Microelectromechanical system (MEMS) capacitive accelerometer for the Internet of Things applications is designed with open-loop structure rather than closed-loop structure to achieve low power ...consumption. In the open-loop structure, voltage control readout structure instead of charge control readout structure is preferred for low cost. However, the voltage control readout structure suffers from low power efficiency in terms of figure of merit (FoM) due to significant parasitic-capacitance-induced noise. In this article, the correlated double amplifying (CDA) technique is proposed to reduce the noise of the voltage control readout circuit with high power efficiency. Although traditional correlated double sampling (CDS) technique can also be used in readout circuit to reduce the parasitic-capacitance-induced noise, it sacrifices driving ability and bandwidth of the readout circuit, while CDA does not. The CDA technique adopts correlated amplifying to reduced noise without significant increase of power consumption. Thus, CDA technique leads to higher power efficiency. The CDA technique is demonstrated in a fully differential readout circuit fabricated in a 0.18-um CMOS process and tested with a sensing element from a commercial MEMS accelerometer. The measurement results show that noise floor of the readout circuit is <inline-formula> <tex-math notation="LaTeX">0.5~ \mathrm {aF}/\!\surd {\mathrm {Hz}} </tex-math></inline-formula> and the noise floor of the whole system is <inline-formula> <tex-math notation="LaTeX">112 ~\mathrm {ug}/\!\surd {\mathrm {Hz}} </tex-math></inline-formula>, with a power consumption of <inline-formula> <tex-math notation="LaTeX">139~ \mu \text{W} </tex-math></inline-formula> and a bandwidth of 12.5 kHz. The full input range of ±4 g, an FoM 1 of 80 pJ, and an FoM 2 of <inline-formula> <tex-math notation="LaTeX">254 ~\mathrm {uW}{\cdot }{\mathrm {ug/Hz}} </tex-math></inline-formula> are achieved.
Abstract Objectives The GT1M ActiGraph has been replaced by the triaxial GT3X which includes an inclinometer to detect postures. The purpose of this study was to investigate comparability of the GT3X ...to the GT1M and to develop activity intensity cut-points for the vector magnitude of the GT3X (VMGT3X ) in children. Additionally, the study aimed to assess the validity of the GT3X inclinometer for detecting postures. Design Forty-nine children aged 10–15 were tested during semi-structured activities in a laboratory setting (lying, sitting, standing, Nintendo Wii boxing, walking and running). Methods Expired respiratory gases were measured continuously using the Cosmed K4b2 portable metabolic system. Simultaneously, ActiGraph counts by a GT3X and a GT1M were recorded. Results Significantly higher counts were found for GT3X vertical mean counts per second (vcps) and antero-posterior counts per second (apcps) during running, relative to the GT1M. Cut-points for the VMGT3X , developed using Receiver Operator Characteristics (ROC) curves (development group N = 32, validation group N = 17), were <3 counts s−1 for sedentary (cross-validation: 87% correctly classified), 3–56 counts s−1 for light (cross-validation: 70% correctly classified) and >56 counts s−1 for moderate to vigorous (mvpa) (cross-validation: 86% correctly classified). The inclinometer correctly classified standing 20%, lying 15%, sitting 94% and the off position 45% of the time. Conclusions The vcps from the two monitors differ for certain activities. Cross-validated cut-points for the classification of VMGT3X counts into sedentary, light and mvpa are presented. Posture classification by the GT3X should be interpreted with care, as misclassifications are common.
To improve the sensitivity and stability of a quartz vibrating beam accelerometer (QVBA), a laterally sensitive structure was developed that utilizes the force-frequency characteristics of a quartz ...double-ended tuning fork (DETF) to realize quasi-digital measurement of acceleration. Two DETFs were purposely designed for the sidewalls of the proof mass, and the hinge of the spring-mass structure was along the proof-mass thickness, which improved the sensitivity. Laterally sensitive structures can also solve the fabrication problems of hinges, including accuracy, deformation, and residual stress. A femtosecond laser was used to release the anchor between the out-of-frame and the proof mass to protect the hinge. The isolation structure was designed to float both the DETFs and hinge to reduce the interference of external stress. Electrodes were deposited on the four surfaces of the vibrating beam in a three-segment configuration to excite the DETF into the antiphase in-plane vibration model. As a result, an accelerometer prototype is fabricated, and the performance characterization results exhibit the sensitivity and stability of 188.61 Hz/g and 7.81 ppm, respectively, and the bias instability (Allan deviation) of 1.26 μg, which proves the design rationality of laterally sensitive QVBA.
