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In this paper, we analyze the effects of textile weaving and finishing processes on the performance of textile-based wearable antennas. Several textile-based patch antennas operating at 2.4 GHz were designed and fabricated for evaluation. All of them had the same geometry comprising a 1-mm-thick felt substrate in the middle, and silver ink screen-printed polyester fabric as the ground and patch at the bottom and on top. However, polyester fabric, the bare textile material for the conductive ground and patch was subjected to different weaving and finishing (tentering, scouring, and calendering) processes. It was observed that the antenna resonant frequency, bandwidth, radiation efficiency, and peak gain were varied by these processes, although the antenna geometry and screen-printing method were identical to each other. The best antenna exhibits a peak gain of 5.2 dBi and a radiation efficiency of 42.4%, while the worst shows corresponding values of 4.17 dBi and 34.8%. This implies that the weaving and finishing processes considerably impact textile-based wearable antenna performances.

This paper presents a design of periodic circuit analog absorbers (PCAAs) for electromagnetic (EM) scattering fields reduction. The performance sensitivities to the geometric parameters in fabrications are examined to estimate the manufacturing uncertainty. We consider randomly nonuniform thicknesses of a conductive ink and the two sandwiching dielectric substrate layers on both sides to fabricate PCAAs. The EM absorbing capability is studied on the S-parameters (the reflection and transmission coefficients) and the resulting power efficiency, using numerical HFSS full-wave simulations at a frequency band of 10 GHz. Experiments on prototype samples are also conducted. They showed that a fabrication accuracy of better than $10^{-4}\lambda$ is required to assure a stable performance.

Flexible electrodes are developed using a novel conductive ink with various ratios of graphene nanoflakes decorated with copper nanospheres as a conductive filler. These electrodes represent potential candidates for energy storage devices and solid-state batteries. The electrodes are studied by AC measurements in the range of (0.1 Hz–500 kHz). Electrical impedance measurement data have been utilized for modeling the electrical properties of the conductive ink. The fitting is done using Z-Fit software and a randomized method followed by the Levenberg-Marquardt using the Cole-Cole model. The equivalent circuits are simulated by the Z-Sim software and values are compared with the theoretical values. The error between simulation value and theoretical value was found to be minimum. The aim of the work described in the present paper is to establish an equivalent electrical circuit for the conductive ink electrodes. The best and simplest circuit representation which gives the best fitting for the Cole-Cole and Nyquist plots consists of two resistors in parallel with a capacitor in series. The values of the electrical components are tabled, and the Cole-Cole plot is fitted to the measured data.

Screen-printing of functional materials is a well-established process in the printed electronics industry. Recent advancements of flexible electronics demand screen-printing of a wide range of functional materials on flexible and stretchable polymeric substrates. The printability, quality of the printed structures, and their reliability during storage and usage are determined by the key fabrication process parameters such as the material properties, printing parameters, curing conditions, and environmental factors. Therefore, proper analysis of distinctive fabrication processes is crucial for problem-solving and process improvements in order to ensure optimum outcomes. In the present study, a low-cost, disposable, multilayer Sweat Rate Electrode (SRE) was fabricated on a flexible and highly stretchable Thermoplastic Polyurethane (TPU) substrate by screen-printing, using a Silver-filled conductive ink and a water-based Carbon-filled conductive ink. Exposure to low humidity and high temperature adversely affected the fabrication process and the robustness of the SRE. These challenges were overcome by better control of environmental conditions in the printing atmosphere and proper selection of the materials, printing parameters, curing conditions, and fabrication process flow. We demonstrate the fabrication of a defect-free, robust SRE on TPU substrate.

