonatal incubators: implications of thermal sensation on new borns
This paper presents a set of measurements of temperature, relative humidity and thermal sensation made in neonatal incubators. The aim of this paper is to open discussion on the effect of thermal sensation on preterm infants when subjected to the micro climate of incubators in everyday use. The results show that the thermal sensation experienced by infants may be greater than 40 °C, even when the air temperature in the incubator is less than 33 °C.

XIII Brazilian MRS meeting 2014 (João Pessoa, Brasil)

Electrical response of open tubular piezoelectrets exposed to low pressures stimulations
When foamed thin electret films are electrically charged, a highly piezoelectric structure known as piezoelectret is obtained. This flexible and lightweight material is very much desired for sensors and transducer applications. Recently, this piezoelectric behavior was obtained with fluoropolymer films assembled in multi-layer systems. This approach led to piezoelectrets with improved thermal stability. However, since this kind of piezoelectret was developed, not much has been done regarding its electro-mechanical behavior under low pressure (< 40 kPa) stimulation. Therefore, in this work we present the first results obtained with an open-tubular structure made of FEP films that was prepared according to the lamination process and submitted to a low-pressure stimulation. This was performed with a dual-chamber system, one previous pressurized (A) and the other containing the piezoelectret sensor (B). The relation between applied pressure and sensor response was then obtained and it was fitted with an exponential curve providing a good approximation for the piezoelectret behavior in this condition.

IEEE EMBC 2014 (Chicago, USA)

Instrumentation for the Detection and Interruption of Apnea Episodes for Premature Newborn
Apnea of prematurity is very frequent in premature newborns (PNB). If the apnea episode is not interrupted in time, it can cause several damages to the newborn's central nervous system. In this paper, we introduce a novel technology for detecting apnea of prematurity episodes, based on cardiac pulse frequency (PF) and arterial oxygen saturation (SpO2) simultaneously, and using vibrotactile stimulation to interrupt such episodes. The thresholds of the newborns' PF and SpO2 had been established to identify the apnea episode automatically through the proposed system: for babies 35 weeks gestation, PF is 100 bpm and SpO2 80%; for babies >35 weeks gestation, PF is 80 bpm and SpO2 80%. The system used vibrotactile stimuli at 250 Hz for 4s. To manage the system that activates the vibratory device automatically and registers those parameters, a program had been developed. It registers apnea occurrence, period of manual stimulation and vibratory stimulation duration. This technique was tested on 4 PNB. It was observed 10 apnea episodes and the device was successful in the detection of all of them. The vibrotactile stimulation was capable of promoting the return of respiratory movements in 9 of the 10 detected events of apnea and seemed to be a promising means of handling them.

Physics Of Dielectrics 2014 (São Petersburgo, Russia)

Improved thermal stability of FEP ferroelectrets through inner voids surface modification
Fluoroethylenepropylen (FEP) is one of the most widely used materials for space-charge electrets. The stability of negative homo-charge in this material is among the highest of all non-polar polymers. However, an asymmetry in the charge stability for different polarities restricts the use of FEP electrets in several applications and in particular in layered ferroelectret systems. Polymer modification can be one of the possible approaches to the solution of the problem of positive homo-charge stabilization in FEP. Several different techniques are available for polymer modification. Among them is molecular-layer deposition, an efficient tool for polymer-surface modification. The technique works by embedding nanostructures that contain the desired chemical elements into the surface of the polymer. Hence, it is possible to modify its chemical and physical properties, including its electret behavior. In the present paper, the surface modification of FEP polymer-electret films by means of titanium tetrachloride vapor is therefore investigated.

Influence of electrodes geometry on images formed by direct contact electrical discharge over electret films
Dielectric polymer films electrically charged also know as electrets can be formed by innumerous polling techniques such corona discharge, direct contact polarization, electron beams, penetrating gamma rays or liquid contacts. And some of this technics can also be implemented with AC, DC or impulse voltages. Depending on the applied polling method and geometry setup different results on charge densities and thermal-charging stability may also be obtained. Besides measuring the charge densities of the polymer surface and its thermal stability, another interesting phenomenon that occurs during electrical charging is the pattern geometry formed by the discharges on the electret surface. These patterns, which are not visible to naked eyes and are very much dependent on the charging voltage, can be observed if toner powder is spread over the films, such as in Xerox process. Concerning the direct contact method and impulse charge voltages, a study comparing spherical and cylindrical electrodes was performed in order to establish a correlation between the geometrical pattern dimensions and the impulse voltage amplitude. This study was motivated since this correlation could be employed on the development of new sensors for detecting impulsive discharge on power transmission lines as reported.

IEEE I2MTC 2014 (Montevideo, Uruguai)

Comparative analysis between impulsive detection methods applied on partial discharge acoustic signals
Partial discharges (PD) plays an important role on power transmission lines and equipment failures therefore previously detect this high-voltage phenomena can prevent severe damages and avoid further outlay. Spark gaps discharges are among the most common PD in power transformers and other efficiency energy equipments. And in order to detect this effect optical and acoustic sensors are normally employed into monitoring systems. However optical sensors are expensive for transmission power lines and detecting acoustical signals from PD can be difficult since they are normally followed by other background sounds. In order to improve detection sound systems in this work we compare two methods that are regularly used on impulsive signal processing, the Variance Method (VM) and the Conditional Median Filter (CMF), to detect PD acoustic signals. From the presented results it is observed that the CMF is more appropriated for detecting impulsive PD although the VM detected less false positive discharge and can still be further optimized.

Images from high-voltage impulse discharges evaluated with a developed graphical software
Power transmission lines are constant targets of high electrical discharges such as corona and lightning. This last is manly characterized as a high impulse voltage, which can rapidly cause severe damages to equipment in the lines. Therefore, detect the amplitude of these discharges in power lines is critical for the proper design of protective systems. Recently an impulse voltage sensor based on electret films was presented. The sensor employs a spherical electrode in direct contact with a grounded thin electret film. Whenever a negative electrical impulse voltage is applied on the spherical electrode, partial discharges occurs all around the electrode forming a circular pattern that can be visualized if toner is spread over the film. Depending on the discharge amplitude circles with larger diameter are formed. In this paper we present a software implementation through which the discharge images with circular patters can be measured and direct correlated to the impulse discharge amplitude, providing a reliable and fast method for measuring electrical discharges in the field. The software was validated performing measurements of the images diameter and correlating it with well defined discharges amplitude.