Technical Field

The present disclosure generally relates to a dielectric heating system for controlling mold, moisture, and/or pests such as weevils in agricultural products. More particularly, the present disclosure describes various embodiments of a dielectric heating system for controlling rice weevils, mold, and/or moisture levels in agricultural products, as well as an application of the dielectric heating system.

Background

Different systems and methods have been used for controlling and/or mitigating infestation of agricultural products and crops, by controlling, killing, and/or eliminating parasites, pests, fungi, insects, and the like in the agricultural products. These parasites, pests, fungi, and insects may include mold, algae, rice weevils, rice moths, corn weevils, and beetles. The agricultural products may include seeds and grains of wheat, corn, rice, paddy, and millet. Some systems and methods have also been used to mitigate or address problems associated with moisture levels in agricultural products.

Rice weevils, which are tiny insects that live in rice, are potentially harmful to rice as they can cause damage to stored rice and rice growing in paddies. One method for controlling or killing rice weevils is to use chemical agents. Methyl bromide (or bromomethane) and phosphine (or phosphane) are two of the commonly used chemical agents. While methyl bromide is efficient in killing rice weevils, the chemical agent is banned in some countries due to its tendency to cause the rice weevils to become more resistant to the chemical agent after prolonged usage. Moreover, the use of methyl bromide is toxic to users and damages the atmospheric ozone layer. Hence, the use of chemical agents to address the problem of rice weevils in rice and paddy is not environmentally friendly.

Alternatives to the use of chemical agents have also been considered in many countries. For example, the oxygen level in rice can be controlled, which in turn controls the infestation of rice weevils. The oxygen level is controllable through the use of nitrogen and carbon dioxide within an environment in which the rice is stored. Moreover, herbal treatment using a stream sauna is also applied for rice weevil control. However, there is no clear evidence on the effectiveness of these methods.

Another alternative solution is the use of radio frequency radiation for controlling the rice weevils. ^' J ^' here is scientific evidence on the effectiveness of using radio frequency radiation for rice weevil control. Such irradiation of the rice or rice paddy causes dielectric heating of the irradiated material, which can increase the temperature of the material. Some dielectric heating systems utilize an electron tube to generate high power radio frequency signal. However, the electron tube is fragile, expensive, and inefficient. Additionally, such radio frequency irradiation traditionally requires high power consumption, and a complex circuit design. As such, radio frequency irradiation is not commonly used for rice weevil control .

However, current technological advancement can improve the power consumption issue, thus making it more economically feasible to use the radio frequency irradiation for controlling rice weevils, instead of other techniques such as the application of chemical agents. The use of radio frequency radiation has been applied in the development of methods, systems, and devices for addressing the at least one of the aforementioned infestation problems in agricultural products, particularly of rice weevils in rice and rice paddies.

United States patent publication number 20060024195 discloses an apparatus and a method for disinfestation of commodities using short duration, high peak power radio frequency pulses and intense electric fields. The disclosure provides an effective alternative to methyl bromide fumigation that does not leave any toxic residues or damage the cosmetic appearance or flavour of the commodity. The commodities are transported along a conveyor and are treated with radio frequency radiation at a fixed portion of the conveyor belt.

European patent number 2399464 discloses a method for preventive protection of agricultural products, particularly cereals, against attack by pests and pathogens. The method includes applying electromagnetic radiation to the agricultural products. The agricultural products are continuously moving by means of a horizontal conveyor belt, and are irradiated by the electromagnetic radiation during their motion on the conveyor belt, albeit only at one fixed portion of the conveyor belt. One problem associated with such prior art systems that use radio frequency or electromagnetic radiation is that the radio frequency system employs a limited input-output design that undesirably lim its power output. Further, such a system directs the radio frequency radiation only to one undesirably limited portion of the setup, such as said portion of the conveyor belt.

Therefore, in order to address at least one of the aforementioned problems and/or disadvantages, there is a need to provide a dielectric heating system and method for controlling rice weevils, mold, and/or moisture levels in agricultural products, in which there are improved features compared to the aforementioned prior art.

