Let’s consider the possibility of using the Agrotec robot to destroy weeds in a field sown with corn with an area of 5 hectares. According to the popular and effective technique of Dieter Spaar on 1 square meter, we will take an average row spacing of 0.4 m, since the treatment against weeds will be carried out in places where there are no crops, then we will allocate two strips of 1 m by 0.05 m for the usable area sown with corn. Thus, for processing with high-density microwave energy, two strips with a width of 0.4 m and a length of 1 m remain.
Continuous working time = 12 hours;
Area to be treated = 5 Ha per charge;
Approximate processing time of the plant by microwave, no more = 0.5 sec.
The robot is equipped with at least 4 microwave installations of 3 kW each (work in half a cycle). The robot is provided with a screen that ensures the safe operation of the robot even when living beings (people, animals) are directly next to it at a distance of less than 1 m in accordance with Directive 89/391 / EEC On the introduction of measures to improve the safety and health of workers at work and the directive European Parliament and Council 2013/35 / eu of 26 June 2013
At a speed of 1 m/s, the robot manages to make 8 applications of microwave energy to the weeds identified by computer vision.
A special algorithm based on neural networks recognizes the type of weed, its weight, volume, approximate moisture content (H2O) in the plant and its height, based on these data, a decision is made on the positioning of the applicator.
The application of a microwave for 0.5 seconds with a power of 3000 W with a high energy density leads to the heating of the cellular and intercellular fluids of the plant to the boiling point, which leads to the explosion of cell membranes and the destruction of the plant.
High energy density is achieved at a specific focal length using a waveguide and horn antenna specially designed for the 2.45 GHz frequency.
The cost of one charge is approximately 15 euros (100 kW at the average cost of electricity in the EU). Accordingly, the cost of processing and destroying weeds on a 5 hectares field is 15 euros, excluding capital investment and depreciation of the robot. Which is about 10 times lower than the price of traditional herbicide treatments.
Service life of the magnetron, not less than 2000 hours. That corresponds to 1600 hectares, treated in a maximum mode of 0.5 seconds of magnetron activity for each 1 second of robot operation.
The robot uses a mass-produced magnetron, the cost of which is low, so the magnetron can be considered a consumable item that must be replaced as part of routine maintenance every 16,000 km (1,600 ha).
The preliminary cost of the robot:
Basic configuration – USD 75,000;
Extended modular configuration – USD 85,000;
Pre-sales of first models – 40000 USD (with additional agreement to provide feedback and conduct collaborative experiments).
In a modular, extended configuration, in which the robot can also be used for precision fertilization, field survey using video and photo shooting, taking soil samples, treating plants for diseases by spraying hydrogen peroxide in the form of dry steam.
Weight = 800 kg (depends on model);
Width = 1.5m;
Length = 1.5m (2m);
Height = 1.5m;
V = 0.5m/s – 1.5m/s;
In case of high weeds density, the speed of the robot can be reduced automatically, similarly, when a clean, non-clogged area is detected, the speed of the robot can be automatically increased to 1.5 m/s.
Robot power and main units:
333 blocks of 14 batteries 32700 LiFePo 3,2V 6A * H;
Board voltage = 48V;
Current consumption (at full power) = 166A;
Ptotal = 100 kW * H
Probot = 2 kW * h (power consumed by the robot for movement, computer vision recognition, signal transmission, etc., except for the operation of microwave installations);
Pmw = 6 kW * h (the power consumed by 4 magnetrons of 3 kW each, since the magnetrons work only ½ second, and the second ½ second rest, then the total power consumption per hour = 6 kW).
Total power consumption = 8 kW * H
Description of the microwave installation:
Magnetron type: 2M285-04ARCM LG 3kW;
Magnetron weight 3 kg;
The magnetron is attached to the movable part of the 3D delta manipulator with, which makes it possible to increase the exposure time without stopping the robot, as well as precisely apply the focused energy. Energy is applied to the most vital part of the plant, just above the ground from which it grows and below half the height of the plant. In this case, the entire plant is exposed to a gradient of decreasing energy.
Treatment should be carried out at the early post-sowing and pre-sowing stages.
A plant weighing (mass of a substance) up to 25 grams is used in the calculations;
Specific heat capacity 3000-3500 J / kg (specific heat capacity of water 4187 J / kg).
