微机电器件的稳健设计

微机电系统（MEMS）是一个新兴的跨学科研究领域,成本和可靠性是MEMS商品化的关键。与传统的机械加工和IC加工相比,MEMS加工的尺寸偏差比较大,而且很难控制,因此需要在设计过程中充分考虑加工的不确定性。稳健设计可以在不提高制造成本的前提下提高设计方案的稳健性。稳健优化设计方法主要包括 Taguchi方法和基于容差模型的方法,后者特别适合于处理带约束的优化设计问题。以微加速度计和微阀为例给出了稳健设计在MEMS设计中的应用,验证了稳健设计可以显著提高MEMS器件的信噪比。     

A dual-mode built-in self-test technique for capacitive MEMS devices

A dual-mode built-in self-test (BIST) scheme which partitions the fixed (instead of movable) capacitance plates of a capacitive microelectromechanical system (MEMS) device is proposed. The BIST technique divides the fixed capacitance plate(s) at each side of the movable microstructure into three portions: one for electrostatic activation and the other two equal portions for capacitance sensing. Due to such a partitioning method, the BIST technique can be applied to surface- and bulk-micromachined MEMS devices and other technologies. Further, the sensitivity and symmetry dual BIST modes based on this partitioning can also be developed. The combination of both BIST modes covers a larger defect set, so a more robust testing result for the device can be expected. The BIST technique is verified by three typical capacitive MEMS devices. Simulation results show that the proposed technique is an effective BIST solution for various capacitive MEMS devices.     

MEMS sensors to resolve spatial variations in shear stress in a 3-D blood vessel bifurcation model

Coronary artery disease (CAD) preferentially develops at the arterial branching points or bifurcations. Hemodynamics, particularly wall shear stress, plays an important role in regulating the development of CAD. The advent of the microelectromechanical systems (MEMS) sensor provides a potential entry point to overcome the difficulty in measuring temporal and spatial variations in shear stress. We, hereby, demonstrate the application of a MEMS sensor to resolve circumferential variations in shear stress using a three-dimensional symmetric bifurcation model. Reynolds numbers ranging from 1.34 to 6.7 were chosen to simulate flow at the microcirculation level. At these low Reynolds numbers, the wall shear stress was highest at the divider of bifurcation, and relaxed to a lower value downstream from the bifurcation. Skin friction coefficient values (C/sub f/), defined as local wall shear stress normalized by the upstream dynamic pressure, varied circumferentially by a factor of 2 or more from the medial wall at the divider to the lateral wall of bifurcation. These experimental skin friction coefficients at various positions were in close agreement with values derived from the Navier-Stokes solution.     

A 3-D anthropometric-muscle-based active appearance model

This paper describes a novel method for modeling the shape and appearance of human faces in three dimensions using a constrained three-dimensional (3-D) active appearance model (AAM). Our algorithm is an extension of the classical two-dimensional (2-D) AAM. The method uses a generic 3-D wireframe model of the face, based on two sets of controls: anatomically motivated muscle actuators to model facial expressions and statistically based anthropometrical controls to model different facial-types. The 3-D anthropometric-muscle-based model (AMBM) of the face allows representing a facial image in terms of a controlled model-parameter set, hence, providing a natural and constrained basis for face segmentation and analysis. The generated face models are consequently simpler and less memory intensive compared to the classical appearance-based models. The proposed method allows for accurate fitting results by constraining solutions to be valid instances of a face model. Extensive image-segmentation experiments have demonstrated the accuracy of the proposed algorithm against the classical AAM.     

