Mechanical Crosstalk Research Articles

Design and Simulation of MEMS Based Tuning Fork Micro-Gyroscope

In this paper, design, analysis and simulation of microelectromechanical system (MEMS) based inertial sensor type of tuning fork micro gyroscope have been presented. CoventorWare has been used for design and simulation. The proposed design has improved the performances and structure for small vibration amplitude to minimize the mechanical crosstalk. Simulation results show that the capacitance in sense mode, which is detected by variable-gap capacitors, is equal to 2.68 pF in each side of sense mode. Oscillations in drive and sense electrodes with 1-DOF and proof mass with 2-DOF ensure that the proposed model has no common mode that causes mechanical crosstalk.

Air-coupled linear and sparse cMUT array manufactured using MUMPs process

An assessment of the standard fabrication Micro-Electro-Mechanical Systems (MEMS) process Multi-User MEMS Processes (MUMPs) for complex air-coupled capacitive Micromachined Ultrasonic Transducer array aperture manufacture is reported. A 1-D linear array and a 2-D sparse symmetric binned-array have been designed and manufactured, and then characterised experimentally using electrical impedance measurements, laser vibrometry and air-coupled field measurement; the experimental data are supported by simulated data using Finite Element technique and field simulation based on Huygens’ principle. A methodology for the manufacture of the array structures using the MUMPs process is described. Electrical characterisation shows the devices operation at 770 kHz and the existence of large parasitic capacitances and electrical losses. Mechanical crosstalk of array substrate has been measured at −40 dB using laser vibrometry. Moreover, the laser vibrometry measurement and the field characteristics of one element reveal that each element operates as a piston radiator.

−1227C>T polymorphism in the pleiotrophin gene promoter influences bone mineral density in postmenopausal women

Our gene expression microarray data of primary cultures of osteoblasts revealed that the expression of the pleiotrophin ( PTN) gene is decreased in osteoporosis. PTN is involved in osteoblasts' proliferation and differentiation, response to mechanical stimuli and cross-talk with Wnt signaling. On the basis of these findings, we studied the PTN gene as a candidate gene for genetic susceptibility to osteoporosis. The aim of the study was to evaluate the association of two PTN gene promoter polymorphisms with osteoporotic phenotype in postmenopausal women. 530 postmenopausal women, 480 without and 50 with hip fracture, were genotyped for the presence of PTN gene promoter polymorphisms −1734C>T (rs161335) and −1227C>T (rs321198). Three common haplotypes, CC (14.2%), CT (42.8%) and TC (42.9%), were inferred. Bone mineral densities (BMDs) at lumbar spine and (contralateral) hip were measured. In non-osteoporotic postmenopausal women without hip fracture, the association of −1227C>T and CT haplotype with lumbar spine BMD was shown (p = 0.014 and 0.014). No other significant association of the studied genotypes and haplotypes in the PTN gene promoter with BMDs was found. Comparing age-matched postmenopausal women with and without hip fractures, no differences in frequency distributions of the studied genotypes and haplotypes was shown. For the first time we have shown that, in postmenopausal women, the PTN gene promoter polymorphism −1227C>T and CT haplotype could contribute to the genetic background of osteoporosis, but these findings need further functional and clinical confirmation.

A Lateral-Axis Microelectromechanical Tuning-Fork Gyroscope With Decoupled Comb Drive Operating at Atmospheric Pressure

In this paper, a silicon bulk micromachined lateral-axis tuning-fork gyroscope (TFG) with a decoupled comb drive and torsional sensing comb capacitors is presented. The novel driving comb capacitors are used to suppress the parasitic out-of-plane electrostatic force and, hence, can decouple the mechanical crosstalk from the sensing mode to the driving mode in a simple manner. The torsional sensing combs are designed to differentially sense the out-of-plane rotational moment and are arranged centroidally to be immune to fabrication imperfections for good linearity and electrostatic force balancing. The torsional sensing combs adopted in the TFG help to lower the air damping of the sensing mode while the driving mode of the gyroscope is dominated by slide-film air damping; hence, it can work even at atmospheric pressure. The process for this lateral-axis gyroscope can also be used to fabricate z-axis gyroscopes; therefore, low-cost miniature monolithic inertial measurement units can be realized without vacuum packaging. The TFG is tested at atmospheric pressure with a sensitivity of 17.8 mV/°/s and a nonlinearity of 0.6% in a full-scale range of 1000°/s. The bias stability is measured to be 0.05°/s (1 ?) in 30 min with an equivalent noise angular rate of 0.02°/s/Hz1/2.

