Capacitive Displacement Sensor Research Articles

Measurement of Thickness of High-Resistivity Substrate by Photoconduction Enhanced Capacitance Displacement Sensor

Capacitive displacement sensors provide non-contact, extreme resolution, and absolute accuracy thickness measurements. However, if the resistivity of a target substrate is within 105-107 ohm-cm, an uncertainty will appear in the thickness measurement. The common solution is to adjust the resistivity to be outside the range that causes the measurement uncertainty by implanting dopants and followed by an activation anneal, but this will unavoidably lead to changes in the material properties and morphology. Here, we exploit the photoconductive effect to generate sufficient high amount of electron-hole pairs, thereby temporarily decreasing the resistivity and thus enabling the capacitive displacement sensor to accurately measure the thickness at nanoscale resolution. After the measurement is complete, the resistivity of the substrate will return to its original status. The photoconductive effect can be simply induced via laser irradiation at the sensing point, which narrows or eliminates the gap in the measurement range of capacitive sensors to include high-resistivity substrate.

LDI 노광기용 초정밀 스테이지의 진동 저감 기구에 관한 연구

Recently, Laser Direct Imaging (LDI) has been used to replace lithography in Flexible Printed Circuit Board (FPCB) manufacturing. However, repeated motion of a linear motor caused residual vibration in the granite on which the workpiece was placed when the motor either accelerated or decelerated. Because the residual vibration made positioning less accurate, there were more defective products and worse productivity. This paper proposes a way to reduce vibration in the granite during the precision stage. First, the frequency domain of the vibrations of a pneumatic vibration isolator is identified. Second, we present the design of the mechanism using a voice coil actuator and a capacitive displacement sensor. Third, we apply a feedback control algorithm based on PID to cancel displacement. Consequently, we are able to propose an optimal way to reduce vibration for the laser direct imaging equipment. The amount of vibration reduction is evaluated in terms of amplitude and settling time.

A novel multi-probe method for separating spindle radial error from artifact roundness error

Conventional three-probe method of artifact roundness and spindle error measurements is subjected to the trouble of harmonic suppression, which is also mathematically complicated due to complex transformation processing. A novel three-probe method by solving system of multivariable equation (SSME) method is presented in this paper. The presented method simplifies the mathematical processing and has good robustness to the measurement angles which are difficult for conventional three-probe method. This paper gives mathematical models, detailed theoretical derivations, and numerical simulations. Selection criteria of the optimal measurement angle combinations can be determined in accordance with rank and condition number of the coefficient matrix. Then, to validate the feasibility and repeatability of the proposed method, experimental measurements are performed on a vertical machine tool spindle by using nanometer-resolution capacitive displacement sensors, high-precision indexing table, and professional data acquisition system. Artifact roundness error and spindle radial error are tested to validate separation accuracy by specialized instruments. The comparisons demonstrate that the proposed method has good feasibility and repeatability (the maximum deviations of spindle error and roundness error are 9.62 and 3.86%). SSME method, due to its simplicity in computation and the uniqueness of the solution provided, is more suitable to separate spindle radial error from the artifact roundness error.

Measurement of Thickness of High-Resistivity Substrate By Photoconduction Enhanced Capacitance Displacement Sensor

Capacitive displacement sensors can offer non-contact, extreme resolution, and absolute accuracy thickness measurements. However, for general capacitive displacenent sensors, if the resistivity of a target substrate is within 105-107 ohm-cm, a measurement uncertainty will occur in the thickness measurement. The measnurement uncentration may be several microon meters. The common solution is to adjust the resistivity to be outside the range that causes the measurement uncertainty by implanting dopants and followed by an activation anneal, but this will unavoidably lead to changes in the material properties and morphology. Here, we exploit the photoconductive effect to generate sufficient high amount of electron-hole pairs, thereby temporarily decreasing the resistivity and thus enabling the capacitive displacement sensor to accurately measure the thickness at nanoscale resolution. After the measurement is complete, the resistivity of the substrate will return to its original status. The photoconductive effect can be simply induced via laser irradiation at the sensing point, which narrows or eliminates the gap in the measurement range of capacitive sensors to include high-resistivity substrates.

Physical modelling of freezing and thawing of unsaturated soils

Increasing interest in the development of thermo-hydro-mechanical numerical models has heightened the need for results from fully instrumented physical models that present the evolution of the soil properties during freezing and thawing. This paper presents a set of results from a physical model of freezing/thawing cycles of unsaturated soils to improve the state of the art regarding moisture transport in soils. The physical model that was developed used a set of measuring devices, which included a gamma-ray densitometer, temperature transducers, tensiometers, capacitive moisture transducers and displacement sensors. These sensors allow measurement of the evolution of ice content, unfrozen water content, temperature, pore water pressure and dry density. Fine sand and silt in initially unsaturated states were used in the study. These soils were successively submitted to capillary rise and two cycles of freezing and thawing.