Summary

According to a first aspect of the present disclosure, there is a dielectric heating system for controlling rice weevils, mold, and/or moisture levels in agricultural products. The system comprises an adjustable output power unit configured to generate and output an electric Held. The adjustable output power unit comprises a high-power amplifier circuit having a set of inputs and a plurality of outputs, each input configured to receive a radio frequency (RF) signal, and each output configured to provide an amplified RF signal. The adjustable output power unit also comprises a high-power combiner having a plurality of inputs electrically coupled to the plurality of outputs of the high-power amplifier circuit, and having an output configured to provide a high-power RF output signal. The adjustable output power unit further comprises an impedance matching circuit electrically coupled to the output of the high-power combiner. The adjustable output power unit yet further comprises an output stage or heating unit electrically coupled to the impedance matching circuit. The output stage or heating unit comprises a structure through which a volume of agricultural products can flow and which exposes the agricultural products to the electric field produced by the adjustable output power unit as the agricultural products flow through the structure.

According to a second aspect of the present disclosure, there is a dielectric heating method for controlling rice weevils, mold, and/or moisture levels in agricultural products. The steps of the dielectric heating method correspond to the features of the dielectric heating system in the first aspect of the present disclosure. The dielectric heating system of the present disclosure utilizes semiconductor devices to generate high-power radio frequency signals required for the dielectric heating technique. An advantage of using the semiconductor devices over the electron tube is that the system can adaptively adjust the frequency and power according to the volume of the agricultural products. By controlling the optimal frequency and power, the system can efficiently control the rice weevils without damaging rice due to overheating. Moreover, any excess heat helps to reduce the moisture level in the rice and reduces the growth of mold therein.

Another advantage of the dielectric heating system of the present disclosure is that semiconductor devices are more efficient than the electron tube and reduces the rate of power consumption. The semiconductor devices have a longer operating life and are also smaller than the electron tube, resulting in a more compact system. Furthermore, no chemical agents are used and as such, the system is environmentally friendly and safe for consumers.

Preferably, the system further comprises a power splitter having an input configured to receive a source RF signal, and a plurality of outputs coupled to the plurality of inputs of the high-power amplifier circuit. The splitting of the source RF signal allows each split RF signal to be individually amplified by a subsequent circuit in the dielectric heating system.

The high-power amplifier circuit preferably has 4 outputs, the high-power combiner preferably has 4 inputs, and the power splitter preferably has 4 outputs. The high-power amplifier circuit preferably has a power rating greater than or equal to 500 Watts, and more preferably between 500 and 1 000 Watts. The high-power RF output signal provided by the high-power combiner preferably has a power level of at least 2000 Watts, and more preferably between 2000 and 4000 Watts. The high-power RF output signal preferably has a frequency in the range of 1 0 to 100 MHz.

The combination of multiple radio frequency signal inputs allows for a higher powered resultant radio frequency output signal . A high-power radio frequency output signal is more efficient in killing rice weevils in rice. The selection of the frequency of the RF output signal allows the selection of the proper frequency for killing the rice weevils without damaging the rice. The impedance matching circuit of the system is preferably configured for dynamically adjusting an electrical impedance of the output stage or heating unit as the agricultural products flow therethrough. As different types and sizes of the agricultural products have different individual impedances, the impedance matching circuit functions to maintain consistent overall impedance.

The output stage or heating unit preferably comprises a plurality of physically separated conductive elements, including a first conductive element and a second conductive element maintained at different electrical polarities. The agricultural products can flow between the conductive elements, and the heating unit is configured to expose the agricultural products to the electric field. The plurality of physically separated conductive elements preferably comprises a pair of parallel plates. The space between the pair of parallel plates allows the agricultural products to flow through and be exposed to the electric field between the parallel plates.