Decoupled Comb Capacitors for Microelectromechanical Tuning-Fork Gyroscopes

This letter presents a novel comb capacitor which can decouple the mechanical crosstalk between the sensing and driving modes of gyroscopes. The capacitance and electrostatic force of the comb capacitor are simulated and analyzed to verify the decoupling principle. A lateral-axis tuning-fork gyroscope is used successfully to demonstrate the decoupling capability of the comb capacitor, resulting in a nonlinearity of 0.6% with full scale of 1000 °/s and a bias stability of 0.05 °/s (1?) for 30 min.

Humoral and Mechanical Cross-Talk in the Vasculature: Perspectives in Vascular Disease

Humoral and Mechanical Cross-Talk in the Vasculature: Perspectives in Vascular Disease

A Compact Angular Rate Sensor System Using a Fully Decoupled Silicon-on-Glass MEMS Gyroscope

This paper presents the development of a compact single-axis angular rate sensor system employing a 100- mum-thick single-crystal silicon microelectromechanical systems gyroscope with an improved decoupling arrangement between the drive and sense modes. The improved decoupling arrangement of the gyroscope enhances the robustness of sensing frame against drive-mode oscillations and therefore minimizes mechanical crosstalk between the drive and sense modes, yielding a small bias instability. The gyroscope core element is fabricated by through-etching a 100-mum -thick silicon substrate which is anodically bonded to a recessed glass handling substrate. A patterned metal layer is included at the bottom of the silicon substrate, both as an etch-stop layer and a heat sink to prevent heating- and notching-based structural deformations encountered in deep dry etching in the silicon-on-glass process. The fabricated-gyroscope core element has capacitive actuation/sensing gaps of about 5 mum yielding an aspect ratio close to 20, providing a large differential sense capacitance of 18.2 pF in a relatively small footprint of 4.6 mm times 4.2 mm. Excitation and sensing electronics of the gyroscope are constructed using off-the-shelf integrated circuits and fit in a compact printed circuit board of size 54 mm times 24 mm. The complete angular rate sensor system is characterized in a vacuum ambient at a pressure of 5 mtorr and demonstrates a turn-on bias of less than 0.1 deg/s, bias instability of 14.3 deg/h, angle random walk better than 0.115 deg/radic(h), and a scale-factor nonlinearity of plusmn0.6% in full-scale range of plusmn50 deg/s. [2007-0158].

Improved Sensitivity of Dual-Axis Micro-Mechanical Probe for Friction Force Microscope

Improvement of the sensitivity of a dual-axis probe for friction force microscopy is presented. The dual-axis micro-mechanical probe combines a double cantilever and torsion beams. This probe could reduce the mechanical cross-talk between the lateral and vertical force detections. In addition, dual-axis forces can be detected by measuring the dual-axis displacement of the probe end using the optical lever-based method. A low reflection region is formed at the probe end. The region is irradiated with an optical lever laser light and the reflected light is focused onto a four-segmented photo diode (PD). The lateral force can be detected by measuring the displacement of the probe end using the dark region displacement on PD. A shallow step structure was used as a low reflection region in our previous study. However, its darkness was not enough and the improvement of the sensitivity was difficult. In this paper, a new type of low reflection region is presented. The low reflection region using a slope-structure could improve the lateral deflection sensitivity by a factor of 1.4 as compared with conventional one. And the minimum detection limits of the lateral deflection and force were of the order of 1 nm and 1 nN, respectively. This leads to accurate investigation of nanotribological phenomena.

