Bruno Ando

Nonlinear mechanism in MEMS devices for energy harvesting applications

This paper reports a novel bistable microelectromechanical system for energy harvesting applications. In particular, we focus here on methodologies and devices for recovering energy from mechanical vibrations. A common energy harvesting approach is based on vibrating mechanical bodies that collect energy through the adoption of self-generating materials. This family of systems has a linear mass–spring damping behaviour and shows good performance around its natural frequency. However, it is not generally suitable for energy recovery in a wide spectrum of frequencies as expected in the vast majority of cases when ambient vibrations assume different forms and the energy is distributed over a wide range of frequencies. Furthermore, whenever the vibrations have a low frequency content the implementation of an integrated energy harvesting device is challenging; in fact large masses and devices would be needed to obtain resonances at low frequencies. Here, the idea is to consider the nonlinear behaviour of a bistable system to enhance device performances in terms of response to external vibrations. The switching mechanism is based on a structure that oscillates around one of the two stable states when the stimulus is not large enough to switch to the other stable state and that moves around the other stable state as soon as it is excited over the threshold. A response improvement can be demonstrated compared to the classical linear approach. Indeed, both a wider spectrum will appear as a consequence of the nonlinear term and a significant amount of energy is collected at low frequencies. In this paper the bistable working principle is first described and analytically modelled, and then a numerical study based on stochastic differential equations (SDE) is realized to evaluate the behaviour of a MEMS device. A micromachined SOI prototype has been realized and a measurement campaign validated the nonlinear mechanism. As expected, the study shows that the nonlinear system exhibits a low pass filter behaviour suitable for harvesting ambient energy at low frequency.

Sentinella: Smart Monitoring of Photovoltaic Systems at Panel Level

The monitoring of photovoltaic (PV) systems is important for the optimization of their efficiency. In this paper, a low-cost smart multisensor architecture equipped with voltage, current, irradiance, temperature, and inertial sensors, for the monitoring (at the panel level) of a PV system, is presented with the aim of detecting the causes of efficiency losses. The system is based on a Wireless Sensor Networks with sensing nodes installed on each PV panel. The acquired data are then transferred to a service center where dedicated paradigms continuously perform the assessment of electrical efficiency as well the estimation of correlated causes, at the single panel level. In this paper, the detection of critical faults (temporary and permanent shadowing, dirtying, and anomalous aging) is addressed. The methodology adopted to estimate efficiency losses and related causes is based on the comparison between the measured efficiency of each PV panel and the nominal one estimated in the real operating conditions. Moreover, the anomalous aging estimation is based on the five parameter model approach that exploits a dedicated minimization paradigm to analyze the mismatch between the nominal current-voltage model of the PV panel and the measured one. The main advantage of the proposed approach is the continuous monitoring of PV plants and the assessment of possible causes of power inefficiency at the PV panel level, allowing for the implementation of a really efficient distributed fault diagnosis system. The experimental results are presented along with the analysis of the uncertainty affecting the measurement system.

A Novel Ferrofluidic Inclinometer

Inertial transducers based on the use of ferrofluids as inertial mass can be of great interest due to their peculiarities and due to the advantages that they show when compared to traditional devices. Ferrofluids are special solutions of magnetic particles in a carrier liquid whose density and other physical features can be controlled by an external magnetic field. In this paper, the development of a ferrofluidic inclinometer, which exhibits a tunable operating range and a valuable metrological feature and an intrinsic robustness against inertial shocks, is presented. The device consists of one excitation coil and two sensing coils wound around a glass pipe where a drop of ferrofluid is contained in a water environment. The magnetic force, which is induced by the excitation coil, attracts the ferrofluidic mass in a position that depends on the device inclination. The voltage at the output of the two sensing coils is related to the ferrofluidic mass displacement and thus reflects the tilt to be measured. Analytical models, simulations, and experimental results are presented to demonstrate the suitability of the proposed approach.

