Liquid Crystal Polymer Substrate Research Articles

High Directivity Microstrip Patch Antenna design using Binary Ebola Search Optimization for Radio Frequency Identification Application

Microstrip patch antenna has gained significant popularity in wireless communication field, because of its compact size, less profile, and ease of installation. It is widely used in various applications such as Radio-Frequency Identification (RFID) systems, where dependable and long-range communication is made possible by the great directivity and efficiency. In this manuscript, a High Directivity Microstrip Patch Antenna design using Binary Ebola Search Optimization for Radio Frequency Identification Application (MPA-RFID-BESO) is proposed.The design of microstrip patch antennas is the difficulty in achieving high directivity while maintaining compact size and low profile. This research explains design and application-specific optimisation of the Microstrip Patch Antenna (MPA) of biomedical utilizing Binary Ebola Search optimization (BESO) algorithm. Microstrip patch antenna is designed to function in double and multi band applications due to its low cost, light weight, and ease of installation. MPA is made with flawed ground construction to lessen cross-polarized radiation emitted by microstrip patches and to achieve the necessary radiation parameters. Here, the cost of the materials is reduced by using a liquid crystal polymer substrate, and aerial performance is enhanced by using the appropriate geometrical parameters. The small design of the BESO optimised improves the performance of antenna as 50mm×50mm compact size. The MATLAB program uses high frequency to do the simulation method. The proposed antenna design is a preferable option for applications involving Radio Frequency Identification (RFID). The performance metrics, such as radiation pattern, constant gain, directivity, bandwidth, and antenna efficiency and return loss are measured and compared to the existing techniques. The proposed MPA-BA-BESO design provides 10.51%, 12.85% and 16.04% higher bandwidth and 23.63%, 47.86% and 32.06% higher gain compared with existing designs, like Designing MPA utilizing Moth–Flame optimization approach (MPA-UWB-MFOA), Predicting Rectangular Patch Microstrip Antenna Dimension utilizing Machine Learning (MPA-ANN), Dual Band Antenna Design and Prediction of Resonance Frequency Utilizing Machine Learning Algorithms (DBAD-RF-CNN) respectively. The proposed technology serve as a better design alternative for microstrip patch antennas in communication systems to address biological applications.

Pd nanocubes enclosed by {100} facets for activating electroless Cu deposition on liquid crystal polymer substrates with strong adhesion strength

In this study, we investigate the catalytic performance of palladium (Pd) nanocatalysts with different surface atomic structures for activating electroless copper (Cu) deposition on liquid crystal polymer (LCP) substrates. These nanocatalysts include Pd nanocubes featuring {100} facets of square atomic arrangement as their predominant surface structure and Pd spherical nanoparticles characterized by random atomic arrangements, synthesized using an aqueous method. Our electrochemical measurements reveal that the induction time for the growth of Cu films is significantly shorter when utilizing Pd nanocubes compared to Pd nanospheres. This shorter induction time signifies a quicker initiation of Cu growth, primarily due to the presence of Pd {100} facets. Furthermore, we also develop a surface modification approach involving a crosslinking reaction that utilizes the highly branched polyethylenimine and linear polyvinylpyrrolidone on the Pd nanocubes. This method not only facilitates the adsorption of Pd nanocubes onto the LCP substrates but also achieves a robust peel adhesion strength (630 gf/cm) of the resulting Cu films, exceeding the industrial adhesion goal of 500 gf/cm. Moreover, in-depth synchrotron X-ray photoelectron spectroscopy analysis provides valuable insights into the depth-dependent chemical changes within the Cu films and proves the removal of Cu oxides after the acid treatment.

