Novel fabrication methodologies for microwave engineering

Abstract

With the rapid development of materials science and interdisciplinary communications, microwave engineering has been intensively involved in the frontier advances such as two-dimensional (2D) materials, biochemical sensing and flexible electronics. In this thesis, novel fabrication methodologies incorporating new materials and advanced post-processing techniques are developed for new microwave devices and antennas in the emerging microwave multidisciplinary applications. Firstly, we provide the first hand experimental results for chemical vapor deposition (CVD) based graphene film in microwave regions, which was not found in literatures before. Meanwhile, a suite of fabrication techniques are developed to successfully integrate graphene into microwave circuits. It is found that CVD graphene behaves like a frequency-independent surface resistance from direct current (DC) to 40 GHz. This work not only verifies the experimental application of the theoretical Kubo formula but also paves the way for the graphene characterization at the microwave frequencies. A novel graphene-integrated terminator is further proposed for microwave applications utilizing its peculiar properties. Secondly, in order to overcome the inseparable integration between microwave sensing unit and external stimulating/readout circuit. A new detachable microwave sensor is proposed by introducing a peelable microfluidic thin film resonator. By employing the developed microfabrication techniques, the metallic resonator is completely encapsulated in a transparent and flexible polymer film with a total thickness of 10 μm. Apart from differentiation of various chemicals, the proposed sensor offers the capability of retrieving sample's permittivity information, which is of great value to biomedical applications. In addition, a novel detachable and implantable radio frequency (RF) coil is further proposed for magnetic resonance imaging (MRI). Based on the developed selective sealing technology, the implantable coil and the external tuning circuit become separable, which facilitates the transplantation procedure. Thirdly, a new on-demand band-rejected wideband antenna is proposed based on the peelable double electric-LC (DELC) resonator membrane. Compared with conventional designs, the proposed antenna shows the advantages of reversibility, simplicity, compactness and recyclability. The developed membrane has great design flexibility and could be integrated with microfluidic channels to form to a tunable module for the packaged communication system. Finally, a novel detachable feeding technique is proposed for the liquid crystal polymer (LCP) based flexible antenna. The signal probe could be easily attached to and detached from the antenna surface, which not only simplifies the feeding procedure but also improves user experience in the antenna wearing. Several manufacturing techniques have been developed for the low-cost and time-efficient LCP antenna fabrication. They could be implemented and applied to various flexible substrates.