Smart clothing is where the capability of sensing, responding, and adapting to environmental stimuli such as electrical, mechanical, chemical, and thermal is embedded into textiles to ensure functional, fashionable, and comfortable solutions to everyday human needs. Hence, it is an ideal avenue to bring wearable technology closer to human beings and enable easy access to Internet of Things (IoT). Integration of electronic functionality to textiles is essential to realize the true potential of many smart clothing applications. Further, the ability of such electronics systems to stretch, without significant deterioration in electrical properties, is a key performance requirement in many of the smart clothing applications. The electromechanical reliability of conductors under tensile strains is influenced by the conductor geometry and the properties of the substrate. The objective of the present work is to understand the collective effect of print orientation, width, and thickness on the electromechanical behaviors of meandering conductors printed on an anisotropic, stretchable textile substrate. Meandering conductors with distinct features were fabricated on a knitted fabric substrate with a commercially available stretchable silver conductive ink. Printed conductors were optically and electrically characterized under loaded and unloaded conditions. Statistical analysis revealed that the print orientation, width, and thickness of the printed conductors could significantly affect their electromechanical performance.

Printed electronics are rapidly increasing and competing against the traditional way of manufacturing electronics. Different aspects of the processes are already being taken over that avoids material wastage, reduces cost and lead times. For example, printing technologies are very popular in depositing reliable and very fine conductive traces as opposed to conventional etching. Previously, authors have developed process studies by utilizing Aerosol Jet Printing technology in realizing multi-layer metallization with successive metal and dielectric layers and additively printing a donut micro-via. However, the merits of printing technologies do not stop here. Recently, assembly of Surface Mount Devices (SMD) on a flexible substrate has been of interest that requires low processing temperatures. Conventionally, this is done by components mounted on a solder paste and reflowing to about 220 °C. This temperature is extremely high and induces many reliability concerns. With the use of printing technologies, this can be avoided. A viable method would be to utilize low temperature solder for which the peak reflow temperature could be much lower than 220 °C. Nevertheless, with new methods, there comes new complications. For example, reliability concerns involving the interconnection joints between SMD and substrate. Since this is to be done additively, another concern comes about the printer’s capability to dispense the solder paste as well as the metal conductive pad simultaneously. Having to additively print conductive pad, and screen print the solder brings about much manual work and just not feasible. In this work, authors have utilized state-of-art micro-dispense additive printer to dispense the metal conductive ink and the Low Temperature Solder (LTS) for SMD attachment. Process studies are done that addresses the physical profile of the low temperature solder for various print parameters. Multiple SMDs such as resistors, capacitors, and Inductors are mounted with semi-automatic pick-and-place machine. The reflow will still be done but at a lower temperature. Process development of additive part of the assembly will be done, along with the characterization of physical, electrical and mechanical properties.

Selective dielectric deposition using a dam and filling process utilizing additive manufacturing (AM) is presented, and used for the design of millimeter wave (mmWave) circuits. Aerosol jet printing (AJP) is used to build the dams using polyimide and filling with benzocyclobutene. Dielectric islands with different thicknesses and high aspect ratios can readily be deposited with good print resolution. Fully AM printed patch antenna (center frequency = 94.08 GHz) is demonstrated on these dielectric structures using silver conductive ink also deposited using AJP. Embedded circuits are discussed with a demonstrated 0 dB attenuator die placed in liquid crystal polymer (LCP) pocket filled with BCB. Details of design, fabrication, and measurement are presented. This process is attractive where a mix and match of substrates are desired in the design of high density mmWave packages.

The feasibility of using chip-based RFID designs as wireless sensor tags open a wide range of application possibilities in the field of robotics. However, multi-step lithography manufacturing and/or MEMS techniques are often required for the industrial-grade fabrication of such sensors. In this paper, we present a simple, home-based, two-step fabrication process to produce chipless RF-based wireless sensors. We use an office-based inkjet printer to produce the antenna traces using silver conductive ink. Kirigami-inspired designs are used to produce four sensors responsive to various mechanical stimuli commonly used for DIY robotic projects (contact, compression, extension, and bend). We demonstrate sensing and wireless transmission of the detected mechanical stimuli through the proposed chipless sensor tags with reliable consistency. The tags can be replicated quickly with the inkjet-printing method. This paper also contains analyses on the effects of varying the dimensions and electrical parameters of the tags. The developed antennas in this work can be used as wireless mechano-responsive sensors for robotic applications.