Regulation of Corneal Fibroblast Morphology and Collagen Reorganization by Extracellular Matrix Mechanical Properties

To investigate how extracellular matrix mechanical properties influence cell and matrix patterning in three-dimensional culture. Human corneal fibroblasts were seeded within 30 x 10 mm collagen matrices that were unconstrained (UN), fully constrained (CO) along the long axis by attaching the construct to two immobilized plastic bars, or partially constrained (PC) by allowing linear elastic displacement of one bar. After 24 hours, constructs were labeled with phalloidin and were imaged using fluorescent and reflected light (for collagen) confocal microscopy. Cell morphology and local collagen fibril density and alignment were measured using digital image processing. Corneal fibroblasts in UN matrices were less elongated (UN < PC < CO; P < 0.05) than those in constrained matrices. Cells were aligned parallel to the long axis in the anisotropic region of constrained matrices but were randomly aligned in unconstrained (isotropic) matrices (UN < PC = CO; P < 0.05). Both the local collagen density and the degree of cell/collagen coalignment were higher in constrained matrices (UN < PC < CO; P < 0.05). In regions of higher cell density, additional bands of aligned collagen were often observed between individual cells. These data suggest that cell spreading, alignment, and contractile force generation are directly influenced by the mechanical properties of the surrounding extracellular matrix (ECM). Corneal fibroblasts generally align and compact collagen parallel to the axis of greatest ECM stiffness. Mechanical cross-talk between adjacent cells leads to enhancement of matrix reorganization, and results in additional, more complex matrix patterning.

Feedback based simultaneous correction of imaging artifacts due to geometrical and mechanical cross-talk and tip-sample stick in atomic force microscopy

This paper presents a feedback scheme that simultaneously corrects, in real time, for the imaging artifacts caused by cantilever and photosensor misalignments as well as misinterpretations in relative lateral position of the tip with respect to the sample due to the tip-sample stick in atomic force microscopy (AFM). The optical beam bounce method, typically used in AFM for imaging, is sensitive to inaccuracies of cantilever geometry and the relative misalignment of the laser source, cantilever, and the laser sensitive diode from the intended design. These inaccuracies, which contribute to the geometrical cross-talk between the normal and the lateral signals, become prominent at the atomic and subnanometer scales, and thereby impede high resolution imaging studies. The feedback scheme accounts for these artifacts and makes imaging insensitive to, in fact, practically independent of these inaccuracies. This scheme counteracts the lateral twisting dynamics of the cantilever, and as a result, it avoids the misinterpretation problem of the relative lateral position of the cantilever tip from the sample and thereby avoids the corresponding imaging artifacts that are typically prominent in contact mode friction force microscopy (FFM). The feedback scheme consists of simultaneously regulating the normal as well as the lateral cantilever deflection signal at their respective set points. This not only removes the imaging artifacts due to geometrical misalignments, mechanical cross-talk, and irregular sliding but also the corresponding compensatory control signal gives a more accurate real time measure of the lateral interaction force between the sample and the cantilever as compared to the lateral deflection signal used in FFM. Experimental results show significant improvement, and in some cases, practical elimination of the artifacts. The design and implementation of a split piezoassembly needed for the lateral actuation for the feedback scheme are also presented.

Asymmetrical twin cantilevers for single molecule detection

Recently, there has been growing interest in sensors based on frequency shift detection of mechanical resonators, that has led to extremely sensitive diagnostic methods for medicine and biology. Here the authors propose and demonstrate a strategy capable of detecting the presence of a few macromolecules, which uses an asymmetrical cantilever structure of several microns in size, operated at room temperature, and under ordinary vacuum conditions. The idea is to detect the presence of one or more molecules by detecting the mechanical cross-talk induced by the molecular link between a short cantilever and an array of longer cantilevers facing the short one.

Mechanical design and force calibration of dual-axis micromechanical probe for friction force microscopy

A dual-axis micromechanical probe that combines a double cantilever and torsion beams is presented. This probe can reduce the mechanical cross-talk between the lateral and vertical force detections. In addition, dual-axis forces can be detected by measuring the dual-axis displacement of the probe end using the optical lever-based method used in conventional friction force microscopes (FFMs). In this paper, the mechanical design of the probe, the details of the fabrication method, FFM performance, and calibration of the friction force are discussed. The mechanical design and the microfabrication method for probes that can provide a force resolution of the order of 1nN without mechanical cross-talk are presented. Calibration of the lateral force signal is possible by using the relationship between the lateral force and the piezodisplacement at the onset of the probe scanning. The micromechanical probe enables simultaneous and independent detection of atomic and friction forces. This leads to accurate investigation of nanotribological phenomena and visualization of the distribution of the friction properties, which helps the identification of the material properties.

