18. Wildcard week¶
Design and produce something with a digital fabrication process (incorporating computer-aided design and manufacturing) not covered in another assignment, documenting the requirements that your assignment meets, and including everything necessary to reproduce it. Possibilities include (but are not limited to) composites, textiles, biotechnology, robotics, folding, and cooking.
In this week, I am planning to make a flexible antenna fabrication. My assignment includes composite making with butyl rubber as matrix and strontium cerium titanate-based ceramic as filler for the composite. The second part of my assignment includes design and fabrication of antenna on the top of the developed butyl rubber-ceramic composite using vinyl cut adhesive copper tape in the Fablab Oulu. Finally, the fabricated antenna is tested using a vector network analyser to see the return loss of the developed antenna.
Wireless communication is one of the most vibrant areas in the communications (industry) field in this era. As the clock speeds of electronic devices are approaching microwave frequencies, the researchers are urged to develop novel low permittivity and low dielectric loss materials for microwave components. On the other hand, flexible electronics is a technology for assembling electronic circuits by mounting electronic devices on flexible substrates. It is also also known as flex circuits. The development of flexible electronics dates back to the 1960s. The first flexible solar cell arrays were made by thinning single crystal silicon wafer cells to ≈100μm and then assembling them on a plastic substrate to provide flexibility. Brody and colleagues developed the first flexible thin film transistor (TFT) of tellurium in 1968. Brody’s group later made TFTs on a wide range of flexible substrates such as mylar, polyethene and anodized aluminium wrapping foil. Mechanical flexibility in electronic devices would enable new applications which are incompatible with conventionally rigid integrated circuits. In general, flexible materials are pure phase or composites which are engineered materials made from two or more constituent materials with significantly different physical or chemical properties and which remain separate and distinct on a macroscopic level within the finished structure. Composite materials can be tailored by appropriately choosing their components, proportions, distributions, morphologies, degree of crystallinity, crystallographic textures as well as the structure and composition of the interface between components for various applications. In composite, making contains matrix phase or continuous phase and filler which are ceramic or metals. In the present assignment, I used butyl rubber as composite and strontium cerium titanate as ceramic filler for the flexible composite fabrication. The ceramic particles do not contact to each other, but the polymer phase is self-connected in all directions in the 0-3 connectivity.
Materials and Methods¶
Sr2Ce2Ti5O15 ceramic powder was prepared following the conventional solid state ceramic route. Butyl rubber–Sr2Ce2Ti5O15 (BS) composites were prepared by room temperature extrusion and hot pressing. Ceramic powder is already prepared previously based on an article by Janardhanan et al. in 2011. This is an ongoing research activity for 6G antenna research in our unit. See the extruder used for the preparation of the present flexible composite and materials (matrix and filler) used.
The detailed composition of the BS composite are shown below table, all materials are listed in parts per million compositions. The first matrix is softened by mixing the butyl rubber about 30 minutes with rpm of 50 at room temperature. Followed by adding the vulcanizing agent in the table below and finally added filler ceramic and extruded out automatically. The materials are other than filler and matrix used for the vulcanisation of thermoset butyl rubber used after the mixing process during hot pressing stage.
Stainless steel dies are used for the substrate making after the extrusion process. The hot pressing temperature for the BS composite is 200 degree Celsius for 90 minutes with the pressure of 2 Mpa. Thermal glows are used for the safety of hands during die loading and releasing stages of hot pressing. See the uniaxial hot pressing unit with the stainless steel mould used for the substrate preparation. The final removed substrate after cooling from the mould is also shown in the below figure. In the figure, it is clear that the developed composite is flexible and stretchable.
The next step is to develop an antenna based on the developed substrate. I used a pre-designed dual-band antenna design used for the antenna pattern making. I draw the ground plane and top patch of the antenna in the fusion. See the antenna design part of the ground plane and top patch plane.
It is followed by making the define the design dimension to ground and patch for viny cutting of adhesive copper laminate. See the dimensions used for the antenna design,
Finally, design file extruded and converted to PDF file recommended for vinyl cutting.
The process of viny cutting and post-processing are followed based on the week 4 assignment. After vinyl cutting, I carefully transfer the adhesive copper tape to developed BS composite substrate, see the figures below,
Next step is to connect SMA connector by soldering the top and ground plane of the antenna for giving feed for resonating. See the SMA connector soldering on the flexible antenna,
Finally, the antenna is tested using vector network analyser operating the frequency of 1- 20 GHz using S22 to provide the feed for the antenna. See the expected dual band return loss picture from the VNA between 2-4 GHz range. It further confirms that the developed antenna is resonating for the WLAN area.
In this week, I utilize materials to devise level prototyping using the flexible composite approach. Demonstrated an antenna fabrication and its testing using by integrating fab lab experiences.
Fundamentals of Wireless Communication, David Tse and Pramod Viswanath, Cambridge University Press, 2005
D. P. Button, B. A. Yost, R. H. French, W. Y. Hsu, J. D. Belt, M. A. Subrahmanian, H.-M. Zhang, R. E. Geidd, A. J. Whittacker and D. G. Onn, Ceramic Substrates and Packages for Electronic Applications, Advances in Ceramics, American Ceramic Society, Westerville OH, 26, 353, (1989).