Coplanar Sensor Research Articles

Optimisation strategy for coplanar array capacitance imaging in rotational scanning mode

ABSTRACT Coplanar array capacitive imaging represents a non-destructive testing technology. To address the challenge of reduced utilisation of the high-sensitivity region caused by the ‘soft field’ effect characterised by severe nonlinear and inhomogeneous distribution of coplanar array capacitance sensitivity, resulting in difficulties in solving the problem of medium distribution, the proposed approach involves coplanar array capacitance sensor rotational scanning technology. This paper establishes both a physical rotation model and a sensitive field rotation model for a coplanar array capacitance sensor, demonstrating the inability to resolve the low-sensitivity region for medium distribution and illustrating how rotary scanning detection can enhance the utilisation rate of the high-sensitivity region. In conjunction with improved regional energy contrast, the images acquired under various rotation angles are fused, and experimental verification is conducted. The experimental results underscore that rotational scanning detection techniques can increase the utilisation rate of the high-sensitivity region within the coplanar array capacitance sensor by 74.69%. This enhancement effectively captures essential information within the reconstructed image and successfully addresses the challenge of solving difficulties in dielectric distribution. The research outcomes provide valuable insights for advancing non-destructive testing technologies employing coplanar array capacitance sensors.

Electrostatic interaction energy between the electrodes of a concentric coplanar sensor

The capacitive testing method using coplanar capacitive sensors represents a relatively new technique for non-destructive evaluation of the properties of a given material. The most conventional design of a coplanar capacitive sensor is that of two oppositely charged coplanar electrodes located at some separation distance from each other. The electrodes can have any shape including designs with circular symmetry. The concentric coplanar sensor is a special case of a device with circular symmetry. It comprises a disk as the inner electrode and an annulus as the outer one. In this work we analyze the features of the electrostatic interaction energy between the two electrodes of a concentric coplanar sensor by considering a model consisting of a uniformly charged disk and a uniformly charged annulus that is concentric and coplanar to the disk. For the sake of generality, we assume that the two objects carry an arbitrary amount of net charge and their dimensions are arbitrary. We obtain an exact expression for the electrostatic interaction energy of the system as a function of three important length scales, radius of disk and inner/outer radii of the annulus. The interplay between these parameters determines the features of the electrostatic interaction energy between the electrodes as well as the overall performance of the sensor.

Defect imaging and identification in asphalt materials using coplanar capacitance sensors with single-pair electrodes

Coplanar capacitance imaging technology (CCIT) is a non-destructive method with intuitive and accurate identification. This paper aims to realize defect identification in asphalt materials based on the CCIT using coplanar single-pair electrode capacitance sensor (CSCS). Firstly, the Linear Back Projection (LBP) algorithm, the Landweber algorithm, and the Kalman-Filter (KF) algorithm, are compared and evaluated. Then, the principal component analysis (PCA) method is utilized to fuse the reconstructed images. In addition, the OTSU method, the iterative threshold (IT) method, and the genetic algorithm (OA) method, is compared and utilized to quantify the defective region. Finally, this investigation analyzes the reconstructed and segmented images of defects in asphalt materials. It is concluded that the KL algorithm is the most suitable algorithm to reconstruct the defective images. The PCA method improve the quality of the reconstructed defective images. The defective region is determined by the OTSU method, which is the most approximate imaging segment method. It is found that the CCIT can detect the invisible defect depth in asphalt materials. The different defect mediums in various asphalt materials can be identified by the CCIT. The segmented defective region error in asphalt materials is less than 13%, demonstrating that the CCIT is effective for the identification of defect shape details in asphalt materials. The segmented imaging precision of square defects in asphalt materials is the highest; circular defects are the next lowest; and triangular defects are the lowest. The outcomes of this research can assist engineers in realizing intuitive and high-accuracy identification of various invisible defects in shallow asphalt layers in bridge deck asphalt pavement utilizing the CCIT.

