Transparent Flexible Substrates Research Articles

High-Performance Flexible Ionically Conductive Superhydrophobic Papers via Deep Eutectic Polymer-Enhanced Interfacial Interactions.

Endowing paper with highly flexible, conductive, and superhydrophobic properties will effectively expand its applications in fields such as green packaging, smart sensing, and paper-based electronics. Herein, a multifunctional superhydrophobic paper is reported in which a highly flexible transparent conductive substrate is prepared by introducing a hydrophobic deep eutectic polymer into the ethylcellulose network via a matrix swelling-polymerization strategy, and then the substrate is modified using fluorinated silica to impart superhydrophobicity. By introducing soft deep eutectic polymers, (1) the superhydrophobic paper can efficiently dissipate energy during deformation, (2) intrinsically ion-conducting deep eutectic polymers can endow the material with good electrical sensing properties, and (3) meanwhile, enhanced interfacial interactions can anchor inorganic particles, thereby improving the coating stability. The prepared superhydrophobic paper has an ultrahigh water contact angle (contact angle ≈ 162.2°) and exhibits a stable electrical response signal to external deformation/pressure, and the electrical properties are almost unaffected by external water molecules. In addition, the superhydrophobic paper was able to withstand 5000 bending-recovery cycles at a large angle of 150°, exhibiting stable electrical performance. The design concepts demonstrated here will provide insights into the development of superhydrophobic paper-based flexible electronic devices.

Defect-initiated formation mechanism of 3D carbon tracks on flexible transparent substrates by laser irradiation

Laser direct writing of 3D carbon structures onto flexible polymer substrates offers potential of rapid roll-to-roll manufacturing for a variety of key applications, including large area sensors, flexible electronics, robotics, energy storage/conversion, and other consumer applications. The specific formation mechanism of the carbon structures has been an issue of debate for many years with the prevailing notion of a simple photothermal conversion reaction that mainly depends on the total energy input. However, this view has been shown to be inconsistent with experimental observations of nonlinear changes in the resulting structures when multiple processing parameters are simultaneously changed. In this study, we propose a formation mechanism based on the nucleation and growth of laser-induced defects, which is experimentally validated by irradiating a continuous wave laser beam onto polydimethylsiloxane. The model is further validated by intentionally introducing controlled defects by femtosecond laser irradiation, and indicate the implications of a two-laser laser direct writing technique to go beyond the current processing limits. These results clarify the previously ambiguous mechanisms by which carbon structures form under laser irradiation and provide a deeper understanding of how to control photothermal processes for advanced material processing.

Haptic Feedback Device Using 3D-Printed Flexible, Multilayered Piezoelectric Coating for In-Car Touchscreen Interface.

This study focuses on the development of a piezoelectric device capable of generating feedback vibrations to the user who manipulates it. The objective here is to explore the possibility of developing a haptic system that can replace physical buttons on the tactile screen of in-car systems. The interaction between the user and the developed device allows completing the feedback loop, where the user's action generates an input signal that is translated and outputted by the device, and then detected and interpreted by the user's haptic sensors and brain. An FEM (finite element model) via ANSYS multiphysics software was implemented to optimize the haptic performance of the wafer structure consisting of a BaTiO3 multilayered piezocomposite coated on a PET transparent flexible substrate. Several parameters relating to the geometric and mechanical properties of the wafer, together with those of the electrodes, are demonstrated to have significant impact on the actuation ability of the haptic device. To achieve the desired vibration effect on the human skin, the haptic system must be able to drive displacement beyond the detection threshold (~2 µm) at a frequency range of 100-700 Hz. The most optimized actuation ability is obtained when the ratio of the dimension (radius and thickness) between the piezoelectric coating and the substrate layer is equal to ~0.6. Regarding the simulation results, it is revealed that the presence of the conductive electrodes provokes a decrease in the displacement by approximately 25-30%, as the wafer structure becomes stiffer. To ensure the minimum displacement generated by the haptic device above 2 µm, the piezoelectric coating is screen-printed by two stacked layers, electrically connected in parallel. This architecture is expected to boost the displacement amplitude under the same electric field (denoted E) subjected to the single-layered coating. Accordingly, multilayered design seems to be a good alternative to enhance the haptic performance while keeping moderate values of E so as to prevent any undesired electrical breakdown of the coating. Practical characterizations confirmed that E=20 V/μm is sufficient to generate feedback vibrations (under a maximum input load of 5 N) perceived by the fingertip. This result confirms the reliability of the proposed haptic device, despite discrepancies between the predicted theory and the real measurements. Lastly, a demonstrator comprising piezoelectric buttons together with electronic command and conditioning circuits are successfully developed, offering an efficient way to create multiple sensations for the user. On the basis of empirical data acquired from several trials conducted on 20 subjects, statistical analyses together with relevant numerical indicators were implemented to better assess the performance of the developed haptic device.