Additive manufacturing (AM), commonly known as three-dimensional (3D) printing, refers to a method of rapid prototyping through material stacking. In the field of human-computer interaction, many researchers have used technology to realise rapid prototyping, such as printing parts, mechanical structures and product shells. Some researchers have explored interactive product manufacturing based on AM, such as flexible electronic fabric, four-dimensional self-forming structure and conductive ink. Most of these studies reformed the printing nozzle and printing materials on the basis of the traditional fused deposition modelling 3D printer, but the research on the printing path is still in the initial stage in the exploration of new interactive product manufacturing. Accordingly, this paper focuses on interactive manufacturing technology and the innovations of printing paths and parameters. The results are hoped to provide inspiration for future interactive manufacturing.

As the conductive ink becoming mature in preparation and use, this smart material is gradually used in various industrial activities. Conductive ink can automatically change its resistance depending on the contact area, which can convert different mechanical signals into electrical signals for output. Nevertheless, the properties are affected by the substrate material on which the conductive ink is printed. A soft substrate will increase the non-linearity and result in a considerable error and unacceptable for the sensor. This paper presents an approach based on the topology optimization, the Solid Isotropic Material with Penalization (SIMP) method. To optimize the structure of the substrate, the compliance is minimized with certain constraints. The optimized structure is simulated by Comsol Multiphysics (version 5.5), and the mechanical property is tested. The measured results are fitted to obtain the relationship between stress and contact area. As a result of topology optimization, the substrate membrane's mechanical property in the piezoresistive sensor is improved, and the requirement of increasing the stability of detection is met. Meanwhile, the ability to respond to rapid loading does not lose. The results show that the method is beneficial to improve the mechanical property of the substrate. The topology optimization on the substrate has application value in piezoresistive sensors.

The bending effects of proximity coupled 4x4 patch arrays with printed patch elements operating in the X-band near 10 GHz is presented. The patch arrays have circular patch elements with inclusive slots residing on the top surface of four layers (10mil/layer) of DuPont Pyralux AP. The inclusive slots decrease the axial ratio of the antenna and increase the impedance bandwidth. Each array has a microstrip feed network of quarterwave transformers and T-junction power dividers in the middle of the four layer stackup. The microstrip lines are proximity (or capacitively) coupled to the patch elements. A ground plane on the bottom surface of the four layer stackup provides surface agnostic behavior. The patch elements and microstrip feed network are printed with DuPont CB028 conductive ink using a liquid dispense technique. For the purpose of comparison to PCB processed antennas, 4x4 patch arrays with 1$/_{2}$ oz. electroplated copper for the patch elements and microstrip feed network are also reported. The gain, 3 dB beamwidth, and VSWR bandwidth behavior have been studied for uniaxial bending of the two arrays for radii of curvature down to a 1 inch. The nominal (i.e., no bending) measured far-field gain of the arrays is 14.5 dBi (printed) and 14.7 dBi (copper). The printed and copper arrays behave very similarly with changes in gain of 9.3 dB (printed) and 8.3 dB (copper) for bending down to 1 inch in an axial direction and changes in gain of2.6 dB (printed) and 2.8 dB (copper) for bending down to 1 inch in a circumferential direction.

Herein, a water-based environmental conductive ink based on silver fractal dendrites is formulated and screen-printed onto the fabrics to fabricate the multifunctional e-textiles. Multifunctional e-textiles exhibit high conductivity (0.12 ohm/sq), excellent strain sensing performance (workable strain range of 105% with a gauge factor of 906.45), and outstanding joule heating performance (heated to 89 □ at 1 V). The developed multifunctional e-textiles have been successfully used to monitor the motion of human joint (elbows and knees).

