Thin Flexible Substrate Research Articles

Flexible surface plasmon based coupled triple band UHF-microwave sensor for glucose sensing application

Although the correlation between a glucose concentration and its permittivity is somewhat weak to be measured, the glucose concentration is a strong function of the dispersion. In terahertz or microwave frequencies, dispersion can be observed or measured along the interface between an object under test and a metamaterial or surface plasmonic surface, which is basically a metal structure characterized by periodically arrayed holes, grooves, or metal grating. In this work, we have focused on the method for improving the accuracy of a glucose measurement by proposing a new triple-band microwave sensor design and by measuring the resonant frequency shift associated with a glucose concentration at three frequencies simultaneously. A new triple-band glucose sensor of dimension (30 mm x 10 mm) was designed with the main sensing region as compact as 14 mm with two conducting microstrip lines on both ends of the sensor. The sensor design has been realized on a thin flexible substrate of 0.15 mm thickness. The proposed sensor has been designed to measure glucose concentration through the measurement of a resonant frequency shift at 650 MHz, 4.45 GHz, and 10.35 GHz. Overall, the glucose concentration has been found to be correlated positively and linearly with the resonant frequency shift at these frequencies.

Real-Time Radiation Beam Monitoring by Flexible Perovskite Thin Film Arrays.

Real-time and in-line transversal monitoring of ionizing radiation beams is a crucial task for several applications which span from medical treatments to particle accelerators in high energy physics. Here a flexible and large area device based on 2D hybrid perovskite thin films (phenylethylammonium lead bromide), fabricated onto a thin flexible polyimide substrate, able to map the transversal beam profile of high energy radiation beams is reported. The performance of this novel tool is here compared with the one offered by standard commercial large-area technology, namely radiochromic sheets. The great potential of this class of devices is demonstrated by successfully mapping in real-time a 5 MeV proton beam at fluxes between 108 and 1010 H+s-1 cm-2, confirming the capability to operate in a radiation-harsh environment without output signal saturation issues. The versatility and scalability of here proposed detecting system are demonstrated by the development of a multipixel array able to map in real-time a 40 kVp X-ray beam spot (dose rate 8 mGy s-1). Perovskite thin film-based detectors are thus assessed as a very promising class of thin, flexible devices for real-time, in-line, large-area, conformable, reusable, transparent, and low-cost transversal beam monitoring of different ionizing radiation.

Peeling pressure-sensitive adhesive elastica from elastica with pinned and roller ends

Quasi-static peeling of a horizontal elastica (the tape) from another horizontal elastica (the beam) supported by a pinned end and a roller end is analyzed. Bending resistance is assumed to dominate the behavior, and large deflections and rotations are allowed. The tape is shorter than the beam and is pulled upward at a constant angle with the horizontal. A transversality (debonding) condition is derived for peeling, based on the common fracture mechanics approach. Displacement control is considered. The associated force exhibits its peak value at the onset of peeling. The vertical deflection of the pulled end of the tape also is of interest, especially when the tape detaches from the beam. Equilibrium curves are determined, and the effects of the following parameters on the peak force and the detachment deflection are investigated: the relative thicknesses and moduli of elasticity of the tape and the beam; the relative lengths of the tape and the beam; the angle of pulling; and the nondimensional work of adhesion. The system may be used as a model of peeling bandages, medical patches, biosensors, and other wearable devices from skin. Other possible thin flexible substrates include fabric, paper, leather, rubber, and plastics.

Batch Fabrication of Microelectrode Arrays with Glassy Carbon Microelectrodes and Interconnections for Neurochemical Sensing: Promises and Challenges.

