Reconfigurable Antennas Using Liquid Crystalline Elastomers

A method for fabricating long, soft, and reversibly actuatable liquid crystal elastomer (LCE) fibers by using direct ink write (DIW) printing was developed. Here, the LCE was produced based on a two-stage thermal-photo curingreaction between a difunctional acrylate monomer and thiol. The LCE ink, mixed with nanoclay to increase the viscosity, was extruded through a nozzle onto a rotating mandrel to obtain a long fiber. After printing, the fiber was first thermally cured on the mandrel, then mechanically stretched, and photocured to achieve liquid crystal chain alignment for stress-free reversible activation. Upon optimizing the ink viscosity and DIW printing parameters, long fibers (up to 1.5 m long from the laboratory) were obtained. The resulting fiber had a modulus of 2 MPa, 51% actuation strain, and a failure strain of well over 100%. The potential of these fibers for applications was demonstrated. The LCE fibers were knit, sewn, and woven to form a variety of smart textiles. The fiber was also used to mimic bicep muscles with both large activation force and activation strain. By incorporating further intelligent characteristics, such as conductivity and biosensing into a single fiber, the LCE fibers could be potentially used for smart clothing, soft robotics, and biomedical devices.

Supramolecular liquid crystal elastomers (LCEs) incorporating chalcogen bonds (ChBs) have been synthesized and investigated for shape memory and actuation properties. LCEs featuring strong Se⋯N ChBs (-40 to -43kJ mol-1) exhibit both shape memory effects (SME) and reversible actuation, while those with weaker S⋯N ChBs (-32 to -34kJ mol-1) do not. The Se⋯N-based LCEs transition from one-way to two-way SME after three days at room temperature, enabling programmable 2D/3D shape transformations and rewritable surface patterns. They also enable the fabrication of light-powered crawling robots as well as temperature-responsive knot-like actuators. These results highlight the critical role of the ChB strength and specificity in designing functional materials. Solid-state NMR, Raman spectroscopy, and density functional theory calculations provide further molecular-level insights into ChB interactions, laying the groundwork for advanced supramolecular actuators and shape-morphing LCEs.

Supramolecular liquid crystal elastomers (LCEs) incorporating chalcogen bonds (ChBs) have been synthesized and investigated for shape memory and actuation properties. LCEs featuring strong Se⋯N ChBs (−40 to −43 kJ mol−1) exhibit both shape memory effects (SME) and reversible actuation, while those with weaker S⋯N ChBs (−32 to −34 kJ mol−1) do not. The Se⋯N‐based LCEs transition from one‐way to two‐way SME after three days at room temperature, enabling programmable 2D/3D shape transformations and rewritable surface patterns. They also enable the fabrication of light‐powered crawling robots as well as temperature‐responsive knot‐like actuators. These results highlight the critical role of the ChB strength and specificity in designing functional materials. Solid‐state NMR, Raman spectroscopy, and density functional theory calculations provide further molecular‐level insights into ChB interactions, laying the groundwork for advanced supramolecular actuators and shape‐morphing LCEs.

The antenna design presented here supports a new generation of battery-free RFID sensing technology in which the antenna element dynamically conforms to the changing environment in a controlled manner. Specifically, we propose a sensing antenna that reversibly and repeatedly switches operating frequencies from 905MHz to 923.5 MHz based on a temperature threshold crossing. The developed antenna is a patch antenna matched to an RFID IC and integrated with a customized slot. The antenna shifts its operating frequency by using a novel thermal responsive polymer or Liquid Crystal Elastomer (LCE) which is programmable and operates reversibly. Furthermore, 4D printed LCE structures are to be coupled with an Ultra Subminiature Mechanical Switch (USMS) which shorts the slot when the LCE is activated. Finally, as the thermal excitation is removed, the switch returns to the open state. The short and open states of the switch will enable the frequency shift of the antenna structure. In this paper, the methodology of the frequency shift in the patch antenna and the novel LCE switch mechanism are described through simulation and measurements.

Applying thin electrically conductive coatings to Liquid Crystalline Elastomers (LCEs) is an effective way of functionalizing two-way shape memory polymers with the ability to respond to electrical currents. However, achieving robust adhesion between a given electrically conductive coating and the surface of LCEs can be challenging. This can limit the functionality, performance, and potential applications of these materials. This work describes a facile method to develop electrically responsive Liquid Crystalline Elastomer polymeric artificial muscles with strain-sensing, self-actuation-sensing, and joule-heating features. In this work, the effect of treating LCEs with polydopamine (PDA) prior to functionalizing the LCE with an electrically conductive gold-sputtered coating was explored. The findings confirmed that the PDA treatment considerably improved the adhesion of the gold sputter coating to the LCEs, thereby leading to the fabrication of multi-functional strain-sensing, electrically conductive, and electro-responsive LCEs.

