Characterization of Flexible RF Microcoil Dedicated to Surface Mri

In Magnetic Resonance Imaging (MRI), to achieve sufficient Signal to Noise Ratio (SNR), the electrical performance of the RF coil is critical. We developed a device (microcoil) based on the original concept of monolithic resonator. This paper presents the used fabrication process based on micromoulding. The dielectric substrates are flexible thin films of polymer, which allow the microcoil to be form fitted to none-plane surface. Electrical characterizations of the RF coils are first performed and results are compared to the attempted values. Proton MRI of a saline phantom using a flexible RF coil of 15 mm in diameter is performed. When the coil is conformed to the phantom surface, a SNR gain up to 2 is achieved as compared to identical but planar RF coil. Finally, the flexible coil is used in vivo to perform MRI with high spatial resolution on a mouse using a small animal dedicated scanner operating at in a 2.35 T.Comment: Submitted on behalf of TIMA Editions (http://irevues.inist.fr/tima-editions

Copper Planar Microcoils Applied to Magnetic Actuation

Recent advances in microtechnology allow realization of planar microcoils. These components are integrated in MEMS as magnetic sensor or actuator. In the latter case, it is necessary to maximize the effective magnetic field which is proportional to the current passing through the copper track and depends on the distance to the generation microcoil. The aim of this work was to determine the optimal microcoil design configuration for magnetic field generation. The results were applied to magnetic actuation, taking into account technological constraints. In particular, we have considered different realistic configurations that involve a magnetically actuated device coupled to a microcoil. Calculations by a semi-analytical method using Matlab software were validated by experimental measurements. The copper planar microcoils are fabricated by U.V. micromoulding on different substrates : flexible polymer (Kapton®) and silicate on silicon. They are constituted by a spiral-like continuous track. Their total surface is about 1 mm2

Planar Microcoil OptimPlanar Microcoil Optimization of MEMS Electrodynamic Microspeakers

International audienceA method for optimizing the planar microcoil of MEMS electrodynamic microspeakers with the aim of maximizing the electroacoustic efficiency is presented. The poposed approach is based on a mixed-model using both analytical models and finite element method (FEM). FEM simulation was used for computing the spatial distribution of the magnetic field created by the permanent magnets, making thus possible to analyze any geometry of permanent magnets. Different configurations of magnets were considered, and for each the planar copper microcoil was optimized while taking into account the technological constraints due to the microfabrication process, the associated electronics and the targeted acoustic power emission. The results showed that the proposed method predicts the force factor in very good agreement with experimental measurements carried out on the micromachined device. Morover, according to the electro-mechano-acoustic model, these results showed that the optimized microcoil associated to the best magnet configuration increases the electroacoustic efficiency by more than 200% compared to conventional microspeakers

High current densities in copper microcoils : influence of substrate on failure mode

Copper planar microcoils were processed by U.V. lithography on SiO2/Si and Kapton®. The coils were packaged on different supports in order to create varying thermal exchange conditions. The electric current was increased step by step until the electric connection breaks, the microcoils remaining free on a thermal point of view. The copper temperature was estimated from its resistivity. It allowed to show that the thermal exchange mode of the wire-bonded microcoils is conductive. The current density was calculated taking into account the deterioration of the coils by oxidation. Its maximum value is linearly decreasing with the thermal exchange ability of the support. The failure modes of the microcoils are related to track melting and oxidation, the current density remaining one order too weak to induce electromigration

Thick Electrode Biochip for in Vitro Studies of the Nanoporation of Living Cells

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Low Temperature Irreversible Poly(DiMethyl) Siloxane Packaging of Silanized SU8 Microchannels: Characterization and Lab-on-Chip Application

International audienceIn this paper, we describe and characterize a novel method, based on silanization, for strong bonding of SU8 microchannels to poly(dimethyl)siloxane (PDMS) flexible covers. First, the SU8 surface treatment process (silanization) is characterized through atomic force microscopy and contact angle measurements. The aging study proves grafting stability during more than two days. Silanized SU8 patterns and PDMS cover are finally bonded to seal the microchannel network. Such assembled microdevices can be used without leakage at flow rates above 2.4 mL/min, corresponding to 1.2 MPa if the PDMS deformation is neglected. The bonding tensile pressure exceeds 1.5 MPa, proving the packaging strength. Furthermore, SU8-PDMS composite devices display stable bonding after several weeks of storage. This rapid low cost and low temperature bonding technique is finally successfully employed to fabricate a fully packaged biochip for electric and fluidic handling of biological cells

A Microfluidic Biochip Dedicated to Highly Parallelized Electrofusion

International audienceThis paper deals with the development of a biochip dedicated to fusion between two types of cells, in a highly parallelized way. The fusion process is initiated by an electric field pulse applied to cells paired in fluidic traps. The paper will present different strategies for the capture and pairing of cells prior to the electrofusion, combining fluidic and electrical forces. The design is highly parallelized in order to fulfill our objective which is the high throughput production of hybrid cells. The microfabrication process is described. Experimental results confirm the efficiency of the proposed device for cell trapping, pairing and fusion

Electrodynamic MEMS: Application to Mobile Phone Loudspeakers

International audienceThis paper presents an electrodynamic MEMS for mobile phone loudspeaker applications. The whole structure of the loudspeaker is a new conception to reach higher performances than in existing devices: a linear behavior to ensure a high acoustic fidelity and a high efficiency to increase the power autonomy. So, the motor is ironless, constituted of permanent magnet only. Several electrodynamic structures are presented and studied with analytical formulations of the magnetic field. The emissive part is a plane silicon surface, very rigid and light, the suspension is achieved by silicon beams, which are not sensitive to mechanical fatigue, the electroplated copper coil is thick and requires a specialist technique to be deposited. The moving part displacements are in a range far larger than in existing MEMS (600 μ m). The trends for dimensioning the structure are investigated and prototypes realized and tested, with NdFeB ring magnets. As a result, the 70 dB SPL at 10 cm bandwidth reaches up to 100 kHz, and the behavior is particularly linear

Nanomanipulation of living cells on a chip using electric field: general concepts and microdevices

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