Flexible wearable strain sensors based on laser-induced graphene (LIG) have attracted significant interest due to their simple preparation process, three-dimensional porous structure, excellent electromechanical characteristics, and remarkable mechanical robustness. In this study, we demonstrated that LIG with various defects could be prepared on the surface of polyimide (PI) film, patterned in a single step by adjusting the scanning speed while maintaining a constant laser power of 12.4 W, and subjected to two repeated scans under ambient air conditions. The results indicated that LIG produced at a scanning speed of 70 mm/s exhibited an obvious stacked honeycomb micropore structure, and the flexible strain sensor fabricated with this material demonstrated stable resistance. The sensor exhibited high sensitivity within a low strain range of 0.4–8.0%, with the gauge factor (GF) reaching 107.8. The sensor demonstrated excellent stability and repeatable response at a strain of 2% after approximately 1000 repetitions. The flexible wearable LIG-based sensor with a serpentine bending structure could be used to detect various physiological signals, including pulse, finger bending, back of the hand relaxation and gripping, blinking eyes, smiling, drinking water, and speaking. The results of this study may serve as a reference for future applications in health monitoring, medical rehabilitation, and human–computer interactions.

A 2 × 2 dual-band dual-circularly polarized (CP) Fabry-Pérot cavity (FPC) multiple input multiple output (MIMO) antenna is proposed in this paper. It is formed by arranging four identical FPC antenna elements with 90° rotation. The FPC antenna element is composed of a single linearly polarized (LP) feeder and a chiral metamaterial (CMM)-based partially reflective surface (PRS), which acts as a polarization converter. The feeder is with a hybrid structure of a slot radiator operating in the low band and a patch radiator in the high band. As the orthogonal currents on the end and center arms of the H-shaped patch break the degeneracy of two CP waves at different frequencies, the PRS simultaneously realizes left-hand CP (LHCP) and right-hand CP (RHCP) features at two different bands, respectively. To enhance the port isolation between two adjacent antenna elements, a broadband, wide-angle, polarization-independent metamaterial absorber (MMA) is introduced to suppress the space wave coupling. To verify the design concept, the proposed MIMO antenna prototype is fabricated and measured. The measured bandwidth with a voltage standing wave ratio (VSWR) of less than 2 covers 3.32-3.42 GHz and 6.23-6.93 GHz, and the LHCP pattern and RHCP pattern are realized at 3.33-3.42 GHz (2.7%) and 6.59-6.75 GHz (2.4%), respectively. A maximum gain enhancement is up to 5.31 dBi in the low band and up to 4.3 dBi in the high band. In addition, the port isolation is better than 42 dB, and the ECC is less than -40 dB. With these performances, the proposed MIMO antenna is suitable for vehicular satellite communication applications.

In this article, a gain-enhanced wideband multiple-input multiple-output (MIMO) antenna with high isolation and quasi-omnidirectional radiation is proposed. It is a hexagonal structure and includes six identical endfire log-periodic dipole array (LPDA) elements. These antenna elements are distributed in the same plane and uniformly placed in a rotating arrangement with an angle difference of 60°, and then are suspended over a large metallic plate (LMP). To enhance the wideband gain, a different metasurface (MS) lens with a high refractive index is deployed around the endfire log-periodic dipole. The uniform MS lens makes electromagnetic waves deflect toward the array axis of the LPDA, whereas the gradient MS lens could form focused plane electromagnetic waves in the endfire direction. Furthermore, these antenna elements are isolated with a complementary split ring resonator (CSRR)-based electromagnetic band-gap (EBG) structure owing to its wide bandstop frequency and small-size characteristics. To validate the design concept, the prototype is fabricated and measured. The measured −10-dB impedance bandwidth covers 2.85–10.9 GHz (FBW 117.1%) and the gain varies from 10.37 to 14.82 dBi. Moreover, high isolation of better than 22.4 dB and low envelope correlation coefficient (ECC) of less than −62.3 dB is achieved between antenna elements. The proposed wideband MIMO antenna could be suitable for vehicular radar.

