J. G. Rocha

Energy Harvesting From Piezoelectric Materials Fully Integrated in Footwear

In the last few years, there has been an increasing demand for low-power and portable-energy sources due to the development and mass consumption of portable electronic devices. Furthermore, the portable-energy sources must be associated with environmental issues and imposed regulations. These demands support research in the areas of portable-energy generation methods. In this scope, piezoelectric materials become a strong candidate for energy generation and storage in future applications. This paper describes the use of piezoelectric polymers in order to harvest energy from people walking and the fabrication of a shoe capable of generating and accumulating the energy. In this scope, electroactive ß-polyvinylidene fluoride used as energy harvesting element was introduced into a bicolor sole prepared by injection, together with the electronics needed to increase energy transfer and storage efficiency. An electrostatic generator was also included in order to increase energy harvesting.

Fabrication of flexible thermoelectric microcoolers using planar thin-film technologies

The present work reports on the fabrication and characterization of a planar Peltier cooler on a flexible substrate. The device was fabricated on a 12 µm thick Kapton(c) polyimide substrate using Bi2Te3 and Sb2Te3 thermoelectric elements deposited by thermal co-evaporation. The cold area of the device is cooled with four thermoelectric junctions, connected in series using metal contacts. Plastic substrates add uncommon mechanical properties to the composite film–substrate and enable integration with novel types of flexible electronic devices. Films were deposited by co-evaporation of tellurium and bismuth or antimony to obtain Bi2Te3 or Sb2Te3, respectively. Patterning of the thermoelectric materials using lift-off and wet-etching techniques was studied and compared. The performance of the Peltier microcooler was analysed by infrared image microscopy, on still-air and under vacuum conditions, and a maximum temperature difference of 5 °C was measured between the cold and the hot sides of the device.

The piezoresistive effect in polypropylene—carbon nanofibre composites obtained by shear extrusion

The piezoresistive effect on poly(propylene) (PP)–carbon nanofibre (CNF) composites fabricated by twin-screw extrusion and compression moulding has been investigated. The electrical and mechanical properties of PP/CNF composites have been obtained as a function of CNF concentration. Electrical conductivity exhibited low thresholds and values close to the required levels for EMI shielding applications at 2.4 vol%. Meanwhile the elastic modulus showed an enhancement with a maximum up to 130% for one of the composites at 0.9 vol% loading. Further, the piezoresistive response has been evaluated in four-point bending. Positive gauge factors between 2 and 2.5 have been obtained. The highest gauge factors are found within the percolation threshold. The characteristics of the materials and the production technique make them suitable for large scale applications.

Development of inkjet printed strain sensors

Strain sensors with different architectures, such as single sensors, sensor arrays and a sensor matrix have been developed by inkjet printing technology. Sensors with gauge factors up to 2.48, dimensions of 1.5 mm × 1.8 mm and interdigitated structures with a distance of 30 μm between the finger lines have been achieved based on PeDOT (poly(3,4-ethylenedioxythiophene) and conductive ink. Strain gauges based on silver ink have also been achieved with a gauge factor of 0.35. Performance tests including 1000 mechanical cycles have been successfully carried out for the development of smart prosthesis applications.

Evaluation of the main processing parameters influencing the performance of poly(vinylidene fluoride–trifluoroethylene) lithium-ion battery separators

Poly(vinylidene fluoride–trifluoroethylene) (PVDF–TrFE) membranes are evaluated for lithium-ion battery separator applications. Some of the main parameters affecting separator performance such as porosity, dehydration of lithium ions, and processing technique (Li-ion uptake versus composite formation) are investigated. The polymer characteristics, as determined by infrared spectroscopy, do not change as a function of porosity, dehydration of lithium ions in the electrolyte solution, or processing technique. The electrochemical impedance spectroscopy represented through the Nyquist plot, Bode plot, and the ionic conductivity as a function of temperature strongly depends on the aforementioned parameters. The membrane that exhibits the highest ionic conductivity is a porous membrane without dehydration of lithium ions and prepared by the uptake technique. The performance of the membrane for battery applications are, therefore, strongly influenced both by porosity and processing technique.