Bioinspired planar switched beam network using Butler matrix on a flexible substrate targeting multifaceted millimeter-wave applications

Abstract This paper details the design and development of a planar switched beam network using 4 × 4 Butler matrix (BM) over a thin and flexible type biocompatible substrate. Four mils thick liquid crystal polymer (LCP) is used as a substrate here (ϵr = 2.92, tanδ = 0.002). The proposed design is centered at 28 GHz, targeting commercial millimeter-wave applications. Floral-shaped antenna with defective ground structures has been implemented as basic radiating elements. The whole structure is based on microstrip line configuration. The architecture occupies an area of 23.85 × 19.20 mm2 over the LCP substrate. Individual components of the BM are detailed here, followed by a system analysis of the whole integrated structure. The present work also covers the electrical equivalent circuit modeling of the whole beam-forming network. The fabricated prototype offers better than 18 dB return losses at each input port for the desired frequency band with 6 dBi (max.) peak gain and 500 MHz bandwidth around the center frequency. Port-to-port isolation of better than 15 dB is achieved with this topology. Experimental and simulated results are in good agreement in all aspects. A comparative study is also chalked out to highlight the significance of the current research work with respect to alike earlier reported structures.

Compact Liquid Crystal Polymer Based Tri-Band Flexible Antenna for WLAN/WiMAX/5G Applications

In this paper, a new compact coplanar waveguide (CPW)-fed liquid crystal polymer (LCP) based tri-band antenna is presented and fabricated for Wireless Local Area Network (WLAN), Worldwide Interoperability for Microwave Access (WiMAX) and 5th-Generation (5G) systems. The antenna combines two strips with the main radiation rectangular patch and coplanar waveguide ground. The proposed antenna is printed on a LCP substrate with a thickness of 0.1 mm and has a small overall dimensions of 20mm×32mm×0.1mm. To analyze the characteristics, the antenna is designed and fabricated, and then the performance of the antenna is measured and tested. The measurement results show that the proposed antenna has three operating bandwidths, including 2.38-2.79 GHz, 3.27-4.05 GHz, and 4.80-8.44 GHz. To test the flexibility of the antenna, the antenna is simulated and measured in bent configurations for radii of 10 mm and 50 mm. In addition, the antenna is attached to different parts of the human body to test the integration effect in wearable equipment. The experimental results show that the performance of the antenna remains reliable under bending conditions and that the specific absorption ratio (SAR) value meets the European Union (EU) standard. The proposed antenna shows reasonable gains and good radiation characteristics in the operating bands. The flexible, compact, simple design and multiband performance indicates that the antenna is suitable for integration in flexible electronic devices.

Metallized liquid crystal polymer with low interfacial roughness and excellent adhesive strength based on semi-additive process for high-frequency signal transmission

Fifth-generation communication (5G) with the feature of high frequency puts forward harsh requirements on the roughness of the transmission lines due to the skin effect. Metallization liquid crystal polymer (LCP) with low interfacial roughness and high adhesive strength simultaneously poses a huge challenge for the modern electronics. Herein, based on semi-additive process, molecular grafting is reported to highly bridge smooth LCP substrate and thickened copper layer by chemical bonds. The process comprises the wettability of LCP surface tuned via oxygen plasma with negligible roughness changes. γ-aminopropyl triethoxysilane (APTES) plays a role in the integration of LCP substrate and metal layer. Followed by electroless plating, a thin nickel is planted on LCP as conductive seeds for electroplating copper. Compared with addition manufacturing, which directly coarsens the interface of circuits, semi-addition process just etches the edge of circuits. Through APTES grafting, 10 μm thick copper on LCP substrate reaches to the level of 5B according to the criteria of ASTM D3359, overcoming the trade-off between low interfacial roughness and high adhesive strength of existing techniques. Additionally, the interfacial strengthening mechanism of APTES grafting is carefully investigated. The proposed grafting-assisted semi-additive process is potentials for scalable fabrication of high-frequency electronics on various substrates.