Real-time 3-D ultrasound guidance of interventional devices

We have previously developed 2-D array transducers for many real-time volumetric imaging applications. These applications include transducers operating up to 7 MHz for transthoracic imaging, up to 15 MHz for intracardiac echocardiography (ICE), 5 MHz for transesophageal echocardiography (TEE) and intracranial imaging, and 7 MHz for laparoscopic ultrasound imaging (LUS). Now we have developed a new generation of miniature ring-array transducers integrated into the catheter deployment kits of interventional devices to enable real-time 3-D ultrasound scanning for improved guidance of minimally invasive procedures. We have constructed 3 new ring transducers. The first consists of 54 elements operating at 5 MHz. Typical measured transducer element bandwidth was 25%, and the 50 Ohm round trip insertion loss was -65 dB. Average nearest neighbor cross talk was -23.8 dB. The second is a prototype 108-element transducer operating at 5 MHz. The third is a prototype 108-element ring array with a transducer center frequency of 8.9 MHz and a -6 dB bandwidth of 25%. All transducers were integrated with an 8.5 French catheter sheath of a Cook Medical, Inc. vena cava filter deployment device.     

A miniaturized catheter 2-D array for real-time, 3-D intracardiac echocardiography

The design, fabrication, and characterization of a 112 channel, 5 MHz, two-dimensional (2-D) array transducer constructed on a six layer flexible polyimide interconnect circuit is described. The transducer was mounted in a 7 Fr (2.33 mm outside diameter) catheter for use in real-time intracardiac volumetric imaging. Two transducers were constructed: one with a single silver epoxy matching layer and the other without a matching layer. The center frequency and -6 dB fractional bandwidth of the transducer with a matching layer were 4.9 MHz and 31%, respectively. The 50 omega pitch-catch insertion loss was 80 dB, and the typical interelement crosstalk was -30 dB. The final element yield was greater than 97% for both transducers. The transducers were used to acquire real-time, 3-D images in an in vivo sheep model. We present in vivo images of cardiac anatomy obtained from within the coronary sinus, including the left and right atria, aorta, coronary arteries, and pulmonary veins. We also present images showing the manipulation of a separate electrophysiological catheter into the coronary sinus.     

Characterization of piezoelectric polymer composites for MEMS devices

Composite piezoelectric ceramics are important materials for transducer applications in medical diagnostic devices and MEMS devices. In micrometer scale the material properties of piezopolymers or piezoceramics do not coincide with that of bulk materials. The present work is aimed at simulating the material properties of piezoceramics and piezo-polymer composite thin films in the micrometer scale and then to determine the piezo-composite material properties. Piezoceramics have very high electromechanical coupling coefficient (k). But they have very high acoustic impedance and they are very brittle especially when thin films are fabricated. Piezopolymer like PVDF has low acoustic impedance and can be fabricated into thin films but it has very low k value and high dielectric losses. The combination of piezoceramics and piezopolymers form the piezocomposites, which have suitable material properties for transducer applications. The composites can have different connectivities. For 2?C2 composite, we can select two layers or a stack of PZT and PVDF layers. It is intended to determine the material properties both analytically and by simulation using computer simulation ANSYS software which implements finite element method (FEM). Although the simulation process presents approximate results, it can be verified from the large available experimental data from the literature with the simulated data.     

A class of data structures for 2-D and 3-D adaptive mesh refinement

A ‘family’ of tree data structures for adaptive mesh refinement is described and details concerning the associated logic are provided. The data structures encompass triangular elements and quadrilateral elements in two dimensions and quadrilateral bricks in three dimensions. Furthermore, both linear (bilinear) and quadratic (biquadratic) element types, respectively, are developed. Representative refinement results are given for the bilinear, trilinear and biquadratic types and associated performance studies made for the refinement procedure.     

显微干涉法在MEMS结构三维形貌测试中的应用

鉴于三维形貌在微机电系统(MEMS)测试领域的重要地位及显微干涉法在光学计量领域的高精度性能,开展了显微干涉法在MEMS结构三维形貌测试中的应用研究.基于小波变换极高的去噪性能及处理无载波条纹的优点,包裹相位采用连续小波变换的方法提取.基于展开相位拐点与符号歧义点的单应性,开展了通过检测展开相位拐点并对展开相位进行校正的方法恢复非单调条纹图的真实相位的研究.采用上述方法,成功测试了微梁的静、动态三维形貌及手机芯片的翘曲变形.该项研究为MEMS结构的三维形貌测试提供了高精度且简单快速的测量手段.     

