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International audience; Recently, filling zeolites with gaseous hydrocarbons at high pressures in diamond anvil cells has been carried out to synthesize novel polymer-guest/zeolite-host nanocomposites with potential, intriguing applications, although the small amount of materials, 10–7 cm3, severely limited true technological exploitation. Here, liquid phenylacetylene, a much more practical reactant, was polymerized in the 12 Å channels of the aluminophosphate Virginia Polytechnic Institute—Five (VFI) at about 0.8 GPa and 140 °C, with large volumes in the order of 0.6 cm3. The resulting polymer/VFI composite was investigated by synchrotron X-ray diffraction and optical and 1H, 13C, and 27Al nuclear magnetic resonance spectroscopy. The materials, consisting of disordered π-conjugated polyphenylacetylene chains in the pores of VFI, were deposited on quartz crystal microbalances and tested as gas sensors. We obtained promising sensing performances to water and butanol vapors, attributed to the finely tuned nanostructure of the composites. High-pressure synthesis is used here to obtain an otherwise unattainable true technological material.

A technique and electronic circuit for contactless electromagnetic interrogation of piezoelectric micro-electromechanical system (MEMS) resonator sensors are proposed. The adopted resonator is an aluminum-nitride (AlN) thin-film piezoelectric-on-silicon (TPoS) disk vibrating in radial contour mode at about 6.3 MHz. The MEMS resonator is operated in one-port configuration and it is connected to a spiral coil, forming the sensor unit. A proximate electronic interrogation unit is electromagnetically coupled through a readout coil to the sensor unit. The proposed technique exploits interleaved excitation and detection phases of the MEMS resonator. A tailored electronic circuit manages the periodic switching between the excitation phase, where it generates the excitation signal driving the readout coil, and the detection phase, where it senses the transient decaying response of the resonator by measuring through a high-impedance amplifier the voltage induced back across the readout coil. This approach advantageously ensures that the readout frequency of the MEMS resonator is first order independent of the interrogation distance between the readout and sensor coils. The reported experimental results show successful contactless readout of the MEMS resonator independently from the interrogation distance over a range of 12 mm, and the application as a resonant sensor for ambient temperature and as a resonant acoustic-load sensor to detect and track the deposition and evaporation processes of water microdroplets on the MEMS resonator surface.

In this paper, the possibility to steer and confine live human cells by means of acoustic waves, such as flexural plate waves (FPWs), generated by piezoelectric actuators applied to non-piezoelectric substrates, has been explored. A device with two lead zirconate titanate (PZT) actuators with an interdigital transducer (IDT) screen-printed on an alumina (Al2O3) substrate has been fabricated and tested. The experimental results show that, by exciting the actuators at their resonant frequencies, FPW modes are generated in the substrate. By exploiting the device, arrangements of cells on lines at frequency-dependent distances have been obtained. To maintain the alignment after switching off the actuator, cells were entrapped in a fibrin clot that was cultured for several days, enabling the formation of cellular patterns.

A novel quartz crystal resonator sensor, which embeds a conductive printed planar coil that enables electromagnetic contactless interrogation techniques is presented. An aerosol-jet process is used to precisely and accurately deposit electronic inks onto a 330 µm-thick bare piezoelectric quartz crystal to print the planar coil and the electrodes. The proposed interrogation technique enables distance-independent operation, and is based on the measurement of the reflected impedance of the quartz resonator sensor through the planar primary coil of the coupled inductors. The resonant frequency, measured without contact using the primary coil connected to an impedance analyzer, results 4.790260 MHz. Contactless operation distances up to 12.2 mm have been obtained. The experimental results have a maximum deviation of about 50 Hz, i.e. 10.5 ppm, with respect to reference measurements taken via contact probes.

This paper proposes a MEMS piezoelectric converter for energy harvesting from vibrations which exploits nonlinear effects to broaden the operating bandwidth. The converter is composed of an array of cantilevers with different geometric dimensions. Piezoelectric layer and electrodes have been deposited on the cantilevers by a custom low-curing temperature post process. Nonlinearity is achieved by the magnetic interaction of a magnet and ferromagnetic particles deposited on the cantilever tips. Preliminary results show that the converter behaves like a nonlinear system and a downshift of the resonant frequency of the cantilevers with respect to the linear resonant frequency is observed, as expected.

This paper proposes an oscillator circuit based on a phase-locked loop which automatically compensates for the parasitic capacitance of Thin-film Piezoelectric-on-Silicon (TPoS) contour-mode resonators. The circuit enables accurate tracking of the mechanical parameters of the resonators in demanding sensor applications by advantageously combining their favorable Q-factor with the electrical resonance enhancement arising from the automatic cancellation of parallel capacitance. Preliminary results on tracking the resonant frequency of a TPoS resonator due to temperature variations show a temperature coefficient of frequency of 53.4 ppm/°C.