CHO and HepG2 Single-Cell Characterization With Planar Microchip Sensors up to 40 GHz

The article deals with broadband microwave measurements performed on single dead and living biological cells from CHO and HepG2 cell lines. It reports results obtained with coplanar waveguide reflection and transmission type sensors, respectively. A straight-forward single liquid calibration procedure allows to extract the complex cell permittivity and compare it to that of the surrounding medium. The contrast is analyzed through <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$p$</tex-math></inline-formula> -value tests and in terms of the usual Cole-Cole parameters. The results demonstrate the distinguishability of the cell lines based on the permittivity.

Evaluation of coplanar line type thin film magnetic field sensor with narrow slits

We have proposed coplanar line type thin-film magnetic field sensor with narrow slits. The slit is employed to flow more carrier current on the signal line by improving the impedance matching. Several sensors having 6, 10, 26, 36, and 50 μm slit widths were fabricated and evaluated from the phase and the amplitude of the transmission coefficient (S21) and reflection coefficient (S11) measured by the network analyzer. The amplitude of S21 with slit was improved about five times larger than the sensor without one at around 2 GHz. The appropriate slit width was evaluated as around 10 μm for the coplanar line type thin film magnetic field sensor and the sensitivity will enhance more than 10 times higher than the sensor without slits.

Identification of defects in the inner layers of composite components based on capacitive sensing.

This paper describes the development and validation of a rapid internal defect detection method for multilayer composite components. Coplanar array capacitive imaging is based on electrical capacitance tomography, in which all electrodes are arranged in a single plane. The coplanar array capacitive sensor system is based on the capacitive edge effect and reconstructs the dielectric distribution in the sensitive area by measuring the capacitance of the sensor. A 4 × 3 array of coplanar electrode sensors is established and used to image the defects in the inner layers of multilayer composite components. Using a 3D model of the sensor and the sensitivity field, the variation pattern of the sensitivity field is analyzed. By placing different objects into the sensitivity area of the system, changes in the dielectric constant can be observed. Multilayer composite components with void defects are placed in the measurement area for defect detection. The dielectric distribution is visualized by reconstruction algorithms from the capacitance data and sensitivity field data. The results show that the imaging system based on a coplanar array capacitive sensor can reproduce the location of defects and realize the nondestructive testing of complex multilayer composite components.

Label-free glucose monitoring using Meandered Signal Coplanar Sensor (MSCS) loaded with inter-digitated conductor bricks

This paper presents the microwave glucose sensor configured by loading a Meandered Signal Coplanar Sensor (MSCS) with the inter-digitated conductor bricks in the meander inductor. Two designs are presented in which the meander inductor is placed at the central part of the signal conductor strip of 50 Ohms coplanar waveguide (CPW), where the electric field has been intensified by loading the meander inductor with inter-digitated conductor bricks which are (i) grounded and (ii) ungrounded. The sensor device prototypes are fabricated in-house on the FR4 Printed Circuit Board (PCB), in which the sensing region is realized with Polydimethylsiloxane (PDMS). The RF parameters of each sensor device prototype have been measured to determine the aqueous glucose concentration. Experimental S-parameters have been closely observed to quantify the glucose concentration.

Mediator-Free and Rapid Glucose Sensing Using 5-Turn Meandered Signal Coplanar Sensor (MSCS) with Rectangular PDMS Cavity for the Sensitivity Enhancement

The emphasis of the paper is on the development of the microwave mechanism-based cost-effective and sensitive Meandered Signal Coplanar Sensor (MSCS) with rectangular PDMS cavity for the mediator-free, rapid, quantitative and non-destructive characterization of the aqueous glucose solution. MSCS sensor is configured of the coplanar waveguide (CPW) with the meander structured inductor embedded at the center of the signal conductor, where the meander structured inductor being utilized as the sensing area. The rectangular cavity made of PDMS (Polydimethylsiloxane) polymer has been used to restrict the Sample Under Test (SUT) to the sensing area. Aqueous samples with varying glucose concentrations have been prepared with deionized water and 0.9% NaCl (Sodium Chloride) solution. Analysis of the experimental RF (radio frequency) measurements revealed that the increase in glucose concentration exhibited distinct and distinguishable S-parameters (scattering parameters). The findings support the potential application of the proposed sensor for quantification.

