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This paper reports on an all-oxide thin film piezotronic P-N heterojunction diode incorporating vertically-stacked structure of N+-ITO/P-type nickel oxide/N-type zinc oxide as a flexible energy scavenger and its diode characteristics on signal regulation which simplifies an essential element for harvesting which is signal rectification circuitry. An energy band diagram, theoretical modeling and equivalent small-signal circuit elaborate its working principle and device physics. Signal amplification due to introduction of in-series capacitances related to junction formation has also been addressed. A preliminary experimental study demonstrates applicability of such a flexible energy scavenger in various gratis non-stop thrusts originating from human body motions such as: simple tapping (as in typing) and walking actions for generating $\mu $ W-range power. Moreover, focusing on a simple power management system along with analysis of voltage waveforms in response to both resistive and capacitive loads unveils that the device is capable of quickly charging a capacitor and discharging it slowly allowing for possible energy storage. The estimation on generated power by a pixelated array that is obtainable due to ease of large-area fabrication processes and a single-pixel strip-based device exabits its feasibility as an energy source to power up some IoT nodes.

Objective: We propose a modular stretchable coil design using conductive threads and commercially available embroidery machines. The coil design increases customizability of coil arrays for individual patients and each body part. Methods: Eight rectangular coils were constructed with custom-fabricated stretchable tinsel copper threads incorporated onto textile. Tune, match, and detune circuits were incorporated on the coil. A hook-and-loop mechanism was used to attach and decouple the modular coils. Phantom and in vivo scans at various anatomical flexion angles were acquired to highlight performance, and a temperature test was performed to verify safety. Results: In vivo MRI experiments demonstrate high sensitivity and coverage of each anatomy. As the coils are stretched, the sensitive volume increases at a rate of 10.93 mL/cm2. The SNR reduction of a single coil was greater during compression than when stretched, but this did not affect image quality for the array. The modularity of the array allows for adaptability for any anatomy with simple on-demand adjustment to the number and position of coil elements. Conclusion: The images demonstrated high sensitivity and coverage of the stretchable array for various anatomies and flexion angles. Stretching the coils increases the sensitive volume, allowing for a larger region to be effectively imaged. The resonance shift and SNR decrease during stretch and compression support further investigation of methods to reduce frequency shift in stretchable coils. Significance: The proposed array design allows for highly stretchable, flexible, modular, and conformal patient-centered coils that allow for increased imaging quality, greater comfort, and rapid production.

Cellulose nanofibril (CNF) substrates that are inexpensive, biodegradable, and quickly incinerable, are potential substrates for disposable RF applications. In this paper, high-performance flexible microwave lumped elements and filters fabricated on flexible CNF substrates are reported. A spiral inductor with a resonance frequency of 29.8 GHz and quality (Q) factor of 8.5 and a metal-insulator-metal (MIM) capacitor with a resonance frequency of 45 GHz and Q factor of 85.2 were achieved in a 200 μm thick CNF substrate. Meanwhile, the inductor and capacitor exhibit outstanding mechanical bendability, that is negligible performance changes were observed when they were bent to a radius as small as 15 mm. Based on the spiral inductor and MIM capacitor, a 5-GHz band-stop filter and a 4 GHz band-pass filter with excellent mechanical bendability were further demonstrated on the CNF substrate. These results indicate the potential of using CNF as substrates for broader microwave applications.

A facile blade-coating process is developed for large area deposition of uniform thick organic active layers in organic photodiodes (OPDs). Large-area semi-transparent top metal electrodes are thermally evaporated with an optimal deposition rate to achieve good balance between transparency and conductivity for top illumination integration structure with the organic thin-film transistor (OTFT) backplane. The maximum process temperature of the OPD is 85 °C, so that the performance of the OTFT underneath is not affected. Based on the developed integration structure and processes, an all-organic integrated flexible active-matrix imager is developed, having the largest size (130 mm ${\times } 130$ mm), highest resolution ( $1536 {\times } 1536$ pixels, 300 ppi) and lowest process temperature (100 °C) reported so far for the OPD based imagers.

The excellent mechanical properties of Polydimethylsilane (PDMS) has been widely used in hybrid flexible photodetectors, but there is hardly any research on it as the active layer of the direct X-ray detectors. In this letter, the low detection and high flexibility X-ray detector was fabricated based on pure PDMS. The metal/polymer/metal (MPM) vertical structure detector has a detection limit of 49.69 nGy $_{air}\text{s}$ −1. Carrier migration occurs in PDMS under X-ray irradiation with the sensitivity of $57.7~\mu \text{C}$ Gy $_{air}^{-1}$ cm−2 at the electric field of 2 V/ $\mu \text{m}$ and the dose rate of $23.9~\mu $ Gy $_{air}$ s−1. The device still maintains a good performance after bending tests (different bending radius and 10000 cycles). This work provides a new possibility for the next development of direct X-ray detectors. [ABSTRACT FROM AUTHOR]

Die shift in fan-out wafer-level packaging (FOWLP) is a major roadblock, limiting package scaling and performance. It not only limits the wire pitch but also results in reliability problems and yield loss. In this work, we systematically investigate and predict the in-plane and out-of-plane die shift through numerical and experimental analysis in FlexTrate, which is a flexible hybrid electronics (FHE) platform based on FOWLP for flexible heterogeneous integration. First, the in-plane die shift is studied through simulation of the molding process and the substrate cure shrinkage. The molding process is simulated through a fluid analysis which explores the shear force. In addition, a thermo-mechanical analysis simulates the polydimethylsiloxane (PDMS) curing process followed by handler release. Based on this model, the effect of die size, die spacing, die thickness, and PDMS thickness on die shift are analyzed. The results indicate that smaller die size has a larger impact on die shift compared to the other factors. The predicted die shift is compared with the experimental results to verify the validity. Further, the experimental characterization of out-of-plane die shift is analyzed through the study of substrate warpage and die placement force which reveal the deleterious effect of high temperature processes. Finally, using the developed numerical model, the die placement is optimized for a surface electromyography (sEMG) system. This detailed analysis sheds light on the various factors which influence die shift, and hence is an important step to push the boundaries of current FHE to new limits. [ABSTRACT FROM AUTHOR]

