# A Simple AMC Antenna for Liquid Monitoring in an Infusion Bag
## 5 Antenna for Hospital Application  
To validate the application of the antenna in real-world hospital scenarios, the communication links between the antenna sensors and a hospital Wi-Fi receiver were established. Additionally, the link budget for these communication scenarios is also presented. In the transmission system, an RF signal with a central frequency of 2.4 GHz is generated by the signal generator. The RF signal is then transmitted by the antenna. In the receiving system, the RF signal received by the Wi-Fi antenna is amplified by a low-noise amplifier, followed by filtering through a filter, and finally, it is received by the oscilloscope. To calculate the link budget, we used the Friis transmission equation (Equation (1)) and relevant parameters for the antenna sensor and Wi-Fi system to assess the feasibility of this integration. The received power \(P_{r}\) is given as follows:  
\[P_{r}=\frac{G_{t}\cdot G_{r}\cdot\lambda^{2}\cdot P_{t}}{\left(4\pi R\right)^{ 2}}-L_{ext} \tag{1}\]  
where \(G_{t}\) is the gain of the transmitting antenna, \(G_{r}\) is the gain of the receiving antenna, \(\lambda\) is the wavelength of the signal, \(P_{t}\) is the transmitting power, and \(R\) is the communication distance in a hospital room. The parameter values used for the transmitting and receiving system are provided in Table 3. The transmitting power \(P_{r}\) is set at 10 dBm and the operating frequency is set to 2.4 GHz within the ISM band. The transmitting antenna gain \(G_{t}\) is 6.45 dBi, while the receiving antenna gain \(G_{r}\) is 4.8 dBi. The distance between the transmitter and receiver is 10 m. In a hospital environment, electromagnetic interference and obstacles (such as walls, medical equipment, etc.) typically lead to additional signal attenuation, primarily including multipath loss and interference loss. The environmental attenuation, \(L_{ext}\), is typically set at 30 dB. Based on these values, the received power \(P_{r}\) is calculated to be \(-68.7\) dBm. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Ref.** & **Frequency** & **Contact** & \
\begin{tabular}{c} **Implementation** \\ **Technology** \\ \end{tabular} & **Sensitivity (\(\triangle\)\(\beta\)/\(\triangle\)\(L\))** & **Size** &
\begin{tabular}{c} **Frequency** \\ **Shift** \\ \end{tabular} \\ \hline
[17] & 0.910 GHz & No & RFID & — & \(70\times 14\) mm & — \\
[18] & 0.913 GHz & No & RFID & 0.0006 & \(65\times 65\) mm & 0.053 GHz \\
[20] & 2.4 GHz & Yes &
\begin{tabular}{c} Microstrip \\ Antenna \\ \end{tabular} & — & \(37\times 37\) mm & — \\
[21] & 4.7 GHz & No &
\begin{tabular}{c} Microstrip \\ Antenna \\ \end{tabular} & 0.011 & \(36\times 40\) mm & 0.6 GHz \\
[22] & 2.48 GHz & Yes &
\begin{tabular}{c} Microstrip \\ Antenna \\ \end{tabular} & 0.006 & \(38.8\times 38.8\) mm & 0.6 GHz \\
[23] & 4.6 GHz & Yes & FSS & 0.0865 & \(192\times 192\) mm & 0.68 GHz \\
[30] & 2.45 GHz & Yes & EBG & 0.017 & \(111\times 111\) mm & 0.37 GHz \\
[25] & 2.45 GHz & Yes & AMC antenna & 0.011 & \(68\times 68\) mm & 0.89 GHz \\ Our work & 2.4 GHz & No & AMC antenna & 0.033 & \(100\times 20\) mm & 0.5 GHz \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison with the proposed antenna sensor and other reported sensors. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameters** & **Value** & **Parameters** & **Value** \\ \hline \(P_{t}\) & 10 dBm & \(G_{t}\) & 6.45 dBi \\ \(G_{r}\) & 4.8 dBi & \(\lambda\) & 0.125 m \\ \(R\) & 10 m & \(L_{ext}\) & 30 dB \\ \(T\) & 300 K & \(B\) & \(2\times 10^{7}\) Hz \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Parameter values of the communication system. The output signal-to-noise ratio (SNR) of the receiving antenna can be calculated using the following equation:  
\[SNR=\frac{P_{r}}{P_{n}}=\frac{P_{r}}{k\cdot T\cdot B} \tag{2}\]  
where \(P_{n}\) is the noise power, \(k\) is the Boltzmann constant, \(T\) is the temperature, and \(B\) is the bandwidth of the Wi-Fi channel.