A flexible CPW-fed tri-band four-port MIMO antenna for 5G/WIFI 6E wearable applications

This paper introduces a novel flexible tri-band four-port Multiple Input Multiple Output (MIMO) antenna with coplanar waveguide (CPW)-fed for modern 5G/WIFI 6E wearable applications. The proposed antenna operates in three frequency bands by using an etching of rectangular monopole with inverted U-shape slot and a L-shape branch. The prototype of the design is manufactured on flexible Liquid crystal polymer (LCP) substrate with a miniature size of 56 mm × 56 mm × 0.1 mm. The presented antenna operating bands are 2.54–3.56 GHz, 4.28–4.97 GHz and 5.37–8.85 GHz, which can cover Chinese 5G standards n78 (3.4–3.5 GHz), n79 (4.8–4.9 GHz) and WIFI 6E (5.945–7.125 GHz) band. The isolation of the MIMO antenna is higher than 20 dB over whole operating bands by loading a crossed branch with two circular rings. Moreover, the significant performance parameters of the designed MIMO antenna are evaluated, including gain, efficiency, radiation pattern, ECC, DG and TARC. At the same time, the bending test and human test of the flexible antenna are studied in this article. All simulate and measured results demonstrate that the designed tri-band four-port MIMO antenna is promising for 5G/WIFI 6E wearable applications.

Selection of metallic liquid in sub-6 GHz antenna design for 6G networks

The rapid evolution of wireless communication systems toward 6G demands efficient antennas with the features of adaptability and versatility. Liquid antennas have gained significant research interest due to their unique features in realizing small, flexible, transparent, and reconfigurable antennas for promising applications in future wireless systems. In this paper, in order to find a suitable metallic liquid for effective antennas, we design and compare the performance of metallic liquid antennas using Mercury, gallium indium alloy (EGaIn), and Graphene metallic liquid in the sub-6 GHz frequency. The antenna is realized by the metallic liquid in a poly methyl methacrylate microfluidic channel over a liquid crystal polymer substrate at 5.6 GHz frequency. The performance of these metallic liquid antennas is analyzed by their electromagnetic and radiation performance. The Graphene-based metallic liquid antenna shows better electromagnetic performance in comparison to Mercury and EGaIn metallic liquid antennas.

Liquid Crystal Polymer-Based Miniaturized Fully Implantable Deep Brain Stimulator.

A significant challenge in improving the deep brain stimulation (DBS) system is the miniaturization of the device, aiming to integrate both the stimulator and the electrode into a compact unit with a wireless charging capability to reduce invasiveness. We present a miniaturized, fully implantable, and battery-free DBS system designed for rats, using a liquid crystal polymer (LCP), a biocompatible and long-term reliable material. The system integrates the simulator circuit, the receiver coil, and a 20 mm long depth-type microelectrode array in a dome-shaped LCP package that is 13 mm in diameter and 5 mm in height. Wireless powering and control via an inductive link enable device miniaturization, allowing for full implantation and, thus, the free behavior of untethered animals. The eight-channel stimulation electrode array was microfabricated on an LCP substrate to form a multilayered system substrate, which was monolithically encapsulated by a domed LCP lid using a specialized spot-welding process. The device functionality was validated via an in vivo animal experiment using a neuropathic pain model in rats. This experiment demonstrated an increase in the mechanical withdrawal threshold of the rats with microelectrical stimulation delivered using the fully implanted device, highlighting the effectiveness of the system.

Compact Integrated Lumped-Element Bandpass Filter Loaded with Defected Ground Structure Based on Multilayer Liquid Crystal Polymer Substrate

Compact Integrated Lumped-Element Bandpass Filter Loaded with Defected Ground Structure Based on Multilayer Liquid Crystal Polymer Substrate

A Ka-Band 64-Element Deployable Active Phased-Array TX on a Flexible Hetero Segmented Liquid Crystal Polymer for Small Satellites

A <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Ka$</tex-math> </inline-formula> -band 64-element deployable active phased-array transmitter (TX) on a hetero segment liquid crystal polymer (LCP) substrate for small satellites is proposed. The proposed phased-array TX achieved a large array size implementation and a small form factor with integrated six-layer and two-layer LCP substrates. Antenna and transmission line designs considering hetero layer structure are presented in detail. Achieving 46.7 dBm electronically isotropically radiated power (EIRP), the proposed phased-array TX can support 256-APSK DVB-S2X. As a result, the proposed deployable active phased-array TX successfully realizes low-launch cost with a 9.65 g lightweight and large antenna aperture size with superior EVM performance.

