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.

An artificial sphincter prototype has been developed, specifically designed for comfortable remote control by fecally incontinent patients. The artificial sphincter includes a fluid reservoir, an occlusive cuff, and a micropump based on piezo-technology in a single unit. Continence and implantation management were evaluated around isolated porcine anal canals and in vivo. The design of the prosthesis reduces the occlusion pressure and allows low inflation volumes (6.5-16 mL). Operating pressures between 24 and 58 mm Hg indicate a minor risk of ischemic injury to the bowel. The operation time is estimated at about 7 days with no recharging of the battery. The novel prototype is a highly integrated prosthesis for placement around the anal canal or lower rectum, effecting continence with comfortable control.

Versatile low temperature wafer bonding and bond strength measurement by a blister test methodAbstract We present a low temperature plasma assisted bonding process that enables the bonding of silicon, silicon oxide and silicon nitride wafers among each other at annealing temperatures as low as room temperature. The process can be applied using standard clean room equipment. Surface energies of differently treated bonded samples are determined by a blister test method for square shaped cavities. For this reason, we extend the well-known blister test method for round shaped cavities to the square shaped case by a combined analytical and numerical approach. Accordingly, the energetic favored crack front propagation in the bond interface is determined by numerical simulations. The surface energies of the tested samples are calculated and compared to anodic silicon-to-Pyrex Ò bonds. Surface energies of up to 2.6 J/m 2 can be achieved between silicon and silicon oxide wafer pairs at low annealing temperatures. Room temperature bonded samples show a surface energy of 1.9 J/m 2 . The surface energy of silicon-to-Pyrex glass bonds yields 1.3 J/m 2 . Small structures, e.g., bridges down to 5 lm can be bonded using the discussed bonding process. Selective bonding of silicon-to-silicon oxide wafer pairs is performed by structuring the oxide layer. The successful integration of the bonding process into the fabrication of micropumps is highlighted.

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We present a novel concept of an implantable active microport based on micro technology that incorporates a high-resolution volumetric dosing unit and a drug reservoir into the space of a conventional subcutaneous port. The controlled release of small drug volumes from such an "active microport" is crucial e.g. for innovative methods in cancer treatment or pain therapy. Our microport system delivers a flow rate in the range of 10-1,000 mul/h and enables a patient-specific release profile. The core of our device is a two-stage piezoelectric micropump. It features a backpressure-independent volumetric dosing capability i.e. a stable flow rate is ensured up to a backpressure of 30 kPa. The stroke volume and hence the resolution of the mircopump is voltage controlled and can be preset between 10 and 200 nl. A miniaturized high-performance electronic control unit enables freely programmable dosing profiles. This electronic circuit is optimized for both energy consumption and weight which are both essential for a portable device. The data of an implemented pressure sensor are used to permanently monitor the dosing process and to detect a potential catheter occlusion. A polyurethane soft lithography process is introduced for the fabrication of the prototype. Therewith, a compact multilayer system has been developed which measures only 50 x 35 x 25 mm(3).

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This article presents experimental characterization and numerical simulation techniques used to create large amplitude and high frequency surface waves with the help of a metal/ceramic composite transducer array. Four piezoelectric bimorph transducers are cascaded and operated in a nonlinear regime, creating broad band resonant vibrations. The used metallic plate itself resembles a movable wall which can align perfectly with an airfoil surface. A phase-shifted operation of the actuators results in local displacements that generate a surface wave in the boundary layer for an active turbulence control application. The primary focus of this article is actuator design and a systematic parameter variation experiment which helped optimize its nonlinear dynamics. Finite Element Model (FEM) simulations were performed for different design variants, with a primary focus in particular on the minimization of bending stress seen directly on the piezo elements while achieving the highest possible deflection of the vibrating metallic plate. Large output force and a small yield stress (leading to a relatively small output stoke) are characteristics intrinsic to the stiff piezo-ceramics. Optimized piezo thickness and its spatial distribution on the bending surface resulted in an efficient stress management within the bimorph design. Thus, our proposed resonant transduction array achieved surface vibrations with a maximum peak-to-peak amplitude of 500 μm in a frequency range around 1200 Hz.