Touch Screen Sensor Research Articles

Stretchable, self-healing, transparent macromolecular elastomeric gel and PAM/carrageenan hydrogel for self-powered touch sensors

The booming of next-generation soft electronics has aroused great demand for the flexible touch sensors, and their key problem is to ensure good transparency and durability. Herein, glycerin and hydroxyethyl cellulose elastomer (GHEC), and PAM/carrageenan double network (DN) hydrogel are prepared by a simple one-pot polymerization method. The as-prepare DN hydrogel are sandwiched between two GHEC layers to act as a self-powered and self-healing triboelectric nanogenerator (SS-TENG), with the average peak value of VOC and ISC reaching 347.5 V and 0.98 μA respectively. When the SS-TENG is damaged, it can complete self-healing without degradation of the electrical output performance and mechanical property, guaranteeing good durability. The prepared SS-TENG exhibits excellent flexibility and high transmittance up to 93%. Further, a 3 × 3 sef-powered transparent touch sensor array based on the SS-TENG is developed. Our SS-TENG paves the way for the development of new flexible self-powered touch screen sensors.

Perspective on the band structure engineering and doping control of transparent conducting materials

Transparent conducting materials (TCMs), which combine high electrical conductivity and high optical transmission in the visible spectral range, are needed in many modern optoelectronic devices such as solar cells, flat-panel displays, touch-screen sensors, light emitting diodes, and transparent thin film transistors. However, many physical properties of the TCMs are still not very well understood. Understanding the band structure and physical origin of the unique properties of the TCMs is, therefore, crucial for the future design of these fascinating materials. In this Perspective, we will first present a brief review of the unique band structure and doping control of TCMs. In particular, we will discuss (i) the fundamental band structures and defect properties for the TCMs and why most of them are oxides (transparent conducting oxides, TCOs); (ii) how to achieve simultaneously high transparency and conductivity in n-type TCMs; (iii) why p-type TCOs are difficult to achieve; (iv) how to modify the band structure or design new materials to achieve p-type TCMs or even bipolarly dopable TCMs. Finally, we will discuss some of the remaining challenges and opportunities for the development of TCMs in the near future.

Environmentally Friendly Graphene Inks for Touch Screen Sensors

AbstractGraphene‐based materials have attracted significant attention in many technological fields, but scaling up graphene‐based technologies still faces substantial challenges. High‐throughput top‐down methods generally require hazardous, toxic, and high‐boiling‐point solvents. Here, an efficient and inexpensive strategy is proposed to produce graphene dispersions by liquid‐phase exfoliation (LPE) through a combination of shear‐mixing (SM) and tip sonication (TS) techniques, yielding highly concentrated graphene inks compatible with spray coating. The quality of graphene flakes (e.g., lateral size and thickness) and their concentration in the dispersions are compared using different spectroscopic and microscopy techniques. Several approaches (individual SM and TS, and their combination) are tested in three solvents (N‐methyl‐2‐pyrrolidone, dimethylformamide, and cyrene). Interestingly, the combination of SM and TS in cyrene yields high‐quality graphene dispersions, overcoming the environmental issues linked to the other two solvents. Starting from the cyrene dispersion, a graphene‐based ink is prepared to spray‐coat flexible electrodes and assemble a touch screen prototype. The electrodes feature a low sheet resistance (290 Ω □−1) and high optical transmittance (78%), which provide the prototype with a high signal‐to‐noise ratio (14 dB) and multi‐touch functionality (up to four simultaneous touches). These results illustrate a potential pathway toward the integration of LPE‐graphene in commercial flexible electronics.

Using Technology to Identify Children With Autism Through Motor Abnormalities.

Autism is a neurodevelopmental disorder typically assessed and diagnosed through observational analysis of behavior. Assessment exclusively based on behavioral observation sessions requires a lot of time for the diagnosis. In recent years, there is a growing need to make assessment processes more motivating and capable to provide objective measures of the disorder. New evidence showed that motor abnormalities may underpin the disorder and provide a computational marker to enhance assessment and diagnostic processes. Thus, a measure of motor patterns could provide a means to assess young children with autism and a new starting point for rehabilitation treatments. In this study, we propose to use a software tool that through a smart tablet device and touch screen sensor technologies could be able to capture detailed information about children’s motor patterns. We compared movement trajectories of autistic children and typically developing children, with the aim to identify autism motor signatures analyzing their coordinates of movements. We used a smart tablet device to record coordinates of dragging movements carried out by 60 children (30 autistic children and 30 typically developing children) during a cognitive task. Machine learning analysis of children’s motor patterns identified autism with 93% accuracy, demonstrating that autism can be computationally identified. The analysis of the features that most affect the prediction reveals and describes the differences between the groups, confirming that motor abnormalities are a core feature of autism.