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•A laterally sensitive QVBA is presented, with two quartz DETFs mounted on the two sidewalls of pendulum.•The force-frequency characteristics of DETF is utilized to realize the quasi-digital measurement of acceleration.•Isolation structures are designed to suspend the hinge and DETFs from out-of-frame.•The improved sensor structure reduces machining difficulty, and a femtosecond laser is used to release the hinge.•The sensitivity and its stability are 188.61 Hz/g and 7.81 ppm, respectively, and the bias instability is 1.26 μg.
Horse breeders suffer massive economic losses due to dystocia, abortion, and stillbirths. In Thoroughbred mares, breeders often miss the foaling process because approximately 86% of the foaling ...events occur from 19:00 to 7:00; consequently, breeders cannot assist mares experiencing dystocia. To solve this problem, various foaling alarm systems have been developed. However, there is a need to develop a new system to overcome the shortcomings of the existing devices and improve their accuracy. To this end, the present study aimed to (1) develop a novel foaling alarm system and (2) compare its accuracy with that of the existing FoalertTM system. Specifically, eighteen Thoroughbred mares (11.9 ± 4.0 years old) were included. An accelerometer was used to analyze specific foaling behaviors. Behavioral data were transmitted to a data server every second. Depending on the acceleration value, behaviors were automatically classified by the server as categorized behaviors 1 (behaviors without change in body rotation), 2 (behaviors with sudden change in body rotation, such as rolling over), and 3 (behaviors with long-term change in body rotation, such as lying down laterally). The system was designed to alarm when the duration of categorized behaviors 2 and 3 was 12.9% and that of categorized behavior 3 was 1% during 10 min. The system measured the duration of each categorized behavior every 10 min and transmitted an alarm to the breeders when foaling was detected. To confirm its accuracy, the foaling detection time of the novel system was compared with that of FoalertTM. The novel foaling alarm system and FoalertTM alarmed foaling onset respectively 32.6 ± 17.9 and 8.6 ± 1.0 min prior to foal discharge, and the foaling detection rate of both systems was 94.4%. Therefore, the novel foaling alarm system equipped with an accelerometer can precisely detect and alert foaling onset.
This paper investigates an effective approach to estimate vertical channel accelerometer bias in strapdown inertial navigation system. At first, a novel inertial frame based mechanisation algorithm ...for strapdown inertial navigation system is introduced and its equations are derived. The difference between the outputs of the proposed mechanisation and a special type of the local-level frame mechanisation is considered as an error signal. Through this approach, the vertical accelerometer bias estimation procedure is converted to a control problem. By designing an appropriate optimal controller, the error signal is minimised and the vertical accelerometer bias is accurately estimated. The proposed approach attains a more robust and accurate estimation of the vertical accelerometer bias compared to the conventional Kalman filter based self-alignment and calibration method. Two different scenarios are conducted to assess the effectiveness of the proposed approach. In the first scenario, the IMU is stationary with respect to the Earth and the second scenario evaluates the condition where IMU experiences undesirable dynamic motions. The experimental test results illustrate that unlike the conventional Kalman filter based self-alignment and calibration method, the proposed approach obtains a robust estimation in the presence of undesirable dynamic motion as well as the static condition.
Micro-Opto-Electro-Mechanical Systems (MOEMS) accelerometer is a new type of accelerometer which combines the merits of optical measurement and Micro-Electro-Mechanical Systems (MEMS) to enable high ...precision, small volume and anti-electromagnetic disturbance measurement of acceleration. In recent years, with the in-depth research and development of MOEMS accelerometers, the community is flourishing with the possible applications in seismic monitoring, inertial navigation, aerospace and other industrial and military fields. There have been a variety of schemes of MOEMS accelerometers, whereas the performances differ greatly due to different measurement principles and corresponding application requirements. This paper aims to address the pressing issue of the current lack of systematic review of MOEMS accelerometers. According to the optical measurement principle, we divide the MOEMS accelerometers into three categories: the geometric optics based, the wave optics based, and the new optomechanical accelerometers. Regarding the most widely studied category, the wave optics based accelerometers are further divided into four sub-categories, which is based on grating interferometric cavity, Fiber Bragg Grating (FBG), Fabry-Perot cavity, and photonic crystal, respectively. Following a brief introduction to the measurement principles, the typical performances, advantages and disadvantages as well as the potential application scenarios of all kinds of MOEMS accelerometers are discussed on the basis of typical demonstrations. This paper also presents the status and development tendency of MOEMS accelerometers to meet the ever-increasing demand for high-precision acceleration measurement.