This paper proposes a wideband high-gain transmit-array (TA) antenna for vehicular sensing and communication, which employs a dual-layer ultrathin Huygens' meta-surface (HMS). It consists of a 33 × 33 HMS unit cells-based TA, a feeder horn, and a three-dimensional printed fixture to hold them. Each HMS unit cell has two identical metal patterns (MPs) of two symmetrical U-shaped patches and one H-shaped patch, which are distributed on both surfaces of the ultrathin substrate. A pair of top U-shaped patches form the first single-wavelength loop mode, and another pair of bottom U-shaped patches forms the second single-wavelength loop mode. Due to the different phases of the incident waves on the top and bottom U-shaped patches, the two loop modes are generated at different frequencies. A third half-wavelength dipole mode is provided by the H-shaped patch. The three modes correspond to three different frequencies, forming a wide transmission frequency band. Three near-unity transmission peaks are yielded to ensure high and stable aperture efficiency (AE). As well, the transmission phase of the HMS unit cell varies with geometric dimensions, and five unit cell types are quantized to obtain 360° phase range with a low loss of less than 2.6 dB. To verify the design concept, a prototype is fabricated. Measurements show a 3-dB gain bandwidth of 17.9%, a maximum gain of 30.5 dBi at 26.2 GHz, and a high AE of 41.9%. It has unidirectional radiation pattern while reducing backlobe.

As a novel method to prepare graphene, the laser-induced graphene (LIG) technology has numerous outstanding properties and has been widely applied in various fields. Nevertheless, the challenge remains to easily and efficiently prepare multifunctional surfaces of graphene through laser microregulation and fine structure design. Here, we successfully fabricated a micron-structure gully graphene surface with hydrophobicity and electrothermal functionality under atmospheric conditions using a 10.6 μm CO₂ laser to directly write on the surface of a polyimide film (PI). The impact of the laser scanning speed on the surface morphology and chemical composition of the product was investigated by analyzing the SEM (scanning electron microscope) observations and Raman spectra, respectively. The mechanical stability of the surface was studied by analyzing the contact angle of water droplets on the surface after mechanical circulation and the delayed icing effect after repeated icing. The deicing and anti-icing performance of the surface were analyzed based on its resistance to surface icing and electric deicing time. According to the experimental results, we first observed a linear negative correlation between the generated structure linewidth and the laser scanning speed. Additionally, we successfully achieved one-step preparation of primitive continuous graphene structures with a superhydrophobic capability (151°). Furthermore, our findings indicate that micron-structured graphene surfaces exhibit excellent mechanical stability, effectively delay icing formation, and demonstrate efficient electric deicing effects. These results demonstrate the potential application of CO₂ laser-induced graphene technology in the field of surface preparation for deicing and anti-icing. This work offers a novel one-step approach for the fabrication of micron-structured heatable graphene surfaces with simultaneous superhydrophobicity, deicing, and anti-icing functionalities on polymer substrates.

This paper presents the axial ratio (AR) bandwidth enhancement of a dual-band dual-circularly polarized (DBDCP) antenna. It utilizes a novel polarization-independent partial reflective surface (PRS) unit cell, which consists of two same metallic patterns with a relative 90o rotation on both surfaces of a substrate. Each metallic pattern is composed of a C-shaped arc and a circular patch. The LP field from the feeder is transformed into two different circularly polarized (CP) field at two respective bands by the unit cell. Due to the asymmetric structure and separated topology of two C-shaped arcs, a slight resonant deviation appears in AR for different polarized waves. Moreover, both x- and y-polarized waves are produced simultaneously by using Fabry-Pérot cavity (FPC) structure when a y-polarized feeder is used. Thus, the AR bandwidths for both x-and y-polarized incident waves are close to each other and combined deliberately into wide AR bandwidth. To validate the design concept, a prototype of the proposed MIMO antenna is fabricated and measured. The measured voltage standing wave ratio (VSWR) of less than 2 covers from 11.55 GHz to 14.8 GHz, and the LHCP pattern and RHCP pattern are realized in low band of 12-12.6 GHz (4.88%) and high band of 14.1-14.61 GHz (3.55%), respectively. The maximum gain is 13.5 dBi (13.1 dBi) at the low-band (high-band). Besides, the port isolation is better than 40 dB, and the ECC is less than -80 dB. With these performances, the proposed MIMO antenna can be employed for vehicular MIMO communications and sensing at Ku-band.