Accelerometer Device Research Articles

Translating accelerometer counts into energy expenditure: advancing the quest

Research that uses accelerometers to measure physical activity has expanded exponentially over the past decade. There were approximately 90 papers per year published in 2003 and 2004 compared with fewer than 10 per year in 1993 and 1994 ([6][1]). Since the beginning of the development and

Analysis of Quality Design Techniques for Electrostatic Actuators

A three-step technique for MEMS quality optimization is presented. It exploits the relative merits of its constituent optimization components. Analog Devices accelerometer was the test device with microstructure dimensions serving as design parameters [6]. Manufacturing design rules [7] and sensor performance requirements served as design constraints. A static model relating input acceleration to sensed voltage was used, neglecting sensor and signal conditioning dynamics. The trimming yield of the ADXL50[6], with sensitivity as the design target, was improved by 37%. We show that the three-step method enables the search for an optimal design in a semi-automatic manner by facilitating user interaction. Our final goal is to enable the generation of MEMS mask layout while ensuring robust designs with minimum sensitivity to fabrication process variations

Two-dimensional position detection system with MEMS accelerometers, readout circuitry, and microprocessor for padless mouse applications

A hybrid two-dimensional position sensing system is designed with microelectromechanical systems (MEMS) for padless mouse applications. The X/Y-axis acceleration of the user's hand movements is measured by two MEMS accelerometer devices. These acceleration values are pulsewidth modulated and converted into (X, Y) coordinates on the screen by integral operations on a microprocessor. The overall system consists of four major components: 1) MEMS accelerometers; 2) CMOS analog readout circuitry; 3) an acceleration magnitude extraction module; and 4) a 16-b RISC microprocessor. Mechanical and analog simulation shows that the designed mouse system can detect acceleration as small as 5.3 mg (g=9.8 m/s/sup 2/) with 100-kHz sampling frequency for low power consumption.

A description of an accelerometer-based mobility monitoring technique

Accurate monitoring of the mobility status of older adults, over the long-term, is important in rehabilitation medicine, as regular physical activity is central to maintaining both physical and mental health, as well as evaluating quality of life. This technical note describes an accelerometer-based mobility monitoring technique, which can distinguish between static and dynamic activities and can detect the basic postures of sitting, standing and lying. The technique allows thresholds for these postures to be set and two different posture threshold methods are described: mid-point and “best estimate”. Preliminary results from using these methods are presented. This preliminary evaluation of the technique was carried out over the long-term (>29 h) in an uncontrolled environment and the method used to carry out the evaluation is described in detail. The two different posture thresholding methods were tested on long-term mobility data from one older adult subject. The subject did not have to follow a specific activity protocol during the recording period (4 days) and was shadowed by an observer in order to evaluate the accuracy of this technique. The monitoring hardware consisted of two accelerometer devices, one on the trunk and the other on the thigh and a pocket-sized ambulatory data-logger. Applying ‘best estimate’ thresholding, as opposed to mid-point thresholding, improved sitting detection accuracy by 18%, to 93% and lying detection accuracy by 5%, to 84%. Thus, based on these preliminary data, an accurate mobility monitoring system for older adults is described and it was observed that the actual posture threshold limits applied have a high impact on the mobility monitoring system's accuracy and are particularly important for accurately detecting postures when used over the long-term, in an uncontrolled environment.

Investigating body motion patterns in patients with Parkinson's disease using matching pursuit algorithm.