Low‐Cost Fabrication Method for Thin, Flexible, and Transparent Touch Screen Sensors

AbstractThis study presents a new fabrication method for touch screen sensors using inexpensive, flexible, and transparent polyethylene terephthalate (PET) films. In the proposed method, a transparent capacitive touch sensor array is implemented with two independent axes of invisible electrodes consisting of indium tin oxide (ITO) patterns and bridge electrodes. A low‐cost implementation of the bridge electrodes is achieved by using near‐field electrospinning (NFES) method for the conductive lines with linewidth of 3–5 µm. Then, the printed bridge electrode is sintered using green laser without damaging the PET film. It is demonstrated that two transparent electrodes deposited on a single sheet of PET film can detect the touch location by scanning the driving signal while simultaneously measuring the capacitances from the sensing lines connected via bridge electrodes.

Enhancing Security on Touch-Screen Sensors with Augmented Handwritten Signatures.

We aim at enhancing personal identity security on mobile touch-screen sensors by augmenting handwritten signatures with specific additional information at the enrollment phase. Our former works on several available and private data sets acquired on different sensors demonstrated that there are different categories of signatures that emerge automatically with clustering techniques, based on an entropy-based data quality measure. The behavior of such categories is totally different when confronted to automatic verification systems in terms of vulnerability to attacks. In this paper, we propose a novel and original strategy to reinforce identity security by enhancing signature resistance to attacks, assessed per signature category, both in terms of data quality and verification performance. This strategy operates upstream from the verification system, at the sensor level, by enriching the information content of signatures with personal handwritten inputs of different types. We study this strategy on different signature types of 74 users, acquired in uncontrolled mobile conditions on a largely deployed mobile touch-screen sensor. Our analysis per writer category revealed that adding alphanumeric (date) and handwriting (place) information to the usual signature is the most powerful augmented signature type in terms of verification performance. The relative improvement for all user categories is of at least 93% compared to the usual signature.

Triboelectric Touch‐Free Screen Sensor for Noncontact Gesture Recognizing

AbstractAn intelligent human–machine interface (HMI) is a crucial medium for exchanging information between people and electronics. As one of the most important HMI devices, touch screen sensors are widely applied in personal electronics in daily life. However, as the most commonly used touch screen sensor, capacitive sensors can only detect limited kinds of gestures such as touching and sliding. Here, a triboelectric touch‐free screen sensor (TSS) is reported for recognizing diverse gestures in a noncontact operating mode by utilizing the charges naturally carried on the human body. Compared with conventional capacitive sensors, the TSS is capable of detecting various gestures such as the drop and lift of finger with different speeds, making a fist, opening palm, and flipping palm with different directions. Based on the TSS, an intelligent noncontact screen control system is further developed, which is used to unlock the smartphone interface by the noncontact operating mode. This research for the first time proposes the concept that taking the human body itself to participate in triboelectric self‐powered noncontact sensing and provides a touch‐free design concept to develop the next generation of screen sensors. It can alter the usual way that people operating their personal electronics.

Phase 3 diagnostic evaluation of a smart tablet serious game to identify autism in 760 children 3–5 years old in Sweden and the United Kingdom

IntroductionRecent evidence suggests an underlying movement disruption may be a core component of autism spectrum disorder (ASD) and a new, accessible early biomarker. Mobile smart technologies such as iPads contain...

Parameter optimization in femtosecond pulsed laser etching of fluorine-doped tin oxide films

In this study, the fluorine-doped tin oxide (FTO) film on a glass substrate was etched by using a femtosecond pulsed laser with a wavelength of 1030 nm, a repetition rate of 1 MHz and a pulse duration of 262 fs. The effect of laser fluence and scanning speed on the quality of the groove etched on the FTO film surface was systematically studied, trying to improve the groove quality. The results indicated that in order to obtain high quality grooves for use on touch screens, a balance needed to be achieved between laser fluence and scanning speed. Excessive laser fluence caused cracks at the bottom of the groove with shoulder protrusions formed at the edge of the groove, and the scanning speed had a considerable influence on the groove width at the same time. After discussing and comparing the results of five groups of experiments, the best groove quality was determined at the scanning speed of 3000 mm/s and the laser fluence of 1.1 J/cm2. In this case, the edge of the groove was sharp without obvious cracks and shoulder-like protrusions, and the groove width was 7.92 μm, which made it possible to process small etched areas for touch screen. Furthermore, the optimal parameters were confirmed to be available for processing a pattern on the touch screen sensor layer with a line spacing of 5 μm.