A probabilistic fracture mechanics analysis for cracked pipe using 3-D model

For the purpose of probabilistic fracture mechanics (PFM) estimation based on elastic-plastic fracture mechanics (EPFM) in the field of reliability analysis of pressure vessels and piping, a 3-D EPFM database of fully plastic solutions for surface cracks and a PFM code for the integrity evaluation of nuclear structural components based on the above database are given. As an example, a comparison study of the PFM analysis is then performed between the 2-D and the 3-D solutions to demonstrate the 3-D effects on the solutions.     

A fiber placement device and methodology for preparing 2-D and 3-D combinatorial microcomposites

A fiber placement device is described and methodology is given for preparing two-dimensional (2-D) and three-dimensional (3-D) combinatorial microcomposites. Although 2-D microcomposites with uniform fiber spacing have been prepared previously, the preparation of uniformly spaced 3-D microcomposites with 6–20 μm diameter fibers is new. The preparation of these combinatorial specimens was motivated by research results from reference [Li et al. (1995) Compos Sci Technol 54:251]. These results showed that the mean fragment length of the broken fibers in an array of fibers of the shear-lag models increases as the inter-fiber separation decreases. It was noted that shear-lag theory predicts the opposite effect. Therefore, specimens of this type are needed to unambiguously verify this trend. In addition, data from this new technology should delineate the factors that influence critical flaw nucleation in unidirectional laminate composites. This paper is declared as a work of the U.S. Government and is not subject to copyright protection in the United States.

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Dual-fiber collimator with elliptical spot for optical MEMS devices

Fiber collimators are widely used in optical communication components and fiber-optic sensors. Ordinary fiber collimators are made with a circular beam waist radius from 100?μm to 300?μm. The circular beam waist is too large to switch or shut the beam for certain micro-electro-mechanical system (MEMS) actuators (such as MEMS linear mirrors). In this paper, a dual-fiber collimator with an elliptical spot is proposed to meet the demands of MEMS optical devices. The elliptical spot collimator has been designed and fabricated, the beam waist spot of which is an elliptical spot with a 231.6?μm long-axis radius and a 12.87?μm short-axis radius, and its coupling loss is 0.37?dB.     

2-D Wavelet Segmentation in 3-D T-Ray Tomography

In this letter, segmentation techniques for terahertz (T-ray) computed tomographic (CT) imaging are investigated. A set of linear image fusion and novel wavelet scale correlation segmentation techniques is adopted to achieve material discrimination within a 3-D object. The methods are applied to a T-ray CT image dataset taken from a plastic vial containing a plastic tube. This setup simulates the imaging of a simple nested organic structure, which provides an indication of the potential for using T-ray CT imaging to achieve T-ray pulsed signal classification of heterogeneous layers     

Sparse 2-D arrays for 3-D phased array imaging--design methods

One of the most promising techniques for limiting complexity for real-time 3-D ultrasound systems is to use sparse 2-D layouts. For a given number of channels, optimization of performance is desirable to ensure high quality volume images. To find optimal layouts, several approaches have been followed with varying success. The most promising designs proposed are Vernier arrays, but also these suffer from high peaks in the sidelobe region compared with a dense array. In this work, we propose new methods based on the principles of suppression of grating lobes to form symmetric and non-symmetric regular sparse periodic and radially periodic designs. The proposed methods extend the concept of sparse periodic layouts by exploiting either an increased number of symmetry axes or radial symmetry. We also introduce two new strategies to form designs with nonoverlapping elements. The performance of the new layouts range from the performance of Vernier arrays to almost that of dense arrays. Our designs have simplicity in construction, flexibility in the number of active elements, and the possibility of trade off sidelobe peaks against sidelobe energy.     

