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Electrospinning is the most widely used nanometer-sized polymer fiber production technique. The properties of the deposited fiber mats are strongly dependent on the ability to control the fiber extrusion and its deposition location. In this work we demonstrate the ability to steer the charged fiber by external Coulomb forces generated by a set of auxiliary electrodes. A mathematical model describing the fiber trajectory was used to estimate the unknown material properties of the fiber by matching the experimental and simulation results.

Polymer nanofibers have a specific set of material properties that are favorable for many applications in biomedical engineering (scaffolds, stents or tissues engineering). In this article, influence of the electrostatic field distribution on the fiber deposition pattern is examined. The electrode pair used in the study is part of a lineal quadrupole trap used in ion trapping experiments. The impact of the bias potential on the nanofiber collection patterns and the electrospinning process is examined through a series of experiments and finite-element analysis of the resulting field distribution. A set of optimal amplitudes of the steering electric field components is also reported.

Sean J McCafferty,1–4 Eniko T Enikov,5 Jim Schwiegerling,2,3 Sean M Ashley1,3 1Intuor Technologies, 2Department of Ophthalmology, University of Arizona College of Medicine, 3University of Arizona College of Optical Science, 4Arizona Eye Consultants, 5Department of Mechanical and Aerospace, University of Arizona College of Engineering, Tucson, AZ, USA Purpose: The aim of the study was to quantify the isolated tear film adhesion error in a Goldmann applanation tonometer (GAT) prism and in a correcting applanation tonometry surface (CATS) prism.Methods: The separation force of a tonometer prism adhered by a tear film to a simulated cornea was measured to quantify an isolated tear film adhesion force. Acrylic hemispheres (7.8mm radius) used as corneas were lathed over the apical 3.06mm diameter to simulate full applanation contact with the prism surface for both GAT and CATS prisms. Tear film separation measurements were completed with both an artificial tear and fluorescein solutions as a fluid bridge. The applanation mire thicknesses were measured and correlated with the tear film separation measurements. Human cadaver eyes were used to validate simulated cornea tear film separation measurement differences between the GAT and CATS prisms.Results: The CATS prism tear film adhesion error (2.74±0.21mmHg) was significantly less than the GAT prism (4.57±0.18mmHg, p

Background Goldmann applanation tonometry (GAT) error relative to intracameral intraocular pressure (IOP) has not been examined comparatively in both human cadaver eyes and in live human eyes. Futhermore, correlations to biomechanical corneal properties and positional changes have not been examined directly to intracameral IOP and GAT IOP. Methods Intracameral IOP was measured via pressure transducer on fifty-eight (58) eyes undergoing cataract surgery and the IOP was modulated manometrically on each patient alternately to 10, 20, and 40 mmHg. IOP was measured using a Perkins tonometer in the supine position on 58 eyes and upright on a subset of 8 eyes. Twenty one (21) fresh human cadaver globes were Intracamerally IOP adjusted and measured via pressure transducer. Intracameral IOP ranged between 5 and 60 mmHg. IOP was measured in the upright position with a Goldmann Applanation Tonometer (GAT) and supine position with a Perkins tonometer. Central corneal thickness (CCT) was also measured. Results The Goldmann-type tonometer error measured on live human eyes was 5.2 +/−1.6 mmHg lower than intracameral IOP in the upright position and 7.9 +/− 2.3 mmHg lower in the supine position (p

A novel method for collection of electrospun polymer nanofibers is proposed. This method can be applied to extrusion of various polymers and deposition on various types of substrates or without use of a substrate at all. The fiber is forced to alternate in its deposit in between two different segments of a collector electrode by a pair of square electric potential functions in anti-phase applied to these two electrode segments. As the fiber oscillation frequency is equal to the potential function frequency, the fiber deposition rate in between these two collector segments can be controlled. If an electrically non-conductive material is placed in between the two segments of the collector electrode, aligned fibers are simply deposited on the surface of this material. The method is used to perform stiffness measurements of the fibers demonstrating Young's modulus of 200.1 MPa with a standard deviation of 30.7 MPa. The stiffness measurement does not require any specialized equipment and requires minimal sample preparation. A sample consists of known amount of aligned fibers collected between a pair of thin coaxial rods leading to a cylindrical bundle with known number of fibers. A tensile test is then performed to obtain stress-strain curve and to find the Young's modulus of the fiber material.

