No presente trabalho, foi construído um transdutor para medir as variações da indução magnética (B) e magnetostricção (?) de materiais ferromagnéticos macios em função de campo magnético aplicado (H) (voltagem V) e tensões mecânicas (?). O transdutor possui duas bobinas de excitação ligadas a uma fonte de corrente/voltagem (para aplicar o campo magnético no elemento magnetostrictivo) e um núcleo magnético, para concentrar o fluxo magnético no material ferromagnético. A magnetostricção é medida por extensômetria, a tensão mecânica é aplicada por uma máquina de ensaios universal (EMIC), a indução magnética é medida utilizando uma bobina de captura conectada a um fluxímetro e a aquisição dos dados foi realizada por um programa em Labview. O sistema mede curvas de M vs V e ? vs V para ? constante e também M vs ? e ? vs ? para V constante. A partir dessas curvas, é possível adquirir a sensibilidade do material e analisar a sua viabilidade em aplicações como sensores e atuadores. Utilizando este transdutor, foi possível caracterizar uma liga de FeAlB e comparar com uma amostra de GALFENOL, que é o material mais usado desta classe. As ligas apresentam sensibilidades (acima de 10 MPa) da ordem de 0,020 T/MPa para o GALFENOL e 0,012 T/MPa para a liga de FeAlB. Considerando que a liga de FeAlB não apresenta a melhor composição química, há muitas coisas para estudar ainda, como diferentes composições químicas e o processamento adequado para obter a textura desejada. / In the present research, a transducer was built to measure the changes of magnetic induction (B) and magnetostriction (?) for soft ferromagnetic materials in function of applied magnetic field (H) (voltage V) and mechanical stress (?).The transducer comprises two excitation coils connected at a current/voltage supply (to apply the magnetic field in the magnetostrictive element) and a magnetic core, to concentrate the magnetic flux in the ferromagnetic material. The magnetostriction is measured by strain gauges, the mechanical stress is applied by a material test system (EMIC), the magnetic induction is measured using a pick-up coil connected to a fluxmeter and the acquisition of the data was measured by a Labview software. These systems measure the curve B vs. V and ? vs. V for constant ? and B vs. ? e ? vs. ? for constant V. From this curves, it is possible to acquire the material´s sensibility and analyse the feasibility of then in application like sensor and actuators. Using this transducer, it was possible to characterize a FeAlB alloy and to compare it with a GALFENOL sample, which is the most used material of this class. The alloys show sensibility (up to 10 MPa) about 0,020 T/MPa to the GALFENOL and 0,012 T/MPa to FeAlB alloy. If we consider that the FeAlB alloy does not have the best chemical composition to reach the higher magnetostriction, there is a lot o thing to study, like different composition and the appropriate processing to obtain the desired texture.

No presente trabalho, foi construído um transdutor para medir as variações da indução magnética (B) e magnetostricção (?) de materiais ferromagnéticos macios em função de campo magnético aplicado (H) (voltagem V) e tensões mecânicas (?). O transdutor possui duas bobinas de excitação ligadas a uma fonte de corrente/voltagem (para aplicar o campo magnético no elemento magnetostrictivo) e um núcleo magnético, para concentrar o fluxo magnético no material ferromagnético. A magnetostricção é medida por extensômetria, a tensão mecânica é aplicada por uma máquina de ensaios universal (EMIC), a indução magnética é medida utilizando uma bobina de captura conectada a um fluxímetro e a aquisição dos dados foi realizada por um programa em Labview. O sistema mede curvas de M vs V e ? vs V para ? constante e também M vs ? e ? vs ? para V constante. A partir dessas curvas, é possível adquirir a sensibilidade do material e analisar a sua viabilidade em aplicações como sensores e atuadores. Utilizando este transdutor, foi possível caracterizar uma liga de FeAlB e comparar com uma amostra de GALFENOL, que é o material mais usado desta classe. As ligas apresentam sensibilidades (acima de 10 MPa) da ordem de 0,020 T/MPa para o GALFENOL e 0,012 T/MPa para a liga de FeAlB. Considerando que a liga de FeAlB não apresenta a melhor composição química, há muitas coisas para estudar ainda, como diferentes composições químicas e o processamento adequado para obter a textura desejada. / In the present research, a transducer was built to measure the changes of magnetic induction (B) and magnetostriction (?) for soft ferromagnetic materials in function of applied magnetic field (H) (voltage V) and mechanical stress (?).The transducer comprises two excitation coils connected at a current/voltage supply (to apply the magnetic field in the magnetostrictive element) and a magnetic core, to concentrate the magnetic flux in the ferromagnetic material. The magnetostriction is measured by strain gauges, the mechanical stress is applied by a material test system (EMIC), the magnetic induction is measured using a pick-up coil connected to a fluxmeter and the acquisition of the data was measured by a Labview software. These systems measure the curve B vs. V and ? vs. V for constant ? and B vs. ? e ? vs. ? for constant V. From this curves, it is possible to acquire the material´s sensibility and analyse the feasibility of then in application like sensor and actuators. Using this transducer, it was possible to characterize a FeAlB alloy and to compare it with a GALFENOL sample, which is the most used material of this class. The alloys show sensibility (up to 10 MPa) about 0,020 T/MPa to the GALFENOL and 0,012 T/MPa to FeAlB alloy. If we consider that the FeAlB alloy does not have the best chemical composition to reach the higher magnetostriction, there is a lot o thing to study, like different composition and the appropriate processing to obtain the desired texture.

