Self-calibration Technique Research Articles

Self-calibration of dual, closed surface microphone arrays

With the recent availability of very inexpensive, miniature digital MEMS microphones, the construction of large count microphone arrays is financially within the reach of the basic researcher. Using various mathematical techniques such as the Helmholtz-Kirchhoff integral and the equivalent source method (ESM), dual surface microphone arrays provide the ability to separate incident and scattered fields instantaneously in time. When these arrays form a closed surface, this separation is extremely accurate. However, one of the concerns with any microphone array is the calibration of the individual elements, especially near the resonance frequency of the diaphragm. In this paper, a self-calibration technique is proposed, based on ESM, that uses external loudspeakers in a simple laboratory facility not required to be anechoic. The approach is tested numerically on a dual surface, 256 element pair spherical microphone array, and uses an algorithm for the minimization of a cost function based on the extinction of the scattered field when the unknown individual calibration coefficients of the array elements are varied. Use of a Burton-Miller approach to model the ESM sources of the scattered field improves dramatically the accuracy at specific frequencies. The problematic interior Dirichlet eigenfrequencies are addressed. [Work supported by the Office of Naval Research.]

A Three-Stage Accelerometer Self-Calibration Technique for Space-Stable Inertial Navigation Systems.

As a specific force sensor, the tri-axis accelerometer is one of the core instruments in an inertial navigation system (INS). During navigation, its measurement error directly induces constant or alternating navigation errors of the same order of magnitude. Moreover, it also affects the estimation accuracy of gyro drift coefficients during the initial alignment and calibration, which will indirectly result in navigation errors accumulating over time. Calibration can effectively improve measurement accuracy of the accelerometer. Device-level calibration can identify all of the parameters in the error model, and the system-level calibration can accurately estimate part of these parameters. Combining the advantages of both the methods and making full use of the precise angulation of the space-stabilized platform, this paper proposes a three-stage accelerometer self-calibration technique that can be implemented directly in the space-stable INS. The device-level calibration is divided into two steps considering the large amount of parameters. The first step is coarse calibration, which identifies parameters except for the nonlinear terms, and the second step is fine calibration, which not only identifies the nonlinear parameters, but also improves the accuracy of the parameters identified in the first step. The follow-on system-level calibration is carried out on part of the parameters using specific force error and attitude error to further improve the calibration accuracy. Simulation result shows that by using the proposed three-stage calibration technique in the space-stable INS, the estimation accuracy of accelerometer error can reach order of magnitude. Experiment results show that after the three-stage calibration, the accuracy of latitude, longitude, and attitude angles has increased by over 45% and the accuracy of velocity has increased by over 22% during navigation.

Verifications of Scaling Relations Useful for the Intrinsic Alignment Self-calibration

The galaxy intrinsic alignment (IA) is a major challenge of weak lensing cosmology. To alleviate this problem, Zhang (2010, MNRAS, 406, L95) proposed a self-calibration method, independent of IA modeling. This proposal relies on several scaling relations between two-point clustering of IA and matter/galaxy fields, which were previously only tested with analytical IA models. In this paper, these relations are tested comprehensively with an $N$-body simulation of $3072^3$ simulation particles and boxsize 600 $h^{-1} \, \mathrm{Mpc}$. They are verified at the accuracy level of $\mathcal{O}(1)\%$ over angular scales and source redshifts of interest. We further confirm that these scaling relations are generic, insensitive to halo mass, weighting in defining halo ellipticities, photo-$z$ error, and misalignment between galaxy ellipticities and halo ellipticities. We also present and verify three new scaling relations on the B-mode IA. These results consolidate and complete the theory side of the proposed self-calibration technique.