Digitization and time delay are known to modify the stability properties of feedback controlled systems. Although their effects have been widely investigated and they occur in most of the systems equipped with digital processors, they are usually neglected in industrial approaches, by virtue of the high sampling frequencies of modern processors. However, these approaches are not conservative with respect to stability. In this work, we investigate, first analytically, then numerically and experimentally, the stability properties of the so-called Aeropendulum. The Aeropendulum is a mechanical pendulum with a propeller at its free end. A motor, activating the propeller, allows an active control of the pendulum in a feedback loop. The system exhibits most of the difficulties encountered in more involved industrial robotic systems. The estimation of the parameter values is performed through a model-based estimation, which allows to successfully define damping coefficients of order zero, one and two. Stability charts obtained with different controllers are compared, showing the larger stability region obtainable with the act-and-wait controller under proper conditions, as predicted by the theory.

This paper presents a feasibility study of the application of giant magneto resistive (GMR) sensors in detecting motion of slow moving fluids. A motivating application for the proposed effort is the development of a smart catheter capable of monitoring the amount of body fluid drained from the ventricles of the brain. Microfabricated ferromagnetic flaps are used to detect motion of the surrounding fluid. The deflection of the flaps is detected by an ultrasensitive GMR sensor placed outside of the lumen of the catheter. Numerical and experimental results are provided demonstrating a resolution of 1.4 mL/h. Numerical analysis of the fluid past the sensing element show an optimal hinge length of the flexible flaps, as well as a significant increase in sensitivity with reduction of the by-pass gap to $\sim 50~\mu $ m. The effect of electro-magnetic interference and other sources of low-frequency noise (drift) has also been investigated. The results from the study are used to derive a set of design rules that may lead to the successful development of a smart catheter. [2014-0148]

Retinal diseases such as Age-Related Macular Degeneration (ARMD) affect nearly one in three elderly patients. ARMD damages the central vision photoreceptors in the fovea. The Photostress Test is a simple technique for testing for the early effects of ARMD. Here, the illumination sources in a novel self-administered Photostress Testing device were modeled for safety and distribution in illumination software. After satisfying the design constraints in the model, a prototype of the illumination system was fabricated and tested to confirm the modeling results. The resultant prototype can be used to aid in the diagnosis of retinal disease and is well within retinal safety levels.

This article describes a feasibility study of a novel trans-scleral tonometer based on the use of an instrumented form of digital palpation tonometry. Similar to manual digital palpation tonometery, trans-scleral tonometer utilizes two force probes offset by a fixed distance. Force indentation data from these probes have been shown to correlate with the intraocular pressure (IOP) of the eye. Enucleated porcine eyes were used to experimentally validate the approach. The observed hysteresis in the force data was analyzed using an analytical model that accounts for the outflow of the aqueous humor. The predictions of the model indicate that the primary reason behind the observed hysteresis is stress relaxation (accommodation) in the visco-elastic corneo-scleral shell. Experimental data from eye distention and indentation tests were then used to infer the conditions under which the novel tonometer would be expected to have an accuracy of ±1 mmHg. Analysis of the data shows that indentation rates should be kept below 0.5 mm/s for a pressure range of 10-35 mmHg. Two commonly used pressure control protocols were tested in an effort to ensure accurate IOP values during the palpation tests. Due to the large increase of IOP during digital palpation, the trans-scleral (intra-vitreous) pressurization was found to be inadequate, leading to clogging of the line by the displaced vitreous. No such problems were identified when the eye was pressurized through the cornea and into the anterior chamber. Force data from multiple palpation experiments are used to generate calibration curves for a two-probe conceptual tonometer. The calibration showed that a 10 mN of force variation corresponds to 1 mmHg of IOP change. A possible implementation using a contoured facial mask is also presented.

