Analysis of Temperature Stability and Change of Resonant Frequency of a Capacitive MEMS Accelerometer

Xuan Luc Le,Kihoon Kim,Sung-Hoon Choa 한국정밀공학회 2022 International Journal of Precision Engineering and Vol.23 No.3

Temperature stability is a very important factor that determines the performance and reliability of the MEMS accelerometer. A change in the temperature of the accelerometer will cause complicated coupled effects, in particular changes in the material properties, deformation, and thermo-mechanical stress, resulting in changes in the resonant frequency of the accelerometer. In this study, we investigate the effects of temperature changes on the resonant frequency of an accelerometer. The effects of material properties and deformation with temperature changes on the resonant frequency of the accelerometer were investigated by the simulation and experimental analysis. As the temperature was increased from 25 to 75 °C, the silicon structure and the accelerometer chip were deformed in a concave shape, and the amounts of warpage of the silicon structure and the accelerometer chip were 0.018 and 0.178 μm, respectively. The warpage was mainly caused by the thermal expansion mismatch of the materials. The suspension beam and moving comb structures were also deformed very slightly. As the temperature was increased from − 40 to 75 °C, the resonant frequency of the accelerometer decreased linearly from 1269 to 1193 Hz, indicating that the temperature drift of the resonant frequency is − 0.66 Hz/°C. In order to investigate the effects of deformation of the silicon structure on the resonant frequency, the numerical analysis of an accelerometer with identical top and bottom glass thicknesses was conducted. This accelerometer model showed almost zero warpage regardless of changes in the temperature. However, temperature drift of the resonant frequency of − 0.52 Hz/°C continued to occur. Therefore, the changes of Young’s modulus of the silicon with the temperature could be the main cause of the change in the resonant frequency. This study will present a design guideline and optimal parameters for the development of a robust MEMS accelerometer to minimize the effects of temperature changes.

High-Shock Silicon Accelerometer with a Plate Spring

이재민,장창욱,최창준,권기범,한정삼,권남열,고종수 한국정밀공학회 2016 International Journal of Precision Engineering and Vol.17 No.5

In this paper, a high-shock 2,000 g accelerometer with a plate spring has been designed, fabricated, and tested. The proposed accelerometer with a plate spring uses a device layer of an SOI (silicon on insulator) wafer. Moreover, the accelerometer has the merits of a simple fabrication process and the possibility of precisely controlling the thickness of the spring. In addition, the accelerometer has high structural stability because it is fabricated such that the plate spring surrounds the mass of the accelerometer. The detailed design dimensions of the proposed accelerometer were determined through an optimal design process. Furthermore, the proposed accelerometer was fabricated via MEMS processes. When a shock of 2,000 g was applied, the sensitivity of the fabricated accelerometer was 34.6 μV/g. When a shock within 2,000 g was applied, the non-linearity of the accelerometer was measured to be 1.4% or below. In addition, the transverse sensitivity of the fabricated accelerometer was 15% less than the measured sensitivity. The newly fabricated acceleration sensor showed stability to the extent that it was not destroyed even under a shock of 6,034 g, which was three times higher than the sensing range.

가속도계로 측정된 한국 성인의 신체활동 : 제6기 국민건강영양조사 가속도계 자료 분석

임정준 ( Jungjun Lim ),성호용 ( Hoyong Sung ),이온 ( On Lee ),김연수 ( Yeonsoo Kim ) 한국스포츠정책과학원(구 한국스포츠개발원) 2020 체육과학연구 Vol.31 No.2

