Luz Antonio Aguilera-Cortés

Resonant Magnetic Field Sensors Based On MEMS Technology.

Microelectromechanical systems (MEMS) technology allows the integration of magnetic field sensors with electronic components, which presents important advantages such as small size, light weight, minimum power consumption, low cost, better sensitivity and high resolution. We present a discussion and review of resonant magnetic field sensors based on MEMS technology. In practice, these sensors exploit the Lorentz force in order to detect external magnetic fields through the displacement of resonant structures, which are measured with optical, capacitive, and piezoresistive sensing techniques. From these, the optical sensing presents immunity to electromagnetic interference (EMI) and reduces the read-out electronic complexity. Moreover, piezoresistive sensing requires an easy fabrication process as well as a standard packaging. A description of the operation mechanisms, advantages and drawbacks of each sensor is considered. MEMS magnetic field sensors are a potential alternative for numerous applications, including the automotive industry, military, medical, telecommunications, oceanographic, spatial, and environment science. In addition, future markets will need the development of several sensors on a single chip for measuring different parameters such as the magnetic field, pressure, temperature and acceleration.

A resonant magnetic field microsensor with high quality factor at atmospheric pressure

A resonant magnetic field microsensor with a high quality factor at atmospheric pressure has been designed, fabricated and tested. This microsensor does not require vacuum packaging to operate efficiently and presents a compact and simple geometrical configuration of silicon. This geometry permits us to decrease the size of the structure and facilities its fabrication and operation. It is constructed of a seesaw plate (400 × 150 × 15 µm3), two torsional beams (60 × 40 × 15 µm3), four flexural beams (130 × 12 × 15 µm3) and a Wheatstone bridge with four p-type piezoresistors. The resonant device exploits the Lorentz force principle and operates at its first resonant frequency (136.52 kHz). A sinusoidal excitation current of 22.0 mA with a frequency of 136.52 kHz and magnetic fields from 1 to 400 G are considered. The mechanical response of the microsensor is modeled with the finite element method (FEM). The structure of the microsensor registered a maximum von Mises stress of 53.8 MPa between the flexural and the torsional beams. Additionally, a maximum deflection (372.5 nm) is obtained at the extreme end of the plate. The proposed microsensor has the maximum magnetic sensitivity of 40.3 µV G−1 (magnetic fields <70 G), theoretical root-mean square (rms) noise voltage of 57.48 nV Hz−1/2, theoretical resolution of 1.43 mG Hz−1/2 and power consumption less than 10.0 mW.

Analytical Modeling for the Bending Resonant Frequency of Sensors Based on Micro and Nanoresonators With Complex Structural Geometry

Micro- and nanoresonator sensors have important applications such as in chemical and biological sensing, environmental control, monitoring of viscosity and magnetic fields, and inertial forces detection. However, most of these resonators are designed as complex structures that complicate the estimation of their resonant frequencies (generally of the bending or torsional mode). In this paper, we present an analytical model to estimate the resonant frequency of the first bending mode of micro- and nanoresonators based on a beam system under different load types. This system is constructed of beams with different cross sections joined through a series-parallel arrangement. The analytical model is derived using the Rayleigh and Macaulay methods, as well as the Euler-Bernoulli beam theory. In addition, we determined the deflection function of the beam system, which can be used to establish its bending structural response under several load types. We applied the model to both a silicon microresonator (with a thickness of 5 μ m) for an experimental magnetic field sensor developed in our laboratory and for a polycrystalline silicon nanoresonator (with a thickness of 160 nm) of a mass sensor reported in the literature. The results of our analytical model have a comparable agreement with those obtained from the finite-element models (FEMs) and with the experimental measurements. Our analytical model can be useful in the mechanical design of micro- and nanoresonators with complex structural configurations.

