Alexander Doll

A generic analytical model for micro-diaphragm pumps with active valves

We present a fully analytical model for micro-diaphragm pumps with active valves, based on the peristaltic working principle. Our model is suited for very fast as well as for very slow actuation mechanisms. Therefore it can be applied to a variety of actuation principles, e.g. piezoelectric, pneumatic, thermo-pneumatic or pre-stressed shape memory actuation. We show that the dynamics of this kind of micropump can be fully described by a lumped element approach taking only the mechanical behaviour of the diaphragms and the viscous losses at the valves into account. The full flow versus frequency and backpressure characteristic is derived. Our model is capable of predicting the maximum achievable flow rate and the maximum sustainable backpressure of micro-diaphragm pumps with active valves. Different modes of operation, which are distinguished by the speed of the actuation mechanism, the pressure history inside the pump and the applied driving scheme, are identified. We show that micro-diaphragm pumps with active valves generally suffer from a linear dependence of the flow rate on the applied backpressure. This fact, which is already known from micropumps with passive valves, is remarkable, because it is in contradiction to the characteristics of macroscopic peristaltic pumps. A set of design rules for the dimensioning of the valves in dependence on the actuation force and the desired hydrodynamic characteristics (maximum flow rate and maximum sustainable backpressure) are derived. Our theoretical results are proven by experimental results of our piezoelectrically actuated micropump. A maximum flow rate of 1.4 ml min−1 and a maximum sustainable backpressure of 40 kPa were achieved.

A novel two-stage backpressure-independent micropump: modeling and characterization

A novel design of a piezoelectric silicon micropump is proposed, which provides a constant flow rate over a wide backpressure range of up to 30 kPa. This highly appreciable feature is based on a new serial arrangement of two active valves and relies on both an appropriate electrical actuation sequence of the piezo-actuators and an immanent limitation of the membrane deflection by the valve seats. The design is optimized for the low flow regime ranging from 0.1 to 50 µl min−1. A detailed lumped-parameter model is derived in order to reveal the physics behind this pumping principle and to identify the optimum control scheme. For the fabrication of our device, a comparably simple and robust 2-wafer process is utilized. A thorough experimental investigation demonstrates the high performance of the micropump. The backpressure independence of the flow rate enables high-resolution volumetric dosing within the aforementioned flow range. The stroke volume and hence the resolution of the micropump is adjustable via the upstroke voltage of the actuator between 50 and 200 nl. Depending on this setting typical actuation frequencies range from 0.05 to 5 Hz and the flow rate scales proportional to the frequency within that frequency range.

Pressure-Independent Micropump with Piezoelectric Valves for Low Flow Drug Delivery Systems

We present - for the first time - a novel design of a micropump which enables a backpressure-independent flow rate up to 20 kPa within the low flow regime required for drug delivery systems. Our concept, based on two piezoelectrically actuated diaphragms, allows an accurate dosing in the range of 1 - 50 µ l/min with freely programmable release profiles and offers the potential to minimize chip size and power consumption in comparison to 3-actuator peristaltic micropumps. The stroke volume is adjustable between 50 - 200 nl by means of voltage control which enables a high resolution volumetric dosing. Within the relevant frequency range below 2 Hz the flow rate is proportional to the frequency. Our design also excels in its comparably simple and robust 2-layer fabrication process.

Low temperature plasma-assisted wafer bonding and bond-interface stress characterization

This paper presents the development and characterization of a low temperature plasma-assisted direct wafer bonding process for structured silicon wafer pairs. We have achieved spontaneous bonding at room temperature with a surface energy of up to 1.2 J/m/sup 2/. It turned out that the bonding process is not deteriorated by the history of the wafers, even after etching for several hours. The yield of the process is 80-95%. A blister test was used to determine the bond strength and the failure distribution for different plasma gases and annealing treatments. Film stress of the bonded interfacial oxide was found to transfer to the bonding partner. Selective wafer bonding was made by structuring the interfacial oxide layer. Design rules for proper bonding are given.

