The structural health monitoring by piezoelectric wafer active sensor (PWAS) using electromechanical impedance method used for monitoring of structure. In present work impedance method of elasto-plastic beam structure is studied. In order to model the effect of a plastic in beam, the moment-curvature relationship for elasto-plastic region for loading and unloading is used. The finite difference method is used to discretize beam with piezoelectric. The piezoelectric actuator is modeled by equivalent moment. Then output current of piezoelectric sensor is calculated. Firstly, elastic modeling of beam is considered that this is leads to linear system equation. In linear system, time domain system equations are calculated and Fourier transform of current output obtained, and then impedance of PWAS in frequency domain is calculated. Secondly, the elasto-plastic of beam is modeled. This phenomenon leads to the nonlinear system equations. These nonlinear equations are solved using finite difference method for any harmonic voltage applied to actuator. Then impedance of PWAS is calculated. Two methods are used to detect elasto-plastic modeling on PWAS impedance. At the first, frequency response of elastic beam as intact model is compared with elasto-plastic results in a desired frequency range. Second, only frequency response of one harmonic is computed with its super-harmonics. Finally, the detection method of linear is compared with nonlinear model.

The thin film solar cells (TFSCs) are becoming more widely implemented due to their light weight, lower cost, and flexibility when compared to the conventional monocrystalline silicon wafer solar cells. Common materials used in the TFSCs today are amorphous silicon (a-Si) and microcrystalline silicon due to their abundance. However, these materials suffer from decreased absorption efficiency especially in the infrared range due to the sub-micron thickness of the absorber. Cadmium Telluride/Cadmium Sulfide (CdTe/CdS) is a promising candidate for TFSC material due to the near ideal, direct band gap of the CdTe, which allows it to be implemented without suffering greatly from decreased absorption efficiency. Nano-texturing is a widely researched and implemented way to increase the absorption of TFSCs. In this project, the wave optical analyses for the wavelength range of 300–1100 nm were executed using ANSYS High Frequency Structural Simulator (HFSS) to study the interaction of the geometric parameters of the nano-structures in CdS/CdTe TFSCs. A 3X3 factorial design of experiments was implemented to investigate 3 different levels of the height (H), diameter (D), and period (Pd) for a conical shaped nano-texture pattern and to study their effect on the absorption and the short circuit current (J sc ). A total of 27 different combinations were investigated. It was found that the model with H = 1000 nm, D = 1000 nm, and P/D = 1 had the highest J sc of 26.66 mA/cm 2 , a 29.14 % increase from the planar control cell. In addition, it was noted that when the P/D ratio is 1, an increase in both height and diameter will increase J sc . Finally, when the height was 200 nm, an increase in the diameter has little to no effect on J sc . These findings are important to TFSCs manufactures to better design the nano-texturing implemented in TFSCs.

In this paper, we have introduced a negative Dielectrophoresis based microfluidic system using a novel arrangement of microelectrodes to perform switching of micro objects. Both the experimental and numerical results are presented. Two sets of interdigitated electrodes, extending slightly into the microchannel from each sidewall, are embedded on the bottom of the microchannel. A finite element model in COMSOL Multiphysics 5.2a was developed to demonstrate switching of Red Blood Cells in the microchannel followed by multiple parametric studies to study the effect of several parameters on cell trajectories and optimize the design parameters. To verify numerical results, a PDMS-based microfluidic device on glass wafer was fabricated. The switching of Red Blood Cells in the microfluidic device with a single inlet and three outlets was also demonstrated.

