Capacitive Touch Panels Research Articles

A self-powered, high-precision and minimum-channel touch panel coupling triboelectrification and uniform resistance film

Touch panels utilizing surface-capacitive mechanism are ubiquitous in our daily life. However, the need for an additional probe signal generator and receiver module to detect the resistance distribution and variation caused by finger touching adds complexity and energy consumption to the system. Herein, we propose a self-powered and high-precision tribo-touch-position sensor (TPS) that can operate without an external probe signal generator and receiver module. By detecting the contact electrification signal and extracting the signal ratio between the edges of a uniform resistance film, TPS exhibits precise touch position detection with minimal channels. The mechanism and feasibility of this sensor is systematically analyzed from theory and experiment. Moreover, the resistance range and parameters that affect the sensing performance are discussed in depth. Compared to traditional capacitive touch panels, TPS can function in high moisture conditions and is not limited to grounded objects. Finally, the designed TPS achieves spatial resolutions of 0.001 and 1 mm in touching space and size, and a prototype 2D touch panel is fabricated experimentally. The signals ratio of 2D touch panel changes more obviously in the middle than on the sides while the fingers touch various positions. This work provides an alternative platform for simple and diverse contact localization using triboelectric effect.

Optical Panel Inspection Using Explicit Band Gaussian Filtering Methods in Discrete Cosine Domain.

Capacitive touch panels (CTPs) have the merits of being waterproof, antifouling, scratch resistant, and capable of rapid response, making them more popular in various touch electronic products. However, the CTP has a multilayer structure, and the background is a directional texture. The inspection work is more difficult when the defect area is small and occurs in the textured background. This study focused mainly on the automated defect inspection of CTPs with structural texture on the surface, using the spectral attributes of the discrete cosine transform (DCT) with the proposed three-way double-band Gaussian filtering (3W-DBGF) method. With consideration to the bandwidth and angle of the high-energy region combined with the characteristics of band filtering, threshold filtering, and Gaussian distribution filtering, the frequency values with higher energy are removed, and after reversal to the spatial space, the textured background can be weakened and the defects enhanced. Finally, we use simple statistics to set binarization threshold limits that can accurately separate defects from the background. The detection outcomes showed that the flaw detection rate of the DCT-based 3W-DBGF approach was 94.21%, the false-positive rate of the normal area was 1.97%, and the correct classification rate was 98.04%.

Sustainable wood electronics by iron-catalyzed laser-induced graphitization for large-scale applications

Ecologically friendly wood electronics will help alleviating the shortcomings of state-of-art cellulose-based “green electronics”. Here we introduce iron-catalyzed laser-induced graphitization (IC-LIG) as an innovative approach for engraving large-scale electrically conductive structures on wood with very high quality and efficiency, overcoming the limitations of conventional LIG including high ablation, thermal damages, need for multiple lasing steps, use of fire retardants and inert atmospheres. An aqueous bio-based coating, inspired by historical iron-gall ink, protects wood from laser ablation and thermal damage while promoting efficient graphitization and smoothening substrate irregularities. Large-scale (100 cm2), highly conductive (≥2500 S m−1) and homogeneous surface areas are engraved single-step in ambient atmosphere with a conventional CO2 laser, even on very thin (∼450 µm) wood veneers. We demonstrate the validity of our approach by turning wood into highly durable strain sensors, flexible electrodes, capacitive touch panels and an electroluminescent LIG-based device.

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Grid-type transparent conductive thin films of carbon nanotubes as capacitive touch sensors

Transparent conductive films are used in a wide variety of devices. While solar cell top electrodes as well as tablet and mobile phone screens require high optical transparency and low sheet resistance (>80% and <10 Ω/□) to maximize power efficiency; other, less demanding applications, such as those in capacitive touch panels and antistatic coatings, in which only small currents are involved, can be managed with coatings of moderate conductivity. In this paper, we show that area-selective argon plasma treated polyethylene terephthalate surfaces are suitable for localized deposition of carbon nanotubes from their aqueous dispersions by a simple dip coating and subsequent drying processes. The as-deposited carbon nanotubes form entangled networks in microscopic patterns over the plasma-treated surface areas with sheet resistance of <1 kΩ/□ and optical transparency of ~75%. Based on this process, we demonstrate grid-type transparent conductive thin films of carbon nanotubes as capacitive touch sensors. Since each process step is robust, easy to up and downscale, and may be implemented even in roll-to-roll and sheet-to-sheet fabrication, the demonstrated technology is promising to produce grid-type structures even at an industrial scale in the future.

Fluorescent Lamp Effect Correction on Capacitive Touch Panel by Timely Update Predicted Covariance Matrix

This paper proposes an adaptive Kalman filter (AKF) control algorithm for capacitive touch panels under the radiation effect of a commercial fluorescent lamp. The predicted covariance matrix of the proposed algorithm is timely updated by two-dimensional gesture compensation. It adaptively adjusts the filter correction manner between fast tracking and smoothing modes. The trajectory area and velocity concept builds up the compensation method and proves in real-time practice by a microprocessor unit. The electromagnetic radiation effect is investigated to obtain the lamp emission noise level. A comprehensive system structure provides the flexibility and efficiency in competing with different algorithms for comparison. A microprocessor unit completed the AKF method calculation in 8.23 ms under fluorescent lamp lightening condition in real time. All Python environments are implemented in the merit of hardware peripheral support, rich programming environments, and open source modules.