Flexible multielectrode arrays with glassy carbon (GC) electrodes and metal interconnection (hybrid MEAs) have shown promising performance in multi-channel neurochemical sensing. A primary challenge faced by hybrid MEAs fabrication is the adhesion of the metal traces with the GC electrodes, as prolonged electrical and mechanical stimulation can lead to adhesion failure. Previous devices with GC electrodes and interconnects made of a homogeneous material (all GC) demonstrated exceptional electrochemical stability but required miniaturization for enhanced tissue integration and chronic electrochemical sensing. In this study, we used two different methods for the fabrication of all GC-MEAs on thin flexible substrates with miniaturized features. The first method, like that previously reported, involves a double pattern-transfer photolithographic process, including transfer-bonding on temporary polymeric support. The second method requires a double-etching process, which uses a 2 µm-thick low stress silicon nitride coating of the Si wafer as the bottom insulator layer for the MEAs, bypassing the pattern-transfer and demonstrating a novel technique with potential advantages. We confirmed the feasibility of the two fabrication processes by verifying the practical conductivity of 3 µm-wide 2 µm-thick GC traces, the GC microelectrode functionality, and their sensing capability for the detection of serotonin using fast scan cyclic voltammetry. Through the exchange and discussion of insights regarding the strengths and limitations of these microfabrication methods, our goal is to propel the advancement of GC-based MEAs for the next generation of neural interface devices.

Ultrathin and conformal frequency selective surfaces bandpass filter to eliminate the 5G bands on radio altimeters

AbstractThis work proposes a frequency‐selective surface‐based radome structure to selectively allow the radar altimeter operating band and also minimize the interference from Sub‐6GHz 5 G frequency bands. A Jerusalem cross and combinational loop (JCL) based frequency selective surfaces (FSS) unit cell of overall dimension 0.37λ was synthesized using a thin flexible substrate for use in fuselage of airborne systems. The proposed FSS unit cell exhibits transmission zero at 3.61 and 6.025 GHz and highly selective pass band at 4.3 GHz. The effect of bends and angle of incidence on the frequency response of the synthesized FSS was studied in transverse electric and transverse magnetic modes. A lumped element‐based equivalent circuit model for the proposed design was also presented. Finally, the fabricated prototype was experimentally validated in an Anechoic chamber setup and the suitability of the proposed FSS layers for aviation radar systems was confirmed.

Inkjet‐Printed Flexible Thin‐Film Thermal Sensors for Detecting Elevated Temperature Range

All inkjet‐printed thermal sensors are manufactured based on a metal–insulator–metal (MIM) interface or capacitor architecture, for the adapted device size ranging from 16 to 36 mm2 active area. Two different material inks, namely a nanoparticle conductive silver ink and an inorganic‐polymer‐based hybrid insulator ink, are applied layer by layer on a thin flexible polyimide substrate, for developing the printed MIM devices. To ensure the desired electronic conductivity and insulation from the layers, the manufacturing process steps and parameters are tuned, accordingly. The results show that the inkjet‐printed MIM devices could constitute up to 15 μm thickness and demonstrate average detection of a change in electrical capacitance ranging from 20 to 100 pF, when the temperature is varied between 100 and 300 °C. The investigations also summarize that the change in the electrical response is enough to detect an increment of 50 °C. The printed sensors also display high operational stability and repeatability, when subjected to thermal cycling.

A low loss microstrip line on thin flexible substrate film by defected ground structure

A low loss microstrip line on thin flexible substrate film by defected ground structure

Optimizing the Conductivity of a New Nanoparticle Silver Ink for Aerosol Jet Printing and Demonstrating Its Use as a Strain Gauge

Aerosol Jet Printing (AJP) shows promise for printable electronics and additive manufacturing as it is capable of printing conformally on nearly any substrate due to its direct write patterning, non-contact printing process, and compatibility with a wide range of printing materials. However, nearly all printed inks require some form of post-processing sintering to achieve acceptable properties, such as electrical conductivity. In this paper, a design of experiment (DOE) using Van der Pauw printed pads is presented which can be applied to characterizing any conductive ink. We focus on a new silver nano-particle ink from NovaCentrix (JS-A426) that was developed specifically for aerosol jet printing and study its electrical conductivity under a variety of sintering time and temperature conditions. From these results, a linear regression model is developed that accurately predicts the experimentally measured electrical conductivity of the printed ink. This DOE characterization process and resulting predictive model are especially useful for applications requiring limited thermal budgets, such as flexible electronics. SEM images are also used to analyze how the silver particles coalesce and densify due to thermal diffusion. Finally, the above results are used to design and fabricate an in-situ miniature strain gauge sensor using the NovaCentrix JS-A426 silver nano-particle ink on a thin flexible substrate. After printing and sintering, the miniature custom strain gauge had a nominal resistance of 355 Ω and a gauge factor of 1.74. These values are similar to commercial metal foil strain gauges and demonstrate that the aerosol jet printing is a viable manufacturing process for the production of custom miniature in-situ strain gauges. Advantages of this methodology include quick prototyping, custom digital design, conformal printing on essentially any surface, elimination of any adhesive layer, and manufacturing in less than a minute. This work is also the first to characterize the JS-A426 silver nano-particle ink thermal curing process and demonstrate its use as a viable sensing element using direct write aerosol jet printing.