With the emergence of augmented and virtual-reality based information delivery technologies the gap between availability of communication devices for visually impaired people and sighted people is emerging. The current study describes a communication tool which provides a reading platform for visually impaired people by means of a haptic display. In this paper the development and human subject study based evaluation of an electromagnetic microactuator-array based virtual tactile display is presented. The actuator array is comprised of a 4 by 5 array of micro voice-coil actuators (tactors) providing vibrotactile stimulation on the user’s fingertip. The size and performance of the actuators is evaluated against the thresholds of human tactile perception. It is demonstrated that a 2.65 mm (diameter) × 4 mm (height) generic tactor is suitable for practical applications in dynamic tactile displays. The maximum force of the actuator was 30 mN generated at current levels of 200 mA. At a stroke of 4.5 mm, the force is reduced to 10 mN. The peak force was generated at a displacement of 1.5 mm. A total of 10 alpha-numeric symbols were displayed to the users via dynamically changing the location of the vibrating point in a predefined sequence, thus creating a tactile perception of continuous curve. Users were asked to sketch out the perceived symbols. Each subject carried out three experiments. The first experiment exposed all subjects to ten different characters. Data obtained from human subject tests suggest that users perceive most shapes accurately, however the existence of jump discontinuities in the flow of presentation of the curves lowers recognition efficiency most likely due to loss of sensation of solid reference point. Characters containing two or more discontinuous lines such as ‘X’ were more difficult to recognize in comparison to those described with a single line such as ‘P’, or ‘Z’. Analysis of the average character recognition rate from 10 volunteers concluded that any presented character was identified correctly in 7 out 10 tests. The second test included characters that were reused from the first experiment. Users had improved their character recognition performance as a consequence of repeated exposure and learning. A final set of experiments concluded that recognition of groups of characters, forming words, is the least efficient and requires further perfecting. Recommendations for improvements of the recognition rate are also included.

Electrospinning is the most widely used production method for polymer fibers formed from an electrified fluid jet. This method is very versatile, relatively inexpensive and simple. When the sufficiently high electric potential (about 20kV) is applied to the polymer solution, the electrostatic forces overcome the surface tension of the polymer and a thin liquid jet is ejected from the nozzle. However, after short straight distance of the motion of the fiber it rapidly grows into an electric charge driven bending instability and results in a 3D spiraling trajectory leading to a very random deposition on the grounded collector. This significantly reduces the positive qualities of the fiber and its use in biomechanical engineering like a production of tissue scaffolds mimicking the structure of the extracellular matrix or a delivery of expandable chemo- and radio-therapeutic stents. In this work we present the initial results from investigating the feasibility of using dynamic focusing of the electrified jet in a linear quadrupole trap. This is a new alternative to the more generally used mechanical approach with rotating mandrel, could in principle lead to the ability to control the deposition location without the use of any moving components. The proposed approach was originally developed for trapping and transporting individual charged ions. In contrast to ions, an electrified continuous fiber represents an infinite degree of freedom system, with potentially much richer dynamics and unknown stability regions in the parameter space. In order to understand the dynamics of the fiber, we present a discretized 2D reduced-order mathematical model which is investigated numerically. The resulting ODEs represent multi-dimensional form of a non-linear Mathieu’s and Meissner’s differential equations for harmonic, and step excitation functions, respectively. The model parameters were obtained from static experiments with electrodes compressing the fibers in a single plane. Finite-element model of the electrodes resulted in detailed potential maps, which were used to develop estimates of the required strength of the electrostatic field needed to steer the fibers. The estimated parameters were used to obtain stable solutions of the reduced-order approximate of a spring-mass-charged dumbbell model of the fiber.

This paper describes the development of a highly sensitive microfluidics flow sensor using MTJ magnetic sensors to detect motion of slow-moving fluids. A motivating application for the proposed device is the development of an implantable flow sensor, capable of monitoring the amount of cerebral spinal fluid drained from the ventricles of the brain. Micro-fabricated ferromagnetic flaps are used to detect motion of the surrounding fluid. The deflection of the flaps is detected by an ultra-sensitive MTJ magnetic field sensor placed outside of the lumen of the catheter. Previous studies have presented a working device with a resolution of up to 1.4 mL/hr. This paper presents the improvements made to the device in terms of sensitivity, thermal noise rejection, and dynamic response. Upon investigation of possible noise sources, a thermally induced sensor drift was found to be the most significant factor affecting the sensors response. A static temperature compensation reduced this drift to less than 120 mL per 12-hr period. Further improvements to the design of the ferromagnetic transducers resulted in a 4.5-fold increase in sensitivity over the previous designs. Results from dynamic testing of the sensor revealed a time constant of 0.4 seconds, which was found adequate for the envisioned application.Copyright © 2016 by ASME

