High sensitivity nanostructure incorporated interdigital silicon based capacitive accelerometer

Interdigital structures are realized on silicon substrates with high sensitivity to acceleration. The process employs a combination of anisotropic back-side micromachining with front-side vertical deep reactive ion etching of silicon. The incorporation of silicon-based nano-structures on the vertical planes of fingers leads to a significant increase in the capacitance of the device from 0.45 for simple planes to 40 pF for the nano-structured planes. Such structures show high sensitivity to inclination and accelerations, which could be due to field emission of electrons from nano-metric features. Around 8% change in the capacitance is observed upon a tilting sensor from 0° to 90° angle, which makes it proper for possible use as an earthquake sensor. A preliminary model for the capacitance and its dependence on the measurement voltage is presented.     

Design and Analysis of MEMS Comb Drive Capacitive Accelerometer for SHM and Seismic Applications

This work presents the design of a MEMS accelerometer that is specifically intended for Structural Health Monitoring (SHM) applications where sensing low frequency low amplitude accelerations with high resolution is essential. The surface micromachined comb drive capacitance accelerometer structure has been considered in this design. The simulation experiments conducted on these devices using IntelliSuite MEMS design tool show that it has excellent displacement sensitivity of 21.39 μm/g, a capacitive sensitivity of 1.22 pF/g and voltage sensitivity of 1783 mV/g/V when it is designed to measure 0–0.1 g. Further, it is seen that it has a very low noise floor of 1.32 μg/√Hz and therefore high resolution. Since the accelerations can be as low as 0.04 g in SHM applications, excellent resolution is the primary goal in this design. Further, one more sensor specifically meant for strong motion seismic application has also been reported. This device has a bandwidth of 0–250 Hz and a noise floor of 5.612 μg/√Hz in addition to a sensor level voltage sensitivity of 97.9 mV/g/V. Finally, the comparison of these results with other similar devices reported in the past clearly illustrates the comparable performance of the present devices. Further, these devices, unlike the commercial low frequency accelerometers and other similar devices reported in the past can be fabricated by surface micromachining and CMOS compatible processes.     

Evanescent-field photonic microcells and their applications in sensing

This paper reports the results of our recent studies on evanescent-field photonic microcells (PMCs) made by post-processing commercial micro-structured optical fibers and by encapsulating tapered micro/nano fibers within glass capillaries. The PMCs have a wavelength/sub-wavelength scale wave-guiding core housed within a miniature hollow compartment. The housing isolates the waveguide core from external contamination and provides a robust platform for efficient evanescent field interaction with the materials filling the compartment. The techniques for fabrication are described and the applications of the PMCs for sensing temperature, gas pressure, refractive index and mechanical acceleration are discussed.     

Efficient dynamic time warping for 3D handwriting recognition using gyroscope equipped smartphones

Handwriting character recognition from three-dimensional (3D) accelerometer data has emerged as a popular technique for natural human computer interaction. In this paper, we propose a 3D gyroscope-based handwriting recognition system that uses stepwise lower-bounded dynamic time warping, instead of conventional 3D accelerometer data. The results of experiments conducted indicate that our proposed method is more effective and efficient than conventional methods for user-independent recognition of the 26 lowercase letters in the English alphabet.     

Passive detection of accelerometer-recorded fetal movements using a time–frequency signal processing approach

This paper describes a multi-sensor fetal movement (FetMov) detection system based on a time–frequency (TF) signal processing approach. Fetal motor activity is clinically useful as a core aspect of fetal screening for well-being to reduce the current high incidence of fetal deaths in the world. FetMov are present in early gestation but become more complex and sustained as the fetus progresses through gestation. A decrease in FetMov is an important element to consider for the detection of fetal compromise. Current methods of FetMov detection include maternal perception, which is known to be inaccurate, and ultrasound imaging which is intrusive and costly. An alternative passive method for the detection of FetMov uses solid-state accelerometers, which are safe and inexpensive. This paper describes a digital signal processing (DSP) based experimental approach to the detection of FetMov from recorded accelerometer signals. The paper provides an overview of the significant measurement and signal processing challenges, followed by an approach that uses quadratic time–frequency distributions (TFDs) to appropriately deal with the non-stationary nature of the signals. The paper then describes a proof-of-concept with a solution consisting of a detection method that includes (1) a new experimental set-up, (2) an improved data acquisition procedure, and (3) a TF approach for the detection of FetMov including TF matching pursuit (TFMP) decomposition and TF matched filter (TFMF) based on high-resolution quadratic TFDs. Detailed suggestions for further refinement are provided with preliminary results to establish feasibility, and considerations for application to clinical practice are reviewed.     