Wearable Textile-Based Sensor Tag for Breath Rate Measurement

Breath rate is an important vital sign for monitoring the well-being and detecting underlying illnesses related to the respiratory system. The spirometer is widely used for evaluating the health of the respiratory system by measuring lung capacity and respiration rate (RR). Although this test yields accurate results, however, it is significantly inconvenient and invasive, as the test subject must breathe through a tube inserted in the mouth. Therefore, this device is not suitable for continuous monitoring of respiration. In this article, a novel contactless wearable breath rate measurement system is presented. The proposed sensor is based on a spiral resonator (SR) tag printed on a thin flexible textile substrate. The sensor exploits the body expansion and contraction during respiration to provide an estimate of the breathing frequency. This movement is measured by a microstrip probing loop that acts as the antenna of the reader. The reader operates at one frequency; the resonant frequency of the tag, and the sensing principle relies on the near-field coupling between the probe and the resonating tag at this frequency. The proposed sensor is characterized with its simple and lightweight design, can be easily integrated in garments, and its capability of providing continuous monitoring of the breathing rate. The proposed sensor has been tested through experimental measurements, and the results matched measurements from a reference ground-truth breath rate sensor based on a nasal cannula equipped with a thermistor. The solution proposed in this work provides a novel contactless technique for RR estimation.

Direct fabrication of single-phase multiferroic BiFe0.95Co0.05O3 films on polyimide substrates for flexible memory

• Low-temperature prepared BiFe 0.95 Co 0.05 O 3 films exhibited excellent characteristics. • A solution-based seeded photocatalytic precursor method has been developed. • The physical mechanism of the low-temperature prepared films is explained. Multiferroic memory exhibits unusual physical properties due to the electrical writing and magnetic reading of data to achieve low power consumption and efficient data processing. The flexibility of the multiferroic memory can realize its application in portable and wearable smart electronic products. The main challenge of integrating multiferroic oxides onto flexible substrates is to lower their processing temperature below the degradation temperature of plastic substrates. In this paper, the bendable inorganic BiFe 0.95 Co 0.05 O 3 polycrystalline thin films were prepared directly on flexible polyimide substrates with Pt electrode at only 350 ℃ by solution-based seeded photocatalytic precursor method. The flexible multiferroic element could bend safely to a small bending radius of 3 mm and exhibited excellent ferroelectricity, ferromagnetic, and magnetoelectric coupling characteristics at room temperature. Its remanent polarization was as high as 36 μC/cm 2 , remanent magnetization up to 4110 A/m, and magnetoelectric coupling coefficient up to 0.0135 V/A. The polarization did not deteriorate significantly during 10 3 bending-release cycles, 10 7 fatigue cycles, and 10 4 s data retention.These results prove the concept of integrating single-phase multiferroic thin films and flexible plastic substrates with low temperature by seeded photocatalytic precursor method and demonstrate the application potential of single-phase multiferroic films prepared at low temperature in the next generation of flexible multiferroic memory.

Development of Solar Energy Systems Based on High Performance Bulk and Film Thermoelectric Modules

Abstract: Due to the increase in energy demand and depletion of natural resources, the development of energy harvesting technologies becomes very important. Thermoelectric devices, based on the direct conversion of heat into electrical energy, are being the essential part of cost-effective, environmental-friendly, and fuel-saving energy sources for power generation, temperature sensors, and thermal management. High reliability and long operation time of thermoelectric energy systems lead to their extensive use in space industry and gas pipe systems. Development and wide application of solar thermoelectric converters (generators) is mainly limited by relatively low thermoelectric conversion efficiency. In this work, we suggest for the first time to use direct conversion of solar energy by systems based on high-performance multistage thermoelectric modules operating in the temperature range of 300 - 900 K for creation of autonomic systems with electric power up to 500 W and electric efficiency up to 15 %. Furthermore, we developed film thermoelectric modules on thin flexible substrates with the figure of merit Z corresponding to that of bulk modules. Such film thermoelectric converters with output voltage of several volts and electric power of several microwatts can be used at micro-solar energy systems.