Terahertz Electromagnetically Induced Transparency with Electric-Field-Coupled Inductor-Capacitor Resonators on LCP Substrate

Electromagnetically induced transparency (EIT) metamaterials (MTMs) based on the bright-dark mode theory have gained great interest in slow light, sensing, and energy storage in recent years. Typically, various split ring resonators with magnetic response have been proposed as dark resonators in EIT MTMs. Here, we have employed a cut-wire (CW) and two electric-field-coupled inductor-capacitor (ELC) resonators with a pure electrical response on a liquid crystal polymer (LCP) substrate with a low loss tangent to fulfill the EIT effect in the terahertz (THz) region. The former works as the bright mode, and the latter functions as the dark mode. The EIT phenomenon results from the destructive interference between these two modes, which can be verified by numerical simulation and near field distribution. In addition, a Lorentz oscillator model was studied to quantitatively analyze the relationship between the coupling strength and the coupling distance. As a demonstration, an EIT MTM device with 5000 units was fabricated and characterized, which showed a transmission window with a peak value of 0.75 at 0.414 THz. This work may inspire new multifunctional EIT MTMs, especially the flexible applications at THz frequencies.

Frequency Division Multiplexer With Directional Filters in Multilayer LCP Films at - and -Band

A quasi-reflectionless frequency division multiplexer (FDM) with directional filters (DFs) in multilayer liquid crystal polymer (LCP) substrates is proposed for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$ </tex-math></inline-formula> - and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$W$ </tex-math></inline-formula> -band applications. The in-series cascaded DFs are designed at 74, 84, and 94 GHz, each of which comprises two microstrip lines in the first layer, two pairs of coupling slots in the second layer, and loop resonators in the third layer. The distance between DFs is optimized for suppressing reflection and insertion losses, and the asymmetric distribution of DFs is designed to obtain a low profile. The experimental data demonstrate a 3-dB passband of 8.3%, 8.8%, and 9.7% centered at 74, 84, and 94 GHz, respectively, for the proposed FDM, showing a good match with the simulation. The corresponding insertion loss is measured as 3.63, 3.4, and 2.72 dB at 74, 84, and 94 GHz, respectively. The proposed device may find many applications in multiband and ultrawideband communication and radar systems.

Automotive communication applications based circular ring antenna with reconfigurability and conformal nature

SummaryThis work presents a compact and conformal frequency reconfigurable antenna for automotive applications. The antenna is designed on a liquid crystal polymer substrate of footprint 40 × 30 × 0.1 mm3. The proposed antenna is having coplanar waveguide feeding with a circular ring radiating element and a pair of parasitic circular elements to obtain the multiband operation. The proposed antenna is studied for frequency reconfigurable characteristics by placing the PIN diodes as switching elements in the desired locations and obtained the reconfigurability in the 4.5–6.5 GHz region. Further, the bending effects of the antenna with respect to its operating bands and the conformal effects with PIN diodes for the reconfigurable performance make this study a trailblazing work. The simulated and measured results describe that the on‐glass conformal antenna is covering 1.58–2.33 (GPS, PCS, GSM1800/1900), 3.22–3.7 (WiMAX), and 4.25–6.8 GHz (WLAN, DSRC, WAVE, V2X) bands for vehicular communications with various switching cases. The obtained gain varies from 3.2 to 4.1 dB in the boresight direction and 6.9 to 9.8 dB in the lateral directions of the vehicle with placement on the vehicle body. As per the obtained results, the antenna is suitable to use for conformal usage on the windshield glass of the vehicle for connected driving scenarios.

