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Data: 29-feb-2012
Autori: Beninato, Angela
Titolo: Development of innovative transducers based on Magnetic Fluids
Abstract: It is quite common, in the advances on scientific research, to witness how material properties are exploited toward sensing applications in order to realize novel devices with high performances and tunable characteristics. The synthesis of materials that are not in nature but that are rea-lized in chemical laboratories is often a response to such a requirement. In particular meta materials and, in general, those materials made by the aggregation of several components to result into a multi-phase compound, are often very flexible and can provide very interesting performance in many different application fields. Among these, magnetic materials have gained great relevance thanks to the possibility of controlling many of their features via external magnetic fields but also to the fact that their presence, position or space distribution, is easily detectable by using magnetic sensors. In this Thesis an innovative approach to the development of com-plex devices made by multiple sensing parts together with actuators, and an integrated micro-fluidic system are considered. The basic concept here is the use of new materials, called ferrofluids or magnetic fluids, made by a suspension of magnetic nanoparticles in a carrier fluid; several different devices have been developed and are shown here in order to demonstrate the possibility to use ferrofluids as a core material to realize both the actuating section of a fluidic system and the sensing. The devices realized have been developed as laboratory prototypes and as proofs of concept of the ideas that have been first conceived, and then mathematical and numerical modeled prior to be designed as experimental devices. Due to the intrinsic magnetic nature of the ferrofluids, a briefly introduction on basic concepts about magnetism is discussed in Chapter 1. A classification of materials in nature according to their magnetic behavior is reported, together with some details about the two fundamental source of magnetism: permanent magnets and electromagnets. Finally the main typologies of magnetic sensors commercially available are discussed. In Chapter 2 the magnetic fluids are presented, together with their applications both in the market and in the research world. The main forces acting on a ferrofluid mass are discussed and modeled. In Chapter 3 the attention is focused toward sensors realized during this Ph.D. research activity: a gyroscope, a displace-ment/acceleration sensor, a flow sensor and an inclinometer are dis-cussed, together with their physical model and with the experimental characterization. In Chapter 4 research results on ferrofluids when used in actuators are presented. Plungers, valves and a position control system for ferrofluids drop in water have been developed. Two devices are presented: a pump in which a ferrofluid mass is controlled by an array of electromagnets, and a path tracking system, in which a mass is moved along a pre-defined path by a matrix of electromagnets. The implementation toward integrated device is nowadays of paramount importance in the development of novel systems and transducers. The devices presented here has been developed as laboratory prototype and their scaling toward microsystems is straightforward and has been also addressed during this Ph.D. activity. In Chapter 5 two examples of integrated system in which ferrofluids can be used both in the fluidic part and in the sensing devices are presented. The former structure is a system that can be used for biological measures; in this case ferrofluid is used both in the fluidic part implementing valves and plunger, and as magnetic label for biological entities. The latter one represents a multi-sensorial systems, in which ferrofluids are used in order to implement valves and also as inertial mass of the sensors integrated in the structure.
InArea 09 - Ingegneria industriale e dell'informazione

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