Dual-axis micromechanical probe for independent detection of lateral and vertical forces

A dual-axis micromechanical probe that combines a double cantilever and torsion beams is presented. This probe can reduce the mechanical cross-talk between the lateral and vertical forces and detect dual-axis forces by measuring the dual-axis displacement of the probe end using the optical lever-based method used in conventional friction force microscopes. By reducing the cross-talk, this new probe design yields improved frictional force measurements for the identification of materials.

A high-performance silicon-on-insulator MEMS gyroscope operating at atmospheric pressure

This paper presents a new, high-performance silicon-on-insulator (SOI) MEMS gyroscope with decoupled oscillation modes. The gyroscope structure allows it to achieve matched-resonance-frequencies, large drive-mode oscillation amplitude, high sense-mode quality factor, and low mechanical cross-talk. The gyroscope is fabricated through the commercially available SOIMUMPS process of MEMSCAP Inc. The fabricated gyroscope has minimum capacitive sense gaps of 2.6 μm and a structural silicon thickness of 25 μm, and it fits into a chip area smaller than 3 mm × 3 mm. The fabricated gyroscope is hybrid connected to a CMOS capacitive interface ASIC chip, which is fabricated in a standard 0.6 μm CMOS process. The characterization of the hybrid-connected gyroscope demonstrates a low measured noise-equivalent rate of 90°/h/Hz 1/2 at atmospheric pressure, eliminating the need for a vacuum package for a number of applications. R 2-non-linearity of the gyroscope is measured to be better than 0.02%. The gyroscope has a low quadrature signal of 70°/s and a short-term bias stability of 1.5°/s. The angular rate sensitivity of the gyroscope is 100 μV/(°/s) at atmospheric pressure, which improves 24 times to 2.4 mV/(°/s) at vacuum. The noise-equivalent rate of the gyroscope at 20 mTorr vacuum is measured to be 35°/h/Hz 1/2, which can be improved further by reducing the electromechanical noise.

Development of a miniature uniaxial pressure-acceleration probe for bioacoustic applications

The bioacoustics community has recently expressed an interest in using collocated measurements of the acoustic pressure and the particle velocity to categorize how certain species of marine life transmit and receive sound. For most applications the frequency range of interest spans from tens of hertz to a few kilohertz. Because the test specimens and the test facilities can be relatively small, a miniature pressure-acceleration (b−a) probe was developed. The probe conforms to the geometry of a cube having a principal side length of 31.75 mm (1.25 in.) and contains flexural mode piezoelectric transducers to measure the acoustic pressure and one component of the acoustic particle acceleration vector. The cube also houses a low-noise two-channel preamplifier and is compliantly suspended inside a light frame. This paper highlights the design evolution of a few prototypes and addresses issues associated with the electronic noise floor of the accelerometer, mechanical cross talk between the transducers, damping of the external suspension system and transducers, and the dynamics of the signal cable. [Work supported by Acoustech Corporation IR&amp;D.]

Monolithic silicon smart tactile image sensor with integrated strain sensor array on pneumatically swollen single-diaphragm structure

In this paper, a novel concept of silicon-microelectromechanical system tactile image sensor aimed at fingertip tactile applications and evaluation results of a prototype device are presented. Array of strain-sensitive sensor pixels is integrated on a pneumatically swollen silicon diaphragm with signal processing circuits in monolithic configuration. Elastic surface of the tactile image sensor is realized using repulsive force of the air pressure applied to diaphragm backside. Contact force distribution of an object is detected from the stress distribution change on the diaphragm using piezoresistor array. Force range and force sensitivity can be controlled by the pressure even after device packaging step. In this principle, fine pitch of pixels and a large-scale sensing array can be easily realized using the abilities of silicon CMOS technology. In addition, the movable stroke of sensor surface can be made much longer than the individually formed micromechanical pixels. A prototype device, of the new concept, with 3040 /spl times/ 3040 /spl mu/m/sup 2/ sensing diaphragm was fabricated with integrated 6 /spl times/ 6 array of 420-/spl mu/m pitch pixels. Increased movable stroke of the swollen diaphragm from the original surface is around 30 /spl mu/m at 23-kPa pressure at the top. Realized spatial resolution of the prototype device is approximately 400 /spl mu/m, which is determined by the relationship between the pixel pitch and mechanical crosstalk among the pixels. Positions of touch and their contact force amplitudes were detected as a two-dimensional distribution of the output voltage from the pixel array in a multipoint contact test. The maximum input-force range can be controlled from 21 to 176 mN by changing the backside pressure from 5 to 64 kPa. Through the evaluation of the fabricated device, major advantages of this tactile image sensor have been demonstrated successfully.