Self-sustained devices, which can harvest energy from the environment, have the potential to overcome the limitations of battery-powered systems and, thus, are suitable for powering flexible or wearable electronics based on embedded microsensors. Compared with other materials used for energy harvesting, piezoelectric polymers exhibit significant advantages, such as high flexibility and durability as well as excellent stability. However, their low electricity-generating capability limits practical applications. In this work, the energy-harvesting performance of poly(vinylidene trifluoroethylene) [P(VDF-TrFE)] films with various chemical compositions and thicknesses is explored. The test circuit is connected to a picoammeter instead of an oscilloscope to maximize the energy output performance. A new self-powered sensing system is designed by switching off the microcontroller unit (MCU) to minimize power consumption rather than switching to the sleep mode. The results show that piezoelectric P(VDF-TrFE) generators meet the power consumption level of 1.1 $\mu \text{A}$ standby current and sustain the intermittent monitoring system. In addition, the system parameters, such as the generator size or the storage capacitance, are tunable, indicating the great potential of P(VDF-TrFE) to be applied to lightweight or flexible self-powered sensors. [ABSTRACT FROM AUTHOR]

This article presents a state-of-the-art 3-D-printed dielectric reflectarray antenna featuring one-shot deployability and wide-angle beam-scanning ability. The design is enabled by a series of a “kirigami”-inspired two-stage snapping-like element structure that can be retracted by 66% to save space. The prototype is fabricated with a stereolithography (SLA) 3-D printing method with the Formlabs Flexible 80A photopolymer. A bifocal phase distribution method is utilized to optimize the RF performance of the array, realized −30° to −10° and 10° to 30° beam-scanning ability. The outcome of this work demonstrated a high-performance dielectric reflectarray design with ease of fabrication for 5G and satellite communication applications. [ABSTRACT FROM AUTHOR]

Transparent transistors are mainly investigated in view of their integration in displays and their employment in wearable electronics where the integration of flexible and imperceptible systems is an important requirement. Here, the fabrication and ac performance of flexible InGaZnO thin-film transistors (TFTs) and circuits are presented to evaluate their suitability for analog sensor conditioning applications. Functional oxides are employed to guarantee the transparency of the device, while their fabrication processes are suitable to directly realize electronics on a flexible polyimide substrate. The TFTs show state-of-the-art performance with a field-effect mobility $\mu _{\text {eff}}\,\,= {19}.{39}\,\, \text {cm}^{{2}} \text {V}^{-1} \text {s}^{-1}$ and functionality while bent to radii as low as 5 mm. Reliable scattering parameters measurements confirm transit frequencies as high as $f_{t}~\approx ~7.84$ MHz. Simultaneously, nMOS ring oscillators (ROs) show functionality at supply voltage ${V} _{\text {DD}}$ ranging from 1.75 to 12.25 V with a maximum oscillation frequency ${f} _{\text {osc}}\,\,=132.9$ kHz. Finally, common-source amplifiers (CSAs) exhibit the voltage gains up to 10.7 dB, the cutoff frequencies up to 10.8 kHz, and a power consumption down to $4.4~\mu \text{W}$. [ABSTRACT FROM AUTHOR]

Cross-linking polymer gate dielectric is an efficient strategy to improve its intrinsic properties for high-performance flexible organic field-effect transistors (OFETs). However, the detail optimization process of the polymer films with the various cross-linking degrees is often ignored, which can bring a significant effect on the electrical performance of OFETs. In this work, the cross-linked poly (vinylalcohol) (CPVA) is introduced as the gate dielectrics for the high-performance ultraflexible OFETs. The dielectric property and the surface property of CPVA thin films with various cross-linking degrees are investigated in detail. The OFETs with a high average mobility of 7.3 cm $^{2}\cdot V^{-1}\cdot s^{-1}$ , a current ON/ OFF ratio of over 107, and a lower density of trap states of $8.7\times10$ 11 eV $^{-1}\cdot cm^{-2}$ are achieved successfully. Moreover, the ultraflexible OFET presents a high mobility of over 5.1 cm $^{2}\cdot V^{-1}\cdot s^{-1}$ even bending around a copper wire with a small radius of $400 ~\mu \text{m}$ , due to the ultrathin thickness of the device. These results demonstrate that the CPVA thin film is a promising candidate dielectric material for flexible organic transistors, presenting huge potential for the next-generation flexible electronic devices. [ABSTRACT FROM AUTHOR]

In amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs), the conduction mechanism of percolation and trap-limited conduction prevails within the limits of gate voltage. In these limits, the gate voltage-dependent mobility follows a power law. The temperature dependence of gate-functioned mobility is modeled by introducing very few empirical parameters (P and $\gamma $), where P follows the Arrhenius equation and $\gamma $ is found to be constant for varying temperature ranges. The proposed model effectively incorporates the combined effects of mobility as a function of temperature and gate voltages of the device using a single formulation for accurate thermal characterization. This model reproduces the measured characteristics of oxide TFT for a wide temperature range with an average error less than 2.5%. The model is implemented in Verilog-A to facilitate circuit simulations. Further, an 11-stage Ring-Oscillator is simulated with the proposed model. These results are compared with the measured circuit response under similar testing conditions to validate the model accuracy in the complete region of operation over a wide range of temperature variations. These simulation results show a good agreement with measured results within 8% accuracy, reinforcing the model validation. [ABSTRACT FROM AUTHOR]

Information encryption has become an essential trend in the era of big data. Ultrasound can be used as an excellent encrypted transmission medium carrying information due to its strong concealment and small interference. And, better wearable needs cannot be ignored. Here, we propose a flexible graphene-based fabric ultrasound source (GUS) for machine learning enhanced information encryption. GUS is prepared by one-step laser method to generate laser-induced graphene on NOMEX fabric substrate. The easily captured low-frequency sound signals are modulated to high frequency to become ultrasound signals and emit through GUS. The key to success of this work is excellent sound pressure level (SPL) output of GUS in high frequency. Besides, the Mel Frequency Cestrum Coefficient (MFCC) feature of ultrasound is extracted by convolutional neural network, and the accuracy of speech recognition is 98.2 %. [ABSTRACT FROM AUTHOR]

In this article, we report on the electrical performance of AlGaN/GaN high-electron mobility transistors (HEMTs) fabricated using gold (Au)-free process, after being transferred onto flexible Kapton tape. The transfer process followed in this work can be easily scaled-up to wafer level and involves a relatively simple process of epoxy bonding of the thin device layer onto the Kapton substrate. Electrical characteristics of the flexible HEMT indicate 5%–10% higher ON-current when bent with a radius of curvature of 2.1 cm (at low drain bias voltages), while the OFF-state performance remains unaffected. Initially, 2-DEG properties such as field-effect mobility and carrier concentration have been extracted. While FATFET measurements indicate negligible change in field-effect mobility, ${C}$ – ${V}$ measurements indicate $\sim 10$ % reduction in 2-DEG concentration after transfer. The comparison of the electrical characteristics of Au-free HEMTs indicates $\sim 50$ % reduction in the ON-current of the transferred devices. This is attributed to heating of the transistor channel caused due to low thermal conductivity of the polymer Kapton tape. Electrical characteristics of the flexible HEMT carried out under drain pulsing further support the above observation. This work is among one of the few reports on Au-free AlGaN/GaN HEMT operation on flexible Kapton tape. [ABSTRACT FROM AUTHOR]