No description available.

No description available.

No description available.

In this paper a new equivalent circuit is presented which describes the dynamics of a prototype micro-gyro sensor. The concept takes advantage of the principles employed in vibratory gyro sensors and the ductile attributes of GalFeNOL to target high sensitivity and shock tolerance. The sensor is designed as a tuning fork structure. A GalFeNOL patch attached to the y-z surface of the drive prong causes both prongs to bending the x-z plane (about the y axis) and a patch attached to the x-z surface of the sensing prong detects Coriolis-force induced bending in the y-z plane (about the x axis). A permanent magnet is bonded on top of each prong to give bias magnetic fields. A solenoid coil surrounding the drive prong is used to produce bending in the x-z plane of both prongs. The sensing prong is surrounded by a solenoid coil with N turns in which a voltage proportional to the time rate of change of magnetic flux is induced. The equivalent circuit enables the efficient modeling of a gyro sensor and an electromechanical behavioral simulation using the circuit simulator SPICE. The prongs are modeled as wave guiding bending beams which are coupled to the electromagnetic solenoid coil transducer. In contrast to known network approaches, the proposed equivalent circuit is the first tuning fork model, which takes full account of the fictitious force in a constant rotating frame of reference. The Coriolis force as well as the centrifugal force on a concentrated mass are considered.

Giant magnetostrictive RFe2 type (R represents rare earths) intermetallics form an important class of magnetic materials keeping in view of their potential applications as sensors and/ or actuators. In this thesis, one such mixed rare earth compound (Tb,Dy)Fe2 has been chosen for investigations. Being a technologically important material system, several investigations concerning physical and magnetic properties of the material and effect of processing parameters on magnetic properties have been reported in the available literature. However, existing literature does not provide a clear insight into some important aspects such as phase equilibria, evolution of texture and microstructure of directionally solidified Tb-Dy-Fe alloys. Therefore, the present work was undertaken to bring out tangible process-structure-property correlations with an emphasis to clarify the grey areas in the available literature. The investigation on the nature of ternary phase equilibria of Tb-Dy-Fe was taken up with an aim to understand the effect of Tb/Dy ratio on phase equilibria and magnetic properties of TbxDy1-xFe1.95 (x=0-1) alloys. Microstructural and micro-chemical analysis along with study of lattice parameter has been used to predict the nature of phase equilibria and the deviation from the assumed pseudo-binary behaviour. Further, from the microstructural investigations and study of lattice parameter and Curie temperature, a schematic sketch of a section of the ternary diagram, where (Tb,Dy) / Fe =1.95, was formulated and presented. Directional solidification technique is the most widely adopted method for processing the (Tb,Dy)Fe2, to impart grain orientation for practical applications. Therefore, it was aimed in the present study to understand the evolution of texture and microstructure in directionally solidified Tb0.3Dy0.7Fe1.95 alloy by modified Bridgman and zone melting techniques. The alloy was directionally solidified by modified Bridgman technique with a series of growth rates 5 - 100 cm/h, at a constant temperature gradient of 150oC/ cm. Microstructural investigation revealed formation of island banding at lower growth rate and peritectic coupled growth at higher growth rates. The texture study indicated a transition of growth texture from <113> to <110> and finally to <112> with increase of growth rate. A mechanism based on atomic attachment kinetics is proposed to explain the orientation selection with growth rate. The texture and microstructure have been correlated with magnetostriction and static strain co-efficient (dλ/dH) of the Bridgman solidified alloys. The solidification morphology observed in Bridgman solidified samples was found to be mostly plane front. Therefore, in order to understand the microstructure and texture evolution in cellular/ dendritic regime, directional solidification of Tb0.3Dy0.7Fe1.95 was attempted by zone melting technique with a lesser temperature gradient of 100oC/cm. A detailed texture study indicated a transition in preferred growth direction from <110> to <112> with increase of growth rate. In this case of cellular/ dendritic growth regime, a mechanism based on atomic attachment kinetics has been proposed and the preferred morphologies of the solid-liquid interface for <110> and <112> growth have been modelled. The modelled interfaces have been correlated to the shape of cell/ dendrite cross-section observed for the growth rates adopted in this study. Apart from the investigation carried out on the (Tb,Dy)Fe2 alloys, attempts have been made to understand the role of microstructure, especially the ordered phases on the magnetostriction of an emerging magnetostrictive material Fe-Ga. A series of alloy compositions of Fe-x at % Ga (x=17, 20, 23 and 25) were prepared and subjected to different thermal treatments and characterized for microstructural features and magnetostriction. Microstructure investigation of slow cooled, quenched and quenched + aged alloys reveals formation of ordered DO3 phase from disordered A2 phase by first order transformation in 17 and 20 at% Ga alloys, whereas for 23 and 25 at% alloys, the transformation takes place by continuous ordering. It could be observed that large magnetostriction arises owing to the presence of disordered A2 phase or ordered DO3 phase alone. The magnetostriction however decreases substantially when these two phases are co-existing.