Vincenzo Marletta

Exploiting Nonlinear Dynamics in Novel Measurement Strategies and Devices: From Theory to Experiments and Applications

This paper is focused on the exploitation of intrinsic nonlinear dynamics toward novel measurement systems and readout methodologies. In particular, sensors that can be represented as nonlinear dynamical systems and are often reducible to systems described by a static nonlinearity are considered; the nonlinear behavior therefore reduces to the dynamics of a system characterized by two or more (meta)stable equilibrium states (or attractors) separated by energetic thresholds to be overcome to transition from one attractor to the other. The presence of a weak unknown target signal is assessed via the monitoring of the “residence times” in the attractors. This operational scenario that is based on the monitoring of suitable “events” avoids an “amplitude-based” readout and provides a very simple and sensitive readout-processing scheme. Many noise effects are also mitigated by the intrinsic decoupling between the amplitude domain of the input signal and the event or time domain of the output signal. We present here the general transduction methodology for this class of “residence-times difference” sensors, together with the experimental results obtained from the working versions of these sensors (in particular, a simple fluxgate magnetometer). We then introduce some novel dynamical behavior that occurs when the active nonlinear (in this case, bistable) elements are coupled using well-crafted coupling topologies. Sensors based on these coupling schemes provide several advantages over their single-element counterparts. We discuss the dynamics of the coupled-element device, summarizing recent theoretical and experimental results. Finally, we describe the construction and performance of working devices (magnetic- and electric-field sensors) based on these concepts.

A Sensing Architecture for Mutual User-Environment Awareness Case of Study: A Mobility Aid for the Visually Impaired

In this paper, a platform to manage user-environment interaction is addressed. The core of the methodology consists of a continuous communication between a sensing module hosted on the user and a sensor network distributed in the environment. Such strategy provide the cognitive system with a continuous perception of both the environment and the user. The cognitive system can hence be made aware of user-environment interaction and can provide the user with awareness of the surroundings. A case of study is presented which demonstrates the applicability of such strategy to real orientation aids for the visually impaired.

A Low-Cost Snap-Through-Buckling Inkjet-Printed Device for Vibrational Energy Harvesting

This paper covers a novel methodology for the realization of devices that are able to harvest energy from background mechanical vibrations. The novelties reside in the nonlinear mechanism ruling the harvester behavior and the printed technology used to realize the lab-scale prototype. The nonlinearity of the harvester is desirable, because vibrational energy is usually distributed in a band at low frequency and does not, therefore, lend itself to harvesting through a (linear) resonant device. Printed technology has the advantage of being ultracheap and, hence, suitable for proof-of-concept and rapid laboratory prototyping. In particular, inkjet printing technology affords the realization of low-cost electrodes with high resolution and multiple functional layers. This paper covers the mechanical properties of a snap-through buckling beam and details the results of experiments aimed at investigating the (nonlinear) mechanical properties as well as a theoretical fit to the experimental observations. Moreover, the electrical response of the device and, hence, its suitability for energy-harvesting applications are addressed. Powers on the order of 100 nW have been experimentally estimated by a lab-scale prototype with the aim of demonstrating the proof-of-concept of the snap-through buckling mechanism for energy harvesting.

A Multisensor Data-Fusion Approach for ADL and Fall classification

This paper deals with an advanced approach for the monitoring of elders and people with neurological pathologies (e.g., Alzheimer). The system that adopts a multisensor approach is able to recognize critical events, such as falls or prolonged inactivity, to monitor the user posture, and to notify the alerts to caregivers. In particular, this paper focuses on smart algorithms developed for the activities of daily living (ADL) classification, which use the information provided by inertial sensors embedded in the user device. In particular, a novel multisensor data-fusion approach, combining data from an accelerometer and a gyroscope, is presented. Apart from alert management, the information provided by this system is useful to track the evolution of the user pathology, also during rehabilitation tasks. Results obtained during tests with users demonstrate suitable performances of the adopted paradigm, in terms of sensitivity and specificity, in performing falls and ADL classification tasks. The average value of the sensitivity index for the classes of falls and ADL considered through this paper is 0.81, while the average value of the specificity index is 0.98.