Analysis of coplanar line-type thin-film magnetic field sensor by electromagnetic field simulation

Analysis of coplanar line-type thin-film magnetic field sensor by electromagnetic field simulation

Coplanar electrical/ultrasonic dual-modality tomography for water continuous gas/oil/water three-phase distribution imaging

Multiphase distributions are common in industrial processes, such as the gas/oil/water three-phase flow, where the visualization of three media is of great significance for state monitoring and fault prediction of industrial production processes. Industrial process tomography possesses unique advantages of non-invasive, non-radiation, and low-cost in multiphase distribution imaging, attracting more and more attention. Due to the complexity of the physical parameters of gas/oil/water three media, traditional single-modality tomography technology is usually difficult to reconstruct and distinguish three media simultaneously. To overcome this problem, an electrical/ultrasonic dual-modality tomography method is proposed, where a coplanar dual-modality sensor is designed to obtain electrical and ultrasonic measurement data. To achieve image fusion, the same mesh model is used in electrical resistance tomography (ERT) and ultrasonic transmission tomography (UTT) inverse problems. The logistic regression and two-dimensional wavelet-transform fusion methods are proposed to fuse the ERT and UTT reconstructed images and visualize the gas/oil/water three media. Numerical and experimental tests are conducted, and image reconstruction results show that the proposed coplanar electrical/ultrasonic dual-modality tomography method can simultaneously reconstruct and distinguish three media in water continuous gas/oil/water three-phase distribution. Especially, the proposed logistic regression and two-dimensional wavelet-transform fusion methods can also improve the imaging quality compared with the traditional single-modality and weighted-average fusion methods.

Preliminary study on the new wound monitoring technology using co-planar waveguide sensor: Modeling and simulation.

BACKGROUND:Wound monitoring is very meaningful for the clinical research, diagnosis and treatment. But the existing wound monitoring technology is hard to meet the needs of modern medical care in terms of real-time, non-invasive and anti-interference.OBJECTIVE: To solve this problem, this paper proposed a new kind of monitoring technology based on the co-planar waveguide transmission line theory and assessed the application value of this method as a wound monitoring technology.METHODS: The simplified wound model included the skin, fat, muscle, tissue fluid and bandage and a new co-planar waveguide sensor were designed and established. All of the simulation was achieved in the electromagnetic special software. The data processing method was based on the transmission line theory.RESULTS: Detailed analyses of the results from the simulation were conducted. The sensor has a good monitoring effect in the low frequency band. The monitoring results could be influenced by the thickness of the bandage outside the wound. The thickness of the bandage should not be larger than 10 mm. The effective monitoring area of the sensor is 30 20 mm. CONCLUSIONS: The proposed sensor based on the CPW transmission principle in this paper has good wound monitoring potential.

Enhanced Response of Co-Planar MEMS Microheater-Based Methane Gas Sensor

A high performance coplanar MEMS microheater based gas sensor, in respect of its portability and power consumption, with enhanced response, has been designed, fabricated and characterized. Pt microheater, along with interdigitated electrodes (IDE) and Methane sensing layer were deposited on micro machined silicon substrates. Performance of the microheater was analyzed in terms of power consumption and heat distribution uniformity. Existence of a leakage voltage was detected which was found to reduce the overall sensor performance. Source of this leakage voltage was theoretically and experimentally investigated. To reduce the effect of such leakage voltage on sensor performance, a low drift OPAmp based high gain cancellation circuit was subsequently designed, implemented and an enhanced response of about 70% was observed as against 40% for uncompensated coplanar sensors. An exhaustive sensor characterization study was carried out for different concentrations of methane and performance was analyzed in terms of sensitivity, response, recovery time etc. A sensitivity of about 73% was observed for 5000ppm methane concentration with a moderate response (110 sec) and good recovery (30 sec) time.