A 1024-QAM Capable WLAN Receiver with -56.3dB Image Rejection Ratio Using Self-Calibration Technique

A 1024-QAM Capable WLAN Receiver with -56.3dB Image Rejection Ratio Using Self-Calibration Technique

Design and Implementation of Low Cost Digital Energy Meter for Smart Grid Applications

This paper presents a new design of a single-phase digital energy meter with self-calibration technique based on PIC16F84A microcontroller for monitoring the consumed energy of any load with high accuracy and stability. The design has the advantage of self-calibration and the meter can be fully managed from the PC. A graphical user interface (GUI) was designed to manage the functions of the proposed digital meter using the free application Visual Basic 6.0 (VB 6.0), Through PC standard serial port interfacing. The proposed digital meter can be used in the smart metering systems which are present in the first stage of the smart grid project. In addition, the cost of the proposed digital energy meter is about 20 $, which is lower as compared to the traditional electromechanical meters.

Iterative approach for 3D reconstruction of the femur from un-calibrated 2D radiographic images

Three-dimensional reconstruction of the femur is important for surgical planning in patients with cerebral palsy. This study aimed to reconstruct the three-dimensional femur shape from un-calibrated bi-planar radiographic images using self-calibration to allow for low-dose preoperative planning. The existing self-calibration techniques require anatomical landmarks that are clearly visible on bi-planar images, which are not available on the femur. In our newly developed method, the self-calibration is performed so that the contour of the statistical shape matches the image contour while the statistical shape is concomitantly optimized. The proposed approach uses conventional radiograph systems and can be easily incorporated into existing clinical protocols, as compared to other reconstruction methods.

Self-calibration technique for on-machine spindle-mounted vision systems

On-machine measuring (OMM) systems are being more and more applied in machine tools in order to measure workpieces on the machine itself. Many of these systems are directly mounted in the machine spindle, so the measuring uncertainty is affected by clamping positioning and orientation variations, especially when integrating optical systems based on machine vision. This paper presents a self-calibration technique for vision systems by using redundant information of on machine measurements, avoiding extra mechanical anchoring or calibration means. It has been applied to a vision system with the angular placement uncertainty of a tool holder coupling being the main uncertainty contributor. A milling machine pilot case has been selected for demonstration, showing an effective self-calibration capability both in laboratory and industrial conditions.

A low power and small area digital self-calibration technique for pipeline ADC

A digital self-calibration implementation with discontinuity-error and gain-error corrections for a pipeline analog-to-digital converter (ADC) is presented. In the proposed calibration method, the error owing to each reference unit capacitor of the multiplying D/A converter is measured separately using a calibration capacitor and an enhanced resolution back-end pipeline ADC acting as an error quantizer. The offset and finite open loop DC-gain of the operational amplifier and capacitor mismatches, the reference voltage mismatch can all be calibrated. The calibration can be achieved by that only used addition and subtraction. Hence, it needs low power and area consuming. A prototype ADC with the proposed calibration was fabricated on a 0.5μm double-poly triple-metal CMOS process. The power consumption and area of the calibration circuit are only 10.1mW and 1.05mm2, respectively. At a sampling rate of 30MS/s, the calibration improves the DNL and INL from 2.59 LSB and 14.98 LSB to 0.72 LSB and 1.82 LSB, respectively. For a 1.25MHz sinusoidal signal, the calibration improves the signal-to-noise-distortion ratio and spurious-free dynamic range from 43.1dB and 52.1dB to 75.51dB and 83.61dB, respectively. The 12.25 effective number of bits at 30MS/s ADC consumes a total power of 136mW.

High-precision lateral distortion measurement and correction in coherence scanning interferometry using an arbitrary surface.

