Electrical Signals In Response Research Articles

Multifunctional Meta-Tribomaterial Nanogenerators for Energy Harvesting and Active Sensing.

Discovering novel multifunctional metamaterials with energy harvesting and sensing functionalities is likely to be the next technological evolution of the metamaterial science. Here, we introduce a novel concept called self-aware composite mechanical metamaterial (SCMM) that can transform mechanical metamaterials into nanogenerators and active sensing mediums. In pursuit of this goal, we examine new paradigms where finely tailored and seamlessly integrated self-recovering snapping microstructures composed of topologically different triboelectric materials can form self-powering and self-sensing meta-tribomaterial systems. We explore various deformation mechanisms required to induce contact electrification between these snapping microstructures under periodic deformations. The multifunctional meta-tribomaterial systems created under the SCMM concept will act as triboelectric nanogenerators capable of generating electrical signals in response to the applied mechanical excitations. The generated electrical signal can be used for active sensing of the applied force and can be stored for empowering sensors and embedded electronics. We conduct theoretical and experimental studies to understand the mechanical and electrical behavior of the multifunctional SCMM systems. The broad application of the proposed SCMM concept for designing artificial materials with novel properties and functionalities is highlighted via prototyping self-powering and self-sensing blood vessel stents and shock absorbers.

Triboelectric and Piezoelectric Nanogenerators for Future Soft Robots and Machines.

SummaryThe triboelectric nanogenerator (TENG) and piezoelectric nanogenerator (PENG) are two recently developed technologies for effective harvesting of ambient mechanical energy for the creation of self-powered systems. The advantages of TENGs and PENGs which include large open-circuit output voltage, low cost, ease of fabrication, and high conversion efficiency enable their application as new flexible sensors, wearable devices, soft robotics, and machines. This perspective provides an overview of the current state of the art in triboelectric and piezoelectric devices that are used as self-powered sensors and energy harvesters for soft robots and machines; hybrid approaches that combine the advantages of both mechanisms are also discussed. To improve system performance and efficiency, the potential of providing self-powered soft systems with a degree of multifunctionality is investigated. This includes optical sensing, transparency, self-healing, water resistance, photo-luminescence, or an ability to operate in hostile environments such as low temperature, high humidity, or high strain/stretch. Finally, areas for future research directions are identified.

Inkjet-printed Ti3C2Tx MXene electrodes for multimodal cutaneous biosensing

Among the existing two-dimensional materials, MXenes, i.e. transition metal carbides, nitrides and/or carbonitrides, stand out for their excellent electrochemical properties. Due to their high charge storage capacity, metal-like conductivity, biocompatibility as well as hydrophilicity, Ti3C2Tx MXene-based inks hold great potential for scalable production of skin conformable electronics via direct printing methods. Herein, we develop an aqueous MXene ink and inkjet-print MXene films on freestanding, flexible, and conducting polymer-based substrates. These skin-adherent MXene electrodes detect electrocardiography signals with high signal-to-noise ratio while exhibiting preserved electrical performance after 1000 cycles of bending with a 50 d long shelf life in ambient conditions. We show that printed MXene films can be further functionalized to perform as multifunctional biosensing units. When integrated with a sodium (Na+) ion selective membrane, MXene electrodes detect Na+ in artificial sweat with a sensitivity of 40 mV per decade. When the films are functionalized with antibodies, they generate an electrical signal in response to a pro-inflammatory cytokine protein (interferon gamma) with a sensitivity of 3.9 mV per decade. Our findings demonstrate how inkjet-printed MXene films simplify the fabrication of next-generation wearable electronic platforms that comprise multimodal sensors.