In this study, a kind of meta-surface was designed for the improvement of nonlinear ultrasonic guided wave detection by creating bandgaps. It is composed of aluminum alloy cylinders arranged in a periodic pattern bounded on an aluminum plate. By artificially adjusting the height of the cylinders, the meta-surface can open up bandgaps over desired frequency ranges. Guided waves within the bandgap cannot propagate through the meta-surface and will be mechanically filtered out. To perform non-destructive evaluation (NDE) of structural components with fatigue cracks, the guided waves generated by a piezoelectric wafer active sensor (PWAS) propagate into the structure, interact with the crack, acquire nonlinear features, and are picked up by the receiver PWAS. In an ideal case, the waves excited by the transmitter PWAS should only contain signals at the fundamental frequency. However, due to the inherent nonlinearity of the electronic instrument, the generated signals are often mixed with weak superharmonic components. And these inherent higher harmonic signals will adversely affect the identifiability of nonlinear characteristics in the sensing signals. The bandgap mechanism and the wave vector dispersion relationship of the meta-surface are investigated using the modal analysis of a finite element model (FEM) by treating a unit structural cell with the Bloch-Floquet boundary condition. In this way, the meta-surface is carefully designed to obtain bandgaps at the desired frequency ranges. Then, a FEM harmonic analysis of a chain of unit cells is performed to further explore the bandgap efficiency. Finally, a coupled field transient dynamic FEM is constructed to simulate the improved nonlinear ultrasonic guided wave active sensing procedure with the bandgap meta-surface. The proposed method possesses great potential for future SHM and NDE applications.

Pneumatic non-contact holders have been put to practical use for transporting semiconductor wafers and foodstuffs (hereafter “workpiece”) in manufacturing processes. The two main types of pneumatic non-contact holder are the Bernoulli and vortex types. In our previous study, we used a Bernoulli-type non-contact holder to achieve full non-contact holding by attaching a diffuser, but the workpiece underwent irregular rotation. With a vortex-type holder, this rotation could be prevented by generating two vortex flows with opposite rotations. However, the workpiece tended to slip away from the holder so that a guard structure was required, which introduced point contact with the guard into the holding process. This study’s purpose was to create a holder that is fully non-contact and does not cause workpiece rotation. By combining both the Bernoulli and vortex types, we succeeded in holding a workpiece without both contact and rotation.

The sensitivity and linearity trade-off problem has become the hotly important issues in designing the piezoresistive pressure sensors. To solve these trade-off problems, this paper presents the design, optimization, fabrication, and experiment of a novel piezoresistive pressure sensor for micro pressure measurement based on a combined cross beam - membrane and peninsula (CBMP) structure diaphragm. Through using finite element method (FEM), the proposed sensor performances as well as comparisons with other sensor structures are simulated and analyzed. Compared with the cross beam-membrane (CBM) structure, the sensitivity of CBMP structure sensor is increased about 38.7 % and nonlinearity error is reduced nearly 8%. In comparison with the peninsula structure, the maximum non-linearity error of CBMP sensor is decreased about 40% and the maximum deflection is extremely reduced 73%. Besides, the proposed sensor fabrication is performed on the n-type single crystal silicon wafer. The experimental results of the fabricated sensor with CBMP membrane has a high sensitivity of 23.4 mV/kPa and a low non-linearity of −0.53% FSS in the pressure range 0–10 kPa at the room temperature. According to the excellent performance, the sensor can be applied to measure micro-pressure lower than 10 kPa.

There are strong needs for flexible and stretchable devices for the seamless integration with soft and curvilinear human skin or irregular textured cloths. However, the mechanical mismatch between the conventional rigid electronics and the soft human body results in many issues including contact breakage, or skin irritation. Due to the mechanical and electrical versatility of nanoscale forms, various nanomaterials have rapidly established themselves as promising electronic materials, replacing rigid wafer-based electronics in next-generation wearable devices. Here, we introduce a flexible, wearable bioelectronic system using an elastomeric hybrid nanocomposite, composed of zero-dimensional Carbon Black (CB) and one-dimensional Carbon Nanotubes (CNTs) and silver nanowires (AgNWs) in a polydimethylsiloxane (PDMS) matrix. Those materials were chosen due to their good electrical properties and their different length scale providing a continuous connection in the flexible PDMS matrix. To achieve a homogeneous dispersion, these nanomaterials were mechanically mixed in PDMS under shear flow using an overhead mixer. A hybrid nanocomposite membrane with dimensions of 15 mm diameter was then prepared by replica molding process. The electrical properties of the nanocomposite were measured over 5, 10 and 15hrs mixing time to investigate the point of electrical stability of the electrode and the electrical performance during EMG signal measurement. This soft nanocomposite, laminated on the skin, enables highly sensitive recording of electromyograms.

