Smart Surfaces Research Articles

Switchable bacteria-killing and bacteria-releasing surface fabricated from regenerable PNIPAM-based N-halamine cotton fabrics

So far, more and more multifunctional antibacterial materials qualified with “bacteria-killing” and “bacteria-releasing” capacities have been developed by researchers to kill live bacteria and release the killed bacteria. However, most of these surfaces are biologically incompatible and have a complex production process. In this work, we created a PNIPAM-based N-halamine cotton fabric via simple Si-ATRP (surface-initiated atom transfer radical polymerization) and chloridized in ordinary diluted sodium hypochlorite solutions. Notably, the NCl bond at N-halamine cotton fabrics and the NH bond at PNIPAM can interconvert with each other easily. The NCl bond provides the possibility of bacteria-killing. Simultaneously, the NH bond can change the surface wettability and cooperate with the stretch of PNIPAM chains at a lower temperature, providing the ability of bacteria-releasing. As a result, the PNIPAM-based N-halamine cotton fabrics have excellent antibacterial efficiency in the form of “N-Cl” and a remarkable bacteria-releasing efficiency in the form of “N-H”. In addition, the functional surface has good biocompatibility. Overall, we develop an easy way to create switchable “bacteria-killing” and “bacteria-releasing” cotton fabrics, and this smart surface shows a potential application in biomedical and hospital surfaces.

Explainable AI (XAI)-driven vibration sensing scheme for surface quality monitoring in a smart surface grinding process

Local Interpretable and Model-agnostic Explanation (LIME), an explainable artificial intelligence (XAI) approach is adapted to identify the globally important time-frequency bands for predicting average surface roughness (Ra) in a smart grinding process. The smart grinding setup consisted of a Supertech CNC precision surface grinding machine, instrumented with a Dytran piezoelectric accelerometer attached to the tailstock quill along the tangential direction (Y-axis). For every grinding pass, vibration signatures were captured, and the ground truth surface roughness values were recorded using a Mahr Marsurf M300C portable surface roughness profilometer. The roughness values ranged from 0.06 to 0.14 microns over the complete set of experiments. Time-frequency domain spectrogram frames were extracted for each of the vibration signals collected during the grinding process. Convolutional Neural Networks (CNNs) were modeled to predict the surface roughness based on these spectrogram frames and their image augmentations. The best CNN model was able to predict the roughness values with an overall R2-score of 0.95, training R2-score of 0.99, and testing R2-score of 0.81 with only 80 sets of vibration signals corresponding to 4 experiments with 20 trials each. Although the data size is not large enough to guarantee such performance metrics in real-world scenarios, one can extract statistically consistent explanations underlying the relationships these complex deep learning models capture. The LIME methodology was implemented on the developed surface roughness CNN model to identify the important time-frequency bands (i.e., the superpixels of a spectrogram) influencing the predictions. Based on the identified important regions on the spectrogram frames, the corresponding frequency characteristics were determined that influence the surface roughness predictions. The important frequency range based on LIME results was approximately 11.7 to 19.1 kHz. The power of XAI was demonstrated by cutting down the sampling rate from 160 kHz to 30, 20, 10, and 5 kHz based on the important frequency range and considering Nyquist criteria. Separate CNN models were developed for these ranges by only extracting time-frequency contents below their corresponding Nyquist cut-offs. A proper data acquisition strategy is proposed by comparing the model performances to argue the selection of a sufficient sampling rate to capture the grinding process successfully and robustly.

Multi-functional approach in the design of smart surfaces to mitigate bacterial infections: a review.

Advancements in biomedical devices are ingenious and indispensable in health care to save millions of lives. However, microbial contamination paves the way for biofilm colonisation on medical devices leading to device-associated infections with high morbidity and mortality. The biofilms elude antibiotics facilitating antimicrobial resistance (AMR) and the persistence of infections. This review explores nature-inspired concepts and multi-functional approaches for tuning in next-generation devices with antibacterial surfaces to mitigate resistant bacterial infections. Direct implementation of natural inspirations, like nanostructures on insect wings, shark skin, and lotus leaves, has proved promising in developing antibacterial, antiadhesive, and self-cleaning surfaces, including impressive SLIPS with broad-spectrum antibacterial properties. Effective antimicrobial touch surfaces, photocatalytic coatings on medical devices, and conventional self-polishing coatings are also reviewed to develop multi-functional antibacterial surfaces to mitigate healthcare-associated infections (HAIs).

