Electromechanical Sensors Research Articles

Growth and characterization of horizontally suspended CNTs across TiN electrode gaps

A technique is proposed to grow horizontal carbon nanotubes (CNTs) bridgingmetal electrodes and to assess their electrical properties. A test structure wasutilized that allows for selective electrochemical sidewall catalyst placement. Theselectivity of the technique is based on the connection of the desired metal electrodesto the silicon substrate where the potential for electrochemical depositionwas applied. Control over the Ni catalyst size (15–30 nm) and density (up to3 × 1011 particles cm − 2) is demonstrated. Horizontal CNTs with controlled diameter and densitywere obtained by CVD growth perpendicular to the sidewalls of patternedTiN electrode structures. Electrode gaps with spacings from 200 nm up to5 µm could be bridged by both direct CNT–electrode contact and CNT–CNT entanglement. TheTiN–CNT–TiN and TiN–CNT–CNT–TiN bridges were electrically characterizedwithout any further post-growth contacting. Resistance values as low as40 Ω were measured for the smallest gap spacing and depended mainly on the number andconfiguration of the CNT bridges. The proposed method could be implemented forCNT-based horizontal interconnections and be a route to make different nanoelectronicdevices such as chemical and electromechanical sensors.

Ionic Polymer Transducers in sensing: the streaming potential hypothesis

Accurate sensing of mechanical strains in civil structures is critical for optimizing structure reliability and lifetime. For instance, combined with intelligent control systems, electromechanical sensor output feedback has the potential to be employed for nondestructive damage evaluation. Application of Ionic Polymer Transducers (IPTs) represents a relatively new sensing approach with more than an order of magnitude higher sensitivity than traditional piezoelectric sensors. The primary reason this sensor has not been widely used to date is an inadequate understanding of the physics responsible for IPT sensing. This paper presents models and experiments defending the hypothesis of a streaming potential sensing mechanism.

MEMS 가속도계를 적용한 ELT 시스템 개발과 검증

ELT(Emergency Locator Transmitter) is used to send distress signal in the event of an aircraft crash. It is very useful but the ELT may transmit wrong signal caused by misjudging between crash and hard-landing. The reason of this problem is the low accuracy of the mechanical G-switch currently in use. To improve the ELT, we developed an ELT system using the MEMS(Micro Electro-Mechanical Sensor) accelerometer. The ELT system consists of acceleration data acquisition/analysis system, program of crash recognition, and GPS receiving system for the position information of an aircraft crash site. A free-drop table was developed for verification of the ELT system. The free-drop table was designed to replicate the acceleration and the pulse duration of the hard landing and the crash. By using the free-drop table, we showed that the ELT system performed well.

Dispersion curves of shear horizontal wave surface velocities in multilayer piezoelectric systems

A precise knowledge of the frequency responses, velocity dispersion, and distinct vibration modes in multilayer piezoelectric structures would permit the optimization of new designs for electromechanical sensor, actuator, and surface acoustic wave (SAW) filter devices under broad and narrow band conditions. In this paper, the singular-value decomposition technique, combined with the global matrix method and scaling procedure, are applied for studying the solutions of shear stationary waves in symmetric multilayer composite piezoelectric systems. This approach eliminates numerical instabilities sometimes appearing in the analysis of this type of piezoelectric systems, by using a multiple scaling strategy in the global matrix processing. The dispersion curves of the surface velocities, obtained by application of the proposed approach, have shown the presence of clearly separated odd and even bands in such a type of piezoelectric devices, which is explained by considering the eigenstates of the system. Details of this bands pattern are calculated and analyzed.

Modelling and testing of a MEMS accelerometer controlled and read-out beyond the pull-in instability limit

Electrostatic forces caused by the readout circuit and parasitic capacitances have much relevance in the scaling considerations of Micro and Nano electro mechanical (M/NEMS) parallel-plate motion sensors. The reduction of minimum geometrical dimensions (spring width, air gap), aimed at an improvement of the sensitivity/area ratio, is indeed limited by the pull-in instability determined by the electrostatic attraction between parallel plates. In this paper it is presented a compact MEMS accelerometer built in the ST Microelectronics ThELMA technology, together with a 0.35μm CMOS switched-capacitor circuit, suitably designed to avoid the pull-in. In particular we focus on the model of the MEMS, written in a Hardware Description Language file to be used directly in the VLSI circuit simulator. Although the MEMS is unstable at the chosen biasing conditions when read-out at fixed voltage, the experimental results show that the closed-loop circuit allows the biasing beyond the pull-in voltage, in good agreement with the simulation prediction. The sensing range is larger than ±9 g with a resolution of 2mg/Hz.

