In the last 30 days

• Open/close A wireless high-speed data acquisition system for geotechnical centrifuge model testing

  C Gaudin et al 2009 Meas. Sci. Technol. 20 095709 Tag this article

  Article References Full text PDF (1.90 MB)

  This paper describes a novel high-speed wireless data acquisition system (WDAS) developed at the University of Western Australia for operation onboard a geotechnical centrifuge, in an enhanced gravitational field of up to 300 times Earth's gravity. The WDAS system consists of up to eight separate miniature units distributed around the circumference of a 0.8 m diameter drum centrifuge, communicating with the control room via wireless Ethernet. Each unit is capable of powering and monitoring eight instrument channels at a sampling rate of up to 1 MHz at 16-bit resolution. The data are stored within the logging unit in solid-state memory, but may also be streamed in real-time at low frequency (up to 10 Hz) to the centrifuge control room, via wireless transmission. The high-speed logging runs continuously within a circular memory (buffer), allowing for storage of a pre-trigger segment of data prior to an event. To suit typical geotechnical modelling applications, the system can record low-speed data continuously, until a burst of high-speed acquisition is triggered when an experimental event occurs, after which the system reverts back to low-speed acquisition to monitor the aftermath of the event. Unlike PC-based data acquisition solutions, this system performs the full sequence of amplification, conditioning, digitization and storage on a single circuit board via an independent micro-controller allocated to each pair of instrumented channels. This arrangement is efficient, compact and physically robust to suit the centrifuge environment. This paper details the design specification of the WDAS along with the software interface developed to control the units. Results from a centrifuge test of a submarine landslide are used to illustrate the performance of the new WDAS.

• Open/close Ultraprecision micro-CMM using a low force 3D touch probe

  A Küng et al 2007 Meas. Sci. Technol. 18 319 Tag this article

  Article References Full text PDF (1.75 MB)

  METAS developed a new 3D coordinate measuring machine (CMM) dedicated to traceable measurement for small parts with nanometre accuracy. The innovative design of the touch probe is based on a parallel kinematic structure of flexure hinges in order to minimize the moving mass and ensure an isotropic low stiffness. This head features very weak probing forces, below 0.5 mN, and supports exchangeable probes down to 0.1 mm diameter. It was combined with a highly accurate positioning stage developed at Philips CFT. The machine features a 90 mm × 90 mm × 38 mm air bearing stage with interferometric position measurement with no Abbe offset. The relevant calibration measurements reported here proudly highlight a repeatability of about 5 nm achieved by our micro-CMM. At the reached level of precision, the shape deviation of the probing sphere becomes a major contribution to the uncertainty. Therefore a calibration method for spheres based on error separation techniques was implemented. The result of roundness measurements on three calibration spheres is also presented. In addition, a scanning measurement procedure was implemented without any loss of accuracy, as attested by a comparison using a roundness measuring machine.

• Open/close A new sensing method based on PVDF film for material identification

  A Kimoto and N Sugitani 2010 Meas. Sci. Technol. 21 075202 Tag this article

  Article References Full text PDF (402 KB)

  This paper proposes a new sensing method based on polyvinylidene fluoride (PVDF) film for material identification. The proposed method makes it possible that the voltages (contact voltages) induced by the piezoelectric and electrostatic effects at the contact between the PVDF film and the material are simultaneously measured. The material identification including the hardness is possible by using their voltages. In the experiment, the identification of ten kinds of materials including hardness was demonstrated by the simultaneous measurement of the voltages. The results indicate that it is possible to simultaneously measure the contact voltages, although there are still some problems that should be solved.

• Open/close Multicycle synchronous digital phase measurement used to further improve phase-shift laser range finding

  Siyuan Liu et al 2007 Meas. Sci. Technol. 18 1756 Tag this article

  Article References Full text PDF (1.24 MB)

  Multicycle synchronous digital phase measurement is proposed in this paper to further improve the phase measurement in phase-shift laser range finding. In the method, heterodyne processing is employed to convert the phase measurement of a high frequency signal into that of a low frequency signal, and by keeping phase measurement independent of the signal frequency to be measured and the gate signal synchronous with the measurement signal during multicycle phase measurement, errors caused by the frequency drift of a local oscillator during conventional auto-digital phase measurement are totally eliminated, and the time required to complete range measurement is shortened. Experimental results show that an uncertainty better than ±1.5 mm can be achieved at a data rate up to 20 Hz ( t = 0.05 s) for a laser range finder using the method proposed with f _e = 10.000 MHz.

• Open/close A flow field investigation in the diffuser of a high-speed centrifugal compressor using digital particle imaging velocimetry

  Mark P Wernet 2000 Meas. Sci. Technol. 11 1007 Tag this article

  Article References Full text PDF (1.61 MB)

  Digital particle imaging velocimetry (DPIV) has become a widely used optical diagnostic technique for the study of both transient and steady state flows. The DPIV technique provides instantaneous planar maps of the flow velocity. The challenges remaining are in implementing the PIV technique in real world test facilities, where the instantaneous, planar velocity measurements provide researchers with information in less time than traditional point-based measurement techniques. The instantaneous planar velocity measurements obtained using PIV make it an attractive technique for use in the study of the complex flow fields encountered in turbomachinery. This paper discusses techniques for optical access, light sheet delivery, CCD camera technology and particulate seeding requirements for the successful application of PIV to turbomachinery. Time-averaged results obtained in the diffuser region of a high-speed centrifugal compressor are presented and discussed. In addition, combined correlation/particle-tracking results yielding super-resolution velocity measurements are presented.

