Interdigitated Electrodes Research Articles

Spectral line confocal sensor signal analysis and correction: Unlocking reflectance difference sample measurements

Spectral line confocal imaging (LCI) technology enables high-resolution, rapid 3D surface morphology analysis of transparent materials and other samples, positioning it as a leading optical measurement tool. Nevertheless, where the sensor measures samples with significant variations in surface reflectance, the peak signals of the acquired images exhibit low signal-to-noise ratios or become distorted, hampering the peak extraction algorithm from accurately locating their peak positions. Consequently, it's arduous to reconstruct their precise surface topography. To enhance the sensor's dynamic measurement range and adaptability, this paper introduces an adaptive correction approach. It utilizes a regularized non-negative matrix to decompose images with various grey levels. This is followed by weighted frequency filtering and Gaussian enhancement of all the grey layers. Eventually, these layers are fused into one image with high contrast and uniformity. Using this approach, the sensor is capable of achieving precise 3D reconstruction with high-quality peak signals. Additionally, this study experimentally demonstrates the efficacy of the suggested approach by measuring the interdigital electrode and printed circuit boards (PCB). It should be noted that the technique presented in this paper is not limited to spectral line confocal instruments and is also effective for line laser and line structured light instruments.

Achieving Mode Detection and Precise Mechanical Trimming of Uncoated Micro Shell Resonator Using Interdigital Electrode

Achieving Mode Detection and Precise Mechanical Trimming of Uncoated Micro Shell Resonator Using Interdigital Electrode

Wireless Flexible System for Highly Sensitive Ammonia Detection Based on Polyaniline/Carbon Nanotubes.

Ammonia (NH3) is a harmful atmospheric pollutant and an important indicator of environment, health, and food safety conditions. Wearable devices with flexible gas sensors offer convenient real-time NH3 monitoring capabilities. A flexible ammonia gas sensing system to support the internet of things (IoT) is proposed. The flexible gas sensor in this system utilizes polyaniline (PANI) with multiwall carbon nanotubes (MWCNTs) decoration as a sensitive material, coated on a silver interdigital electrode on a polyethylene terephthalate (PET) substrate. Gas sensors are combined with other electronic components to form a flexible electronic system. The IoT functionality of the system comes from a microcontroller with Wi-Fi capability. The flexible gas sensor demonstrates commendable sensitivity, selectivity, humidity resistance, and long lifespan. The experimental data procured from the sensor reveal a remarkably low detection threshold of 0.3 ppm, aligning well with the required specifications for monitoring ammonia concentrations in exhaled breath gas, which typically range from 0.425 to 1.8 ppm. Furthermore, the sensor demonstrates a negligible reaction to the presence of interfering gases, such as ethanol, acetone, and methanol, thereby ensuring high selectivity for ammonia detection. In addition to these attributes, the sensor maintains consistent stability across a range of environmental conditions, including varying humidity levels, repeated bending cycles, and diverse angles of orientation. A portable, stable, and effective flexible IoT system solution for real-time ammonia sensing is demonstrated by collecting data at the edge end, processing the data in the cloud, and displaying the data at the user end.

Sensitivity studies and optimization of an impedance-based biosensor for point-of-care applications

In this study, we examined the relationship between the sensitivity of interdigitated electrode (IDE) impedimetric biosensors and the gap between the IDEs. Our aim is to find an optimal design to maximize sensitivity. A three-dimensional COMSOL model was constructed for determining the effects of electrode gap, width, and height on impedance sensitivity, revealing a singular linear correlation with the inner gap. Considering both the simulation results and fabrication processes, we have developed three IDE prototype chips with electrode gaps of 3 μm, 4 μm, and 5 μm, respectively. For empirical validation, human anti-SARS-CoV-2 monoclonal antibody (mAb) was utilized, with immobilization of the SARS-CoV-2 spike protein on the chip's surface for mAb capture. This interaction, further amplified by Protein G conjugation, induced shifts in the impedance spectrum. The sensitivity of each prototype chip was evaluated across mAb concentrations ranging from 50 ng/mL to 500 ng/mL. The 3 μm configuration emerged as the most sensitive, demonstrating the ability to detect mAb concentrations as low as 50 ng/mL, a threshold unattainable by the other designs. This outcome underscores the critical influence of reduced inter-electrode gap on enhancing biosensor detection limits. The findings from this investigation offer a foundational approach for advancing biosensor sensitivity via electrode geometric optimization, with broad potential applications extending beyond COVID-19 diagnostics to a wide spectrum of clinical and research contexts.