This article describes the design of a novel trans-scleral tonometer based on the use of multiple force sensors forming a mechanical stiffness sensor. The approach is akin to an instrumented form of digital palpation tonometry in which manual paplation is used to infer the stiffness, and hence, the intraocular pressure of the eye. Force indentation data from multiple probes has been shown to correlate with the intraocular pressure (IOP) using encucleated porcine eyes. A noticeable amount of hysteresis has been observed during indentations at higher rate. Analysis of the experimental data indicates that stress relaxation (accommodation) in the visco-elastic corneo-scleral shell is the primary factor of the observed hysteresis. Further tests under different indentation rates show that the novel tonometer is expected to have an accuracy of ±1 mmHg when the indentation rate is kept below 0.5 mm/sec for pressure range of 10–35 mmHg. Using a calibrated finite element model of the measurement, the effect of lateral and angular misalignment is also examined. The results show that the position and orientation of the tactile sensor has to be controlled to within ±1 mm and ±3° in order to achieve a target accuracy of ±1 mmHg.

A novel 4 by 4 array of electromagnetic micro-actuators operating on the principle of voice-coil actuators is presented. The intended application of the array is dynamic tactile stimulation, where multiple actuators generate an illusion of touching a moving pattern. In comparison to earlier designs [1-3], the device has smaller dimensions of 2.28 mm in diameter and 7 mm in length, which allowed its use in an array capable of hosting up to a 5 by 5 set of actuators with a rectangular shape covering an area of 18 mm by 21 mm. Using finite element analysis of several conceptual designs of actuators [1,4,5], it was established that the voice-coil type device (where the coil is the moving part) has most beneficial characteristics for the envisioned application. These include sufficient force over a relatively large distance, allowing tactile stimulation of surfaces with irregular shape, fast response, and small foot-print that matches the density of the tactile sensory neurons in the human finger. Eexperimental evaluation of the operation of neighboring actuators spaced at 3.3 mm apart, indicates that there is no crosstalk between the actuators. The resulting density exceeds that of previously reported alternative designs based on moveable permanent magnets [4,6]. Static force measurement indicate that each micro-actuator can produce at least 26 mN of repulsive force over a stroke of 2100 μm with a peak force of 34 mN. The driving circuit operates at 13.5V and generates a vibration frequency of up to 265 Hz without significant change of the force-displacement characteristics. In the higher frequency range (above 100 Hz) the actuator provides at least 15 mN of force over a slightly reduced stroke of 2300 μm, and a peak force of 21 mN. All of the above parameters meet the required threshold values of tactile human perception known from [2] and [3].

Polymer nanofibers, with their specific set of material properties, are favorable for many applications in biomedical engineering (scaffold, stent, or tissue engineering). This application, however, requires the ability to control the manufacturing process together with organization and orientation of the deposited fiber. Electrospinning device parameters leading to a stable fiber extrusion were already found, together with the influence of the individual working parameters on the fiber properties. It was also found that fiber steering via the external electrostatic field, created by auxiliary electrodes, has very limited steering capabilities. In this article, electrodynamic steering of the electrospun polymer nanofiber is discussed, with focus on the macroscopic fiber deposition pattern and microscopic fiber alignment and straightness. Different electric field distributions are examined, and the corresponding fiber collection patterns are demonstrated on a series of experiments. Finally, a mathematical model of a discretized fiber is created. Matching the simulation and experimental results allows for the determination of unknown fiber properties, like the structural damping coefficient or Stokes drag coefficient.

The design and analysis of a miniature electromagnetic actuator for use in a novel virtual tactile display is described. The actuator operates in repulsive mode so that it can be used for vibro-tactile stimulation of a human fingertip. Pulsed current and permanent magnet based approaches are investigated and compared. Four frequencies (10, 50, 100, and 150 Hz) were used to test the perception limit of three human subjects. The results indicated that the perception is not strongly dependent on frequency in the test range. The required stimulation energy of individual pulses was estimated to be below 57 micro-Joules, while the average peak-force needed for reliable stimulation was 59 milli-Newtons. The perception of simple test shapes was also tested by attaching the actuator onto the fingertip of the human subjects and turning it on and off as a function of its position.

This article introduces an optical device for measuring and recording the vibrations during milling. The constructed apparatus is able to discriminate between stable cutting and chatter vibration. A review of various chatter detection methods is presented. It lists basic numerical approximation methods to predict chatter and the devices used to detect unstable cutting. A discussion on the importance of experimental detection versus theoretical predictions is also included. The article further presents the measurement setup, its basic components, and their parameters along with the basic principles of the measurements and the theoretical framework of the stability analysis. The theoretical framework is then applied to show the chatter determining frequencies and to determine what has to be detected during the measurements. Experimental results for slotting and down milling with different immersion ratios are also presented. These include stability maps based on the power spectrum density (PSD) graphs of th...