Electromagnetic shielding is one of the most important branches of Electromagnetic Compatibility. Traditionally, metals were commonly used for shielding materials due to their high conductivity. Recently, however, increasing needs have emerged for lightweight, flexible, optical transparent, non-corrosive shielding materials to be used in flexible electronics, aerospace, and automotive manufacturing. For these reasons, carbon-based materials, such as graphene, have attracted increased attention for shielding applications. The main objective of this work is to evaluate ideal monolayer graphene as a shielding material for cylindrical configurations in the RF/microwave region. The numerical modeling of the involved structures is performed by the Method of Auxiliary Sources (MAS). Particularly, since the standard MAS suffers from numerical difficulties when applied in highly-conductive regions, a modified version of MAS is employed in which the graphene layer is replaced by an Impedance Matrix Boundary Condition (IMBC). The same condition is also applied for the case of a Few Layer Graphene (FLG) shield. The derived numerical results are found to be in excellent agreement with those obtained by FEM-based commercial software. [ABSTRACT FROM AUTHOR]

Bowel sounds (BSs) have important clinical value in the auxiliary diagnosis of digestive diseases, but due to the inconvenience of long-term monitoring and too much interference from environmental noise, they have not been well studied. Most of the current electronic stethoscopes are hard and bulky without the function of noise reduction, and their application for long-term wearable monitoring of BS in noisy clinical environments is very limited. In this paper, a flexible dual-channel digital auscultation patch with active noise reduction is designed and developed, which is wireless, wearable, and conformably attached to abdominal skin to record BS more accurately. The ambient noise can be greatly reduced through active noise reduction based on the adaptive filter. At the same time, some nonstationary noises appearing intermittently (e.g., frictional noise) can also be removed from BS by the cross validation of multichannel simultaneous acquisition. Then, two kinds of typical BS signals are taken as examples, and the feature parameters of the BS in the time domain and frequency domain are extracted through the time-frequency analysis algorithm. Furthermore, based on the short-term energy ratio between the four channels of dual patches, the two-dimensional localization of BS on the abdomen mapping plane is realized. Finally, the continuous wearable monitoring of BS for patients with postoperative ileus (POI) in the noisy ward from pre-operation (POD0) to postoperative Day 7 (POD7) was carried out. The obtained change curve of the occurrence frequency of BS provides guidance for doctors to choose a reasonable feeding time for patients after surgery and accelerate their recovery. Therefore, flexible dual-channel digital auscultation patches with active noise reduction will have promising applications in the clinical auxiliary diagnosis of digestive diseases. [ABSTRACT FROM AUTHOR]

In this work, flexible In0.7Ga0.3As metal-oxide-semiconductor field-effect-transistors (MOSFETs) are demonstrated by utilizing liquid polyimide (LPI) transfer. The flexible In0.7Ga0.3As MOSFET on polyimide showed excellent logic performances including threshold voltage (Vth) = 0.16 V, subthreshold swing (SS) = 95 mV/dec and drain induced barrier lowering (DIBL) = 64 mV/V with $\text{L}_{\mathbf {g}} \text {= 5}\,\, \boldsymbol {\mu }\text{m}$ at VDS = 0.5 V. In addition, ex-situ bending experiment was employed to demonstrate electro-mechanical performance, which include stable Ion/Ioff ratio and Ron from 85 mm to 9 mm of bending radius, and deviation of subthreshold swing is less than 5.3 % under bending radius from 85 mm to 4 mm. Our findings indicate that the LPI transfer method on fabricated devices without additional complex bonding methods would be one of effective solutions to enable flexible III-V compound semiconductor electronics and opto-electronic devices. [ABSTRACT FROM AUTHOR]

A novel generalized Gamma-Laguerre polynomial chaos expansion is proposed to account for the effect of random variations in lower bounded design parameters on antenna performance. After fitting a shifted generalized Gamma distribution to datasets of such random variables, a predistorted polynomial chaos expansion is generated based on a set of orthogonal generalized Laguerre polynomials. The new statistical methodology is applied to assess the random change in resonance frequency when bending a wearable antenna around different parts of the human body, such as a leg, an arm, and a head. For different datasets, an excellent statistical fit is found to both the estimated probability density function of the bending radius and the resulting statistical distribution of the resonance frequency, while requiring up to 480 times fewer sample evaluations. [ABSTRACT FROM AUTHOR]

Flexible, self-powered, and intelligent tactile sensors are essential for accurate sensing in prosthetic devices. This paper explores piezoelectric polyvinylidene difluoride - zinc oxide (PVDF-ZnO) nanocomposite layer-based sandwich assembly as tactile sensor. ZnO nanoparticle addition as filler can overcome the challenges associated with PVDF-based tactile sensors. The effect of filler particle size on the enhancement of sensing performance of PVDF-ZnO-based tactile sensors is investigated. Structural, morphological, piezoelectric and thermal studies were performed on the PVDF-ZnO composite layers using SEM, EDS, DC-EFM and Raman Spectroscopy. A comparative investigation of the potential developed across the sensor samples with different filler particle sizes was performed for touch and bending actions. The obtained results showed a remarkable improvement in performance due to particle size reduction of the ZnO fillers. The nanocomposite sensor with less filler particle size generated more voltage on the same applied force. The experimental analysis demonstrates that the filler size reduction can improve the piezo-voltage response up to 123 mV/N for dynamic touch events. The self-powered sensor also has excellent potential in detecting finger bending action with a response of 29 mv/°. The results demonstrate the promising application of the polymer nanocomposite-based sensor in the prosthetic application. [ABSTRACT FROM AUTHOR]

This work presents the design and implementation of a porous polydimethylsiloxane (PDMS)-based wide-range flexible pressure sensor for autonomous underwater vehicles. The capacitive sensor, with porous PDMS as dielectric, is encapsulated in bulk PDMS polymer. The fabricated sensor was evaluated over a wide pressure range (0-230 kPa), which is similar to pressures experienced up to approx. 23 m below the sea level. The sensors showed linear response when tested in air and near-linear response (98%) when submerged in water. The sensor showed much higher sensitivity (0.375 kPa−1) in water than in the air environment. However, the sensor exhibited the performance and sensitivity similar to the air condition (0.005 kPa−1) when the readout electronics (encapsulated inside a watertight enclosure) was also submerged inside the water along with the sensor. The fabricated sensor also exhibited fast response and recovery time (190 ms), as well as excellent repeatability and stability (no drift) over tested range of 50 loading and unloading cycles. These results demonstrate the suitability of presented sensors for potential use in applications requiring a wide range of pressure, particularly the underwater robotics where real-time pressure monitoring is critical for autonomous operation. [ABSTRACT FROM AUTHOR]