The MindfulBreather: Motion Guided Mindfulness.

For millennia, humans have focused their attention on the breath to develop mindfulness, but finding a scientific way to harness mindful breathing has proven elusive. Existing attempts to objectively measure and feedback on mindfulness have relied on specialist external hardware including electroencephalograms or respirometers that have been impractical for the majority of people learning to meditate. Consequently, training in the key skill of breath-awareness has lacked practical objective measures and guidance to enhance training. Here, we provide a brief technology report on an invention, The MindfulBreather® that addresses these issues. The technology is available to download embedded in a smartphone app that targets, measures and feedbacks on mindfulness of breathing in realtime to enhance training. The current article outlines only the technological concept with future studies quantifying efficacy, validity and reliability to be reported elsewhere. The MindfulBreather works by generating Motion Guided Mindfulness through interacting gyroscopic and touchscreen sensors in a three phase process: Mindfulness Induction (Phase I) gives standardized instruction to users to place their smartphone on their abdomen, breathe mindfully and to tap only at the peak of their inhalation. The smartphone’s gyroscope detects periodic tilts during breathing to generate sinusoidal waveforms. Waveform-tap patterns are analyzed to determine whether the user is mindfully tapping only at the correct phase of the breathing cycle, indicating psychobiological synchronization. Mindfulness Maintenance (Phase II) provides reinforcing pleasant feedback sounds each time a breath is mindfully tapped at the right time, and the App records a mindful breath. Lastly, data-driven Insights are fed back to the user (Phase III), including the number of mindful breaths tapped and breathing rate reductions associated with parasympathetic engagement during meditation. The new MGM technology is then evaluated and contrasted with traditional mindfulness approaches and a novel Psychobiological Synchronization Model is proposed. In summary, unlike existing technology, the MindfulBreather requires no external hardware and repurposes regular smartphones to deliver app-embedded Motion-Guided Mindfulness. Technological applications include reducing mindwandering and down-regulation of the brain’s default mode through enhanced mindful awareness. By objectively harnessing breath awareness, The MindfulBreather aims to realize the ancient human endeavor of mindfulness for the 21st century.

Multitouch ultrasonic touchscreen

Touchscreen sensors are widely used in many devices such as smart phones, tablets, laptops, etc. We present the design, analysis, and implementation of an ultrasonic touchscreen system that utilizes interaction of transient Lamb waves with objects in contact with the screen. The governing principle revolves around the propagation and reverberation of guided elastic waves in a bounded space, in which the localization of touch points can be challenging. Reverberant fields in enclosures can potentially carry useful information, however, in an incoherent way. Incoherency comes from consecutive reflections of the wave energy several times in the domain, ultimately leading to mixing of the wave energy in a seemingly random way. However, spreading of the wave energy can lead to multiple interrogations of each point in the enclosure. Hence, temporal information buries information about substructural changes making it feasible to conduct only a few spatial measurements. We present a learning localization algorithm capable of localizing multiple simultaneous touch points (up to 12 touches on a tablet) and with a very limited number of measurements (one or two). This in turn can significantly reduce the manufacturing cost. We also present an algorithm to improve on robustness to environmental and thermal noise.

Rollerball‐Pen‐Drawing Technology for Extremely Foldable Paper‐Based Electronics

It is reported that graphene oxide (GO) can work as the dispersing, associate thickening, stabilizing, adhesive, oxidation‐resistant, and mechanical reinforcing agents simultaneously to formulate a drawable conductive ink with silver nanowire (AgNW). The synergistic effect of combining AgNW with GO can bring forth the AgNW‐GO dynamic network, which imparts appropriate viscosity and rheological property to the ink for reliable rollerball‐pen drawing on paper and plastic substrates and enables the drawn conductive traces to simultaneously possess high conductivity, remarkable foldability, and stability. The electrical conductivity of the rollerball‐pen drawn electrodes with mild post‐treatment condition by drying at 25 °C for ≈5 min after writing on paper can achieve 2.3 × 104 S cm−1. The drawn electrodes are used as extremely foldable electrodes that can retain a record high conductivity of 1.4 × 104 S cm−1 after 1000 folding–unfolding cycles. The feasibility of the drawable conductive ink is further demonstrated by fabricating paper‐based conductive circuits and a capacitive touch screen sensor with outstanding foldability.