A 3D shape display method based on electromagnetic localization and actuation is presented and the correspondent miniature device is developed. Evaluation of the single actuator device shows that majority of shape information can be delivered. The device containing multiple actuators is designed to improve the small shape and large curvature perception. The scaling analysis of EM force is performed to determine the maximal allowable actuators per unit area. The prototype device containing 4 £ 4 actuators array is developed for further evaluation. The need to display graphics to visually impaired people has been growing with the emergence of World Wide Web (WWW). Although several types of computer-aided software were devised to transfer selective information into Braille language, the major obstacle of the communication for the visually impaired people is the deflcient delivery of the graphic information. As a reason, the interest has arisen in developing shape display devices. Electronic devices aiming to fulflll this function can be categorized into two groups. One is to use active touch method where the proflle of the shape is produced by using a tactile matrix (1,2) or virtual environment through force feedback (3). These devices, however, either demand a relatively large platform to incorporate a touching interface, or require large driving element to produce enough force to users. The other group of devices is to use passive sensing method where the pattern is locally produced onto human skin by using spatially discriminated stimulation (4), which is mainly successful for two dimensional graphs. This paper presents an approach that combines both active and passive tactile method to dis- play three dimensional virtual objects by using the miniature vibrator(s). The presented device incorporates an electromagnetic (EM) position detector and EM actuator(s) to selectively stimu- late user's flnger based on its location. The working principle is shown by the block diagram in Figure 1. Human brain interacts with the EM actuator as receiving stimulation and guides the flnger to move following user's estimate of the reference shape. The position comparison results in a decision to engage the actuator in selective locations. The iterations of receiving stimulation and modifying shape estimates produce to users an optimal estimation of the shape.

The objective of this National Science Foundation (NSF)-funded undergraduate engineering training project is to introduce nanoscale science and engineering through an innovative use of a technical elective sophomore-level mechatronics course, followed by an Accreditation Board for Engineering and Technology (ABET)-mandated senior-level engineering capstone design project. A unique partnership between University of Arizona’s department of surgery, its neurosurgical division, and the College of Engineering presents a creative environment, where medical residents serve as mentors for undergraduate engineering students in developing product ideas enabled by nanotechnology. Examples include: a smart ventricular peritoneal (VP) shunt with flow-sensing; a bio-resorbable inflatable stent for drug delivery, and a hand-held non-invasive eye tonometer. Results from the first year of the student projects, as well as qualitative assessment of their experience, is presented. Several institutional challenges were also identified.Copyright © 2015 by ASME

International audience; To date, most autonomous micro air vehicles (MAV-s) operate in a controlled environment, where the location of and attitude of the aircraft are measured with an infrared (IR) tracking systems. If MAV-s are to ever exit the lab, their flight control needs to become autonomous and based on on-board image and attitude sensors. To address this need, several groups are developing monocular and binocular image based navigation systems. One of the challenges of these systems is the need for exact calibration in order to determine the vehicle's position and attitude through the solution of an inverse problem. Body schemas are a biologically-inspired approach, emulating the plasticity of the animal brain, which allows it to learn non-linear mappings between the body configurations, i.e. its generalized coordinates and the resulting sensory outputs. The advantages of body schemas has long been recognized in the cognitive robotic literature and resulting studies on human-robot interactions based on artificial neural networks, however little effort has been made so far to develop avian-inspired flight control strategies utilizing body and image schemas. This paper presents a numerical experiment of controlling the trajectory of a miniature rotorcraft during landing maneuvers suing the notion of body and image schemas. More specifically, we demonstrate how trajectory planning can be executed in the image space using gradient-based maximum seeking algorithm of a pseudo-potential. It is demonstrated that a neural-gas type artificial neural network (ANN), trained through Hebbian-type learning algorithm, can be effective in learning a mapping between the rotorcraft's position/attitude and the output of its vision sensors. Numerical simulation of the landing performance, including resulting landing errors are presented using an experimentally validated rotorcraft model. Copyright © 2015 by ASME.