Investigation of a Capacitor Array of a Composite Capacitive Touch Panel

The work is devoted to studying a capacitor array of sensor and contactless identifier entry devices of the capacitive type on the example of sensory devices made from composite silver-containing materials on a ceramic substrate. The theoretical investigations involve calculations of the topology of the capacitor arrays, in particular, improved dimensions of the segments (3.5 × 3.5 mm) and the arrangement of array layers with the aim of more exactly recognizing input objects, reducing the malfunction of the controller, and increasing the electromagnetic pickup tolerance. In addition to searching for the dimensional parameters, the electrophysical parameters of the capacitive panel under study, namely, voltage, capacitance of 1.8 nF in the case of a matrix with square segments and 2.3 nF in the case of a matrix with round segments, and the charge before and after approaching the input objects (6 and 7 nC, respectively), are measured and calculated. Experimental investigations of the capacitor arrays are carried out, according to which it is determined that a round shape of the segments is preferable in order to increase the linearity of the dependence of the distance of the input objects from the centers of the sensor segments. It is also more effective to locate the integrated plate of a capacitor array from the bottom rather than the top. In this case, the set of holes in the array layers becomes unnecessary. The results of the calculations of the dimensional and electrophysical parameters and their experimental measurements help in the design of topologies of the arrays of the sensor elements of capacitive touch panels from materials which are an alternative to indium and tin oxides (ITOs) (silver nanowires, graphene, polymers, foil, silver-containing organic composites, etc.), as well as in the design of ADT diagrams and controllers for them.

Tracking Touched Trajectory on Capacitive Touch Panels Using an Adjustable Weighted Prediction Covariance Matrix

This study presents a smooth tracking algorithm for a proposed capacitive touch panel system that consists of a 7-in panel, a microcontroller unit, a sensor IC, an interface board, and a laptop computer. The proposed adaptive Kalman filter (AKF) algorithm is capable of reducing the complexity of the computation by the processor and the effect of unstable measurement noise on zigzag trajectory as the speed of the tracked trajectory varies. Experimental results indicate that the various reporting rates decrease estimative ability of touched position, which is solved by using an AKF method to achieve the accurate estimation of touched position. The results also demonstrate that the proposed method can accurately match the reference trajectory compared with the trajectories of the moving average filter and the Kalman filter. The root-mean-square errors of the proposed AKF method are all lower than 0.5 cm under the specifications of various movement speeds and reporting rates.

P‐209: Augmenting Capacitive Touch with Piezoelectric Force Sensing

In this work, force touch sensing is achieved in conventional capacitive touch panels, by employing piezoelectric materials. To achieve high sensitivity and stability in force detection, deep analysis of employing piezoelectric material in interactive displays is provided, together with possible solutions for piezoelectric principle related force sensing issues.

P-180: Force Sensing Technique for Capacitive Touch Panel

A force sensing technique is presented for capacitive touch panels. By measuring force induced stress, force touch can be detected even when the panel deflection is very small. In addition to that, image based down-sampling methods are proposed to reduce power consumption and boost readout speed of touch panel.

Defect detection of capacitive touch panel using a nonnegative matrix factorization and tolerance model.

Capacitive touch panels (CTPs), as a medium of information interactions, have become essential parts in many consumer electronics. However, current methods such as image edge matching and frequency notch filter cannot suit the defect detection for the new-type complex CTP patterns, which have neither basic primitives nor periodicity. For solving the issues, we proposed a nonnegative matrix factorization (NMF)-based large-size image registration method, and combined it with image tolerance models to detect defects in such CTP patterns. The NMF-based image registration method can fast extract each CTP from a large image. And then, any three of registered images are selected as reference images, which are further processed by threshold processing and simple mathematical morphological operation to obtain tolerance models. Afterward, we can use the tolerance models to obtain a nondefective template. In the normal inspection stage, the defects in CTP patterns can be identified as long as comparing the tolerance models of the template and sensed images. The experimental results show that the proposed method can efficiently and accurately detect various types of defects in CTP patterns. Moreover, the detection results are robust under different illuminations. Therefore, this algorithm can be reliably applied in actual inspection of such new-type CTP patterns.

Piezoelectric vs. Capacitive Based Force Sensing in Capacitive Touch Panels

High sensitivity force sensing is a desirable function of capacitance touch screen panels. In this paper, we report on a dynamic force detection technique by utilizing piezoelectric materials. The force-voltage responsivities are investigated for four widely used stack-ups, with various panel thicknesses and touch locations. Based on the theoretical analysis and simulation results, the maximum responsivity and the signal-to-noise ratio are achieved at 0.42 V/N and 59.1 dB, respectively. The proposed technique implements force sensing successfully, enhancing the human–machine interactivity experience.