Recently, p-type tin monoxide (SnO) thin-film transistors (TFTs) have gained interest for all-oxide complementary metal–oxide semiconductor (CMOS) circuits for flexible electronics and back-end-of-line integration with Si. However, most SnO TFTs demonstrated so far exhibit a low on– off-current ratio and limited field effect mobility. To understand and improve SnO TFT performance, it is necessary to quantitatively characterize the subbandgap defects in SnO and at its dielectric interface. In this work, we establish numerical models which provide this understanding. By concurrent fitting of simulated ${I}_{\text{D}}$ – ${V}_{\text{GS}}$ and effective mobility versus ${V}_{\text{GS}}$ to experimentally measured data, we can accurately extract SnO defect state profiles. Using the extracted simulation models, we then identify ways to improve SnO TFT performance. Specifically, a reduction in the density of shallow, bulk Gaussian acceptor states, is necessary to reduce the off-current, while reducing the contact resistance and interface donor-like tail state density can improve the SnO field effect mobility. [ABSTRACT FROM AUTHOR]

In this study, the electrical performance and bending stress endurance of flexible low-temperature polycrystalline silicon thin film transistors (LTPS TFTs) are enhanced by increasing the helium concentration (1500 sccm) during gate insulator (GI) manufacture to create a high-quality GI device. Experimental results confirm that the subthreshold swing (S.S.) and mobility of these new “high-flow” devices are better than those with a lower helium concentration, which we term “low-flow” devices. The flow of helium gas is increased to achieve a better-quality oxide layer. The energy-dispersive X-ray spectroscopy (EDS) line data show a clear enhancement in oxygen content in the devices under this helium gas process. After mechanical compression and tensile bending stresses of 100000 iterations in the channel width-axis direction, perpendicular to the channel, with bending at ${R} = {2}$ mm, the modified GI devices with their more Si-O bond content exhibit less stress damage in the GI layer than do low-flow devices. As a result, this new manufacturing condition can effectively reduce the electrical degradation after negative-bias temperature stress (NBTS), and improve the overall electrical performance. [ABSTRACT FROM AUTHOR]

A roll-to-roll (R2R) manufacturing system has been considered the most suitable candidate for commercializing flexible electronic devices owing to its large-area and mass-production characteristics. A high-precision register control should be ensured when fabricating devices using the R2R system. Contrary to conventional manufacturing systems that are applied to rigid materials, the control target in an R2R system is a flexible film that can lead to a substantial time delay in the control response and degrade the register control performance. This article proposes a novel control scheme, namely response acceleration input, to provide a rapid response in the register control of flexible substrates. Mathematical models to achieve the proposed scheme were developed. A register control system based on the developed models was designed, followed by experimental verifications using an industrial-scale R2R system. The results show that the register error is successively controlled below ±10 µm with a high yield of over 80% for 1800 s. We believe that the proposed control strategy can realize a high-precision register control below ±10 µm in industrial-scale R2R manufacturing systems, thus enabling the commercialization of multilayered, flexible electronic devices. [ABSTRACT FROM AUTHOR]

Solution-processed devices are in general compatible with flexible and conformable electronics. However, some promising materials needs to be processed at high temperatures, which limits the applications and the use of different substrates. Among these materials we can highlight zinc oxide (ZnO), a semiconductor that stands out for transistors applications and is, in general, obtained at temperatures around 300 °C-400 °C. Here, we reported the combination of annealing at 150 °C, ultraviolet (UV) treatment and blending of ZnO nanoparticles (ZnO-NPs) with zinc nitrate and urea as a strategy to fabricate an inkjet printed electrolyte-gated transistor (EGT) with reduced temperature and improved performance, including a significant mobility improvement to 0.21 cm2/V $\cdot$ s, operating below 2 V bias, which is around 460% higher than the mobility of the EGT fabricated purely with ZnO-NPs. [ABSTRACT FROM AUTHOR]

Multifunctional flexible electronics have been a hot spot in scientific research and technology development. From the view of practical application, high-performance flexible heating devices with the capability to respond to commands are an urgent need for thermal management. Herein, we propose a strategy for multifunctional integration by assembling two pieces of laser-scribed Nomex paper, thus enabling the combination of heating and sensing modules. On account of the good electrothermal and piezoresistive properties of laser-induced graphene, the device can generate high steady-state temperature with a low voltage excitation and recognize valid commands from users finger to switch between operating states. Besides, the fast and efficient fabrication method entirely based on direct laser writing technology is another unique advantage. [ABSTRACT FROM AUTHOR]

Surgical planning to visualize a complete procedure before surgical intervention, paired with the advanced surgical techniques of a surgeon, has been shown to improve surgical outcomes. Efforts to improve surgical planning have included tracking real-time surgeon movements via surgical instruments in a confined body cavity space in the human body to enhance specific techniques when performing minimally invasive surgery. In this work, a surgical tool tracking approach is presented that leverages small scale electronics to enable real-time position capture for use in iterative surgical planning. By integrating a lightweight 9 degree-of-freedom Inertial Measurement Unit (IMU), our system captures both spatial and temporal information of the surgical tool without requiring a direct line-of-sight. The IMU is printed on a flexible film and attached to and integrated with a surgical tool demonstrating its tracking capabilities. Data from the IMU is analyzed to determine the full range of motion during angular displacement for measurement and tracking. The results show an accuracy of 2.20, 2.90 and 3.10 of the full range of motion of the X (Yaw), Y (Roll) and Z (Pitch) Euler angle coordinate system respectively demonstrating the potential for surgical tool tracking measurement without the need for a direct line of sight and with future impact including flexible electronics and motion tracking. This work will be helpful in a diversity of fields including surgery, surgical training, biomaterials, and motion tracking. [ABSTRACT FROM AUTHOR]

In the present work, we testify a strategy to achieve high-performance ZnO thin film transistors (TFTs) on a flexible PET substrate at a maximum process temperature no more than 100 °C. Interestingly, the ZnO TFTs exhibit superior electrical properties, including a field-effect mobility of 14.32 cm2V−1s−1, a sub-threshold swing of 0.21 V/decade, and an on-to-off current ratio of $3.03\times 10^{7}$ . Also, ideal uniformity, hysteresis property, contact resistance, and stability are achieved. Threshold voltage shift ( $\Delta \text{V}_{\mathrm{ TH}}$ ) under positive and negative bias stress are 0.17 and −0.18 V, respectively. Moreover, the ZnO TFTs manifest good mechanical performance at a bending radius of 10 mm. We expect that our findings propel practical application of the oxide TFTs in flexible electronics.