Improvement of capacitive humidity sensors using tris(8-hydroxyquinoline) gallium (Gaq3) nanofibers as a dielectric layer

In this research work, we improved the sensing response of the organic-based co-planar humidity sensors using tris(8-hydroxyquinoline) gallium (Gaq3) nanofibers as a dielectric material. The humidity sensor was fabricated by a drop-casting solution in the gap between pre-deposited silver (Ag) electrodes to form Ag/Gaq3/Ag-based capacitive-type humidity sensor. The morphology of the Gaq3 films has been investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). At room temperature, the capacitive response of the sensor is evaluated in the range of 0 to 95%RH at 120 Hz & 1 kHz. Notably, at 1 kHz frequency, the sensor shows fast response, good sensitivity, and low hysteresis. The response & recovery times were found to be 6 s each, which are way smaller than those reported in the literature. Such features demonstrate that Gaq3 nanofibers are an up-and-coming candidate for making very sensitive and fast humidity sensors.

Non-Destructive Real-Time Glucose Quantification Using 5-Turn Meandered Signal Coplanar Sensor Integrated with Circular PDMS Cavity

In this paper, the experimental demonstration in the prospective application of the novel label-free microwave-based Meandered Signal Coplanar Sensor (MSCS), for the non-destructive quantification of the glucose in aqueous solution, has been presented. The sensor has been designed by embedding 5-turn meander inductor in the signal conductor of a 50 Ω coplanar waveguide (CPW) transmission line, where the sensing area is configured with Polydimethylsiloxane (PDMS). Precursory modelling of the CPW transmission line and the meander inductor have been executed in MATLAB and further optimization has been carried out in 3D CST Microwave Studio Suite 2017 simulator. The experimentally measured magnitude and peak frequency for S11 and S21, respectively, showed good sensitivity of 18.42 dB/g/ml, 265.72 MHz/g/ml, 36.51 dB/g/ml and 1050 MHz/g/ml, respectively. The regression analysis with high linearity of 0.921, 0.944, 0.762, and 0.839, respectively, validated the correlation of the glucose concentration with the magnitude and peak frequency of the S-parameters.

Analysis and Design of a Microwave Coplanar Sensor for Non-Invasive Blood Glucose Measurements

In this paper a design for a microwave sensor for the non-invasive measurement of blood glucose concentrations is proposed. The sensor is intended for usage as part of a non-invasive glucose-quantifying device. With this aim, three different microwave resonator structures are analyzed as possible candidates, and strengths and weaknesses are highlighted in each case. The chosen resonator is an open structure in which a finger of the patient is placed, fulfilling the role of a sample to be characterized by the sensor. The shape and size of the finger thus condition those of the resonator. Variations in the concentration of blood glucose modify the dielectric properties of the tissue, which is part of the microwave resonator-finger system, and as such, the changes translate to the resonance frequency of the whole structure. Among the three studied topologies, it was found that a single resonator designed using a coplanar structure with a ground plane showed the best trade-off in frequency sensitivity, stability and repeatability of the measurements. A notable correlation, between the resonance frequency of the proposed sensor and the blood glucose levels measured with a traditional glucometer, was found. This highlights a potential interchangeability of both glucose measurement methods.

Characterization of Low-Cost Capacitive Soil Moisture Sensors for IoT Networks

The rapid development and wide application of the IoT (Internet of Things) has pushed toward the improvement of current practices in greenhouse technology and agriculture in general, through automation and informatization. The experimental and accurate determination of soil moisture is a matter of great importance in different scientific fields, such as agronomy, soil physics, geology, hydraulics, and soil mechanics. This paper focuses on the experimental characterization of a commercial low-cost “capacitive” coplanar soil moisture sensor that can be housed in distributed nodes for IoT applications. It is shown that at least for a well-defined type of soil with a constant solid matter to volume ratio, this type of capacitive sensor yields a reliable relationship between output voltage and gravimetric water content.