Smart-Optical Detector CMOS Array for Biochemical Parameters Analysis in Physiological Fluids

This paper describes the implementation of a smart-optical detector array for detection and concentration measurement of biochemical parameters in physiological fluids. Its application is in the low-cost microchip size analytical laboratories that use colorimetric detection, by optical absorption, as the analytical technique. The microlaboratory structure is composed of a microplate cuvette array containing the physiological fluids into analysis and an optical detector array underneath, which quantifies the light absorbed by those fluids. The detectors, together with their analog-to-digital (A/D) conversion, are designed and fabricated using a standard CMOS process. The on-chip A/D conversion is performed, simultaneously, using a 1-b first-order sigma-delta converter for each optical detector. The output signal of the device is a bit stream containing information about the absorbed light, which allows simple microcontroller interfacing. The proposed architecture has the main advantage of performing the simultaneous measurement of the light absorbed by the fluids, which avoids the errors that can be introduced due to light fluctuations in uncontrolled environments. In addition, the architecture allows on-chip calibration during each measurement. This means that the device can be reliably used in environments with noncalibrated light sources, e.g., in a doctors office. The A/D conversion design described here represents significant improvements when compared with the existing designs. Moreover, the microlaboratory application holds great promise, by both improving benefits (quality of health services provided) and reducing costs (of physiological fluid analysis services).

All-Inkjet-Printed Bottom-Gate Thin-Film Transistors Using UV Curable Dielectric for Well-Defined Source-Drain Electrodes

Technological restrictions of the inkjet printing technology for printed electronics can hinder its application potential, mainly due to the limited resolution and layer homogeneity in comparison to conventional manufacturing techniques for electronics. The manufacturing of active devices such as thin-film transistors with appropriate performance using printing technologies is still one of the current challenges towards industrial applications. This work demonstrates the application of an ultraviolet (UV) curable ink as insulating material for the gate dielectric. The advantage of the UV curable ink is its fast curing and the smooth surface enabling high resolution patterns on top of it. In this way, all-inkjet-printed organic thin-film transistors (OTFTs) were fabricated with silver electrodes, UV curable gate dielectric, and 6,13-bis(triisopropylsilylethynyl)pentacene for the active semiconductor layer. By fine tuning of processing parameters and pattern geometries, a stable channel length of about 10 μm was obtained in the bottom-gate configuration without the need of additional steps, suggesting a way to build low-cost all-inkjet-printed OTFTs with well-defined source-drain electrodes and fast UV curable dielectric without any additional steps. The inkjet-printed device is characterized by an electron mobility of 0.012 cm2 V−1 s−1 and on/off ratio of 103.

3 Axis Capacitive Tactile Sensor and Readout Electronics

A way to determine the force that is applied to an object, for example by a manipulator, consists in the use of capacitive pressure sensors, like the one presented in this article. The major problems when reading capacitive sensors are the parasitic capacitances between the wires that connect the sensing elements to the interface electronics. The present article describes a capacitive tactile sensor that measures the force in the three axis xx, yy, and zz) and its interface electronics, which consists in a technique that reduces substantially the parasitic capacitance effects. The readout electronics basically is constituted by a 40 kHz voltage source and a current to voltage converter that works as an ammeter. Despite some practical limitations in the complete elimination of the parasitic capacitances, caused by the output impedance of the voltage source and the input impedance of the ammeter, the present work demonstrates that the three axis capacitive tactile sensor and its readout circuit are valid concepts to be applied in the robotics field

Lab-on-a-Chip With β-Poly(Vinylidene Fluoride) Based Acoustic Microagitation

This paper reports a fully integrated disposable lab-on-a-chip with acoustic microagitation based on a piezoelectric ß-poly(vinylidene fluoride) (ß-PVDF) polymer. The device can be used for the measurement, by optical absorption spectroscopy, of biochemical parameters in physiological fluids. It comprises two dies: the fluidic die that contains the reaction chambers fabricated in SU-8 and the ß-PVDF polymer deposited underneath them; and the detection die that contains the photodetectors, its readout electronics, and the piezoelectric actuation electronics, all fabricated in a CMOS microelectronic process. The microagitation technique improves mixing and shortens reaction time. Further, it generates heating, which also improves the reaction time of the fluids. In this paper, the efficiency of the microagitation system is evaluated as a function of the amplitude and the frequency of the signal actuation. The relative contribution of the generated heating is also discussed. The system is tested for the measurement of the uric acid concentration in urine.

Piezoresistive effect in spin-coated polyaniline thin films

Polymeric materials have been replacing other materials in various applications, from structural to electronic components. In particular, since the discovery of conducting polymers, the use of these materials is growing up in the manufacture of electronic components, such as organic light-emitting diodes, organic electrodes, energy storage devices and artificial muscles, among others. On the other hand, examples of sensors of conductive polymers based on the piezoresistive effect, with large potential for applications, are not sufficiently investigated. This work reports on the piezoresistive effect of an intrinsically conductive polymer, polyaniline, which was prepared in the form of thin films by spin coating on polyethylene terephthalate substrates. The relationship between electrical response and mechanical solicitations is presented for different preparation conditions. The values of the gauge factor ranges from 10 to 22 for different samples and demonstrates the viability of these materials as piezoresistive sensors.