This paper deals with a novel strategy for the detection of weak static electric fields. The approach proposed here is
based on the exploitation of the nonlinear behaviors shown by a circuit made up by the ring connection of an odd number
of elements containing a ferroelectric capacitor. The presence of a weak external dc perturbation interacting with the
system state can be detected and quantified via its effect on the oscillation frequency and on the asymmetry of the system
The dynamic behavior of the ferroelectric ring can be described by using the equations of the "quartic double well"
potential that model the ferroelectric capacitors where the target electric field is considered as a perturbation in the
polarization status of each ferroelectric element.
Simulation results have been obtained where it can be observed, for a coupling factor greater than the critical one, as
related to the external field amplitude, the change in the harmonic content of the permanent oscillation that the coupled
A detailed spice model of the ferroelectric capacitor and of the ring circuit will be described in this paper together with
some results regarding the experimental characterization and modeling of ferroelectric capacitors to be included in the
Several experimental confirmation have been already obtained. Work is currently in progress toward the realization of a
novel ring circuit that will include the ferroelectric capacitors presented here.
In this work we discuss the implementation of sensing devices based on ring-coupled hysteretic systems. In particular, the emergent oscillations in a ring coupled system formed by overdamped nonlinear devices having an hysteretic magnetic and electric behaviour are considered with applications to B-field and E-field measurements, respectively. Details on the implementation strategy, on the materials adopted and on the technologies will be given. The concept introduced is then extended to the area of E-field sensors taking into account nonlinear ferroelectric devices where oscillations can be obtained through a suitable connection topology in a similar way as for the magnetic field systems. The evaluation of the output signal dependence on the target electric field to be measured will be discussed and some device implementation issues will be reported. The proposed system combines benefits coming from reconsidering dated physical electro-static phenomena, with miniaturization levels provided by micro-technologies, to realize important electric field amplification. Devices based on different technologies, ranging from PCB to hybrid integrated microsystems, will be presented and discussed. Preliminary experimental results on E field sensor will be presented; the studies on B-field sensor are more mature and more comprehensive experimental results will be discussed to validate the working principle and to qualify the sensors in terms of sensitivity and noise floor.
This work deals with the development of integrated relative humidity dew point sensors realized by adopting standard CMOS technology for applications in various fields. The proposed system is composed by a suspended plate that is cooled by exploiting integrated Peltier cells. The cold junctions of the cells have been spread over the plate surface to improve the homogeneity of the temperature distribution over its surface, where cooling will cause the water condensation. The temperature at which water drops occur, named dew point temperature, is a function of the air humidity. Measurement of such dew point temperature and the ambient temperature allows to know the relative humidity. The detection of water drops is achieved by adopting a capacitive sensing strategy realized by interdigited fixed combs, composed by the upper layer of the adopted process. Such a capacitive sensor, together with its conditioning circuit, drives a trigger that stops the cooling of the plate and enables the reading of the dew point temperature. Temperature measurements are achieved by means of suitably integrated thermocouples. The analytical model of the proposed system has been developed and has been used to design a prototype device and to estimate its performances. In such a prototype, the thermoelectric cooler is composed by 56 Peltier cells, made by metal 1/poly 1 junctions. The plate has a square shape with 200 μm side, and it is realized by exploiting the oxide layers. Starting from the ambient temperature a temperature variation of ΔT = 15 K can be reached in 10 ms thus allowing to measure a relative humidity greater than 40%.
