Examinando por Autor "Esteve, J."

Mostrando 1 - 7 de 7

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A New Single-Sensor Magnetic Field Gradiometer
(Igneta Connect, 2009-08-13) Lucas, I.; Díaz Michelena, M.; De Manuel, V.; Plaza, J. A.; Duch, M.; Esteve, J.; Guerrero, H.
In this work a magnetic field gradiometer device has been developed. This device is not composed by two sensors separated a certain distance but by a single-sensor device which measures the real gradient value just at the point where it is wanted to be measured. The experimental set-up consists of a sensor head (a membrane with a fixed permanent magnet on it) vibrating at its resonance frequency, due to an alternating magnetic field gradient. Detection is performed using an optoelectronic method. Two different measurement techniques have been used: frequency measurements (the resonance frequency is measured for every external magnetic field gradient value) and amplitude measurements (the signal amplitude is measured without changing the resonance frequency obtained without an external magnetic field gradient applied). The mechanical stresses of the membrane are related with the dependence of both magnitudes (frequency and amplitude) on the external magnetic field gradient. The minimum and maximum value of the resonance frequency and signal amplitude respectively, correspond with magnetic forces equal to the magnet weight of the sensor head. This prototype shows a noise-limited sensitivity of 2 Gauss/m/√Hz at zero gradient. This device could be used also as a magnetic susceptometer.
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Comparative performance of static-mode ferrous MEMS gradiometers fabricated by a three-step DRIE process
(IOP Science Publishing, 2010-05-21) Campanella, H.; Del Real, R. P.; Duch, M.; Guerrero, H.; Esteve, J.; Díaz Michelena, M.; Plaza, J. A.
Two MEMS structures—a cantilever beam and a quad-beam—have been designed and fabricated through a three-step deep reactive ion etching (DRIE) process. Devices feature target patterns to align with an external optical detection system and a micromachined cavity to embed an NdFeB hard mini-magnet, thus releasing the stress of structures. Structures are intended for magnetostatic gradient measurements. Induced magnetic fields generate an attracting force on the magnet that deflects the sensor. Deflection is optically detected through nanometer-resolution confocal microscopy. The static-mode sensitivity of up to 1.86 × 10−4 T m−1 demonstrates that MEMS gradiometers are able to perform in situ gradiometry with a single sensor and miniaturized size. Suitable techniques for integrated detection are discussed.
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Focused-Ion-Beam-Assisted Magnet Fabrication and Manipulation for Magnetic Field Detection Applications
(ACS Publications, 2009-02-16) Campanella, H.; Del Real, R. P.; Díaz Michelena, M.; Duch, M.; Guerrero, H.; Esteve, J.; Plaza, J. A.
A focused-ion-beam-assisted technique intended for ultrasmall, hard-magnet fabrication has been developed. By means of ion-beam-induced milling and deposition, reduced-size NdFeB magnets were extracted from a macroscopic quarry and bonded to the surface of a thin-film bulk acoustic resonator (FBAR). Electrical characterization of the FBAR before and after bonding of the magnet was carried out, thus observing both a downshifting of the resonance frequency and a reduction of the quality factor of the resonator. The magnetic behavior of the nanomagnet has been confirmed by means of magnetometry measurements based on atomic force microscopy.
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In situ MEMS gradiometer with nanometer-resolution optical detection system
(Elsevier, 2010-04-05) Campanella, H.; Del Real, R. P.; Duch, M.; Serre, C.; Lucas, I.; De Manuel, V.; Guerrero, H.; Esteve, J.; Díaz Michelena, M.; Plaza, J. A.
Mechanically resonant ferromagnetic MEMS sensors intended for magnetic field gradient measurements are presented. Suspended quad-beams with proof mass have been designed to improve their sensitivity and to simplify the detection. Fabricated devices exhibit the compact size of current MEMS technologies and are built within a simple deep-reactive-ion etching-based process. Nanometer-resolution detection based on optical interferometry and signal processing techniques have been employed to find out dynamic-mode transformation factors of 6.25 × 10−3 T/m/Hz with 0.1-Hz resolution. The device performs in situ gradiometry with a single-sensor structure, which represents a technological advance to current-art gradiometers.
