|M.Sc Thesis||Department of Mechanical Engineering|
|Supervisor:||Prof. Emeritus Hetsroni Gad|
Micro-electro-mechanical systems (MEMS) have enabled a wide range of actuators to be achieved by allowing microchips to contain versatile devices. One of the first components to be realized in micro-scale using silicon technology was microflow systems. In the first step of harnessing this technology into reality, modeling is a start point to estimate the key parameters, which govern the already complex problem of Shape Memory Alloys (SMA).
This thesis involves a research and fabrication of a shape memory alloy micropump with sputter-deposited Nickel-Titanium (NiTi) thin film actuator, working as a membrane. A general overview of micropumps is presented and analyzed. We located the main drawbacks of the reviewed micropumps, and as a consequence, introduced a novel concept of reciprocating SMA micropump. NiTi actuators are capable of both high forces and high strains, and have electrical resistivity, which is suitable for Joule heating that enables direct control of the device.
Throughout the work, a simplified theoretical model has been formulated in order to cover the physical phenomena connected to the micropump. We laid-out a set of equations, which we believe to be optimal for the realization of our proposed SMA micropump. We chose this model because it is describing, in a simple but accurate way, the functionality of the SMA membrane.
Afterwards, a lab device was fabricated by using conventional MEMS techniques for the device structure, and the NiTi thin film was manufactured by sputter-deposition. The NiTi membrane went through heat treatment under external mechanical constraint, in a vacuum surrounding, in order to gain its shape memory effect. This procedure is also known as “Training”. As a result, we have succeeded in performing shape setting to the thin film, and moreover, we came upon a unique phenomenon associated with SMA, named Two-Way Shape Memory Effect (TWSME). After packaging the micropump device, we characterized its performance by measuring the flow-rate with respect to the actuation frequency and backpressure, respectively. A maximum (Deionized) water flow-rate of 79μl/min was achieved at 2Hz actuation frequency, and a flow-rate / backpressure linear dependence was shown.