The paper presents electrical characteristics of conductive ink of type Graphit 33, acting as a converter between applied pressure and output electrical signal. It mentions basic properties of the ink, including the explanation of the principle of function. Further it describes the measurement process on tactile sensors with circular electrodes of various types and dimensions. It studies the dependency of electrical resistance of the ink on the applied pressure. Various setups with different ink layer thicknesses are compared and their suitability to act as pressure converter is finally discussed.

Copper sintering is gaining prominence as a prospective alternative to silver sintering in die-attach applications. However, process temperatures and sintering times are still high compared to silver sintering and a challenge for large scale industrialization. In this paper, rapid and low temperature die-attach bonding using copper formate based inks is investigated. While these inks are successfully used to form metal traces on substrates by inkjet and aerosol printing, they reveal a substantial challenge for die-attach bonding. Based on results using polyethylene glycol (PEG) as binder, different pastes were realized and investigated using binders which form metal complexes with copper formate. Beside the promising result using PEG, best bonding results were obtained using α- terpineol as binder while traditional conductive ink binders amino-2-propanol and hexylamine caused challenges during pre-drying, degassing and in establishing a reliable interconnect.

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 peak-peak voltages greater than 0.5 V and a 259 mV/N sensitivity. Using these techniques, flexible piezoelectric sensing can be done in an array format, paving the way for unique forms of wearable physical biomarker sensing.

Wearable sensors have attracted great attention over the past decade due to the potential application in personalized medicine. Bimodal silver nanoparticles (AgNPs) have been used in printed flexible electronics in some studies. In the study, we synthesized a range of AgNPs via controlling experimental parameters. A conductive ink with high stability was formulated by mixing two kinds of AgNPs (20 and 100 nm in diameter). The fine patterns of electric circuit were printed on the desired areas of nitrile gloves. The electric circuits have an excellent stretchability and the change in electric resistance of electric circuits can be detected when finger bending.

This study examines the conductive ink minimization of 5G engineered electromagnetic surfaces (EESs) made from meshed conductors. The paper demonstrates that the uniform meshed EES has (considerably) less conductor coverage than a solid metal area version without significantly compromising the performance, with the added benefit of increased optical transparency. Simulated results are presented in support of the novel EES topologies.

In this study, a fully flexible inkjet-printed graphene-based capacitive humidity sensor is investigated using graphene oxide (GO) as sensing material mixed with Polyacrylic Acid, PAA. The printed humidity sensor consists of i) an optimally designed interdigitated electrode (IDE) made from reduced graphene oxide conductive ink material decorated with silver nanoparticle (rGO/Ag), ii) inkjet-printed GO as sensing material and iii) polyethylene terephthalate, PET as flexible substrate. The conductive ink is synthesize in house with a stable and consistent temperature setting which has successfully improve the yield performance of the graphene-based inkjet and the method of preparation has prevent the ink from agglomeration during printing. The multilayer inkjet-printed GO on top of the rGO/Ag IDE is employ to increase the contact area between the sensing layer and water vapor, thus leading to a high sensitivity sensor. The results shows that as the relative humidity is varies in the range of 30%RH to 90%RH, the proposed humidity sensor is able to achieve a highest sensitivity of 0.15pF/%RH at 50°C. The sensor show a stable capacitance value with a linear output at low humidity and increase exponentially at above 60%RH. The developed sensor also show a good temperature dependence at temperature below 60°C and humidity lower than 70%RH.

In the past ten years, wearable electronics underwent tremendous growth. Undoubtedly, one of the fields that led this trend is represented by biomedical applications. In this field, wearable technologies can provide unique features such as the unobtrusive monitoring of biopotentials. Polymerbased electrodes developed for this purpose can take advantage of their seamless integration in the garments. However, the available solutions exhibit fragility in relation with the stretchability of the fabric, causing significant performance degradation.In this work, this problem is tackled by a novel deposition approach based on screen-printing technology. The electrodes are deposited onto the pre-stretched fabric to ensure the full functionality during common operating conditions. To this aim, a novel PEDOT:PSS conductive ink formulation and printing procedure were conceived. In order to prove the electrode performance for surface electromyography, we printed the electrodes directly onto a commercial stretchable polyester sleeve for sport applications. The electrodes allowed to reliably record the muscular activity of the forearm with performance comparable to that of commercial gelled Ag/AgCl electrodes. The obtained results suggest that the proposed approach can be valuably used in health and fitness applications.