In recent times, there has been a great increase in the demand of flexible micro-supercapacitors for use in many commercial applications. Flexible capacitors have the potential to replace conventional batteries as they can provide competitive energy storage while being much smaller in size and having greater lifetime than average lithium-ion batteries. The most used design for in-plane flexible micro-supercapacitors is the interdigitated design. However, from findings of various recent studies, it is believed that the capacitance of in-plane EDLC micro-supercapacitors can further be improved by changing electrode designs. Different fractal designs have shown great promise to enhance the electrochemical performance of in-plane micro-supercapacitors by maximizing the active surface area and minimizing the energy lost during ion-transport. In this work, we successfully fabricate graphene-based, laser-scribed flexible micro-supercapacitors and study the effects of change in geometry parameters on total capacitance. Four different geometries for electrode were designed i.e., (1) interdigitated design, (2) fractal F1 (Hilbert) design, (3) fractal F2 (Peano) design, and (4) fractal F3 (Moore) design, and were patterned onto the thin layer of graphene oxide using laser scribing technique. Detailed analysis was presented for the change in capacitance using cyclic voltammetry, galvanic charge-discharge, electrochemical impedance spectroscopy and electrostatic simulation using COMSOL Multiphysics. It was found that fractal design micro-supercapacitors give better performance with higher capacitance and energy density values in comparison to conventional design interdigitated micro-supercapacitors. Among all, Fractal F3 design showed the highest capacitance and energy density value in comparison to other devices. It was found that there were two factors affecting the performance of devices, i.e., (1) a higher active surface area for fractal designs as compared to interdigitated designs with the same unit area, and (2) in addition to electric double layer capacitance, there was also electric field being generated on the edges of electrodes, defined as edging effect. Among both factors, the latter was the major enhancer of capacitance in the fractal design devices.

Advancements in the field of flexible electronics have enabled many novel applications such as wearables, flexible large-area displays, and textile-based sensor systems. A widely used semiconductor material for flexible electronics is amorphous indium gallium zinc oxide (a-IGZO). When compared to other semiconductors suitable for flexible technologies, this material is attractive for its higher mobility, better bias stability and improved uniformity. This paper presents an overview of current trends in analog and mixed signal circuit design and in architectures for a-IGZO TFT based sensor systems. We highlight the specific design challenges associated with the main sub-blocks found in sensors and bio-signal acquisition systems based on a-IGZO TFT technologies: front-end amplifiers and data converters. We then present an overview of several state-of-the-art sensor systems based on a-IGZO TFTs and their applications. Finally, conclusions are drawn, and a roadmap for the future development of analog and mixed signal circuit design in a-IGZO TFT is presented.

Recent advances in flexible electronics have offered a good opportunity in designing a variety of wearable devices for healthcare monitoring, prevention medicine, and robotic control. Wearable sensors are entering the era of digital health, with compelling functionalities in recording vital signs, physiological signals, body kinetics, and dynamic biomolecular state. Meanwhile, energy harvesters that scavenge waste energy from body motions and the ambient environment have received intense attention, which are expected to realize self-powered or energy-autonomous systems. Moving towards the inside of the body, the implantable device also plays an indispensable role in monitoring key biomedical and physiological information and effective treatment of chronic diseases. Besides, wearable robotic exoskeletons have enabled advanced functionalities of assisting or augmenting human mobilities unprecedently. These technologies and platforms will be merged, giving way to the bodyNET: a network of wearable sensors, implantable devices, and exoskeletons for improved healthcare and health outcomes. In this article, we offer a brief review of recent advances in flexible and wearable sensors and summarize the progress of self-powered wearable sensors based on piezoelectric and triboelectric nanogenerators. We also discuss the implantable devices and self-powered neuromodulation systems and offer recent works of lower-limb exoskeletons. Lastly, we present a future trend towards a comprehensive and capable bodyNET for advanced healthcare and reinforced life quality.

Wireless power transmission and data telemetry technology has been widely adopted in healthcare applications based on flexible electronics. It is challenging to achieve high data rate (up to Mbps), low bit-error-rate (BER< 0.1%) data telemetry, as well as simultaneous high energy-efficiency power transmission, with small-volume flexible devices. In this paper, an energy-autonomous power-and-data telemetry circuit with digital-assisted-phase lock loop (PLL)-based binary-phase-shift-keying (BPSK) demodulator for implantable flexible electronics applications has been proposed. Only a single pair of coils has been employed to transmit both power and data based on a BPSK modulated Class-E amplifier. The energy recovery circuit enables a battery-less energy-autonomous implantable device. The proposed digital-assisted control circuitry resets the PLL to maintain the lock state and demodulate the BPSK data. As a result, the maximum data rate is no longer limited by the PLL’s bandwidth, which can be improved significantly. The chip has been implemented with standard 180nm CMOS process, occupying an area of 0.96 mm2. The post-layout simulation shows up to 2.26 Mbps data rate can be achieved with a low BER less than 8.6x10−5 with the coupling factor ranging from 0.13 to 0.17. Thanks to the digital-assisted-PLL-based demodulator, the power consumption of the receiver is only $817.4 ~\mu \text{W}$ and the demodulator Figure-of-Merit (FoM) is 362 pJ/bit with 13.56 MHz carrier frequency. The energy-autonomous circuit based on a single and small-volume pair of coils demonstrates its potential capability to be applied to various kinds of implantable biomedical applications.

In recent years, the aggressive downscaling of electronic components has led to highly dense and power-hungry devices. With Moore’s law expected to soon reach its physical limit, there is a pressing need to significantly improve the efficiency and performance not only of nanodevices, but also of the embedding environment in which such nanodevices are integrated. In this context, key for improving the performance and for reducing both system cost and size is electronics packaging. However, electronics packaging at the nanoscale (i.e., nanopackaging) is currently facing several technological challenges, as in such scale conventional materials present intrinsic physical limitations. To address this, it becomes necessary to replace these latter with novel alternatives, such as low-dimensional carbon-based nanomaterials. Carbon nanotubes (CNTs) and graphene (materials with 1D and 2D dimensionality, respectively) have the potential to be successfully integrated into traditional silicon-based electronics as well as with beyond-silicon electronics, and their unique electrical, thermal, mechanical, and optical properties could be key enablers for significant performance improvements. In this short review we describe why these nanomaterials are very promising for electronics nanopackaging, and we outline the key application areas, mainly interconnects, thermal management, and flexible devices.