One of the main objectives of the structural health monitoring by piezoelectric wafer active sensor (PWAS) using electromechanical impedance method is continuously damage detection applications. In present work impedance method of beam structure is considered and the effect of early crack using breathing crack modeling is studied. In order to model the effect of a crack in beam, the beam is connected with a rotational spring in crack location. The Rayleigh–Ritz method is used to generate ordinary differential equation of cracked beam. Firstly, only open crack is considered that this is leads to linear system equation. In linear system, time domain system equations are converted to frequency domain, and then impedance of PWAS in frequency domain is calculated. Secondly, the breathing crack is modeled to be fully open or fully closed. This phenomenon leads to the nonlinear system equations. These nonlinear equations are solved using pseudo-arc length continuation scheme and collocation method for any harmonic voltage applied to actuator. Then impedance of PWAS is calculated. Two methods are used to detect early crack using breathing crack modeling on PWAS impedance. At the first, frequency response of breathing crack in the frequency range with its sub-harmonics is calculated. Second, only frequency response of one harmonic is computed with its super-harmonics. Finally, the detection method of linear is compared with nonlinear model.

In this work, an impact experiment on a composite plate with unknown material properties (its group velocity profile is unknown) is implemented to localize the impact points. A pencil lead break is used to generate acoustic emission (AE) signals which are acquired by six piezoelectric wafer active sensors (PWAS). These sensors are distributed with a particular configuration in two clusters on the plate. The time of flight (TOF) of acquired signals is estimated at the starting points of these signals. The continuous wavelet transform (CWT) of received signals are calculated with AGU Vallen wavelet program to get the accurate values of the TOF of these signals. Two methods are used for determining the coordinates of impact points (localization the impact point). The first method is the new technique (method 1) by Kundu. This technique has two linear equations with two unknowns (the coordinate of AE source point). The second method is the nonlinear algorithm (method 2). This algorithm has a set of six nonlinear equations with five unknowns. Two MATLAB codes are implemented separately to solve the linear and nonlinear equations. The results show good indications for the location of impact points in both methods. The location errors of calculated impact points are divided by constant distance to get independent percentage errors with the site of the coordinate.

In this paper, we study the closed-loop subspace identification of MIMO motion system with flexible structures. The fundamental objective of identification experiment is to achieve the state space model for motion control. The model with flexible structures of the motion system is analyzed and deduced to the form of state space model, which is composed with rigid modes and flexible modes. As the stability and safety case, the closed-loop subspace identification method is employed. The proposed identification method is suitable for modern control algorithms to construct space state model. The rigid and flexible modes are obtained and updated by the modal approach. Identification experiment is carried on the industrial wafer stage, which is the typical MIMO motion system with flexible structures. The results of experiment verify the feasibility and validity of the proposed identification method.

The variation of the strength of a grain and a grain boundary was measured by a micro tensile test system fabricated in an electron microscope. A micro-scale beam structure was fabricated from a single-crystalline silicon wafer and a fine nano-scale sample cut from a thin film using a focused ion beam was attached to the center of the beam by deposition of tungsten in the microscope. The other end was attached to a micro probe similarly. Finally, the micro probe was activated to pull the sample and the deformation of the sample was observed by a scanning electron microscope. The fracture strength of a bicrystal sample was measured by detecting the deflection of the beam at the breakage of the sample. The crystallinity of both a grain and a grain boundary was quantitatively evaluated by using electron back-scatter diffraction analysis from the viewpoint of the change of the order of atom arrangement in them. It was found that the strength of a grain and a grain boundary varied clearly depending on their crystallinity. In addition, there was a critical value of the crystallinity at which the fracture mode of a polycrystalline material changed from intergranular fracture to transgranular fracture.