Several recent studies have quantified abnormalities in Parkinsonian gait. However, few studies have attempted to quantify the regularity of body motion during walking in patients with Parkinson's disease. The aim of the paper was to characterise body motion patterns in healthy, elderly subjects and patients with Parkinson's disease during walking. Body motion was recorded during walking for 16 patients with Parkinson's disease and ten healthy, elderly subjects using a tri-axial accelerometer device. To characterise the body motion patterns, time-frequency patterns of the body acceleration signal were estimated using a matching pursuit algorithm. Data from the study showed that the healthy, elderly subjects and patients with Parkinson's disease had different time-frequency patterns. The time-frequency patterns were classified into four distinct patterns based on their time durations: vertical (< 0.15 s), circular (0.15-0.5 s), short horizontal (0.5-2.0 s) and long horizontal (> 2.0 s). The data showed that the energy of the long horizontal patterns, representing long-term smooth and regular (rhythmic) activities, significantly decreased, but the energy of the circular patterns, representing irregular activities, increased in the patients with mild Parkinson's disease, compared with those of the healthy, elderly subjects (p < 0.01). Futhermore, these features were seen more clearly in the body motions of severe case patients than is that of mild case patients. It was concluded that these differences are probably due to a lack of ability to control normal and smooth movement is Parkinson's disease.

A novel accelerometer tilt switch device for switch actuation in the patient with profound disability

Perring S, Summers A, Jones EL, Bowen FJ, Hart K. A novel accelerometer tilt switch device for switch actuation in the patient with profound disability. 2003:84:921-3. We describe the design and operation of a new switch that can be operated by patients with severely limited movement. The basis for the switch is an inexpensive single-chip accelerometer device. The switch responds to a relatively rapid rotation of the active components. We have ensured that the sensitivity of the switch device is adjustable over a wide range. The device automatically adjusts for changes in attitude of the device that result from a patient changing posture. We show that the device can operate in a wide range of attitudes. We describe 2 case studies in which the switch was successfully used as a head tilt switch.

Micromachining of glass inertial sensors

We demonstrate the feasibility of a powder blasting micro-erosion process for the micromachining of accelerometer devices in glass. Using high-speed abrasive microparticles and a metal contact mask, we structure millimeter-size cantilever beams from simple glass slides. By metalizing one side of the glass substrate, we demonstrate both capacitive and piezoresistive/strain gauge detection of the vibrating cantilever mass and measure the frequency response of mechanically excited cantilever beams. We think that our approach opens new perspectives for manufacture of inertial sensing devices in a technology alternative to Si.

The introduction of powder blasting for sensor and microsystem applications

We introduce powder blasting using a pressurised nozzle and a metallic mask as a new promising technology for microsystem fabrication. We study basic parameters of this powder blasting erosion process as well as mask-geometry effects on the erosion rate. We demonstrate the application potential of this technique in three important fields of microsystems research: (i) the realisation of microfluidic chips for biochemical separations, (ii) the micropatterning of composite hard magnetic layers for mechatronic and magnetic sensor applications, and (iii) the realisation of inertial sensors in glass. We present for the first time a mechanical and electrical characterisation of powder-blasted accelerometer devices.

Detection of posture and motion by accelerometry: a validation study in ambulatory monitoring

The suitable placement of a small number of calibrated piezoresistive accelerometer devices may suffice to assess postures and motions reliably. This finding, which was obtained in a previous investigation, led to the further development of this methodology and to an extension from the laboratory to conditions of daily life. The intention was to validate the accelerometric assessment against behavior observation and to examine the retest reliability. Twenty-four participants were recorded, according to a standard protocol consisting of nine postures/motions (repeated once) which served as reference patterns. The recordings were continued outside the laboratory. A participant observer classified the postures and motions. Four sensor placements (sternum, wrist, thigh, and lower leg) were used. The findings indicated that the detection of posture and motion based on accelerometry is highly reliable. The correlation between behavior observation and kinematic analysis was satisfactory, although some participants showed discrepancies regarding specific motions.

Technology for the high-volume manufacturing of integrated surface-micromachined accelerometer products

Since the inception of silicon surface micromachining more than fifteen years ago, the technology has successfully emerged from academic research and has found practical applications in many high-volume sensor products. The integration of on-chip electronics, in particular, represents the highest level of technological accomplishment to date in surface micromachining technology. The integrated approach offers tremendous performance enhancements while presenting numerous challenges to actual production implementation. This paper uses the Analog Devices accelerometer product series as an example to review the integrated surface micromachining technology and the practical solutions to overcome many of its challenges for high-volume manufacturing.