This paper describes a piezoelectric energy harvester employing a snap-through buckling (STB) mechanism for frequency-up conversion (FuC). The harvester consists of two main components: a bistable mechanical structure and one piezoelectric cantilever beam. The device is designed by means of analytical methods and numerical simulations. A proof-of-concept prototype is manufactured and tested under low frequency mechanical excitation. Experimental results show that, if the STB is induced, from the second stable configuration back to the undeformed one, the FuC is obtained and the response of the beam presents frequency components in a wide range, even though the resonant frequency of the cantilever beam is not excited. The results are hence in agreement with the expected behavior: if the device, forced in the second stable configuration, is subject to a low-frequency excitation whose amplitude exceeds a threshold, STB is triggered and the ensuing FuC provokes a widening of the beam vibrations frequency range and consequently a significant effectiveness in terms of power output. A maximum power of 4 mW is obtained by using an optimal resistive load as STB from a stable configuration of the bistable mechanism to the other one is triggered, a maximum energy of 4 . 5 J is obtained in case of a rectifier circuit with storage capacitor.

An electromagnetic contactless interrogation technique to induce and sense mechanical vibrations on miniaturised electrically conductive resonant structures is presented. The structures can be used as passive resonant sensors with proximate contactless readout. No use is made of poling magnets or wired connections to the resonator that is not required to have magnetic properties. An external coil arrangement has one driving and two pickup coils. The driving coil generates a DC magnetic field and two AC magnetic fields at different frequencies: one for excitation and one for probing. Both the AC magnetic fields induce eddy currents on the conductive surface of the resonating structure. The eddy currents at the frequency of the excitation field interact with the DC magnetic field causing alternating forces, which can set the resonating structure into vibration. The eddy currents at the frequency of the probing field generate a magnetic field that is modulated by the vibrations and detected by the pickup coils. A mathematical model of the interrogation principle has been derived and confirmed by numerical solutions. The experimental demonstration is provided by results obtained on an aluminium cantilever resonator.

As the typical surface separations in Micro Electro-Mechanical Systems (MEMS) are reduced to below one micrometer, detailed knowledge of the interaction forces down to this scale is required. In this context, we have developed a dedicated experimental platform to directly investigate electrostatic and physical effects in a high-aspect-ratio electrostatic-capacitive MEMS device based on commercial technology. In the present work, we report on an extensive experimental characterization, focused on the influence of the surface separations, electric surface potentials, and pressure on the static and dynamical behaviour of the device under precisely controlled conditions. For the proper analysis of the bias position and small-displacement response of the device, we have developed a comprehensive electro-mechanical model capable of describing the aforementioned effects, and allowing to extract the mechanical and electrical device parameters from the experimental data. Based on the developed model, a strong experimental evidence is found for significant variations in device characteristics upon reduction of surface separation to below one micrometer. (C) 2017 Elsevier B.V. All rights reserved.

A novel quartz crystal resonator (QCR) sensor with a printed-on-crystal conductive coil, named sensor coil, is presented. The sensor coil electromagnetically coupled to an external readout coil allow to perform contactless interrogation of the QCR working as a stand-alone sensor unit. A frequency-domain readout technique is adopted that allows dual-harmonic operation by detecting the QCR frequencies of the fundamental and third harmonic, and offers first-order independence from the stand-off distance between the sensor and the readout unit. The QCR electrodes and sensor coil have been printed on a 330- ${\mu }\text{m}$ -thick bare AT-cut quartz crystal exploiting the aerosol jet printing technology. The fabricated QCR sensor has reference values of the fundamental and third harmonic frequencies at 4.77 and 14.22 MHz, respectively. Distance-independent contactless operation has been demonstrated for distances up to 12 mm. The readout frequencies deviate from reference values less than 10 and 90 ppm for the fundamental and third harmonic, respectively, thus validating the proposed principle.

This paper presents a novel quartz crystal resonator (QCR) sensor, which embeds a conductive planar coil connected to the QCR electrodes that enables electromagnetic contactless interrogation techniques. The planar coil and the QCR electrodes are printed on a 330 µm-thick bare piezoelectric quartz crystal exploiting the aerosol-jet printing technology. The printed coil acts as the secondary coil of a pair of coupled inductors, allowing for a self-contained sensing element which avoids the need to connect an external coil for interrogation. The adopted interrogation technique, which advantageously enables distance-independent operation, is based on the measurement of the reflected impedance of the QCR sensor through the planar primary coil of the coupled inductors. The resonant frequency of the QCR has been measured without contact using the primary coil connected to an impedance analyser. The measured resonant frequency is 4.790260 MHz, and has a maximum deviation of about 50 Hz, i.e. 10.5 ppm, with respect to reference measurements taken via contact probes. Contactless operation distances up to 12.2 mm have been obtained.