Preparation and characterization of carbon black/polybutylene terephthalate/polyethylene terephthalate antistatic fiber with sheath–core structure

In this study, antistatic sheath–core composite fibers with the core composed of polyethylene terephthalate (PET) polymer and a sheath composed of carbon black/polybutylene terephthalate (CB/PBT) polymer were fabricated using a conjugate spinning process. CB powders of various particle sizes were compounded with PBT polymers to prepare the antistatic CB/PBT pellets, and their electrical resistivities strongly depended on the intrinsic properties and dispersion of CB powders. The CB/PBT/PET fibers consisted of well-mixed CB powders within the polymer matrix showed an outstanding antistatic function, and they were employed to manufacture an antistatic glove with commercial acrylic yarns for practical applications. The antistatic glove with a reliable washing fastness is capable of being used on capacitive touch panels of smart phones, tablets, and other wearable electronic devices. This approach offers new possibilities for a variety of textile applications requiring antistatic properties.

68.1: Invited Paper: Panel Structure Evolution of In‐cell Capacitive Touch Sensor

In this paper, various integration schemes for in‐cell capacitive touch panels will be reviewed. Continuous efforts have been made to eliminate the interference between display and touch sensor structure. A in‐cell LCD module with self‐capacitance touch sensor integrated will be presented.

Preparation of transparent conducting films with improved haze characteristics using single-wall carbon nanotube-silver nanowire hybrid material

Transparent conducting films (TCFs) were fabricated using single-wall carbon nanotube (SWCNT)–silver nanowire (AgNW) hybrid materials on flexible substrates. The hybrid solution was prepared with various weight ratios of SWCNTs and AgNWs, followed by bar-coating on polyethylene terephthalate (PET) film. As the SWCNT content increased, the haze of the film decreased markedly, while transparency and sheet resistance were a little bit impaired. As a result, the prepared hybrid TCFs exhibited a sheet resistance of 120Ω/sq and a transparency of 90.8%, with a haze of as low as 1.6% when the weight ratio of SWCNTs to AgNWs was 2:3. These properties appear suitable for the application of TCFs in high-performance, flexible capacitive touch panels.

Electromagnetic field analysis of capacitive touch panels

The characteristics of capacitive touch panels were examined via electromagnetic field numerical analysis, with focus on the comparison between self- and mutual-capacitive panels. The results indicate the need for an AC-voltage-applied shield electrode and a high-sensitivity self-capacitive panel. The results also highlight a spatial resolution issue and the electrical role of dummy electrodes in the mutual-capacitive panel.

P.128: Virtual Force Sensing Using Smooth Stroke Reconstruction Algorithm for Capacitive Touch Panels

AbstractThis work adopts a method to detect the force signal from z‐directional with a stylus and finger for capacitive touch panels (CTPs). To obtain the accuracy of force signal, the Kalman filter (KF) is utilized to reduce the noise of force signal. Moreover, the directional weighted method is used to achieve the smooth drawing and stroke reconstruction after processing force signal by the KF algorithm. The experiment results demonstrate the effectiveness of drawing and stroke reconstruction with both stylus and finger.

P.129: A Simple and Effective Way to Improve Projected Capacitive Touch Panel Architecture

AbstractWe have demonstrated a new touch panel architecture that improve the touch sensitivity of stripe type projected capacitive touch panels. This approach only requires a slight modification to the sensing electrodes. By introducing dangling contacts to the sensing electrode close to the sense‐drive overlapping region, this effectively reshape the electric field over the region, and the contacts serve as extra antennas of E‐field that magnifies the touch effect. Such method would be particular useful for in‐cell touch technology due to the highly adaptability and the signal amplification effect.

Pressure Sensitive Stylus and Algorithm for Touchscreen Panel

This work presents a new simple passive 3D stylus and its associated stroke reconstruction algorithm for capacitive touch panels that detects the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> , <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> -directional position and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</i> -directional strength without the help of a pressure sensor. The proposed algorithm can successfully detect touch information while eliminating noise. Moreover, unintended touch will be recognized and its effects are eliminated while the desired signal will be accessed by the touch system to enhance the handwriting experience. The results of experiments on a touch panel system were analyzed, demonstrating the effectiveness of the proposed stylus and its stroke reconstruction algorithm.

Automated quality inspection of surface defects on touch panels

Capacitive touch panels (CTPs) with advantages of water-proof, stain-proof, scratch-proof, and fast response are widely used in various electronic products built in touch technology functions. It is a difficult inspection task when defects imbedded on surfaces of CTPs with structural textures. This research proposes a Fourier transform-based approach to inspect surface defects of CTPs. When a CTP image with four directional and periodic lines of texture is transformed to Fourier domain, four principal bands with high-energy frequency components crisscross at the center of Fourier spectrum. A multi-crisscross filter is designed to filter out the frequency components of the principal band regions. The filtered image is then transformed back to spatial domain. Finally, the restored image is segmented by a simple threshold method and defects are located. Experimental results show the proposed method achieves a high defect detection rate and a low false alarm rate on defect inspection of touch panels.