Communication—Eliminating Thickness Measurement Uncertainty of Capacitive Displacement Sensor in High Resistivity Substrate by Photoconduction

Capacitive displacement sensors provide non-contact and absolute accuracy thickness measurements. However, if the resistivity of a target substrate is within 105–107 Ω-cm, a measurement uncertainty will occur. Incorporating dopants in the substrate can adjust the resistivity to be outside the range that causes the measurement uncertainty, but also permanently changes the electronic properties. Here, we exploit the photoconductive effect to generate an adequate amount of electron-hole pairs, thereby temporarily decreasing the resistivity and thus enabling the capacitive displacement sensor to accurately measure the thickness at nanoscale resolution. After the measurement is completed, the resistivity of the substrate will return to its original value.

A new method for measuring the rotational accuracy of rolling element bearings

The rotational accuracy of a machine tool spindle has critical influence upon the geometric shape and surface roughness of finished workpiece. The rotational performance of the rolling element bearings is a main factor which affects the spindle accuracy, especially in the ultra-precision machining. In this paper, a new method is developed to measure the rotational accuracy of rolling element bearings of machine tool spindles. Variable and measurable axial preload is applied to seat the rolling elements in the bearing races, which is used to simulate the operating conditions. A high-precision (radial error is less than 300 nm) and high-stiffness (radial stiffness is 600 N/μm) hydrostatic reference spindle is adopted to rotate the inner race of the test bearing. To prevent the outer race from rotating, a 2-degrees of freedom flexure hinge mechanism (2-DOF FHM) is designed. Correction factors by using stiffness analysis are adopted to eliminate the influences of 2-DOF FHM in the radial direction. Two capacitive displacement sensors with nano-resolution (the highest resolution is 9 nm) are used to measure the radial error motion of the rolling element bearing, without separating the profile error as the traditional rotational accuracy metrology of the spindle. Finally, experimental measurements are performed at different spindle speeds (100-4000 rpm) and axial preloads (75-780 N). Synchronous and asynchronous error motion values are evaluated to demonstrate the feasibility and repeatability of the developed method and instrument.

A MoS2-Based Capacitive Displacement Sensor for DNA Sequencing

We propose an aqueous functionalized molybdenum disulfide nanoribbon suspended over a solid electrode as a capacitive displacement sensor aimed at determining the DNA sequence. The detectable sequencing events arise from the combination of Watson-Crick base-pairing, one of nature's most basic lock-and-key binding mechanisms, with the ability of appropriately sized atomically thin membranes to flex substantially in response to subnanonewton forces. We employ carefully designed numerical simulations and theoretical estimates to demonstrate excellent (79% to 86%) raw target detection accuracy at ∼70 million bases per second and electrical measurability of the detected events. In addition, we demonstrate reliable detection of repeated DNA motifs. Finally, we argue that the use of a nanoscale opening (nanopore) is not requisite for the operation of the proposed sensor and present a simplified sensor geometry without the nanopore as part of the sensing element. Our results, therefore, potentially suggest a realistic, inherently base-specific, high-throughput electronic DNA sequencing device as a cost-effective de novo alternative to the existing methods.

Lagrange multiplier‐based error compensation of heterodyne interferometer

The heterodyne laser interferometer is an ultra-precise measurement apparatus. However, its susceptibility to environmental error is an obstacle to improve its nanometre-scale measurement accuracy. To minimise the environmental error factor, a compensation algorithm using a Lagrange multiplier method is proposed. The improved accuracy of the proposed method was verified by means of experiments using nanometre-scale measurements of a capacitive displacement sensor.

A Novel Quadrature Signal Estimation Method for a Planar Capacitive Incremental Displacement Sensor

Abstract This paper presents a novel phase-shift arctangent (PSA) interpolation method to improve the measurement accuracy of a planar capacitive incremental displacement sensor. Signals of planar capacitive micro-sensors acquire waveform errors, including sensitivity differences and phase-shift errors, because of static errors and dynamic disturbances. In the proposed PSA scheme, such errors are removed completely by loading a particular arctangent function. Moreover, measuring efficiency of the proposed planar capacitive sensors is improved by combining coarse measurement and fine estimation. Experiments show unanimous results to model-based fitting. When electrode length is four times the gap distance, applying the PSA interpolation method decreases waveform errors from more than 4 % to 1.72 %.

