Strategies and Techniques for Powering Wireless Sensor Nodes through Energy Harvesting and Wireless Power Transfer

The continuous development of the internet of things (IoT) infrastructure and applications is paving the way for advanced and innovative ideas and solutions, some of which are pushing the limits of state-of-the-art technology. The increasing demand for Wireless Sensor Nodes (WSNs) able to collect and transmit data through wireless communication channels, while often positioned in locations that are difficult to access, is driving research into innovative solutions involving energy harvesting (EH) and wireless power transfer (WPT) to eventually allow battery-free sensor nodes. Due to the pervasiveness of radio frequency (RF) energy, RF EH and WPT are key technologies with the potential to power IoT devices and smart sensing architectures involving nodes that need to be wireless, maintenance free, and sufficiently low in cost to promote their use almost anywhere. This paper presents a state-of-the-art, ultra-low power 2.5 W highly integrated mixed-signal system on chip (SoC), for multi-source energy harvesting and wireless power transfer. It introduces a novel architecture that integrates an ultra-low power intelligent power management, an RF to DC converter with very low power sensitivity and high power conversion efficiency (PCE), an Amplitude-Shift-Keying/Frequency-Shift-Keying (ASK/FSK) receiver and digital circuitry to achieve the advantage to cope, in a versatile way and with minimal use of external components, with the wide variety of energy sources and use cases. Diverse methods for powering wireless Sensor Nodes through energy harvesting and wireless power transfer are implemented providing related system architectures and experimental results

Cascaded "Triple-Bent-Beam" MEMS Sensor for Contactless Temperature Measurements in Nonaccessible Environments

International audienceA microelectromechanical systems (MEMS) temperature sensor based on a cascade three-stage "bent-beam" structure is described in this paper. A suspended structure mechanically deforms in response to the change in ambient temperature, and then, a displacement is obtained; the structure is composed of three cascaded systems in order to enhance sensor sensitivity. The final conversion is made to an electrical signal that is obtained by using an interdigitated capacitor having one electrode fixed to the substrate and one electrode embedded into the moving tip of the MEMS sensor. The device has been conceived to operate passively in harsh environments where high temperatures could harm active electronic devices. The readout of the unknown temperature is therefore remotely performed by coupling the variable MEMS capacitor to a fixed inductor to compose a resonant LC circuit, which ismagnetically coupled to a reader circuit placed outside the environment where the measurement takes place. The temperature to be measured is therefore first converted into a displacement that, in turn, induces a change in a capacitor value; a variation in the resonant frequency of an LC circuit is finally observed through the remote readout circuit. This paper focuses on the analytical and numerical modeling of both the temperature-todisplacement and displacement-to-capacitance conversions, on the design and fabrication of an experimental prototype, on the experimental validation where results are extensively presented and commented, and, finally, on the design of the integrated resonant device for contactless measurements

Passive Extraction of Signal Feature Using a Rectifier with a Mechanically Switched Inductor for Low Power Acoustic Event Detection

Analog hardware used for signal envelope extraction in low-power interfaces for acoustic event detection, owing to its low complexity and power consumption, suffers from low sensitivity and performs poorly under low signal to noise ratios (SNR) found in undersea environments. To overcome those problems, in this paper, we propose a novel passive electromechanical solution for the signal feature extraction in low frequency acoustic range (200–1000 Hz), in the form of a piezoelectric vibration transducer, and a rectifier with a mechanically switched inductor. A simulation study of the novel solution is presented, and a proof-of-concept device is developed and experimentally characterized. We demonstrate its applicability and show the advantages of the passive electromechanical device in comparison to the active electrical solution in terms of operation with lower input signals (<20 mV compared to 40 mV), and higher robustness in low SNR conditions (output voltage loss for −10 dB ≤ SNR < 40 dB of 1 mV, compared to 10 mV). In addition to the signal processing performance improvements, compared to our previous work, the utilization of the presented novel passive feature extractor would also decrease power consumption of a detector’s channel by over 76%, enabling life-time extension and/or increased quality of detection with larger number of channels. To the best of our knowledge, this is the first solution presented in the literature that demonstrates the possibility of using a passive electromechanical feature extractor in a low-power analog wake-up event detector interface

Hybrid Micro Electro Mechanical Sensor based onGraphene Oxide/Polyvinyl Alcohol for Humidity Measurements

In this paper, we present a redundant micromachined sensor based on Bulk and Etch. Silicon-on-Insulator (BESOI) process for measurements of relative humidity (RH) by using Graphene-Oxide/Polyvinyl-Alcohol (GO/PVA) composite. The microsensor is a mechanical oscillator composed of a proof mass with multilayer of nanomaterials (GO/PVA) and suspended by four crab leg springs. The realized redundant approach concerns the possibility to use different readout strategies in order to estimate the same measurand: RH. This is an intriguing solution to realize a “robust measurement system”, with multiple outputs by using the GO/PVA as functional material. In presence of RH variation: (1) it changes its mass and; as consequence; a variation of the natural frequency of the oscillator can be observed in the frequency domain; (2) it also varies the conductivity which can be measured by using two integrated electrodes. The sensor has been designed; studied; modeled and experimental results demonstrate the effectiveness of our implementation

A vibrational energy harvester based on soft-nonlinearity for truly random excitation

