| Wireless sensor network is a distributed data acquisition technology which has been widely applied in the field of forestry environmental information monitoring. However, due to the application environment and cost constraints, how to provide uninterruptible and reliable energy for forestry wireless sensor network nodes is still a key issue that must be addressed in this area of applied research. The technology for harvesting and utilizing environmental energy, which includes solar energy, vibration energy, electromagnetic energy, wind energy, and geothermal energy, is widely developed. However, they have certain limitations in forestry environment and can not provide reliable energy for sensor nodes. As a unique environmental energy in forest, the tree-based energy is extremely suitable to power the forestry sensor nodes. However, this type of energy is weak, and the parameters of the tree-based power source are unclear. Therefore, the development of a method to utilize the tree-based energy is still a key issue that must be further studied.Based on the present technology for harvesting and utilizing environmental energy, this paper studied the method to utilize the tree-based energy, including ascertaining the power supply parameters, energy collection, energy harvesting and storage, and development of tree-based energy harvesting and storage device.The main research contents and conclusions are as follows.1. In order to ascertain the tree-based power supply parameters, a remote monitoring system based on networking technology was developed. The system is able to automatically and continuously measure the power supply parameters and environmental parameters, providing a technological foundation for ascertaining the tree-based power supply parameters.2. Parameters of the tree-based power source and the environmental factors were continuously monitored, and the change rule and mechanisms of the tree-source internal resistance were intensively studied. The internal resistance of the tree-based power source in this study was large, typically in the range from 1 kΩ to 5 kΩ. The level exhibited circadian and seasonal rhythmicity, in response to the sap content level and physiological activities of the tree. This finding provides a reference for increasing the tree-source output power and the design of tree-based energy harvesting and storage device.3. Effects of electrode material and size on the tree-based voltage were ascertained.1) The conductivity of the metal electrode has an effect on the contact resistance of the electrode-soil and electrode-trunk contact surfaces, which significantly influences the voltage level. The metal with the higher conductivity leads to a smaller contact resistance, as well as to a higher voltage level.2) The metal reactivity of an electrode has no significant effect on the voltage. However, passivation of the electrode materials markedly reduces the voltage.3) The voltage has a logarithmic relationship with the effective surface area of the soil electrode: E=a+b×lnS, where E is the voltage of the tree-based power source, and S is the effective surface area of the soil electrode. With increasing effective area of the electrode, the voltage grows correspondingly, but its growth rate declines.4. A tree-based energy harvesting and storage device was developed based on above conclusions. The device contains an energy processor CBC915 as the control core. A low-voltage charge pump is used to provide a startup power supply for CBC915. As an essential part of the device, a boost converter has the ability to boost the tree voltage, and energy is stored into a solid state battery CBC51200. Test results show that the device is able to harvest and store the tree-based energy efficiently, thereby powering the forestry sensor nodes.This article provides a viable power supply scheme for forestry wireless sensor network and lays a technological foundation for the development of forestry network. |
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