Cantilever biosensors in drug discovery

Importance of the field: There is a growing need for inexpensive and highly sensitive methods in high-throughput format for measuring drug–target interactions. Cantilever biosensors are ultra-high sensitive electromechanical sensors that have been successfully used for label-free detection of a large number of biological entities. They are emerging as a technology that appears attractive for high-throughput drug discovery applications. Therefore, a brief description of this technology is provided here.Areas covered in this review: The objective of this review is to present an overview of the development in cantilever biosensor field reported to date and examine applications of cantilever biosensors for biomolecular interaction characterization and drug discovery. The subareas included in the review are: cantilever measurement principles, various interactions measured such as DNA–DNA, protein–protein, membrane protein–ligand and DNA–protein. Discussion on biomarker detection is also included.What the reader will gain: We analyze the recent publications on cantilever biosensors with an emphasis on drug discovery and biomarker detection. The reader will become informed on the detection sensitivity and limit of detection achieved to date. A description of ongoing commercial activity that is likely to result in a practical instrument for researchers is also included. Technical issues that concern current researchers in the field of cantilever biosensors are also summarized.Take home message: The cantilever biosensors provide an extraordinarily sensitive method for binding affinity measurement using label-free reagents. They can be fabricated in array format for high-throughput applications using semiconductor manufacturing techniques. When they become commercially available in future, it is anticipated that they will be cost-competitive and easy to use in a research bioanalytical laboratory.

Ballistocardiogaphic studies with acceleration and electromechanical film sensors

The purpose of this research is to demonstrate and compare the utilization of electromechanical film (EMFi) and two acceleration sensors, ADXL202 and MXA2500U, for ballistocardiographic (BCG) and pulse transit time (PTT) studies. We have constructed a mobile physiological measurement station including amplifiers and a data collection system to record the previously mentioned signals and an electrocardiogram signal. Various versions of the measuring systems used in BCG studies in the past are also presented and evaluated. We have showed the ability of the EMFi sensor to define the elastic properties of the cardiovascular system and to ensure the functionality of the proposed instrumentation in different physiological loading conditions, before and after exercise and sauna bath. The EMFi sensor provided a BCG signal of good quality in the study of the human heart and function of the cardiovascular system with different measurement configurations. EMFi BCG measurements provided accurate and repeatable results for the different components of the heart cycle. In multiple-channel EMFi measurements, the carotid and limb pulse signals acquired were detailed and distinctive, allowing accurate PTT measurements. Changes in blood pressure were clearly observed and easily determined with EMFi sensor strips in pulse wave velocity (PWV) measurements. In conclusion, the configuration of the constructed device provided reliable measurements of the electrocardiogram, BCG, heart sound, and carotid and ankle pulse wave signals. Attached EMFi sensor strips on the neck and limbs yield completely new applications of the EMFi sensors aside from the conventional seat and supine recordings. Higher sensitivity, ease of utilization, and minimum discomfort of the EMFi sensor compared with acceleration sensors strengthen the status of the EMFi sensor for accurate and reliable BCG and PWV measurements, providing novel evaluation of the elastic properties of the cardiovascular system.

Electromechanical Properties of Suspended Graphene Nanoribbons

Graphene nanoribbons present diverse electronic properties ranging from semiconducting to half-metallic, depending on their geometry, dimensions, and chemical composition. Here we present a route to control these properties via externally applied mechanical deformations. Using state-of-the-art density functional theory calculations combined with classical elasticity theory considerations, we find a remarkable Young's modulus value of approximately 7 TPa for ultranarrow graphene strips and a pronounced electromechanical response toward bending and torsional deformations. Given the current advances in the synthesis of nanoscale graphene derivatives, our predictions can be experimentally verified opening the way to the design and fabrication of miniature electromechanical sensors and devices based on ultranarrow graphene nanoribbons.

