The Analytical and Clinical Validity of the pfSTEP Digital Biomarker of the Susceptibility/Risk of Declining Physical Function in Community-Dwelling Older Adults
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Measures of stepping volume and rate are common outputs from wearable devices, such as accelerometers. It has been proposed that biomedical technologies, including accelerometers and their algorithms, should undergo rigorous verification as well as analytical and clinical validation to demonstrate that they are fit for purpose. The aim of this study was to use the V3 framework to assess the analytical and clinical validity of a wrist-worn measurement system of stepping volume and rate, formed by the GENEActiv accelerometer and GENEAcount step counting algorithm. The analytical validity was assessed by measuring the level of agreement between the wrist-worn system and a thigh-worn system (activPAL), the reference measure. The clinical validity was assessed by establishing the prospective association between the changes in stepping volume and rate with changes in physical function (SPPB score). The agreement of the thigh-worn reference system and the wrist-worn system was excellent for total daily steps (CCC = 0.88, 95% CI 0.83–0.91) and moderate for walking steps and faster-paced walking steps (CCC = 0.61, 95% CI 0.53–0.68 and 0.55, 95% CI 0.46–0.64, respectively). A higher number of total steps and faster paced-walking steps was consistently associated with better physical function. After 24 months, an increase of 1000 daily faster-paced walking steps was associated with a clinically meaningful increase in physical function (0.53 SPPB score, 95% CI 0.32–0.74). We have validated a digital susceptibility/risk biomarker—pfSTEP—that identifies an associated risk of low physical function in community-dwelling older adults using a wrist-worn accelerometer and its accompanying open-source step counting algorithm.Piezoelectric accelerometer
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Piezoelectric accelerometer
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There exist a discrepancy between the usage of the expensive standard accelerometer and the cheap and accessible consumer device accelerometer for the measurement of whole-body vibration (WBV). This study investigated the validity of accelerations (g-forces) obtained from a consumer device accelerometer by simultaneously using the consumer device accelerometer with a standard accelerometer during evaluation of WBV experienced by earthmoving equipment operators. The consumer device accelerometer is a software (WBV) compatible with iOS devices from operating system 5 and above (LIS331DLH, 3-axis, ±2 g acceleration range, MEMS type) while the standard accelerometer used during this study is a GCDC tri-axial accelerometer (GCDC X16-4 3-Axis, G-Force Data logger, ±18 g acceleration range, MEMS type). The two accelerometers were mounted following the basicentric axes of the seated operators and put on before earthmoving operation. Data from both the accelerometers were analysed using MATLAB. Results gotten from both accelerometers revealed extreme values of WBV. Some fell within the Health Guidance Caution Zone (HGCZ i.e. 0.47 m/s2 and 0.93 m/s2) while some were above 0.93 m/s2. There were however differences between values gotten from the two accelerometers indicating inaccuracy from the consumer device accelerometer. This research created ground for improvement of accelerometers available on mobile devices and perhaps waken the need for developing new and economic methods of WBV measurement and evaluation.
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This paper presents the products of micro accelerometer from 1960′s to now. Three typical styles of micro accelerometer are analyzed. The advantages and disadvantages of each micro accelerometer are pointed out. Three dimensional accelerometer, the trend of micro accelerometer, is also introduced in this paper.
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The calculation amount of nine-accelerometer non-gyro micro inertial measurement unit(NGMIMU) is smallest in all designs,so it is the most appreciate to be applied in the real time system.This design needs some accelerometers to be fixed at the same point.But the accelerometers have the volume which can bring about the huge system error.In this paper,based on the NGMIMU algorithm and the accelerometer characteristic,a new applied algorithm is proposed.The algorithm divides the accelerometers into some groups to calculate on requiring the accelerometers to be fixed basing on some assumptions.So it can detect the error due to the volume of the accelerometer without any increase of the calculation amount.The experiment results also show that the measurement error is less that 8% using the proposed algorithm.
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The article introduces a testing method of triaxial accelerometer in allusion to one kind of triaxial MEMS accelerometers, and performance analysis is applied according to the MEMS accelerometer test results.The design principle and its internal structure is introduced briefly, and the advantages and performance parameters is given too.A test device and the corresponding test circuits are designed for this accelerometer.Comparing tests of the MEMS accelerometer are applied under many times.The output of standard reference accelerometer and the three axial outputs of MEMS accelerometer are recorded synchronously,so that the compare between the two accelerometer outputs in impacting directions and coupling analysis of the triaxial MEMS accelerometer among the three axes can be done.The test result indicates that,this measure method and the testing equipment are reliability, effectivity and versatility, can be used in other similar sensor measuring experiments.
Piezoelectric accelerometer
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A single-range accelerometer can not meet with the requirements of some special working environments,in which require testing the acceleration parameters ranged from several g to thousands of g.On the other hand,many measurement errors and inconvenience will be produced due to the spatial and mounting limitation from the usage of several accelerometers.To solve the above-mentioned problems,a multi-ranged micro accelerometer containing four accelerometer units(10g,100g,500g,and 10000g) was introduced in the present works.The structural design and static/dynamic simulation of the multi-ranged micro accelerometer were also elaborated,and the static and dynamic characteristics of the encapsulated multi-ranged micro accelerometer were calibrated.The calibration results showed that the multi-ranged micro accelerometer displayed good static and dynamic characteristics, and can be used for the measurement of the high-low range acceleration.
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This chapter discusses the purpose, principle, specifications, and applications of accelerometer. Accelerometers are widely used as sensors for wearable medical devices to measure and assess physical activity in clinical/laboratory settings or free-living environments. Accelerometers are sensors that are designed to measure the acceleration of an object in motion along reference axes. The most common type of sensors used to measure acceleration are piezoresistive accelerometer, piezoelectric accelerometer, differential capacitive accelerometer, and microelectromechanical sensors-based accelerometer. Three-axis accelerometers can detect motion in three different directions. A typical accelerometer is characterized by several features that include bandwidth, number of axes, and output range. Accelerometers are finding increasing application mostly related to fitness and sports activities. Besides the usual applications involving walking and running, accelerometer-based step counters are promoted to encourage people to walk a few thousand steps each day.
Piezoresistive effect
Piezoelectric accelerometer
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Aim Explaining which information of acceleration are included in the output signal of an accelerometer. Methods Deducing analytic formula of its output signal according to the physical model of an accelerometer. Results and Conclusion There are four types of information as follows in the output signal of an accelerometer: the acceleration of the centre of mass of moving object; vibration accelerations caused by the position of the accelerometer fixed versus the centre of its mass; the response of on acceleration the structured part fixing the accelerometer and the response of the accelerometer on excitation.
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Accelerometers are used in numerous industries including aircrafts and missile navigations systems, rotary machines, and electronic devices such as tablets, cell phones, and cameras. Accelerometers of different purposes and specifications are being produced in large quantities. The large demand for accelerometers forces the need for accelerometer testing methodology that is more convenient and accurate. Inertial Micro-Electromechanical Systems Accelerometer (MEMS) require a series of tests that include physical stimuli. One of the key challenges is the cost associated with testing. Therefore, the accurate prediction of the sensor functions not only reduces the testing time but also more importantly contributes to reducing testing cost.
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