[목적] 본 연구의 목적은 가속도계로 측정된 중-고강도 신체활동 및 좌식행동을 분석하고, 동일인의 자기보고식 설문 결과로 나타난 신체활동 수준과 지침 충족률을 비교하는 데 있다. [방법] 2014-2015 국민건강 영양조사의 참가자 중 가속도계 착용에 동의한 1,417명의 하루 평균 좌식시간 및 중-고강도 신체활동 시간, 그리고 신체활동 지침 충족률을 연령과 성별에 따라 분석하였다. 또한, 자기 보고식 설문지와의 연관성을 확인하기 위해, 동일인의 신체활동 설문의 결과를 산출하여 Chi-square test 및 상관분석을 실시하였다. [결과] 첫째, 1분 이상 모든 신체활동을 포함한 가속도계(accelerometer-total AT)의 하루 평균 중-고강도 신체활동은 남성 40.6분 여성 31.1이었으며, 좌식시간은 남성 502.9분 여성 498.9분이었다. 지속된 10분 이상가속도계(accelerometer-bout AB)의 중-고강도 신체활동의 경우 남성 16.4분 여성 14.2분으로 나타났다. 반면 설문의 중-고강도 신체활동은 남성 95.8분 여성 64.3분, 좌식시간은 남성 471.2분 여성 455.2분으로 나타났다. 둘째, 신체활동 지침 충족률은 설문지 55.6%, AT 56.1%, AB 21.4%로 나타났다. 셋째, 신체활동 강도에 따른 설문지와 가속도계의 상관계수는 모두 통계적으로 유의하였으나(p < 0.01), 약한 상관도를 보였다(rho = 0.112-0.351). 넷째, AB와 설문지의 신체활동 지침 충족률의 연관성은 없었으며(p < 0.01), 설문지의 민감도 71.3%, 특이도 48.6%, 양성예측도 27.5%, 음성예측도 86.1%였으며 정확도는 53.4%로 나타났다. [결론] 본 연구의 결과 설문은 가속도계에 비해 많은 신체활동 시간과 적은 좌식시간을 보고하였다. 또한, 설문과 가속도계의 신체활동 지침 충족률은 상이하였으며, AB 결과를 비교할 경우 그 차이가 크게 증가하였다. 그러므로 두 측정 도구를 상호 보완하여 사용할 수 있는 구체적인 방법에 관한 추가 연구가 필요할 것이다. 따라서 설문지와 가속도계의 신체활동 결과를 해석할 때는 큰 주의를 기울여야 하며, 서로 다른 두 측정 도구를 상호 보완하여 사용할 수 있는 구체적인 방법에 관한 추가 연구가 필요할 것이다. [Purpose] The purpose of this study was to evaluate the moderate to vigorous physical activity(MVPA) and sedentary time measured by accelerometer. Furthermore, the level of physical activity and adherence rate of physical activity guideline(PAG) were compared with the self-reported questionnaire. [Methods] The MVPA, sedentary time, and adherence rate of PAG according to age and sex were examined to people who agreed to wear accelerometers among the participants of the 2014-2015 Korea National Health and Nutrition Examination Survey. To compare the relationship between accelerometer and self-reported questionnaire, Chi-squared test and Spearman correlation analysis were performed. [Results] The MVPA of the accelerometer-total(AT) was 40.6 minutes/day for men and 31.1 minutes/day for women. Sedentary time was 502.9 minutes/day for men and 498.9 minutes/day for women. The MVPA of accelerometer-bout(AB) estimates was 16.4 minutes/day for men and 14.2 minutes for women. On the other hand, the MVPA of the self-report was 95.8 minutes for men and 64.3 minutes for women, and the sedentary time was 471.2 minutes for men and 455.2 minutes for women. The adherence rate of PAG was 55.6% of the self-report, 56.1% of the AT, and 21.4% of the AB. The correlation between self-report and accelerometer was statistically significant(p < 0.01), but showed a weak correlation coefficient(rho=0.112-0.351). There was no association between AB and self-report(p < 0.01). The sensitivity and specificity of the self-report were 71.3% and 48.6%, respectively. The positive and negative predictive values of the self-report were 27.5% and 86.1%, respectively. [Conclusions] As a result of this study, self-reported physical activity level by questionnaire had more MVPA and less sedentary time than the accelerometer-determined physical activity. In addition, the adherence rate of the PAG differed from accelerometer and self-report. The difference was significantly increased when comparing AB with the self-report. Therefore, great care must be taken when interpreting accelerometer and self-report questionnaire. Further research will be needed on specific methods that can be used by complementing the two measurement tools.

A Simple Analytical Model for MEMS Cantilever Beam Piezoelectric Accelerometer and High Sensitivity Design for SHM (structural health monitoring) Applications

Raaja, Bhaskaran Prathish,Daniel, Rathnam Joseph,Sumangala, Koilmani The Korean Institute of Electrical and Electronic 2017 Transactions on Electrical and Electronic Material Vol.18 No.2

Cantilever beam MEMS piezoelectric accelerometers are the simplest and most widely used accelerometer structure. This paper discusses the design of a piezoelectric accelerometer exclusively for SHM applications. While such accelerometers need to operate at a lower frequency range, they also need to possess high sensitivity and low noise floor. The availability of a simple model for deflection, charge, and voltage sensitivities will make the accelerometer design procedure less cumbersome. However, a review of the open literature suggests that such a model has not yet been proposed. In addition, previous works either depended on FEM analysis or only reported on the fabrication and characterization of piezoelectric accelerometers. Hence, this paper presents, for the first time, a simple analytical model developed for the deflection, induced voltage, and charge sensitivity of a cantilever beam piezoelectric accelerometer.The model is then verified using FEM analysis for a range of different cases. Further, the model was validated by comparing the induced voltages of an accelerometer estimated using this model with experimental voltages measured in the accelerometer after fabrication. Subsequently, the design of an accelerometer is demonstrated for SHM applications using the analytical model developed in this work. The designed accelerometer has 60 mV/g voltage sensitivity and 2.4 pC/g charge sensitivity, which are relatively high values compared to those of the piezoresistive and capacitive accelerometers for SHM applications reported earlier.

