In the last 30 days

• Open/close A single-board NMR spectrometer based on a software defined radio architecture

  Weinan Tang and Weimin Wang 2011 Meas. Sci. Technol. 22 015902 Tag this article

  Article References Full text PDF (1.37 MB)

  A single-board software defined radio (SDR) spectrometer for nuclear magnetic resonance (NMR) is presented. The SDR-based architecture, realized by combining a single field programmable gate array (FPGA) and a digital signal processor (DSP) with peripheral radio frequency (RF) front-end circuits, makes the spectrometer compact and reconfigurable. The DSP, working as a pulse programmer, communicates with a personal computer via a USB interface and controls the FPGA through a parallel port. The FPGA accomplishes digital processing tasks such as a numerically controlled oscillator (NCO), digital down converter (DDC) and gradient waveform generator. The NCO, with agile control of phase, frequency and amplitude, is part of a direct digital synthesizer that is used to generate an RF pulse. The DDC performs quadrature demodulation, multistage low-pass filtering and gain adjustment to produce a bandpass signal (receiver bandwidth from 3.9 kHz to 10 MHz). The gradient waveform generator is capable of outputting shaped gradient pulse waveforms and supports eddy-current compensation. The spectrometer directly acquires an NMR signal up to 30 MHz in the case of baseband sampling and is suitable for low-field (<0.7 T) application. Due to the featured SDR architecture, this prototype has flexible add-on ability and is expected to be suitable for portable NMR systems.

• Open/close Needle-type environmental microsensors: design, construction and uses of microelectrodes and multi-analyte MEMS sensor arrays

  Woo Hyoung Lee et al 2011 Meas. Sci. Technol. 22 042001 Tag this article

  Article References Full text PDF (3.31 MB)

  The development of environmental microsensor techniques is a revolutionary advance in the measurement of both absolute levels and changes in chemical species in the field of environmental engineered and natural systems. The tiny tip (5–15 µm diameter) of microsensors makes them very attractive experimental tools for direct measurements of the chemical species of interest inside biological samples (e.g., biofilm, flocs). Microelectrodes fabricated from pulled micropipettes (e.g., dissolved oxygen, oxidation–reduction potential, ion-selective microelectrode) have contributed to greater understanding of biological mechanisms for decades using microscopic monitoring, and currently microelectromechanical system (MEMS) microfabrication technologies are being successfully applied to fabricate multi-analyte sensor systems for in situ monitoring. This review focuses on needle-type environmental microsensor technology, including microelectrodes and multi-analyte MEMS sensor arrays. Design, construction and applications to biofilm research of these sensors are described. Practical methods for biofilm microprofile measurements are presented and several in situ applications for a biofilm study are highlighted. Ultimately, the developed needle-type microsensors combined with molecular biotechnology (such as microscopic observation with fluorescent probes) show the tremendous promise of micro-environmental sensor technology.

• 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 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 Measurements and analysis of surface damage on oil-impregnated insulation paper caused by partial discharge

  Jiaming Yan et al 2011 Meas. Sci. Technol. 22 055703 Tag this article

  Article References Full text PDF (2.30 MB)

  Surface topography, surface roughness, and surface conductivity of oil-impregnated insulation paper were studied during the damage process caused by partial discharge within the cavity of the paper. Products generated on the surface during this process were studied, as well. According to phase-resolved partial discharge patterns, the damage process can be divided into five stages. At each of the stages, surface conditions of insulation were analyzed by optical microscopy, scanning electron microscopy, atomic force microscopy and high-resistance meter. 'Ablating', 'peeling', 'cracking in silk', 'pitting' and 'electrical treeing' appear on insulation surfaces one after another during the five stages of the damage process, along with sequential generation of droplets and crystalline solids. Surface roughness initially decreases, then increases. Finally, surface conductivity exhibits a general increasing trend, before it eventually stabilizes. However, its growth rate varies in different stages of damage.