• Open/close A task specific uncertainty analysis method for least-squares-based form characterization of ultra-precision freeform surfaces

  M J Ren et al 2012 Meas. Sci. Technol. 23 054005 Tag this article

  Article References Full text PDF (2.22 MB) Enhanced article HTML

  In the measurement of ultra-precision freeform surfaces, least-squares-based form characterization methods are widely used to evaluate the form error of the measured surfaces. Although many methodologies have been proposed in recent years to improve the efficiency of the characterization process, relatively little research has been conducted on the analysis of associated uncertainty in the characterization results which may result from those characterization methods being used. As a result, this paper presents a task specific uncertainty analysis method with application in the least-squares-based form characterization of ultra-precision freeform surfaces. That is, the associated uncertainty in the form characterization results is estimated when the measured data are extracted from a specific surface with specific sampling strategy. Three factors are considered in this study which include measurement error, surface form error and sample size. The task specific uncertainty analysis method has been evaluated through a series of experiments. The results show that the task specific uncertainty analysis method can effectively estimate the uncertainty of the form characterization results for a specific freeform surface measurement.

• Open/close Energy harvesting vibration sources for microsystems applications

  S P Beeby et al 2006 Meas. Sci. Technol. 17 R175 Tag this article

  Article References Full text PDF (667 KB)

  This paper reviews the state-of-the art in vibration energy harvesting for wireless, self-powered microsystems. Vibration-powered generators are typically, although not exclusively, inertial spring and mass systems. The characteristic equations for inertial-based generators are presented, along with the specific damping equations that relate to the three main transduction mechanisms employed to extract energy from the system. These transduction mechanisms are: piezoelectric, electromagnetic and electrostatic. Piezoelectric generators employ active materials that generate a charge when mechanically stressed. A comprehensive review of existing piezoelectric generators is presented, including impact coupled, resonant and human-based devices. Electromagnetic generators employ electromagnetic induction arising from the relative motion between a magnetic flux gradient and a conductor. Electromagnetic generators presented in the literature are reviewed including large scale discrete devices and wafer-scale integrated versions. Electrostatic generators utilize the relative movement between electrically isolated charged capacitor plates to generate energy. The work done against the electrostatic force between the plates provides the harvested energy. Electrostatic-based generators are reviewed under the classifications of in-plane overlap varying, in-plane gap closing and out-of-plane gap closing; the Coulomb force parametric generator and electret-based generators are also covered. The coupling factor of each transduction mechanism is discussed and all the devices presented in the literature are summarized in tables classified by transduction type; conclusions are drawn as to the suitability of the various techniques.

• Open/close Induction coil sensors—a review

  Slawomir Tumanski 2007 Meas. Sci. Technol. 18 R31 Tag this article

  Article References Full text PDF (1.13 MB)

  This review describes induction coil sensors, which are also known as search coils, pickup coils or magnetic loop sensors. The design methods for coils with air and ferromagnetic cores are compared and summarized. The frequency properties of coil sensors are analysed and various methods for output signal processing are presented. Special kinds of induction sensors, such as Rogowski coil, gradiometer sensors, vibrating coil sensors, tangential field sensors and needle probes are described. The applications of coil sensors as magnetic antennae are also presented.

• Open/close Piezoelectric MEMS sensors: state-of-the-art and perspectives

  S Tadigadapa and K Mateti 2009 Meas. Sci. Technol. 20 092001 Tag this article

  Article References Full text PDF (2.96 MB)

  Over the past two decades, several advances have been made in micromachined sensors and actuators. As the field of microelectromechanical systems (MEMS) has advanced, a clear need for the integration of materials other than silicon and its compounds into micromachined transducers has emerged. Piezoelectric materials are high energy density materials that scale very favorably upon miniaturization and that has led to an ever-growing interest in piezoelectric films for MEMS applications. At this time, piezoelectric aluminum-nitride-based film bulk acoustic resonators (FBAR) have already been successfully commercialized. Future innovations and improvements in inertial sensors for navigation, high-frequency crystal oscillators and filters for wireless applications, microactuators for RF applications, chip-scale chemical analysis systems and countless other applications hinge upon the successful miniaturization of components and integration of piezoelectrics and metals into these systems. In this article, a comprehensive review of micromachined piezoelectric transducer technology will be presented. Piezoelectric materials in bulk and thin film forms will be reviewed and fabrication techniques for the integration of these materials for microsensor applications will be presented. Recent advances in various piezoelectric microsensors will be presented through specific examples. This review will conclude with a critical assessment of the future trends and promise of this technology.

• Open/close Two-dimensional digital image correlation for in-plane displacement and strain measurement: a review

  Bing Pan et al 2009 Meas. Sci. Technol. 20 062001 Tag this article

  Article References Full text PDF (943 KB)

  As a practical and effective tool for quantitative in-plane deformation measurement of a planar object surface, two-dimensional digital image correlation (2D DIC) is now widely accepted and commonly used in the field of experimental mechanics. It directly provides full-field displacements to sub-pixel accuracy and full-field strains by comparing the digital images of a test object surface acquired before and after deformation. In this review, methodologies of the 2D DIC technique for displacement field measurement and strain field estimation are systematically reviewed and discussed. Detailed analyses of the measurement accuracy considering the influences of both experimental conditions and algorithm details are provided. Measures for achieving high accuracy deformation measurement using the 2D DIC technique are also recommended. Since microscale and nanoscale deformation measurement can easily be realized by combining the 2D DIC technique with high-spatial-resolution microscopes, the 2D DIC technique should find more applications in broad areas.