Piezoelectricity has proved effective in capturing changes in structures caused by various damage mechanisms. In one approach, piezoelectric wafer active sensors (PWAS) are mounted on the surface of the host structure and utilized as both actuators and sensors to interrogate the structure and monitor its health. This is achieved by subjecting the PWAS to a transient electric pulse and reading the resulting voltage. Changes in the stiffness of the substrate due to structural damage affect the response of the PWAS, which could be correlated to integrity of the structure. Applying this technique to fibrous composite laminates encounters particular challenges due to the presence of multiple damage mechanisms in one or more plies. Simulation of the procedure using advanced computational techniques and material models helps in understanding the reliability of PWAS in sensing damage in fibrous laminates. This paper combines the finite element method and micromechanical modeling of composites to simulate damage detection using surface mounted PWAS. The finite element solution is obtained by the ABAQUS code with user defined material properties, which reflect the underlying damage modes. The latter are obtained in a preprocessing exercise in which the composite laminate is first subjected to a given mechanical load level and the damage mechanisms in the plies are identified using transformation field analysis, TFA (Bahei-El-Din el al., 2010). In the present work, the Mori-Tanaka averaging model is utilized within the TFA and local failure modes, which are a function of the matrix average stresses were specified. Material properties of the individual plies, which correspond to the damage mechanisms introduced at the given load level are then determined numerically in terms of the overall moduli and utilized in the finite element solution of the laminate using ABAQUS. The methodology is applied to a quasi-isotropic, symmetric laminated beam subjected to bending. In the finite element simulation, each fibrous composite ply of the laminated beam is modelled using shell elements while the surface mounted PWAS are modeled with 3D solid elements. The bending moment is applied to the beam intermittently to allow interrogation of the laminate by applying a transient electric pulse to the PWAS and allowing the beam to vibrate for a very short period of time, which is followed by reading the voltage response. The voltage readings are correlated to the damage mechanisms in the plies.

Piezoelectric sensors are used in many structural health monitoring (SHM) methods to interrogate the condition of the structure to which the sensors are affixed or imbedded. Among SHM methods utilizing thin wafer piezoelectric sensors (PWAS), electro-mechanical impedance monitoring is seen as a promising approach to assess structural condition in the vicinity of a sensor. Using the converse and direct piezoelectric effects, this health monitoring method utilizes mechanical actuation and electric voltage to determine the impedance signature of the structure. If there is damage to the structure, there will be a change in the impedance signature. It is important to discern between actual damage and environmental effects on the piezoelectric ceramic sensors and the structure. If structural health monitoring is to be implemented in space structures on orbit, it is imperative to determine the effects of the extreme space environment on piezoelectric sensors and the structures to which they are affixed. The space environment comprises extreme temperatures, vacuum, atomic oxygen, microgravity, micro-meteoroids and debris, and significant amounts of radiation. Radiation in space comes from three sources: solar events, background cosmic radiation, and trapped particles in the Van Allen Belts. Radiation exposure to structures on orbit will vary significantly depending on the duration of the flight and the altitude and inclination of the orbit. In this contribution, the effect of gamma radiation on piezoelectric ceramic sensors and space grade aluminum is investigated for equivalent gamma radiation exposure to 3-months, six-months, and 1-year on Low Earth Orbit (LEO). An experiment was conducted at White Sands Missile Range, Gamma Radiation Facility using Cobalt-60 as the source of radiation. A free PWAS and a PWAS bonded to a small aluminum beam were exposed to increasing levels of gamma radiation. Impedance data were collected for both sensors after each radiation exposure. The total radiation absorbed dose was 200 kRad (Si) by the end of the experiment. The results show that piezoelectric ceramic material is affected by gamma radiation. Over the course of increasing exposure levels to Cobalt-60, the impedance frequency of the free sensor increased with each absorbed dose. The impedance measurements of the sensor bonded to the aluminum beam reflects structural and sensor’s impedance. The data for this sensor show an increase in impedance amplitude with each level of absorbed dose. The mechanism at work in these impedance changes is suggested and future experimental work is identified. A survey of previous results of radiation exposure of piezoelectric ceramic sensors and aluminum alloys is presented and are compared to previous studies.