A New Capacitive Displacement Sensor With Nanometer Accuracy and Long Range

A highly stable motion with orthogonally alternating electric field is established to build the relationship between spatial displacement and time standards. Displacement is measured by counting the time pulses that serve as measurement standards. Thus, a displacement method is called time grating. An orthogonally alternating electric field is generated using two rows of differential capacitive sensing electrodes excited by four sinusoidal voltages. Sine-shaped grating planes rather than hyperfine grating lines are used to pick up the displacement signals. Electrode lead wires are designed below the middle of the electrodes and fabricated using multilayer thin-film technology to suppress the cross-sensitivity effect. A time-grating sensor has been fabricated to evaluate the proposed method. The range of measurement is 200 mm, the width of the electrode is 0.2 mm, the interval between two adjacent electrodes is 20 $\mu \text{m}$ , and the gap for capacitive sensing is 0.3 mm. Experimental results indicate that the measurement accuracy reaches ±200 nm with 1-nm resolution. Nanometer accuracy and resolution are achieved using sensing units with sub-millimeter periods. So, the cost for manufacturing the time-grating sensor can be decreased effectively in comparison to traditional nanometrology displacement sensors, and it may be a suitable low-cost alternative to long-range nanometrology.

A comprehensive experimental setup for identification of friction model parameters

Parameter identification for advanced friction models is the most demanding task and involves a wide range of experimental dynamic analysis. The identification results directly affect the quality of the friction model and significantly depend on the setup. While many setups have been proposed to investigate the various characteristics of friction, rather less attention has been paid to designing one that is practical for parameter identification dedicated to certain common models. An experimental setup featuring simplicity, flexibility and good versatility is proposed here. The setup consists of a mass block connected to a motor-powered ball screw mechanism. Such a block slides on a metal base and the friction at the contact junction is varied accordingly. The materials and lubricants in the contact surface can be easily altered if needed. A capacitance displacement sensor is designed and installed at where the precise presliding profiles can be captured. The experimental setup, the calibration procedure for the displacement sensor and the experimental results are presented. It is shown that the experimental data produced by our setup leads to the success in parameter identification procedures of the selected friction models. Some limitations of the friction models, from the perspective of parameter identification, are discussed.

A MEMS XY-stage integrating compliant mechanism for nanopositioning at sub-nanometer resolution

This paper reports a microelectromechanical systems (MEMS) based XY-stage integrating compliant motion amplification mechanism for nanopositioning at sub nanometer resolution. The MEMS stage is driven by bidirectional Z-beam electrothermal actuators that generate large output forces to actuate the motion amplification mechanism. The motion amplification mechanisms are used in their inverse (motion reduction) mode to convert micrometer input displacements (from the Z-beam actuators) into nanometer output displacements at a constant motion reduction ratio with good linearity. This unique design significantly enhances the positioning resolution of the XY-stage. An analytical model is developed to predict output displacements of the XY-stage as a function of the input voltages applied to the Z-beam actuators, and the predicted results agree with the experimental results. Capacitive displacement sensors are arranged along both X- and Y-axes for measuring the input displacements of the amplification mechanisms, enabling closed-loop nanopositioning control of the XY-stage. The device calibration results show that, within an actuation voltage of ±15 V, the MEMS stage offers a motion range close to ±1 μm and a displacement resolution better than 0.3 nm −1.

АНАЛОГОВИЙ ІНТЕРФЕЙС ДЛЯ ЄМНОСТІ ДАТЧИКА ПЕРЕМІЩЕНЬ З ВІДКРИТИМ ПОЛЕМ

An analytical review of existing methods for measuring small capacitances is performed. Analogue interface for remote measurements of initial parameters capacitance displacement sensors with an open field with improved metrological characteristics is designed.

A novel instrument for generating angular increments of 1 nanoradian.

Accurate generation of small angles is of vital importance for calibrating angle-based metrology instruments used in a broad spectrum of industries including mechatronics, nano-positioning, and optic fabrication. We present a novel, piezo-driven, flexure device capable of reliably generating micro- and nanoradian angles. Unlike many such instruments, Diamond Light Source's nano-angle generator (Diamond-NANGO) does not rely on two separate actuators or rotation stages to provide coarse and fine motion. Instead, a single Physik Instrumente NEXLINE "PiezoWalk" actuator provides millimetres of travel with nanometre resolution. A cartwheel flexure efficiently converts displacement from the linear actuator into rotary motion with minimal parasitic errors. Rotation of the flexure is directly measured via a Magnescale "Laserscale" angle encoder. Closed-loop operation of the PiezoWalk actuator, using high-speed feedback from the angle encoder, ensures that the Diamond-NANGO's output drifts by only ∼0.3 nrad rms over ∼30 min. We show that the Diamond-NANGO can reliably move with unprecedented 1 nrad (∼57 ndeg) angular increments over a range of >7000 μrad. An autocollimator, interferometer, and capacitive displacement sensor are used to independently confirm the Diamond-NANGO's performance by simultaneously measuring the rotation of a reflective cube.