Application of Transparent Fluorphlogopite Substrate in Flexible Electromagnetic Devices

Flexible electromagnetic devices are an important area of research in the twenty‐first century. Although polymer substrates are the most commonly used transparent flexible substrates, they have certain disadvantages like low‐temperature resistance and a high thermal expansion coefficient, limiting the preparation conditions of flexible devices and diminishing their performance. Herein, the characteristics and research status of inorganic flexible transparent fluorphlogopite are summarized. Herein, the structure, properties, and applications of fluorphlogopite are primarily discussed. Finally, the application of fluorphlogopite in flexible electromagnetic devices is envisioned so as to provide a novel idea for the development of high‐performance flexible electromagnetic devices.

Citric acid modified semi-embedded silver nanowires/colorless polyimide transparent conductive substrates for efficient flexible perovskite solar cells.

Flexible solar cells, with the merits of structure compactness and shape transformation, are promising power sources for future electronic devices. However, frangible indium tin oxide-based transparent conductive substrates severely limit the flexibility of solar cells. Herein, we develop a flexible transparent conductive substrate of silver nanowires semi-embedded in colorless polyimide (denoted as AgNWs/cPI) via a simple and effective substrate transfer method. A homogeneous and well-connected AgNW conductive network can be constructed through modulating the silver nanowire suspension with citric acid. As a result, the prepared AgNWs/cPI shows low sheet resistance of about 21.3 ohm sq.-1, high transmittance at 550 nm of 94%, and smooth morphology with the peak-to-valley roughness value of 6.5 nm. The perovskite solar cells (PSCs) on AgNWs/cPI exhibit power conversion efficiency of 14.98% with negligible hysteresis. Moreover, the fabricated PSCs maintain nearly 90% initial efficiency after bending for 2000 cycles. This study sheds light on the importance of suspension modification for the distribution and connection of AgNWs and paves a way for the development of high-performance flexible PSCs for practical applications.

Helical Stacking Assembly of Orderly Silicon Nanowire Multilayers for Ultrastrong Dissymmetrical Amplification of Circularly Polarized Light

AbstractCircularly polarized organic light‐emitting diodes (CP‐OLEDs) are ideal candidates to explore novel applications such as 3D displays, optical storage, and quantum computing. However, the low dissymmetry (g) factor of most chiral organic materials remains as a major challenge for practical applications. In this work, a helical stacking assembly of orderly silicon nanowires (hs‐SiNWs) into a flexible multilayer 3D superstructure is demonstrated to accomplish a strong chiroptical activity. These orderly SiNWs are batch‐fabricated via a low temperature in‐plane solid–liquid–solid growth mechanism, with precisely‐controlled spatial arrangement and mean diameter and length of Dnw = 126 ± 24 nm and Lnw > 100 µm, respectively. To construct such helically‐stacked superstructure, the SiNW arrays are transferred and stacked upon transparent glass or flexible polymer substrates, with incremental rotational angle for each layer, which can strongly augment the circularly polarized electroluminescence (CPEL) from conventional CP‐OLEDs. Strikingly, the dissymmetry factor increases with more stacking layer up to g = ±0.17, which is more than 40 times of magnitude higher than that of the original CPEL, among the highest ones reported for CP‐OLEDs. These results indicate a promising helical‐stacking avenue to boost the chiroptical performance of various CP‐OLEDs for scalable and flexible chiroptical applications.

Novel Biphasically and Reversibly Transparent Phase Change Material to Solve the Thermal Issues in Transparent Electronics.