Experimental evaluation of the onset of subcooled flow boiling at high liquid velocity and subcooling

The knowledge of the onset of subcooled boiling in water forced convective flow at high liquid velocity and subcooling is of importance in thermal hydraulic studies of high heat flux components in fusion reactors. The present paper reports the results of an experimental research on the onset of subcooled boiling in water forced convective flow. From the measurement of the pressure drop along the heated test channel (D = 8 mm, L = 100 mm) it is possible to evaluate the heat flux at which the subcooled boiling occurs. As far as the coolant is in single-phase flow, it is possible to simply calculate its pressure drop, also taking into account the temperature effect on the friction factor, for the temperature variation along the heated channel and in the cross section (due to the steep thermal gradients). The classical corrections available in the literature have been used. Once bubble formation is established, the additional, significant contribution of the bubbles presence to the pressure drop leads to a deviation of the experimental pressure drop curve from the single-phase theoretical line. This latter identifies the onset of subcooled boiling. A comparison of the experimental heat flux at the subcooled boiling incipience with that provided by the major correlations available in the literature is given. A further comparison with measurements performed with an accelerometer device is provided in the paper. The accelerometer detects the additional noise due to bubbles formation close to the heated wall and subsequent collapse in the subcooled bulk of the liquid. The results given by the accelerometer and those obtained with the present evaluation method are in close agreement.

Evaluation of the Torsional VOR in Weightlessness

The experimental concept and findings from a recent manned orbital spaceflight are described. Together with ongoing terrestrial and parabolic studies, the present experiment is intended to further our knowledge of the sensory integrative processing of information from the semicircular canals and the otolithic receptors, and to quantify the presumed otolithic adaptation to altered gravito-inertial force environments in a more reliable manner than to date. The experiment included measurement of the basic vestibulo-oculomotor response during active head rotation about each of the three orthogonal axes. Priority was given to the recording of ocular torsion, as elicited by head oscillation about the roll axis, and thus due to the concomitant stimulation of the semicircular canals and otolith receptors. Videooculography was employed for the measurement of eye movements; head movement was measured by three orthogonally arranged angular rate sensors and a triaxial linear accelerometer device. All signals were recorded synchronously on a video/data recorder. Preliminary results indicate alterations in the torsional VOR under zero-g conditions, suggesting an adaptive modification of the torsional VOR gain over the course of the 6-day orbital flight. In addition, the inflight test findings yielded discrepancies between intended and performed head movement, indicating impairment in sensorimotor coordination under prolonged microgravity conditions.

Portable accelerometer device for measuring human energy expenditure.

We have developed and tested a portable device that measures energy expenditure per unit time of a human subject. A modified ceramic phonocartridge senses the acceleration of the body. After amplification and rectification a Curtis 120 CP3 elapsed time meter integrates the output. This may prove to be useful in providing an objective measurement of the level of physical activity of human subjects and can be used in studying habitual and leisure time activities in a large population setting. It is worn on the waist, weighs 400 g, measures 14 X 8 X 4 cm, costs $ 30 plus 5 h assembly time, and runs 10 days on two 9 V transistor batteries.

Analysis of the Reconstruction of Rail Geometry from Curvature Data

The reconstruction of rail geometry from measured curvature data is analyzed. The mathematical concept of curvature is developed and utilized in numerical integration of differential equations describing the rail path. Formulas are derived for various chord-displacement methods of measuring curvature and for their measurement response functions. The reconstruction of rail shapes is demonstrated by means of computer simulation, and the effects of measurement response and measurement error are analyzed. Accuracies are compared with those that might be obtained with accelerometer devices used to measure curvature. The techniques and results can be applied to the design of practical rail measurement systems.