Thermally-induced two-way shape memory polymers: Mechanisms, structures, and applications

Shape memory polymers (SMPs) possess the remarkable ability to recover their original shape after being severely deformed, triggered by the right stimulus. This chapter reviews recent progress in shape memory materials, focusing on traditional types like shape memory alloys (SMAs) and SMPs, as well as emerging shape memory hybrids, which enable customizable properties for specific applications in a “do-it-yourself” manner. SMPs, in particular, show great promise for morphing aircraft applications due to their temperature- and time-dependent mechanical properties. Tests on SMPs under monotonic loading in high shear demonstrate their ability to recover original shapes while resisting large loads. Advances in SMP composites (SMPCs), which incorporate functional materials and nanostructures, further enhance their deformation recovery, mechanical properties, and controllable actuation. SMPs have broad applications across aerospace, biomedical devices, flexible electronics, and more. This chapter also provides an in-depth analysis of the shape recovery mechanisms, multifunctionality, and potential future directions for SMP development.

Liquid crystal elastomers (LCEs) with reversible thermal actuation are promising platforms for multifunctional flexible electronics. Herein, we present a PVDF/LM-LCE (PVDF, polyvinylidene fluoride; LM, liquid metal) composite in which PVDF is polymerized in situ within the LCE matrix to achieve seamless mechanical coupling and efficient stress transfer. LM nanodroplets enhance mechanical robustness, charge transport, and photothermal conversion, enabling LCEs to serve as photothermally driven transducers that amplify the piezoelectric and pyroelectric outputs in these flexible systems. The optimized composite achieves a pyroelectric coefficient of -4.81 nC·cm- 2·K- 1, 1.8 times higher than conventional PVDF films. Furthermore, the composite device powers two LEDs and digital sensors using low-grade photothermal fluctuations. This LCE-based light-driven thermomechanical-to-electrical conversion strategy offers a generalizable pathway for high-performance, flexible pyroelectric and piezoelectric energy-harvesting materials.

This paper presents the design and analysis of a reconfigurable microstrip slot antenna using RF PIN diodes as switching device for S and C band. Here pattern and frequency reconfigurable microstrip antenna is designed by changing the slot length on ground plane through six MPP4203 PIN Diodes. These six PIN diodes are used to electrically connect and disconnect the slot to alter the total slot length 76 mm in x axis and 56 mm in y axis. Here three switches are positioned in slot which is cut along the x-axis and another three switches are positioned in the slot along the y-axis. The analysis of reconfigurable antenna using PIN diode is done using the simulation performed on Ansys HFSS. The pattern and frequency reconfigurability of proposed antenna is analyzed for S (2–4 GHz) and C band (4–6 GHz) in terms of return loss and radiation pattern. The microstrip antenna design shows the pattern and frequency reconfigurability at 11 resonating frequencies. The proposed reconfigurable antenna is capable to resonate at three resonating frequencies (2.2, 2.3, and 2.4 GHz) in S band and 8 resonating frequencies (5.7, 5.8, 5.9, 6, 6.1, 6.3, 6.4, and 6.5 GHz) in C band. The simulated radiation patterns at various resonating frequencies shows pattern reconfigurability with acceptable gain in xz and yz plane of microstrip patch antenna. Furthermore the re-configurable antenna reduced the front end system's size and offers pre-filtering at the receiver. The proposed microstrip patch slot antenna is quite suited to be integrated with WLAN and Bluetooth devices with less structure complexity.

Multifunctional shape memory composites composed of shape memory polymers and shape memory alloys exhibit superior shape memory properties; therefore, it is of great interest to researchers to model their thermo-mechanical behavior numerically. Although a number of constitutive models of shape memory alloys and shape memory polymers have been developed, very few models have been developed for shape memory composites and validated with experimental data. In this study, we first review separately constitutive models of shape memory alloys and shape memory polymers developed in previous studies. Both models were validated with thermo-mechanical tests conducted on a shape memory alloy fiber and shape memory polymer, respectively. A constitutive model for the shape memory composite was then developed utilizing the homogenization scheme. Shape memory composites containing 0.5% or 1% of the shape memory alloy fiber volume content embedded in the shape memory polymer matrix were fabricated. Thermo-mechanical tests were carried out on these shape memory composites to validate the proposed constitutive model. The experimental results showed that the proposed shape memory composite model was able to predict the general trend of the thermo-mechanical behavior of the shape memory composites.

Recent advances in shape memory alloys (SMAs) and shape memory polymers (SMPs) have inspired researchers to create intelligent textiles as self-regulating shape-changing structures responding to environmental variation, contributing to a new field in the scientific frontier of smart materials. This paper shows how appropriate shape memory training can engineer fabric designs to enhance their performance and their aesthetic appeal. Main technologies include the training procedure of shape memory effect (SME) in SMAs and SMPs, the regulation of phase transformation temperatures in SMAs, the manufacture of SMP yarns and SMP coating on fabrics for specific requirements of fabric design. Further attention is also paid to the combination of SMPs or SMAs with textile design of different fabric yarn for promoting specific dynamic aesthetic effects.

