L. Francioso

Synthesis, electrical characterization, and gas sensing properties of molybdenum oxide nanorods

Gas sensors have been prepared by using single crystalline MoO3 nanorods. Structures 50–150nm and up to 15μm in length were synthesized by template directed hydrothermal synthesis. Gas sensing tests showed responses to NO2 up to 740% and to NH3 up to 570%. Moreover, preliminary electrical characterizations were performed, as a function of temperature in 20–520°C range temperature, by means of current-voltage measurements. I-V dependence studies show a linear increase in current at low voltage and a quadratic increase at higher voltages. A study of the current-temperature dependence shows that at high temperature current is thermally active and successively decreases that can be explained by taking in account a change of material morphology.

Automotive application of sol–gel TiO2 thin film-based sensor for lambda measurement

We report on the preparation and characterization of titanium dioxide thin film gas sensor devices for application in lambda measurement. The sensor responses to different oxygen concentrations have been analyzed. Moreover, according to a computing software that simulates the composition of exhaust gases for different λ values, we exposed the sensors to different complex mixtures of exhaust gases, calibrating in such a way the sensor for the measurement of lambda.

Flexible thermoelectric generator for wearable biometric sensors

In this work we proposed design, fabrication and functional characterization of a very low cost energy autonomous, maintenance free, flexible and wearable micro thermoelectric generator (μTEG), finalized to power very low consumption electronics Ambient Assisted Living (AAL) applications. The prototype, integrating an array of 100 thin films thermocouples of Sb2Te3 and Bi2Te3, generates, at 40 °C, an open circuit output voltage of 430 mV and an electrical output power up to 32 nW with matched load. In real operation conditions of prototype, which are believed to be very close to a thermal gradient of 15°C, the device generates an open circuit output voltage of about 160 mV, with an electrical output power up to 4.18 nW. In this work we proposed design, fabrication and functional characterization of a very low cost energy autonomous, maintenance free, flexible and wearable micro thermoelectric generator (μTEG), finalized to power very low consumption electronics Ambient Assisted Living (AAL) applications. The prototype, integrating an array of 100 thin films thermocouples of Sb2Te3 and Bi2Te3, generates, at 40 °C, an open circuit output voltage of 430 mV and an electrical output power up to 32 nW with matched load. In real operation conditions of prototype, which are believed to be very close to a thermal gradient of 15°C, the device generates an open circuit output voltage of about 160 mV, with an electrical output power up to 4.18 nW.

PDMS/Kapton Interface Plasma Treatment Effects on the Polymeric Package for a Wearable Thermoelectric Generator

The present work highlights the progress in the field of polymeric package reliability engineering for a flexible thermoelectric generator realized by thin-film technology on a Kapton substrate. The effects of different plasma treatments on the mechanical performance at the interface of a poly(dimethylsiloxane) (PDMS)/Kapton assembly were investigated. To increase the package mechanical stability of the realized wearable power source, the Kapton surface wettability after plasma exposure was investigated by static contact-angle measurements using deionized water and PDMS as test liquids. In fact, the well-known weak adhesion between PDMS and Kapton can lead to a delamination of the package with an unrecoverable damage of the generator. The plasma effect on the adhesion performances was evaluated by the scratch-test method. The best result was obtained by performing a nitrogen plasma treatment at a radio-frequency power of 20 W and a gas flow of 20 sccm, with a measured critical load of 1.45 N, which is 2.6 times greater than the value measured on an untreated Kapton substrate and 1.9 times greater than the one measured using a commercial primer.

Investigation of a Micro Dielectric Barrier Discharge Plasma Actuator for Regional Aircraft Active Flow Control

This paper reports a multitechnique investigation of a micro dielectric barrier discharge plasma actuator (DBDPA) as a promising system to control separated flows. The device was manufactured through a photolithographic technique and its performances and capabilities were compared with the ones of conventional macro DBDPAs. Alternate current operation under sinusoidal voltage excitation was studied in the absence of external flow by means of many experimental techniques like discharge imaging, flow visualizations, particle image velocimetry, infrared thermography, and electrical characterization. The influence of the operating parameters was investigated. The main results underlined that an increase in the voltage amplitude or frequency brought to a rise in the maximum induced velocity, electrical power dissipation, and actuator surface temperature. Moreover, it was assessed that the small heating of the micro DBDPA did not affect the actuated flow. A jet velocity up to 1.36 m/s was obtained at a 9.01 W/m electrical power dissipation per unit electrode length. The device realized by microelectronic fabrication technology allowed reaching a flow velocity magnitude comparable with the one of conventional macro DBDPAs, with a reduction in applied voltage, power dissipation, and actuator size. Furthermore, the induced wall jet was more confined in the area in proximity of the device, because of the limited plasma discharge extension.