Highly integrated transparent electronic systems are experiencing significant thermal bottlenecks due to the rapid growth of transparent electronics and the lack of suitable transparent thermal management solutions. Therefore, transparent thermal management materials are highly desirable in modern transparent electronics. Based on the phase change properties of polyethylene glycol (PEG) and the encapsulable properties of epoxy resin (EP), we synthesize a biphasically and reversibly transparent PEG/EP composite for thermal energy storage (TPE-TES). Energy-driven structural rearrangements in cross-linked networks are responsible for the high transparency with practical thickness. According to SEM and TEM investigations, PEG and EP achieve submicron phase dispersion, while TPE-TES forms a smooth and continuous surface that suppresses diffuse reflections and contributes to improved visible light penetration. The unique combination of phase change and optical transparency gives TPE-TES the ability to regulate thermal storage, rapid temperature change, and spatial temperature uniformity of transparent electronics. Due to its flexibility, stability, and processability, TPE-TES is also suitable and ideal as thin surface coating films or thick transparent flexible substrates for a wide range of applications in the integration of electronic devices.

Three-Dimensional Printed Bimodal Electronic Skin with High Resolution and Breathability for Hair Growth.

People with neurological deficits face difficulties perceiving their surroundings, resulting in an urgent need for wearable electronic skin (e-skin) that can monitor external stimuli and temperature changes. However, the monolithic structure of e-skin is not conducive to breathability and hinders hair growth, limiting its wearing comfort. In this work, we prepared fully three-dimensional (3D) printed e-skin that allowed hair penetration and growth. This e-skin also achieved simultaneous pressure and temperature detection and a high tactile resolution of 100 cm-2, which is close to that of human fingertips. The temperature sensor maintained linear measurements within 10-60 °C. The pore microstructure prepared by a sacrificial template method helped the pressure-sensing unit achieve a high sensitivity of 0.213 kPa-1. Considering the distribution of human hair, the design of the main structure of the e-skin was studied to realize hair penetration and growth. High-performance pressure-sensitive inks and transparent flexible substrate inks for 3D printing were developed, and e-skins combining these functions were realized through multimaterial in situ 3D printing with high accuracy and high consistency. The temperature and pressure sensors separately performed simultaneous detection without interference, and the tactile sensor array accurately identified stimuli at different locations.

Structural Integrity Preserving and Residue-Free Transfer of Large-Area Wrinkled Graphene onto Polymeric Substrates

Wrinkled graphene offers many advantageous features resulting from modifying the structural and physical properties as well as the chemical reactivity of graphene. However, its inadequate transferability to other substrates has limited its usability. This paper reports a roll-based clean transfer approach that enables the damage-free and contamination-free transfer of large-area wrinkled graphene onto polymeric substrates without compromising the integrity of wrinkle structures. The method implements the simultaneous imidazole-assisted etching and doping of chemical vapor-deposited graphene to fabricate multilayer graphene on a thermoplastic polystyrene (PS) substrate coated with a water-soluble poly(4-styrenesulfonic acid) (PSS) sacrificial layer via a roll-based transfer process. The compliant PSS layer affords the conformal contact between the PS substrate and graphene during the wrinkle formation process, enabling the controllable fabrication of graphene wrinkle structures on a large area. The water-soluble properties of PSS simplify the typically difficult separation of wrinkled graphene from the PS substrate after its transfer onto a target substrate. This improves the transferability of wrinkled graphene, rendering the transfer process solvent-free and residue-free. This work demonstrates the feasibility of the formulated method by transferring centimeter-scale wrinkled graphene onto currently used transparent flexible substrates (i.e., polyethylene terephthalate and polydimethylsiloxane). The results indicate that the transferred wrinkled graphene possesses the desirable combination of superior stretchability, optical transmittance, sheet resistance, and electromechanical stability, rendering its suitable application to transparent flexible and stretchable electronics.

A transparent ultra-broadband microwave absorber based on flexible multilayer structure

In this work, a transparent ultra-broadband microwave absorber (MA) based on flexible multilayer structure was demonstrated. The designed resonant structure consists of a resistive film pattern of indium tin oxide (ITO) on a flexible substrate PET. By adjusting the size of the resonant layer ITO pattern and the array position arrangement, an ultra-broadband absorption of over 90% is achieved in the frequency range 8.6–75.8 GHz, with a relative absorption bandwidth of 159%. At the same time, the transparent flexible medium polydimethy-lsiloxane (PDMS) and PET substrate are used to obtain good optical transmittance. Due to the quadruple symmetry of the resistive film resonance pattern, MA shows high polarization insensitivity. For TE and TM polarised waves, the proposed MA can maintain an absorption rate greater than 80% as the angle of incidence is increased to 40°. The current distribution of each resonant layer at strong resonant frequency is simulated and analysed to determine the absorption mechanism of MA. A sample consisting of 11 × 11 cells was produced and the experimental measurements were in general consistent with the numerical simulation results. Due to its ultra-wideband absorption characteristics and wide incident angle stability, it has potential application value in the fields of radar stealth system and transparent electromagnetic shielding.

