Patent number 8608700 is assigned to
The following quote was obtained by the news editors from the background information supplied by the inventors: "Microelectromechanical systems (MEMS) are small, generally movable devices which are made using semiconductor integrated circuit fabrication techniques. Because of these batch processing techniques, large numbers of small MEMS devices can be made on a single wafer substrate at low cost with high precision. MEMS devices typically have dimensions on the order of microns, and can thus be used to make very small actuators which are capable of very small and precise movements. Such actuators can make use of any of a number of phenomena to produce motion in the movable member. MEMS actuators are known which use electrostatic, thermal, magnetostatic and piezo electric effects, for example, to produce motion in the movable actuator member.
"Microelectromechanical systems (MEMS) techniques may therefore be used to produce microfabricated piezoelectric actuators. Piezoelectric materials are those which undergo a strain when a voltage is applied, or generate a voltage when a stress is applied. Prior art actuators exist which use piezoelectric materials, and may be used as the pumping mechanism for a microfluidic pump. The piezoelectric microactuator can be made by depositing a stack of piezoelectric layers on a thin diaphragm which defines the pumping chamber. Application of a voltage to the piezoelectric stack results in a deformation of the diaphragm, which draws the fluid into the chamber through an inlet valve. When the voltage is discontinued, the diaphragm returns to its original shape, forcing fluid out of the chamber through an outlet valve. Piezoelectric microactuators generally produce a force perpendicular to the plane of the substrate on which they are deposited, and thus move primarily in this direction. A thorough analysis of the attributes of such a pump is set forth in 'Simulation of MEMS Piezoelectric Micropump for Biomedical Applications', which discusses the speed and displacement of such an actuator, and can be accessed at http://www.algor.com/news_pub/tech_white_papers/MEMS_micropump/default.as- p.
"Lead zirconate titanate, Pb(Zr,Ti)O.sub.3 (PZT), is a common piezoelectric material that can be deposited on silicon wafers by RF sputtering, for example. However, care must be taken to relieve the stresses in the deposited material in order to avoid static deformation, or warpage, of the pumping diaphragm. Alternatively, high performance PZT wafers are also under development; however they are not yet available in sufficiently large (150 mm round) format to facilitate wafer-to-wafer bonding, an essential process for low cost manufacturing. Accordingly, the exemplary piezoelectric micropump discussed above is an idealized case, with zero residual stress, and such pumps tend to be expensive and difficult to fabricate.
"This technology has several other drawbacks, the most significant of which are that the piezoelectric actuator has limited throw and requires large actuation voltages. If non-resonant excitation of the above structure is used to actuate the diaphragm, the displacement of the design described above is less than 10 .mu.m for a 200V input. If resonant excitation is used; i.e. a modulated voltage waveform is applied to the device to amplify the displacement, a ten fold increase in the displacement can be achieved; however, it takes about 100 msec to achieve this displacement. The low resonant frequency is a result of the weight of the piezoelectric material and the size of the pumping diaphragm needed to achieve the necessary pumping volume. The mass of the volume of fluid may also play a role in the low resonant frequency. If the pump is operated above this resonant frequency, the displacement is greatly diminished to only about 3 .mu.m at 500 Hz for 200V input.
"Furthermore, when used in a pumping device, the piezoelectric device described above has chambers and a layout that do not allow the passage of relatively large particles. For example, particles in excess of about 10 .mu.m will not pass readily through the fluid path, because of the severe turns and small apertures in the path. Vertical pumps such as that described may also be relatively expensive and difficult to fabricate, because the valves are necessarily formed vertically below the diaphragm using other layers. Finally, since the piezoelectric material can only generate a strain in a single direction in response to an applied voltage, the actuator can only deform in one direction, i.e. it can only 'push' and cannot 'pull'.
"Accordingly, a need exists for a microactuator capable of delivering small volumes of fluids as well as particulate matter suspended in the fluid stream, and which is inexpensive and easy to fabricate. The microactuator ideally operates at low voltages and is capable of being powered by a small battery."
In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventor's summary information for this patent: "Disclosed herein is a MEMS electromagnetic actuator which can pull as well as push. When deployed as a fluid pump, the actuator is also capable of pumping slurries of particulate matter suspended in a fluid stream. The microactuator may be batch fabricated, and so may be relatively inexpensive and easy to fabricate, and operates at low voltages and powers. Although referred to herein as a 'push-pull actuator,' it should be understood that this term is intended to refer to an actuator that can move in two substantially different directions in response to a force-generating apparatus. Thus the term does not limit the actuator to one with antiparallel motion.