Four-Dimensional Printing of Temperature-Responsive Liquid Crystal Elastomers with Programmable Shape-Changing Behavior.

Liquid crystal elastomers (LCEs) are polymer networks that exhibit anisotropic liquid crystalline properties while maintaining the properties of elastomers, presenting reversible high-speed and large-scale actuation in response to external stimuli. Herein, we formulated a non-toxic, low-temperature liquid crystal (LC) ink for temperature-controlled direct ink writing 3D printing. The rheological properties of the LC ink were verified under different temperatures given the phase transition temperature of 63 °C measured by the DSC test. Afterwards, the effects of printing speed, printing temperature, and actuation temperature on the actuation strain of printed LCEs structures were investigated within adjustable ranges. In addition, it was demonstrated that the printing direction can modulate the LCEs to exhibit different actuation behaviors. Finally, by sequentially conforming structures and programming the printing parameters, it showed the deformation behavior of a variety of complex structures. By integrating with 4D printing and digital device architectures, this unique reversible deformation property will help LCEs presented here apply to mechanical actuators, smart surfaces, micro-robots, etc.

Hierarchical microtextures generated by pulsed-laser manufacturing for surface geometry modulation

Enduring surface technologies draw much attention to improving friction performance and prolonging the lifespan of multi-alternative contact pairs. Laser surface texturing is smart to modify effectively the microscopic surface geometries and mechanical performances for the service's improvement of friction pair. This study explored the formation mechanisms and morphology evolution of hierarchical microtextures, with a focus on the thermal field and phase transformation resulting from the laser heating effect on the alloy surface. The controlling variates of laser machining were analyzed considering their influences on microtextures' height and diameter, the pulse numbers are 3 times and 1.7 times of the unit laser power, 81 times and 82.5 times of the unit pulse width. We contributed to the development of laser manufacturing techniques for creating hierarchical microtextures' controllable morphology and smart surface design for tribology engineering and energy management applications.

Silicon nanostructure – Smart antibacterial, cost-effective implantable material for health care applications

Silicon nanocomposites and nanomaterials have been instrumental in diagnose and effective treatment of bacterial complications. Over the years, usage of antibiotics for antibacterial applications has been a conventional remedy for their highly effectiveness nature, early pain relaxation, and cost effectiveness. But due to bacterial resistance to antibiotics, these medicines do not neutralise the bacteria completely rather provide a temporary solution against the microbes. The techniques applied for treatment of bacterial cells involves fusion of drug coated nanoparticles on bacterial cell walls and its impinging to the targeted bacterial cell wall for release of drug molecules to enter into the microorganisms. These nanoparticles can be polymeric nanoparticles, solid lipid nanoparticles as well as liposomes for anti microbial drug delivery. Also, nanoparticles-based technique for drug delivery has certain advantages over local antibiotic treatment since they favour release of drug at appropriate sites, offers no side effects having minimum drug resistance developments, enables drug solubility, and transport multiple drugs at a time. Further, tailoring of Silicon Nanostructures (SiNs) to obtain porous SiNs enhances their drug loading capacity for targeted delivery of antibiotics on affected cells. Effective bacteria neutralisation is hindered by the formation of biofilms around bacterial cellular cells to which antibiotics prove to be ineffective, however usage of SiNPs and SiNs provide to be an effective solution for easy malfunctioning of bacterial cells. In our prospects, Metal Assisted Chemical Etching (MAC-Etching) is adopted as the cost-effective fabrication methodology for obtaining versatile nanostructures of Si. The operating temperature and etching time have considerable effects on geometries of SiNs ranging from Si Nanoporous structures to highly branched zigzag porous Si Nanostructures. The high porosity levels of as obtained SiNs can be exploited as a potential advantage for drug coating and as an application in bio- implantable material in biomedical field. The so-obtained SEM images of SiNs are analysed using iMAGEJ software producing area distribution plots of all nanostructures. The results of simulation work depict that majority of SiNPs have negligible area having large surface to volume ratio, and so can be largely exploited for effective interfacing onto bacterial cells. Our work demonstrates the use of SiNs synthetization using MAC-Etching as smart anti-bacterial surfaces since the optimized response is obtained as the morphology of as-synthesised SiNs varies.

