# Nozzle with a Feedback Channel for Agricultural Drones
## 1 Introduction  
Drones are unmanned aerial vehicles, ranging from large ones that can fly thousands of kilometers to small ones that can fly in limited spaces [1]. Early drones were developed for military purposes and to aid search and rescue operations, but drones have since been developed for various civilian purposes, such as transportation and fire suppression [2]. In 2014, the global market size of drones reached 700 million USD, and it is expected to grow to approximately 1.7 billion USD by 2025 [3]. Most studies on drones have focused on improving the flight time for practical commercial applications. [PERSON] et al. [4, 5] estimated the weight of the drone and number of rotors depending on the maximum power demand of the battery and made suggestions regarding the propellers and some performance requirements underlying the design. In addition, an aerodynamic analysis method that improves durability by maintaining the balance is proposed. [PERSON] et al. [6] presented a capacity model for the lithium-polymer batteries used in commercial quad-rotors, resulting in maximum durability at the optimum mass value and an excellent propulsion system. Drones are also employed in agricultural fields, because the aerial spraying technology reduces labor costs and removes the risk of physical damage to the crops and soil from the wheels or tracks of a machine. In addition to improving the durability of the battery life and propulsion, [PERSON] et al. [7] developed an agricultural drone that can generate management maps of vineyards through multispectral image analysis for ease ofnavigation. To improve the practical applications of agricultural drones in spraying water and pesticides, it is necessary to investigate the spraying system further. [PERSON] [8] developed electrostatic spraying machines and presented system specifications to increase the effectiveness of the deposition of pesticides, and experimentally verified the possibility of spraying a volume median diameter of 50 \(\upmu\)m. [PERSON] et al. [9] developed a variable speed direct spraying nozzle for uniform spraying. [PERSON] et al. [10] conducted experiments and COMSOL software simulations of spraying water on targets with different shapes to establish a direct relationship between water flow and current in electrostatic spraying methods. [PERSON] et al. [11] proposed a local automatic selectivity control nozzle that can accurately control the amount of pesticide to reduce environmental pollution, while reducing the costs. However, these studies on optimizing the spraying system are only applicable to ground spraying systems. Aerial spraying technology was first used in large manned aircraft to combat pests in early 1906. Later, in 1975, electrostatic spraying technology was applied to medium-sized aircraft [12; 13; 14]. [PERSON] et al. [15] developed precision technologies that can adjust the spraying rate, such as variable-speed spraying technology and positioning technology. In 1990, the first unmanned aerial spraying technology was employed in the agricultural sector [16; 17]. Most of the previous aerial spraying techniques had been applied to medium-sized unmanned aerial vehicles. However, recently, compact-sized small drones have received significant attention in the field of aerial spraying technology, owing to their high maneuverability. Even though different companies develop agricultural drones, the spraying system generally consists of a commercial pump and nozzle. In recent years, research has also been conducted to select suitable nozzles and pumps for use in agricultural drones. [PERSON] et al. [18] evaluated the performance of three types of pumps and 18 types of nozzles currently in use, by using a pressure-flow curve, injection flow rate, injection angle, and droplet size. [PERSON] et al. [19] compared the performance by selecting three nozzles, to extend the flight time of agricultural drones by reducing the amount of pesticide spraying per unit area.