Contacting Inkjet-Printed Silver Structures and SMD by ICA and Solder

Digitally printed conductive structures often need to be electrically connected to batteries, microcontrollers, or other devices. A consensus of industry and research is that such hybrid printed electronics will play a major part in the future of printed electronics. To promote the technology of hybrid printed electronics, surface mount technologies for electronic components using isotropic conductive adhesives (ICAs) and low melting tin bismuth solders on inkjet-printed silver structures on injection molded liquid crystal polymer (LCP) substrates were investigated in this publication. The special needs for inkjet-printed electronics were considered as well as the reliability of assembled surface mounted devices (SMDs) and their failure mechanisms. Connected 0603 and 1206 SMD components achieved a characteristic fatigue life of more than 3500 cycles during thermal cycling at +125 °C/−40 °C and withstood over 1000 h under a damp-heat atmosphere of +85 °C/85% RH. The coefficient of thermal expansion (CTE) of the substrate and the selection of solder have major impacts on the reliability of the assemblies.

Surface pretreatment by photo-irradiated chlorine dioxide radical for metallization of liquid crystal polymer dielectric materials

Surface metallization of the liquid crystal polymer (LCP) substrate will play a vital role in a large variety of potential technological applications in the high-frequency and high-speed 5G era. However, the pretreatment of surfaces is a major issue in the polymer metallization process. A facile green and mild surface oxidation method is proposed for the fabrication of flexible, stretchable, compressible, for enhanced metal-LCP interfacial adhesion. The surface oxidation process is accomplished by exposing the LCP substrate to the ultraviolet light-activated chlorine dioxide (ClO2) radical ambiance. The chlorine dioxide radical will chemically alter and modify the LCP substrate surface to promote increased adhesion of the metal and LCP layer during the lamination and electroless plating process. Moreover, flexible metal-LCP substrates are obtained based on the electroless deposition of metal (copper, nickel) on the LCP films. For the case of Cu-LCP substrate, excellent metallic conductivity of 2.6 × 107 S m−1, and excellent fatigue resistance under various deformations are shown. Adhesion strength of the modified LCP was enhanced by increasing the oxidation temperature and time. This work also provides a successful strategy for the pretreatment of other polymer substrates used for the selective metallization with precise patterns.

A compact coplanar waveguide‐fed band‐notched four‐port flexible ultra‐wide band‐multi‐input‐multi‐output slot antenna for wireless body area network and Internet of Things applications

In this letter a novel notched multi-input-multi-output (MIMO) flexible slot antenna with a C-slot is proposed and designed for wireless body area network (WBAN) and Internet of Things (IoT) applications. The proposed antenna is comprised of four similar elements with the feed line of coplanar waveguide (CPW). Antenna is printed on flexible liquid crystal polymer (LCP) substrate with compact dimensions. The proposed UWB-MIMO slot antenna can operate in range of 2.85–10.85 GHz with notched band from 4.9–6.425 GHz. The achieved notched band can filter the interference of WLAN (5.15–5.825 GHz), by adding an inverted orthogonal branch, great isolation is achieved, which is better than 24 dB over working bands. What's more, the parameters of diversity performance like gain, envelope correlation coefficient (ECC) and diversity gain (DG) are also analyzed. The actual measurement of bending test and the effect of human body indicates that the presented antenna is suitable for WBAN and IoT applications.

A CPW-fed flexible ultra-wideband MIMO antenna based on liquid crystal polymer for IoT applications

In this study, an ultra-thin CPW-fed ultra-wideband flexible MIMO antenna for Internet of Things (IoT) applications is proposed. The antenna is etched on a liquid crystal polymer (LCP) substrate. Two antenna elements of the presented MIMO antenna are placed parallelly without an isolator. The measured S 11 is less than −6 dB from 4.7 to 45 GHz, covering China’s 5G and 5G millimeter-wave bands. The measured S 21 is less than −20 dB in most bands except 8.5–11.7 GHz, and the minimum |S 21| is 15.7 dB at 10.5 GHz. In addition, the simulation and measurement results of flexible MIMO antenna indicate the antennas have good radiation characteristics, and the maximum gain can get 6.4 dB. Then ECC, DG and TARC are evaluated. The proposed antennas are suitable for 5G-enabled IoT applications.