The dynamics of polymerized carbon nanotubes in semiconductor polymer electronics andelectro-mechanical sensing

Polymerized carbon nanotubes (CNTs) are promising materials for polymer-basedelectronics and electro-mechanical sensors. The advantage of having a polymernanolayer on CNTs widens the scope for functionalizing it in various ways forpolymer electronic devices. However, in this paper, we show for the first timeexperimentally that, due to a resistive polymer layer having carbon nanoparticle inclusionsand polymerized carbon nanotubes, an interesting dynamics can be exploited.We first show analytically that the relative change in the resistance of a singleisolated semiconductive nanotube is directly proportional to the axial and torsionaldynamic strains, when the strains are small, whereas, in polymerized CNTs, theviscoelasticity of the polymer and its effective electrical polarization give rise to nonlineareffects as a function of frequency and bias voltage. A simplified formula is derivedto account for these effects and validated in the light of experimental results.CNT–polymer-based channels have been fabricated on a PZT substrate. Strainsensing performance of such a one-dimensional channel structure is reported. For asingle frequency modulated sine pulse as input, which is common in elastic andacoustic wave-based diagnostics, imaging, microwave devices, energy harvesting,etc, the performance of the fabricated channel has been found to be promising.

Fast growth responses of barley and durum wheat plants to NaCl- and PEG-treatment: resolving the relative contributions of water deficiency and ion toxicity

Effects of adding osmotically comparable concentrations of PEG and NaCl to nutrient solution were studied in 1-week-old durum wheat (Triticum durum Desf., salt-sensitive) and barley (Hordeum vulgare L., more salt tolerant). Both treatments arrested leaf extension immediately, followed by partial recovery within 40–60 min. Similarities and differences were observed between the responses of the two species and between the two treatments. Typically, PEG-treatment increased leaf extensibility of both barley and wheat as measured by changes in leaf extension rate monitored by an electromechanical sensor to which a stretching counter-weight was added. In barley, NaCl-treatment increased extensibility in a similar way to PEG, but in wheat, extensibility did not change within 40 min of NaCl-treatment. The contrasting fast responses of wheat plants to NaCl and PEG treatments suggests that, unlike barley, wheat leaf extension was sensitive not only to osmotic effects of salinity, but also to ion toxicity. Thus, separate PEG- and NaCl-treatments enabled us to distinguish between ionic and osmotic effects and to show, for the first time, that ionic effects of salinity on leaf extension can commence after only short-term exposure (<1 h) in the case of a salt-sensitive species such as durum wheat.

Piezoresistive InGaAs/GaAs Nanosprings with Metal Connectors

This paper presents the fabrication, assembly, and characterization of piezoresistive nanosprings for creating nanoelectromechanical systems. The fabrication process is based on conventional microfabrication techniques to create a planar pattern in a 27nm thick, n-type InGaAs/GaAs bilayer that self-forms into three-dimensional structures during a wet etch release. As the nanosprings have lower doped thin and flexible layers, small metal pads have been attached to both sides for achieving stable ohmic contact with electrodes. Nanorobotic manipulation is applied to assemble the nanosprings between electrodes using electron-beam-induced deposition inside a scanning electron microscope, and the bridged nanosprings were then characterized for electromechanical properties. With their strong piezoresistive response, low stiffness, large-displacement capability, and excellent fatigue resistance, they are well-suited to function as sensing elements in high-resolution, large-range electromechanical sensors.

Extracting Piezoresistance in SiNWs using Thermal Induced Buckling of Micro-bridges

AbstractThe recent reports on giant piezoresistance effect in highly resistive silicon nanowires (SiNWs) have offer greater sensitivity in stress measurements. Despite enhanced sensitivity, the piezoresistance of highly conductive silicon are preferred as they are less prone to thermal noises and hence better accuracy. Here we report a thermal induced buckle micro-bridge technique to accurately characterize the temperature dependent piezoresistivity effect in SiNWs. Phosphorus doped &lt;110&gt; SiNWs with 50 nm width, 95 nm thickness and 100 μm length were encapsulated within SiO2 micro-bridges. The electrical measurement of both reference SiNWs and SiNWs at micro-bridges was carried out, followed by the optical profiling of the micro-bridges with embedded SiNWs. N-type SiNWs with doping of 1×1020 ion/cm3 exhibit a strong dependence on temperature with a piezoresistive coefficient that decreases by 22.5 % between 25 oC to 60 oC; whereas its bulk counterpart is independent of temperature across this range. The results demonstrated that thermal noises may be more detrimental to nano-scale electromechanical sensors than its bulk counterparts.