"The electromagnetic actuator may have two separate components: a flux-generating portion and a separate, permeable, movable portion. The movable portion may be formed on a substrate with at least one magnetically permeable feature, and the flux-generating portion, may be formed separate from the substrate. The flux-generating portion generates lines of flux which are collected by the at least one magnetically permeable feature, wherein the flux-generating portion includes a plurality of electrical coils, each of which generates a magnetic field in a substantially different direction, wherein the fields produced by the plurality of coils causes a movement in the movable structure in a plurality of directions. For example, one first set of coils may produce a flux along the axis of the coil in one direction. Another second set of coils disposed perpendicularly to the first will generate flux in the perpendicular direction. The first set of coils may drive the movable portion away from the flux-generating portion, wherein the second set of coils may draw the movable portion toward the flux-generating portion, yielding a push-pull actuator. The operation of this anti-parallel, push-pull electromagnetic actuator is described in detail below.
"The movable portion of the push-pull electromagnetic MEMS actuator may be fabricated by forming a magnetically permeable, movable feature affixed to support diaphragm or membrane, using MEMS fabrication techniques, for example. The separate flux-generating portion may be a hand-wound core, for example. The flux-generating portion is then brought into close proximity to the movable portion, such that the two are separated by a narrow gap. Then, a first of the set of conducting coils is energized in the flux-generating portion. This produces flux along the axis of the coil and in the permeable core. The flux circulating in the flux-generating portion jumps across the narrow gap, entering the permeable feature of the movable diaphragm, and provides a magnetic field gradient whose details depends on the orientation and disposition of these permeable features. This field gradient may push the diaphragm back, toward the permeable features and away from the flux-generating portion. The pushing of the diaphragm may be used to expel a fluid from a fluidic chamber, and draw fluid into another fluidic chamber.
"The first coil is then disengaged from the power supply, and the other coil is energized, producing a magnetic field along its orthogonal axis. This field may interact differently with the permeable features, and draw the movable portion in a different direction, such as toward the flux-generating portion. This may reduce the volume of the pumping chamber, thus forcing fluid through an outlet valve. This motion may expel fluid from one chamber, and draw fluid into another.
"The push-pull electromagnetic actuator moves substantially in the plane of the substrate. For at least this reason, relatively complex structures may be used for the actuator element. For example, restoring springs may have a complex shape, in order to achieve the required spring constant. Thus, the push-pull electromagnetic actuator is relatively inexpensive and easy to fabricate, using MEMS surface micromachining techniques. Furthermore, the push-pull electromagnetic actuator uses electromagnetic actuation, which is capable of generating at least about 3 mN of actuation force and at least 10 um displacement. This actuation force may be sufficient for use as a fluid pump, to force the fluid through a 200 .mu.m aperture cannula. Because of its relatively large pumping force, the push-pull electromagnetic MEMS actuator may be coupled with a cannula or hypodermic needle and drug reservoir, to deliver a drug subcutaneously from a drug reservoir to a patient in need of the drug.
"Because the pump displacement is small, the microfabricated pump is capable of delivering dosages in very small, well controlled amounts. Because the power requirements are also small, battery operation with a button-type battery is foreseen. For these reasons, it is anticipated that this pump design may be appropriate for the delivery of small amounts of drugs such as insulin on a nearly continuous basis to a diabetic patient. The push-pull electromagnetic MEMS pump may be designed to fit within an adhesive patch worn against the skin of diabetic patients, such that the device is able to operate in a way that closely mimics the function of the human pancreas. However, potential applications are not limited to diabetes treatments. It may also be used to deliver any of a wide range of medications, including chemotherapies, pain medication and other therapeutic compounds that are best administered in small, controlled dosages. For example, the push-pull electromagnetic MEMS pump may be used for the delivery of nitroglycerin (for chest pain), scopolamine (for motion sickness), nicotine (for smoking cessation), clonidine (for high blood pressure), and fentanyl (for pain relief), as well as hormones (for menopausal symptoms) and many other drugs/applications.
"While the push-pull electromagnetic actuator is described with respect to a particular application, that of a fluid pump, it should be understood that the actuator may be applied to many other situations as well. Its reciprocating motion may be adapted to the rotation of a shaft, for example, when coupled with appropriate gears and bearings.
"These and other features and advantages are described in, or are apparent from, the following detailed description."
URL and more information on this patent, see: Rubel, Paul J.. Microfabicated Electromagnetic Actuator with Push-Pull Motion. U.S. Patent Number 8608700, filed
Keywords for this news article include: Therapeutics,
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