Origin of electric field response signals in gate modulation spectroscopy for organic field effect transistors

Although gate modulation (GM) spectroscopy performed by combining optical measurements with gate bias application in a field effect transistor (FET) is one of the most straightforward techniques for electronic state evaluation of operating FETs, the origin of the spectral response to the gate bias application has not been fully elucidated. We here address the origin of the GM signals from variety of GM spectroscopic techniques performed for pentacene-based organic FETs. The GM spectrum under the negative gate bias in the condition that the source and drain electrodes are short-circuited exhibits a complicated lineshape with many unresolved peaks. We demonstrate that the GM signal under FET driving condition with drain bias applied is dominated by second-derivative (SD) Stark signals. From the comparison of the first and second harmonic response GM signals, the SD-Stark signal is found to be given by local electric fields from hole carriers injected from the electrodes, rather than given by an external electric field from the gate-bias. The SD signal intensity is enhanced when a high degree of molecular orientation exists around the carriers, thus the SD signal can be used to investigate molecular orientation around gate-induced carriers. • Gate bias application causes Stark signals as well as carrier signals in OFETs. • Gate modulation spectroscopy under drain bias applied is performed. • Stark signals arise from local electric field by injected hole carriers. • Molecular orientation around carriers can be examined by gate-induced Stark signals.

Enhancement of PVDF Sensing Characteristics by Retooling the Near-Field Direct-Write Electrospinning System.

This research aimed to develop a direct-write near-field electrospinning system (DW-NFES) with three-axis positioning of controllable speed, torque and position to produce sizable and high-quality piezoelectric fibers for sensing purposes. Sensor devices with high electrical response signals were developed and tested. To achieve DW-NFES purpose, a servo motor controller was designed to develop a high response rate, accurate positioning, and stable mobile device through the calculation of bandwidth and system time delay. With this retooled system of DW-NFES, controllable and uniform size fibers in terms of diameters, stretching force, and interspaces can be obtained. Sensor devices can be made selectively without a complicated lithography process. The characteristics of this DW-NFES platform were featured by high response rate, accurate positioning, and stable movement to make fibers with high piezoelectric property. In this study, polyvinylidene fluoride (PVDF) was used to explore and enhance their sensing quality through the platform. The parametric study of the process factors on piezoelectric sensing signals mainly included the concentration of electrospinning PVDF solution, high voltage electric field, and collection speed. Finally, the surface morphology and piezoelectric properties of the as-electrospun PVDF fibers were examined by scanning electron microscopy (SEM) and characterized by electrical response measurement techniques. The results showed that the fiber spinning speed of the DW-NFES system could be increased to ~125 from ~20 mm/s and the accuracy precision was improved to ~1 from ~50 μm, compared to conventional step motor system. The fiber diameter reached ~10 μm, and the electrospinning pitch reached to as small as ~10 μm. The piezoelectric output voltage of the electrospun fibers was increased ~28.6% from ~97.2 to ~125 mV; the current was increased ~27.6% from ~163 to ~208 nA, suggesting that the piezoelectric signals can be enhanced significantly by using this retooled system. Finally, an external control module (Arduino-MAGE) was introduced to control the PVDF piezoelectric fiber sensors integrated as a sensing array. The behavior of long-term sedentary patients can be successfully detected by this module system to prevent the patients from the bedsores.

The effect of an ultrasound-activated needle tip tracker needle on the performance of sciatic nerve block on a soft embalmed Thiel cadaver.

In this study, we measured the performance of medical students and anaesthetists using a new tracker needle during simulated sciatic nerve block on soft embalmed cadavers. The tracker needle incorporates a piezo element near its tip that generates an electrical signal in response to insonation. A circle, superimposed on the ultrasound image surrounding the needle tip, changes size and colour according to the position of the piezo element within the ultrasound beam. Our primary objective was to compare sciatic block performance with the tracker switched on and off. Our secondary objectives were to record psychometrics, procedure efficiency, participant self-regulation and focused attention using eye-tracking technology. Our primary outcome measures were the number of steps successfully performed and the number of errors committed during each block. Videos were scored by trained experts using validated checklists. Sequential tracker activation and deactivation was randomised equally within subjects. With needle activation, steps improved in 10 (25%) subjects and errors reduced in six (15%) subjects. The most important steps were: needle tip identification before injection, OR (95%CI) 2.12 (1.61-2.80; p<0.001); and needle tip identification before advance of the needle, 1.80 (1.36-2.39; p<0.001). The most important errors were: failure to identify the needle tip before injection, 2.40 (1.78-3.24; p<0.001); and failure to quickly regain needle tip position when tip visibility was lost, 2.03 (1.5-2.75; p<0.001). In conclusion, needle-tracking technology improved performance in a quarter of subjects.