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Micromachined optical fiber current sensor
(OSA (The Optical Society) Publishing, 1999-09-01) López Heredero, R.; Fernández de Caleya, R. F.; Guerrero, H.; Los Santos, P.; Cruz Acero, M.; Esteve, J.; 0000-0002-2197-8388; 0000-0001-9440-7984; 0000-0003-2922-3489; 0000-0002-2131-1081
We describe a micromachined optical fiber current sensor. The sensing element consists of a squared silicon membrane (8 mm long and 20 µm thick) that has a cylindrical permanent magnet (NdFeB alloy, 3-mm diameter, 1.5 mm high) fixed on its central region. This structure allows the permanent magnet to vibrate in the presence of the magnetic field gradient generated by an ac. A linear relation between the electrical current and the magnet displacement was measured with white-light interferometry with an optical fiber low-finesse Fabry–Perot microcavity. A measurement range of 0–70 A and a minimum detectable intensity of 20 mA were obtained when distance D between the membrane and the electrical power line was 5 mm. The output signal directly shows a linear response with distance D.
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Resonance frequency dependence on out-of-plane forces for square silicon membranes: Applications to a MEMS gradiometer
(Elsevier BV, 2010-09-12) Lucas, I.; Del Real, R. P.; Díaz Michelena, M.; De Manuel, V.; Duch, M.; Esteve, J.; Plaza, J. A.
The dynamic properties of membranes have been object of many researches since they can be used as sensor heads in different devices. Some methods have been proposed to solve the problem of determining the resonance frequencies and their dependence on the stress caused by forces applied on the membrane surface. The problem of the vibrating rectangular membrane under a stress caused by a uniform in-plane force is well known. However, the resonance frequency behaviour when the force is out-of-plane instead of in-plane, is not so well understood and documented. A gradiometer which uses a silicon square membrane with a magnet fixed on it as a sensor head has been developed in a previous work. This device reports a quadratic dependence of the frequency on the out-of-plane magnetic force. In this work, simulations to obtain the dependence of the frequency of the fundamental flexural mode on the stress have been performed. It has been studied the influence of in-plane and out-of-plane forces applied to the membrane. As expected, a square root dependence has been found for in-plane forces. Nevertheless, the problem is more complex when out-of-plane forces are considered. Out-of-plane forces give rise to an initial quadratic dependence which turns into a square root dependence from a certain stress value. The quadratic range increases and the rate of change of the frequency decreases as the surface of the magnet fixed on the membrane increases. The study has addressed these problems and both, experimental and simulated results have been compared and a good agreement between experimental and simulated results has been found.
Restringido
Resonance frequency dependence on out-of-plane forces for square silicon membranes: Applications to a MEMS gradiometer
(Elsevier, 2010-09-10) Lucas, I.; Del Real, R. P.; Díaz Michelena, M.; De Manuel, V.; Duch, M.; Esteve, J.; Plaza, J. A.
The dynamic properties of membranes have been object of many researches since they can be used as sensor heads in different devices. Some methods have been proposed to solve the problem of determining the resonance frequencies and their dependence on the stress caused by forces applied on the membrane surface. The problem of the vibrating rectangular membrane under a stress caused by a uniform in-plane force is well known. However, the resonance frequency behaviour when the force is out-of-plane instead of in-plane, is not so well understood and documented. A gradiometer which uses a silicon square membrane with a magnet fixed on it as a sensor head has been developed in a previous work. This device reports a quadratic dependence of the frequency on the out-of-plane magnetic force. In this work, simulations to obtain the dependence of the frequency of the fundamental flexural mode on the stress have been performed. It has been studied the influence of in-plane and out-of-plane forces applied to the membrane. As expected, a square root dependence has been found for in-plane forces. Nevertheless, the problem is more complex when out-of-plane forces are considered. Out-of-plane forces give rise to an initial quadratic dependence which turns into a square root dependence from a certain stress value. The quadratic range increases and the rate of change of the frequency decreases as the surface of the magnet fixed on the membrane increases. The study has addressed these problems and both, experimental and simulated results have been compared and a good agreement between experimental and simulated results has been found.