Flexible and Photo-responsive superwetting surfaces based on porous materials coated with Mussel-Inspired Azo-Copolymer

The decoration of porous materials with stimulus-responsive polymers is an efficient strategy for the fabrication of superwetting surfaces; however, the weak interfacial interaction between the polymers and the substrates limits their application. Herein, inspired by the molecular structure of the mussel foot protein, a series of catechol-functionalized azobenzene-containing copolymers with diverse chain structures are synthesized via solution radical polymerization and used for the preparation of smart superwetting surfaces. After dip-coating with the mussel-inspired azo-copolymers, the modified cotton fabrics and melamine sponges possessed smart surfaces with photo-switchable wettability. These as-prepared flexible smart surfaces exhibited rapid wettability transition between high hydrophobicity and superhydrophilicity with alternating ultraviolet (UV) and visible light irradiation. Meanwhile, these superwetting surfaces were also experimentally found to be robust without apparent degradation in their photo-responsiveness, even after being soaked in acid/base solutions and subjected to repetitive mechanical deformation. Especially, the functionalized melamine sponges as bulk superwetting materials have excellent mechanical stability, which can tolerate harsh abrasion cycles and repetitive compressive deformations. More importantly, it was also confirmed that the mussel-inspired azo-copolymers exhibited excellent adhesion properties at the interface of various substrates. This bioinspired strategy and developed functional copolymers paves the way for facile and large-scale fabrication of superwetting surfaces, which may find a wide range of advanced potential applications in microfluidic devices, biomedicine and sensors.

Near-Infrared Light Responsive Surface with Switchable Wettability in Microstructure and Surface Chemistry

Intelligent surfaces with reversibly switchable wettability have recently drawn considerable attention. One typical strategy to obtain such a surface is to change the surface chemistry or the microstructure. Herein, we report a new smart surface for which the wettability was controlled by both the surface chemistry and microstructure. Various wetting states were reversibly and precisely controlled through heating, pressing, NIR irradiation, and oxygen plasma treatment. The excellent shape memory characteristics of shape memory polyurethane (SMPU) and the controlled release of hydrophobic/hydrophilic oxygen-containing functional groups contributed to this ability. Microcapsules were used to design these smart surfaces. They controlled the release of a fluorinated alkyl silane (FAS) through shell melting, changed the surface composition, and played a decisive role in protecting the FAS against hydrolysis and evaporation to ensure that the surface's wettability is recyclable. Controlling of the surface chemistry or microstructure was repeated for at least 19 or 16 cycles, respectively, which indicated excellent repeatability compared to other smart surfaces. Based on the excellent controllability, the surface exhibited multiple functions, such as liquid directional transport and coefficient of friction control. In addition, it maintained this extraordinary ability under harsh environments owing to the great stability of the SMPU and adequate protection of the FAS by the microcapsules. With switchable wettability based on the surface chemistry and microstructure, this work provides a new principle for designing smart surfaces with wettability controlled in two ways.

Nano-liposomes: Historical Perspectives and Major Advances in Cancer Therapy. A critical Review

Since the discoveryof liposomes by Bangham and co-workers in 1960, giant strides in the field ofliposomes as drug carriers for cancer therapy have been achieved. From the veryfirst generation of liposomes known as conventional liposomes to the stealthliposomes which are surface decorated with polyethylene glycol attachments toprotect the liposomes from phagocytic attack, and finally, a more recent nano-liposomedelivery innovation which involves specific antibody targeting and stimulussensitivity. Advanced research on enhancing the stability of liposomes throughvarious smart surface modifications has been ongoing. Some liposomalformulations have made it from benchtop research to pharmaceuticalmanufacturing and marketing. Commercially available are stealth liposomeformulations which have been approved for use, including Doxil® (a PEGylatedliposomal formulation of doxorubicin hydrochloride). These formulations haveshown increased bioavailability at the target site compared to conventionaldrugs.