This article presents the early results from a 10-person human subject study evaluating the accuracy of a novel method of indirect estimation of intraocular pressure using tactile sensors. Manual digital palpation tonometery is an old method used to estimate the eye pressure through palpation with ones fingers. Based on this concept, we present an instrumented measurement method, where multiple tactile stiffness sensors are used to infer the intraocular pressure of the eye. The method is validated using experimental data gathered from human subjects with eye pressures from 15 to 22 mmHg and determined by Goldman applanation tonometry (GAT). Bland-Altman plots comparing the GAT measurements and the proposed through-the-eye-lid tonometry indicate a statistical error of 5.16 mmHg, within the 95% confidence interval, which compares favorably with the FDA-mandated error bound of 5 mmHg. Details on the unit operation and data filtering are also presented. Due to its indirect and non-invasive nature, the proposed new tactile tonometry method can be applied at home as a self-administered home tonometer for management of glaucoma.Copyright © 2015 by ASME

This paper is focused on the design of metal (Ni) electro- thermal micro-actuators, fabricated via a single electro- plating step. Analytical and finite-element solutions of the electro-thermal and thermo-elastic problems are presented to aid in the design of the devices. A separate section is devoted to the problem of displacement determination using charge sensitive amplifiers for high-precision capacitance measurements. Finally, a possible future use of these actuators in impedance-based biosensors is outlined.

Scanning probe microscopy(SPM)-based nanolithography with injected charges into layered electrets, such as silicon dioxide (SiO 2 ) and silicon nitride, is a promising tool with far-reaching applications, such as controlled nano-assembly of macro-molecules and data storage. Despite its potential, some practical limitations exist. This paper describes an experimental investigation of the process of charging and charge dissipation in SiO 2 using an AFM probe tip and surface potential (Kelvin probe) microscopy. The stability of charge bits on hexamethyl disilazane(HMDS)-treated SiO 2 under low dielectric constant liquids, fluorocarbon, and benzene has been demonstrated. Results from a numerical simulation of a theoretical charging model, in which the charge traps are assumed to be localized on the silicon/SiO 2 interface, are also presented. The charge transport mechanism considered is modified Fowler–Nordheim tunneling.

This paper describes the development and the numerical analysis of an electrochemical model for the analysis of a novel polymer/metal composite actuator. A general continuum model describing the transport and deformation processes of these actuators is briefly presented, along with a detailed description of the simulation scheme used to predict deformation, current, and mass transport. The predictions of the model are compared with experimental data, indicating a significant role of water transport in the large‐scale deformation. Comparison of the simulations and experimental data showed good agreement confirming the central role of water transport in the deformation process. For the sake of completeness the fabrication process and testing apparatus are also described.

An analytical solution of the thermoelastic bending/buckling problem of thermal microactuators is presented. V-shaped beam actuators are modeled using the theory of beam-column buckling. Axial (longitudinal) deformations including first-order nonlinear strain-displacement relations and thermal strains are included. The resulting nonlinear transcendental equations for the reaction forces are solved numerically and the solutions are compared with a nonlinear finite element (FE) model. A test actuator has also been fabricated and characterized. The obtained accuracy of the prediction is within 1.1% of the nonlinear FE solution and agrees well with the experimental data. A corresponding one-dimensional (1-D) heat transfer model has also been developed and validated against experimental i-V measurements at various temperatures. The developed analytical models are then used to analyze maximum stress and the heat transfer paths. It has been confirmed that the heat flux toward the substrate is a dominant heat dissipation route in sacrificially released devices.

An analysis is conducted of a novel ion-exchange polymer–metal composite (IPMC) actuator under large external voltage. The model is simplified to a three-component system comprised of a fixed negatively charged polymeric matrix, protons, and free water molecules within the polymer matrix. The proposed coupled model includes mass transport in the membrane, chemical reactions at boundaries, and deformation as a function of a concentration of water molecules. The electrochemical process occurring at both electrodes are the boundary conditions analyzed during the deformation of the actuator in a regime of large voltage (over 1.2 V). This coupled model successfully captures the stress relaxation phenomenon due to water redistribution governed by diffusion. The fabrication process and testing apparatus are also described. Comparison of simulations and experimental data showed good agreement.

