International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 04 Issue: 07 | July -2017
p-ISSN: 2395-0072
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Quality Factor analysis for Nitinol based RF MEMS Resonator Ajay Sudhir Bale1, Harish Koujalgi2 1,2 M.Tech
in Digital Electronics, KLE Tech, Hubli, Karnataka, India ---------------------------------------------------------------------***---------------------------------------------------------------------
Abstract – A paper is proposed for the study of quality
flexibility and thus allowing relatively large deformations. As the temperature is made higher, martensitic phase transforms to austenitic phase and in this phase the same material loses its flexibility and finally the strain is recovered. This heating of SMA actuators is based on joule’s heating effect and it requires only small amount of voltage. Not only low driving voltage, SMA actuators also provides high energy density and large forces. Only drawback is that it possess high response time which is around 50ms as electrostatic actuators have a response time in the order of micro seconds.
factor for various materials of the cantilever beam to be used as a Micro Electro Mechanical Systems(MEMS) resonator. In order to develop such resonators the simulation of Thermoelastic Damping (TED) becomes very important. Qfactor is greatly affected by the energy dissipation mechanism in TED. The material such as Ge, GaAs, Si, Insb,Ti and Nitinol is used here. Out of all the materials the Shape memory alloy (SMA), Nitinol shows the better value of Q-factor at Eigen frequency of (0.27MHz). COMSOL Multiphysics software is used for the simulation of TED. In this study, two sided fixed beams are used and their material property effects on the Q-factor are brought out.
2.THEORETICAL BACKGROUND
Key Words: Cantilever beam, COMSOL, Eigen frequency, Q-factor, SMA, TED
According to Zener, quality factor for a isotrophic beam which is vibrating in the fundamental mode can be presented with an analytical expression. Zener’s expression is given by [9] and [10]:
1.INTRODUCTION In an MEMS resonator, TED is considered to an important loss mechanism [l]-[4]. Due to the properties such as low energy consumption, small size and less weight, MEMS resonators are often used in filters [1]. TED results in flexural vibrations of the cantilever beam. Such vibrations cause tensile and compact strains which tends to build on two different sides leading to a imbalance of the system. The dissipation of the vibrational energy is caused by the irreversible heat flow in the material [7]-[8]. Therefore, when compared to quartz crystal resonators, Silicon MEMS resonators are the best choices [5] [6]. But there are also well-established quartz technology, therefore silicon MEMS resonators should provide better performance characteristics. In achieving this, choosing of resonators having high Q-factor or a little loss in energy becomes a most important factor. The dissipation that occurs when compared to the total sytem energy in the system can be termed as Qfactor. In order to derive the energy dissipation caused by the irreversible flow of heat in oscillating structures, TED is an important factor. A high Q-factor means an system possess high signal-to-noise ratio and also there is low consumption of power, whereas low Q-factor has high dissipation resulting in reduced sensitivity and power consumption increases[6]. Therefore it is important to eliminate the dissipation as much as possible. These sources can be changed by altering the design of the model.
(1) where E can be defined as the Elastic modulus of the beam, α is thermal expansion , ω is the resonant frequency (angular) . For Q to be high, the resonant frequency should be greater when compared to the thermal relaxation time, 1/τ . And this constant τ is defined as: (2) where h is the beam thickness and κ is the thermal conductivity of the mode. The resonant frequency of the beam can be calcualted as: (3) q values differ with structure. q equals 4.73 for beams which has both ends clamped and equals when both ends are simply supported.
3.CANTILEVER BEAM The model consists of a single beam vibrating in its fundamental mode, perpendicular to its long axis. The model geometry is shown in Figure 1. The two ends of the beam are
Shape memory alloys are activated thermally. At low temperatures the alloy is in the martensitic phase providing
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