Split-ring resonator with interdigital Split electrodes as detector for liquid and ion chromatography

The analysis of food and drugs as well as the monitoring of chemical processes and bioreactors by high-performance liquid chromatography and ion chromatography requires universal, cost-effective, and sensitive detectors. Therefore, this work presents a split-ring resonator that detects changes in the electrical and dielectric properties of the eluate from liquid chromatography or ion chromatography by monitoring the amplitude of the transmitted signal using an envelope detector. The used split-ring resonator consists of a simple printed circuit board featuring two microstrip lines. One is formed to a ring with interdigital split electrodes. The interdigital split electrodes forming the sensitive area significantly enhance the sensitivity to changes in relative permittivity, dielectric losses and electrical conductivity of the eluate In addition, the split-ring resonator is a small, inexpensive and easy-to-use detector that uses several dielectric parameters simultaneously for the measurement. Furthermore, the split-ring resonator measures these parameters at a significantly lower frequency than optical detectors and therefore measures different changes in frequency-dependent permittivity. For demonstrating feasibility of a split-ring resonator as a detector for high-performance liquid chromatography and ion chromatography, various anion and cation standards, basic and acidic amino acids, sugars, as well as sugar alcohols were separated and detected. A conductivity detector for ion chromatography and a refractive index detector for high-performance liquid chromatography were used as reference detectors.

A Simple and Sensitive Approach for Real‐Time Sensing of Enzymatically Catalyzed Hydrogelation

AbstractDespite the critical role of hydrogels in material science and biotechnology, current methods for analyzing their formation lack real‐time monitoring and require complex sample preparation and instrumentation. In this work, an innovative methodology is introduced for the real‐time analysis of enzymatically catalyzed hydrogelation. Electrochemical impedance spectroscopy (EIS) coupled with interdigitated electrodes (IDEs) to sense and transduce the gelation reaction of model precursor carboxymethyl cellulose‐tyramine (CMC‐TA) conjugates that undergoes enzymatic cross‐linking by horseradish peroxidase (HRP) and hydrogen peroxide (H2O2). Real‐time monitoring involves single‐frequency analyses at 3 × 105 Hz, where the measured impedance consists solely of a resistive component, and the admittance equates to solution conductance. The gelation trajectories for all tested enzymatically cross‐linked hydrogel component combinations are determined by substituting the conductance data in the modified Michaelis–Menten kinetic model. Specifically, for CMC‐TA cross‐linked by HRP, the authors calculate apparent KM and kcat values of 82.1 µM and 95.5 s−1, respectively. These findings are further validated through rheological characterization, including oscillatory shear measurements and microrheology. Overall, this research paves the way for a streamlined, accurate, and cost‐effective approach to controllable enzymatically initiated hydrogel synthesis, enhancing their successful application in various fields ranging from material science to biotechnology.