Preferably, the agricultural products comprises rice expected to contain rice weevils, wherein the system further comprises an RF signal generator configured for providing an adjustable frequency source RF signal, such that the frequency of the RF source signal can be varied according to a volume of rice weevils and/or rice in the system. The selection of the frequency of the RF source signal allows the selection of the proper frequency for killing the rice weevils without damaging the rice. The system preferably further comprises a power splitter configured to receive a first RF signal, and configured to output a plurality of reduced power RF signals to the high-power amplifier circuit. More preferably, the system further comprises a preamplifier configured to receive a source RF signal, and configured to output the source RF signal to the power splitter as the first RF signal. The splitting of the first RF signal allows each reduced power RF signal to be individually amplified by a subsequent circuit in the dielectric heating system. The inclusion of the preamplifier allows a source RF signal to attain an initial amplification, before being transmitted to the power splitter as the first RF signal for subsequent splitting into reduced power RF signals. A dielectric heating system for controlling mold, moisture, and/or pests such as weevils in agricultural products according to the present disclosure is thus disclosed hereinabove. Various features, aspects, and advantages of the present disclosure will become more apparent from the following detailed description of the embodiments of the present disclosure, by way of non-limiting examples only, along with the accompanying drawings in which like numerals represent like components.

Brief Description of the Drawings

FIG. 1 is a schematic of a dielectric heating system according to an embodiment of the present disclosure. FIG. 2 is a diagram of an output stage of the dielectric heating system according to an embodiment of the present disclosure.

Detailed Description

Various embodiments of the present disclosure are directed toward structural and functional aspects of a dielectric heating system for controlling rice weevils, mold, and/or moisture levels in agricultural products. In the context of the present disclosure, the term "agricultural products" is defined to encompass one or more types of agricultural crops, crop materials, or crop products, which in various embodiments includes rice. While aspects of the present disclosure will be described in conjunction with the embodiments provided herein, it will be understood that they are not intended to limit the present disclosure to these embodiments. On the contrary, the present disclosure is intended to cover alternatives, modifications and equivalents, which can be included within the spirit and scope of the present disclosure as defined by the appended claims. Furthermore, in the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be recognized by one of ordinary skill in the art that the present disclosure can be practiced without at least some of these specific details. In other instances, well-known systems, methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the embodiments of the present disclosure. Unless explicitly stated otherwise, in the description herein the recitation of particular numerical values or value ranges is taken to be a recitation of particular approximate numerical values or approximate value ranges (e.g., to within +/- 10%, or +/- 5%). For purposes of brevity and clarity, descriptions of embodiments of the present disclosure are limited hereinafter to a dielectric heating system for controlling rice weevils, mold, and/or moisture levels in agricultural products, as well as a method of an application of the dielectric heating system, in accordance with the drawings in FIG. 1 and FIG. 2. This, however, does not preclude embodiments of the present disclosure where fundamental principles prevalent among the various embodiments of the present disclosure such as operational, functional or performance characteristics are required.

In a representative or preferred embodiment of the present disclosure, a dielectric heating system 100 for controlling rice weevils, mold, and/or moisture levels in agricultural products, is described hereinafter.

The dielectric heating system 100 and a corresponding method thereof controls and/or mitigates infestation in agricultural products and crops, such as by controlling rice weevils, mold, and/or moisture levels in the agricultural products. FIG. 1 shows a schematic illustration of a dielectric heating system 100 for mitigating infestation of rice weevils in agricultural products comprising rice expected to contain rice weevils, by controlling the rice weevils according to particular embodiments of the present disclosure. In an embodiment, the dielectric heating system 100 comprises an adjustable output power unit 160 configured to generate and output an electric field using radio frequency signals received therein. The dielectric heating system 100 comprises a radio frequency signal generator 120 for generating the radio frequency signals for the adjustable output power unit 160. The radio frequency signal generator 120 includes an oscillator 120 for providing an adjustable frequency source radio frequency signal. The oscillator 120 is typically an electronic circuit that produces a repetitive, oscillating electronic signal, often a sine wave or a square wave, converted from a direct current (DC) signal. The DC signal supplied to the oscillator 120 is provided by a power supply 130. Unless otherwise stated, the DC signal has a predetermined voltage or power level, e.g., a 12-Volts DC. A generated radio frequency signal is generally between 10 to 100 MHz, and may be adjustable depending on requirements and specifications, such as a volume of rice and/or rice weevils exposed to the dielectric heating system 100.