Lamb Wave Multitouch Ultrasonic Touchscreen

Touchscreen sensors are widely used in many devices such as smart phones, tablets, and laptops with diverse applications. We present the design, analysis, and implementation of an ultrasonic touchscreen system that utilizes the interaction of transient Lamb waves with objects in contact with the screen. It attempts to improve on the existing ultrasound technologies, with the potential of addressing some of the weaknesses of the dominant technologies, such as the capacitive or resistive ones. Compared with the existing ultrasonic and acoustic modalities, among other advantages, it provides the capability of detecting several simultaneous touch points and also a more robust performance. The localization algorithm, given the hardware design, can detect several touch points with a very limited number of measurements (one or two). This in turn can significantly reduce the manufacturing cost.

Rapid detection of E. coli cells in urine samples using a self-capacitance touchscreen device.

Escherichia coli is one of the main causes of urinary tract infections (UTIs). E. coli is commonly detected from urine using standard culture method. However, the urine sampling and analysis required for these methods can be costly, time consuming (requires 24 to 48 hours) and labor-intensive. This work proposes a capacitive touch screen sensor concept as possible alternative device for rapid detection of E. coli in urine samples. E. coli solutions prepared at different concentrations and urine samples (with spiked and nor spike E. coli) obtained from healthy women participants, have been analyzed using a capacitance evaluation kit. It has been demonstrated in this study that the use of this evaluation kit provides a low-cost and simple alternative system for detecting E. coli present in urine. Several experimental tests were performed to determine the optimal testing volume, the sensitivity of the sensor, limit of detection and repeatability. The optimal testing volume was 80 microliters and the analytical sensitivity was 17 counts per picofarad (pF). The lowest detectable concentration is around 3.98 × 10(5) CFU/ml. The repeatability (r) was found to be 7.2 or 6.2 % (in r%). The capacitive touch sensor gave promising results that could be used to design and realize a portable diagnostic device for early-stage detection of UTIs.

Transparent Nanowire Electrodes As a Tool for Electrochemical Detection

The development of new nanomaterial like carbon nanotubes, graphene and nanowires brings new possibilities to existing technologies. With the emergence of transparent electrode based on these materials, we could imagine new type of sensors, which combines transparency and flexibility. Silver nanowire transparent electrodes are currently transforming this industry. Touch screen sensors, OLED and solar panel can now be fabricated on flexible plastic sheets with low cost printing techniques. In the same way, this new type of electrode could bring electrochemical sensor toward new transparent and flexible sensing application for life science. In our study, we fabricate and characterize transparent electrode based in metal nanowires for electrochemical detection. By changing the length, diameter and amount of deposited nanowires, we can vary their transparency (up to 90% transparent), sheet resistance (up to 0.1 ohm/square) and effective surface area. Compared to conventional evaporated plain electrodes, printed nanowire electrodes can achieve more than 80% transparency (in visible range) with the same electrochemical effective surface area. Using these electrodes, we can fabricate new sensors with high transparency (> 90%), flexibility and high sensitivity to oxygen and hydrogen peroxide. The detection of these two components is predominant in healthcare and environmental monitoring. The combination of those properties could allow us to use this type of sensors as opto-electrochemical sensors for monitoring living cells and also for glucose detection on humans. Transparent nanowire electrodes can also be a real alternative to existing indium tin oxide (ITO) transparent electrodes for other applications. Figure 1.Pictures of electrochemical sensors based on metal nanowires on PET transparent substrate. WE and REF electrodes are made from metal nanowire have 80% transparency, CE electrode are made from gold. Figure 2. SEM image of silver nanowire electrode and the size distribution of nanowires. Figure 3. Voltammetry response of the nanowire based electrochemical sensor to hydrogen peroxide in phosphate buffer (pH=7) Figure 4. Dose-response curve to hydrogen peroxide using the nanowire-based sensor in phosphate buffer (pH=7) Figure 1

Fabrication of a single-layer metal-mesh touchscreen sensor using reverse-offset printing

The touchscreen sensor is one of the most innovative parts of modern electronic devices. Transparent conductive materials such as indium-tin oxide, silver nanowire, carbon nanotube, and metal mesh are used for the capacitance-sensing electrodes of touchscreen sensors. For patterning, most transparent conductive materials require a conventional patterning process of thin-film deposition or coating, photolithography, and etching to form sensing electrodes, and additional fabrication processes for routing electrodes. Printing techniques, however, can simplify the fabrication process of touchscreen sensors. Especially, reverse-offset printing can implement an ultra-fine pattern of even less than 1µm, and an excellent surface quality, regardless of the pattern size. In this paper, the fabrication process of a 6.5-inch single-layer metal-mesh touchscreen sensor printed on a transparent plastic film is described. Using silver nanoparticle ink, the sensing and routing electrodes are printed at once in a single layer using the reverse-offset-printing technique.