Highly sensitive strained AlN on Si(1 1 1) resonators

In this study, we report two methods to fabricate freestanding single-crystalline aluminium nitride micromechanical device structures on Si(1 1 1) substrates. A method based only on Si etching techniques is demonstrated, and the differences with the conventional process are detailed. The mechanical properties of the released AlN structures are characterized by resonance measurements and micro-Raman spectroscopy. An enhancement of the resonant frequency and quality factor of resonant structures, and thus the sensitivity, is proposed using epitaxial AlN. This high quality material, highly strained due to thermal mismatch with Si substrate, allows the fabrication of improved high sensitivity AlN-based micro/nano electro-mechanical systems and sensors.

Flexible Piezotronic Strain Sensor

Strain sensors based on individual ZnO piezoelectric fine-wires (PFWs; nanowires, microwires) have been fabricated by a simple, reliable, and cost-effective technique. The electromechanical sensor device consists of a single electrically connected PFW that is placed on the outer surface of a flexible polystyrene (PS) substrate and bonded at its two ends. The entire device is fully packaged by a polydimethylsiloxane (PDMS) thin layer. The PFW has Schottky contacts at its two ends but with distinctly different barrier heights. The I- V characteristic is highly sensitive to strain mainly due to the change in Schottky barrier height (SBH), which scales linear with strain. The change in SBH is suggested owing to the strain induced band structure change and piezoelectric effect. The experimental data can be well-described by the thermionic emission-diffusion model. A gauge factor of as high as 1250 has been demonstrated, which is 25% higher than the best gauge factor demonstrated for carbon nanotubes. The strain sensor developed here has applications in strain and stress measurements in cell biology, biomedical sciences, MEMS devices, structure monitoring, and more.

Damage detection in assembly fixtures using non-destructive electromechanical impedance sensors and multivariate statistics

Dimensional integrity of assembled products is a critical factor in defining product functionality and process productivity. It has been reported that fixture faults are one of the root causes of defective sheet metal assemblies. Therefore, integrating new sensor technologies into manufacturing process fixtures will have a direct impact on improving assembly system quality by helping to detect fixture faults faster. A piezoelectric impedance sensor combined with multivariate statistical process control (MSPC) is proposed to accurately monitor the structural integrity of locating fixtures. The new sensing and detection methodology reduces costs associated with production downtime due to faulty fixtures. MSPC is utilized due to its inherent advantages over current sensor monitoring techniques, mainly damage metrics. Previously used damage metrics fail to function properly if voltage or measurement variation is observed. Numerous false alarms result along with an inability to reference or calibrate a fixture to a healthy state. Introducing MSPC concepts and methodologies into piezoelectric fixture sensing systems decreases false alarms, enables healthy sensor state identification, and improves monitoring capabilities.

Thermoplastic elastomer/polyaniline blends: Evaluation of mechanical and electromechanical properties

Conducting polymer blends whose undiluted components have different properties are promising materials for several technological applications such as electromagnetic shielding, electrostatic charge dissipation, optoelectronic displays, chemical sensors, biosensors and electromechanical sensors. The aim of this study was to obtain and evaluate the electrical conductivity and electromechanical properties of a polystyrene- block-poly(ethylene- ran-butylene)- block-polystyrene copolymer (SEBS)/polyaniline doped with dodecylbenzenesulfonic acid (PAni.DBSA) blends. Electrically conductive elastomeric blends based on SEBS/PAni.DBSA were prepared through a solution casting method, at room temperature, after dissolving both components in toluene as a common solvent. SEBS/PAni.DBSA blends were also prepared through polymerization of aniline in the presence of SEBS solution, using a one-step in situ emulsion polymerization method. The protonation degree of the PAni.DBSA used in this study was determined from X-ray photoelectron spectroscopy (XPS) analysis by calculating the amount of different neutral and positive nitrogen species of the polyaniline chain from the properly curve-fitted N-1s core-level spectrum. The PAni.DBSA used to prepare solution casting blends had a 46% protonation degree, with almost all imine groups protonated and only a small amount of residual DBSA, as expected for an emeraldine salt. This protonation degree is responsible for the high conductivity (2.4 S cm −1) and good solubility of this conducting polymer in toluene. The protonation degree of PAni.DBSA in the blends analyzed was higher than that of undiluted PAni.DBSA, due to an additional protonation during the casting or in situ processes. The insulator–conductor transition was not as sharp as those found in carbon black conducting systems and the percolation threshold was lower than 20 wt.% of PAni.DBSA. Above 20 wt.% PAni.DBSA content, the emulsion-polymerized systems had higher volume conductivity values than the corresponding solution casting blends. The mechanical properties such as tensile strength, elastic modulus and elongation at break of SEBS/PAni.DBSA blends were dependent on the blend preparation method. Blends were also characterized by electromechanical properties and optical microscopy.