Miniaturized microwave cavities constructed by the parallel-plate waveguide (PPW) becomes one of the main propagation pathways of the radio-frequency interference (RFI) in 3-D integrated circuits. It is still challenging to suppress RFI in the practical cavities, where the space is extremely constrained. In this work, the working mechanism and design method of the noise suppression sheet (NSS) is quantitatively studied, serving as an efficient approach to suppress RFI within an electrically small size in these microwave cavities. The analysis is based on the dispersion relationship derivation of the NSS-loaded PPW structure. Both the derived formulas and the numerical study reveal that the imaginary part of the permeability, that is, $\mu _{i}$ , of the NSS plays a key role in increasing the reflection and attenuation loss, and thus obtaining a high RFI suppression level. Further study indicates even when the NSS’s profile is lower than 10% of the cavity’s height and the length is lower than $0.1\lambda _{0}$ , its suppression level up to 10 dB can be well accomplished, which is deemed difficult to achieve by using conventional methods. Moreover, this method is, respectively, applied in three practical engineering scenarios for the RFI suppression, that is, heatsink package above a chip, power distributed network (PDN), and flexible circuit. Good agreement is observed between the measurement results and the simulated ones, which confirmed the efficacy of our quantitatively developed NSS. The proposed method is promising for broad industrial applications, such as tiny chip packages, multi-channel systems, and flexible electronics. [ABSTRACT FROM AUTHOR]

Objective: Atherosclerosis is a chronic immuno-inflammatory condition emerging in arteries and considered the cause of a myriad of cardiovascular diseases. Atherosclerotic lesion characterization through invasive imaging modalities is essential in disease evaluation and determining intervention strategy. Recently, electrical properties of the lesions have been utilized in assessing its vulnerability mainly owing to its capability to differentiate lipid content existing in the lesion, albeit with limited detection resolution. Electrical impedance tomography is the natural extension of conventional spectrometric measurement by incorporating larger number of interrogating electrodes and advanced algorithm to achieve imaging of target objects and thus provides significantly richer information. It is within this context that we develop Outward Electrical Impedance Tomography (OEIT), aimed at intravascular imaging for atherosclerotic lesion characterization. Methods: We utilized flexible electronics to establish the 32-electrode OEIT device with outward facing configuration suitable for imaging of vessels. We conducted comprehensive studies through simulation model and ex vivo setup to demonstrate the functionality of OEIT. Results: Quantitative characterization for OEIT regarding its proximity sensing and conductivity differentiation was achieved using well-controlled experimental conditions. Imaging capability for OEIT was further verified with phantom setup using porcine aorta to emulate in vivo environment. Conclusion: We have successfully demonstrated a novel tool for intravascular imaging, OEIT, with unique advantages for atherosclerosis detection. Significance: This study demonstrates for the first time a novel electrical tomography-based platform for intravascular imaging, and we believe it paves the way for further adaptation of OEIT for intravascular detection in more translational settings and offers great potential as an alternative imaging tool for medical diagnosis. [ABSTRACT FROM AUTHOR]

Oxide semiconductors have been considered one of the most promising candidates for flexible electronics applications owing to their low process temperatures and good reliability. However, the low mobility of p-type oxide semiconductors limits the performance of flexible oxide-TFT-based CMOS technology. In this study, p-type SnOx:Ni thin films were deposited by reactive rf magnetron co-sputtering, a technique compatible with the current industrial semiconductor manufacturing technology, from Sn and Ni targets. As the Ni-gun power increased, the distribution of Ni in the SnOx:Ni thin film changed from a more uniform dispersion to nanoclusters, resulting in the crystalline phase transition of SnOx:Ni from $\alpha $ -SnO (110)-dominant polycrystalline to amorphous and then to $\alpha $ -SnO (101)-dominant polycrystalline. A high-mobility inverted-staggered p-type SnOx:Ni TFT was then fabricated on a glass substrate with a maximum process temperature of 225°C, which is compatible with flexible polymeric substrates. The TFT fabricated at an optimal Ni-gun power of 42 W exhibited an impressive field-effect mobility of 11 cm2V−1s−1 and on current of $35.2 ~\mu \text{A}$ per channel width-to-length ratio; these values are comparable to those of a typical n-type oxide TFT. These results should contribute toward flexible oxide-TFT-based CMOS technology. [ABSTRACT FROM AUTHOR]

Arrays of flexible organic thin-film transistors (OTFTs) are the prerequisite to realize commercialization of flexible electronics. However, photolithography and print techniques are uneasy to combine high performance, high integration density, and compatibility with flexible substrates to fabricate OTFT arrays. In this work, OTFT arrays with high resolution, flexibility and process convenience are patterned by femtosecond laser (fs-laser). 1 cm2 of area can accommodate up to 6250 transistors with sharp edges and short channel lengths by selective processing. Furthermore, micron-scale resolution flexible image sensor with integration potential were verified. Hence, these results will impel the development of flexible wearable electronic devices in the future. [ABSTRACT FROM AUTHOR]

Compact model of flexible radio frequency (RF) electronic devices is crucial for flexible circuit designs. In this article, a compact model, including external strain effects for flexible RF gallium nitride (GaN) high-electron-mobility transistor, is presented. First, the carrier density and threshold voltage with external mechanical uniaxial strain is analytically characterized by introducing the strained piezoelectric charge $\Delta \sigma $ , Schottky barrier height $\Delta \phi _{B}$ , and surface state density $D_{\mathrm {it}}$ into the model. Then, the variations of the conduction band offset at the AlGaN/AlN and AlN/GaN interfaces are considered. Finally, the complete large-signal model is established after embedding strain effect into intrinsic drain current and nonlinear capacitance models. The proposed model is verified by measurements, including direct current $I$ – $V$ characteristics, small-signal $S$ -parameters up to 40 GHz, and large-signal power performance—output power, efficiency, and gain. The proposed model will be useful for the RF application of flexible electronics. [ABSTRACT FROM AUTHOR]

Backscatter communication is an emerging paradigm for pervasive connectivity of low-power communication devices. Wirelessly powered backscattering wireless sensor networks (WSNs) become particularly important to meet the upcoming era of the Internet of Things (IoT), which requires the massive deployment of self-sustainable and maintenance-free low-cost sensing and communication devices. This article will introduce the state-of-the-art antenna design and radio frequency (RF) system integration for wirelessly powered backscatter communications, covering both the node and the base unit. We capture the latest development in ultralow-power RF front ends and coding schemes for $\mu \text{W}$ -level backscatter modulators, as well as the latest progress in wireless power transfer (WPT) and energy harvesting (EH) techniques. Newly emerged rectenna system, waveform design, and channel optimization are reviewed in light of the opportunities for adaptively optimizing the WPT/EH efficiency for low-power signals with varying conditions. In addition, advanced device packaging and integration technologies in, e.g., additively manufactured RF components and modules for microwave and millimeter-wave ubiquitous sensing and backscattering energy-autonomous RF structures are reported. Inkjet printing for the sustainable and ultralow-cost fabrication of flexible RF devices and sensors will be reviewed to provide a prospective insight into the future packaging of backscatter communications from the chip-level design to complete system integration. Finally, this article will also address the challenges in fully wireless powered backscatter radio networks and discuss the future directions of backscatter communication in terms of “Green IoT” and “Low Carbon” smart home, smart city, smart skin, and machine-to-machine (M2M) applications. [ABSTRACT FROM AUTHOR]

