## 2 Material and Method
### Design and Production of the Bow-Tie Microstrip Antenna  
A bow-tie microstrip antenna structure is planned to improve the antenna's performance in biomedical applications. The design and simulation study of the proposed antenna is carried out in the CST Microwave Studio. The antennas are designed in Tinkercad, which is an online 3D design platform developed by Autodesk Inc. (San Rafael, CA, USA) and built with Creality Ender 3 Pro 3D printer (Creality, Shenzhen, China). Material selection is one of the pivotal problems to be considered in the design process, as it has a significant impact on antenna performance. Polylactic Acid (PLA; \(\varepsilon_{\mathrm{r}}\) = 2.54 and tan\(\delta\) = 0.015) and Acrylonitrile Butadiene Styrene (ABS) are effective on the antennas' performance. They are frequently preferred in the production of dielectric parts of antennas and microwave components. On the other hand, graphene is a suitable material for producing the conductive part of Microwave and Radio Frequency (RF) products due to its very good properties such as high charge mobility, zero bandgap, high heat conduction, high surface area, and excellent biocompatibility. Composite Conductive Graphene PLA filaments have recently been introduced, allowing graphene to be used with a 3D printer [84]. In this study, the designed antennas are produced using Conductive Graphene PLA filament for the core of the antenna and standard PLA for the dielectric substrate parts. The volume resistivity of the used graphene filament is 0.6 \(\Omega\)-cm [89]. The product of the sheet resistance (\(\Omega\)/sq) and the thickness of the material in centimeters is equal to the volume resistance (\(\Omega\)-cm) [90; 91; 92], and therefore, the sheet resistance can be obtained as given in Equation (3). \[ \begin{array}{l}R=\text{the volume resistivity}/\text{thickness of graphene sheet}\\ R=0.6\;(\Omega-\text{cm})/0.17\;(\text{cm})\;=\;0.359\;\Omega\end{array}  \tag{3}\]  
The radiating patch of the microstrip antenna may be square, rectangular, circular, elliptical, triangular, or any other shape [93]. Generally, triangular structures or curved structures provide better impedance matching. The size and shape of the patch are some of the most determining factors in the properties of the antenna. However, the change of shape does not bring significant changes in the radiation characteristics. The half-power beamwidth is generally 70-90 degrees, and antenna gain is 5-6 dB. By choosing the patch model and shape appropriately, a design can be made in accordance with the desired resonance frequency, pattern, impedance, and polarization. Another novelty of this work is that the slot sizes have been chosen specifically for the required bandwidth and gain. Slots are used to regulate the current path and shape the electric field. For slots, sharp points allow electric field lines to break more easily. Circular slots show an improvement in antenna performance, which is weaker than square and rectangular slots. Filtering is done for a frequency when a slot is opened in a broadband patch made for ultra-broadband. Therefore, the optimum values of the antennas, whose numerical analyses were performed by using the finite integration technique in the CST Microwave Studio simulation program, were used in the designs. In addition, the effect of slots and their different sizes on antenna performance is shown. In this study, three different antennas, one without a slot, Figure 2, the other two with different patch sizes, Figure 3, are designed and produced. The dimensions of the antennas are given in Table 3.  
The three bow-tie antennas produced for use in biomedical applications are shown in Figure 4. If it is desired to be used in more specific applications, it can be easily adjusted with antenna design changes.