Nanoscale flexible organic thin-film transistors.

Direct-write electron-beam lithography has been used to fabricate low-voltage p-channel and n-channel organic thin-film transistors with channel lengths as small as 200 nm and gate-to-contact overlaps as small as 100 nm on glass and on flexible transparent polymeric substrates. The p-channel transistors have on/off current ratios as large as 4 × 109 and subthreshold swings as small as 70 mV/decade, and the n-channel transistors have on/off ratios up to 108 and subthreshold swings as low as 80 mV/decade. These are the largest on/off current ratios reported to date for nanoscale organic transistors. Inverters based on two p-channel transistors with a channel length of 200 nm and gate-to-contact overlaps of 100 nm display characteristic switching-delay time constants between 80 and 40 ns at supply voltages between 1 and 2 V, corresponding to a supply voltage-normalized frequency of about 6 MHz/V. This is the highest voltage-normalized dynamic performance reported to date for organic transistors fabricated by maskless lithography.

Preparation of Transparent Fast-Growing Poplar Veneers with a Superior Optical Performance, Excellent Mechanical Properties, and Thermal Insulation by Acetylation Modification Using a Green Catalyst.

There has been growing interest in transparent conductive substrates due to the prevailing flexible electron devices and the need for sustainable resources. In this study, we demonstrated a transparent fast-growing poplar veneers prepared by acetylated modification, followed by the infiltration of epoxy resin. The work mainly focused on the effect of acetylation treatment using a green catalyst of 4-Dimethylpyridine on the interface of the bulk fast-growing poplar veneer, and the result indicated that the interface hydrophobicity was greatly enhanced due to the higher substitute of acetyl groups; therefore, the interface compatibility between the cell wall and epoxy resin was improved. The obtained transparent fast-growing poplar veneers, hereafter referred to as TADPV, displayed a superior optical performance and flexibility, in which the light transmittance and haze were 90% and 70% at a wavelength of 550 nm, respectively, and the bending radius and bending angle parallel to grain of TADPV were 2 mm and 130°, respectively. Moreover, the tensile strength and tensile modulus of the TADPV were around 102 MPa and 198 MPa, respectively, which is significantly better than those of the plastic substrates used in flexible electron devices. At the same time, the thermal conductivity tests indicated that TADPV has a low coefficient of thermal conductivity of 0.34 Wm−1 K−1, which can completely meet the needs of transparent conductive substrates. Therefore, the obtained TADPV can be used as a candidate for a flexible transparent substrate of electron devices.

Monitoring disinfection in the Covid-19 era. A reagent-free nanostructured smartphone-based device for the detection of oxidative disinfectants

In this work, a ready-to-use colorimetric device for oxidative disinfectants (i.e., H2O2, C2H4O3, and NaClO) detection has been developed and proved for the evaluation of disinfection treatments in the COVID-19 containment framework.The sensing element of the proposed colorimetric indicator consists of a transparent flexible PET substrate integrating gold and silver nanostructures. The nano-equipped indicator was integrated into different devices realized using a craft-cutting plotter taking advantage of adhesive/thermo-adhesive flexible pouches and filter paper. In particular, two devices are presented (i) a flexible multi-analysis sampling plate and (ii) a paper-based sampling pipette, for the determination of oxidant disinfectants concentration, evaluation of disinfection treatments by spraying/fogging, and for the analysis of disinfectant residues.The sensing strategy relies on the ability of the disinfectants to oxidize the silver nanostructures of the indicator substrate, producing a colorimetric variation monitorable by a smartphone, maximizing the sensitivity using a colored background. The proposed colorimetric assay occurs in 5 min and does not use external reagents; contact of the disinfectant with the sensing surface is the only requirement. The devices had very low limits of detection (∼1 ppb) and good reproducibility (RSD ≤ 2 %, n = 3) for direct disinfectants analysis. They were challenged for the evaluation of indoor disinfection treatments, allowing to evaluate spraying and fogging treatments, as well as residues monitoring.The here proposed system is disposable, low-cost both in therm of material and reagents (0.05 €) and instruments required, portable, and able to return information on the good practices recommended for environmental disinfection.