A passive inductive-capacitive (LC) resonant temperature sensor embedded onto a flexible label is presented. The sensor exploits a patterned copper foil on adhesive paper for the inductive coil and a ceramic capacitor as the temperature sensing element. Temperature affects the value of the capacitance and hence of the resonant frequency of the LC tank resonator. The sensor can be contactless interrogated through an external readout coil electromagnetically coupled to the on-label coil. The interrogation technique is based on the measurement of the reflected impedance at the readout coil to monitor the variations of the resonant frequency of the LC pair on the sensor label. Preliminary tests have demonstrated a temperature sensitivity of 330 Hz/°C from room temperature up to 80°C. The proposed flexible label opens future uses as a cost-effective device for sensing applications in enclosures and packages.

In this paper a Micro Electro-Mechanical System (MEMS) inclinometer based on a double-actuator electrical servo-assisted position-feedback mechanism is presented. The mechanical position of the moveable part of the system is kept fixed thanks to a position-feedback loop that exploits a capacitive position sensor and two electrostatic force actuators. By adjusting specific loop parameters, the angle sensitivity can be finely tuned electrically. Experimental results show that the proposed system allows to tune the sensitivity up to 33.1 mV/deg, and to obtain a maximum angle resolution of 40 mdeg.

International audience; A Piezoelectric Micro Electro-Mechanical System (Piezo-MEMS) acoustic transducer able to electrically tune the resonant frequency in receiver and transmitter modes is reported. The proposed 6×6mm squared diaphragm has been simulated by a 2D finite element model, fabricated, and measured. A DC bias voltage applied to the piezoelectric layer produces a controllable stress, thus leading to a matching of the series and parallel resonant frequencies. This allows to increase performances when the transducer is operated as both transmitter and receiver. The resonance can be tuned in a range of ±70 Hz by a DC voltage of ±8 V with an estimated sensitivity of 8.87 Hz/V.

International audience; This work presents a MEMS device with Aluminum Nitride (AlN) piezoelectric actuators on a silicon suspended plate developed for driving mechanical vortexes in aqueous solution, and hence obtain centrifugation of fluids. Innovatively, the MEMS device has the capability to force ClockWise (CW) or CounterClockWise (CCW) rotations of a fluid drop placed in contact with the MEMS suspended plate. Experimental results show that CW and CCW rotations have been obtained using a 2-mm-diameter drop of water.This capability advantageously could allow the use of the proposed MEMS device for applications where drop centrifugation with different rotation directions can change the chemical or biological properties of the fluids.

This paper presents a contactless measurement system for a mixed array of resistive and capacitive sensors exploiting a low-frequency radio-frequency identification (RFID)-based approach. The system is composed of a reader unit which provides power to and exchanges measurement data with a battery-less sensor unit. The sensor unit is based on a transponder operating at 134.2 kHz and a microcontroller. The microcontroller sequentially measures the elements of the sensor array composed of n capacitive and m resistive sensors which share a common terminal. The adopted technique measures the charging time of a resistor&ndash, capacitor (RC) circuit, where the resistor or the capacitor can be either the sensing element or a reference component. With the proposed approach, the measured values of the resistive or capacitive elements of the sensor array are first-order independent from the supply voltage level. A prototype has been developed and experimentally tested with resistive elements in the range 400 kΩ&ndash, 1.2 MΩ and capacitive elements in the range 200 pF&ndash, 1.2 nF showing measurement resolution values of 1 kΩ and 5 pF, respectively. Operative distances up to 3 cm have been achieved, with readings taken faster than one element of the array per second.

This article deals with modeling and characterization of a thermo-magnetically activated piezoelectric generator, we provide breakthrough in addressing the modeling issue of such power generators by reporting equivalent electrical circuit and its characterization. The circuit is based on the standard Butterworth van Dyke model. It includes mechanical, dielectric, and piezoelectric losses by using complex elastic, dielectric and piezoelectric constants that are obtained through fitting measured admittance of piezoelectric transducer. The model is developed of lumped circuits elements and it is valid under both parallel and series wired bimorph connection. Experimental and simulation results show good agreement, within 10.2% (for maximum output voltage), on the generator behavior for both the rectifier circuits implemented.

Auxetic structures are attracting increasing interest because of their large variety of applications at both the macro and micro scales. In this work, an innovative auxetic unit cell is presented, numerically studied, fabricated at the microscale and experimentally tested. Its versatility in terms of stiffness and Poisson's ratio and its compatibility with commercial Micro Electro-Mechanical Systems (MEMS) fabrication processes suggest applications such as motion conversion and amplification mechanism in MEMS devices or on-chip biaxial tests. A MEMS auxetic and periodic structure exhibiting an overall equivalent Poisson's ratio lower than -1 is then proposed. The static and dynamic behaviours are studied both numerically and through a simplified analytical model. Experimental results confirm the simulated behaviour of the structure thus verifying the first MEMS auxetic structure with electrostatic actuation and capacitive readout.