Origin of near-failure in Au contacts to polycrystalline β-Ga2O3 at high temperatures using interfacial studies

Suitable contacts to gallium oxide are a controversial topic with contact behavior depending heavily on the pre- and post-processing conditions. Especially for the extreme environment applications such as those involving high temperatures, contact chemistry is varied and severely lacks understanding. Herein, we report on conventional pure Au contacts to polycrystalline β-Ga2O3, used as Schottky contacts, and explore the origin of their near-failure at high temperature up to 850 °C. For this purpose, β-Ga2O3 with Au interdigitated electrodes is subjected to high temperature annealing and their interface chemistry is studied and correlated with device performance for solar-blind photodetection. Around the optimized temperature of 450 °C, the performance of the PDs is found to be maximum, whereas it reduces drastically at 850 °C. Physical damage to the electrodes along with the formation of intermetallic gold-gallium alloy is observed via XPS depth profile studies and found to be the reason for the near-failure of device at extreme conditions. Although the alloy formation begins to slightly appear at 650 °C and reduces the performance, still it does not lead to device breakdown. This study proves that unlike its counterparts GaN and GaAs, which have reported alloy formation at lower temperatures, β-Ga2O3 shows a higher resilience to the formation of Au–Ga alloy and can withstand higher temperatures before the actual device failure is reached. The proposed study shows the stability of standard metal contacts to Ga2O3 based devices, which have far-reaching implications for the future commercialization of wideband gap semiconductor based (opto)electronics.

BacteSign: Building a Findable, Accessible, Interoperable, and Reusable (FAIR) Database for Universal Bacterial Identification.

With the increasing incidence of diverse global bacterial outbreaks, it is important to build an immutable decentralized database that can capture regional changes in bacterial resistance with time. Herein, we investigate the use of a rapid 3D printed µbiochamber with a laser-ablated interdigitated electrode developed for biofilm analysis of Pseudomonas aeruginosa, Acinetobacter baumannii and Bacillus subtilis using electrochemical biological impedance spectroscopy (EBIS) across a 48 h spectrum, along with novel ladder-based minimum inhibitory concentration (MIC) stencil tests against oxytetracycline, kanamycin, penicillin G and streptomycin. Furthermore, in this investigation, a search query database has been built demonstrating the deterministic nature of the bacterial strains with real and imaginary impedance, phase, and capacitance, showing increased bacterial specification selectivity in the 9772.37 Hz range.

Analysis of excitation and detection capability of hemispherical resonator based on interdigital electrodes

In this paper, a theoretical model of excitation and detection is established based on the excitation and detection method of the uncoated hemispherical resonator with interdigital electrodes, which proves the feasibility of the excitation and detection of the interdigital electrodes in principle. The simulation and analysis of its influence parameters are also carried out to provide theoretical support for the design and optimization of the interdigital electrode to realize the excitation and detection of the hemispherical resonator. Finally, the excitation and detection of uncoated hemispherical resonators by interdigital electrodes were successfully verified through experiments.

Study of the interdigital electrode sensor at resonance frequency during water transition

This paper uses the co-planar interdigital electrode (IDE) sensor to measure water level. The researchers generally characterize the interdigital electrode sensor as a fringe field capacitor sensor developed on the printed circuit board and utilize the capacitor sensor's properties for liquid-level measurement. The interdigital electrode sensors illustrate more than one resonance at the higher frequencies, and in this study, the first resonance frequency fr -has been utilized for the water level measurement. Three water types are examined here: distilled, tap, and river. The study assesses that with the transition of water, the permittivity between the electrodes is changed and, it leads to a change in capacitance hence, the change in resonance frequency was observed. The proposed sensor can be represented by the lumped element equivalent series RLC circuit. The developed IDE sensor has good repeatability, small variability, and small hysteresis error. The maximum standard error for distilled, tap, and river water are 0.02833, 0.02503, and 0.02618, respectively, and the hysteresis error is less than 1.903% of full-scale output variation. The maximum error for the fr estimation is about ±2 Hz.

