Optically Transparent Adhesives for Microwave Metamaterial Absorber With PET–PDMS Interface

Bonding of the heterogeneous layers of polymers as a trilayered (or multilayered) transparent metamaterial absorber (MA) is challenging, since the hydrophobic nature of interfacial surfaces does not allow direct bonding. Apart from the mechanical challenges to bond, microwave and optical functionalities of the chosen material need to be studied quantitatively for an optimal choice. Therefore, simulations are performed to study the effect of dielectric constant and thickness of adhesive on the microwave characteristics of polyethylene terephthalate (PET)–polydimethylsiloxane (PDMS)-based microwave MA (MMA). Composites of polyvinyl butyral (PVB) and 3-aminopropyltriethoxy silane (APTES) that address the need for strongly adhesive yet transparent in optical regime and non-interacting in the microwave regime have been developed. Lap-shear tests with plasma-treated PET–PDMS adherends demonstrated to have lap-shear adhesion strengths greater than 0.21 MPa. The optical transmittance of electromagnetic (EM) waves through MA after being adhered with glue is 74.9%. A numerical analysis shows that the proposed microwave absorber absorbs more than 90% of EM waves within the range of 7.97–20.72 GHz after an additional layer of optimal adhesive, which is validated through experiments conducted in anechoic measurements.