| Wireless Underground Sensor Network(WUSN)is a sensor network that uses soil as a propagation medium and which entails burying all the main equipment underground.WUSN will have a wide range of applications in agriculture,military,and natural disaster warning as a new sector of wireless sensor network research and application.WUSN electromagnetic waves are still in an early stage of research in the soil medium,and few suitable models can reveal the attenuation law of WUSN electromagnetic waves there.The node system,electromagnetic wave attenuation characteristics,and node deployment scheme of the WUSN soil moisture monitoring system for farmland were studied in this thesis,the node system was designed and developed,and communication test experiments were conducted in an indoor electromagnetic shielding box and in tillage fields.To obtain validation for WUSN node deployment and system construction,analyze the effect of node deployment parameters and soil parameters on the underground attenuation of the WUSN electromagnetic wave,establish the characteristics equations and attenuation law of WUSN electromagnetic waves in farmland tillage layer soils,and build a validated WUSN unit system.In this thesis,the following main research contents are presented.(1)An agricultural soil moisture monitoring system based on WUSN nodes was developed.Based on low power consumption and low packet loss,we completed the WUSN node system design with software and hardware components which consisted of an HC-12 wireless module working in 433 MHz band,low power consumption STC89C52 RC chip,VMS-3000 soil moisture sensor using time-domain reflection technology and other main hardware,and conducted attenuation tests in tillage fields.According to the results,the WUSN node system meets the requirements of soil moisture monitoring in tillage fields.(2)The characteristic equations of WUSN electromagnetic wave attenuation in farmland tillage layer soil were established.For the two main communication modes of the underground to underground and underground to aboveground,the effects of node burial depth,horizontal distance,soil moisture content,soil compactness,soli temperature,acidity,and alkalinity on the received signal strength,communication packet loss rate were analyzed by an indoor electromagnetic shielding box and tillage fields communication test experiments,and the data fitting method was used to reveal and establish the WUSN electromagnetic wave attenuation law in farmland tillage layer soil.The results indicate that the received signal strength varies linearly with the horizontal distance between nodes,linearly with the node burial depth,soil moisture content,and soil compactness,quadratically with soil temperature,acidity,and alkalinity,and quadratically with the loss rate for communications between nodes and horizontal distance.(3)Validation tests and experiments of the WUSN unit system were conducted.The derived WUSN electromagnetic wave and underground communication characteristics were used as a basis for designing the WUSN unit system with three underground nodes and one aboveground node,and those were tested in an indoor electromagnetic shielding box and tillage fields,and the results showed an average percentage error for soil moisture content compared with the actual value of 3.7%,and for WUSN electromagnetic wave signal strength compared with the actual value of 2.1d Bm,as well as a communication packet loss rate below 10%,ensuring compliance with farmland monitoring requirements.These results demonstrate that the equations for the WUSN electromagnetic wave characteristic equations derived from this study can provide technical assistance for the deployment and construction of WUSN nodes and systems. |
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