Polymer memristors with good flexibility are promising electronic devices for edge computing paradigms in wearable electronics. However, most reported works present nonvolatile devices, which are suitable for applications in resistive random-access memory or artificial synapse. The volatile devices, which are indispensable in artificial neuron circuits, have rarely been reported, as the resistive switching property of organic devices is usually unstable in volatile devices. Moreover, most reported works use polymers in a way that is not compatible with traditional memristor fabrication technology, which limits the further applications of polymer memristors to large-scale neuromorphic circuits. In this letter, an Ag/Nafion/Au threshold switching memristor was fabricated via electrohydrodynamic printing technology and employed as a core of a leaky integrate and fire neuron circuit. The threshold switching memristor shows excel device size, good endurance, good device-to-device and cycle-to-cycle uniformity, flexibility, and stability at high temperatures. The combination of electrohydrodynamic printing technology and polymer memristor is promising in fast memristor production and largescale edge-computation network circuits. [ABSTRACT FROM AUTHOR]

In this letter, Ta2O5/WO3 double-layer wearable memristor synapse has excellent recognition accuracy (97%) for just 12 epochs compared to the single-layer device (83%). The insertion of an ultra-thin WO3 layer modulates the oxygen vacancy distribution in Ta2O5 and induces digital-to-analog switching behavior. Excellent AC endurance of (>109 cycles) under 2 mm extreme bending, a rapid speed (25 ns), reliable bending endurance for 104 cycles with 4 mm bending, stable retention (>106 s) up to 200°C, and water-resistant behavior are achieved. The potentiation, and depression having outstanding nonlinearity (0.64) is obtained. The Ta2O5/WO3 design is a promising candidate for wearable neuromorphic applications due to its wearability, flexibility, lightweight, low cost and environmental friendly fabrication. [ABSTRACT FROM AUTHOR]

The development of advanced, human like tactile sensing capabilities is one of the key challenges for next generation robots or prosthetics. Tactile sensors arrays will need to exhibit the desired sensing capabilities, show robustness to external influences as well as good approaches for the integration of large amounts of sensors. We present a tactile sensor array technology, based on the fabrication of a flexible interconnection substrate containing directly integrated tactile sensors. This approach has several advantages: interconnection substrate technology is widely available making upscaling of sensor arrays easy to a large amount of sensors and/or large sensing areas, the direct integration of sensors allows for a simple and very compact approach to densely packed sensor arrays and the structured flexible substrate enables integration into complex, three-dimensional bodies. We present sensors with a size of $600~\mu \text{m}$ and arrays of up to $12\times12$ individually addressable sensors. The sensors have a wide measurement range; free membrane deformation results in a high sensitivity of 2.6 kPa−1 respectively 2600 N−1 for small applied pressures (0–0.6 kPa) whereas deforming polymer studs extend the measurement range for larger applied pressures (5–25 kPa) with a sensitivity of 0.022 kPa−1 respectively 22 N−1. A statistical study of six sensor arrays from three wafers showed repeatable performance of the fabricated structures and robustness tests proved the stable sensing conditions over 10’000 cycles. [2021-0072] [ABSTRACT FROM AUTHOR]

This letter demonstrates a complementary 2-D field-effect transistor (FET) technology with molybdenum disulfide (MoS2) as the active film, hexagonal boron nitride (hBN) as the gate dielectric, and graphene as the gate electrode. The active region of the n-channel (n-FET) and p-channel (p-FET) devices are formed by undoped and Nb-doped MoS2, respectively. The complementary FETs have the desirable threshold voltage polarity, similar current drive, and high on-off current ratios of more than 106. A complementary metal-oxide-semiconductor (CMOS) inverter has been fabricated and the measured gain is about 14 with 90% noise margin at a 2 V power supply. [ABSTRACT FROM AUTHOR]

Flexible photodetectors have attracted much attention due to their great potentials in wearable electronics, bendable image sensors, and environmental monitoring, which requires functional components with good machinal properties. Herein, we introduced a novel metallic two-dimensional (2D) material, MXene, to form the electrodes by a spray-coating method and zero-dimensional (0D) PbS quantum dots (QDs) to work as photoactive layer. All solution-processable fabrication technique contributes to a simplified, low-cost and large-scale route to develop flexible photodetectors. Benefiting from the excellent conductivity of MXene electrodes and broadband photoresponse of PbS QDs, our devices realize a high detectivity up to $2.4\times10$ 11 Jones and exhibit good stability even after 1000 bending cycles. This work provides a new device configuration with 2D electrodes and 0D photoactive layers for designing high-performance flexible electronics. [ABSTRACT FROM AUTHOR]

This paper presents a smart sensor patch with flexible strain sensor and a printed temperature sensor integrated with a Near Field Communication (NFC) tag to detect strain or temperature in a semi-quantitative way. The strain sensor is fabricated using conductive polymer poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) in a polymer Polydimethylsiloxane microchannel. The temperature sensor is fabricated by printing silver electrodes and PEDOT:PSS on a flexible polyvinyl chloride (PVC) substrate. A custom-developed battery-less NFC tag with an LED indicator is used to visually detect the strain or temperature by modulating the LED light intensity. The LED shows maximum brightness for relaxed or no strain condition, and also in the case of maximum temperature. In contrast, the LED is virtually off for the maximum strain condition and for room temperature. Both these could be related to food spoilage. Swollen food packages can be detected with the strain sensor, serving as beacons of microbial contamination. Temperature deviations can result in the growth or survival of food-spoilage bacteria. Based on this, the potential application of the sensor system for smart food packaging is presented. [ABSTRACT FROM AUTHOR]