Enhanced performance of γ-In2Se3 photodetector on ITO-coated interdigital electrodes fabricated via RF-magnetron sputtering

Enhanced performance of γ-In2Se3 photodetector on ITO-coated interdigital electrodes fabricated via RF-magnetron sputtering

Synthesis of PANIHCl/ZnO conductive composite by in-situ polymerization and for humidity sensing application

In this study, the conductive polyaniline doped by hydrochloric acid (PANIHCl)/zinc oxide (PANIHCl/ZnO) conductive composite was synthesized by in-situ polymerization. The conductive PANIHCl solution or PANIHCl/ZnO conductive composite solution was coated on an interdigital electrode (IDE) by drop coating to make a humidity sensor. The synthesis process, chemical structure, surface morphology, and humidity sensing characteristics of PANIHCl and PANIHCl/ZnO conductive composite were investigated. Field emission scanning electron microscope (FE-SEM) images suggested that the surface morphology of the PANIHCl/ZnO conductive composite is fibrous or rod-shaped, with a diameter of about 100 nm. The sensing responses of PANIHCl and PANIHCl/ZnO were 40% and 87%, respectively. The humidity sensing response of PANIHCl/ZnO as the sensing material was more than twice that of PANIHCl as the sensing material. The response time (Tres) is 13 s, and the recovery time (Trec) is 171 s. Research results showed that adding ZnO to PANIHCl can effectively improve the response of the sensor to humidity detection. Therefore, using PANIHCl/ZnO conductive composite as a sensing material will have great potential for application in humidity or other gas sensing devices.

Low-salt organohydrogel electrolytes for wide-potential-window flexible all-solid-state supercapacitors

Flexible supercapacitors have received increasing attention due to their high power density, long cycle life and excellent safety, however, their limited energy density restrains their practical applications. Here, a designed organohydrogel electrolyte strategy boosted the electrochemical potential window (ESW) for flexible all-solid supercapacitor was demonstrated, by which a record-high ESW of 5 V is achieved, accompanied by improved cyclic stability and wider temperature adaptability. Hydrogen-bond of water to DMSO was found to be competitive with cationic hydration, and a wide ESW was achieved at lower salt and DMSO concentrations. DMSO-H2O/alginate/PAAm hydrogel electrolytes were prepared by simple solvent exchange, and it was found that the synergistic interactions between DMSO, water and hydrogel significantly reduced water activity in the hydrogel and realized the high ESW. Moreover, Dimethyl sulfoxide forms abundant hydrogen bonds with water and the hydrogel skeleton, which significantly improves the mechanical properties, freezing resistance, and temperature adaptability of the hydrogel electrolyte. The flexible all-solid-state supercapacitor assembled based on DMSO-H2O/alginate/PAAm hydrogel electrolyte and interdigital electrodes exhibits 2.4 V ESW, stability under different folding angles, adaptability to different temperatures ranging from −20 to 70 °C, and integration performance. The device demonstrates excellent cycling stability and retains 98.66% of capacitance after 10,000 cycles, suggesting that it has the potential to meet the requirements of flexible electronics.

Rationally engineered interdigitated electrodes with heteroatom doped porous graphene and improved surface wettability for flexible micro-supercapacitors

Micro-supercapacitors (mSCs) are crucial components for the miniaturization of electronic devices and the growing demand for portable, wearable, and Internet-of-things (IoT) technology. Among these, electric double-layer mSCs (EDL mSCs) stand out with their rapid charge/discharge capability and extended lifespan. Porous graphene structure has been utilized to EDL-mSCs due to their compatibility with various substrates and ease of integration. However, methods to increase the performance of the EDL-mSCs based on the porous graphene electrode needs to be considered to achieve high performance flexible mSCs. In this study, we introduce rationally designed, heteroatom doped porous graphene electrodes, incorporating highly electrochemical active nitrogen sites (such as pyrrolic-, pyridinic-, and graphitic-N sites), that greatly enhances the performance of the flexible mSCs. The method involves directly laser scribing polyimide film coated with a phthalocyanine-based dopant, resulting in a remarkable 254 % increase in capacitance and an impressive volumetric energy density of 2.5 mWh cm−3 compared pristine EDL-mSC. This heteroatom-doping strategy improves conductivity and surface wettability and creates more active sites for specific capacitance. Additionally, the heteroatom-doped mSCs exhibit excellent capacitance retention under strain and bending tests, demonstrating their suitability for practical circuit applications. This work offers a simple and effective approach to design flexible and high-performance mSCs, meeting the energy-storage demands of modern electronics and IoT devices.