Production of esterified nanofibrillated cellulose from a lesser-known wood Species (Macaranga hypoleuca)

Macaranga hypoleuca, a lesser-known and rarely used wood species, is a pioneer species in the secondary succession that is classified as a fast-growing plant with long fibers. M. hypoleuca was composed of holocellulose, lignin, and extractives, at contents of 68.1 ± 0.5%, 25.5 ± 0.6%, and 4.7 ± 0.1%, respectively. In this study, refined M. hypoleuca pulp was treated by alkali treatment, delignification, and maleic acid hydrolysis. The pre-treated pulp was further disintegrated by mechanical treatment, which produced nanofibrillated cellulose (NFC) with a yield of 53.5 ± 2.7%. The average diameter of the NFC was 43.0 ± 4.9 nm. The use of maleic acid (C4H4O4) hydrolysis also reduced the hydrophilicity of the NFC, as confirmed by the Fourier-transform infrared (FTIR) spectra. It was determined that the Macaranga tree is a suitable lignocellulose source to produce NFC, which can be used in transparent flexible substrates, coating, and composite applications.

Printed Flexible Transparent Electrodes for Harsh Environments

AbstractFlexible transparent electrodes are widely used in flexible displays, optoelectronic devices, flexible heating/electromagnetic shielding devices, and flexible sensors. However, significant challenges remain to obtain stable service under harsh environments, owing to the limitations of flexible transparent substrates and conductive materials. Herein, a simple and cost‐effective fabrication approach for harsh‐environment flexible transparent electrodes (HFTEs) is demonstrated via the electric field‐driven microscale 3D printing of a silver mesh on a colorless polyimide (CPI) substrate. Vertical jet orientation on the CPI substrate is realized by controlling the printing parameters, which effectively reduce the instability of the cone jet and is conducive to the preparation of the high‐precision silver mesh on the CPI substrate. The HFTE exhibits good optoelectronic properties (resistance of 4.82 Ω sq−1 and transmittance of 92.26%), and excellent extreme environmental stability with a negligible increase in sheet resistance under various cyclic tests (200 000 bending cycles, 100 adhesion tests, high temperature heating capacity of 360 °C, 80 h of chemical attack, and 120 days of atmospheric environment attack). Baking of quail eggs and deicing experiments are also conducted, which successfully demonstrate the practical viability of the HFTE. Thus, the proposed technique offers a simple and efficient solution for the manufacturing of HFTEs.

Eco‐Friendly and Particle‐Free Copper Ionic Aqueous Precursor for In Situ Low Temperature Photothermal Synthesizing and Patterning of Highly Conductive Copper Microstructures on Flexible Substrate

Liquid precursor‐based laser‐induced reductive patterning techniques enable fast and economical fabrication of flexible electronics. Herein, an eco‐friendly and particle‐free copper ionic solution for laser‐induced reductive patterning of copper microlines on a low glass transition temperature and transparent flexible substrate is successfully developed. The solvent used is water and the reducing agent is l‐ascorbic acid. A continuous wave 640 nm laser is used as the heat source to initiate the reductive reaction and to deposit copper microlines on the substrate surface. The resistivity of the copper microlines fabricated with optimized laser parameters is remarkably low at 4.7 μΩ cm. To further improve the electrical conductivity and to enhance mechanical durability, the fabricated microlines are annealed using the same laser after the copper ionic liquid precursor is removed. The microstructures and mechanical robustness of the copper microlines, as well as the adhesion between the copper microlines and the substrate, are investigated by cyclic bending test, pull‐off test and scanning electron microscope analyses. Up to 39% reduction of electrical resistance and up to 77% enhancement of mechanical durability after a 1000 cycle bending test can be achieved by laser postprocessing.

Slot‐Die Coating of All Organic/Polymer Layers for Large‐Area Flexible OLEDs: Improved Device Performance with Interlayer Modification

