Thurai Vinay

Novel concept of a single-mass adaptively controlled triaxial angular rate sensor

This paper presents a novel concept for an adaptively controlled triaxial angular rate (AR) sensor device that is able to detect rotation in three orthogonal axes, using a single vibrating mass. Pedestrian navigation is presented as an example demonstrating the suitability of the proposed device to the requirements of emerging applications. The adaptive controller performs various functions. It updates estimates of all stiffness error, damping and input rotation parameters in real time, removing the need for any offline calibration stages. The parameter estimates are used in feedforward control to cancel out their otherwise erroneous effects, including zero-rate output. The controller also drives the mass along a controlled oscillation trajectory, removing the need for additional drive control. Finally, the output of the device is simply an estimate of input rotation, removing the need for additional demodulation normally used for vibratory AR sensors. To enable all unknown parameter estimates to converge to their true values, the necessary model trajectory is shown to be a three-dimensional Lissajous pattern. A modified trajectory algorithm is presented that aims to reduce errors due to discretization of the continuous time system. Simulation results are presented to verify the operation of the adaptive controller. A finite-element modal analysis of a preliminary structural design is presented. It shows a micro electro mechanical systems realizable design having modal shapes and frequencies suitable for implementing the presented adaptive controller

Modeling and simulation of a flat spring for use in an electromagnetic microgenerator

The ability to supply power at the micro level from the ambient energy is an increasingly important area of MEMS. This paper presents a methodology for the design of an electromagnetic micro generator that converts mechanical energy associated with the low amplitude vibration present in structures such us tall buildings and bridges to electrical power. The generator consists of a rigid housing and a moving magnet suspended on a flat spring that induces a voltage on a stationary coil attached to the housing. Finite Element Analysis (FEA) software (ANSYS5.7) has been used to analyse different designs of flat springs and to select one that is capable of large deflection. The effects of the main design parameters: length, width, thickness and material properties on the spring deflection were modelled. Maximum static deflection of 13.43μm is achieved under the gravitational force. Furthermore, Free vibration characteristics of the suspended magnet are also presented. Maximum electric power of 14.5nW is calculated for the spring with natural frequency of 18.56 Hz when the input vibration frequency and its amplitude are assumed to be 3kHz and 5μm. An outline of how the design can proceed in a logical manner is discussed.

High sensitivity capacitive MEMS microphone with spring supported diaphragm

Capacitive microphones (condenser microphones) work on a principle of variable capacitance and voltage by the movement of its electrically charged diaphragm and back plate in response to sound pressure. There has been considerable research carried out to increase the sensing performance of microphones while reducing their size to cater for various modern applications such as mobile communication and hearing aid devices. This paper reviews the development and current performance of several condenser MEMS microphone designs, and introduces a microphone with spring supported diaphragm to further improve condenser microphone performance. The numerical analysis using Coventor FEM software shows that this new microphone design has a higher mechanical sensitivity compared to the existing edge clamped flat diaphragm condenser MEMS microphone. The spring supported diaphragm is shown to have a flat frequency response up to 7 kHz and more stable under the variations of the diaphragm residual stress. The microphone is designed to be easily fabricated using the existing silicon fabrication technology and the stability against the residual stress increases its reproducibility.

Effective Diaphragm Area of Spring-Supported Capacitive MEMS Microphone Designs

Capacitive (condenser) MEMS microphones have been developed using various design and fabrication techniques to improve performance. Mechanical sensitivity of a condenser MEMS microphone can be increased by reducing the residual stress of the diaphragm using several design approaches including corrugated diaphragms, and in recent years, various spring type diaphragms. The electrical sensitivity of the condenser microphone is proportional to the deflection of the diaphragm, however, the parabolic deflection of the diaphragm, and thus its effective diaphragm area, has reduced the sensitivity of parallel plate type capacitor on a condenser MEMS microphone. This paper presents the numerical analysis on the effective diaphragm area of several condenser MEMS microphone designs of 1.1mm x 1.1mm square. The analysis shows that the effective area of a spring-supported diaphragm is about 20% higher, and its capacitance value thus electrical sensitivity, is about 170% higher than a fully clamped flat diaphragm of an equal size. In addition, a flat deflection and higher effective diaphragm area of a spring-supported diaphragm can be achieved by carefully designed spring mechanisms.

Phase differential angular rate sensor-concept and analysis

This paper proposes and analyzes a new differential phase angular rate (AR) sensor employing a vibrating beam mass structure that traces an elliptical path when subject to rotation due to Coriolis force. Two sensing elements are strategically located to sense a combination of drive and Coriolis vibration to create a phase differential representative of the input rotation rate. A general model is developed, describing the device operation. The main advantages of the phase detection scheme are explored, including removing the need to maintain constant drive amplitude, independence of sensing element gain factor, and advantageous response shapes. A ratio of device parameters is defined and shown to dictate the device response shape. This ratio can be varied to give an optimally linear phase difference output over a set input range, a high sensitivity around zero input rate, or a response shape not seen before, that can give maximum sensitivity around an offset from the zero-rate input. This may be exploited in an array configuration for a highly accurate device over a wide input range. A worked example shows how the developed equations can be used as design tools to achieve a desired response with low sensitivity to variation in device parameters.

Phase differential angular rate sensor: concept and analysis

This paper describes the structure and operation of a new differential phase angular rate sensor and analyses its response to input rotation. It employs a vibrating beam mass structure that is forced into an elliptical path when subject to rotation due to the Coriolis effect. Two sensing elements are strategically located to sense a combination of drive and Coriolis force on each to create a phase differential representative of the input rotation rate. A general model is developed describing the device operation. The main advantages of the phase detection scheme are shown, including removing the need to maintain constant drive amplitude, independence of sensing element gain factor and novel response shapes. A ratio of device parameters is defined and shown to determine the device response shape. This ratio can be varied to give a high sensitivity around zero input rate or a response shape not seen before, that can give maximum sensitivity around an offset from the zero-rate input. This may be exploited in an array configuration for a highly accurate device over a wide input range. A worked example shows how the developed equations can be used as design tools to achieve a desired response.

Hydrostatic actuation in MEMS

Hydrostatic actuation is a novel method of actuation in Micro Electro Mechanical Systems (MEMS) and provides advantages over other actuation techniques in current use. Hydrostatic actuation utilises a contained pressurised medium to straighten a bent hollow beam, similar to the Bourdon tube used to measure pressure in the macro world. Research has commenced at RMIT University to design and fabricate a microgripper prototype to validate this work. To simplify the design of this microgripper a virtual prototype has been initiated. This paper looks at the work carried out and verification of this virtual prototype using mathematical and finite element modelling. Further work to be undertaken will also be discussed.

Magnetic MEMS used in smart structures which exploit magnetic materials properties

Magnetic MEMS technology, by exploiting the special properties of magnetic materials, offers many challenging possibilities for useful device development in the future. In this paper we explore some of the magnetic materials used in MEMS devices, and methods of fabricating them. Some of the key design issues are briefly addressed and applications of this technology to electromagnetic devices developed at RMIT and to thermally controlled magnetic devices, which are of increasing interest, are examined.