• 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 Single-stage vibratory gyroscope control methods for direct angle measurements

  Chien-Yu Chi and Tsung-Lin Chen 2011 Meas. Sci. Technol. 22 055201 Tag this article

  Article References Full text PDF (1.14 MB)

  This paper presents a control algorithm that can compensate for imperfect dynamics of vibrating gyroscopes. The compensated gyroscope dynamics can directly measure the rotation angle without integrating the angular rate. The direct angle measurement approach is promising because it is exempt from the error accumulation problem. However, using control methods to compensate for imperfect dynamics for the direct angle measurement is very challenging work, and very few control algorithms were reported to achieve that. Different from existing approaches, the proposed method has the following advantages: it requires the measurements of either the proof mass velocity or position, it does not require a calibration phase prior to normal use, and it compensates different types of imperfection even when the proof mass of a gyroscope is unknown. In a demonstration case, imperfections cause system parameters 20% deviated from their designated values; the measured signals are the proof mass velocities and contaminated by zero-mean white noise with a noise level of 0.1% full scale output (FSO); the angular rate to be measured is 200sin (2π × 10 t) deg s ⁻¹. The proposed algorithm can compensate for those imperfections and achieve an angle measurement accuracy of 0.23°.

• Open/close A new multi-position calibration method for MEMS inertial navigation systems

  Z F Syed et al 2007 Meas. Sci. Technol. 18 1897 Tag this article

  Article References Full text PDF (510 KB)

  The Global Positioning System (GPS) is a worldwide navigation system that requires a clear line of sight to the orbiting satellites. For land vehicle navigation, a clear line of sight cannot be maintained all the time as the vehicle can travel through tunnels, under bridges, forest canopies or within urban canyons. In such situations, the augmentation of GPS with other systems is necessary for continuous navigation. Inertial sensors can determine the motion of a body with respect to an inertial frame of reference. Traditionally, inertial systems are bulky, expensive and controlled by government regulations. Micro-electro mechanical systems (MEMS) inertial sensors are compact, small, inexpensive and most importantly, not controlled by governmental agencies due to their large error characteristics. Consequently, these sensors are the perfect candidate for integrated civilian navigation applications with GPS. However, these sensors need to be calibrated to remove the major part of the deterministic sensor errors before they can be used to accurately and reliably bridge GPS signal gaps. A new multi-position calibration method was designed for MEMS of high to medium quality. The method does not require special aligned mounting and has been adapted to compensate for the primary sensor errors, including the important scale factor and non-orthogonality errors of the gyroscopes. A turntable was used to provide a strong rotation rate signal as reference for the estimation of these errors. Two different quality MEMS IMUs were tested in the study. The calibration results were first compared directly to those from traditional calibration methods, e.g. six-position and rate test. Then the calibrated parameters were applied in three datasets of GPS/INS field tests to evaluate their accuracy indirectly by comparing the position drifts during short-term GPS signal outages.

• Open/close Methods for in-field user calibration of an inertial measurement unit without external equipment

  W T Fong et al 2008 Meas. Sci. Technol. 19 085202 Tag this article

  Article References Full text PDF (330 KB)

  This paper presents methods to calibrate and compensate for non-zero biases, non-unit scale factors, axis misalignments and cross-axis sensitivities of both the tri-axial accelerometer and gyroscopic setups in a micro-electro-mechanical systems (MEMS) based inertial measurement unit (IMU). These methods depend on the Earth's gravity as a stable physical calibration standard. Specifically, the calibration of gyroscopes is significantly improved by comparing the outputs of the accelerometer and the IMU orientation integration algorithm, after arbitrary motions. The derived property and proposed cost function allow the gyroscopes to be calibrated without external equipment, such as a turntable, or requiring precise maneuvers. Both factors allow the IMU to be easily calibrated by the user in the field so that it can function as an accurate orientation sensor. A custom-made prototype IMU is used to demonstrate the effectiveness of the proposed methods, with data that are carefully obtained using prescribed motions, as well as those less rigorously collected from the IMU when it is mounted on the head of a user or held in hands with brief random movements. With calibration, the observed average static angular error is less than a quarter of a degree and the dynamic angular error is reduced by a factor of 2 to 5.

• 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.