Persons

An improvement of micromechanical accelerometers (MMA) is relevant due to the constant expansion of their applications and the use of such devices in increasingly demanding conditions. In the paper the sandwich designs of the sensitive element (SE) of a capacitive micromechanical accelerometer (MMA) with folded springs have been studied from the point of view of ensuring the high sensitivity to acceleration, resistance to temperature change and the presence of residual mechanical stresses in the structures while providing the relative simplicity of their manufacturing technology. The modeling has been executed in ANSYS program. The gaps between the movable and stationary electrodes are increased compared to analogs up to 20 microns. It has been shown that the high sensitivity to changes of the acceleration is provided due to the optimization of the sensitive element design, using folded springs with lower values of stiffness coefficient. It has been determined that the capacity change under the action of acceleration along the working axis ( Z ) is almost 20 times more than changes in capacity along axes X and Y and the effect of temperature in the range of -40 ºC to 85 ºC on changes in capacitances along the working axis ( Z ) is small ±0.0025 - 0.003 pF. The mechanical stresses, which occur in constructive elements of the sensitive element under acceleration to 50 g, do not exceed 2.29 MPa, while silicon has strength 440 MPa. The natural frequency of oscillation of the second mode of the sensitive MMA does not affect the natural frequency of oscillation of the first mode of the sensitive element due to a significant difference of these frequencies approximately by 2 kHz. The analysis has shown that the studied sandwich constructions are characterized by high sensitivity and stability of parameters with relatively simple manufacturing.

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In micro-electromechanical systems the resonators are used in the construction of generators, sensors of inertial navigation systems, in RF transceivers, for increasing the sensitivity (acoustic, biological, mechanical, etc.). In this paper the change in the natural frequency of four characteristic resonators under the influence of mechanical force has been investigated and the simulation results in the ANSYS program have been presented. The effect of thermoplastic damping on the natural frequencies of the resonator, which occurs as a result of the mechanical oscillation of the resonator, as well as the residual stress, arising in the structure of the resonator due to the difference in manufacturing technique, has been investigated. The Q-factors of these resonators have been calculated using the COMSOL program and the optimum resonator design have been chosen to increase the sensitivity of the frequency microaccelerometer. The obtained results are assumed to be used in real constructions of the micro-electromechanical devices to be developed.

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The frequency micromechanical accelerometer (MMA) measures the acceleration, based on a change of the resonator frequency, when the acceleration is caused by the displacement of the inertial mass. Its sensitivity can be influenced by such factors as vibration noise, temperature, etc. In this study using the calculation and modeling in the ANSYS program the influence of the temperature on the natural oscillation frequency of resonators of various designs has been studied. It has been shown that in a number of studied designs of the frequency MMA resonators the frequency change ∆ f , caused by the temperature increase, is comparable and even exceeds a change of the frequency due to the acceleration effect. It has been determined that the known designs of the resonators, operating based on the oscillations of a two-fixed beam, do not ensure the stability of the oscillations natural frequency with the temperature change. The frequency, due to the temperature increase, of the resonators, working on the cantilever beam base, practically does not change. The best result from the point of view of the temperature stability has been shown by the resonator in the form of a cantilever beam with the beam resonator inside it, for which change ∆ f with an increase of temperature up to 70 °C. The study of the basic MMA construction, consisting of an inertial mass with a resonator made in the form of a cantilever beam with a beam resonator inside it has shown that the invariance of the natural oscillation frequency of this construction when the temperature increases up to 70 °C.

• Counter: 1999 | Comments : 0

For modern information, measuring and optoelectronic systems based on micro-and nanomechanical sensors of angular velocity and linear acceleration it is important to ensure their stable operation in presence of external factors. In the work the results of the study on the effect of random vibration on the characteristics experimental samples of micromechanical accelerometers (MMA), obtained using the LDS V455 vibration stand, have been presented. The dependence of the vibroacceleration on the frequency of one of the samples, intended for measurement of the acceleration in the range of up to ±1.2 g, has a noticeable shift from its given profile. Therefore, to determine the causes of the discrepancy, the design of the sensing element (CHE) MMA, the effect of random vibration on it, the calculations and simulation in the ANSYS program have been performed. The calculations and simulation have been executed in the ANSYS program. The deformation e of this MMA along the z axis of sensitivity and capacitance changes under the influence of acceleration and random vibration along the X , Y and Z axes have been determined taking into account the crystallographic orientation of the silicon-CHE material. When performing the calculations and modeling, the influence of the crystallographic orientation, used for manufacturing CHE MMA as a structural material of silicon, has been considered, since it affects the deformation (deviation) of the rotor, which should be taken into account by designers-developers of MEMS sensors. The results of the theoretical and experimental research and computer modeling have been presented.

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When designing MEMS accelerometers, it is necessary to provide the high sensitivity of the instrument, which is directly related to the amplitude of deflection of the inertial mass under the acceleration effect. The inertial mass increase results in the sensor sensitivity increase. The results of the calculation of the spring constant of the micro-mechanical accelerometer folded beam have been presented. The modeling using the ANSYS program, confirming the calculation results, has been performed. The use of the folded beams having compact sizes permits to increase the efficiency of the resonator operation, to achieve greater displacement in direction of the acceleration and stability of the inertial mass in other directions, taking into account the flexibility and rigidity in different directions.

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In microelectromechanical (MEMS) sensors the construction of a comb actuator is used for excitation of the resonator. In this article, we found a refined equation for the calculation of the electrostatic force of such an actuator. With the help of simulation in ANSYS program the effect of overlap amount between the teeth of the combs on the electrostatic force and the capacitance has been studied as well as the changes of the frequency of the resonator when it is exerted by the force. Similar studies have been implemented for a bar construction of the resonator, the usage of which, as comb design with small overlap of teeth, allows to decrease the parasitic electrostatic forces (along axes y , z ) and to increase the sensitivity of the frequency microaccelerometer due to a larger change in the frequency of the resonator oscillations when subjected to forces.

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Reliable operation of mechanical sensors of the angular velocity and linear acceleration in modern conditions is possible only when their stable operation under effect of the external factors has been provided. The mechanical effects-broadband (sinusoidal) vibration and the shock on the experimental samples of micromechanical accelerometers (MMA) on the vibration stand LDS V455 have been studied. The obtained amplitude-frequency characteristics (AFC) of the experimental samples can be used to characterize their quality. The high quality, has been reflected in the linearity of the frequency response in a fairly wide frequency range and in absence the resonant peaks. To achieve this, it is necessary to work out the technology of manufacturing samples. The areas of application of the MMA samples can be selected according to the AFC type obtained for them. The shock pulses can be approximated by a series of semi-sinusoidal pulses with the duration equal to half the period of the sine function. With the help of a vibrating table the intensity and duration of the impact have been set. The results of the experiments have shown that the shock load is worked out differently for MMA samples, calculated for different ranges of the measured acceleration values. From the data obtained it can be seen that the output signal of the MMA samples to acceleration measurement range ±1.2 is limited from above, the output signal of the MMA samples in the range up to ±5 g is not included into a specified profile. It has been determined that MMA PLU 5-17 samples fulfill well the impact profile. The selection of permissible impact loads on the MMA samples should be made based on the feedback, i.e. the output signal on the impact.

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