Lateral optical distortion is present in most optical imaging systems. In coherence scanning interferometry, distortion may cause field-dependent systematic errors in the measurement of surface topography. These errors become critical when high-precision surfaces, e.g. precision optics, are measured. Current calibration and correction methods for distortion require some form of calibration artefact that has a smooth local surface and a grid of high-precision manufactured features. Moreover, to ensure high accuracy and precision of the absolute and relative locations of the features of these artefacts, requires their positions to be determined using a traceable measuring instrument, e.g. a metrological atomic force microscope. Thus, the manufacturing and calibration processes for calibration artefacts are often expensive and complex. In this paper, we demonstrate for the first time the calibration and correction of optical distortion in a coherence scanning interferometer system by using an arbitrary surface that contains some deviations from flat and has some features (possibly just contamination), such that feature detection is possible. By using image processing and a self-calibration technique, a precision of a few nanometres is achieved for the distortion correction. An inexpensive metal surface, e.g. the surface of a coin, or a scratched and defected mirror, which can be easily found in a laboratory or workshop, may be used. The cost of the distortion correction with nanometre level precision is reduced to almost zero if the absolute scale is not required. Although an absolute scale is still needed to make the calibration traceable, the problem of obtaining the traceability is simplified as only a traceable measure of the distance between two arbitrary points is needed. Thus, the total cost of transferring the traceability may also be reduced significantly using the proposed method.

Design and Self-Calibration Techniques for Inductor-Less Millimeter-Wave Frequency Dividers

This paper presents several design techniques to widen the operating frequency range and increase the locking range of dynamic current-mode latch-based inductor-less millimeter-wave frequency dividers. A self-calibration technique is introduced to guarantee frequency locking over a wide frequency range with low-input amplitude and over process, voltage, and temperature variations, thereby optimizing power consumption and ensuring robustness. Three divide-by-four prototypes incorporating the aforementioned techniques are designed to cover a frequency range exceeding 16–67 GHz. Fabricated in a 65-nm CMOS technology, the prototypes achieve min-average-max increases of 10%–47.5%–121.4% in fractional bandwidth over the state of the art. The first and third prototypes consume 3.7/6.2 mA (min/max) from a 1-V supply and achieve a figure of merit of 4.1/7.15 GHz/mW (min/max), while the second prototype consumes 3.9/6.7 mA (min/max) from a 1.1-V supply and achieves a figure of merit of 3/6.98 GHz/mW (min/max). The prototypes occupy the active areas of $11 \times 42/11 \times 53~\mu \text{m}^{2}$ (min/max). Finally, with the self-calibration scheme, the dividers operate with input power less than −10 dBm, supply voltage variation of ±100 mV.

High-fidelity VLA imaging of the radio structure of 3C 273

3C273, the nearest bright quasar, comprises a strong nuclear core and a bright, one-sided jet extending ~ 23 arcseconds to the SW. The source has been the subject of imaging campaigns in all wavebands. Extensive observations of this source have been made with the Very Large Array and other telescopes as part of a campaign to understand the jet emission mechanisms. Partial results from the VLA radio campaign have been published, but to date, the complete set of VLA imaging results has not been made available. We have utilized the VLA to determine the radio structure of 3C273 in Stokes I, Q, and U, over the widest possible frequency and resolution range. The VLA observed the source in all four of its configurations, and with all eight of its frequency bands, spanning 73.8 MHz to 43 GHz. The data were taken in a pseudo-spectral line mode to minimize the VLA's correlator errors, and were fully calibrated with subsequent self-calibration techniques to maximise image fidelity. Images in Stokes parameters I, Q, and U, spanning a resolution range from 6 arcseconds to 88 milliarcseconds are presented. Spectral index images, showing the evolution of the jet component are shown. Polarimetry demonstrates the direction of the magnetic fields responsible for the emission, and rotation measure maps show the RM to be very small with no discernible trend along or across the jet. This paper presents a small subset of these images to demonstrate the major characteristics of the source emission. A library of all ~500 images has been made available for open, free access by interested parties.