A finite difference model for cMUT devices

A finite difference method was implemented to simulate capacitive micromachined ultrasonic transducers (cMUTs) and compared to models described in the literature such as finite element methods. Similar results were obtained. It was found that one master curve described the clamped capacitance. We introduced normalized capacitance versus normalized bias voltage and metallization rate, independent of layer thickness, gap height, and size membrane, leading to the determination of a coupling factor master curve. We present here calculations and measurements of electrical impedance for cMUTs. An electromechanical equivalent circuit was used to perform simulations. Our experimental measurements confirmed the theoretical results in terms of resonance, anti-resonance frequencies, clamped capacitance, and electromechanical coupling factor. Due to inhomogeneity of the tested element array and strong parasitic capacitance between cells, the maximum coupling coefficient value achieved was 0.27. Good agreement with theory was obtained for all findings.     

A 3-D micromechanical model for predicting the elastic behaviour of woven laminates

This paper presents an analytical model for the prediction of the elastic behaviour of plain-weave fabric composites. The fabric is a hybrid plain-weave with different materials and undulations in the warp and weft directions. The derivation of the effective material properties is based on classical laminate theory (CLT).The theoretical predictions have been compared with experimental results and predictions using alternative models available in the literature. Composite laminates were manufactured using the resin infusion under flexible tooling (RIFT) process and tested under tension and in-plane shear loading to validate the model. A good correlation between theoretical and experimental results for the prediction of in-plane properties was obtained. The limitations of the existing theoretical models based on classical laminate theory (CLT) for predicting the out-of-plane mechanical properties are presented and discussed.     

A 256 x 256 2-D array transducer with row-column addressing for 3-D rectilinear imaging

We present simulation and experimental results from a 5-MHz, 256times256 2-D (65536 elements, 38.4times38.4 mm) 2-D array transducer with row-column addressing. The main benefits of this design are a reduced number of interconnects, a modified transmit/receive switching scheme with a simple diode circuit, and an ability to perform volumetric imaging of targets near the transducer with transmit beamforming in azimuth and receive beamforming in elevation. The final dimensions of the transducer were 38.4 mm times 38.4 mm times 300 mum. After a row-column transducer was prototyped, the series resonance impedance was 104 Omega at 5.4 MHz. The measured -6 dB fractional bandwidth was 53% with a center frequency of 5.3 MHz. The SNR at the transmit focus was measured to be 30 dB. At 5 MHz, the average nearest neighbor crosstalk was -25 dB. In this paper, we present 3-D images of both 5 pairs of nylon wires embedded in a clear gelatin phantom and an 8 mm diameter cylindrical anechoic cyst phantom acquired from a 256 times 256 2-D array transducer made from a 1-3 composite. We display the azimuth and elevation B-scans as well as the C-scan for each image. The cross-section of the wires is visible in the azimuth B-scan, and the long axes can be seen in the elevation B-scan and C-scans. The pair of wires with 1-mm axial separation is discernible in the elevational B-scan. When a single wire from the wire target phantom was used, the measured lateral beamwidth was 0.68 mm and 0.70 mm at 30 mm depth in transmit beamforming and receive beamforming, respectively, compared with the simulated beamwidth of 0.55 mm. The cross-section of the cyst is visible in the azimuth B-scan whereas the long axes can be seen as a rectangle in the elevation B-scan and C-scans.     

A 2-D mesoscopic model coupling mechanical and diffusion for electromigration in thin films

Electromigration is an important mechanism of deformation and failure in miniaturized electronics materials. In this paper, a 2-D mesoscopic simulation method is developed for analyzing electromigration-induced stress in thin films and finite element method is implemented for solution. Numerical simulations are compared with theoretical result and comparisons validate the model. The method has advantage in describing boundary conditions for constrained diffusion when focusing on creep process of thin films.