Hierarchical ‘rose-petal’ ZnO/Si surfaces with reversible wettability reaching complete water repellence without chemical modification

Smart surfaces with externally controlled wettability patterns are ubiquitous building blocks for micro-/nanofluidic and lab-on-chip devices, among others. We develop hierarchical surfaces of ZnO nanorods grown on laser-microstructured silicon with reversible photo-induced and heat-induced wettability. The as-prepared surfaces are superhydrophilic, with very low water contact angles (~ 10°), and transition to a wetting state with high water contact angles (~ 150°) when annealed in vacuum. As the annealing temperature increases to 400 °C, the surfaces become completely water-repellent. Even though the annealed surfaces present high water contact angles, at the same time, they are very adhesive for water droplets, which do not roll off even when tilted at 90° or 180o (rose-petal effect), unlike standard hydrophobic surfaces which typically combine high water contact angles with low roll-off angles. The surfaces return to the superhydrophilic state when irradiated with UV light, which indicates a reversible wettability with external stimuli. Based on this transition, we demonstrate local modification of the wetting state of the surfaces by UV irradiation through a mask, which results in directed liquid motion, useful for microfluidic applications. The high contact angles obtained in this work are usually obtained only after chemical modification of the ZnO surface with organic coatings, which was not necessary for the hierarchical surfaces developed here, reducing the cost and processing steps of the fabrication route. These rose-petal surfaces can be used as “mechanical hands” in several applications, such as no-loss transport of small liquid volumes, precision coatings, spectroscopy, and others. Furthermore, the completely water-repellent surfaces, rarely reported elsewhere, may find important applications in frictionless liquid transport for microfluidic and other devices.

Programmable microfluidics for dynamic multiband camouflage

Achieving multiband camouflage covering both visible and infrared regions is challenging due to the broad bandwidth and differentiated regulation demand in diverse regions. In this work, we propose a programmable microfluidic strategy that uses dye molecules in layered fluids to manipulate visible light- and infrared-semitransparent solvent to manipulate infrared light. With three primary fluid inputs, we achieve 64 chromaticity values and 8 emissivities from 0.42 to 0.90. In view of the wide tuning range, we demonstrate that the microfluidic film can dynamically change its surface reflectance to blend into varying backgrounds in both visible and infrared images. Moreover, we fabricate the microfluidic device in a textile form and demonstrate its ability to match exactly with the colors of natural leaves of different seasons in the full hyperspectrum range. Considering the broadband modulation and ease of operation, the programmable microfluidic strategy provides a feasible approach for smart optical surfaces in long-span optical spectra.

Sustainable Secondary-Raw Materials, Natural Substances and Eco-Friendly Nanomaterial-Based Approaches for Improved Surface Performances: An Overview of What They Are and How They Work.

To meet modern society's requirements for sustainability and environmental protection, innovative and smart surface coatings are continually being developed to improve or impart surface functional qualities and protective features. These needs regard numerous different sectors, such as cultural heritage, building, naval, automotive, environmental remediation and textiles. In this regard, researchers and nanotechnology are therefore mostly devoted to the development of new and smart nanostructured finishings and coatings featuring different implemented properties, such as anti-vegetative or antibacterial, hydrophobic, anti-stain, fire retardant, controlled release of drugs, detection of molecules and mechanical resistance. A variety of chemical synthesis techniques are usually employed to obtain novel nanostructured materials based on the use of an appropriate polymeric matrix in combination with either functional doping molecules or blended polymers, as well as multicomponent functional precursors and nanofillers. Further efforts are being made, as described in this review, to carry out green and eco-friendly synthetic protocols, such as sol-gel synthesis, starting from bio-based, natural or waste substances, in order to produce more sustainable (multi)functional hybrid or nanocomposite coatings, with a focus on their life cycle in accordance with the circular economy principles.

Spontaneous Patterning of Binary Ligand Mixtures on CdSe Nanocrystals: From Random to Janus Packing.

Binary compositions of surface ligands are known to improve the colloidal stability and fluorescence quantum yield of nanocrystals (NCs), due to ligand-ligand interactions and surface organization. Herein, we follow the thermodynamics of a ligand exchange reaction of CdSe NCs with alkylthiol mixtures. The effects of ligand polarity and length difference on ligand packing were investigated using isothermal titration calorimetry (ITC). The thermodynamic signature of the formation of mixed ligand shells was observed. Correlating the experimental results with thermodynamic mixing models has allowed us to calculate the interchain interactions and to infer the final ligand shell configuration. Our findings demonstrate that, in contrast to macroscopic surfaces, the small dimensions of the NCs and the subsequent increased interfacial region between dissimilar ligands allow the formation of a myriad of clustering patterns, controlled by the interligand interactions. This work provides a fundamental understanding of the parameters determining the ligand shell structure and should help guide smart surface design toward NC-based applications.