UWB and MEMS Based Indoor Navigation

Thanks to its physical characteristics, Ultra-wideband (UWB) is one of the most promising technologies for indoor pedestrian navigation. UWB radio localisation systems however experience multipath phenomena that decrease the precision and the reliability of the user's location. To cope with complex indoor environments, UWB radio signals are coupled with inertial measurements from Micro Electro Mechanical Sensors (MEMS) in an extended Kalman filter. Improved performances of the filter are presented and compared with reference trajectories and with pure inertial solutions. Only specific selection methods enable this improvement by detecting and removing outliers in the raw localisation data.

Sensor Self-diagnosis Using a Modified Impedance Model for Active Sensing-based Structural Health Monitoring

The active sensing methods using piezoelectric materials have been extensively investigated for the efficient use in structural health monitoring (SHM) applications. Relying on high frequency structural excitations, the methods showed the extreme sensitivity to minor defects in a structure. Recently, a sensor self-diagnostic procedure that performs in situ monitoring of the operational status of piezoelectric (PZT) active sensors and actuators in SHM applications has been proposed. In this investigation, previously developed impedance models were revisited in order to investigate the effects of sensor and/or bonding defects on the admittance measurement. New parameters for sensor quality assessment of a PZT and coupling degradation effects between a PZT and bonding layer were incorporated into the traditional electromechanical impedance model for better estimation of the electromechanical impedance signatures and sensor diagnostics. The feasibility of the modified impedance model for sensor self-diagnosis using the admittance measurements was demonstrated by a series of parametric studies using a simple example of PZT-driven single degree of freedom spring-mass-damper system. This paper summarizes the description of the proposed modified electromechanical impedance model, parametric studies for impedance-based sensor diagnostics, and several issues that can be used as a guideline for future investigation.

Design and Real Time Implementation of a Fuzzy Tuned H∞ Estimator in a Low Cost AHRS

In this paper a Fuzzy Tuned extended H∞ (FTH∞) estimator is designed and implemented in an Attitude Heading Reference System (AHRS), which is specialized to vehicular applications. In AHRS, 3-axis accelerometers are allotted to measure the earth's gravity field vector and then to update the roll and pitch angles obtained from gyros’ dynamic. Therefore, the AHRS on an accelerated vehicle will be affected by large disturbances. Additionally, in ground vehicles, the measurements of 3-axis magnetometers are corrupted by both soft and hard iron time varying disturbances. The FTH∞ estimator is an extended H∞*** filter in which only noise and attenuation bounds are tuned based on fuzzy linguistic if-then rules. The mentioned features make the estimator more reliable and suitable for hardware implementation. FTH∞ estimator relies on a consistent fuzzy combination of two change detection tests; namely, likelihood ratio and averaged norm error. Real-time implementation of new attitude-heading estimator is performed on a TMS320VC5416 Digital Signal Processor (DSP). Incorporating this powerful and small size DSP with micro electro mechanical inertial and resistive magnetic sensors leads to a low cost, small size and low power consumption AHRS. Performance of the AHRS was evaluated in Monte Carlo simulations of vehicle's attitude-headings. The FTH∞ estimator results in a superior performance compared to that of the extended H∞ estimator in simulation and real tests.

Analytical modeling of sandwich beam for piezoelectric bender elements

Piezoelectric bender elements are widely used as electromechanical sensors and actuators. Au analytical sandwich beam model for piezoelectric bender elements was developed based on the first-order shear deformation theory (FSDT), which assumes a single rotation angle for the whole cross-section and a quadratic distribution function for coupled electric potential in piezoelectric layers, and corrects the effect of transverse shear strain on the electric displacement integration. Free vibration analysis of simply-supported bender elements was carried out and the numerical results showed that, solutions of the present model for various thickness-to-length ratios are compared well with the exact two-dimensional solutions, which presents an efficient and accurate model for analyzing dynamic electromechanical responses of bender elements.