Integrated read-out and temperature control interface with digital I/O for a gas-sensing system based on a SnO 2 microhotplate thin film gas sensor

A complete gas-sensing system for portable ambient monitoring purpose, consisting of a sensor (with embedded heater and thermometer) and an integrated interface (with read-out channel and closed-loop temperature control circuit) is presented. The micromachined sol-gel tin-oxide sensor features a 450 nm thick silicon nitride/oxide membrane, an active area of 170 mum times 170 mum and a power consumption of 25 mW at 350degC in isothermal operation. The read-out circuit uses a current integration and resistance-to-frequency conversion, providing digital output. The sensor is biased with a constant voltage and its temperature is regulated by an on-off closed-loop control circuit, consisting of a thermometer conditioning network, an A/D converter and a digital control block that drives the on-chip output p-MOS power stage. The circuit can operate with different sensors to grant maximum flexibility. Chemical measurements with different gases have been performed, operating the sensor at different temperatures.

An 80 mV Startup Voltage Fully Electrical DC–DC Converter for Flexible Thermoelectric Generators

This paper presents a fully electrical dc-dc converter designed for thermoelectric generator (TEG) for energy harvesting applications. The proposed flexible TEG has been achieved by a screen printing technology on a 80 μm thick common paper and thin Kapton foil and integrates 280 thermocouples for an output voltage of about 75 mV with 5 K of thermal gradient. In order to step up the voltage at the output of the thin-film flexible TEG, a dc-dc converter has been designed. This latter operates with an input voltage ranging from 80 up to 370 mV. The proposed dc-dc converter achieves an automatic control based on pulsewidth modulation, ensuring 1 V output voltage. The control circuit includes two sections. The first one provides a forward control operating in the 80-150 mV input voltage range. The second one operates a feedback control, as the output voltage of TEG is higher than 150 mV. The dc-dc converter is implemented in a 65 nm CMOS technology, achieving a 73% peak efficiency.

Aircraft Distributed Flow Turbulence Sensor Network with Embedded Flow Control Actuators

Several active and passive flow control systems are studied to improve the performances of fluid machineries and to increase aerodynamic efficiency of propulsion systems. Among all the well-known active flow control devices, the dielectric barrier discharge plasma actuator (PA) is in full expansion and of great interest in the scientific community. A PA modifies the following behaviour of a fluid by providing an electronically controllable disturbance that brings to drag reduction, flow separation control, enhanced mixing, and noise suppression. PA is potentially easy to construct, has no moving parts and has low power requirements. This leads to its possible applications for separation control in low pressure turbine blade and compressor cascade, tip clearance flow control and compressor stability range extension. The present work reports the design and fabrication of cheap Kapton-based flow turbulence capacitive sensors able to be embedded into aircraft wing profiles and airfoil structures for critical turbulence conditions detection and early-detected separated flows control. The embedded system will provide a Kapton-foil based pressure detection and linear/synthetic jet plasma actuators working in feedback, for prevention and active reduction of separated flow for regional aircraft applications.

Wearable and flexible thermoelectric generator with enhanced package

Present work shows recent progresses in thin film-based flexible and wearable thermoelectric generator (TEG), finalized to support energy scavenging and local storage for low consumption electronics in Ambient Assisted Living (AAL) applications and buildings integration. The proposed TEG is able to recover energy from heat dispersed into the environment converting a thermal gradient to an effective electrical energy available to power ultra-low consumption devices. A low cost fabrication process based on planar thin-film technology was optimized to scale down the TEG dimensions to micrometer range. The prototype integrates 2778 thermocouples of sputtered Sb2Te3 and Bi2Te3 thin films (1 μm thick) on an area of 25 cm2. The electrical properties of thermoelectric materials were investigated by Van der Pauw measurements. Transfer Length Method (TLM) analysis was performed on three different multi-layer contact schemes in order to select the best solution to use for the definition of the contact pads realized on each section of the thermoelectric array configuration to allow electrical testing of single production areas. Kapton polyimide film was used as flexible substrate in order to add comfortable lightweight and better wearability to the device. The realized TEG is able to autonomously recover the thermal gradient useful to thermoelectric generation thanks to an appropriate package designed and optimized by a thermal analysis based on finite element method (FEM). The proposed package solution consists in coupling the module realized onto Kapton foil to a PDMS layer opportunely molded to thermally insulate TEG cold junctions and enhance the thermal gradient useful for the energy scavenging. Simulations results were compared to experimental tests performed by a thermal infrared camera, in order to evaluate the real performance of the designed package. First tests conducted on the realized TEG indicate that the prototype is able to recover about 5°C between hot and cold thermocouples junctions with a thermal difference of 17°C initially available between body skin and environment, generating about 2 V of open circuit output voltage.

A miniaturized gas-chromatographic system for the evaluation of fish freshness

A miniaturized simplified gas-chromatographic system for fast, easy and reliable fish freshness and quality analyses is proposed. Microsystem technologies are used for the miniaturization of the two main components of the system, namely the packed GC separation column and the Metal Oxide solid state detector. The proposed system is highly application-specific, integrating all the components necessary for automatic analyses of fish samples to determine the freshness by quantifying volatile amines. The system prototype is described in detail and preliminary in-field validation results are reported.