47 documents found, page 1 of 5
Small-size MEMS accelerometer encapsulated in vacuum using Sigma-Delta modulation
Lima, Vasco António Lourenço; Cabral, Jorge; Kuhlmann, Burkhard; Gaspar, Joao; Rocha, Luís Alexandre MachadoA vacuum encapsulated MEMS accelerometer using Sigma-Delta modulation is here presented. Three different modulation orders (second, third, and fourth) were implemented in a field-programable gate array (FPGA), enabling flexibility for tuning the loop parameters in real-time. Three devices were measured, and the results are in good agreement with simulations performed in Simulink. A noise figure of 123 μg/√Hz fo...
Highly sensitive MEMS frequency modulated accelerometer with small footprint
Esteves Moreira, Eurico; Kuhlmann, Burkhard; Serra Alves, Filipe; Dias, Rosana Maria Alves; Cabral, Jorge; Gaspar, João; Rocha, Luís Alexandre MachadoA single-axis resonant MEMS accelerometer is presented here. The goal is to achieve the maximum sensitivity on a set of predefined constraints: small footprint of 500 μm × 500 μm, vacuum operation under 150 Pa (requirement for a single-chip IMU) and fabrication using a Bosch silicon surface micromachining process. The sensor is composed by double-ended tuning fork resonators in differential architecture and a f...
Influence of mechanical stress in a packaged frequency-modulated MEMS accelerom...
Moreira, Eurico Esteves; Kuhlmann, Burkhard; Alves, Filipe Manuel Serra; Dias, Rosana Maria Alves; Cabral, Jorge; Gaspar, JoaoFrequency modulated accelerometers composed of two double-ended tuning fork (DETF) resonators on a differential configuration were characterized for their sensitivity to force applied to their package. Commonly, differential architectures are employed to cancel common mode errors, such as the mechanical stress or temperature dependency. The device dependence to mechanical stress was experimentally measured for ...
Strain sensors based on knocked down carbon nanotubes and bucky papers thin films
Santos, Ana Raquel Ribeiro; Amorim, Luís Manuel Machado; Nunes, J. P.; Rocha, Luís Alexandre Machado; Ferreira da Silva, Alexandre; Viana, J. C.Recently, carbon nanotubes (CNTs) thin films have been widely applied in sensing applications due to their piezoresistive response. Furthermore, CNT anisotropic electric properties, due to its alignment, can provide useful information regarding strain direction. We present a comparative study between knocked down vertically aligned CNT based sensor, reported in our previous work [1], and CNT bucky papers (BP) b...
High frequency FM MEMS accelerometer using piezoresistive resonators
Coelho, Cláudia; Gaspar, João; Rocha, Luís Alexandre MachadoA novel frequency modulated (FM) accelerometer based on piezoresistive resonators is presented. The accelerometer uses two differential resonators, connected to the accelerometer proofmass by an amplifying leverage mechanism. The piezoresistive double-mass resonators are electrostatically driven in anti-phase and the output signal is measured piezoresistively by applying a bias current to the connecting microbe...
Resonant accelerometer based on double-ended tuning fork and a force amplificat...
Moreira, Eurico Esteves; Kuhlmann, Burkhard; Gaspar, João; Rocha, Luís Alexandre MachadoResonant accelerometers are an alternative to amplitude modulated devices due to their higher integration capabilities, since they are encapsulated in vacuum and are stable at low pressures. Vacuum is required for some sensors (i.e., gyroscopes) but amplitude modulated accelerometers tend to be unstable under such conditions and therefore cannot be integrated in the same package. Herewith, a device composed by ...
Frequency modulated magnetometer using a double-ended tuning fork resonator
Moreira, Eurico Esteves; Gaspar, João; Rocha, Luís Alexandre MachadoA Lorentz force MEMS magnetometer based on a double-ended tuning fork (DETF) for out-of-plane sensing is presented here. A novel configuration using a hexagonal-shaped Lorentz force transducer is used, which simplifies the sensor configuration and improves its sensitivity. Frequency modulated devices were fabricated in an in-house process on silicon on insulator wafers (SOI) and then tested in vacuum. The final...
Validation of a knee angle measurement system based on imus
Ribeiro, Nuno Miguel Ferrete; Ferreira, César; Reis, L. P.; Silva, Hélder David Malheiro; Macedo, Pedro; Rocha, Luís Alexandre Machado; Santos, CristinaInertial Measurements Unit (IMU) based systems are a purposeful and alternative tool to monitor human gait mainly because they are cheaper, smaller and can be used without space restrictions compared to other gait analysis methods. In the scientific community, there are well-known studies that test the accuracy and efficiency of this method compared to ground truth systems. Gait parameters such as stride length...
A novel synchronizer for a 17.9ps Nutt Time-to-Digital Converter implemented on...
Machado, Rui; Rocha, Luís Alexandre Machado; Cabral, JorgeThe evolution of Field-Programmable Gate Array (FPGA) technology triggered the appearance of FPGAs with higher operating frequencies and large number of resources. Simultaneously, the evolution of the FPGAs design tools has simplified the development process, reducing the time to market. These factors made FPGA platforms attractive for several applications, including time-of-flight applications that require the...
Low-pressure small MEMS accelerometer using Sigma-Delta modulation
Lima, Vasco; Cabral, Jorge; Kuhlmann, Burkhard; Rocha, Luís Alexandre MachadoEncapsulation of MEMS accelerometers in vacuum is advantageous, since it allows integration with other sensors, leading to size and cost reduction. One technique to operate MEMS accelerometers in vacuum is the use of closed-loop Sigma-Delta modulation, which has many advantages. In this paper, the design of a vacuum encapsulated small size MEMS accelerometer (0.2 mm<sup>2</sup>) and the preliminary measured res...