Simultaneous Wireless Power Transfer and Data Telemetry Using Dual-Band Smart Contact Lens

An efficient noninvasive system for simultaneous transmission of wireless power and data is vital for continuous human health monitoring. In this article, we present a self-tuned spiral-shaped antenna with dual-band characteristics operating at 920 MHz and 2.4 GHz for efficient wireless power transfer (WPT) and data telemetry, respectively. To avoid vision blockage, the proposed smart contact lens (SCL) dipole antenna comprises two symmetrical spiral arms with inner and outer diameters of 10 and 14 mm, respectively. The SCL antenna was printed on a thin flexible polyimide substrate with a biocompatible polydimethylsiloxane (PDMS) coating. The influence of dispersed dielectric properties of PDMS on SCL antenna performance was investigated. Furthermore, the antenna was combined with a miniaturized rectifier and a micro-LED to demonstrate wireless LED illumination on a saline-filled model head. The power transfer efficiency (PTE) as a function of eye movement in the form of a path gain was also investigated. In addition, the PTE across the distance variations from 10 to 30 mm was computed, and a −17.85 dB was achieved at a separation of 12 mm. A specific absorption rate analysis was performed to determine human eye safety under radio frequency exposure from the external transmitter and the results complied with the International Commission on Non-Ionizing Radiation Protection guidelines. Furthermore, a theoretical link power budget analysis was experimentally validated using software-defined radio. Measurements of s-parameters were noted through the use of a saline solution to mimic a realistic human eye and were found to have a reasonable correlation with the simulated results.

A circularly polarized meander loop antenna for unmanned aerial vehicle satellite navigation system

A circularly polarized (CP) meander loop antenna used in the unmanned aerial vehicle (UAV) satellite navigation system is proposed. The planer size of the proposed antenna is 45.6 × 38.4 mm2 and it was printed on a thin flexible substrate with a thickness of only 0.063 mm. Thus, it has the advantages of a lightweight, low profile, and ease in manufacturing. The proposed antenna design utilizes a loop antenna and has applied a perturbed element into the loop to excite two equal amplitude electric fields with a 90° phase difference, thereby exciting a good CP radiation. The measured 10-dB impedance bandwidth of the proposed antenna was 9.3% (1.48–1.624 GHz), and its corresponding 3-dB axial ratio (AR) bandwidth was 2.3% (1.555–1.591 GHz). The CP operating band of the proposed antenna can cover the GPS L1, Galileo E1, and Beidou B1 band (1.559–1.591 GHz).

Thermoelectric properties of p-type Bi-=SUB=-0.5-=/SUB=-Sb-=SUB=-1.5-=/SUB=-Te-=SUB=-3-=/SUB=- films on flexible substrate

Bi2Te3-based compounds are excellent candidates for the low-temperature thermoelectric application. In the present work, a technology for fabrication of p-Bi0.5Sb1.5Te3 films with high thermoelectric efficiency on a thin flexible polyimide substrate has been developed. The preparation of films was carried out by a flash evaporation method. A systematic study of the transport properties (Hall coefficient, Seebeck coefficient, electrical conductivity, transverse Nernst coefficient) over the entire temperature range of 80-400 K for p-Bi0.5Sb1.5Te3 films has been performed. The power factor (PF) for the Bi0.5Sb1.5Te3 (doped with 0.5 wt% Te) film reached the value of ~ 30 μW/cm · K2, which is among the highest values of the PF reported in the literature to date for a film on a flexible polyimide (amorphous) substrate. The measured thermal diffusivity along the film allowed us to accurately estimate the figure of merit Z for p-Bi0.5Sb1.5Te3 films considering the anisotropic effect of Bi2Te3-based materials. A significant enhancement of Z up to ~ 3.0·10-3 K has been obtained for these films, which is state-of-the-art even compared to bulk materials. This research can provide insight into the fabrication of p-type branch of the film thermoelectric modules (FTEM), which could be a candidate for application in micro-scale thermoelectric generators. Keywords: p-Bi0.5Sb1.5Te3 film, thin flexible substrate, thermoelectric properties.