Advances in Healthcare Electronics Enabled by Triboelectric Nanogenerators

AbstractThe treatment, diagnosis, and monitoring of diseases have attracted more and more attention in recent years. Healthcare electronics help effectively treat and real‐time monitor diseases. Triboelectric nanogenerators (TENGs) show great potential for healthcare applications because of their superiority including low cost, flexible structures, and self‐powered property. Herein, the recent key advancements in TENG‐based healthcare applications are comprehensively reviewed. TENGs could not only harvest the mechanical energy from the body to make electrical stimulation but also generate different electrical signals in response to external stimuli. Integrated systems combined with TENGs and other sensors could also promote sensing stability. The materials, structures, working mechanisms, and performance of each application are discussed. The existing limitations and prospects for further TENG‐based healthcare are finally put forward.

High loading cotton cellulose-based aerogel self-standing electrode for Li-S batteries

Lithium-sulfur (Li-S) batteries have attracted considerable attention due to their high energy density (2600 Wh kg−1). However, its commercialization is hindered seriously by the low loading and utilization rate of sulfur cathodes. Herein, we designed the cellulose-based graphene carbon composite aerogel (CCA) self-standing electrode to enhance the performance of Li-S batteries. The CCA contributes to the mass loading and utilization efficiency of sulfur, because of its unique physical structure: low density (0.018 g cm−3), large specific surface area (657.85 m2 g−1), high porosity (96%), and remarkable electrolyte adsorption (42.25 times). Compared to Al (about 49%), the CCA displayed excellent sulfur use efficiency (86%) and could reach to high area capacity of 8.60 mAh cm−2 with 9.11 mg S loading. Meanwhile, the CCA exhibits the excellent potential for pulse sensing applications due to its flexibility and superior sensitivity to electrical response signals.

Electrode System Analysis for Bioimpedance Cardiac Diagnosis

Electrodes and their placement play a vital role in medical diagnosis. Electrical signal in human body such as ECG, EEG and EMG etc., are the critical diagnosis parameter. Measurements of such signals are obtained by proper selection of electrode and their placement on human body surface. Electrical bioimpedance diagnoses used to detect various disorders are critically depends on type of the electrodes used and their position. In impedance measurements two electrodes are used to send electrical signal and minimum two electrodes to pick the electrical signal response on tissues in terms of voltage across two terminals. In this paper different electrode systems used for bioimpedance cardiac monitoring are analyzed based on the type of electrodes used, location of electrodes in human body and positioning of electrodes in specific location.

Preparation of Electrode Modified with Methanobactin Functionalized Gold Nanoparticle and Mimic Superoxide Dismutase Activity.

Using a mixed self-assembly method, this research utilized modified Mb-functionalized gold nanoparticles (Mb-AuNPs-MPA) on the gold electrode surface to prepare a biosensor which was applied to detect superoxide anion-free electron mediators. Together with the study on the performance of the sensor, the characteristics of modified nanoclusters were investigated by UV-Vis and FTIR and the electrochemical characteristics of the electrode surface were investigated using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV), respectively. It was demonstrated that the charge transfer resistance (Rct) of the modified electrode (Mb-MPA-AuNPs/Au) was 7862 Ω, the exchange current density (i0) was 32.7 μA/cm-2. And a pair of reversible and symmetrical redox peaks appeared after the coordination of Cu2+, and the electrical signal response of Cu2+/Mb-AuNPs-MPA/Au reached the highest. The superoxide anion generated in the basic DMSO system was determined by CV using the modified electrode Cu2+/Mb-AuNPs-MPA/Au. It was discovered that the superoxide anion had a strong disproportionation effect.

Anaesthesia with diethyl ether impairs jasmonate signalling in the carnivorous plant Venus flytrap (Dionaea muscipula).