Traditional micro-electro mechanical systems (MEMS) actuators have limited stroke and force characteristics. This paper describes the development of a hybrid actuation solution, which utilizes a micro-machined actuator array to provide switching of the mechanical motion of a larger meso-scale piezo-electric actuator. One motivating application of this technology is the development of a tactile display, where discrete mechanical actuators apply vibratory excitation at discrete locations on the skin. Specifically, this paper describes the development, fabrication, and characterization of a 4 × 5 micro-actuator array of individual vibrating pixels for fingertip tactile communication. The individual pixels are turned on and off by pairs of microscopic thermal actuators, while the main vibration is generated by a vibrating piezo-electric plate. The fabrication sequence and actuation performance of the array are also presented.

Interest in using electrostatics for active nano-assembly has grown significantly over the last five years. One common electret structure for such electrostatic constructs is the silicon–silicon dioxide interface. In this paper, an experimental and mathematical analysis of the process of writing negative charge spots in Si–SiO2 is presented. It is demonstrated that controlling the spread of the charge can reduce the spot size and the drop in written potential. Simulation results of a one-dimensional charging model that assumes tunnelling of electrons through the oxide and trapping within SiO2 are presented and compared with the experimental data. The model assumes charge trapping at the Si–SiO2 interface and none at the oxide–air interface or within the oxide bulk. Conducted experiments also show that although the lateral spread of charge places a lower limit on the minimum spot size in silicon–silicon dioxide structures, the use of a hydrophobic hexamethyldisilazane layer can be effective in improving the size stability of the written electrical spots.

The development of thermal micro-actuators on printed circuit boards is described. The fabricated metal actuators are shown to have similar displacement characteristics when compared with silicon-based devices described in the literature. The actuators are benchmarked with respect to power consumption, stroke, and response time. It is further demonstrated that simple analytical estimates for the response time are in good agreement with the experimental measurements and finite element analysis. The thermal cooling transient times are captured using a two-step constant-current excitation method. The fabrication process and potential application areas of the developed device are also provided.

This paper presents design, fabrication and calibration results for a novel 2-DOF capacitive force sensor capable of resolving forces up to 490 µN with a resolution of 0.01 µN in x, and up to 900 µN with a resolution of 0.24 µN in y. A simple fabrication process using deep reactive ion etching (DRIE) on silicon-on-insulator (SOI) wafers forms the 3D high aspect ratio structure. A transverse mode comb drive movement is used to greatly improve device sensitivity. Among other advantages of the developed process is a dice-free release of wafer structures, allowing fragile structures to be individually packaged. Notching or footing effects and bowing effects are well-known problems in DRIE on SOI wafers. Techniques to overcome notching and bowing effects using a PlasmaTherm SLR-770 etcher are presented that do not require hardware modifications. The application of the force sensor is for providing real-time force feedback during individual cell manipulation tasks.

This paper describes the development of a novel optically transparent electrostatic microgripper for assembly of micro-electromechanical systems (MEMS). The principle of operation, design and tests of the new device are described. Fabrication sequence and the materials used are also provided. The resulting gripping force is measured as a function of the applied voltage and compared with a parallel pate capacitor model. The frictional (in-plane) force was also determined for two common materials, silicon and nickel. As expected, a small amount of trapped interfacial charge was observed and characterized via scanning potential microscopy (SPM). The present work provides experimental data on the magnitude of the residual charge, the corresponding force, as well as charge decay data. Although undesirable, in the assembly of high-aspect-ratio interconnects, the part release can be achieved via path planning, since the parts are inserted into micro-machined slots. A simple demonstration assembly cell with image- and laser-based position-sensing modalities has also been described.

We present a new analysis tool for cervical flexion-extension radiographs based on machine vision and computerized image processing. The method is based on semiautomatic image segmentation leading to detection of common landmarks such as the spinolaminar (SL) line or contour lines of the implanted anterior cervical plates. The technique allows for visualization of the local curvature of these landmarks during flexion-extension experiments. In addition to changes in the curvature of the SL line, it has been found that the cervical plates also deform during flexion-extension examination. While extension radiographs reveal larger curvature changes in the SL line, flexion radiographs on the other hand tend to generate larger curvature changes in the implanted cervical plates. Furthermore, while some lordosis is always present in the cervical plates by design, it actually decreases during extension and increases during flexion. Possible causes of this unexpected finding are also discussed. The described analysis may lead to a more precise interpretation of flexion-extension radiographs, allowing diagnosis of spinal instability and/or pseudoarthrosis in already seemingly fused spines.