Synthesis and nonlinear optical behavior of Ag nanoparticles in PMMA

In this work we have synthesized silver nanoparticles in Poly (methyl methacrylate) (PMMA). This was achieved by polymerizing the mixture of monomer and corresponding metal compound, followed by post-heating treatment. The linear absorption coefficient of the samples was measured using a spectrophotometer, where an absorption peak at 420nm was observed. This peak grows up and shifts as a function of the concentration of the radical initiator. The linear refractive index was measured using the Fresnel equations and agrees with previous reported results. The nonlinear properties were obtained using the single lens Z-scan method, where the nonlinear absorption coefficient (Δα) was found between 5.5975514 and 17.9483493cm-1. The nonlinear refractive index coefficient (Δη) was found to be negative and its value oscillates between 12.9099 E-06 and 22.4276 E-06. Finally, the third-order coefficient (χ(3)) was calculated in the range of 233-787 E-9 esu.

Digital Signal Processing by Virtual Instrumentation of a MEMS Magnetic Field Sensor for Biomedical Applications

We present a signal processing system with virtual instrumentation of a MEMS sensor to detect magnetic flux density for biomedical applications. This system consists of a magnetic field sensor, electronic components implemented on a printed circuit board (PCB), a data acquisition (DAQ) card, and a virtual instrument. It allows the development of a semi-portable prototype with the capacity to filter small electromagnetic interference signals through digital signal processing. The virtual instrument includes an algorithm to implement different configurations of infinite impulse response (IIR) filters. The PCB contains a precision instrumentation amplifier, a demodulator, a low-pass filter (LPF) and a buffer with operational amplifier. The proposed prototype is used for real-time non-invasive monitoring of magnetic flux density in the thoracic cage of rats. The response of the rat respiratory magnetogram displays a similar behavior as the rat electromyogram (EMG).

Analytical modeling for the bending resonant frequency of multilayered microresonators with variable cross-section.

Multilayered microresonators commonly use sensitive coating or piezoelectric layers for detection of mass and gas. Most of these microresonators have a variable cross-section that complicates the prediction of their fundamental resonant frequency (generally of the bending mode) through conventional analytical models. In this paper, we present an analytical model to estimate the first resonant frequency and deflection curve of single-clamped multilayered microresonators with variable cross-section. The analytical model is obtained using the Rayleigh and Macaulay methods, as well as the Euler-Bernoulli beam theory. Our model is applied to two multilayered microresonators with piezoelectric excitation reported in the literature. Both microresonators are composed by layers of seven different materials. The results of our analytical model agree very well with those obtained from finite element models (FEMs) and experimental data. Our analytical model can be used to determine the suitable dimensions of the microresonator’s layers in order to obtain a microresonator that operates at a resonant frequency necessary for a particular application.

SnAM: a simulation software on serial manipulators

The solution of kinematics problems for serial manipulators is fundamental for their synthesis, analysis, simulation, and computer control; for this reason, this paper introduces a public domain package and open software called SnAM (Serial n-Axis Manipulators), which is developed under the ADEFID (ADvanced Engineering soFtware for Industrial Development) framework, where the manipulator is conceptualized as a derived class from CRobokin, CMachine and CIpiSModel, which are fundamental ADEFID classes. SnAM has been developed with efficient algorithms in a closed-loop solution to solve direct kinematics, whereas for the case of inverse kinematics, matrix formulation, elimination and numerical methods are implemented. Furthermore, for the architecture definition, the user is able to display a dialog box in which the design parameters are set based on the Denavit–Hartenberg convention with the aid of sliding bars, while the solid model is updated simultaneously showing the actual configuration. Since ADEFID provides tools to graphical interface with embedded control components SnAM adopt them to not only simulate virtually, but also with an adaptive prototype designed for this purpose. Furthermore, SnAM assists the user in tasks related to trajectory planning, collision-avoidance and three-dimension objects scanning.