General anaesthetics are compounds that induce loss of responsiveness to environmental stimuli in animals and humans. The primary site of action of general anaesthetics is the nervous system, where anaesthetics inhibit neuronal transmission. Although plants do not have neurons, they generate electrical signals in response to biotic and abiotic stresses. Here, we investigated the effect of the general volatile anaesthetic diethyl ether on the ability to sense potential prey or herbivore attacks in the carnivorous plant Venus flytrap (Dionaea muscipula). We monitored trap movement, electrical signalling, phytohormone accumulation and gene expression in response to the mechanical stimulation of trigger hairs and wounding under diethyl ether treatment. Diethyl ether completely inhibited the generation of action potentials and trap closing reactions, which were easily and rapidly restored when the anaesthetic was removed. Diethyl ether also inhibited the later response: jasmonic acid (JA) accumulation and expression of JA-responsive genes (cysteine protease dionain and type I chitinase). However, external application of JA bypassed the inhibited action potentials and restored gene expression under diethyl ether anaesthesia, indicating that downstream reactions from JA are not inhibited. The Venus flytrap cannot sense prey or a herbivore attack under diethyl ether treatment caused by inhibited action potentials, and the JA signalling pathway as a consequence.

Ratiometric electrochemical sensor for sensitive detection of sunset yellow based on three-dimensional polyethyleneimine functionalized reduced graphene oxide aerogels@Au nanoparticles/SH-β-cyclodextrin

Electrochemical methods have been deemed effective strategies for the detection of dye additive sunset yellow (SY) owing to their low cost, good stability, and high sensitivity. However, the application of the existing sensors with single electrical signal response is limited by their inadequate sensitivity and large background interference. Herein, a ratiometric electrochemical strategy with a dual signal was developed to detect SY. The strategy had an intrinsic built-in correction to the effects from the system, and thus reduced the influence of environmental change. 3D polyethyleneimine functionalized reduced graphene oxide aerogels@Au nanoparticles/SH-β-cyclodextrin (PEI-rGAs@AuNPs/SH-β-CD) was used as the sensing material due to its 3D macroporous microstructure with high specific surface area and excellent electronic conductivity. Guest molecule methylene blue (MB) was chosen as a probe molecule, which formed an inclusion host–guest complex with a SH-β-CD host in advance. The target molecule SY displaced MB from the CD cavities, resulting in the decrease of MB current and the increase of SY current. With the logarithmic value of ISY/IMB as the readout signal, the detection limit of the developed ratiometric electrochemical sensor reached as low as 0.3 nM, confirming the excellent sensitivity. Furthermore, this strategy exhibited good selectivity and repeatability, and could be used for the detection of SY in a real sample.

Real-time strain monitoring and damage detection of composites in different directions of the applied load using a microscale flexible Nylon/Ag strain sensor

Composites are prone to failure during operating conditions and that is why vast research studies have been carried out to develop in situ sensors and monitoring systems to avoid their catastrophic failure and repairing cost. The aim of this research article was to develop a flexible strain sensor wire for real-time monitoring and damage detection in the composites when subjected to operational loads. This flexible strain sensor wire was developed by depositing conductive silver (Ag) nanoparticles on the surface of nylon (Ny) yarn by electroless plating process to achieve smallest uniform coating film without jeopardizing the integrity of each material. The sensitivity of this Nylon/Ag strain sensor wire was calculated experimentally, and gauge factor was found to be in the range of 21–25. Then, the Nylon/Ag strain sensor wire was inserted into each composite specimen at different positions intentionally during fabrication depending upon the type of damage to detect. The specimens were subjected to tensile loading at a strain rate of 2 mm/min. Overall mechanical response of composite specimens and electrical response signal of the Nylon/Ag strain sensor wire showed good reproducibility in results; however, the Nylon/Ag sensor showed a specific change in resistance in each direction because of the respective position. The strain sensor wire designed not only monitored the change in the mechanical behavior of the specimen during the elongation and detected the strain deformation but also identified the type of damage, whether it was compressive or tensile. This sensor wire showed good potential as a flexible reinforcement in composite materials for in situ structural health monitoring applications and detection of damage initiation before it can become fatal.

