With the advent of 5G and new 6G network infrastructure, flexible and bendable IoT devices are becoming more popular1,2. In this regard, the concept of wearable and bendable antennas is an important problem to overcome.3,4. The scientific effort concerned the design of small flexible antennas that accommodate modern requirements such as wearability.
High market demand has made rapid prototyping and cost-effective techniques for antenna manufacturing important, and multiple techniques must be combined to meet the very demanding goals required for antenna design. there is. On the one hand, the antenna footprint can be reduced by increasing the operating frequency.Five. However, the higher the transmission frequency, the more likely interference phenomena such as multipath fading and attenuation will occur.6. The second option is to make the antenna smaller. This technology aims to reduce antenna resonance by increasing the antenna’s electrical length, allowing the antenna to radiate at lower frequencies for the same geometric dimensions. The main drawbacks of this strategy are degraded radiation properties and reduced bandwidth. In addition to a compact footprint, optimal radiation characteristics are required. These requirements further complicate the design procedure, as the shape of the antenna typically needs to be efficiently optimized, especially on very thin substrates.
Artificial intelligence (AI) can help in situations like this. AI algorithms have been used for many years to solve a wide variety of optimization problems, including antenna design. Among other techniques, genetic algorithms (GA) are one of the most commonly used approaches for various electromagnetic problems such as photonics.7 and antenna8, 9, 10, 11.
Genetic algorithms generate a set of trivial solutions, or antenna shapes, that evolve step by step until the best solution is reached.Antennas generated according to this approach are said to be evolving12.Meetra13 was one of the first authors to utilize research in this area.reference8 I will report on this with reference to a tutorial on GA applied to this type of application.9 Let us now discuss in detail the design of antennas employing GA and method of moments (MoM).inTenGA is applied to miniaturize patch antennas for cardiac pacemakers operating at 402-405 MHz. The coding scheme used to handle this problem consists of subdividing the patch into smaller subpatches. Each subpatch can be either metal or air. The same approach is used in the following areas:11Here, a genetic algorithm is applied to a patch antenna to shift its resonance from 4.8 GHz to 2.16 GHz.
Antenna design by genetic algorithm has been proven to be a good choice. However, if only miniaturization is promoted, the radiation efficiency will be low.
The approach used to improve this functionality is the introduction of metamaterials. Each material in nature is made up of atoms, whose properties and spatial orientation affect their electrical behavior. The idea behind metamaterials is a logical extension of this concept on a macroscopic scale. By creating arrays of single cells with specific properties, the electrical and magnetic properties of the entire structure can be tuned.
Metamaterials have applications in a wide variety of fields, and one of the most promising concerns the enhancement of the radiation properties of small antennas.
Split ring resonators (SRRs) are an ideal solution because their planar geometry and easy integration simplify the manufacturing process.14. In particular, SRR can be used to realize artificial magnetic conductor (AMC) layers with an effective magnetic permeability close to zero, i.e. zero-index metamaterials (ZIM). Recent research uses ZIM to improve the radiation characteristics of antennas by placing such supermaterials between the top layer of the antenna and the ground plane.15,16,17,18,19,20,21,22. In this case, the ZIM acts as a highly accurate mirror that does not introduce any phase changes in the reflected electromagnetic waves, improving the radiation characteristics of the ground plane at the bottom of the antenna. A problem arising from the use of metamaterials is that the inclusion of the superstrate adds a metal layer to the stack that makes up the antenna, so an alignment process must be performed.
A very attractive technological process for producing flexible antennas even in multilayer stacks23,24inkjet printing.twenty fiveBecause it’s the most economical, fastest, and cleanest solution. In this technology, the antenna is achieved by applying conductive ink through hundreds of mechanically controlled nozzles. Despite its optimal properties, this method has several problems. The quality of the print depends on the viscosity and size of the conductive ink droplets.twenty five.
Additionally, the alignment step becomes difficult for multilayer antennas fabricated on commercially available substrates that cannot be directly printed. This occurs because two different printing processes need to be performed on both sides of the same dielectric. This last case could be that of metamaterial antennas designed on stretchable substrates.
in26 Examples of flexible antennas reinforced with metamaterials have been reported. The antenna consists of a polyimide substrate with a 3×3 array of metamaterial structures and a top radiating element placed on his second substrate with a ground plane at the bottom. However, in this case precise alignment is not strictly required, as the superstate only requires metallization on its bottom surface. Furthermore, the two layers are not fully integrated; they are simply stacked on top of each other.
As a result, although there are many antennas realized using GA, metamaterials, and inkjet printing in the literature, to the best of our knowledge, no antenna has yet been reported that leverages these three technologies in combination. yeah.
The biggest problem to overcome is the lack of rapid prototyping manufacturing techniques on flexible substrates, a process that features multilayer printing with optimal alignment between all the parts that make up the antenna. In this study, we propose an advanced antenna for flexible multilayer inkjet printing. The stack consists of 5 layers (3 metal layers and 2 dielectric layers). The radial layer (i.e., the top layer) is designed using a genetic algorithm to reduce the footprint. Gain is enhanced by a split ring resonator that acts as a metamaterial, and a ground plane is placed at the bottom to minimize back radiation. The operating frequency is in the sub-6 GHz band of the 5G spectrum, specifically around 4 GHz.
The metal layer is fabricated by a multimaterial 3D printer that requires a precise alignment process on a 250 μm polyethylene naphthalate (PEN) substrate. The dielectric layers are attached to each other by a 40 μm polydimethylsiloxane (PDMS) adhesive interlayer.
Finally, the antenna was characterized in terms of S.11 Parameters and 2D radiation pattern by VNA. This paper is organized as follows. “Genetic Algorithms” briefly explains the main steps of GA, “Antenna Design and Split Ring Resonators” reports on the antenna design, and “Manufacturing” describes the manufacturing steps. “Characterization” details the characterization of the prototype, and finally, “Conclusion” presents the conclusions.