Modern-day microprocessors consist of over one billion integrated circuits on silicon chips as small as a human fingernail. Normal operation of this circuitry produces an enormous amount of heat on a very small footprint. Dissipating this heat is a very challenging task, perhaps the largest roadblock to continued increases in computing technology. Microchannel heat sinks utilizing either single-phase flow or phase-change are an effective means of cooling stacked 3-D microelectronics. A roadblock to practical implementation of microchannels is the presence of flow instabilities. The asymmetric saw-toothed microchannel heat sink is proposed to address this issue. Deep reactive-ion etching is used to produce channels comprised of asymmetric sawtoothed structures that alter the local flow structure within the microchannel. All experiments are conducted using the dielectric fluid, FC-72. Each microchannel array has a footprint of 1 cm × 1 cm, comprised of thirty-four channels etched into a silicon wafer. A series of thin film serpentine copper heaters is fabricated on the other side of the silicon wafer to provide a uniform heat flux boundary condition. Experimental information is presented for a range of mass fluxes from 381 to 1777 kg/m 2 s, and inlet subcooling from 5°C to 20°C. Parameters presented and analyzed includes boiling curves, onset of boiling (ONB), averaged two-phase heat transfer coefficient.

The ultra-precision wafer stage is an important mechatronic unit in a wafer scanner for manufacturing integrated circuits while its motion control is still the main concern. To overcome the performance-limiting trade-offs of fixed-gain discrete sliding mode control (DSMC), a novel variable-gain DSMC strategy with PID-type sliding surface is proposed for an ultra-precision wafer stage. Specially, PID-type sliding surface is employed to avoid the steady-state error induced by external disturbances. Via the exponential reaching law approach, DSMC with PID-type sliding surface is synthesized. Variable-gain control methodology is newly introduced into DSMC, and the control gain varies with the trajectory phase that the wafer stage is in and the tracking error magnitude. Performance assessment on a developed wafer stage validates that with nano-scale tracking accuracy the proposed strategy not only improves the low-frequency tracking ability without the amplification of high-frequency noise, but also possesses the excellent robustness to external disturbances.

In this study, the sensitivity of two-dimensional four-terminal piezoresistive sensors commonly referred to as “van der Pauw (VDP)” structure is investigated and analyzed. VDP sensors have the potential to obviate some of the limitations of resistor based sensors such as size and temperature effects. In this study, we will consider the VDP sensor to be fabricated on (100) silicon due to its potential application in MEMS pressure sensors or electronic packaging stress measurements. The sensitivity of the VDP sensor may be affected by misalignment (i.e., orientation) during the etching/diffusion process, the size of the sensor relative to the size of the underlying diaphragm, pad size where the current and voltage are determined, and on their global positions. In this study, we have presented how the VDP stress sensitivity is affected by variations in pad size and sensor orientation with respect to the wafer flat direction. First, a 3D finite element analysis (FEA) model is developed representing a piezoresistive VDP sensor fabricated on (100) silicon diaphragm. Then, the FEA model is validated with the closed form analytical solution for different bi-axial loads. Once the FEA model is validated, additional simulations are conducted to understand the influence of different parameters on the resistance measurements. The change in resistivity of the VDP will then be analyzed to predict its sensitivity under a certain set of sensor parameters.