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•An efficient monitoring method for high-speed broaching is presented.•Time and Frequency domains signals are analyzed, taking into account the tooth passing frequency and ...harmonics.•Tool wear is estimated in real-time, by monitoring process vibrations recorded by accelerometers.•Experiments in nickel alloy type Inconel 718 (aged) pieces were carried out.
Real-time monitoring in CNC machine tools is focused on the early detection of tool wear, and in this way to assess part piece quality. The machining process known as broaching is critical for firtree slots (dovetails) production in turbomachinery components, such as turbine disks. Tight tolerances on one hand, even less than 5 µm in firtree-slots pressure faces, and high productivity on the other, are the two main requirements. Besides, broaching tools are very expensive and the cutting edges wear must be estimated during the process; in fact, tool wear in difficult-to-cut materials machining may cause a waste not only in terms of the tool but also of the very expensive workpieces. Broaching usually is one of the last operations in the process chain, so components start the operation with a very high-added value. Hence, only one bad slot implies an unrecoverable piece and therefore a huge waste of time and money.
In this paper, a monitoring method for efficient broaching is proposed by combining real-time monitoring and off-line tool wear inspection. Firstly, the cutting tool characteristics are defined, and those affected by tool degradation. Secondly, some broaching cycles were carried out while measuring a) process accelerations through two accelerometers, b) cutting force by load cells, and c) motor drive consumption. They were simultaneously recorded. Furthermore, the sensitivity between tool wear and broaching process natural frequencies is established.
Finally, a series of experimental tests were executed for verification, showing the useful approach for daily life production. The paper focuses on signals and their sensitivity to significant process variations.
Describing patterns in activity and behaviour of animals as they move through their environment helps to reveal fundamental aspects of their ecology and identify key habitat requirements. Nursery ...areas are used by many shark species and play an important role in maintaining the viability of populations. Although shark movements within nursery areas have been well studied, far less is known about how space use correlates with activity levels and specific behaviour. In the present study, we used combined accelerometer-acoustic transmitter tag packages to investigate fine-scale space use, activity and behavioural patterns of nursery-bound lemon sharks, Negaprion brevirostris. First, we constructed an ethogram to categorize specific behaviours from accelerometer data collected from seven sharks (97–122cm total length) that were caught, tagged and observed in captivity for 3–6 days. Second, we conducted field trials with 19 sharks (78–169cm total length), each tagged and actively tracked during 3–5 deployment days. We then used baited remote underwater video (BRUV) surveys to investigate potential overlap between shark foraging effort and prey distributions. Accelerometer and tracking data showed that the tidal phase significantly affected space use, activity and behaviour. Sharks used nearshore areas during the high tide periods where resting increased and activity levels were reduced. On falling tides, sharks moved farther from the shoreline and increased overall activity. Foraging effort peaked at low tide periods and foraging events overlapped with areas of disproportionately high preferred prey abundance. Ontogenetic patterns were also found in which larger sharks generally occupied larger home ranges, spent more time in areas farther offshore, rested less and foraged more than smaller individuals. These findings represent novel insights into nursery habitat use and behavioural trade-offs in lemon sharks and support more informed management for this threatened species.
•Tidal phase drove patterns in activity and behaviour of nursery-bound lemon sharks.•Lemon sharks showed a trade-off between tide-related predation risk and foraging.•Lemon sharks increased foraging in areas of higher preferred prey abundance.•Diminishing predation risk over ontogeny defined changes in lemon shark habitat use.
A method for denoising accelerometer data based on the L2‐norm total variation (LTV) algorithm is presented. In order to collect accelerometer data, a wireless accelerometer sensor was developed that ...is directly connected to a central node. By benefiting from the LTV algorithm, the obtained signals from the accelerometer are denoised. The proposed method is tested by denoising in different accelerometer signals and the results are evaluated by signal‐to‐noise ratio and power spectral density functions of the signals. The obtained results reveal that noise reduction has been implemented satisfactorily. Hence, the measurement accuracy of accelerometer signals for the proposed method have improved ∼4–10% than other the three low‐pass filters including Savitzky–Golay, equiripple‐pass‐band and Butterworth.
In recent years, sensors have been installed in buildings for various purposes to record building conditions. In this research, the objective is to clarify the possibility of linking building ...information with sensor information and future issues. For this purpose, we focused on BIM data, which enables systematic digital description of building information, and conducted prototyping for describing and linking information between the building to be measured and the MEMS accelerometer. The target building was a two-story wooden detached house, and the BIM data was described in IFC format.
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