Investigation on Mechanically Bistable MEMS Devices for Energy Harvesting From Vibrations

In this paper, mechanically bistable microelectromechanical systems devices are investigated for energy harvesting from mechanical vibrations. This approach is particularly suitable when random, weak, and broad-band vibrations in the low-frequency range are considered. These working conditions are, in fact, quite challenging and are often approached via arrays of linear resonant microdevices. Our approach allows, with a single device, to efficiently collect kinetic energy in the whole spectrum of frequencies of the incoming signal. Bistable behaviors are achieved through purely mechanical and fully compliant micromechanisms. Different structures have been analytically and numerically investigated, both in static and dynamic working conditions, and optimized results are proposed. The advantages of the proposed device, which exploit bistable dynamic behaviors, over linear and monostable strategies are presented in this paper: In the case of the incoming kinetic energy spread over a large bandwidth and confined at low frequencies, a larger fraction of the input mechanical energy is transferred to the mechanical-to-electrical conversion section of the harvester and, therefore, to the final user. A complete device design is proposed in this paper by taking into account a dedicated fabrication process which allows to obtain large inertial masses; electrostatic conversion has been considered and embedded into the device to evaluate the device performances in terms of the electric energy scavenged.

Inkjet-printed sensors: a useful approach for low cost, rapid prototyping [Instrumentation Notes]

Over the past ten years, the development of low cost graphic technology-based sensors has been proceeding rapidly. The use of innovative materials and substrates has also picked up momentum. The interest in such sensors is justified by the need for both low cost, rapid prototyping techniques for research laboratories and mass-production processes for the realization of very low cost devices. Examples of addressed devices are RFID tags, antennas, keyboards, displays and especially sensors. The rapid prototyping of inexpensive devices and sensors by printing technologies is of great importance for the everyday activities of the scientific community including research laboratories and academia.

Multisensor Strategies to Assist Blind People: A Clear-Path Indicator

The development of electronic sensing devices for the visually impaired requires knowledge of the needs and abilities of this class of people. This paper presents a rough analysis that can be used to properly define the criteria to be adopted for the design of such devices. In particular, attention will be focused on clear-path indicators, highlighting their role in orientation and mobility tasks. A new device belonging to this class is presented. The detector is based on a multisensor strategy and adopts smart signal processing to provide the user with suitable information about the position of objects hindering his or her path. Experimental trials demonstrate the efficiency of the device developed.

All-Inkjet Printed Strain Sensors

Low cost approaches for the direct printing of electric components usually require two different technologies for conductive patterns and functional layers. Conductive structures (wires, coils, and electrodes) are usually screen printed while low cost inkjet systems can be used for the realization of functional layers (e.g., resistive and dielectric film, sensing areas). This hybrid approach, motivated by the poor availability of conductive inks compatible with low cost printing systems, does not fulfill requirements of rapid prototyping. In this paper, the realization of strain gauge sensors by a low cost all-inkjet process exploiting a Metalon water-based silver ink by Novacentrix is presented as a possible and convenient approach for the rapid prototyping of sensors by cheap inkjet printing techniques. The latter could be dramatic for specific contexts where short developing times and low cost features of printing equipments are mandatory, such as lab scale prototyping and research laboratories. The experimental results confirm both the suitability of the proposed approach and expected performances of lab-scale prototypes developed.

Magnetic Fluids and Their Use in Transducers

Magnetic fluids are now widely used to implement transducer architectures. These fluids have valuable properties compared to traditional materials. In this column, a brief overview of magnetic fluids and their traditional uses in the field of transducers are given and some applications developed at the DIEES laboratory at the University of Catania, Italy are presented

Residence times difference fluxgate magnetometers

We present analytical and experimental results on fluxgate magnetometers that make use of a readout technique based on residence times. This approach allows for enhancing sensitivity to weak target signals in particular when the reduction of the sensor dimensions are considered. Our approach, exploiting the inherent nonlinear character of the bistable core dynamics, is based on the time domain characterization of the transitions between the two saturation states of the hysteresis loop that is inherent in the ferromagnetic core dynamics. This readout technique can be implemented with bias signals having lower amplitude and frequency than those used in conventional fluxgate processing schemes, thus reducing the device power requirements. The efficacy of this strategy is shown through an analytical approach and via experimental results which suggests guidelines for optimal device design and realization. The experiments have been carried out on a miniaturized laboratory fluxgate prototype; this device shows numerous desirable characteristics, including very good sensitivity and resolution, as well as ease of operation and a very low cost.

A Smart Multisensor Approach to Assist Blind People in Specific Urban Navigation Tasks

Visually impaired people are often discouraged in using electronic aids due to complexity of operation, large amount of training, nonoptimized degree of information provided to the user, and high cost. In this paper, a new multisensor architecture is discussed, which would help blind people to perform urban mobility tasks. The device is based on a multisensor strategy and adopts smart signal processing.