Piezoelectric films fabricated with lead-free piezoelectric inks by means of a mask-less Direct-Writing (DW) technique are presented. A lead-free piezoelectric material, K 0.5 Na 0.5 NbO 3-δ (KNN), has been produced via Solid State Reaction (SSR) and Molten Citrate (MC) route in order to improve the microstructural properties of powders. The slurry composition and rheology have been optimized in order to obtain inks with physical properties compatible with the DW technique and layers with enhanced mechanical and piezoelectric properties. Experimental results obtained with pellets and films deposited on alumina substrates demonstrate the piezoelectric properties of the fabricated devices. The developed direct-writing technique will be implemented for the realization of precise patterns of piezoelectric sensors or actuators inside microsystems, without the requirement of manufacture expensive masks.

In this work, a contactless interrogation via electromagnetic coupling based on time-gated techniques has been proposed for Quartz Crystal Resonator (QCR) to investigate on liquid solution microdroplets. The sensing of the resonator response is innovatively based on a heterodyne demodulation and autocorrelation analysis, providing high performances yet avoiding the use of expensive instruments and allowing to estimate both the sensor damped resonant frequency and the quality factor Q. The system works with interrogation distances up to few centimeters and has been experimentally validated by loading the QCR with microdroplets of different liquid microsamples.

Contactless readout of passive LC sensors composed of a capacitance sensor connected to a coil can be performed through an electromagnetically coupled readout coil set at distance d. Resonant frequency fs and Q-factor QS of the LC sensor can be extracted from the measurement of the impedance at the readout coil by using a technique theoretically independent of d. This work investigates the effects on the measurement accuracy due to the unavoidable parasitic capacitance CP in parallel to the readout coil, which makes the measured values of fs and QS dependent on d. Numerical analysis and experimental tests confirm such dependence. To overcome this limitation, a novel electronic circuit topology for the compensation of CP is proposed. The experimental results on assembled prototypes show that for a LC sensor with fs ≈ 5.48 MHz a variation of less than 200 ppm across an interrogation distance between 2 and 18 mm is achieved with the proposed compensation circuit.

A Current-Mode (CM) TransImpedance Amplifier (TIA) based on Second Generation Current Conveyors (CCIIs) for capacitive microsensor measurements is presented. The designed electronic interface performs a capacitance-to-voltage conversion using 3 CCIIs and 3 resistors exploiting a synchronous-demodulation technique to improve the overall detection sensitivity and resolution of the system. A CM-TIA solution designed at transistor level in AMS0.35 µm integrated CMOS technology with a power consumption lower than 900 µW is proposed. Experimental results obtained with a board-level prototype show linear behavior of the proposed interface circuit with a resolution up to 34.5 fF and a sensitivity up to 223 mV/nF, confirming the theoretical expectations.

In this work, the ability of an impedance sensor to rapidly detect bacteria growth in a culture medium has been investigated. A test configuration with two electrodes embedded in a Petri dish has been proposed. Impedances corresponding to a sterile medium and one inoculated with bacteria have been measured and compared during the growth process. Remarkable differences have been observed in the time evolutions of the two behaviors. In particular, impedance behavior measured at 100 Hz allows such achievement after only 1 h. An equivalent circuit of the measured impedances have been proposed. Considerations regarding the effects of the bacteria growth on the components describing the electrode-medium interface have been reported. The variations of these elements have been identified as the more significant for the early detection. From these promising results, improved configurations consisting of a matrix of electrodes can be proposed for localized and rapid detection by means of automated analysis systems.

In this work we investigated high viscous oil in water dispersions (Do/w) in pipe. The experiments are performed in a 22.8-mm-id 9-m-long horizontal glass pipe using a high viscous oil (density of 886 kg/m 3 and viscosity of 900 mPa s) and tap water as test fluids. Pressure gradients are collected; hold-up data are measured using the quick-closing-valves technique (QCV) and a capacitance sensor, specifically optimized for dispersed flows detection. A new two-fluid model for liquid–liquid dispersed pipe flow to predict hold-up, pressure gradient, and the slip ratio between the liquid phases is presented. The experimental data are compared at first with homogeneous model predictions. Then the presented two-fluid model is validated against experimental data of this work and against experimental data taken from the literature showing a good agreement. The predicted and measured slip ratio is grater than unity for all oil–water dispersions investigated.