Depending on the model, the number of magnetrons can be increased to 8.
Results of calculations and experiments, scientific component.
The factors that contribute to microwave heating include: the physical and chemical structure of the heated material; the frequency of the microwaves; in some cases, such as wood, the orientation of the electrical field relative to the structure of the dielectric material is also important; reflections from the interfacial surface of the heated material; electric field strength; the geometry of the microwave applicator; the geometry, size, electrical and thermal properties of the dielectric material; the exposure time; and the moisture content of the dielectric material.
The density of microwave energy is one of the most important factors in plant death, increasing which decreases the exposure time almost proportionally. Thus, it becomes apparent that the deliberate application of a highly focused microwave pulse will rapidly weaken the weed. We design and develop horn antenna to focus microwaves – it is represented on figure 8.
Also, the total energy required for weed control can be significantly reduced by applying AI-based computer vision for weed locating systems and applying pinpoint stimulation to weed areas.
So, to achieve maximum heating efficiency, maximum energy density at a local site, minimum exposure time, energy efficiency comparable at or less than the cost of using herbicides at the same site, taking into account the cost of the magnetron and the possibility of its serial production, it was proposed to develop an original device by using a mass-produced 2.45GHz magnetron.
Standard frequencies for microwave use are 915MHz and 2.45GHz.
For our development, a method is proposed for creating an inexpensive, compact and efficient magnetron with tissue heating indicators several times higher than standard 2.45 GHz magnetron.
To create a continuous magnetron with an average power of 1-3 kW with overall dimensions comparable to a standard magnetron at a frequency of 2450 MHz with an efficiency of at least 80%, coupled with an industrial power supply, it is necessary:
– Increase the inductance of the resonator block by decreasing the height of the lamellas by 30 ÷ 60% in the area adjacent to the cylinder of the anode block while maintaining the heat sink to the magnetron body.
– Increase the capacity of the coupling rings by making their height equal to 15-20% of the lamella height without the influence of their electric fields in the interaction zone by means of a symmetrical connection to the lamellas.
– Changes in the magnetic field along the cathode height should be no more than 2.5%, which provides approximately the same current density from the magnetron cathode.
– To maintain the minimum dimensions of the magnetron while ensuring the attenuation of the backward extra-tract radiation through the cathode leg of at least 20 dB, use a filter in the form of a folded structure based on a quarter-wave line.
As a result of this work, a magnetron from mass production product line was selected and adopted for our requirements:
– with reduced weight and dimensions;
– with the values of supply voltages equal to those for the magnetron at a frequency of 2450 MHz, but with increased efficiency and output power in comparison with the analogue;
– with a compact choke on the cathode stem, which provides at least 20 dB attenuation of extra-tract radiation from the cathode stem.
– a small-sized magnetron will be tested for weed control.
The minimum spot diameter at the focus is approximately equal to the operating wavelength, i.e. approximately λ = 122 mm. Accordingly, in order to achieve an acceptable accuracy in the application of microwave radiation, it will be necessary to increase the operating frequency by 2-3 times.
In simple terms, we have a real opportunity to get an economically viable and efficient weed control system without the use of chemicals based on microwave.
This will change the game in agriculture, improve the quality of products, neutralize the negative impact on the environment, automate the process of weed control and make it fully digital, smart, modern and safe.
We came to these conclusions after conducting a series of experiments with the research center of the Kharkiv National University of Radio Electronics and Professor Frolova Tatiana. Such as:
– conducted a series of experiments using a magnetron and two magnetrons in superposition ;
– conducted a series of experiments with different frequencies of microwave radiation;
– checked how long and what energy density is needed to destroy weeds at different stages of growth and different sizes;
– checked the system performance and energy efficiency.
On the figure 1 you can see results of conducted experiments.
Microwave frequency 2,456 GHz
Microwave Power 3kW
Exposure time – 1 sec
Distance – 0, 035 m
Figure 1 – Experiment with high power density MW weeding
After 5 hours after 1-second treatment, we can see that the experimental plants began to wither, lost their stable structure, according to our calculations, the temperature of the intracellular space during treatment reached 90-100 degrees. Our calculations at this stage are confirmed and we move on to further development of the experiment and preparation of the robot for work in real conditions.
Alex Reznichenko RobotecUA