Analysis of Braking Response Time for Driving Take Based on Tri-axial Accelerometer

( Hwa-kyung Shin ),( Ho-cheol Lee ) 대한물리치료학회 2010 대한물리치료학회지 Vol.22 No.6

Purpose: Driving a car is an essential component of daily life. For safe driving, each driver must perceive sensory information and respond rapidly and accurately. Brake response time (BRT) is a particularly important factor in the total stopping distance of a vehicle, and therefore is an important factor in traffic accident prevention research. The purpose of the current study was (1) to compare accelerometer-BRTs analyzed by three different methods and (2) to investigate possible correlations between accelerometer-BRTs and foot switch-BRTs. Methods: Eighteen healthy subjects participated in this study. BRT was measured with either a tri-axial accelerometer or a footswitch. BRT with a tri-axial accelerometer was analyzed using three methods: maximum acceleration time, geometrical center, and center of maximum and minimum acceleration values. Results: Both foot switch-BRTs and accelerometer-BRTs were delayed. ANOVA for accelerometer BRTs yielded significant main effects for axis and analysis, while the interaction effect between axis and analysis was not significant. Calculating the Pearson correlation between accelerometer-BRT and foot switch-BRT, we found that maximum acceleration time and center of maximum and minimum acceleration values were significantly correlated with foot switch-BRT (p<0.05). The X axis of the geometrical center was significantly correlated with foot switch-BRTs (p< 0.05), but Y and Z axes were not (p >0.05). Conclusion: These findings suggest that the maximum acceleration time and the center of maximum and minimum acceleration value are significantly correlated with foot switch-BRTs.

성인의 13가지 신체활동의 에너지 소비량 및 가속도계 정확성의 남녀비교

최연정,주문정,박정혜,박종훈,김은경 한국영양학회 2017 Journal of Nutrition and Health Vol.50 No.6

Purpose: The purpose of this study was to measure energy expenditure (EE) the metabolic equivalents (METs) of 13 common physical activities by using a portable telemetry gas exchange system (K4b2) and to assess the accuracy of the accelerometer (Actigraph GT3X+) by gender in Korean adults. Methods: A total of 109 adults (54 males, 55 females) with normal BMI (body mass index) participated in this study. EE and METs of 13 selected activities were simultaneously measured by the K4b2 portable indirect calorimeter and predicted by the GT3X+ Actigraph accelerometer. The accuracy of the accelerometer was assessed by comparing the predicted with the measured EE and METs. Results: EE (kcal/kg/hr) and METs of treadmill walking (3.2 km/h, 4.8 km/h and 5.6 km/h) and running (6.4 km/h) were significantly higher in female than in male participants (p < 0.05). On the other hand, the accelerometer significantly underestimated the EE and METs for all activities except descending stairs, moderate walking, and fast walking in males as well as descending stairs in females. Low intensity activities had the highest rate of accurate classifications (88.3% in males and 91.3% females), whereas vigorous intensity activities had the lowest rate of accurate classifications (43.6% in males and 27.7% in females). Across all activities, the rate of accurate classification was significantly higher in males than in females (75.2% and 58.3% respectively, p < 0.01). Error between the accelerometer and K4b2 was smaller in males than in females, and EE and METs were more accurately estimated during treadmill activities than other activities in both males and females. Conclusion: The accelerometer underestimated EE and METs across various activities in Korean adults. In addition, there appears to be a gender difference in the rate of accurate accelerometer classification of activities according to intensity. Our results indicate the need to develop new accelerometer equations for this population, and gender differences should be considered.

공진형 MEMS 가속도계의 음향가진 반응특성 연구

이상우(Sang Woo Lee),이형섭(Hyung Sub Lee),유명종(Myeong-Jong Yu),김도형(Do Hyung Kim) 대한전기학회 2015 전기학회논문지 Vol.64 No.9

It is necessary to study on acoustic and vibratory response of a MEMS resonant accelerometer before applying to military applications. In this paper, we analyze why the resonant accelerometer reacts to an acoustic wave and a high frequency vibration. And we describe experimental results on acoustic and vibratory response of the accelerometer. The accelerometer consists of a proof mass and a dual ended tuning fork. It is a differential resonant accelerometer with arranging a pair of accelerometers. The mode shape was analyzed to find out the input mode frequency by using a FEM simulation. Some experiments regarding the acoustic noise was carried out by using a tweeter and a microphone in the anechoic room. Results showed that the accelerometer reacted to the acoustic wave and vibration which had the input mode frequency as we had expected. We showed experimentally not only that the susceptibility of the accelerometer to an acoustic wave was 70 dB but also that the effectiveness of applying an acoustic absorber and a metal case was 20 dB, respectively. Also, we could minimize the vibratory response property of the accelerometer by installing a IMU with a silicone rubber mount pad.