A passive inductive/capacitive (LC) sensor label based on a coil and a capacitive sensor embedded in a flexible substrate, combined with a novel electronic technique for contactless interrogation is presented. The interrogation technique is based on the time-gated approach via electromagnetic coupling using a primary coil to periodically excite the passive LC sensor label. When the excitation to the primary coil is switched off, the damped response of the passive LC label is detected. As a fundamental advantage, this approach ensures that the readout frequency is to first order independent of the interrogation distance between the primary coil and the coil on the sensor label. The sensor label has been tested with reference capacitors and the experimental results show the possibility to operate with interrogation distances up to few centimeters. In addition, applications of the sensor label coupled with a conductive plane as either thickness or compressive force sensor have been tested. The obtained results show the possibility to detect thickness in a range of few millimeters with sensitivity up to −260 kHz/mm, and force with a sensitivity of 3.57 kHz/N across the 0–10 N range.

The possibility to generate acoustic modes based on FPWs (Flexural Plate Waves) in a generic non-piezoelectric substrate for microfludic applications by means of piezoelectric actuators has been explored and described in this paper. The FPW acoustic modes are generated by means of actuators made of Lead Zirconate Titanate (PZT) layers with InterDigital Transducers (IDTs) screen-printed on alumina (Al2O3) substrate. The experimental results show that, by exciting the resonances of the actuators, circular vortex rotations are obtained in a fluid drop placed on the substrate between the IDTs. Micrometric particles dispersed in the drop allow to demonstrate that standing waves can be generated in the liquid obtaining particle accumulation along circular lines. These results suggest the possibility to employ the proposed actuators for fluid mixing and controlled positioning of dispersed particles.

A technique for contactless electromagnetic interrogation of AT-cut quartz piezoelectric resonator sensors is proposed based on a primary coil electromagnetically air-coupled to a secondary coil connected to the electrodes of the resonator. The interrogation technique periodically switches between interleaved excitation and detection phases. During the excitation phase, the resonator is set into vibration by a driving voltage applied to the primary coil, whereas in the detection phase, the excitation signal is turned off and the transient decaying response of the resonator is sensed without contact by measuring the voltage induced back across the primary coil. This approach ensures that the readout frequency of the sensor signal is to a first order approximation independent of the interrogation distance between the primary and secondary coils. A detailed theoretical analysis of the interrogation principle based on a lumped-element equivalent circuit is presented. The analysis has been experimentally validated on a 4.432 MHz AT-cut quartz crystal resonator, demonstrating the accurate readout of the series resonant frequency and quality factor over an interrogation distance of up to 2 cm. As an application, the technique has been applied to the measurement of liquid microdroplets deposited on a 4.8 MHz AT-cut quartz crystal. More generally, the proposed technique can be exploited for the measurement of any physical or chemical quantities affecting the resonant response of quartz resonator sensors.

In this paper the possibility to generate acoustic waves such as FPW (Flexural Plate Wave) for fluid and particle manipulation by piezoelectric actuators applied on non-piezoelectric substrates is explored. A test device with two Lead Zirconate Titanate (PZT) actuators deposited on an alumina (Al2O3) substrate by screen printing technique is presented. The experimental results show that, by exciting the actuators at their resonance frequencies, FPW modes are generated in the substrate. Circular vortex rotations are obtained in a fluid drop placed on the substrate by exciting a single actuator. In addition, micrometric particles dispersed in the drop allow to demonstrate that particle accumulation along circular lines is obtained by exciting both the actuators. These results suggest the possibility to employ the proposed actuators for fluid mixing and controlled positioning of dispersed particles.

This paper presents a capacitive Micro ElectroMechanical System (MEMS) force sensor coupled with a properly-designed interface circuit based on Direct Digital Synthesizer (DDS) that allows tunable sensitivity exploiting an electrical servo-assisted position-feedback mechanism. The position of the probe tip is kept fixed exploiting a feedback loop that includes a variable-gap capacitive position sensor and a pair of variable-area electrostatic actuators. Signals provided by the DDS are used to excite and read the capacitive position sensor and to perform a synchronous demodulation used for the position control and the electrostatic compensation of the external applied force Fext. By adjusting specific loop parameters, the force sensitivity and the tip working point can be finely tuned electrically. Experimental results show that the proposed system is able to measure the applied force in nanonewton range, making the system promising for measuring forces generated by living biological cells.

A microfabricated silicon device can locally measure the intensity of an electric field without any significant field distortion.

A planar ThermoElectric Generator (TEG) containing five thermocouples based on nanostructured metal-oxide elements wired electrically in series and thermally in parallel has been designed and fabricated. The thermoelectric elements consist of ZnO ( n -type) and CuO ( p -type) bundles of quasi-monodimensional nanowires deposited utilizing shadow masks. The TEG has been experimentally characterized, confirming feasibility of fabricating planar thermoelectric devices based on metal-oxide nanowires with the future aim to powering portable electronics and autonomous sensors and microsystems.