The effect of coplanar sensor spacing on determining the angular acceleration of vehicles

Vehicle vibration presents challenges to a packaged product that is inevitable in any distribution environment. Typically products are tested in only a single, vertical axis; researchers have shown that there is energy in all six axes of motion. In this work, we study the recording methods of the six degrees of freedom (6DOF) motion of a transport vehicle. Using a co‐planar sensor array, three tri‐axial linear accelerometers and three angular rate sensors mounted in a L shape are used to calculate the rotational accelerations that occur in the back of a vehicle. Missing from prior work is a scientific study designed to determine the minimum sensor spacing necessary to accurately capture the yaw, pitch, and roll of transport vehicles. A sensitivity study is conducted to determine the effect of the misplacement and misorientation of sensors on the angular acceleration calculation. A laboratory study is used to determine the distance error begins to accumulate in the angular acceleration calculation in response to a sinusoidal input. A field study is conducted to calculate the rotational motions of a vehicle on a rough road. It is found that a mounting fixture is valuable in assuring the necessary sensor placement accuracy needed to accurately determine angular accelerations of a truck. Additionally, laboratory and field analysis show that as the sensor spacing location approaches the origin sensor, angular acceleration calculation error increases due to a loss in distinctiveness. It is desired for a close sensor mounting array, but there is a trade off between measurement accuracy and compactness of the recording array. A limit exists where the sensors can not be mounted in close proximity.

All-Textile Electronic Skin Enabled by Highly Elastic Spacer Fabric and Conductive Fibers.

Electronic fabrics that combine traditional fabric with intelligent functionalities have attracted increasing attention. Here an all-fabric pressure sensor with a wireless battery-free monitoring system was successfully fabricated, where a 3D penetrated fabric sandwiched between two highly conductive fabric electrodes acts as a dielectric layer. Thanks to the good elastic recovery of the spacer fabric, the capacitance pressure sensor exhibits a high sensitivity of 0.283 KPa-1 with a fast response time and good cycling stability (≥20 000). Water-soluble poly(vinyl alcohol) template-assisted silver nanofibers were constructed on the high-roughness fabric surface to achieve high conductivity (0.33 Ω/sq), remarkable mechanical robustness, and good biocompatibility with human skin. In addition, the coplanar fabric sensor arrays were successfully designed and fabricated to spatially map resolved pressure information. More importantly, the gas-permeable fabrics can be stuck on the skin for wireless real-time pressure detection through a fiber inductor coil with a resonant frequency shift sensitivity of 6.8 MHz/kPa. Our all-fabric sensor is more suitable for textile technology compared with traditional pressure sensors and exhibited wide potential applications in the field of intelligent fabric for electronic skin.

Strategy for Determining a Magnet Position in a 2-D Space Using 1-D Sensors

In this paper, we present a strategy employing four coplanar magnetic sensors with a single sensitive direction to detect the position of a magnet in a 2-D plane parallel and above the sensors’ plane. By positioning the magnet in such a way that its magnetic moment vector lies on the direction orthogonal to the sensing elements’ sensitive direction, the signal on the sensor plane assumes a quadrupolar characteristic, which takes advantage of both the negative and positive sensing ranges of the magnetic sensors, maximizing signal variability in the sensing plane. To validate this strategy, a sensing device with a $3\times 3$ mm2 active area containing four magnetic tunnel junction arrays as magnetic sensors was fabricated. Since the combination of the measured signal in each sensor is correlated with the magnet position, these were fitted using predictive methods to map both the quantities to each other. The two best performing predictive methods, artificial neural network fitting and regression forest fitting, were verified against an independently acquired data set, yielding a position root mean square error of 178 and $96~\mu \text{m}$ , respectively.

Direct Printing of Capacitive Touch Sensors on Flexible Substrates by Additive E-Jet Printing With Silver Nanoinks

In this paper, techniques of direct printing of capacitive touch sensors on flexible substrates are presented. Capacitive touch sensors were fabricated by using electrohydrodynamic inkjet (E-jet) printing onto flexible substrates. Touch pad sensors can be achieved with optimized design of silver nanoink tracks. An analytical model was developed to predict touch pad capacitance, and experiments were conducted to study the effects of sensor design (e.g., number of electrodes, electrode length, and electrode distance) on the capacitance of printed coplanar capacitance touch sensors. Details of the fabrication techniques were developed to enable rapid prototype flexible sensors with simple structure and good sensitivity. The presented techniques can be used for the on-demand fabrication of different conductive patterns for flexible electronics with high resolution and good transparency