A high linearity current-controlled CMOS relaxation oscillator with frequency self-calibration technique

A complementary metal oxide semiconductor relaxation oscillator adopting a new frequency self-calibration technique (FSCT) to improve the linearity is proposed in this paper. The FSCT can detect the peak voltage of the timing capacitor when start-up and change the reference voltage adaptively. Then, the non-linearity of the oscillator caused by the delay of the control circuit and the offset voltage of the comparator can be reduced obviously. The proposed relaxation oscillator with typical frequency of 5 MHz is implemented in 0.5 μm Silicon-On-Insulator Bipolar-CMOS-DMOS process. Measured results show that <0.79% non-linearity in the current---frequency transfer function from 0.1 to 10 MHz without trimming.

Calibration method for articulated industrial robots

Robot calibration is technique used to increase system positioning accuracy. In our research, we have reviewed self-calibration techniques of articulated industrial robots and proposed an original method to reduce production and maintenance down times. The proposed technique is using an inertial measurement unit (IMU) to measure robot poses, plus ultrasonic triangulation sensors to increase processing speed and reduce computational power. Thanks to all of that, robot is more responsive, i.e. we have an improved speed, reliability and accuracy in determining the orientation of the manipulators. The advantages of this method in comprising with the vision based calibration, is that it does not need the complex steps, such as camera calibration, image capture, memory and corner detection. This makes the robot calibration procedure more autonomous in a dynamic manufacturing environment. The proposed technique was applied at Six Degrees of Freedom (6-DOF) robot and compared to existing calibration methods.

A Calibration Technique for Bang-Bang ADPLLs Using Jitter Distribution Monitoring

This brief presents a built-in self-calibration (BISC) technique for minimization of the total jitter in bang-bang all-digital phase-locked loops (ADPLLs). It is based on the addition of a monitoring phase-frequency detector (PFD) with tunable delay cells for the reference clock and the divider clock and a counter for this PFD output signal. This allows for on-chip binary comparison of the jitter distribution widths at the ADPLL PFD input, when ADPLL filter parameters are altered. Since only a relative comparison is performed, no accurate delay calibration is required. The statistical properties of this comparison of two random distributions are analyzed theoretically, and guidelines for circuit dimensioning are derived. The proposed method is used for BISC by adaption of the ADPLL filter coefficients. This allows for jitter minimization under process, voltage and temperature variations as well as gain and period jitter of the digitally controlled oscillator. The proposed calibration technique is verified by system simulations and measurements of a silicon prototype implementation in 28-nm CMOS technology.

INVESTIGATION OF PHOTOTRIANGULATION ACCURACY WITH USING OF VARIOUS TECHNIQUES LABORATORY AND FIELD CALIBRATION

Abstract. Nowadays, aerial survey technology using aerial systems based on unmanned aerial vehicles (UAVs) becomes more popular. UAVs physically can not carry professional aerocameras. Consumer digital cameras are used instead. Such cameras usually have rolling, lamellar or global shutter. Quite often manufacturers and users of such aerial systems do not use camera calibration. In this case self-calibration techniques are used. However such approach is not confirmed by extensive theoretical and practical research. In this paper we compare results of phototriangulation based on laboratory, test-field or self-calibration. For investigations we use Zaoksky test area as an experimental field provided dense network of target and natural control points. Racurs PHOTOMOD and Agisoft PhotoScan software were used in evaluation. The results of investigations, conclusions and practical recommendations are presented in this article.

A flexible technique based on fundamental matrix for camera self-calibration with variable intrinsic parameters from two views

We propose a new self-calibration technique for cameras with varying intrinsic parameters that can be computed using only information contained in the images themselves. The method does not need any a priori knowledge on the orientations of the camera and is based on the use of a 3D scene containing an unknown isosceles right triangle. The importance of our approach resides at minimizing constraints on the self-calibration system and the use of only two images to estimate these parameters. This method is based on the formulation of a nonlinear cost function from the relationship between two matches which are the projection of two points representing vertices of an isosceles right triangle, and the relationship between the images of the absolute conic. The resolution of this function enables us to estimate the cameras intrinsic parameters. The algorithm is implemented and validated on several sets of synthetic and real image data.