Experimental study and analysis of corner compensation structures for CMOS compatible bulk micromachining using 25 wt% TMAH

In the present work, most common compensation structures (〈1 1 0〉 squares and 〈1 0 0〉 bars) have been used for convex corner compensation with 25 wt% TMAH-water solution at 90±1 °C temperature. Etch flow morphology and self-align properties of the compensating structures have been investigated. For 25 wt% TMAH water solution {3 1 1} plane is found to be responsible for corner undercutting, which is the fast etch plane. Etch-front-attack angle is measured to be 24°. Generalized empirical formulas are also discussed for these compensation structures for TMAH-water solution. 〈1 1 0〉 square structure protects mesa and convex corner and is the most space efficient compared to other compensation structures, but unable to produce perfect convex corner as 〈1 0 0〉 bar type structures. Both the 〈1 0 0〉 bar structures provide perfect convex corners, but 〈1 0 0〉 wide bar structure is more space efficient than the 〈1 0 0〉 thin bar structure. Implications of these compensation structures with realization of accelerometer structure have also been discussed. A modified quad beam accelerometer structure has been realized with these compensation structures using 25 wt% TMAH.     

Correction and evaluation of the effect due to parasitic motion on primary accelerometer calibration

Primary accelerometer calibration is carried out under the assumption that a vibration exciter gives a rectilinear motion to an accelerometer to be calibrated. However practical vibration given by the vibration exciter includes parasitic motion such as transverse, rocking, and bending motion. Such parasitic motion would give two serious effects on primary calibration results, transverse motion effect and vibration distribution effect. Transverse motion effect is caused by an inner product of the vectors of both transverse motion and transverse sensitivity. On the other hand, the vibration distribution effect is caused by relative motion between a sensing point of accelerometer and a spot sensed by the interferometer. As these effects have close interaction between parasitic motion and measuring instruments, it would be very difficult to evaluate them by measuring independently each component.     

Effective accelerometer test beds for output enhancement of an inertial navigation system

This paper is submitted upon a research to enhance the output of an accelerometer widely used in inertial navigation units. In our study we introduce relatively simple and effective test beds to collect accurate and diverse reference data. We also carried out calibration runs with a highly accurate electromechanical shaking table. The proposed test beds compare well with sophisticated counterparts. The collected data is used to train artificial neural networks (ANNs) which would improve the accelerometer outputs by estimating the reference data from the actual sensor outputs. The ANN performance is compared with classic low pass filtering methods to provide a relative performance criterion. In this paper we focus on test beds rather than to give the details of the whole study. The test beds introduced in this research can be used for acquiring reference data for implementation of other different filter methods as well.     

The effects of rivet guns on hand-arm vibration

The objective of this study was to investigate the effects of rivet guns on hand-arm vibration. Vibration data were collected from five male and five female subjects using 12 rivet guns (from four different manufacturers depicted here as types 1, 2, 3, and 4 with large, medium, and small sizes in each type) at three different postures (neutral, maximum flexion, and maximum ulnar deviation) and two different levels of applied force (8 and 12 lbs). The results of analysis indicated that the level of vibration entering the hand was significantly higher for type 4 and large size than for other types and sizes. Comparing with the ISO standard, type 4 rivet guns could be used for less than 30 min in a day. Results of detailed analysis and the ergonomic ramifications as well as practical applications of this finding are discussed in the body of the paper. Relevance to industry

The results of this study would assist the manufacturers producing the rivet guns to devise methods of reducing the vibration at the production stage itself. Similarly, these results would help the user industries to take necessary precautionary measures so as to reduce the risk of injury to the employees.     

A system for ubiquitous fall monitoring at home via a wireless sensor network and a wearable mote

Accidental falls of our elderly, and physical injuries resulting, represent a major health and economic problem. Falls are the most common cause of serious injuries and are a major health threat in the stratum of older population. Early detection of a fall is a key factor when trying to provide adequate care to elderly person who has suffered an accident at home. Therefore, the detection of falls in the elderly remains a major challenge in the field of public health. Specific actions aimed at the fall detection can provide urgent care which allows, on the other hand, drastically reduce the cost of medical care, and improve primary care service. In this paper, we present a support system for detecting falls of an elder person by the combination of a wearable wireless sensor node based on an accelerometer and a static wireless non-intrusive sensory infrastructure based on heterogeneous sensor nodes. This previous infrastructure called DIA (Dispositivo Inteligente de Alarma, in Spanish) is an AAL (Ambient Assisted Living) system that allows to infer a potential fall. This inference is reinforced for prompt attention by a specific sensorisation at portable node sensor in order to help distinguish between falls and daily activities of assisted person. The wearable node will not determine a falling situation, it will advice the reasoner layer about specific acceleration patterns that could, eventually, imply a falling. Is at the higher layer where the falling is determined from the whole context produced by mesh of fixed nodes. Experimental results have shown that the proposed system obtains high reliability and sensitivity in the detection of the fall.