Design and Simulation of a New Decoupled Micromachined Gyroscope

This paper reports on a new decoupled micromachined gyroscope. The proposed sensor is a dual mass type, electrostatically driven to primary mode oscillation and senses, capacitively, the output signal. Full decoupling between drive and sense modes minimizes the mechanical crosstalk. Three different designs are introduced in this work. Drive and sense amplitudes, mechanical and electrical sensitivities, quality factors and approximate bandwidths are extracted analytically and the results are confirmed using finite element analysis. The first design shows drive and sense modes resonance frequencies of 4077 Hz and 4081 Hz respectively; with a frequency mismatch lower than 0.1%. The drive and sense capacitance are 0.213 pF and 0.142 pF respectively. The mechanical and electrical sensitivities are 0.011 µm/ (°/s) and 2.75 mV/ (°/s) respectively. The third design shows significantly improved mechanical and electrical sensitivities of 0.027 µm/ (°/s) and 6.85 mV/ (°/s) respectively.

Mechanical crosstalk between vertical and lateral piezoresponse force microscopy

Piezoresponse force microscopy (PFM) provides valuable insight into the inverse lateral and vertical piezoelectric effects on the nanoscale. Ideally, these contributions are separated into vertical and lateral detections of a deflected laser beam on a quadrupole diode. In contrast to the known crosstalk by a rotated diode that causes identical signals in both channels, we report on the crosstalk due to the geometrical constraints of the cantilever that is inherent to the lateral PFM. For a BaTiO3 (001) nanograin we show that the vertical response attributable to the crosstalk is 1∕8th of the lateral response. From this value we deduce the actual mechanism responsible for the crosstalk.

Comparison of the performance of pmn-pt single-crystal and ceramic composite arrays for NDE applications

Ultrasonic array technology is used in many imaging applications across a wide range of industrial sectors. Perovskite single-crystal materials such as pzn-pt and pmn-pt can be used to manufacture arrays with much increased sensitivity and bandwidth, compared to conventional piezoelectric ceramic designs. One way to take advantage of these new active materials is to incorporate the single-crystal material as the active piezoelectric elements, embedded within a passive polymeric material, in a piezoelectric composite structure. This paper describes a theoretical and experimental investigation into the performance of wideband 1-3 composite arrays utilising pzt5h ceramic and pmn-pt single-crystal as the active materials. Six-element prototype arrays were manufactured with a centre frequency of approximately 2.25 MHz. The comparison of the single-crystal and pzt5h devices is based on laser vibrometer surface displacement cross-talk measurements and electrical impedance measurements as well as transmit and receive measurements in water. The measured electrical impedance and mechanical cross-talk from the manufactured arrays correlates well with that predicted using the FE software package PZFlex. Moreover, the design techniques obtained from PZFlex, are shown to produce arrays with low cross-talk. Overall, the single-crystal device shows considerably improved performance over the pzt5h device as demonstrated by its higher bandwidth and superior pulse-echo performance.

Development of a Micro Probe for Friction Force Microscope with Independent Detection of Friction and Load

A novel micro-mechanical probe for friction force microscopy has been presented. The probe has a double cantilever that is supported by a torsion beam. It measures the lateral force by detecting the deflection of the double cantilever and measures the vertical force by the torsion of the torsion beam. It can measure the two forces independently without the mechanical crosstalk. The force resolution is of the order of 1 nN. The probe can clarify the micro/nanotribological phenomena more accurately than conventional cantilever probes and provide useful information for the identification of material properties.