Dielectric Properties of Liquid Crystal Polymer Substrates in the Region from 90 to 140 GHz

In this article, we present a study of the equivalent dielectric constant of two nematic liquid crystals (LCs) with different thicknesses, in the region from 90 to 140 GHz. The equivalent dielectric constant of the LCs was measured using a frequency selective surface (FSS). The LC-based tunable FSS with 22 × 25 unit cells was printed on a quartz substrate with an area of 4 × 4 cm2 and a thickness of 480 µm; the LC layer with thicknesses ranging from 30 to 100 µm acted as a substrate. The FSS featured a maximum frequency-shifting range of 8.15 GHz and 30 µm-thick LC layers with mutually orthogonal rubbing directions were deposited on it. The results show that the initial equivalent dielectric constant of the LC layer increased with the LC layer thickness, while the saturation-equivalent dielectric constant remained almost constant. This work provides LC parameters that can be useful for the design of LC-based devices in the millimeter and terahertz ranges.

MEMS-based reconfigurable and flexible antenna for body-centric wearable applications

The current study presents an MEMS switche-based frequency reconfigurable antenna for conformal and wearable applications. This is a circular ring-shaped monopole antenna loaded with spokes attached to the circular ring and fed by co-planar waveguide feeding (CPW). The antenna is designed on the flexible Liquid crystal polymer substrate material with 40 × 28 × 0.1 mm3. The reconfigurability of the antenna was achieved by placing RF MEMS SP4 T (ADGM 1304) switches. The antenna has a dual-band with reconfigurability at 2.5 GHz (2.12–2.9 GHz) and 5.4 GHz (4.5–5.8 GHz). The measured results demonstrate the antenna operates at 1.73–3.2 GHz and 4.54–6.3 GHz with resonating frequencies of 2.5 and 5.6 GHz. When placed on the human body, the gain of the antenna variesg from 5.32 to 8.38 dBi for different reconfigurable conditions. SAR analysis results in between 0.15 W/Kg and 1.37 W/Kg for different switching conditions, and the simulation results match with the measurements.

A Fully Implantable Miniaturized Liquid Crystal Polymer (LCP)-Based Spinal Cord Stimulator for Pain Control.

Spinal cord stimulation is a therapy to treat the severe neuropathic pain by suppressing the pain signal via electrical stimulation of the spinal cord. The conventional metal packaged and battery-operated implantable pulse generator (IPG) produces electrical pulses to stimulate the spinal cord. Despite its stable operation after implantation, the implantation site is limited due to its bulky size and heavy weight. Wireless communications including wireless power charging is also restricted, which is mainly attributed to the electromagnetic shielding of the metal package. To overcome these limitations, here, we developed a fully implantable miniaturized spinal cord stimulator based on a biocompatible liquid crystal polymer (LCP). The fabrication of electrode arrays in the LCP substrate and monolithically encapsulating the circuitries using LCP packaging reduces the weight (0.4 g) and the size (the width, length, and thickness are 25.3, 9.3, and 1.9 mm, respectively). An inductive link was utilized to wirelessly transfer the power and the data to implanted circuitries to generate the stimulus pulse. Prior to implantation of the device, operation of the pulse generator was evaluated, and characteristics of stimulation electrode such as an electrochemical impedance spectroscopy (EIS) were measured. The LCP-based spinal cord stimulator was implanted into the spared nerve injury rat model. The degree of pain suppression upon spinal cord stimulation was assessed via the Von Frey test where the mechanical stimulation threshold was evaluated by monitoring the paw withdrawal responses. With no spinal cord stimulation, the mechanical stimulation threshold was observed as 1.47 ± 0.623 g, whereas the stimulation threshold was increased to 12.7 ± 4.00 g after spinal cord stimulation, confirming the efficacy of pain suppression via electrical stimulation of the spinal cord. This LCP-based spinal cord stimulator opens new avenues for the development of a miniaturized but still effective spinal cord stimulator.