Page 115 - IJB-9-4

International Journal of Bioprinting An inkjet-printed bendable antenna for wearable electronics

Table 1. Human tissue model parameters at 2.45 GHz [26]
Body tissue Skin Fat Muscle
Relative dielectric constant 38.007 5.280 52.729
Dielectric loss angle 0.283 0.145 0.241
Magnetic conductivity (s/m) 1.49 0.11 1.77
Thickness (mm) 2 10 28

Figure 2. Antenna conformal models. (A) Antenna longitudinal bending models (bending radius = 70 mm, 55 mm, 40 mm, 25 mm, respectively).
(B) Antenna transverse bending models (bending radius = 70 mm, 40 mm, 25 mm, 20 mm, respectively).
deformations, complex bending deformations can the processing is simple. Conductive silver ink spots were
be decomposed into components in two directions: deposited on the polyimide film surface to form the array
longitudinal and transverse components. Hence, in this of antennas . The finished product is shown in Figure 3A.
[28]
study, we investigated the symmetrical deformations. More In this process, the polyimide film was placed flat on the
complex deformation in real applications will be studied glass sheet.
and transformed into symmetric deformation in future The polyimide (PI) substrate was subject to purified
research. The effective conformal operation and curve water cleaning, ethanol cleaning, and hydrophilic
modeling methods are shown in Figure 1C and D. In HFSS, treatment. The antenna’s pattern was imported to the inkjet
an ideal cylinder model with a certain degree of curvature printer through the computer. The silver nanoparticles
can be constructed, and the antenna can be attached (bought from Sigma-Aldrich) were fabricated by an inkjet
layer by layer using the “Wrap Sheets.” The substrate was printer system (Microfab Jetlab®II) at 90°C heating
[29]
thickened by “thick sheet”; the media entity was created; conditions. In addition, the accuracy of this inkjet printing
the region was wrapped, the synthetic radiation patch was system was 5 μm in X and Y directions, so different
united; the engineering variable r of the radius was created; printing runs have high repeatability and slight deviation.
and its parameters were scanned. The transverse and After inkjet printing silver nanoparticles, the antenna was
longitudinal bending with different curvatures (bending sintered at 250°C for 2 h for annealing and removing the
radius from 70 to 20 mm) of the conformal antenna organic solvent in ink. In addition, the printed electrodes
model was established to generate a different bending have a thickness of approximately 800–1000 nm.
degree of the antenna model, and the electric performance
parameters were analyzed, as shown in Figure 2A and B. As shown in Figure 3B and C, the antenna feed end
was fixed and connected with the port of the SubMiniature
2.2. Antenna processing and measurement setup version A (SMA) using conductive silver paste, which
Polyimide film (0.05 mm thick) was used as the flexible was connected to the Agilent E5072A network analyzer
substrate for the antenna, and a silver coating was used as through a 50 Ω coaxial transmission line. Figure 3D–F
a radiation conductor. Silver nanoparticles were selected as show the test setup for the antenna bending condition, and
the conductive material of the CPW-fed antenna because Figure 3G shows the measurement setup for the human

Volume 9 Issue 4 (2023) 107 https://doi.org/10.18063/ijb.722