A multi-chip-nodule micro-system for soil moisture measurements

Abstract

This study presents a Multi-Chip-Module-based (MCM) micro-system suited for irrigation control and management applications. The micro-system includes the soil moisture sensor and an analogue-to-digital converter with signal processing circuitry. The same basic fabrication concepts and materials which made microelectronics successful are now being adapted to making low-cost, small, and high-performance sensor systems with integrated electronics on the same micro-system. Since this sensor has low-cost fabrication for mass production, a network could be implemented in order to achieve an accurate measurement of the soil moisture at the plant root level. A dual-probe heat-pulse technique is used (measurement of the maximum temperature rise at some distance from the heater, after applying a heat-pulse) to determine the volumetric heat capacity and, hence, the water content of the soil. The sensor module is about 30 mm long, 6 mm wide, and 0.8 mm in height; the probe pitch is 3 mm allowing small-scale spatial measurements of soil moisture, which can be made near the soil surface where large root densities are found. The heater uses a nickel-chrome resistor for resistive heating (thermo resistive effect – Joule heat). The temperature sensors (probe and reference) are highaccuracy CMOS smart temperature sensors.