Research On The Standing Tree Bioelectricity Harvesting Method

Due to wireless sensor network with large scale and comprehensiveness of forest environment, power supply problem of wireless sensor network node has became the primary problem. Standing tree bioelectricity is related to chemical processes within the plant body. It showed that sustained, stable voltage and current exist between the tree and the surrounding soil. Considering that there are a lot of trees, and harvesting other environmental energies have defects in the forest, in this paper, an energy harvesting method of standing tree bioelectricity is proposed.Experiments of the bioelectricity in nine species of standing trees in Beijing Forestry University have been carried out. The effects of the electrode into the depth, the electrode connections, trunk electrode position and tree species on bioelectricity were studied. The results of the research can be concluded as following points:(1) Tapping the trunk electrode into phloem can meet the demand of energy harvesting. And effect of energy harvesting is better when the trunk electrode and soil electrode were used by different material.(2) It is beneficial to increase the current that many outputs of standing tree bioelectricity were connected in parallel. At this time, the electrode position has no strict requirements.(3) No correlation between bioelectricity and electrode position on the trunk was found. Clear correlation between bioelectricity and tree species was found.Based on the experimental results, a circuit for harvesting bioelectricity has been proposed. The overall circuit includes charge pump circuit, boost circuit and charge management circuit. We chose a ginkgo tree to conduct the test. Through the test, twenty outputs of bioelectricity of a ginkgo tree could make the whole circuit work. The circuit modules were debugged and the whole system was tested. The results of the tests can be concluded as following points:(1) Charge pump circuit was able to generate a 1.5-1.9V output. The cycle time was 7.5s approximately.(2) Boost circuit was able to generate a 3.7-4.7V output. The cycle time was 2s approximately.(3) Voltage of the lithium battery rose from 2.85 V to 3.06V during 8 hours.The experimental results showed that the circuit can realize energy harvesting and storage. Finally, the practical application of wireless sensor node was tested. The test results showed that bioelectricity harvesting can prolong the working time of node. It has certain practical value to promote the application of the wireless sensor network in the forest.