A low jitter supply regulated charge pump PLL with self-calibration**Project supported by the National Key Basic Research and Development Program of China (No. 2015CB352100).

This paper describes a ring oscillator based low jitter charge pump PLL with supply regulation and digital calibration. In order to combat power supply noise, a low drop output voltage regulator is implemented. The VCO gain is tunable by using the 4 bit control self-calibration technique. So that the optimal VCO gain is automatically selected and the process/temperature variation is compensated. Fabricated in the 0.13 μm CMOS process, the PLL achieves a frequency range of 100–400 MHz and occupies a 190 × 200 μm2 area. The measured RMS jitter is 5.36 ps at a 400 MHz operating frequency.

A Self-Calibration Technique for On-Chip Precise Clock Generator

This brief presents a self-calibration technique for on-chip precise clock generator used in the field of power electronics. In this technique, the operating frequency of the power grid is employed as the frequency reference to eliminate the frequency variation of the clock generator introduced by the fabrication process. To demonstrate the effectiveness of this technique, an on-chip relaxation oscillator has been designed, analyzed and verified with a 0.5- $\boldsymbol{\mu}\mbox{m}$ standard CMOS technology. Measurement results show the oscillator with self-calibration operates at a frequency of about 103.7 kHz and draws 90 $\boldsymbol{\mu}\mbox{A}$ current from a 5-V supply. 2.83% $(\mathbf{3}\boldsymbol{\sigma})$ frequency variation is achieved, which is more than 3× lower than the one without self-calibration.

TERRESTRIAL LASER SCANNERS SELF-CALIBRATION STUDY: DATUM CONSTRAINTS ANALYSES FOR NETWORK CONFIGURATIONS

Abstract. Similar to other electronic instruments, terrestrial laser scanner (TLS) can also inherent with various systematic errors coming from different sources. Self-calibration technique is a method available to investigate these errors for TLS which were adopted from photogrammetry technique. According to the photogrammetry principle, the selection of datum constraints can cause different types of parameter correlations. However, the network configuration applied by TLS and photogrammetry calibrations are quite different, thus, this study has investigated the significant of photogrammetry datum constraints principle in TLS self-calibration. To ensure that the assessment is thorough, the datum constraints analyses were carried out using three variant network configurations: 1) minimum number of scan stations; 2) minimum number of surfaces for targets distribution; and 3) minimum number of point targets. Based on graphical and statistical, the analyses of datum constraints selection indicated that the parameter correlations obtained are significantly similar. In addition, the analysis has demonstrated that network configuration is a very crucial factor to reduce the correlation between the calculated parameters.

Passive Non-Destructive Assay based on gamma-ray spectrometry to verify UO2 samples in the form of powder and pellet

Passive Non-Destructive Assay (PNDA) gamma-spectroscopic method is employed for nuclear material verification. The investigated materials are natural (NU) and low enriched uranium (LEU) in the form of uranium dioxide (UO2) pellets and powder, respectively. A high-resolution gamma-ray spectrometer based on HPGe detector and associated electronics is used for the measurement. The spectrometer efficiency was measured experimentally using the intrinsic self-calibration method taking into account the necessary correction factors.Sample isotopic fractions were obtained using two methods; that based on the measurement of the count rate of 185.7keV gamma line of 235U and 1001keV gamma line of 234mPa (238U) employing the intrinsic self-calibration technique to calculate the activity ratio of 235U/238U. The other method is based on uranium activity ratio measurements without efficiency corrections by choosing two gamma-rays close enough in energy, one related to 235U (84.2keV gamma line of 231Th) and the other to 238U (63.3keV gamma line of 234Th).Samples were characterized by calculating uranium isotopic mass, uranium isotopic activity ratio, total uranium content and enrichment. Special attention was given at calculating absolute error of the measured quantities, as well as the statistical behavior of the measured data in terms of the well known statistical quantities. The experimental results showed good agreement with calculated data.