We survey progress over the past 25 years in the development of microscale devices for pumping fluids. We attempt to provide both a reference for micropump researchers and a resource for those outside the field who wish to identify the best micropump for a particular application. Reciprocating displacement micropumps have been the subject of extensive research in both academia and the private sector and have been produced with a wide range of actuators, valve configurations and materials. Aperiodic displacement micropumps based on mechanisms such as localized phase change have been shown to be suitable for specialized applications. Electroosmotic micropumps exhibit favorable scaling and are promising for a variety of applications requiring high flow rates and pressures. Dynamic micropumps based on electrohydrodynamic and magnetohydrodynamic effects have also been developed. Much progress has been made, but with micropumps suitable for important applications still not available, this remains a fertile area for future research.

https://microfluidics.stanford.edu/Publications/Micropumps_Cooling/Laser%20Review%20of%20Micropumps%20in%20JMM.pdf

A review of micropumps

Wood density (Dt), an excellent predictor of mechanical properties, is typically viewed in relation to support against gravity, wind, snow, and other environ- mental forces. In contrast, we show the surprising extent to which variation in D t and wood structure is linked to support against implosion by negative pressure in the xy- lem pipeline. The more drought-tolerant the plant, the more negative the xylem pressure can become without cavitation, and the greater the internal load on the xylem conduit walls. Accordingly, Dt was correlated with cavi- tation resistance. This trend was consistent with the maintenance of a safety factor from implosion by nega- tive pressure: conduit wall span ( b) and thickness (t) scaled so that (t/b) 2 was proportional to cavitation resis- tance as required to avoid wall collapse. Unexpectedly, trends in Dt may be as much or more related to support of the xylem pipeline as to support of the plant.

/pdf/trends-in-wood-density-and-structure-are-linked-to-328b9yvfwi.pdf

Trends in wood density and structure are linked to prevention of xylem implosion by negative pressure

A set of electrostatically actuated microelectromechanical test structures is presented that meets the emerging need for microelectromechanical systems (MEMS) process monitoring and material property measurement at the wafer level during both process development and manufacturing. When implemented as a test chip or drop-in pattern for MEMS processes, M-Test becomes analogous to the electrical MOSFET test structures (often called E-Test) used for extraction of MOS device parameters. The principle of M-Test is the electrostatic pull-in of three sets of test structures [cantilever beams (CB's), fixed-fixed beams (FB's), and clamped circular diaphragms (CD's)] followed by the extraction of two intermediate quantities (the S and B parameters) that depend on the product of material properties and test structure geometry. The S and B parameters give a direct measure of the process uniformity across an individual wafer and process repeatability between wafers and lots. The extraction of material properties (e.g., Young's modulus, plate modulus, and residual stress) from these S and B parameters is then accomplished using geometric metrology data. Experimental demonstration of M-Test is presented using results from MIT's dielectrically isolated wafer-bonded silicon process. This yielded silicon plate modulus results which agreed with literature values to within /spl plusmn/4%. Guidelines for adapting the method to other MEMS process technologies are presented.

/pdf/m-test-a-test-chip-for-mems-material-property-measurement-2d2w3nnaej.pdf

M-TEST: A test chip for MEMS material property measurement using electrostatically actuated test structures

Piezoresistive sensors are among the earliest micromachined silicon devices. The need for smaller, less expensive, higher performance sensors helped drive early micromachining technology, a precursor to microsystems or microelectromechanical systems (MEMS). The effect of stress on doped silicon and germanium has been known since the work of Smith at Bell Laboratories in 1954. Since then, researchers have extensively reported on microscale, piezoresistive strain gauges, pressure sensors, accelerometers, and cantilever force/displacement sensors, including many commercially successful devices. In this paper, we review the history of piezoresistance, its physics and related fabrication techniques. We also discuss electrical noise in piezoresistors, device examples and design considerations, and alternative materials. This paper provides a comprehensive overview of integrated piezoresistor technology with an introduction to the physics of piezoresistivity, process and material selection and design guidance useful to researchers and device engineers.

/pdf/review-semiconductor-piezoresistance-for-microsystems-2i2jehwa4g.pdf

Review: Semiconductor Piezoresistance for Microsystems

Micromachining and micro-electromechanical system (MEMS) technologies can be used to produce complex structures, devices and systems on the scale of micrometers. Initially micromachining techniques were borrowed directly from the integrated circuit (IC) industry, but now many unique MEMS-specific micromachining processes are being developed. In MEMS, a wide variety of transduction mechanisms can be used to convert real-world signals from one form of energy to another, thereby enabling many different microsensors, microactuators and microsystems. Despite only partial standardization and a maturing MEMS CAD technology foundation, complex and sophisticated MEMS are being produced. The integration of ICs with MEMS can improve performance, but at the price of higher development costs, greater complexity and a longer development time. A growing appreciation for the potential impact of MEMS has prompted many efforts to commercialize a wide variety of novel MEMS products. In addition, MEMS are well suited for the needs of space exploration and thus will play an increasingly large role in future missions to the space station, Mars and beyond. (Some figures in this article are in colour only in the electronic version)

https://iopscience.iop.org/article/10.1088/0964-1726/10/6/301/pdf

Microelectromechanical systems (MEMS):fabrication, design and applications

Chapter 1. Introduction Chapter 2. Stress and Strain: Important Relationships Chapter 3. The Behavior of Bodies Under Stress Chapter 4. Principles and Analytical Methods Chapter 5. Numerical Methods Chapter 6. Experimental Methods Chapter 7. Tension, Compression, Shear, and Combined Stress Chapter 8. Beams Flexure of Straight Bars Chapter 9. Curved Beams Chapter 10. Torsion Chapter 11. Flat Plates Chapter 12. Columns and Other Compression Members Chapter 13. Shells of Revolution Pressure Vessels Pipes Chapter 14. Bodies under Direct Bearing and Shear Stress Chapter 15. Elastic Stability Chapter 16. Dynamic and Temperature Stresses Chapter 17. Stress Concentration Chapter 18. Fatigue and Fracture Chapter 19. Stresses in Fasteners and Joints Chapter 20. Composite Materials Chapter 21. Solid Biomechanics Appendix A. Properties of a Plane Area Appendix B. Mathematical Formulas and Matrices Appendix C. Glossary Index

Warren C Young

Papers

Roark's Formulas for Stress and Strain