Use of RF Signal Attenuation & Delay for the Detection of Pulmonary Oedema

Radiofrequency (RF) signal attenuation and signal delay have been investigated as potential methods for detecting water in a variety of applications. This paper reviews experimental data on the use of RF signal attenuation and signal delay for detecting water in a lab environment and discusses the advantages and limitations of such as system. Measuring the RF signal attenuation as it passes through a material such solid or fissured concrete of a construction beam or the undamaged and tumour tissue of a liver has shown to be an effective imaging technique, in a variety of setting not just structural engineering or medical imaging. This in theory can be applied to sensing water in diagnostic medicine rather than traditional imaging, attempting to sense pulmonary oedema in a continuous fashion. However, RF signal attenuation is also affected by other factors such as the presence of other materials that can interfere with the signal. RF Signal delay involves measuring the time it takes for an RF signal to travel through a medium containing water. It can similarly be used for detecting water. This has been shown to be less affected by interfering materials than RF signal attenuation, and thus may provide more accurate results. This paper goes over experimentation making use of simple robust methods, with an innovative coplanar waveform design, to measure the effects of water on a simple phantom, using dimensions similar to those in the human lung and using a water salt mixture as an analogue to 0.9% saline solution. Polyurethane foam sponges are used to create the phantom of the lung. Water salt mixture was added in 40 g per sponge stages from 0 to 600 g, taking $S_{21}$ transmission readings using a Keysight Fieldfox. Significant reduction in signal gain of up to $0.09\times 10^{-3}$ and significant delay of up to 1 nanosecond is seen with maximum saturation, across an 8 cm antenna separation. Overall, the use of RF signal attenuation and signal delay for detecting water in the lungs shows great potential for improving the diagnosis and monitor of pulmonary oedema. With continued research and development, these methods may eventually become a valuable tool for clinicians and researchers alike. Despite the promising results, further research is needed to validate the accuracy and reliability of these methods, as well as to explore their potential for new applications. With continued research and development, RF signal attenuation and signal delay may become valuable tools for a wide range of industries and fields, from agriculture and geology to medicine and beyond.