A Piezoelectric Bidirectional Micropump for a Medical Application

In this work, we present recent developments of our novel artificial sphincter system. The highly integrated system consists of several inflatable balloons and a micropump. We will analyse the apparatus concerning the volumes that have to be moved and make a specification for a suitable pump. A bidirectional silicon micropump with active valves is used to meet the worked out requirements of the sphincter prosthesis. The fabrication of the pump is described and the working principle will be explained. A summary of an analytical lumped parameter approach to model the pump’s performance is given. Optimization measures derived from this model are pointed out. The driver electronics is described and energy consumption issues are discussed. Two different pump designs were realized. The measured pump performance concerning the flowrate and the achievable pressure were compared to the theoretical model. A good agreement between model and measured data was found. A maximum flowrate of 1.3 ml/min and a maximum backpressure of 40000 Pa was achieved. The realized pump performance is sufficient for first experimental studies with the artificial sphincter system.Copyright

A high performance bidirectional micropump for a novel artificial sphincter system

We present the design, fabrication and testing of a novel medical implant based on a high performance silicon micropump. An analytical model was exploited for further optimization of our micropump design. The experimental data obtained are in a good accordance with theory. Two sphincter prostheses of different sizes were developed and tested. Their general medical capability as a prosthesis has been proven.

German Artificial Sphincter System-GASS II: Erste in vivo Evaluation eines neuen hochintegrativen Neosphinkters zur Therapie der hochgradigen Stuhlinkontinenz / Short time in vivo evaluation of a novel and highly integrated sphincter prosthesis for therapy of major fecale incontinence

Abstract Zur Therapie der hochgradigen Stuhlinkontinenz integriert das German Artificial Sphincter System GASS erstmals alle wesentlichen Funktionsbausteine in einer Schließmuskelprothese. Ein bidirektional arbeitender und hochleistungsfähiger Piezoantrieb, kleinsten Ausmaßes, ermöglicht eine ferngesteuerte Bedienung. Diese Studie berichtet erstmals über die Optimierung der Leistungscharakteristik der Piezopumpe und Weiterentwicklung von GASS zu einem funktionsfähigen Vollimplantat. Am Großtiermodell wurde eine erste Kurzzeitevaluierung vorgenommen. Die Prothese zeichnet sich durch ein einfaches Handling, Betriebsstabilität und hohe Kontinenzeffektivität aus. The German Artificial Sphincter System GASS consists of a support ring which includes a fluid reservoir on the outer side and an occlusive cuff on the inner side. The cuffs are designed as polyurethane hollow bodies with a pre-determined inflation volume and are connected to an integrated piezo micropump/valve unit. To evaluate the threshold of continence, the GASS was placed around the anorectal junction via a perineal approach in one mini pig. The novel cuff design reduces the occlusion pressure and allows low compression volumes. Low operating pressures indicate a minor risk of ischemia injury of the bowel. The operation time is estimated at about 6 days with no recharging of the battery. The novel remote controlled GASS is a highly integrated prosthesis for placement around the anal canal or lower rectum and is effective in restoring continence for liquids and solids in vitro and in vivo.

Design of Micro Diaphragm Pumps With Active Valves

This paper deals with the theory, fabrication and characterization of micro diaphragm pumps with active valves. Three types of micropumps with piezoelectric actuation are presented. Special emphasis is given on the accordance of theory and experiment. The theory is based on a lumped-element approach that is reduced to its basics to enable a reasonable accuracy with a minimized set of conceptional parameters. The experimental results fit well to the theory. The fabrication technology of the micropumps comprises of a silicon bulk micromechanics process in combination with a back-end gluing process of piezoelectric PZT-disks (PZT lead-circonat-titanat) to the silicon diaphragms. The micropumps were developed for different applications. The three- and the four-diaphragm micropumps were designed as high performance drivers for an artificial sphincter prosthesis. They show a maximum flowrate of 4 ml/min and a maximum sustainable backpressure of up to 70 kPa. The two-diaphragm micropump was engineered for an implantable drug delivery device and features a pressure independent dosing for backpressures up to 20 kPa.Copyright

An Implantable Active Microport Based on a Self-Priming High-Performance Two-Stage Micropump

This paper reports on significant progress in the development of an implantable active microport system for an automated administration of aqueous drug suspensions. A novel piezoelectric two-stage micropump ensures the controlled release of minute amounts of fluid with flow rates between 0.1 mul/min and 50 mul/min. A modification of the chamber design reduces the detrimental effect of entrapped air bubbles. Due to an increased compression ratio the micropump has now a full capability to pump gas which enables a reliable self-priming. Moreover, the absence of air bubbles in the pump chamber yields a significantly enhanced accuracy of the delivered fluid volumes.

Non-Destructive Strength Characterization of Full-Wafer Bonds Using a Modified Blister Test Method

This paper presents a novel test method for a non-destructive strength characterization of bonded silicon wafer pairs. The test is based on a controlled crack generation at the bond interface using a modified blister test method. An analytical model was used to establish an essential design parameter. Therewith, different test structures were analyzed and important information about crack generation and crack propagation were gained. Finally, the theory of controlled crack generation was verified and demonstrated by a modified blister test.