This design includes an effective force-amplifying structure as is shown in Fig 2(a). The aim of this structure is to amplify the inertial force F to improve the sensitivity of this microaccelerometer.This force-amplifying structure can be simplified as a leverage system shown in Fig.2(b). and its effectiveness is denoted by the force-amplifying ratio
R(N/F)which is expressed as
R = N/F =L1+L3H1-H2/2-H3/2(1)
By adjusting the structural parameter of the design,the force-amplifying ratio can be as high as 200.Fig.2　the force-amplifying structuse and its simplifide leverage system
　　In this design, DETF has been used as the
core resonant structure and the relationship between the axial force and the resonant frequency of DETF is[8]
ωi=i2π2L2EIρA1+PL2i2π2EI(2)
Whereωi,P,E,I,L,Adenote thei-order resonant
frequency, axial force, Yang’s modulus, inertial momentum, length and area of cross-section of the
DETF respectively.
2　Major vibrating shape analysis This designed structure includes force-amplifying structure, DETF and Proof Mass is shown in Fig.3
and there exists several vibrating modes closely related to the performance of the microsensor. To analyze those modes, FEA has to be used because those modes are too complex to be calculated theoretically.
Fig.3　FEA simulation of newly-designed
resonant microaccelerometer
2.1　Desirable mode analysis
The desirable mode which is shown in Fig. 4
is the mode that appears when the resonant mi-
97第1期陈　健,陈德勇:谐振式微加速度传感器的有限元分析
A simulation of the desirable mode crosensor is under normal operation. The major characteristic of this mode is that two equally matched tines of DETF vibrate in the opposite direction meaning that there exists energy coupling which can enhance the quality factor of the resonator. To obtain this mode, doubling-side excitation has been proposed and the exciting sources on both sides of DETF should be of the same phase to make sure that driving force on two tines are always opposite to each other. The major concern of this mode is its resonant frequency: if the resonant frequency is relatively low, the resonator is relatively easy to be excited while the output signal is subjected to environmental low-frequency disturbance more easily; if the resonant frequency is relatively high the output signal is less subjected to disturbance while the resonator is harder to be excited. What is more, the resonant frequency of this mode should be adjusted far from the resonant frequency of disturbance modes discussed below. By adjusting the structural parameter of Beam 5(shown in Fig 1) resonant frequency of this mode can be adjusted. 2.2　Major disturbance modes analysis.There are two major disturbance modes which deserve our attention. The first one is shown in Fig. 5 and its main characteristic is that two equally matched tines of DETF are vibrating in the same direction.

1、本设计包含一个高效的力放大结构，如图2(a)所示。它的目的是放大惯性力F来提高微加速器的敏感度。
这个力放大器结构可简化为一个杠杆系统，如图2(b)所示。它的有效度可用下述公式表示的力放大率R来表示：
R = N/F =L1+L3H1-H2/2-H3/2.........(1)
通过调整设计的结构参数，力放大率可达到200。

在本设计中，DETF是谐振结构的核心，轴力与DETF共振频率的关系为：
ωi=i2π2L2EIρA1+PL2i2π2EI......(2)
式中Whereωi,P,E,I,L,A 分别表示i级共振频率，轴力，杨氏模量，惯性矩，长度及DETF的截面积。

2、主振型分析
本结构由一个力放大器结构、DETF及质量校验器组成，如图3所示。结构存在与微传感器性能密切相关的
几种振动模态。为分析这些模态，采用有限元方法，因为这些模态太复杂，理论上无法计算。

2.1、预期模态分析
图4所示的模态为谐振器正常操作状态下出现的模态。此模态的主要特征是DETF在两个相反方向的振动具有相同
波动，表示振动时存在能量加倍的情况，能够加强谐振器的质量因子。为了得到此种模态，对DETF进行双向激发，双向激发源必须具有相同的相位，确保两波峰位置的驱动力方向时刻相反，此模态下谐振频率是我们所关心的：如果谐振频率相对较低，那么谐振器在输出信号受环境中低频干扰时更容易被激发；相反地，如果谐振频率相对较高，那么谐振器输出信号不容易受到干扰，谐振器就不容易被激发。而且，必须调整此模态的谐振频率值，使之偏离下面讨论的干扰模式谐振频率值。通过调整结构中5#梁的结构参数，可以调整此模态的谐振频率。
2.2、主干扰模态分析
我们关心的干扰模态主要有两个，第一个如图(5)所示，它的主要特征是DETF在相同方向的振动具有相同
波动。