This paper demonstrates experimentally a wide bandpass filter based on an electrothermally tuned single MEMS arch resonator operated in air. The in-plane resonator is fabricated from a silicon-on-insulator wafer with a deliberate curvature to form an arch shape. A DC voltage is applied across the anchors to pass current through the resonator to induce heat and modulate its stiffness, and hence its resonance frequencies. We show that the first resonance frequency increases up to twice of the initial value while the third resonance frequency decreases until getting very close to the first resonance frequency. This leads to the phenomenon of veering, near crossing, where both modes exchange roles. Hence, the first resonance frequency becomes insensitive to axial forces and thermal actuation whereas the third resonance natural frequency becomes very sensitive. We demonstrate an exploitation of the veering phenomenon to realize a bandpass filter, where the first and third resonance modes are excited electrostatically simultaneously to achieve a bandpass. We demonstrate also that by driving both modes nonlinearly near the veering regime, so that the first mode shows softening behavior and the third mode shows hardening behavior, sudden jumps in the response from both modes are induced leading to sharp roll off from the bandpass to the stop band. We show a flat, wide, and tunable bandwidth and center frequency by controlling the electrothermal actuation voltage.

Carbon fiber laminated thermoset composites have become the industry standard for applications dictating a high strength-to-weight ratio. However, the brittle nature of the carbon fiber composite structure limits its energy dissipation characteristics, often leading to catastrophic failure under low energy impact loadings. This research examines the potential effects of including vertically aligned multi-walled carbon nanotube forests within a layered laminate structure with the goal being to increase the energy dissipation of the structure with attention given to the increase in the aerial density as a result of including the insert. These nanotube forests are of interest due to their broader application in coupled scenarios requiring tenability of structural, thermal and electrical properties. These nanotube forests have unique energy dissipative effects due to their hierarchical architecture (see e.g., Dario et al. (2006), Zeng et al. (2010) and Raney et al. (2011)). We synthesize vertically aligned nanotubes (VACNTs) on a single crystalline silicon wafer. After separation with the wafer, the VACNTs are placed within a carbon fiber laminated structure prior to resin infusion using vacuum assisted resin transfer molding (VARTM). Drop tower tests similar to ASTM D7136 are performed on carbon fiber laminates, carbon fiber laminates with nanotube forests, and carbon fiber laminates with several alternative materials. Results show an improved damage tolerance of the laminate with each of the investigated inserts, with the CNT system showing an increase of 13% in mean peak force. These results show a similar improvement to the alternative inserts while maintaining the potential for their broader application as a multifunctional material.

Compliant off-chip interconnects can accommodate the differential displacement between dissimilar materials such as a silicon substrate and an organic board, and can decrease stresses in a microelectronic system. In this paper, we present the fabrication of an area-array of TriDelta compliant interconnects on a 6- inch silicon wafer using sequential processes. The design consists of about 2000 compliant interconnects at a 400- μm pitch on each 18 mm × 18 mm silicon substrate, and there are 32 substrates on a 6- inch wafer. The three arcuate beams of the compliant interconnects are the main parts that provide both the in-plane and out-of-plane compliance, and thus the arcuate beam width and thickness are the most important factor to be considered. DupontTM Riston® FX920 (thickness = 20/ μm ) negative dry film photoresist is used in our study and the arcuate beam thickness is uniform throughout the pattern. However, by designing the arcuate beam width to be 10 μm , 15 μm , and 20 μm , different compliance values can be achieved in the same or different substrates. The use of the dry film photoresist makes the fabrication process cost effective compared to the use of liquid film photoresist. The mechanical compliance of such fabricated compliant interconnects, intended as second-level interconnects, is presented in this work.

Experiments were performed to examine the ability of surfactants to remove multi-walled carbon nanotubes (MWCNTs) from silicon wafers with nano and micro scaled features. Well-defined microscale topological features on silicon wafers were induced using photo lithography and plasma etching. The etching time was varied to create variation in topological features with the size and height of ∼ 8±1 μm, and ∼2±1 μm, respectively. MWCNTs in the form of pristine liquid solution were deposited on the surface of silicon wafers using the spin coating process. During cleaning, the contaminated surfaces were first sprayed with one of the two surfactants, sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS), or water. MWCNTs were wiped off using a wiping mechanism. The area density of the MWCNTs was quantified prior to and after their removal using scanning electron microscopy (SEM) and post-image processing. The results show decreasing removal efficiency for all the surfactants as the topological features on the wafers deepen through increasing the etching time. Surfactants show better decontamination efficiency compared with water.