Optimization of a reverse-offset printing process and its application to a metal mesh touch screen sensor

Reverse-offset printing provides an alternative method for manufacturing ultra-fine patterned devices, such as thin film transistors and touch screen sensors. In addition to enabling fine patterning on the scale of less than a few micrometers, the method ensures the preservation of high-quality surfaces, which are essential for multi-layer devices. Ultra-fine patterns may be obtained by finely tuning the reverse-offset printing process along several printing parameters, including the printing pressure and printing speed. These parameters affect the adhesion and cohesion of an ink film, which govern the patterning mechanism. In this paper, we analyzed the patterning mechanism and optimized the printing parameters to achieve good printability. Optical transmittance methods were used to quantitatively evaluate the printability in each printing test. Finally, we demonstrated the fabrication of a single-layer metal mesh touch screen sensor based on the optimized printing process.

Healable capacitive touch screen sensors based on transparent composite electrodes comprising silver nanowires and a furan/maleimide diels-alder cycloaddition polymer.

A healable transparent capacitive touch screen sensor has been fabricated based on a healable silver nanowire-polymer composite electrode. The composite electrode features a layer of silver nanowire percolation network embedded into the surface layer of a polymer substrate comprising an ultrathin soldering polymer layer to confine the nanowires to the surface of a healable Diels-Alder cycloaddition copolymer and to attain low contact resistance between the nanowires. The composite electrode has a figure-of-merit sheet resistance of 18 Ω/sq with 80% transmittance at 550 nm. A surface crack cut on the conductive surface with 18 Ω is healed by heating at 100 °C, and the sheet resistance recovers to 21 Ω in 6 min. A healable touch screen sensor with an array of 8×8 capacitive sensing points is prepared by stacking two composite films patterned with 8 rows and 8 columns of coupling electrodes at 90° angle. After deliberate damage, the coupling electrodes recover touch sensing function upon heating at 80 °C for 30 s. A capacitive touch screen based on Arduino is demonstrated capable of performing quick recovery from malfunction caused by a razor blade cutting. After four cycles of cutting and healing, the sensor array remains functional.

A capacitive touch screen sensor for detection of urinary tract infections in portable biomedical devices.

Incidence of urinary tract infections (UTIs) is the second highest among all infections; thus, there is a high demand for bacteriuria detection. Escherichia coli are the main cause of UTIs, with microscopy methods and urine culture being the detection standard of these bacteria. However, the urine sampling and analysis required for these methods can be both time-consuming and complex. This work proposes a capacitive touch screen sensor (CTSS) concept as feasible alternative for a portable UTI detection device. Finite element method (FEM) simulations were conducted with a CTSS model. An exponential response of the model to increasing amounts of E. coli and liquid samples was observed. A measurable capacitance change due to E. coli presence and a tangible difference in the response given to urine and water samples were also detected. Preliminary experimental studies were also conducted on a commercial CTSS using liquid solutions with increasing amounts of dissolved ions. The CTSS was capable of distinguishing different volumes of liquids, also giving an exponential response. Furthermore, the CTSS gave higher responses to solutions with a superior amount of ions. Urine samples gave the top response among tested liquids. Thus, the CTSS showed the capability to differentiate solutions by their ionic content.

16.2: Reverse‐Offset Printed Single‐layer Metal‐Mesh Touch Screen Panel

AbstractTouch screen panel is one of the most innovative parts in modern electronic devices. We developed a single‐layer printed metal‐mesh touch screen sensor using projective capacitive touch sensing. The sensing electrodes and routing electrodes are printed at once forming a single layer by reverse‐offset printing using Ag nanoparticle ink. Each sensing electrode is composed of rectangular metal mesh. In this paper, we described the manufacturing process of 5“ single‐layer printed metal‐mesh touch sensor implemented on transparent plastic film.