## 2 Proposed Smart Farm Structure: Overall System--Inflatable Aeroponic Enclosed Smart Farm
### Water Circulation System '2, 3, 4'
#### 2.2.1 Nutrient Mixer '2'  
The Nutrient Mixer is an apparatus that precisely measures and mixes essential nutrients (such as nitrogen, phosphorus, and potassium) with water to create the nutrient solution needed by plants [41]. In traditional hydroponic systems, the nutrient mixer monitors electrical conductivity (EC) and pH levels, adjusting the solution based on feedback regarding these parameters. To maintain optimal EC and pH, the concentration of the solution is adjusted by diluting or concentrating the water and nutrient ratio as needed. However, as the demand for the solution decreases, especially for micronutrients compared to macronutrients, which require significantly smaller amounts, the precision in mixing becomes increasingly challenging. The dosing pumps currently used in nutrient mixers have a resolution of about 0.1 L and can introduce slight errors, posing a limit to high-precision control. Therefore, there is a need to develop a nutrient mixer system with higher resolution and lower error rates, emphasizing the necessity for a system design capable of more precise control over small quantities of nutrients. In this study, to address the need for high precision in controlling small amounts of nutrient solution, a nutrient cartridge method using inkjet printer cartridge technology is introduced. Inkjet printers distribute ink with high resolution in pico-liter units, a crucial feature for precise printing tasks. Typically, in agriculture, 1 L of nutrient solution is diluted with 1000 L of water. However, if the dilution ratio needs to be achieved with only 500 milliliters of water, the total required amount of fertilizer would be 500 microliters. Figure 3: Two water circulation methods in the air-injected smart farm. The first method (**1**) shows nutrient solution circulation, where the nutrient solution is distributed to the plants and then recirculated back to the water tank. The second method (**2**) illustrates water vapor recirculation, where air is injected to facilitate nutrient absorption, and the evaporated water vapor is collected and returned to the water tank. When the concentration difference between macronutrients and micronutrients exceeds 1000 times (often even greater), the necessary control amount can reach 500 nanoliters. By applying the inkjet cartridge method, it is possible to precisely prepare extremely diluted solutions, not just at 1000 times dilution, but up to 10,000 times. This approach provides the high resolution and precision required in nutrient manufacturing and offers innovative possibilities for creating more complex and finely tailored nutrient solutions. The physical properties of ink suitable for inkjet technology are defined as having a viscosity of 5-6 centipoise (cP), surface tension of 28-30 dyn/cm (dynes per centimeter), and particle size of no more than 500 nanometers. For water-based inks, viscosity can be adjusted using glycerin. The print head nozzles on the cartridges enable ink ejection ranging from 1.5 to 80 pico-liters. When using nutrient solutions as a substitute for ink, it is crucial to carefully adjust and align properties like viscosity, surface tension, and particle size to meet these standards. However, the current research prioritizes initially assessing the basic feasibility of using nutrient solutions instead of ink in the print heads. This involves ensuring that the physical conditions of the nutrient solutions meet the requirements of inkjet printers and that the properties of the nutrient solutions are compatible with the operation of the print heads. This foundational research is vital not only for adapting the nutrient solutions to the inkjet printer's specifications but also for verifying the reliability and efficiency of the overall system when using these modified solutions.