A microfluidic sensor for detection of cells flowing in a microchannel is presented. The sensor consists of a PDMS (PolyDiMethylSiloxane) layer with two planar microreservoirs connected by a microchannel. The bottom sides of the microreservoirs are faced to two sensing electrodes realized on a PCB (Printed Circuit Board). A noncontact measurement is ensured by an insulator layer between the electrodes and the fluid. Particles flowing in the microchannel cause changes in the conductivity of the narrow path formed by the fluid, producing variations in the impedance between the electrodes. A tailored electronic interface based on a DDS (Direct Digital Synthesis) device is proposed to measure the impedance variations. In the experimental tests, the cell flow is detected by changes in the effective capacitance and conductance between electrodes. These preliminary results are promising for biological measurements such as counting and sizing of cells in different matrices.

A microfluidic device with embedded capacitive sensing is proposed. The purpose of the device is fluid discrimination and characterization in a microchannel on the basis of the dielectric permittivity. The device is fabricated in a hybrid cost-effective technology which innovatively combines PDMS (PolyDiMethylSiloxane) soft photolithography and screen printing techniques. A microchannel, realized in a PDMS layer, is placed in the field of a sensing capacitor formed by electrodes screen-printed on a glass substrate. Fluids inside the microchannel affect the capacitance, that is in the order of femtofarads, which is measured by a tailored electronic interface system. The electronic system features a sensitivity of 100 V/pF and a resolution threshold of 0.06 fF. Experimental results obtained for different fluids injected in the microchannel demonstrate the ability of the system to discriminate the fluids and to estimate their dielectric permittivity both as pure samples and as mixtures at varying solute fractions. This makes the device a promising building block for fluid mixing monitoring in microfluidic systems.

Capacitance sensors are widely used in multiphase flows, for example, to estimate the hold-up in a given section of the pipe, taking advantage of the different permittivity values of the two liquids. The estimation is obtained by capacitance measurements between two electrodes, flush mounted on the external surface of the experimental pipe. Usually, capacitance sensors are used to investigate flows with non-conductive fluids, but they have the possibility to work also when, for example, conductive water is used. However, the capacitance technique applied to conductive fluids develops some issues. In this paper, we present a concave electrode sensor system developed for oil/conductive-water flows. A key contribution is to propose a modelization to the problem of capacitive sensing in presence of conductive fluids, based on a new approach to the parasitic couplings outside the measurement section. Thanks to this modelization, we propose a new design method for the working frequency and the electrode measurement head.

Coil-coupled passive sensors can be interrogated without contact, exploiting the magnetic coupling between two coils forming a telemetric proximity link. A primary coil connected to the interface circuit forms the readout unit, while a passive sensor connected to a secondary coil forms the sensor unit. This work is focused on the interrogation of sensor units based on resonance, denoted as resonant sensor units, in which the readout signals are the resonant frequency and, possibly, the quality factor. Specifically, capacitive and electromechanical piezoelectric resonator sensor units are considered. Two interrogation techniques, namely a frequency-domain technique and a time-domain technique, have been analyzed, that are theoretically independent of the coupling between the coils which, in turn, ensure that the sensor readings are not affected by the interrogation distance. However, it is shown that the unavoidable parasitic capacitance in parallel to the readout coil introduces, for both techniques, an undesired dependence of the readings on the interrogation distance. This effect is especially marked for capacitance sensor units. A compensation circuit is innovatively proposed to counteract the effects of the parasitic input capacitance, and advantageously obtain distance-independent readings in real operating conditions. Experimental tests on a coil-coupled capacitance sensor with resonance at 5.45 MHz have shown a deviation within 1.5 kHz, i.e., 300 ppm, for interrogation distances of up to 18 mm. For the same distance range, with a coil-coupled quartz crystal resonator with a mechanical resonant frequency of 4.432 MHz, variations of less than 1.8 Hz, i.e., 0.5 ppm, have been obtained.

Pyroelectric cells based on fabricated screen-printed PZT and commercial PVDF films are proposed as thermal energy harvesting sources in order to supply low-power autonomous sensors. The cells are electrically modelled as a current source in parallel with output impedance. Heating and cooling temperature fluctuations generated by air currents were applied to the pyroelectric converters. The generated currents and charges were respectively in the order of 10−7 A and 10−5 C for temperature fluctuations from 300K to 360K in a time period of the order of 100 s, which agrees with the theoretical model. Parallel association of cells increased the generated current. The dependence of the generated current on relevant technological parameters has been also characterized. Finally, current from cyclic temperature fluctuations was rectified and stored in a 1 F load capacitor. Energies up to 0.5 mJ have been achieved, enough to power typical autonomous sensor nodes during a measurement and transmission cycle.

A principle for contactless interrogation of passive micromechanical resonator sensors is proposed. The principle exploits an external primary coil electromagnetically air-coupled to a secondary coil which is connected to a conductive path on the resonator. The interrogation periodically switches between interleaved excitation and detection phases. During the excitation phase the resonator is driven into vibrations, while in the detection phase the excitation signal is turned off and the decaying oscillations are contactless sensed. The principle advantageously avoids magnetic properties required to the resonator, thereby ensuring compatibility with standard silicon microfabrication processes. The principle has been implemented on a MEMS SOI microcantilever resonator sensor with mechanical resonant frequency of 10.186 kHz and has been demonstrated to work over a distance of up to 1 cm. Tests based on the deposition and evaporation of a water droplet have demonstrated the capability to sense physical and chemical quantities which affect either the resonant frequency or the quality factor of the resonator.