Modeling and analysis of a macro-fiber piezoelectric bimorph energy harvester operating in d33-Mode using Timoshenko theory

Piezoelectric bimorph cantilevered beams are frequently employed in energy harvesting applications. The use of macro-fiber composites, which combine piezoelectric fibers with rectangular cross-sections and interdigitated electrodes, has significantly enhanced their performance by enabling operation in the 33-mode of piezoelectricity, thereby increasing conversion efficiency. In this article, the Timoshenko beam theory is applied to overcome the limitations of the Euler-Bernoulli theory in modeling transverse vibrations of harvesters with low slenderness ratios (length to thickness ratios). The mixture rule formulation is applied to determine the equivalent properties of the macro-fiber composite (MFC) structure. The electromechanical properties of a representative volume element (RVE) bounded by two successive interdigitated electrodes are coupled to the overall electro-elastic dynamic model of the structure using the Timoshenko theory. Frequency response functions for the power and tip vibration displacement of the MFC bimorph beam are determined from the model. Experimental data from the literature are used to validate the improved results predicted by the model developed in this article. A comparative analysis between the electromechanical responses predicted using a model based on Timoshenko and a model based on Euler-Bernoulli theory is conducted showing agreement, for harvesters with large slenderness ratios and discrepancies of up to 30% for low slenderness ratios. It has also been shown that the model based on Euler-Bernoulli theory overestimates both the mechanical and the electrical responses for low slenderness ratios as the shear and rotary inertia effects are not negligible in this case.

Highly reversible extrinsic electrocaloric effects over a wide temperature range in epitaxially strained SrTiO3 films

Electrocaloric effects have been experimentally studied in ferroelectrics and incipient ferroelectrics, but not incipient ferroelectrics driven ferroelectric using strain. Here we use optimally oriented interdigitated surface electrodes to investigate extrinsic electrocaloric effects in low-loss epitaxial SrTiO3 films near the broad second-order 243 K ferroelectric phase transition created by biaxial in-plane coherent tensile strain from DyScO3 substrates. Our extrinsic electrocaloric effects are an order of magnitude larger than the corresponding effects in bulk SrTiO3 over a wide range of temperatures including room temperature, and unlike electrocaloric effects associated with first-order transitions they are highly reversible in unipolar applied fields. Additionally, the canonical Landau description for strained SrTiO3 films works well if we set the low-temperature zero-field polarization along one of the in-plane pseudocubic <100> directions. In future, similar strain engineering could be exploited for other films, multilayers and bulk samples to increase the range of electrocaloric materials for energy efficient cooling.

Highly sensitive screen-printed soil moisture sensor array as green solutions for sustainable precision agriculture

Monitoring soil moisture in real-time is an important parameter that helps farmers decide to enhance agriculture productivity and reduce resource wastage for better production and plant growth. In this work, we presented an easy-to-use and highly sensitive screen-printed flexible soil moisture sensor array to monitor soil moisture remotely for precision agriculture. The proposed sensor is based on a unique interdigitated electrode (IDE)-based capacitive structure with conductive carbon ink printed on a flexible polyethylene terephthalate (PET) substrate using the screen printing technique. Before soil moisture monitoring, the sensor is tested for humidity monitoring in an environmental chamber. A response of ∼144–1760 pF for 20–100%RH with 10%RH variation is observed for a single sensor, while an array configuration ranges from ∼127–1802 pF. The sensor response is observed for a temperature range from 20 to 50 ‘C. The sensor's sensitivity for relative humidity sensing is 19.123%pF/RH, and the response and recovery time are ∼3.3 s and ∼4.2 s. Further, the sensor is tested for soil moisture sensing, as moisture content is gradually added to the completely dry soil. A highly sensitive response for soil moisture content (MC) with a ∼40.7%pF/MC sensitivity is obtained. The sensor data is transmitted wirelessly using a Bluetooth module. The sensor is supported by a wooden stick, which illustrates the capabilities of biodegradability, the sensor is cost-effective and provides a real-time measurement for soil moisture. The sensors have the potential to provide maintenance-free monitoring, facilitating precise control of irrigation practices in precision agriculture. With their affordability and ability to operate on a large scale, the sensor offers promising opportunities for enhancing irrigation systems.