Impact Signal Differences Dependent on the Position of Accelerometer Attachment and the Correlation with the Ground Reaction Force During Running

Sihyun Ryu,Young-Seong Lee,Sang-Kyoon Park 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.22 No.10

Attachment of an accelerometer on the tibia is widely applied in the studies of impact during running as peak acceleration (PA) is highly relevant to peak ground reaction force (PGRF) and loading rate (LR). However, there are no guide lines for the positioning of the accelerometer on the tibia. The purpose of this study was twofold: first, to compare the differences in acceleration during running depending on the positions of the accelerometer’s attachment to the tibia (i.e. the distal tibia vs. proximal tibia); second, to select the better accelerometer position between the two placements in order to measure impact from the ground based on the correlations with the major impact variables of ground reaction force collected by a force plate. The twenty participants ran on an instrumented treadmill. Two three-axis accelerometers were attached to the distal tibia and proximal tibia, respectively. PAs at the distal tibia were greater than those at the proximal tibia ( p < 05). PAs at the distal tibia had a greater effect on predicting PGRF and LR compared to those at the proximal tibia ( p < 05). Therefore, considering the purpose of this study, the position of the accelerometer should be carefully selected. These findings suggest that an accelerometer attached at the distal tibia would provide a better estimation of the measurement of impact during running.

Differences between Objective and Self-Report Measures of Physical Activity. What do they Mean?

Richard P. Troiano,Kevin W. Dodd 한국체육측정평가학회 2008 한국체육측정평가학회지 Vol.10 No.2

Background: Self-reported physical activity is widely used in clinical and research settings. Self-reports are subject to measurement error due to recall difficulty, different interpretations of terms like "moderate intensity" or "leisure time" and possible social desirability bias. Methods: Self-report and objectively measured physical activity data were compared in 3087 adult (ages 20 y or older) participants of the nationally representative US National Health and Nutrition Examination Survey (NHANES) 2003-2004. Participants answered a physical activity questionnaire and wore an accelerometer for four to seven days. Questions addressed activity from transportation; household tasks; and recreational or leisure time exercise, sports, or physically active hobbies and were translated to minutes per day of moderate or greater intensity (mod-vig) activity. Accelerometer data were converted to minutes of mod-vig activity by summing minutes where the accelerometer count exceeded 2020 counts for "modified ten-minute bouts", which allowed for interruptions of one or two minutes below threshold. Data were averaged over the available four to seven days. Results: Between 37.5% (men, 20-59 y) and 73.3% (women, 60+y) of the population had no bouts of activity measured by accelerometer, but only 10.1% (men, 20-59 y) to 25.3% (women, 60+y) reported zero minutes per day. Among the groups with zero accelerometer-measured activity bouts, the reported time in mod-vig activity ranged from 43.1 to 65.2 minutes per day. Cross categorization of accelerometer and self-report quantities found agreement for only 18.3% (men, 20-59 y) to 32.7% (women, 60+y) of the population. Individuals with zero accelerometer-measured activity appeared in considerable numbers across all quantiles of self-reported activity, suggesting that misclassification could be severe. Conclusion: Self-reports provide poor estimates of absolute amounts of physical activity and may also lead to serious misclassification. Researchers and health professionals should be cautious when interpreting self-reported physical activity.

Wafer Level Vacuum Packaged Out-of-Plane and In-Plane Differential Resonant Silicon Accelerometers for Navigational Applications

Kim, Illh-Wan,Seok, Seon-Ho,Kim, Hyeon-Cheol,Kang, Moon-Koo,Chun, Kuk-Jin The Institute of Electronics and Information Engin 2005 Journal of semiconductor technology and science Vol.5 No.1

Inertial-grade vertical-type and lateral-type differential resonant accelerometers (DRXLs) are designed, fabricated using one process and tested for navigational applications. The accelerometers consist of an out-of-plane (for z-axis) accelerometer and in-plane (for x, y-axes) accelerometers. The sensing principle of the accelerometer is based on gap-sensitive electrostatic stiffness changing effect. It says that the natural frequency of the accelerometer can be changed according to an electrostatic force on the proof mass of the accelerometer. The out-of-plane resonant accelerometer shows bias stability of $2.5{\mu}g$, sensitivity of 70 Hz/g and bandwidth of 100 Hz at resonant frequency of 12 kHz. The in-plane resonant accelerometer shows bias stability of $5.2{\mu}g$, sensitivity of 128 Hz/g and bandwidth of 110 Hz at resonant frequency of 23.4 kHz. The measured performances of two accelerometers are suitable for an application of inertial navigation.