An Experimental Study on the Dielectric Properties of Rubber Materials

Innovative synthesis technique for high-performance dielectric resonator antennas: laser-induced shockwave sintering of potassium sodium niobate (KNN)

This study explored the synthesis and sintering of potassium sodium niobate (KNN) nanoparticles, emphasizing morphology, crystal structure, and sintering methods. The as-synthesized KNN nanoparticles exhibited a spherical morphology below 200 nm. Solid state sintering (SSS) and laser-induced shockwave sintering (LISWS) were compared, with LISWS producing denser microstructures and improved grain growth. Raman spectroscopy and x-ray diffraction confirmed KNN perovskite structure, with LISWS demonstrating higher purity. High-resolution x-ray photoelectron spectroscopy spectra indicated increased binding energies in LISWS, reflecting enhanced density and crystallinity. Dielectric and loss tangent analyses showed temperature-dependent behavior, with LISWS-3 exhibiting superior properties. Antenna performance assessments revealed LISWS-3's improved directivity and reduced sidelobe radiation compared to SSS, attributed to its denser microstructure. Overall, LISWS proved advantageous for enhancing KNN ceramics, particularly in antenna applications.

Design and Fabrication of a Flexible Gravimetric Sensor Based on a Thin-Film Bulk Acoustic Wave Resonator

Sensing systems are becoming less and less invasive. In this context, flexible materials offer new opportunities that are impossible to achieve with bulky and rigid chips. Standard silicon sensors cannot be adapted to curved shapes and are susceptible to big deformations, thus discouraging their use in wearable applications. Another step forward toward minimising the impacts of the sensors can be to avoid the use of cables and connectors by exploiting wireless transmissions at ultra-high frequencies (UHFs). Thin-film bulk acoustic wave resonators (FBARs) represent the most promising choice among all of the piezoelectric microelectromechanical system (MEMS) resonators for the climbing of radio frequencies. Accordingly, the fabrication of FBARs on flexible and wearable substrates represents a strategic step toward obtaining a new generation of highly sensitive wireless sensors. In this work, we propose the design and fabrication of a flexible gravimetric sensor based on an FBAR on a polymeric substrate. The resonator presents one of the highest electromechanical coupling factors in the category of flexible AlN-based FBARs, equal to 6%. Moreover, thanks to the polymeric support layer, the presence of membranes can be avoided, which leads to a faster and cheaper fabrication process and higher robustness of the structure. The mass sensitivity of the device was evaluated, obtaining a promising value of 23.31 ppm/pg. We strongly believe that these results can pave the way to a new class of wearable MEMS sensors that exploit ultra-high-frequency (UHF) transmissions.

Modification of the Maxwell-Wagner Heterogeneous Dielectric Model for Heterogeneous Polymers and Emulsions

In heterogeneous polymers and emulsions, the volume fraction of the discrete phase and the frequency of electromagnetic waves affect the accuracy of the dielectric model. The integral method was used to modify the Maxwell–Wagner (M–W) heterogeneous dielectric theory, and a new model for the complex dielectric constant of polymers and emulsions was established. The experimental data were compared with the results of the M–W heterogeneous dielectric integral modification model and other theoretical models for different frequencies and volume fractions of the discrete phase. We discovered that with a decreasing volume fraction of the discrete phase, the dominant frequency range of the integral modification model expanded. When the volume fraction of the discrete phase is 10%, the dominant frequency range reaches 3 GHz. When the volume fraction of the discrete phase is 1%, the dominant frequency range reaches 4 GHz. When the volume fraction of the discrete phase is 0.06%, the dominant frequency range of the real part reaches 9.6 GHz, and the dominant frequency range of the imaginary part reaches 7.2 GHz. These results verify the advantages of the M–W modification model, which provides a theoretical basis to study the dielectric properties of polymers and emulsions, as well as for microwave measurement.

Effects of Graphene Oxide and Reduced Graphene Oxide on the Mechanical and Dielectric Properties of Acrylonitrile-Butadiene Rubber and Ethylene-Propylene-Diene-Monomer Blend

The composites of properties of ethylene-propylene-diene-monomer (E) and acrylonitrile butadiene-rubber (N) composites of graphene oxide (GO) and reduced graphene oxide (G) were prepared by a combination of solution and open-roll method. They include single matrices (EGO and EG) and blends N/E, 20 part of hundreds of rubber (phr)/80 phr (A), 80 phr/20 phr (B), and 50 phr/50 phr(C) blend containing GO and G. The physico-mechanical properties including vulcanization, tensile, glass transition temperature ( $T_g$ ), and dielectric spectroscopic properties were evaluated. The N-rich systems reinforced with GO, cured faster than the E-rich systems. Also, N-rich systems obtained the highest dielectric constant $\left({\varepsilon }^{\prime }\right)$ , especially when GO and G were incorporated, for example, NG and N-GO obtained 317 and 283% increment in ${\varepsilon }^{\prime }$ than EG and EGO, respectively. In terms of tensile properties, AGO exhibited the highest strength and elongation at break properties (%). Therefore, solution mixing technique of rubber blends filled with nanoinclusion can be achieved with the tendency of reducing cost without the use of compatibilizer and still maintain the integrity of the physical properties of the final product. The result obtained therefore shows that the current compositions can find various applications in oil/gas sealants, heat-resistant applications, and energy storage materials with minimal losses.