Flexible Ni/NiOx-Based Sensor for Human Breath Detection.

We developed a simple methodology to fabricate an Ni/NiOx-based flexible breath sensor by a single-step laser digital patterning process of solution-processed NiOx thin-film deposited using NiOx nanoparticle ink. Laser-induced reductive sintering phenomenon enables for the generation of three parts of Ni electrodes and two narrow NiOx-sensing channels in between, defined on a single layer on a thin flexible polymer substrate. The Ni/NiOx-based breath sensor efficiently detects human breath at a relatively low operating temperature (50 °C) with fast response/recovery times (1.4 s/1.7 s) and excellent repeatability. The mechanism of the gas-sensing ability enhancement of the sensor was investigated by X-ray photoelectron spectroscopy analysis. Furthermore, by decoupling of the temperature effect from the breathing gas, the response of the sensor due to the temperature alone and due to the chemical components in the breathing gas could be separately evaluated. Finally, bending and cyclic bending tests (10,000 cycles) demonstrated the superior mechanical stability of the flexible breath sensor.

Eco-design for dye solar cells: From hazardous waste to profitable recovery

Recycling is rarely considered in the field of dye solar cells. However, recycling should be a critical part of holistic eco-design, which considers the efficiency, lifetime, return of energy investment, safety, and availability of materials. The novelty and focus of this work is recycling, and this is the first contribution systematically analyzing how different material choices and their combinations affect the recycling of dye solar cells. By understanding the recycling processes and how the recycling of materials is interlinked in a multicomponent system, it is possible to eco-design systems and guide future research toward selecting materials that support sustainability and enable economically motivated recycling. Economic incentive is the biggest factor determining whether or not recycling will take place. With eco-design, it is possible to avoid future problems, such as trapping rare and expensive critical metals in waste from which they are difficult or even impossible to recover. In fact, the conventional dye solar cells create harmful waste with no economically profitable way of recycling. Interestingly, many of the alternative materials that enable recycling have not been originally designed for that purpose, and it is rarely obvious how the combination of different materials affects recycling. For instance, using thin flexible substrates, which have been developed for roll-to-roll manufacturing, supports the retrieval of Ag, and using high performance Co- or Cu-based electrolytes instead of iodine electrolyte eliminates toxic gas problems in pyrometallurgical recycling processes.

One-dimensional Sb2Se3 enabling ultra-flexible solar cells and mini-modules for IoT applications

Power supply equipment, employed in the Internet of Things (IoT) for instance, calls for efficient harvesting of solar energy from the environment sustainably. Sb 2 Se 3 enjoys the advantages of unique one-dimensional crystal structure and low-temperature film growth, enabling the fabrication of flexible and lightweight solar cells. Therefore, Sb 2 Se 3 solar cells are expected to have intrinsic advantages in powering IoT sensors. Herein, the device configuration and film fabrication of flexible Sb 2 Se 3 solar cell was optimized and an efficiency up to 6.13% and power-per-weight of 2.04 W g -1 were obtained, both of which are the highest records for flexible Sb 2 Se 3 solar cells. Benefitting from the intrinsically high flexibility of Sb 2 Se 3 and the thin flexible substrate, our device retained 96% of its initial performance after 1000-times bending at the extremely small curvature radius of 0.5 mm. Furthermore, the first Sb 2 Se 3 mini-module (25 cm 2 area) was constructed and its application in powering a blue LED under all weather conditions and a flower monitor (IoT sensors) was demonstrated. This work opens an avenue toward flexible Sb 2 Se 3 solar cells and points out its future research direction. Solar cells, with high energy density and reliability, can serve as the power source for the sensors of the Internet of Things (IoT) sensor. Combining the intrinsically high flexibility of Sb 2 Se 3 and careful analysis of stain distribution, lightweight and ultra-flexible Sb 2 Se 3 solar cells and mini-modules were obtained and successfully applied to IoT sensors as energy supply. • The analysis of material mechanics and stain distribution guide the design of ultra-flexible Sb 2 Se 3 solar cells. • The flexible Sb 2 Se 3 solar cells exhibit high efficiency of 6.13%, high power-per-weight of 2.04 W g -1 . • The flexible Sb 2 Se 3 solar cells keep 96% of the initial PCE after 1000-times bending at a curvature radius of 0.5 mm. • The large-area (~ 25 cm 2 ) flexible Sb 2 Se 3 solar mini-modules are successfully applied for power supply of IoT sensors.