A hybrid system consisting of a resonant piezo layer (RPL) and a resonant SOI micromechanical sensor is conceived in this work as highly sensitive gravimetric sensor for applications in various fields. The idea consists in using PZT screen-printed elements, behaving as thickness-mode resonators, coupled to a micro-mechanical resonator based on a SOI technology. The PZT resonator induces oscillations to the micromechanical device and, if the resonance condition is matched for this latter system, a sensitivity of 5000 Hz/μg can be obtained when a variation of the proof mass occurs. Prototypes of both the mentioned two constitutive parts have been separately realized by the authors showing potentials for batch production. Several different experimental MEMS prototypes, mainly made by a central proof-mass sustained by four compliant beams anchored to its four corners, have been realized. Both Front Side and Back Side DRIE etching procedures have been performed improving the proof mass value with respect to a different set of prototypes realized by using a standard CMOS technology. Even if a low resonance frequency characterize the realized micro-prototypes a drastically improved value of the quality factor allow to obtain very high gravimetric sensitivity then to detect very small changes in the proof mass value due i.e. to chemical or physical compound absorption over the mass surface. Electrical or optical sensing can be adopted, depending on materials embedded into the considered device, as already demonstrated by the authors. Polysilicon strain gauges have been embedded into the springs while optical readout can be addressed by using a novel class of metal-dielectric photonic-band gap materials. In this latter case a process step, which consists of depositing suitable thin films, must be take into account.
Electrical properties of polymeric materials, in which a transition metal complex [tris(2,2'-bipyridyl)Ru(II)]Cl2 is dispersed, are investigated, under light irradiation conditions, as a function of the complex concentration and of the light intensity and pulse duration. This idea is based on the fact that light absorption produces, as result of the electronic excitation, a temporary change in the electrical dipole moment of the metal complex and this in turn results in changes induced, under light stimulus, in capacitances, whose dielectric is mainly made by the polymeric compound. The material characterization system is therefore based on interdigitated planar capacitors over which the polymeric compound is deposited. The light action induces changes in the dielectric properties of the polymer and these changes reflect into the capacitance value and are in turn converted into an output voltage by suitable capacitance-to-voltage signal conditioning circuits. A differential configuration is adopted in these circuits, based on a dummy interdigitated transducers coated with the same polymer but shielded from the light stimulus, in order to filter out unwanted spurious signals.
Two health monitoring systems for damage detection in composite structures have been developed. First, a magnetic probe measures the magnetic field reflection during a frequency exploration. The local electrical conductivity of the structure is deduced from the cut-off frequency of the transfer function. Secondly, a probe with piezoelectric elements analyzes the local visco-elastic response of the structure produced at the moment of touching and stressing it. The same piezoceramic elements induces the mechanical solicitation and senses the response signal. The probes are compared in the analysis of damages induced in a coupon of quasi isotropic Carbon-epoxy material by various aggressions: 4 J- and 2 J-impacts inducing delaminations, a local burning by contact with a hot body and a simulated lightning impact by electric spark. Both probes show sensitivities to these various types of damage. For the piezoelectric probe, a "real-time" strategy, based on the processing of spectral power densities of the sensor signals, leads to an automatic measuring system classifying the damages. A software, based on fuzzy logic and implemented on a dedicated micro controller, elaborates the input data in order to realize the material damages classification. Combination the two techniques in a hybrid probe and use of the fuzzy logic procedure to the full signals to classify the structure response in a more subtle and extended way is the starting point of the design of a multisensor tactile probe able to recognize damages for a given material (NDE) or several classes of materials (robotized examinations in hostile environments).
This work deals with the development of a novel class of smart opto-electro-mechanical devices that are based on Photonic Band Gap materials consisting of several periods of suitable metal-dielectric couples. Innovative devices with electrically controllable optical properties are obtained that can be used both as sensors with optical output signals for application in hostile environments and as controlled optical filters. Theoretical models of such novel devices together with experimental prototypes have been developed and characterization of the devices has been performed. Finally an integrated device, realized by using standard CMOS technologies and compatible micromachining processes, in being developed.
In this paper some recent results, regarding the research activity currently in progress in the field of MEMS at the DEES, University of Catania, are reported. In particular some microsystem prototypes, realized by using a standard CMOS process (AMS 0.8 micrometers CMOS) through the EuroPractice service, are described. A novel IC has been realized, it contains several different structures designed both for particular applications and for technology characterization purposes. A set of devices has been realized through 'front side bulk micromachining' and some other novel structures where the polysilicon layer is used as sacrificial layer have been investigated. In order to ensure fully compatibility with CMOS electronics, a wet etching process has been performed by using TMAH. Characterizations of the wet etching process are being performed in order to exploit the absence of crystallographic structure in polysilicon to allow for isotropic etching micromachining. Some applications of Microsystems in different fields are also presented.