A replacement model to simulate the nonlinear dynamics of electro-responsive liquid crystal coatings

An electric circuit replacement model is proposed to simulate the key nonlinear dynamics of electro-responsive liquid crystal polymer networks (LCNs). LCNs are known for having great potential to be integrated into smart functional surfaces due to their ability to generate various surface patterns. However, due to their complex molecular dynamics, low-order dynamic models that can accurately describe and predict their dynamic behavior are still lacking. In light of this research gap, we develop a lumped-parameter replacement model based on the observed dynamics in the experimental data and the physics of LCN dielectric properties. The unique assembly of lumped parameters in its simplest form describes the transformation of a high-frequency input voltage to a relatively slow increase in the local height of the LCN coating in between the electrodes, serving as an excitation mechanism to induce height change. The nonlinear dynamics of this height increase, as a function of both excitation frequency and voltage, is described by the proposed model. Furthermore, the comparison of the simulation results with the experimental data from LCN shows that key LCN response characteristics are captured well by the model. This model makes it possible to accurately predict and control the response of the electro-responsive LCN surfaces to obtain a predefined desired deformation pattern, which is a vital requirement for integrating them in haptic and smart surface devices.

Hybrid Wetting Surface with Plasmonic Alloy Nanocomposites for Sensitive SERS Detection.

In this paper, a hybrid wetting surface (HWS) with Au/Ag alloy nanocomposites was proposed for rapid, cost-effective, stable and sensitive SERS application. This surface was fabricated in a large area by facile electrospinning, plasma etching and photomask-assisted sputtering processes. The high-density 'hot spots' and rough surface from plasmonic alloy nanocomposites promoted the significant enhancement of the electromagnetic field. Meanwhile, the condensation effects induced by HWS further improved the density of target analytes at the SERS active area. Thus, the SERS signals increased ~4 orders of magnitude compared to the normal SERS substrate. In addition, the reproducibility, uniformity, as well as thermal performance of HWS were also examined by comparative experiments, indicating their high reliability, portability and practicability for on-site tests. The efficient results suggested that this smart surface had great potential to evolve as a platform for advanced sensor-based applications.

Flexible Azo-Polyimide-Based Smart Surface with Photoregulatable Surface Micropatterns: Toward Rewritable Information Storage and Wrinkle-Free Device Fabrication

Stimulus-sensitive materials are of great fascination in surface and interface science owing to their dynamically tunable surface properties and/or morphologies. Herein, we have synthesized an azobenzene-containing polyimide (azo-PI) with enhanced chain flexibility for the fabrication of photosensitive surface patterns on a film/substrate wrinkle system or wrinkle-free devices. The phototriggered cis-trans isomerization kinetics of azobenzene groups in the novel azo-PI with various chain structures were systematically investigated. On the basis of the characteristics of stress relaxation that azobenzene reversible cis-trans isomerization induces in the wrinkled azo-PI film/substrate system, a variety of rewritable visual surface patterns with high resolution and a long legibility time (>30 days) could be easily constructed via visible-light irradiation, enabling the wrinkled azo-PI surfaces to be used as rewritable information storage media. Meanwhile, because of the visible-light irradiation strategy, these photoresponsive surfaces could find potential application in the fabrication of wrinkle-free flexible devices. This study not only sheds light on the influence of the azo-polymer chain structure on its photoresponsive behavior but also provides a versatile strategy for realizing tailor-made smart surface patterns on multilayer functional devices.

Study and Simulation of an Under-Actuated Smart Surface for Material Flow Handling

Smart surfaces are becoming more and more popular in the field of intralogistics, as they combine great flexibility with easy reprogrammability. Pursuing this trend, the following article proposes a modular surface to perform handling tasks, such as sorting, stopping, or slowing down material flows. Differently from the current technology, the surface used is under-actuated, thus, it exploits the speed, already possessed by the object, or the gravity to perform, with a simplified hardware, for the aforementioned tasks. In practice, these handling actions are completed using an array of rotors, of which only the direction of the rotation axis is controlled. Moreover, the axis can only assume certain discrete orientations in the plane, further simplifying the design. Thus, what is created is a controllable and under-actuated friction field, which, in contrast with similar existing systems, does not require active driving forces to manipulate the material flow. In the article, the analytic model of the surface is described, and a software simulation environment is introduced to demonstrate its functioning. In addition, examples of sorting, slowing down, and stopping operations and a validation of the simulation itself are presented.

