Integrated and autonomous conductivity-temperature-depth (CTD) sensors for environmental monitoring

A large class of chemical and biological sensors have been based on the electrical characterization of interface impedances. More specifically, electro-chemical sensing is often related to the characterization of interfaces between ion-based and electron-based conductive materials by means of electric variables such as voltage, current and charge. Recent trends of energy-wise design of integrated electronics have provided new tools in this field allowing to shrink very complex bioelectronic interfaces into millimeter square size systems opening a large ground of applications. Among them it should be mentioned the implementation of conductivity-temperature-depth (CTD) sensors for monitoring oceans to understand their effects on climate changes and marine organisms. High-accuracy CTD sensors are present on the market but they are bulky and power hungry. This paper introduces electro impedance spectroscopy (EIS) principles applied to CTD sensing and will propose a general approach for sensing complex impedance of biointerfaces with low power consumption and high accuracy. The presented system is designed to achieve 15 bit resolution and power consumption to ensure lifetime up to 1 year using button-size batteries in ocean environment.