AbstractOrganic light‐emitting diodes (OLEDs) fabricated on flexible transparent substrates have found application in displays, lighting, and signage. Optimization of the fabrication procedures is critical for commercialization to maximize performance and reduce costs. Utilization of the slot‐die coating technique, a solution‐processing roll‐to‐roll method, has emerged as a viable method to manufacture flexible OLED devices. Here, the fabrication of flexible OLEDs via the slot‐die coating technique under ambient condition is reported. The OLEDs have a simple architecture of polyethylene terephthalate (PET)/indium–tin oxide (ITO)/hole injection layer (HIL)/emissive layer (EML)/electron injection layer (EIL)/Ag, where poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is used as the HIL, Super Yellow (SY, poly(1,4‐phenylenevinylene) copolymer) is used as the EML, and poly((9,9‐bis(3′‐(N,N‐dimethylamino)propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)) (PFN) is used as the EIL. The optimization of the PFN layer using slot‐die coating technique is focused by varying solvent, solvent additives, substrate temperature, and coating speeds. The OLEDs that have PFN layers processed with the known solvent additives, 1,8‐diiodooctane (DIO) or diphenyl ether (DPE), show a performance increase compared to OLEDs based on PFN layers processed with no solvent additives. Finally, large‐area multicolor OLEDs are constructed with organic/polymer layers being slot‐die coated in sequence, of which all display homogeneous luminance under bending/folding conditions, highlighting the potential of this simple device structure and processing method.

Curved-Mechanical Characteristic Measurements of Transparent Conductive Film-Coated Polymer Substrates Using Common-Path Optical Interferometry

This study proposes a method for measuring curved-mechanical characteristics based on a whole-folding test for transparent conductive film-coated polymer substrates using common-path optical interferometry. Accordingly, 80-, 160-, and 230-nm indium tin oxide films coated on 40 × 40 mm 125-μm-thick polyethylene terephthalate (PET) substrates, and monolayer graphene films coated on 40 × 40 mm 250-μm-thick PET substrates are inspected and analyzed under the curving conditions of 50-, 30-, 20-, and 10-mm radii before and after an 11,000 whole-folding cycle test based on a 10-mm folding radius. This study utilizes the changes in the phase retardations of transparent conductive film-coated polymer substrates under different curving conditions before and after 11,000 whole-folding cycles to analyze the substrates’ residual stress characteristics that were the direct result of manufacturing process parameters. The results from this study of curved-mechanical characteristic measurements of flexible transparent conductive substrates can provide designers with improved product development and can assist manufacturers in improving the manufacturing design of enhanced coating processes.

P‐3: LTPS Device and Panel Fabrication Using Excimer Laser Dehydrogenation and Crystallization

The dehydrogenation process, which is one of the important processes for manufacturing low temperature polycrystalline silicon (LTPS) devices in the industry, requires high temperature over 430–470 °C. In this paper, the hydrogen content in the a‐Si film was reduced by excimer laser annealing (ELA) at lower temperature compared with the conventional dehydrogenation process using a furnace. Not only dehydrogenation but also crystallization of a‐Si was performed in the same chamber to make poly‐Si Grain size and shape of poly‐Si seemed similar to those of poly‐Si obtained from the conventional high‐temperature furnace process. A thin film transistor (TFT) with poly‐Si channel was fabricated via this low‐temperature dehydrogenation process, and the characteristic value of the device was enough to drive the display panel. As a result, a 5.46 inch QHD panel was successfully demonstrated. It was confirmed that the optical properties of the fabricated QHD panel were at the same level as compared with control sample, which was fabricated by using the furnace process. We regard that low temperature dehydrogenation using ELA in this research is promising approach for low‐temperature process, such as transparent flexible substrates.

Nearly omni‐directional compressed multiband flexible and conformal dipole antenna

A physically compressed, multiband dipole antenna on a partially optically transparent Acrylic sheet flexible substrate material is designed. The multi-band operation is achieved by exploiting the higher-order resonating modes. Due to the use of the flexible substrate, and the less metallic footprint of the radiator, the antenna is flexible and conformal with the nearly omnidirectional radiation characteristic in one of the principal plane. With an S11 = −10 dB impedance matching criterion, the antenna has a measured 0.76 to 0.85 GHz, 2.39 to 2.50 GHz, 2.83 to 2.88 GHz, and 6.09 to 6.5 GHz operating bandwidth. It also has a wide −6 dB measured impedance bandwidth from 0.74 to 0.87 GHz, 2.12 to 2.19 GHz, 2.32 to 2.52 GHz, 2.70 to 3.0 GHz, and 5.9 to 6.7 GHz. The specific absorption ratio (SAR) of the conformal antenna has been studied for the collar garment applications. The planar and conformal antennas have been fabricated and investigated for the nearly-omnidirectional radiation pattern. The simulated and measured radiation pattern shows the nearly omnidirectional pattern for a different radius of curvature. The simulated and measured results are in agreement with each other with a few exceptions. The antenna is suitable for the internet of things (IoT), body area networking (BAN), wireless fidelity (Wi-Fi), and smart city applications.