Miniature proportional control valve with top-mounted piezo bimorph actuator with millisecond response time

In this paper we demonstrate the realization of a micro control valve with a top-mounted piezoelectric bimorph actuator, to obtain a high-bandwidth proportional control valve for gases in the range of several grams per hour. Dynamic fluidic and mechanical characterization shows that the valve is suitable for high-speed flow control with response times on the order of milliseconds. The microvalve contains an integrated capacitive displacement sensor for position-based control, which can be used to improve the control precision. The microvalve is realized in a straight-forward fabrication process based on a single SOI wafer. A high level of integration of the piezo actuator is achieved using a flexible silicone rubber support between the bimorph and the silicon. This leads to a small volume, high speed device.

Novel capacitive displacement sensor based on interlocking stator electrodes with sequential commutating excitation

A novel capacitive displacement sensor is proposed. The stator consists of a pair of interlocking comb-type electrodes, driven by two consistent high frequency voltage sources with opposite phase. The mover consists of double sensing channels with electrical orthogonal relationship. Through capacitive coupling, a relative displacement between the mover and the stator is converted to quasi sine/cosine signals, featured with direction identification and instantaneous displacement interpolation. Theoretical analysis indicates that the physical resolution of the studied sensor is the same as the electrode unit's width. And also, the interchannel's amplitude ratio and phase difference keep stable in a wide range of air gap size. Hence the performance of displacement detection can be enhanced by amplitude normalization and interpolation. Using a Printed Circuit Board (PCB) fabricated prototype, the proposed scheme was experimentally tested. Typical coupling statuses were captured. Main sensing characteristics and performance were investigated, such as the responding of air gap variation, the displacement sensitivity, and the measurement uncertainty.

Performance and characterization of a MEMS-based device for alignment and manipulation of x-ray nanofocusing optics

X-ray microscopy is a powerful, non-invasive tool used for nanometer-scale resolution imaging, and it is widely applied in various areas of science and technology. To push the spatial resolution of x-ray microscopy studies in the hard x-ray regime below 10 nm, Multilayer Laue Lenses (MLL) can be used as nanofocusing elements. To ensure distortion-free x-ray imaging, high-stability microscopy systems are required. MEMS-based manipulators are a promising route to achieve high stability when used for alignment and manipulation of nanofocusing optics. In this work, we present a tip-tilt MEMS-based device suitable for MLL alignment. We fully characterize the device and demonstrate better-than 10 millidegree angular positioning resolution when utilizing capacitive displacement sensors, and better-than 0.8 millidegree resolution when using laser interferometry.

Three-axis pneumatic tactile display with integrated capacitive sensors for feedback control

In this paper, we propose a three-axis pneumatic tactile display that is precisely controlled by using integrated capacitive displacement sensors. The proposed tactile display consists of a core body with a 3 × 3 balloon array on its top surface, four lateral balloons made of latex rubber, and inner and outer frames that include capacitive displacement sensors based on a flexible printed circuit board. The 3 × 3 balloon array on the core body is designed to apply normal haptic stimulation to a human fingertip. In addition, the lateral motions of the core body and each frame produce haptic stimulation in a tangential direction. Precise control of lateral motion was achieved by feedback control using the capacitive displacement sensors. The size of the fabricated tactile display was 26 × 26 × 18 mm3. We experimentally performed manipulation of the proposed device with a custom control system, thereby demonstrating accurate control of displacement.

Characterization of Interlayer Sliding Deformation for Individual Multiwalled Carbon Nanotubes Using Electrostatically Actuated Nanotensile Testing Device

We have developed an in situ scanning electron microscopy (SEM) nanomaterial manipulation system, including a newly designed electrostatically actuated nanotensile testing device (EANAT), in order to investigate the mechanical characteristics of multiwalled carbon nanotubes (MWCNTs) synthesized by atmospheric pressure-chemical vapor deposition. The new EANAT can measure uniaxial tensile displacement of nanomaterials using a capacitive displacement sensor incorporated into a cantilever motion amplification system. The resolution of the measurement displacement was 0.28 nm at the minimum. The nanomaterial manipulation system allows for an individual MWCNT to be picked up from a substrate and to be attached to an EANAT. The stress-strain relationships for the individual MWCNTs were successfully obtained from the nanotensile tests, and Young's moduli were estimated to be in the range from 338 to 623 GPa. The deformation of individual MWCNTs under uniaxial loading was accompanied by repeated stick-slip and hard sticking events like telescopic motion. The shear strength at a stick-slip event during interlayer sliding of MWCNTs under tensile loading was directly derived from the shear interaction force in the tensile load-displacement curves and SEM observations. On the basis of the single-shot extraction model, the shear strength was estimated to be an average of 78 MPa greater than that for high-quality crystalline graphite, which might be caused by the hard sticking between layers.