Ultrafast response of self-powered humidity sensor of flexible graphene oxide film

Next-generation humidity sensor, as one of the smart devices in artificial skin or flexible electronics, will need to be self-powered, flexible, fast and accurately detecting in the microenvironment. Although various flexible humidity sensors have already been demonstrated, most of them rely on large external power sources to operate, and still suffer from slow response, poor selectivity in environmental stimuli, and expensive and complicated procedures. Here, we realize a self-powered humidity sensor with ultrafast response and recovery time of less than 0.3 s by flexible GO film. Importantly, of all state-of-the-art humidity sensors, this is the fastest response for humidity sensor. Moreover, the sensor has a high sensitivity within a wide range of RH from 33% to 98%, and an excellent selective response to humidity under multiple environmental stimuli, due to its moist-induced generator. Theoretical computations reveal that protons generated spontaneously from oxygen-containing groups and water molecules, have a fast diffusion behavior as Grotthuss hopping. In particular, we build four real-time measurement systems capable of respiration monitoring of human, smart leaf surface humidity sensor, and energy harvesting. Our work provides a simple way to fabricate next-generation self-powered sensor using GO film with outstanding humidity sensor performance.

Synthesis of multifunctional superwettable zinc nanoparticle with pH-bidirectional responsive for efficient emulsion separation

Smart pH-bidirectional responsive material has been presented based on zinc nanoparticles with smart surfaces adaptably transform wettability in mutual directions between the superhydrophobicity-superoleophilicity and the superhydrophilicity-underwater superoleophobicity depending on the pH. The smart material fabrication was prepared by immersing the fabric in AA-co-VTES-ZnO (composite A) and APTES-FOTS-ZnO (composite B) reactions. The material was synthesized by free radical polymerization. Characterization by FTIR, and SEM/EDX explained that the chemical compositions were uniformly distributed through the smart fabric surface caused by the strong chelating bond between the hydroxide, carboxylates, and silane active surfaces. The chemical stability, mechanical durability, and separation test results revealed selective separation efficiency for oil/water separation with efficacy ≥99 % and high satisfactory oil flux 7000–8000 L.h−1.m−2 and water flux (5500–6500 L.h−1.m−2). Moreover, the water contact angle (WCA) for neutral water was showing at 167° indicating powerful superhydrophobic properties, and for acidic/basic water was absorbing from 143/153° to 0° over time indicating superhydrophylic properties. Underwater treatment showed that the smart fabric has superoleophobic behavior with around 150° oil contact angle (OAC). Various weights and % NaCl immersion tests also have been applied for mechanical and chemical stability tests. The results displayed brilliant stability under severe conditions confirming great WCA after repeating and increasing mass and concentration. For oil removal and emulsion test, dyed oil was rapidly absorbed within 2 s and oil/water emulsions were easily separated by developed fabric with a good flux and separation efficacy of over 97 %. Interestingly, the prepared materials can also be efficiently and continuously separated for complicated oil/water/oil mixtures without particular treatment.

Study of Pressure Distribution in Floor Tiles with Printed P(VDF:TrFE) Sensors for Smart Surface Applications

Pressure sensors integrated in surfaces, such as the floor, can enable movement, event, and object detection with relatively little effort and without raising privacy concerns, such as video surveillance. Usually, this requires a distributed array of sensor pixels, whose design must be optimized according to the expected use case to reduce implementation costs while providing sufficient sensitivity. In this work, we present an unobtrusive smart floor concept based on floor tiles equipped with a printed piezoelectric sensor matrix. The sensor element adds less than 130 µm in thickness to the floor tile and offers a pressure sensitivity of 36 pC/N for a 1 cm2 pixel size. A floor model was established to simulate how the localized pressure excitation acting on the floor spreads into the sensor layer, where the error is only 1.5%. The model is valuable for optimizing the pixel density and arrangement for event and object detection while considering the smart floor implementation in buildings. Finally, a demonstration, including wireless connection to the computer, is presented, showing the viability of the tile to detect finger touch or movement of a metallic rod.