A new method of integrating passive components on large non-planar parts (example, automotive bumpers) using conductive spray inks and a shadow mask coupled with a damascene-like process is presented. The sprayed conductive ink acts as a catalyst for electro- or electroless-plating of copper. Structures with fine resolution can readily be printed using this process. A Vivaldi antenna operating in the V-band is demonstrated on a 3D printed scaled down automotive bumper. The proposed method is simple, reduces waste, and can readily be adopted in the integration of passive components on large plastic structures, especially for automotive applications. Details of design, fabrication, and measurement are presented.

Smart clothing with electronic functionality is gaining greater recognition as the next-generation electronics. The integration of electronics into textiles, aided by developments of materials and fabrication technologies, has paved the way to the realization of smart clothing that exhibits diverse electronics functionalities. Lamination of printed electronics into textiles, printing conductive inks on polymeric interface layers, and embedding of electronic components via molding techniques have been studied, but less attention has been paid to the viability of direct printing on textiles. In the present study, a meandering structure was directly printed on a knitted fabric with general-purpose and stretchable Silver (Ag) conductive inks. The electromechanical behavior of printed conductive leads was investigated by in-situ monitoring of DC electrical resistance during stretch-to-failure and fatigue cycling tests under uniaxial tensile loading. The influence of the printed leads on the inherent mechanical properties of the fabric was analyzed with respect to Young's modulus and deformation of the substrate under tensile strain.

This paper deals with contacting of the standard electrical SMD components on the textile substrates. SMD components are contacted and also encapsulated in one single step by a thermo-compress method. SMD components are embedded and fixed in the cavities of the plastic housing made by 3D printer. This housing is subsequently melted by the standard thermo-transfer device, which is used in textile industry for pattern transfer. The electrically conductive track can be embroidered by a conductive hybrid thread directly on the textile or printed by conductive ink on the housing.

Due to the exponential growth of electronic textiles, the development of low cost stretchable conductive yarns has become increasingly crucial. In this study, a low cost stretchable conductive yarn is being developed by directly coating the stretchable yarns with a stretchable conductive ink. Some of the preliminary results on the stretchability of the conductive yarns being developed are reported in this paper., 2019 IEEE International Flexible Electronics Technology Conference (IFETC), August 11-14, 2019, Vancouver, BC, Canada

The increase of data-traffic capacity demands for better performance of the new generation of mobile communications (5G) drives new antenna technologies. The main challenge is to produce user devices which easily integrate a 5G network and its inherent services, without compromising neither cost nor performance. 3D printing is a good solution for these issues, as it can produce high accuracy objects while maintaining low production costs. This work presents several horn antennas operating in the 28 GHz band, all manufactured with 3D printing technology. Two techniques were used to metallize the antennas: with copper tape and with conductive ink. All prototypes achieved proper results for integrating the upcoming IoT scenarios.

Paper-based digital microfluidic biochips (PDMFBs) are becoming highly effective among the microfluidic platforms due to its low-cost and in-place fabrication. The designed electrodes and wiring can be fabricated on a piece of paper by an inkjet printer and conductive ink containing carbon nanotube particles (CNTs). However, due to induced control interference, the wires cannot pass by an arbitrary electrode. Each wire that is to be routed possesses its conflict electrode group, which must be avoided for a feasible droplet movement. This paper presents a fluid-control co-design considering several important cost-driving issues like minimization of schedule length, control pin count, and wirelength, together with congestion-free and conflict-free wiring. Observably, design gaps exist among the sub-tasks of the fluid-level, control-level, and fluid-control as a whole, due to their separate considerations. It indeed introduces many design cycles lengthening the design process, and thus increases the overall cost. In this context, this work integrates the sub-tasks as a prior need to obtain a low cost and efficient platform. Several benchmarks have been studied to evaluate the performance.

