Any flexible transparent antenna material needs to have less than 1 OPS sheet resistance in order to provide efficiency and gain that are comparable to patch or microstrip antennas on PCBs. The newest class of materials also needs to be printable, flexible, and highly transparent at visible wavelengths. Once paired with a transparent flexible FSS material on the back side of the antenna, designers now have another lever to control directionality in specific frequency bands.
The newest class of hybrid TCF materials can be formed by depositing or printing a CNT ink deposited on a Cu MM substrate, where the MM is available on a flexible transparent material such as PET. This type of TCF can be manufactured with fewer steps and competitive costs compared to printed metal oxide TCFs. Designers then have freedom to place a conformal antenna anywhere on the device enclosure, including on optical elements. This also leaves additional space on a PCB that would have been dedicated to a specialty SoC, wireless module, or printed Cu antenna (e.g., microstrip antenna or patch antenna array).
The stack of PET, MM, and CNTs forms a unique flexible TCF with lower sheet resistance and higher VLT (> 95%) than metal oxide TCFs, bare metal nanostructures, MMs, and conductive polymer TCFs. The hybrid CNT film also encapsulates the conductive substrate, which provides additional environmental stability and ensures the entire film remains conductive if micro-fractures form during bending.
This type of film has a very simple fabrication process compared to patterned TCFs made from metal oxides, nanostructures, or meshes. CNTs can be placed in an ink suspension, which can then be printed on MM/PET substrates. When coated on the substrate, the CNTs and metal form a flexible TCF with <1 OPS sheet resistance. Rather than using sputtering and ablation processes for patterning, the CNT ink can be printed in the desired pattern, and the uncoated MM substrate layer can be removed from PET with an etchant.
The structure of this type of hybrid CNT film is ideal for printing a patterned antenna structure, where the underlying conductive substrate determines the opacity of the hybrid TCF. When working with an MM substrate, VLT can be kept far above 90% and haze can be kept low as long as ~90% of the MM is left open for CNT deposition. When working at higher RF frequencies, the required gap region in the MM film is smaller (i.e., one-half the carrier wavelength). This gives a designer a simple way to control absorption transmitting/receiving frequency of a TCF antenna.
Above: A UHF antenna demo showcasing the same antenna design in 3 different materials: Transparent AgeNT-1 (right) alongside non transparent versions in etched copper (left) and printed silver (middle).
Bringing it Together
With unique hybrid CNT films on flexible transparent substrates, IoT, 5G, and automotive radar designers can mold a transparent antenna to an enclosure, optical element, or foldable element in their design. For IoT and 5G applications, designers can tailor the emission pattern and directionality through the use of a flexible TCF and transparent FSS as a flexible substrate. For radar, designers can create integrated optical/RF sensors as these transparent antenna materials could be molded onto optical devices, such as cameras and lidar systems.
This hybrid CNT solution gives designers a flexible transparent antenna that can be mounted anywhere on the device, including directly on a PCB. It also gives antenna designers the ability to tailor the bandwidth, resonance structure, directionality, and other antenna characteristics while preserving high VLT with low sheet resistance. Next-generation 5G-capable IoT and automotive products need advanced antenna designs that can only be provided by hybrid CNT TCFs.