# Self-Sustainable Biomedical Devices Powered by RF Energy: A Review
## 3 RF Energy Harvesting Application in Medical Devices
### RF Energy Harvesting for Wearable Medical Devices  
Wearable medical devices contribute significantly to improving the current medical system and supporting physical activities due to their ability to offer extensive monitoring of different physiological functions, emergency alerting, and computer-aided rehabilitation. These devices can be used in the healthcare sector and military sector for evaluating the mental and physical health of soldiers in combat [118; 119]. This current global pandemic outbreak has significantly impacted the global healthcare system and, as such, has necessitated the deployment of remote monitoring systems to monitor its symptoms and perform essential tracking [120]. Researchers have over the years introduced several IoT-based devices and wearables for accurate diagnosis and monitoring of patients in the prodromal phase; these devices can monitor the temperature, \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Reference** & **Biomedical Device** & **Size** & **Power Consumption** & **Application** \\ \hline
[109] & Pulse oximeter & 38.69 cm\({}^{3}\) & 294 mW &
\begin{tabular}{c} Measures the oxygen \\ saturation level \\ \end{tabular} \\ \hline
[109] & Hearing aid & 2.45 cm\({}^{3}\) & 1.82 mW &
\begin{tabular}{c} Amplifies the sound for \\ the patient with hearing \\ loss \\ \end{tabular} \\ \hline
[110] & Cochlear implant & 9.58 \(\times\) 9.23 mm & 100–2000 \(\mu\)W &
\begin{tabular}{c} Stimulates the cochlear \\ nerve electrically \\ \end{tabular} \\ \hline
[109] & Pacemaker IC & 4.9 cm\({}^{3}\) & 0.28 mW & Monitors heart rate \\ \hline
[111] & Drug pump for
\begin{tabular}{c} ophthalmic use \\ \end{tabular} & 9.9 \(\times\) 7.7 \(\times\) 1.8 mm & 400 \(\mu\)W & Controls drug delivery \\ \hline
[112] & Neural activity
\begin{tabular}{c} monitoring recorder \\ \end{tabular} & 3 \(\times\) 3.5 mm & 1–10 mW & Records brain activities \\ \hline
[109] & Combo insulin pump & 97.61 cm\({}^{3}\) & 15 mW &
\begin{tabular}{c} Delivers insulin using an \\ insulin pump while also \\ monitoring blood glucose \\ levels and giving bolus \\ instructions using a blood \\ glucose meter \\ \end{tabular} \\ \hline
[113] & Wireless intraocular \
\begin{tabular}{c} pressure monitor \\ \end{tabular} & 0.5 \(\times\) 1.5 \(\times\) 2 mm\({}^{3}\) & 3.65 mW &
\begin{tabular}{c} Frequent measurement of \\ intraocular pressure \\ \end{tabular} \\ \hline
[114] & Health monitoring sensor \
\begin{tabular}{c} on wristband \\ \end{tabular} & — — & 0.83 mW &
\begin{tabular}{c} Monitors chronic \\ respiratory disease \\ \end{tabular} \\ \hline
[109] & Wireless EKG system & 40.13 cm\({}^{3}\) & 60 mW &
\begin{tabular}{c} Monitors and records vital \\ signs and cardiac \\ information \\ \end{tabular} \\ \hline
[115] & Electrocardiogram \
\begin{tabular}{c} amplifier \\ \end{tabular} & — — & 2.76 \(\mu\)W &
\begin{tabular}{c} Transforms the weak \\ electrical signals from the \\ heart into signals that can \\ be transmitted to a \\ monitoring system. \\ \end{tabular} \\ \hline
[114] & Electronic-nose sensor \
\begin{tabular}{c} system \\ \end{tabular} & — — & 250 \(\mu\)W &
\begin{tabular}{c} Connected to a \\ pattern-recognition system \\ that responds to odors \\ passing over it \\ \end{tabular} \\ \hline
[114] & Spirometer & 6 \(\times\) 6 mm & 0.01 mW &
\begin{tabular}{c} Measures FEV1, PEF, \\ and FVC \\ \end{tabular} \\ \hline
[116] & Cardiac activity sensing & 6 mm & 0.3 \(\mu\)W & Monitors vital signs \\ \hline
[117] & Retinal prostheses & \
\begin{tabular}{c} Diameter = 3 mm \\ Pixel size = 25 \(\mu\)M \\ \end{tabular} & 250 mV &
\begin{tabular}{c} Stimulates the retina \\ \end{tabular} \\ \hline
[114] & ECG chest patch & 84 \(\times\) 39 \(\times\) 8.3 mm & 0.96 mW &
\begin{tabular}{c} Measures \\ electrocardiogram ECG, \\ skin impedance, \\ photoplethysmography \\ (PPG), motion, \\ and acoustic signals \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Average power requirements and specifications of various biomedical devices.