Development of microscale flexible nylon/Ag strain sensor wire for real-time monitoring and damage detection in composite structures subjected to three-point bend test

Composite are prone to failure during operation and that's why vast research had been carried out to develop in-situ sensors and monitoring systems to avoid their catastrophic failure and repairing cost. The aim of this research was to develop a flexible strain sensor wire for real-time damage detection in the composites. This strain sensor wire was developed by depositing conductive silver (Ag) nanoparticles on the surface of nylon (Ny) yarn by electroless plating to achieve the smallest uniform coating without jeopardizing the integrity of each material. The sensitivity of this Ny/Ag strain sensor wire was calculated experimentally and gauge factor (G.F) was found to be in the range of 21–25. Then, Ny/Ag strain sensor wire was inserted in each composite specimen at different position intentionally through the thickness during their fabrication depending upon the type of damage to detect. The specimens were subjected to flexural deflection using a 3-point bend test at the strain rate of 2 mm/min. Overall mechanical response of composite specimens and electrical response signal of the Ny/Ag strain sensor wire showed good reproducibility in results however, Ny/Ag sensor showed a specific change in resistance in each specimen because of their respective position. The sensor wire designed, did not only monitor the change in the mechanical behavior of the specimen until final fracture but also identified the type of damage whether it was compressive, tensile or both. This sensor wire showed good potential as a flexible reinforcement in composite materials for in-situ SHM applications before it can become fatal.

Discrimination of VOCs molecules via extracting concealed features from a temperature-modulated p-type NiO sensor

Poor selectivity of metal oxide semiconductor (MOS) gas sensors (toward volatile organic compounds, VOCs) poses a significant challenge for their applications in the emerging areas of personal health and air quality monitoring. Extensive efforts have been devoted to improving the selectivity of gas sensors via extracting features from their electrical response signals. Alternative to the conventional strategy of enlarging the number of sensor arrays, analyzing the transient signal of a temperature modulated gas sensor provides an efficient approach to extract molecule features. Despite p-type MOS outperforms n-type counterpart in terms of (photo)catalytic properties, further exploration on thermal modulation of p-type MOS sensor has been scarcely reported. In this work, p-type NiO nanoparticles with grain size of 17.4 ± 4.0 nm have been synthesized with the assistance of bacterial cellulose (BC) scaffold. Transient response characteristics of NiO sensor (modulated by a staircase waveform) toward 5 kinds of VOCs have been investigated. The removals of irrelevant electrical signals, particularly induced by large temperature coefficient of resistance (TCR) of p-NiO, allows us to extract the intrinsic features of tested VOCs molecules by discrete wavelet transform (DWT). Successful classification and recognition of tested VOCs molecules, including three kinds of benzene series (benzene, toluene and chlorobenzene), have been achieved by typically non-selective p-type NiO sensor with a low sensitivity. Our work highlights that eliminating the irrelevant thermally modulated electric signals is essential for expanding the recognition capability of a single MOS sensor (toward VOCs molecules), and sheds light on the exploring future smart gas molecule recognition chips.

Oriented freeze-casting fabrication of resilient copper nanowire-based aerogel as robust piezoresistive sensor

One dimensional (1D) metallic nanowires-based flexible electronics have promising applications in strain and pressure detection. However, current research on piezoresistive materials are often hindered by robust mechanical performance, elastic-responsive conductivity and inefficient scale-up capacity. Here, we demonstrate a multi-scale fabrication strategy for three-dimensional (3D) copper nanowire-based aerogel with cost-effectiveness, directional and structural regulation and stable strain–electrical signal response via oriented freezing technique. Added polyvinyl alcohol binder dramatically enhances free-standing property and mechanical compliance of aerogel via gluing effect. Besides, this effect between nanowire and polyvinyl alcohol has been revealed by molecular dynamics simulations. Oriented aerogel displays far superior spring-back abilities than does non-oriented aerogel and exhibits good compressibility (undergoing a cyclic compression-recovery at 60% strain) and tunable piezo-resistance sensitivity (0.267–0.04 kPa−1). Additionally, van der waals force contributes actively to the gluing effect on nanowire and polymer. The presented strategy opens up a new possibility for mass production of nanowire-based aerogel with ordered pore orientation and remarkable force-sensitive response.

