Underwater deployment and performance of curved spiral antennas in mussel backpacks

Abstract

Freshwater mussels are bio-indicators of pollution in rivers because their periodic opening and closing of valves is correlated with the nitrogen content of the water. Our previous work developed noninvasive electronic sensors that are mounted on mussels to measure the valve movement. The backpacks are equipped with a broadband curved spiral antenna that communicates with a surface station through a very low frequency (VLF) radio in freshwater environment. Compared to the conventional flat spiral antennas, their curved counterparts are geometrically suited for deployment on the rounded shell surface. In this work, we present results from measurement and characterization experiments while deploying these such antennas in freshwater. Our experiments indicate relatively constant reflection coefficient of curved spiral antenna in freshwater at 300 MHz with values comparable with the flat spiral geometry.