Power harvesters from mechanical vibrations are commonly linear mechanical resonators that are most effective when excited at resonance. Differently, under wideband vibrations, linear converters are suboptimal. A nonlinear converter is here proposed that implements nonlinearity and bistability by employing a single external magnet, in order to improve conversion effectiveness while simplifying device fabrication. The converter is composed of a piezoelectric bimorph on a ferromagnetic cantilever. The fabrication technology is based on the screen printing of a PZT low-curing-temperature paste on harmonic steel substrate. The ferromagnetic cantilever converter, under proper coupling with the external magnet, bounces between two stable states when excited by random vibrations and generates an electric output via the piezoelectric effect. According to theoretical predictions, when bistable behaviour is present, experimental results demonstrate an improvement of about 400% of the rms voltage generated by the converter with respect to the linear case.

An electromagnetic contactless excitation principle is presented to induce mechanical vibrations on miniaturized electrically conductive resonant structures to be used as passive sensors. An external coil arrangement generates a time-varying magnetic field which induces eddy currents on the structure surface. The interaction between the eddy currents and the magnetic field causes forces which can set the structure into vibration. The principle avoids any contact to the resonator structure to inject current and only requires the structure to be electrically conductive, without the need for specific magnetic properties. The principle is attractive for the development of passive sensors operating in environments with limited accessibility or incompatible with active electronics. A mathematical model of the excitation principle has been derived and has been supported by means of finite-element simulations. Experimental demonstration of the excitation principle has been obtained on cantilever and a clamped-clamped beam miniaturized conductive structures used as resonators. The readout of the vibrations has been performed by either piezoelectric and optical methods.

In some specific applications, the measuring environment can have characteristics unsuitable for the correct working of the electronics, because it is not possible to connect the sensitive element to the conditioning electronics by standard cables or by a radiofrequency link. A possible solution can be a contact-less activation of a passive sensor through a magnetic field. The technique proposed here can be applied to resonant microsensors obtained through a microelectromechanical-system (MEMS) technology based, for example, on a standard CMOS process without any magnetic layers required. A conductive and non-magnetic cantilever, located in a time-variable magnetic field, is brought into resonance thanks to the interaction between the eddy currents in the cantilever and the external magnetic field. In order to test this effect for resonant sensors, an experimental set-up has been built. A piezoelectric bimorph covered by two aluminium sheets is used as cantilever: the aluminium sheets are conductive and non-magnetic layers, while the piezoelectric is only used to detect the induced vibrations. Experimental results demonstrate that, when the time-variable magnetic field is applied, resonant vibrations are induced and measured by the piezoelectric cantilever.

This paper presents a Micro Electro-Mechanical System (MEMS) that performs electrostatic force actuation and capacitive microdisplacement sensing in the same chip. By driving the actuator with a given voltage, a known force can be applied to a microsample under test by using a silicon probe tip, while the obtained displacement is measured. This allows to extract the mechanical properties of the microsample entirely on chip, and to derive its force-displacement curve without external equipment. The proposed device is intended for mechanobiology experiments, where the microsample is made of biological tissues or cells. The device generates a force in the order of few micronewtons and a maximum displacement of 1.8 μm can be measured.

In this work authors present two low-cost nonlinear devices for vibrational energy harvesting which are able to convert low frequency mechanical vibrations into electrical energy. The two developed solutions exploit the advantages of a bistable device in a Snap-Through-Buckling (STB) configuration and a piezoelectric mechanical to electrical conversion mechanism. In fact it has been demonstrated that bistable systems, under the proper conditions, can provide better performances, compared to linear resonant oscillators, in terms of the amount of energy extracted from wide spectrum vibrations.

This paper presents three MEMS platforms that exhibit multiple thermal sensitivities and multi-frequency capabilities. Multiple sensors with a variety of operating frequencies and thermal sensitivities can co-exist in the same device wafer. Aluminum nitride is the active layer of the three platforms. The impact of stack and substrate modifications on the performance of test devices is discussed as well. To test the platforms' performance, temperature sensors are realized using Lamb-acoustic-wave micro-electro-mechanical (MEMS) resonators, each one featuring a different thermal coefficient of frequency that scales with frequency. Resonators designed for frequencies between 200 MHz to 1.5 GHz operate at their first symmetric mode (S0) and feature first-order TCFs in the range from −12 up to −30 ppm °C−1 depending on the frequency and design. Furthermore, TCFs of devices can be tailored to get smaller values through process variations. The platforms exhibit high electromechanical performance, with quality factors in excess of 1500 and maximum effective coupling coefficient of 6.43% for radio frequency (RF) applications above 1 GHz.