Asset Management is an essential task for every industry. Keeping track of assets manually is a monotonous and time consuming task which is also error prone. Integrating asset management with IoT can automate it to a large extent. Proper management of assets can boost the company’s productivity. With the advancements in the field of IoT, tasks like tracking location of assets, managing asset’s parameters can be done with ease. The available solutions to Asset Management use Active or Passive Radio Frequency Identification Device (RFID) tags. These solutions have disadvantages like need of high and continuous battery power and are applicable only for small distances (up to 100m). Usage of Bluetooth Low Energy (BLE) Tags can overcome these problems. The data from sensor nodes can be sent to a cloud based central repository through message queuing telemetry transport (MQTT) protocol and then it can be further analyzed. This data can be visualized and managed through a web application. The motivation for automating and improving current asset management solution has paved the way for a new architecture. This paper provides a detailed run down on that architecture and how it can be deployed for real time application.

This article proposes a novel multifunctional wideband reconfigurable antenna with a frequency selective surface (FSS) reflector to improve gain across all operating bands. Initially, a wideband trapezoidal monopole antenna with a 138% impedance bandwidth (1.53–8.45 GHz) on a FR-4 substrate with a thickness of 0.80 mm and an area of 51 × 56 mm2 was designed. In order to achieve multifunctionality, two inverted L structures with two rectangular slots were introduced at the ground plane. Each slot functions as a filter, producing various resonating bands. To obtain the desired resonating frequency bands, the effective length of the slot was changed by strategically placing RF switching element PIN diodes. The proposed reconfigurable antenna can switch between 10 different frequency bands. To improve the gain of the proposed reconfigurable antenna, a novel FSS reflector with a 5 × 5 array of elements is placed 1.01λ (34.54 mm) below the proposed antenna. The application of the FSS results in a 3–6 dBi improvement in antenna gain, not only for the wideband range, but also for all operating frequency bands. Over the entire operating bandwidth, the radiation efficiency ranges from 93% to 75%. For GPS, RADAR, LTE42/43, WLAN, WiMAX, STM-Link, and UMTS applications, the proposed antenna operates in a wideband state, three single band states, four dual band states, and three tri band states. This work provides more antenna functionality at a lower cost, as well as significantly reduced size and space requirements. The proposed antenna can be easily integrated into portable electronic devices for a variety of wireless applications due to its broad switching capability and unique feasibility.

PurposeIn wireless communication system, use of multiple antennas for different requirements of system will increase the system complexity. However, reconfigurable antenna is maximizing the connectivity to cover different wireless services that operate different frequency range. Pattern reconfigurable antenna can improve security, avoid noise and save energy. Due to their compactness and better performance at different applications, reconfigurable antennas are very popular among the researchers. The purpose of this work, is to propose a novel design of S-shaped antenna with frequency and pattern diversity. The pattern and frequency reconfiguration are controlled via ON/OFF states of the PIN diode.Design/methodology/approachThe geometrical structure of the proposed antenna dimension is 18 × 18 × 0.787 mm3 with εr = 2.2 dielectric constant. Three S-shaped patches are connected to a ring patch through PIN diodes. The approximate circumference of ring patch is 18.84 mm and length of patch is 5 mm, so approximate length of radiating patch is 14.42 mm and effective dielectric constant is 1.93. Conductor backed coplanar waveguide (CPW) is used for feeding. The proposed antenna is designed and simulated on CST microwave studio and fabricated using photolithography process. Measurements have been done in anechoic chamber.FindingsAntenna shows the dual band operation at 2.1 and 3.4 GHz frequency. The first band remains constant at 2.1 GHz resonant frequency and 200–400 MHz impedance bandwidth. Second band is switched at seven different resonant frequencies as 3.14, 3.45, 3.46, 3.68, 3.69, 3.83 and 3.86 GHz with switching of the diodes. The −10 dB bandwidth is more than 1.4 GHz.Research limitations/implicationsPattern reconfigurability can be achieved using mechanical movement of antenna easily but it is not a reliable approach for planar antennas. Electronic switching method is used in proposed antenna. Antenna size is very small so fabrication is very crucial task. Measured results are deviated from simulation results due to fabrication error and effect of leads of diodes, connecting wires and battery.Practical implicationsThe reconfiguration of the proposed antenna is controlled via ON/OFF states of the three PIN diodes. The lower band of 2.1 GHz is fixed, while second band is switched at five different resonant frequencies as 3.27, 3.41, 3.45, 3.55 and 3.88 GHz, with switching of the PIN diodes with all state of diodes and exhibit pattern reconfigurability at 2.1 GHz frequency. At second band center frequency is significantly changed with state of diodes and at 3.4 GHz pattern is also changed with state of diodes, hence antenna exhibits frequency and pattern reconfigurability.Originality/valueA novel design of pattern and frequency reconfigurable antenna is proposed. Here, work is divided into two parts: first is frequency reconfiguration and second is radiation pattern reconfiguration. PIN diodes as switch are used to select the frequency band and reconfigure the radiation pattern. This proposed antenna design is novel dual band frequency and pattern reconfigurable antenna. It resonates at two distinct frequencies, i.e. 2.1 and 3.4 GHz, and has a pattern tilt from 0° to 355°. The conductor backed CPW feed technique is used for impedance matching.

Numerical design of shape memory polymer composites with temperature-responsive SMA fillers