Electrostatic Frequency Tuning of Bulk Acoustic Wave Disk Gyroscopes

Bulk acoustic wave gyroscopes have been researched for potential benefits such as immunity to shock and vibration and the high Q factors achievable with the bulk modes. This paper outlines an approach to address mode matching in bulk acoustic wave (BAW) disk gyroscopes using electrostatic frequency tuning. Electrostatic frequency tuning is achieved by varying the potential difference between the body of the resonator and electrodes surrounding the disk resonator. Tuning of the frequencies of both drive and sense modes is demonstrated in this work as a means to achieving mode matching. The experimental results are also compared to COMSOL simulations reporting mode matching

A Silicon MEMS Disk Resonator Oscillator Demonstrating 36 ppt Frequency Stability

This paper reports experimental results demonstrating excellent short-term frequency stability of 45.6 µLHz (36 [email protected] s integration time) for a bulk acoustic wave (BAW) silicon disk resonator oscillator. The n=4 radial mode of a BAW disk resonator demonstrates an extremely high-quality factor of 1.8*10^6 at 1.25 MHz. The disk is designed with anchors aligned with nodal locations to minimize anchor damping. The results on the measured short-term frequency stability reported here benchmark favourably relative to the state-of-the-art.Engineering and Physical Research Council UK, Silicon Microgravity and Innovate UK

Nonlinear cancellation in weakly coupled MEMS resonators

© 2017 IEEE. For the first time, this paper demonstrates the cancellation of nonlinear response in weakly coupled resonators. It has been observed that by working in the region where the mechanical nonlinearity of the resonators and the electrical nonlinearity of the electrostatic coupling cancel, the output current amplitudes are increased by 4x while the trend of vibration amplitude variation upon stiffness perturbations is preserved as seen in the linear regime of the resonators

Closed-loop tracking of amplitude and frequency in a mode-localized resonant MEMS sensor

In this paper, the amplitude and frequency stability of a mode-localized sensor are characterized in a closed loop setup. The system describes an absolute amplitude ratio sensitivity of 5250 to stiffness perturbations in linear operation. A stability of 432ppm at 500s integration time is observed for amplitude ratio measurements. A resolution of 85ppb corresponding to normalised stiffness perturbations in amplitude ratio measurements is thus demonstrated at 500s integration time. Comparisons to frequency shift sensing within the same device shows that amplitude ratio sensing provides higher accuracies for long term measurements due to intrinsic common mode rejection properties in a mode-localized system

A mode-localized MEMS accelerometer with 7μg bias stability

This paper reports on the experimental characterization of the resolution, sensitivity and common mode rejection metrics for a mode-localized MEMS accelerometer. A bias stability of 7μg is achieved for closed-loop amplitude ratio measurements at an integration time of 30s representing a significant advancement in the development of high-stability accelerometers employing this transduction principle.This work is supported by funding from Innovate UK and Natural Environment Research Council

Toward High-Resolution Inertial Sensors Employing Parametric Modulation in Coupled Micromechanical Resonators

Highly accurate MEMS inertial sensors have a wide range of potential applications, including inertial navigation and seismometry. Conventional approaches to the implementation of inertial sensors rely on transducers that convert the external acceleration into changes in displacement of a proof mass or shifts in resonant frequencies. Recently, it has been demonstrated that inertial forces can also be measured through monitoring spatial energy distribution between two coupled microresonators. To extend this approach, we show that a weak dynamic coupling can be established through periodic modulation of the stiffness for a mechanically coupled microresonator system integrated as part of an accelerometer, enhancing the scale factor and resolution of the accelerometer. The resulting capability of parametric modulation also enabled the tuning of the operating point of the accelerometer through the modulation frequency. Utilizing this technique, we show that the scale factor of the accelerometer can be enhanced by a factor of 188, and a factor of 25 improvement in sensor resolution is demonstrated. Dynamic tuning of the sensor scale factor and inherent noise filtering is also demonstrated

Estudio de la aplicación de sensores Hall en la medida de desplazamientos micrométricos en sistemas de baja tensión de alimentación

En la actualidad existen sensores empleados para la medida de desplazamientos micrométricos basados en el campo magnético. Entre ellos los más comunes son los LVDT (Linear Variable Differential Transformer), unos sensores altamente lineales y precisos que son utilizados en aplicaciones que requieren una gran sensibilidad y resolución, como la medida de variaciones de diámetro en plantas asociadas a estrés hídrico. Los sensores LVDT son, por construcción, sistemas relativamente grandes y pesados (ya que la parte activa del sensor es un transformador), y necesitan en general tensiones en el bobinado primario relativamente altas. En la investigación que estamos llevando a cabo hemos sustituido este tipo de sensores por sensores Hall, cuyo tamaño y consumo en potencia es considerablemente inferior que los LVDT, manteniendo una alta sensibilidad como respuesta a variaciones del campo magnético. A su vez, hemos sustituido el núcleo magnético cuyo desplazamiento genera las variaciones del campo magnético por dos discos magnéticos de neodimio (NdFeB) de 0,29 gramos. A día de hoy hemos conseguido que este sistema polarizado con fuente única de 3V pueda medir variaciones de desplazamiento con una precisión de 1m. Además, el sistema de acondicionamiento de la señal, constituido por un sistema de amplificación de ventana y un microcontrolador es totalmente programable, lo que facilita su implementación en redes de sensores de bajo consumo y alta autonomía

Dynamic modulation of modal coupling in microelectromechanical gyroscopic ring resonators

Abstract: Understanding and controlling modal coupling in micro/nanomechanical devices is integral to the design of high-accuracy timing references and inertial sensors. However, insight into specific physical mechanisms underlying modal coupling, and the ability to tune such interactions is limited. Here, we demonstrate that tuneable mode coupling can be achieved in capacitive microelectromechanical devices with dynamic electrostatic fields enabling strong coupling between otherwise uncoupled modes. A vacuum-sealed microelectromechanical silicon ring resonator is employed in this work, with relevance to the gyroscopic lateral modes of vibration. It is shown that a parametric pumping scheme can be implemented through capacitive electrodes surrounding the device that allows for the mode coupling strength to be dynamically tuned, as well as allowing greater flexibility in the control of the coupling stiffness. Electrostatic pump based sideband coupling is demonstrated, and compared to conventional strain-mediated sideband operations. Electrostatic coupling is shown to be very efficient, enabling strong, tunable dynamical coupling

A Closed-Loop Readout Configuration for Mode-Localized Resonant MEMS Sensors

This letter presents the first experimental results on the closed-loop characterization of a mode-localized microelectromechanical resonator system. Comparisons between the closed-loop oscillator approach and the open-loop frequency sweep approach show good agreement of output metrics including the amplitude ratios and mode frequencies. This new approach enables real-time measurements using emerging mode-localized resonant sensors and represents an important step toward realizing sensors based on this measurement principle.Funding from Innovate UK and the Natural Environment Research Council is gratefully acknowledged