Radio frequency identification (RFID) is a well-established technology utilized in inventory management, security, logistics, product marketing as well as next generation smart flexible sensor platforms. This work reports the development of printed, wearable graphene temperature sensor on flexible textile substrates with structural configuration of RFID coil. Patterning of graphene in the form of sensing RFID coils on textile surfaces was achieved with cost-effective and scalable spray printing of graphene oxide and sequential reduction to reduced graphene oxide. Graphene RFID coil operating at 13.56 MHz with temperature sensing capability, are printed on flexible, ordinary fabrics to enable wearable and flexible electronics applications. The demonstration of reduced graphene oxide on textile as temperature sensitive layer is the distinct feature of this work. Good sensitivity of 0.0125°C−1 is achieved with linear response in the range of 25°C to 45°C and ~12% decrease in resistance was observed over the measured temperature span. Induced voltage of 100 mV peak-to-peak at an area of 30.25 cm 2 is measured. RFID performance of the sensor coil under different bending radii starting from fully flat (0°) to complete bending (90°) was also studied, showing that sensor coil performs well during flat operation (100 mV) and stays above noise floor even under fully bended condition (12 mV). Finally, flexible temperature sensing RFID antenna attached to human body to investigate performance for wearable applications, indicating that the sensor can effectively monitor temperatures in the range of 25°C to 45°C. [ABSTRACT FROM AUTHOR]

We present a method for printing conductive polymers onto P(VDF-TrFE) nanofibers to create all-polymer piezoelectric devices. Inkjet printing is an attractive fabrication approach for rapid prototyping of flexible electronics, but until now with limited applications in developing P(VDF-TrFE) nanofiber-based devices. We have demonstrated an approach to infill the void space within a piezoelectric nanofibrous matrix to allow for the inkjet printing of aqueous inks while avoiding leakage that typically leads to electrical shorting and without significant loss of voltage output. This was done using a diluted PDMS solution and a commercially available conductive ink. The 1 cm2 devices showed a 254 mV/N sensitivity to impact as well as a sensitivity to bending. The device was shown to be able to detect breathing and pulse rate when placed superficially to the carotid and radial arteries. Using these techniques, flexible piezoelectric sensing can be done in an array format, shown with applications in foot movement sensing. [ABSTRACT FROM AUTHOR]

This paper presents multifunctional electronic skin (e-Skin) with a stack of pressure and temperature sensors arrays. The pressure sensor layer comprises of an 8x 8 array of capacitive sensors using soft elastomers as the dielectric medium and the temperature sensing layer comprises of 4 x4 array of conductive polymers based resistive sensors. Three variants of capacitive pressure sensors were developed using two different dielectric materials (PDMS and Ecoflex) to find the best combination of performance and softness. The Ecoflex-based pressure sensor showed high sensitivity (~4.11 kPa−1) at a low-pressure regime (< 1 kPa) and the 7.5:1 PDMS based pressure sensor showed high sensitivity (~2.32 kPa−1) in the high-pressure regime (>1 kPa). Two variants of temperature sensors were fabricated using CNT and CNT & PEDOT:PSS conducting polymer composite and their performance compared. Finally, a highly sensitive CNT+PEDOT:PSS based resistive temperature sensors layer was integrated on top of 7.5:1 PDMS based capacitive pressure sensors layer to realize the e-Skin prototype. The developed e-Skin is capable of sensing pressures greater than 10 kPa with a high sensitivity of ~2.32 kPa−1 at 1 kPa and temperatures with the sensitivity of ~0.64 (%)/(°C) up to 80°C, thus demonstrating high potential for use in robotics and touch based interactive systems. [ABSTRACT FROM AUTHOR]

Capacitive non-contact imaging of electric fields and potentials with micro-metre resolution can provide relevant insights into material characterisation, structural analysis, electrostatic charge imaging and bio-sensing applications. However, scanning electric potential microscopes have been confined to rigid and single-probe devices, making them slow, prone to mechanical damage and complex to fabricate. In this work, we present the design and characterisation of a novel 5-element flexible array of electric potential probes with spatial resolution down to 20 $\mu \text{m}$ to speed up the scanning time. This was achieved by combining flexible thin-film probes for active guarding and shielding with state-of-the art discrete conditioning circuits. The potential of this approach is showcased by using the fabricated array to image latent fingerprints deposited on an insulating surface by contact electrification, obtain the surface topography of conductive samples and to visualise local dielectric variations. [ABSTRACT FROM AUTHOR]

Electric Double Layer Capacitor (EDLC) holds the highest share of commercial supercapacitor market. However, it has been proven that current Helmholtz, Gouy-Chapman and Stern models do not provide comprehensive explanation for energy storage mechanism in EDLC. In this work the effects of interdigitated EDLC design on capacitance of flexible laser scribed interdigitated microsupercapacitor (LSG-MSC) are studied. Three design parameters are tested, (1) current collector-electrode interaction, (2) electrode aperture, and (3) distance between parallel electrodes. Noticeable change was observed in the total capacitance upon change in LSG-MSC design which was analyzed in detail using cyclic voltammetry, electrochemical impedance spectroscopy and electrostatic simulation using COMSOL Multiphysics. It was found that in addition to electric double layer capacitance, an electric field was generated between electrodes and between electrode and current collector which led to small electrostatic capacitance between them. This electric field was also found to cause disturbance in double layer formation at the electrode thus causing change in the overall capacitance as the design parameters were varied.

There is a need to develop a simple cost-effective approach for wireless detection of whether package is or was open en route during transportation. Existing approaches rely on electronic devices that need sensors with on-board and continuous power source for sensing and data logging. This paper presents three different battery-free, cost-effective, Radio-Frequency Identification (RFID)-based solutions for the detection of tampering or package opening. The first solution is for real-time opening detection. Opening or closing the package leads to unfolding or folding of the flexible -based antenna, which activates or deactivates the RFID tag. The second solution is for recording and memorizing package opening using a printed switch that shunts the antenna of the RFID tag. Opening causes a permanent disconnection of this switch activating the RFID. This change is irreversible; thus, the sensor memorizes the specific opening event without any additional electronic memory device. The third solution is for all-around package security using an RFID-based thread. Opening the package from any side allows changes in the radiation profile so the package condition can be wirelessly sensed. The approaches have been simulated and validated experimentally.

In this paper flexible printed electrodes applicable to wearable electronics are presented. Using innovative materials as Laser Induced Graphene (LIG) and printed electronics, three type of electrodes based in LIG, silver chloride and carbon inks have been compared during the acquisition of bipotentials as electrocardiogram, electromyogram and electrooculogram. For this last one, a completely new framework for acquisition have been developed. This framework is based in a printed patch which integers 6 electrodes for the EOG acquisitions and an ad-hoc signal processing to detect the direction and amplitude of the eye movement. The performance of the developed electrodes have been compared with commercial ones using the characteristics parameters of each signal as comparative variables. The results obtained for the flexible electrodes have shown a similar performance than the commercial electrodes with an improvement in the comfort of the user.