Evaluation of Ni-Based Flexible Resistance Temperature Detectors Fabricated by Laser Digital Pattering.

Temperature sensors are ubiquitous in every field of engineering application since temperature control is vital in operating, testing and monitoring various equipment systems. Herein, we introduce a facile and rapid laser digital patterning (LDP) process to fabricate low-cost, Ni-based flexible resistance temperature detectors (RTDs). Ni-based RTDs are directly generated on a thin flexible polyimide substrate (thickness: 50 µm) by laser-induced reductive sintering of a solution-processed nonstoichiometric nickel oxide (NiOx) nanoparticle thin film under ambient conditions. The shape of RTDs can be easily adjusted by controlling computer-aided design (CAD) data without using the physical patterning mask while the sensitivity (temperature coefficient of resistance (α) ~ 3.52 × 10−3 °C−1) of the sensors can be maintained regardless of shape and size of the sensor electrodes. The flexible Ni-based RTDs can operate over a wide temperature range up to 200 °C with excellent repeatability. Additionally, the Ni-based RTDs respond quickly to the temperature change and can operate in corrosive environments including water and seawater. Moreover, the Ni-based RTDs show a superior mechanical and electrical stability with a negligible resistance change up to a radius of curvature of 1.75 mm. Finally, a tape-pull test demonstrates the robust adhesion of Ni-based RTDs on the substrate.

Development of Thermal Detector Based on Flexible Film Thermoelectric Module

Thermal detectors find a significant niche in the market of modern sensors. Bi2T3 and PbTe semiconductors are effective thermoelectrics and excellent candidates for different applications. In the present work, a technology for fabrication of p-Bi0.5Sb1.5Te3 and n-PbTe films with the high thermoelectric efficiency on thin flexible polyimide substrate has been developed. The preparation of films was performed by flash evaporation method. The high sensitivity of the devices is due to the high Seebeck coefficient of 200 mV/K and reduction of thermal conductivity of thin thermoelectric film from the bulk value. The devices operate in the Johnson-Nyquist noise limit of the thermocouple. The performance enables fast and sensitive detection of low levels of thermal power and infrared radiation at room temperature.

Fully printed origami thermoelectric generators for energy-harvesting

Energy-harvesting from low-temperature environmental heat via thermoelectric generators (TEG) is a versatile and maintenance-free solution for large-scale waste heat recovery and supplying renewable energy to a growing number of devices in the Internet of Things (IoT) that require an independent wireless power supply. A prerequisite for market competitiveness, however, is the cost-effective and scalable manufacturing of these TEGs. Our approach is to print the devices using printable thermoelectric polymers and composite materials. We present a mass-producible potentially low-cost fully screen printed flexible origami TEG. Through a unique two-step folding technique, we produce a mechanically stable 3D cuboidal device from a 2D layout printed on a thin flexible substrate using thermoelectric inks based on PEDOT nanowires and a TiS2:Hexylamine-complex material. We realize a device architecture with a high thermocouple density of 190 per cm² by using the thin substrate as electrical insulation between the thermoelectric elements resulting in a high-power output of 47.8 µWcm−² from a 30 K temperature difference. The device properties are adjustable via the print layout, specifically, the thermal impedance of the TEGs can be tuned over several orders of magnitudes allowing thermal impedance matching to any given heat source. We demonstrate a wireless energy-harvesting application by powering an autonomous weather sensor comprising a Bluetooth module and a power management system.