A novel oscillator circuit with automatic capacitance compensation (ACC) capability has been coupled with quartz-crystal-microbalance (QCM) sensors coated with quinoxaline- and pyrazine-bridged cavitands to detect aromatic and chlorinated compounds in water. With double-side immersed 10-MHz crystals coated with the quinoxaline cavitand, the detection of toluene in deionized water was possible down to concentrations of a few parts per million. The ACC oscillator advantageously provides the simultaneous measurement of the sensor resonant frequency, damping, and value of the compensated parallel capacitance. This enabled observing that the analyte sorption in the cavitand coating not only brings about a mass uptake but also an increase of losses and, apparently, a rise in the coating average permittivity.

The aim of this work is the development of vapor detectors formed from composites of conductive carbon black and insulating organic multifunctional polymers having metal ions complexing ability. The new materials are tailored to produce increased sensitivity toward specific classes of analyte vapors. For comparison purpose, poly(vinyl chloride) (PVC) with di(2-ethylhexyl)phthalate (DOP), a traditional low molecular weight plasticizer, is used as representative of the behavior of a traditional composite vapor detector. Resonant frequency shift of a quartz crystal microbalance (QCM) and dc resistance measurements have been performed simultaneously on polymer–carbon black composite materials. The proposed materials showed an enhanced sensitivity upon exposure to acetic acid and amines vapors; the performances of our systems are 103 times higher than those of a traditional composite vapor detector. Moreover the extent of such responses is beyond that expected by mass uptake upon exposure to the same vapors and cannot be attributed solely to differences in polymer/gas partition coefficients. In this respect, several different chemical factors determine the dc electrical response of this system: in our opinion changes in polymer conformation during the adsorption process also play a significant role.

In order to perform the electrical characterisation of the electrolyte thick (about 100 μm) films, layers of La0.83Sr 0.17Ga0.83Mg0.17O2.83 (LSGM) were sandwiched between a pellet and a film of La0.83Sr 0.2MnO3 (LSM). Both LSGM and LSM coatings were deposited on the porous LSM sintered substrate one after the other by screen printing technique; the proper thermal treatment followed each deposition process. The average grain size of the LSGM films was about 3 μm. The electrolyte and the electrode powders were prepared following solgel and solid-state route, respectively. Electrical characterisation was carried out by the complex impedance spectroscopy (IS) technique in air and in the temperature range 300-800°C. The results were compared with those previously obtained on pellets, in the same operating condition. The film and the pellet show about the same value of the bulk conductivity, while total electrical resistivity of the former is two orders of magnitude higher than that of the latter. The large difference between the two resistivity values is due to the high grain boundary contribution of the film, which may be accounted for by either the smaller average grain size of the LSGM layer compared to those of the pellets (on average, about 25 μm) or for the Mn cations diffusion into the electrolyte material at the LSGM/LSM interface; experimental evidences would suggest the latter. © 2004 Elsevier B.V. All rights reserved.

The deposition of diamond films on silicon substrate by MWPECVD is described and microstructural characteristics of the obtained films are reported. The resistive and piezoresistive properties of the diamond-on-silicon films have been measured beyond 200 °C by means of a purposely developed apparatus, and experimental results are reported. The piezoresistive properties at high temperature are exploited in the development of a micromachined pressure sensor capable of operating at up to 350–380 °C. A dedicated signal-conditioning electronic circuit is being designed and its functioning principle is here described.

This paper presents the design, fabrication, and experimental characterization of a pyroelectric sensor array made by 8/spl times/8 pixels of PZT screen printed on alumina substrate. The electrodes are configured as eight columns and eight rows evenly spaced, whose respective crossings form the 64 pixels of the array. When an amplitude-modulated light emitting diode (LED) is placed in front of the array and moved in the XY plane parallel to the array surface, the array and the LED, respectively, work as the reference element and the contactless cursor of a biaxial position sensor. By means of a proper method of readout and processing of the pyroelectric signals, a continuous and linear dependence of the output voltages on XY-position of the LED can be obtained. The system intrinsically rejects background vibrations and microphonics. The configuration can be easily scaled to a larger number of pixels, and migrated to other manufacturing technologies.

A technique for contactless electromagnetic interrogation of quartz resonator sensors is proposed and validated. The technique is based on the separation in time of the excitation and detection phases, exploiting the sensing of the transient response of the resonator. Contactless operation is achieved by means of electromagnetic coupling between spiral planar coils connected to the interrogation circuit and the sensor. The typical operating frequencies of quartz resonators in the megahertz range limit the working range to short distances. Analytical modeling and numerical and finite element simulation of the geometry of the coils have allowed to extend working operating distances up to 10 cm.