Design of wireless underground sensor network nodes for field information acquisition

With the research of the wireless sensor network technology, some wireless underground sensor network nodes and a sink node based on embedded technology and RF technology were designed innovatively. Wireless underground sensor network node consists of sensor, the processor, wireless RF module and power module; here, processor using MSP430 microcontroller, RF modules adopting nRF905 communication module and having 433/868/915 MHz 3 ISM channel. Moreover, the sink node is made up of RF transceiver module, the core control circuit, information processing, data storage, Liquid Crystal Displays (LCD) module and power supply. The nodes which acquired soil parameters information were regularly distributed in the monitoring area. The sink node collected the information of nodes that were sent in way of a single jumping or multiple hops and implemented fusion, analysis, processing, storage and display of information. For 50% sands, 35%silt, and 15% clay, a bulk density of 1.5 g/cm 3 and a specific density of 2.6 /cm 3 , test is conducted for different soil moisture (5, 10, 15, 20 and 25%) in three different frequencies 433/868/915 MHz, result shows that radio signal path loss is the minimum in the low frequency and low moisture. Furthermore, the changes of node deployed depth (0.2, 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8 and 2 m) affected signal attenuation under 433 MHz, it is concluded as the best wireless underground sensor networks (WUSN) node buried depth for effective transmission.