Rotation Sensing Systems: A Self‐Powered Smart Roller‐Bearing Based on a Triboelectric Nanogenerator for Measurement of Rotation Movement (Adv. Mater. Technol. 12/2018)

In article 1800219, Daehwan Choi, Taehoon Sung, and Jang-Yeon Kwon describe a self-powered smart roller-bearing based on a triboelectric nanogenerator. This smart bearing generates the output electrical signals in response to any rotation movement or displacement of an object mounted with the bearing. The cover image shows the structure and a possible application of the smart bearing.

Chemical Sensing Employing Plant Electrical Signal Response-Classification of Stimuli Using Curve Fitting Coefficients as Features

In order to exploit plants as environmental biosensors, previous researches have been focused on the electrical signal response of the plants to different environmental stimuli. One of the important outcomes of those researches has been the extraction of meaningful features from the electrical signals and the use of such features for the classification of the stimuli which affected the plants. The classification results are dependent on the classifier algorithm used, features extracted and the quality of data. This paper presents an innovative way of extracting features from raw plant electrical signal response to classify the external stimuli which caused the plant to produce such a signal. A curve fitting approach in extracting features from the raw signal for classification of the applied stimuli has been adopted in this work, thereby evaluating whether the shape of the raw signal is dependent on the stimuli applied. Four types of curve fitting models—Polynomial, Gaussian, Fourier and Exponential, have been explored. The fitting accuracy (i.e., fitting of curve to the actual raw signal) depicted through R-squared values has allowed exploration of which curve fitting model performs best. The coefficients of the curve fit models were then used as features. Thereafter, using simple classification algorithms such as Linear Discriminant Analysis (LDA), Quadratic Discriminant Analysis (QDA) etc. within the curve fit coefficient space, we have verified that within the available data, above 90% classification accuracy can be achieved. The successful hypothesis taken in this work will allow further research in implementing plants as environmental biosensors.

A Self‐Powered Smart Roller‐Bearing Based on a Triboelectric Nanogenerator for Measurement of Rotation Movement

AbstractTriboelectric nanogenerator technology is one of the most promising technologies with great potential for applications in self‐powered electronics and sensing systems. Herein a simply fabricated, cost‐effective, triboelectric sensor with a roller‐bearing structure which is composed of rollers and electrode is presented. Based on the triboelectric effect, this smart bearing generates the output electrical signals in response to rotation movement or displacement of an object mounted with the bearing. The triboelectric sensor delivers an open‐circuit voltage of ≈45 V and a short‐circuit current of ≈6 µA at a rotation rate of 400 r min−1. Using the output signals of the smart bearing, the angular velocity and position as well as damage in the components can be continuously monitored. Furthermore, the smart bearing mounted to the steering wheel can be utilized as an energy harvester, a rotation direction detector, and a driving style sensing system at the same time. This work greatly expands the applicability of triboelectric nanogenerators as self‐powered sensing systems.

A Charge Sensitive Pre-Amplifier for Smart Point-of-Care Devices Employing Polymer-Based Lab-on-a-Chip

With increasing emphasis on implantable and portable medical devices, low-power, small-chip-area sensor readout systems realized in lab-on-a-chip (LOC) platforms are gaining more and more importance. The main building blocks of the LOC system include a front-end transducer that generates an electrical signal in response to the presence of an analyte of interest, signal processing electronics to process the signal to comply with a specific transmission protocol, and a low-power transmitter, all realized in a single integrated circuit platform. Low power consumption and compactness of the components are essential requirements of the LOC system. This brief presents a novel charge sensitive pre-amplifier developed in a standard 180-nm CMOS process suitable for implementing in an LOC platform. The pre-amplifier converts the charge generated by a pyroelectric transducer into a voltage signal, which provides a measurement of the temperature variation in biological fluids. The proposed design is capable of providing 0.8-mV/pC gain while consuming only $2.1~{\mu }\text{W}$ of power. The pre-amplifier composed of integrated components occupies an area of 0.038 mm2.