A crosstalk-free interdigital electrode piezoresistive sensor matrix-based human-machine interaction system for automatic sitting posture recognition

Sedentarism with poor posture has been a significant concern for students and office workers. In this work, for inappropriate sitting posture monitoring, we developed a human machine interaction (HMI) system based on a piezoresistive sensor matrix, which achieves crosstalk-free pressure distribution detection by the inserting diodes method (IDM) with a structure simplified by the interdigital electrode (IDE) configuration. To measure the pressure distribution, a sensor matrix of 9×14 piezoresistive sensing pixels is fabricated by the standard flexible printed circuit (FPC) technique. The single sensing pixel shows a high sensitivity in the pressure below 20 kPa, covering the range of the human-seat contact pressure, and demonstrates the highest sensitivity of 9.865% kPa−1. The combination of the IDE and the IDM eliminates the crosstalk error completely, enabling the sensor matrix to accurately measure the human-chair contact pressure distribution. To develop an HMI system for sitting posture detection, pressure distribution data from subjects of different body shapes, including sitting upright, leaning forward, slumped sitting, crossing right legs, and crossing left legs, is collected using the proposed sensor matrix and used for training and evaluation of the convolution neural network (CNN) model. Accurate posture classification is achieved both in within-group and cross-group tests, showing the highest accuracy of 99.14% and an excellent generalization performance. With an excellent performance of crosstalk-free pressure distribution detection, the device in this study exhibits great application potential in daily sitting posture monitoring.

Deformable micro-supercapacitor fabricated via laser ablation patterning of Graphene/liquid metal

Deformable and miniaturized energy storage devices are essential for powering soft electronics. Herein, we fabricate deformable micro supercapacitors (MSCs) based on eutectic gallium-indium liquid metal (EGaIn) current collectors with integrated graphene. The well-define interdigitated electrode patterning with controlled gap is successfully realized by using the laser ablation because of a strong laser absorption of graphene and EGaIn. By judicious control of gap size between neighboring interdigitated electrodes and mass loading of graphene, we achieve a high areal capacitance (1336 µF cm−2) with reliable rate performance. In addition, owing to the intrinsic liquid characteristics of EGaIn current collector, the areal capacitance of fabricated MSC retains 90% of original value even after repetitive folding and 20% stretching up to 1000 cycles. Finally, we successfully integrate deformable MSC with a commercial light-emitting diode to demonstrate the feasibility of MSC as a deformable power source. The fabricated MSCs operate stably under various mechanical deformations, including stretching, folding, twisting, and wrinkling.

MXene-based high performance microfluidic pH sensors for electronic tongue

The development of the electronic tongue (e-tongue) significantly relies on the monitoring of taste-inducing molecules and ions in solutions. One of the five primary flavors, sourness, has a direct correlation with pH measurement, making it essential for food assessment. However, real-time food evaluation is constrained by the high cost and limited portability of conventional taste sensors. Ti3C2 MXene is remarkable in the field of two-dimensional (2D) materials for its abundance of functional groups and metallic conductivity. These characteristics contribute to its enormous potential as a material for the fabrication of taste sensors with high sensitivity. This study presents the fabrication and application of reliable and reversible pH sensors based on 2D Ti3C2 MXene for the first time. By integrating a microfluidic channel with interdigitated electrodes (IDEs) and a Nafion layer, the sensors exhibit high selectivity for real-time detection of hydronium ions with the MXene channel. Differentiating soft drinks and evaluating the fermentation of Kimchi are demonstrated. Our work on a low-cost, high-performance MXene-based sensor will pave the way for the future of e-tongue development.