International audience; Actuation and sensing with electroactive polymers should be a chance for flexible MEMS but their micromachining and integration are still not mature. Some innovative materials and microfabrication processes are still expected. In this paper, a first full elaboration of polymeric microtransducers (MTs) including integration and operation has been described. The fabrication process relies on commercially available poly(3,4-ethyledioxy-thiophene): poly(styrene sulfonate) (PEDOT:PSS) conductive ink, onto flexible SU-8 photoresist microchip. Batch-fabrication of complex flexible monolithic units comprising individually addressable MTs of different shapes, is demonstrated. The resulting polymeric MTs show both very promising bending actuation and strain sensing properties in open-air. Remarkably, the microfabrication process did not impact the performances compared to material fabricated with laser cutting. This work paves the way for flexible MEMS development for soft microrobotics, microfluidics in medical and spatial applications.

The project study was conducted to develop a prototype that directly draws conductive traces onto a non-conductive surface. The project study also aimed to test commercially available conductive inks and against different substrates to find the workable materials for the prototype’s application.

We developed 3D printed disposable inductorcapacitor (LC) circuits which is a new wireless sensing platform for sensitively detecting a targeted ion from multiple ions. The LC circuit was fabricated by direct-ink-writing based 3D printing with eco-friendly cellulose conducting ink materials. The conductive ink was prepared by mixing silver nanowires (AgNWs) into the disposable cellulose nanofibers (CNFs) paste. The combined design of LC circuit with polymeric ion selective membrane electrode (ISME) were printed on a flexible polyimide (PI) film. The proposed 3D printed disposable wireless sensor system detects ion concentration by measuring the intensity of reflective coefficient, S11 using a vector network analyser.

In this study, the bimodal sized core–shell structured Cu–Ag nanoparticles (Cu@Ag NPs) of 20 and 110 nm were prepared using lactic acid as stabilizer. The Cu oxides were removed during the formation process of Ag shell. The obtained Cu and Cu@Ag NPs exhibit good oxidation resistance at temperatures below 150 and 200 °C, respectively. A conductive ink with a metal loading of about 50 wt.% was formulated for screen printing by mixing synthesized Cu@Ag NPs, ethyl cellulose and terpineol. The bimodal Cu@Ag NPs based ink shows low resistivity of 4×10-6 and 8.5×10-7 Ω•m after sintering at 120 and 200 °C, respectively, for 30 min in the atmosphere of nitrogen. In addition, a possible mechanism has been proposed to illustrate the sintering process of Cu@Ag NPs.

With 3D-Printing becoming a mainstream technology in industry, the need for online process inspection and quality control arises. In this paper, we propose an approach for optical inspection of fused deposition modeling (FDM) printing with integrated electronics. Our prototype setup combines a traditional FDM extruder with an additional extruder for conductive ink, a vacuum pick-and-place nozzle, and two cameras for object alignment and process control. We describe the camera setup, show typical printing faults encountered on our system, and explain our computer vision algorithms to detect (and repair) those faults. We also describe the integration of the inspection modules into existing slicing- and 3D-printsoftware.

In order to minimize the PCB (Printed Circuit Board) footprint of an IoT microtracker, we analyse the opportunity of deporting a LoRa antenna on the plastic case of the microtracker. This paper aims to compare an antenna conventionally manufactured on a PCB (FR4) and a printed antenna using jetting technology on a PC+ABS (Polycarbonate and Acrylonitrile Butadiene Styrene) polymeric substrate. The influence of the conductive ink, the antenna design and the substrate are underlined. Computational simulation is carried out. The LoRa antenna design is similar to the one used by [1].