Alessandro Golfarelli

Dynamic switching conversion for piezoelectric energy harvesting systems

The current advances in ultra-low power design let foresee great opportunities in energy harvesting platforms for self-powered systems. This paper presents a switching conversion scheme based on active control for harvesting energy with a higher efficiency than traditional approaches. The approach has been validated for piezoelectric energy harvesters with mixed-signal circuital simulations of non-linear equivalent electromechanical systems and a prototype has been developed. The proposed switching converter may increase harvested power of about 30% with respect to solutions based on traditional rectifiers and is expected to achieve up to 755 muW in a train passenger car running at about 100 km/h with a 32 times 6 mm2 cantilever with a 35 g mass attached at the free end.

Aircraft angle of attack and air speed detection by redundant strip pressure sensors

Air speed and angle of attack are fundamental parameters in the control of flying bodies. Conventional detection techniques use sensors that may protrude outside the aircraft, be too bulky for installation on small UAVs, or be excessively intrusive. We propose a novel readout methodology where flight parameters are inferred from redundant pressure readings made by capacitive strip sensors directly applied on the airfoil skin. Redundancy helps lower the accuracy requirements on the individual sensors. A strategy for combining sensor data is presented with an error propagation analysis. The latter enables foreseeing the precision by which the flight parameters can be detected. The methodology has been validated by fluid dynamic simulation and a sample case is illustrated.

Acquisition system for pressure sensor network

The paper presents a data acquisition system, based on strips of capacitive sensors. The architecture has been initially targeted at monitoring dynamic pressures on aerodynamic bodies and can be extended to a wide range of applications. The system is based on a master-slave communication protocol covering distances over dozens of meters using embedded readout electronics. Each capacitive strip, interfaced to a low power readout circuit, represents a slave unit of a distributed network. A comparison between wind tunnel measurements on a wing profile acquired by a conventional electromechanical pressure transducer and data collected to a central host using the proposed architecture is presented. High sensitivity in the transduction of capacitance variations in the tens fF range and reliability in strip to host communication have been reached.

Signal conditioning for capacitive sensors with field programmable analog arrays

The applicability of FPAAs to the signal conditioning involved in interfacing elementary sensors may be non-trivial since FPAAs are generally targeted at processing voltage-mode signals only. Here, we consider the usage of a popular switched-time FPAA to capacitive sensing, with particular regard to the problem of annihilating the influence of parasitic reactance which may easily exceed the capacitance variations to be detected. It is shown that a proper exploitation of the FPAA signal conditioning primitives can make them up to the task of detecting capacitance variations below the hundred fF threshold. A sample application is illustrated as a proof of concept.

Actively Controlled Power Conversion Techniques for Piezoelectric Energy Harvesting Applications

The current advances in ultra-low power design let foresee great opportunities in energy harvesting platforms for self-powered systems. This paper presents two conversion schemes based on active control for harvesting energy with a higher efficiency than traditional passive approaches. A prototype has been developed and the approaches have been validated for piezoelectric energy harvesters with both measurements in realistic conditions (i.e. irregular vibrations) and mixed-signal circuital simulations. The proposed converters may increase harvested power of at least 25% and up to three times with respect to a passive rectifier. The harvested power is about 40 μW in presence of weak vibrations (aRMS = 1.18 m/s2) obtained in a train passenger car in motion with a 28 × 6 × 0.5 mm3 cantilever made of PZT-A4E with a 20 g mass attached at the free end.

Novel Technique for Real Time Individual Object Sorting

The content of the present paper aims at seeking faster speed and lower cost methods for characterizing granular objects in general, and cereal grains in particular. The approach is based on simultaneous cross-combined optical and impedimetric sensing techniques in the MHz range, applied to flowing streams so as to determine real-time 3D morphological characterization of single objects. The main advantages of the proposed approach rely on the high discriminatory capacity of the object classes and on the high degree of parallelism, capable of processing large amounts of material on production lines. The use of integrated electronic systems also allows high operative speed, easy calibration and flexibility to the required classification features.

A thin film strip for aerodynamic body pressure profile monitoring

An array of polyimide-based capacitive pressure sensors, employing thin copper-clad polyimide layers as a sensing membrane, is presented. Transduction is performed by means of a switched capacitor amplifier and a micro-controller. Sensors, targeted to fluid dynamic airfoil applications, have been designed with the aid of finite element method (FEM) models for sensor sensitivity and resolution estimation. Wind tunnel experiment results are shown, comparing the sensor with a conventional pressure transducer. The device represents a cheaper and more reliable option to micro electro-mechanical systems (MEMS) sensors and to conventional electromechanical pressure transducers, being robust, conformable and smart for placement.

Novel measurement method for air-data system based on strip sensors: experimental results

We report the first experiments performed in a wind tunnel to validate a novel measurement equipment, meant to be used in the air-data system of small aircrafts. The apparatus does not rely on conventional probes, but takes advantage of capacitive, strip pressure sensors that enable a survey of the pressure gradients on portions of the aircraft surfaces. Sensors are built by printed circuit board (PCB) technologies as conformable film-like structures that can be directly applied on the aircraft skin. They can read gradients thanks to the many elementary units present in each strip. The measurement equipment employs pressure-gradient information to indirectly infer the aircraft air speed and angle of attack. In the experiments, measurements are taken in a wind tunnel using a NACAOO15 model airfoil hosting a single sensor and results confirm the ability of the system to correctly detect the target quantities

A Method Based on Scattering Parameters for Model Identification of Piezoactuators with Applications in Colloidal Suspension Monitoring

Liquid colloids are mixtures where one substance is dispersed evenly throughout another. Piezoactuators can be reliably used to sense physical properties of colloids. However, to better understand and forecast the behavior of the system, a suitable and reliable model should be used to fit experimental data. In this work we will show how the scattering parameters, introduced for the first time in this field, can greatly improve model identification accuracy and give deeper insight into the resonant response of the system, especially in the case of viscous systems, whenever resonance peaks tend to shift or to vanish. Any change on the density and/or viscosity of the interacting fluid causes a wellpredictable modification on each possible frequency response computable from measured data: the best choice in terms of sensitivity and orthogonal correlation has been investigated by means of parametric simulations with variable loads. Experimental results demonstrate that the conceived sensor is able to reliably discriminate different bentonite clay suspensions.