# Flexible UHF RFID Tag for Blood Tubes Monitoring
## 6 Conclusions  
A novel compact and high-performance tag antenna for blood tube traceability applications, working at the European RFID UHF system, is proposed in this paper. The proposed tag is based on a capacitive dipole design, which consists of two coupled compact capacitive meandered pads. The design of the tag is carried out by considering the electrical properties of the elements in which it must operate. These elements are blood, the clinic tube and the substrate employed for the tag manufacturing. Thus, a characterization technique based on a coaxial probe has been used to obtain the electrical properties of these elements in the frequency band of interest. The designed tag has been manufactured on a Kapton polyimide substrate by using a low cost and fast prototyping technique. This is a flexible substrate with excellent electrical parameters, which allows the tag to conform to the curved shapes of clinic tubes. The high values of relative permittivity of the blood and the capacitive  
Figure 16: Reading ranges obtained for the proposed tag attached to a clinic tube with different blood volumes.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Blood Level (mL)** & **Transmitted Power (dBm)** & **Reading Range (m)** \\ \hline
4 & 15.1 & 2.2 \\
2.5 & 20.1 & 1.1 \\
1.5 & 22.6 & 0.8 \\
0 & 25.9 & 0.6 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Minimum transmitted power required to activate the integrated circuit (IC) chip (NXP UCODE G2 XL) and reading ranges of the proposed tag attached to a clinic tube with different blood volumes, measured at the center frequency \(f_{c}=867\) MHz of the UHF RFID band.  
design of the proposed tag have allowed to achieve a compact structure without sacrificing radiation efficiency. Results have demonstrated that the new tag attached to a clinic tube full of blood exhibits reading ranges above 2 m. Moreover, its capacitive design has shown a strong sensitivity with the presence of the blood inside the tube. Therefore, reading ranges drastically drop when the tube is empty. This property may be interesting for many tracking applications, since it could reduce the amount of information generated from empty tubes. The same property can also be exploited to use the tag as a sensing system to detect and measure the amount of blood in clinic tubes. This novel proposed tag can be useful for the design of new blood traceability systems using RFID UHF technology.  
[PERSON] has contributed to the design, fabrication and characterization of the proposed tag antenna. He participated in the manuscript writing. [PERSON] contributed to the state-of-the art, by identifying the original design of the tag antenna. He also participated in the characterization of the tag and in the manuscript writing. [PERSON] acted as M.E.K.' research director and contributed in the tag design. [PERSON] provided a great assistance during the analysis and design phases of this work. [PERSON] performed the electromagnetic characterization of the materials. [PERSON] participated in the data analysis and the manuscript writing. All the authors have equally contributed to the discussion of results and in the revision of the manuscript.  
The authors gratefully acknowledge financial support from Ministerio de Economia y Competitividad of Spain and the European Regional Development Funds for the financial support (grant no. TEC2016-75934-C04-4-R).  
The authors declare no conflict of interest.