An advanced tracking solution fully based on native sensing features of smartphone

This paper deals with an advanced multi-sensor approach for the implementation of a tracking system exploiting sensing and processing features embedded in smartphone devices. In particular, a methodology based on advanced data fusion paradigms assuring an efficient heading estimation has been developed. The main advantage of the solution proposed resides in the possibility to correctly perform heading estimation also in the presence of serious environmental influence due to magnetic field distortion. Among possible application contexts, the proposed system would be particularly suitable for the development of mobility assistive systems for a safe and efficient exploration of educational/job environments by weak people.

An Event Polarized Paradigm for ADL Detection in AAL Context

The possibility to detect activities of daily living (ADLs), with particular regards to fall detection, is mandatory to implement a rigorous remote monitoring of frail people. Actually, unintentional falls cause a lot of hospitalizations and may lead to serious consequence due to long-lie happenings. Moreover, the ability to properly classify different kinds of falls could represent a strategic diagnostic tool. The widespread use of smartphones equipped with many embedded sensors would represent a suitable solution for ADL monitoring, especially for the future generation of elderly. The activity presented through this paper focuses on the development of a fully smartphone-based ADL detector, which uses an advanced classification paradigm to discriminate between different kinds of falls. The sensitivity and specificity features of the system are in line with the real needs of the Ambient Assisted Living context.

A Haptic Solution to Assist Visually Impaired in Mobility Tasks

Electronic travel aids are used for detecting obstacles, identifying services, and, generally, obtaining useful information from the surroundings, thus enabling a safe and effective exploitation of the environment. A drawback is unnatural codification, which may lead to usability concerns. This paper introduces a haptic device aimed to provide the user with information on the presence of obstacles inside the environment. The haptic interface is intended to reproduce the stimuli provided by a traditional white cane, without any contact with the environment. A prototype, implemented through a short cane with an embedded smart sensing strategy and an active handle, is presented. Twenty-five blindfolded normally sighted users participated to assess system performance in detecting obstacles and correctly conveying their position by the haptic interface. With respect to detecting obstacles and their positions, the average values of the sensitivity in the case of left, center, and right positioned obstacles are 0.735, 0.803, and 0.830, while the specificity values are 0.924, 0.835, and 0.827, respectively.

A Nonlinear Electric Field Sensor That Exploits Coupled Oscillator Dynamics: The Charge Collection Mechanism

In this paper, we investigate the exploitation of nonlinear behavior in ferroelectric (FE) materials in the realization of innovative transducers for detecting weak and low-frequency electric fields (E-fields). Specifically, we describe a nonlinear dynamical system based on FE capacitors coupled into a unidirectional ring circuit which, under the appropriate operating conditions, exhibits an oscillating regime of behavior in the response variable (the electric polarization). In this device, a weak target E-field induces a perturbation of the polarization of the FE material; in turn, the target signal can be detected and quantified via its effect on the coupled system response. Hence, the device entails the synergetic use of bistable FE materials, micromachining technologies that allow for addressing charge density amplification, and novel sensing strategies based on coupling nonlinear elemental cells. The “charge collector” strategy has been employed to detect the target field. An experimental characterization of the sensing device, including three cells (each cell corresponds to an FE capacitor) coupled in a ring configuration, is presented as a function of the charge collector configuration.

A BE-SOI MEMS for inertial measurement in geophysical applications

In this paper, an inertial transducer developed in bulk and etch silicon-on-insulator microelectromechanical-system technology is presented. The device is suitable for low-frequency observation and could represent an interesting solution to implement low-cost monitoring systems for applications requiring a large number of monitoring sites and disposable devices. In particular, the sensor design and the technology adopted are presented here along with models describing the device operation. In addition, an experimental sensor prototype is proposed, and experimental results confirming the suitability of the proposed architecture and its consistence with the predicted behavior are discussed.

RESIMA: A new WSN based paradigm to assist weak people in indoor environment

This paper deals with the RESIMA architecture developed to assist people in performing daily activity in indoor environment. As respect to solutions presented in the SOTA, RESIMA is a smart multi-parametric assistive system which performs a high resolution monitoring of the user position in the spatial-temporal domain as well as a deep inertial monitoring of the user status, thus assuring a reliable and continuous form of assistance to weak users. The system is based on a Wireless Sensor Network and smart paradigms which extract relevant information from data collected through the multi-sensor architecture. The paper mainly focuses on the multi-sensor system architecture and smart paradigms used to implement user localization. Positioning system accuracy of about 3 cm has been obtained while the system shows good reproducibility and reliability.