Abstract In this paper, we present a nonlinear energy harvester that is based on a “soft-mode” nonlinearity and is able to work in presence of a truly random excitations. The proposed harvester is configured with a cantilever beam structure, and, at the tip is a cylindrical container filled with freely moving iron balls. The nonlinearity is implemented through the container, as a piecewise function. This structure, in presence of noise, can be assumed as a second order (mass-spring-damper) nonlinear system where the length of the spring changes as a function of external vibration. As will be demonstrated, this nonlinearity will improve the performance of the energy harvester under random excitation. In comparison, the conventional approach based on resonant oscillators is able to collect energy only around its mechanical natural frequency, while the solution pursued here will present a wide spectrum of response. Furthermore, the implemented nonlinearity here does not possess any barrier of potential or mechanical threshold. Because of this, it is able to work at weak signal levels and without mixture of periodic signals. A piezoelectric element has been used to convert the mechanical vibrations into an electrical signal. The system has been modeled and simulated. Experimental validations have been carried out, demonstrating the suitability of the proposed solution

Analysis of a Hybrid Micro-Electro-Mechanical Sensor Based on Graphene Oxide/Polyvinyl Alcohol for Humidity Measurements

In this paper, we present a redundant microsensor based on the bulk and etch silicon‑on‑insulator (BESOI) process for measuring relative humidity (RH), by using a graphene‑oxide/polyvinyl‑alcohol (GO/PVA) composite. The MEMS is a mechanical oscillator, composed of a proof mass with multilayer of nanomaterials (GO/PVA) and suspended by four crab-leg springs. The redundant approach realized concerns the use of different readout strategies in order to estimate the same measurand RH. This is an intriguing solution to realize a robust measurement system with multiple outputs, by using the GO/PVA as functional material. In the presence of RH variation, GO/PVA (1) changes its mass, and as consequence, a variation of the natural frequency of the integrated oscillator can be observed; and (2) varies its conductivity, which can be measured by using two integrated electrodes. The sensor was designed, analyzed and modeled; experimental results are reported here to demonstrate the effectiveness of our implementation

IoT-Based Microclimate and Vibration Monitoring of a Painted Canvas on a Wooden Support in the Monastero of Santa Caterina (Palermo, Italy)

The main objective of this work is the characterization and observation of the performance of an IoT measurement and monitoring system in the field of cultural heritage conservation for assessing the health condition of artworks. This article also describes the application of this system to the monitoring of a canvas painting applied on a wooden support, an artwork from the 19th century by the painter Giuseppe Patricolo depicting The Deposition, placed inside a niche in the Santa Caterina Monastery in Palermo (Italy). Considering the presence of the wooden structure, it is useful to measure not only microclimatic parameters such as temperature and humidity, but also vibrations that can in fact cause degradation phenomena in these artworks. This is a first step towards the development of mimetic systems integrated in the work of art without causing physical, mechanical or chemical alterations and ensuring that the level of microclimatic parameters is below the threshold values whose exceeding could compromise the entire artefact

On Theoretical and Numerical Aspects of Bifurcations and Hysteresis Effects in Kinetic Energy Harvesters

The piezoelectric energy-harvesting system with double-well characteristics and hysteresis in the restoring force is studied. The proposed system consists of a bistable oscillator based on a cantilever beam structure. The elastic force potential is modified by magnets. The hysteresis is an additional effect of the composite beam considered in this system, and it effects the modal solution with specific mass distribution. Consequently, the modal response is a compromise between two overlapping, competing shapes. The simulation results show evolution in the single potential well solution, and bifurcations into double-well solutions with the hysteretic effect. The maximal Lyapunov exponent indicated the appearance of chaotic solutions. Inclusion of the shape branch overlap parameter reduces the distance between the external potential barriers and leads to a large-amplitude solution and simultaneously higher voltage output with smaller excitation force. The overlap parameter works in the other direction: the larger the overlap value, the smaller the voltage output. Presumably, the successful jump though the potential barrier is accompanied by an additional switch between the corresponding shapes

Nonlinear Dynamics of a Star-Shaped Structure and Variable Configuration of Elastic Elements for Energy Harvesting Applications

The subject of the model research contained in this paper is a new design solution of the energy harvesting system with a star-shaped structure of elastic elements and variable configuration. Numerical experiments focused mainly on the assessment of the configuration of elastic elements in the context of energy harvesting efficiency. The results of computer simulations were limited to zero initial conditions as it is the natural position of the static equilibrium. The article compares the energy efficiency for the selected range of the dimensionless excitation frequency. For this purpose, four cases of elastic element configurations were compared. The results are visualized based on the diagram of RMS voltage induced on piezoelectric electrodes, bifurcation diagrams, Lyapunov exponents, and Poincaré maps, showing the impact of individual solutions on the efficiency of energy harvesting. The results of the simulations show that the harvester’s efficiency ranges from 4 V to 20 V depending on the configuration and the frequency range of the excitation, but the design allows for a smooth adjustment to the given conditions

Design of Smart Drivers for Electrostatic MEMS Switches

International audienceThis paper introduces the design of smart high-voltage CMOS drivers for electrostatic actuators. Smart must be understood as the capability of the driver to deliver the required voltage to close a MEMS switch and to diagnose whether the electrode moves well or not. This way, stuck or broken switches could be easily identified during operation. To implement such an online diagnosis, we propose to equip the driver architecture with a dedicated circuitry that can detect pull-in events. Pull-in corresponds to a rapid change of the actuation capacitance thus producing a charging current peak. The idea is therefore to monitor the charging current, and to track a current peak that could be small with respect to the current that charges parasitic capacitors. In this paper, we propose two different architectures to cancel parasitic capacitance effects. Both are introduced, studied by simulation and implemented on silicon. Complete demonstration is finally performed with an academic prototype of a MEMS switch