This article describes the experimental analysis of a novel trans-scleral tonometer based on the use of multiple force sensors forming a mechanical stiffness sensor. This approach is similar to an instrumented form of digital palpation tonometry in which manual palpation is used to conclude the stiffness, and hence, the intraocular pressure of the eye. Force data obtained from these probes correlate with the intraocular pressure (IOP) of the eye. Enucleated porcine eyes were used to validate the approach. A noticeable amount of hysteresis has been observed during indentations. Analysis of the experimental data indicates that stress relaxation in the visco-elastic corneo-scleral shell is the primary factor of the observed hysteresis. Further tests under different indentation rates show that the novel tonometer is expected to have an accuracy of ± 1mmHg when the indentation rate is kept below 0.5 mm/sec for pressure range of 10-35 mmHg.

A general assembly strategy for assembling hybrid magnetic MEMS devices is proposed. The scaling of MEMS devices leads to the dominance of surface-effect forces such as electrostatic, surface-tension and van der Waals forces. The contact phase of an assembly task is complicated by the presence of these surface-effect forces and magnetic forces. Assembly strategies must account for the presence of these forces in order to guarantee successful repeatable assemblies. A detailed model for the magnetic interaction of microparts is developed and experimentally verified. This model is used to synthesize assembly strategies for micromagnetic parts. A flexible automated assembly workcell has also been developed to validate and demonstrate the proposed microassembly strategies.

An anodic bond is modeled as a moving non-material line forming the intersection of three material surfaces representing the unbonded conductor, the unbonded insulator, and the bonded interface. The component mass balance equations, Gauss' law, and the linear momentum equations are cast in a finite-element formulation, which is used to predict the evolution of the sodium ion concentration, electric potential, and stress during the anodic bonding of Pyrex glass and silicon. The method is applicable to the viscoplasticity of solid electrolytes, and the volume and interface free energies can be modified to model electromechanical interface phenomena such as debonding, space charge accumulation and sliding at grain boundaries in ionic crystals, and a cohesive zone theory of piezoelectric fracture.

The design and fabrication of a novel multi-degree-of-freedom force sensor is described. The three-dimensional structure of the sensor is a result of combining several microfabrication techniques: wet bulk micromachining, fusion bonding, chemical mechanical polishing, deep RIE, LPCVD, PECVD and thermally evaporated thin films. The sensor is designed to operate in the 0-500 µN force range and the 0-10 µNm torque range. The flexibility of the process to create overhanging structures with arbitrary lengths and heights is illustrated by the integration of micro-tweezers directly onto the force sensor. Among other advantages of the developed process is a dicing-free self-release of wafer structures. This allows very fragile structures, such as micromirrors and other optical components, to be individually packaged.

A wet chip electro-fluidic packaging technology based on electroplating is described. An electroplated gold seal provides the sensor's fluid connection to a silicon multi-chip module. A hermetic seal is obtained using the gold–silicon eutectic bond. The sensor's electrical connections to the multi-chip module are made by eutectic bonding electroplated gold–tin solder bumps on the sensor to gold pads on the substrate. The fluid and electrical connections are made simultaneously, and the process is compatible with the flip-chip bonding technique.

An anodic bond is modeled as a moving nonmaterial line forming the intersection of three material surfaces representing the unbonded conductor, the unbonded insulator, and the bonded interface. Global integral equations are written for the conservation of mass, momentum, and energy, Maxwell's equations, and the second law of thermodynamics. The global equations are then localized in the volume, the material surfaces, and the nonmaterial bond line. The second law is used to determine the thermodynamic conjugates in the thermodynamic potential and the dissipation inequality. It is demonstrated that the jump in the Poynting vector across a surface is equal to the surface Joule heating due to surface electric conduction currents.

Without control, the desired motions of machines do not occur, and the desired equilibria and stationary motions are often unstable. Human operator or computer control may be needed to control and stabilize these machines. An important common feature of both analog and digital controllers is the time delay that is introduced into the system. Even when these delayed systems should be stable, the experiments show small stochastic oscillations around the desired motion, as are often experienced in robotics. In case of the stabilization of an inverted pendulum, the analysis of the equation of motion shows that chaotic vibrations occur around the equilibrium even when stochastic effects related to human control are not present. In advanced design work of digitally controlled machines, it is vital to know the characteristics of this chaotic behavior. The estimation of the distribution of vibration amplitudes and the frequency range should be available at the design stage. This initiates the analysis of the so-called microchaos or μ-chaos.