Recent Advances of MEMS Resonators for Lorentz Force Based Magnetic Field Sensors: Design, Applications and Challenges

Microelectromechanical systems (MEMS) resonators have allowed the development of magnetic field sensors with potential applications such as biomedicine, automotive industry, navigation systems, space satellites, telecommunications and non-destructive testing. We present a review of recent magnetic field sensors based on MEMS resonators, which operate with Lorentz force. These sensors have a compact structure, wide measurement range, low energy consumption, high sensitivity and suitable performance. The design methodology, simulation tools, damping sources, sensing techniques and future applications of magnetic field sensors are discussed. The design process is fundamental in achieving correct selection of the operation principle, sensing technique, materials, fabrication process and readout systems of the sensors. In addition, the description of the main sensing systems and challenges of the MEMS sensors are discussed. To develop the best devices, researches of their mechanical reliability, vacuum packaging, design optimization and temperature compensation circuits are needed. Future applications will require multifunctional sensors for monitoring several physical parameters (e.g., magnetic field, acceleration, angular ratio, humidity, temperature and gases).

Development of Resonant Magnetic Field Microsensors: Challenges and Future Applications

Microelectromechanical Systems (MEMS) integrate electrical and mechanical components with feature sizes in the micrometer-scale, which can be fabricated using integrated circuit batch-processing technologies (Gad-el-Hak, 2001). The development of devices using MEMS has important advantages such as small size, light weight, low-power consumption, high sensitivity and high resolution (Herrera-May et al., 2009a). MEMS have allowed the development of several microdevices such as accelerometers (L. Li et al., 2011), gyroscopes (Che et al., 2010), micromirrors (Y. Li et al., 2011), and pressure sensors (Mian & Law, 2010). Recently, some researchers (Mohammad et al., 2010, 2011a, 2011b; Wang et al., 2011) have integrated acceleration, pressure or temperature sensors using MEMS. A potential market for MEMS will include magnetic field microsensors for applications such as automotive industry, telecommunications, medical and military instruments, and consumer electronics products (Lenz & Edelstein, 2006). The most sensitive magnetic field sensor is the Superconducting Quantum Interference Device (SQUID), which has a resolution on the order of several femptoteslas (JosephsFranks et al., 2003). It operates at low temperature based on two effects: flux quantization and Josephson effects. This sensor needs a sophisticated infrastructure that increases its size and cost, which limits its commercial applications. Hall effect sensors have a low cost, small size, and a power consumption from 100 to 200 mW. They are fabricated on standard Complementary Metal-Oxide Semiconductor (CMOS) technology and can measure either constant or varying magnetic field between temperature ranges from -100 to + 100 oC (Ripka & Tipek, 2007). Nevertheless, Hall effect sensors have a low resolution from 1 to 100 mT and require temperature compensation circuits (Popovic, 2004). Fluxgate sensors can measure static or low frequency magnetic field with a resolution of 100 pT (Ripka & Tipek, 2007). They have a size of several millimeters and a power

Design and Modeling of Polysilicon Electrothermal Actuators for a MEMS Mirror with Low Power Consumption

Endoscopic optical-coherence tomography (OCT) systems require low cost mirrors with small footprint size, out-of-plane deflections and low bias voltage. These requirements can be achieved with electrothermal actuators based on microelectromechanical systems (MEMS). We present the design and modeling of polysilicon electrothermal actuators for a MEMS mirror (100 μm × 100 μm × 2.25 μm). These actuators are composed by two beam types (2.25 μm thickness) with different cross-section area, which are separated by 2 μm gap. The mirror and actuators are designed through the Sandia Ultra-planar Multi-level MEMS Technology V (SUMMiT V®) process, obtaining a small footprint size (1028 μm × 1028 µm) for actuators of 550 µm length. The actuators have out-of-plane displacements caused by low dc voltages and without use material layers with distinct thermal expansion coefficients. The temperature behavior along the actuators is calculated through analytical models that include terms of heat energy generation, heat conduction and heat energy loss. The force method is used to predict the maximum out-of-plane displacements in the actuator tip as function of supplied voltage. Both analytical models, under steady-state conditions, employ the polysilicon resistivity as function of the temperature. The electrothermal-and structural behavior of the actuators is studied considering different beams dimensions (length and width) and dc bias voltages from 0.5 to 2.5 V. For 2.5 V, the actuator of 550 µm length reaches a maximum temperature, displacement and electrical power of 115 °C, 10.3 µm and 6.3 mW, respectively. The designed actuation mechanism can be useful for MEMS mirrors of different sizes with potential application in endoscopic OCT systems that require low power consumption.