The dielectric heating system 100 further comprises a preamplifier 140. A source radio frequency signal generated from the oscillator 120 is transmitted to the preamplifier 140. In a representative embodiment, the preamplifier 140 amplifies the power level of the source radio frequency signal to approximately 20 Watts. The amplified radio frequency signal is subsequently transmitted as a first radio frequency signal to a power splitter 150 in the dielectric heating system 100. The power splitter 150 is configured to receive the first radio frequency signal and output a plurality of reduced power radio frequency signals through a plurality of outputs. In the representative embodiment, the power splitter 150 is a 4-way power splitter which splits the first radio frequency signal into 4 equal outputs. Each output of the 4-way power splitter 150 carries a reduced power radio frequency signal having a power level of 5 Watts. Each of the reduced radio frequency signals is transmitted to an adjustable output power unit 160 of the dielectric heating system 100.

The adjustable output power unit 160 comprises a high-power amplifier circuit 170. In the representative embodiment, the power supply 130 provides a 48-Volt DC signal, and delivers the 48-Volt DC signal to the high-power amplifier circuit 170, instead of the aforementioned 12-Volt DC signal which is for other components and circuits of the dielectric heating system 100. The high-power amplifier circuit 170 comprises a set of inputs and a plurality of outputs, each input configured to receive a radio frequency signal, and each output configured to provide an amplified radio frequency signal. The set of inputs of the high-power amplifier circuit 170 is coupled to the plurality of outputs of the power splitter 150. In the representative embodiment, the high-power amplifier circuit 170 includes or allows for 4 inputs and 4 outputs, each input being coupled or connected to one output. In the coupling or connection between an input and an output, the high-power amplifier circuit 170 comprises a power amplifier. Thus, in the representative embodiment, the high-power amplifier circuit 170 comprises a total of 4 power amplifiers arranged in a parallel configuration. In a representative implementation, each of the 4 power amplifiers comprises a metal-oxide-semiconductor field-effect transistor (MOSFET) capable of amplifying the split radio frequency signal received therein. For instance, each of the MOSFET power amplifiers in the high-power amplifier circuit 170 can amplify the reduced power radio frequency signal from 5 Watts to 1000 Watts. Thus, in the representative embodiment, each of the 4 outputs from the high-power amplifier circuit 170 carries an amplified radio frequency signal having a power level of 1000 Watts.

The amplified radio frequency signals from the multiple outputs (e.g., 4 outputs) of the high- power amplifier circuit 170 are transmitted to a high-power combiner 180 of the adjustable output power unit 160. The high-power combiner 180 comprises a plurality of inputs electrically coupled to the plurality of outputs of the high-power amplifier circuit 170, and has an output configured to provide a high-power radio frequency signal. In the representative embodiment, the high-power combiner 180 comprises 4 inputs electrically coupled to the outputs of the high-power amplifier circuit 170, such that the high-power combiner 180 is a 4-way power combiner. The 4-way power combiner 180 combines the 4 amplified radio frequency signals (each with a power level of 1000 Watts) from the outputs of the high-power amplifier circuit 170 into a single output. The resultant output of the 4- way power combiner 180 carries a high-power radio frequency output signal having a power level of 4000 Watts.

The high-power radio frequency output signal is subsequently transmitted to an impedance matching circuit 190 of the adjustable output power unit 160. Thus, the impedance matching circuit 190 is electrically coupled to the output of the high-power combiner 180. After the impedance matching circuit 190, the 4000- Watt high-power radio frequency output signal is transmitted to an output stage 200 of the adjustable output power unit 160.

Referring to both FIG. 1 and FIG. 2, the output stage 200 is a treatment and/or heating unit electrically coupled to the impedance matching circuit 190. The output stage or heating unit 200 comprises a structure through which a volume of agricultural products can flow through along at least one travel path or direction, such as the direction 210 indicated. The heating unit 200 exposes the agricultural products to the electric field produced by the adjustable output power unit 160 as the agricultural products flow through the structure along the direction 210. The heating unit 200 comprises a plurality of physically separated conductive elements, including a first conductive element 220 and a second conductive element 230 maintained at different electrical polarities. In the representative embodiment, the first and second conductive elements 220 and 230 include or are a pair of parallel plates. The parallel plates 220 and 230 are configured such that the agricultural products can flow along the direction 210 between the parallel plates 220 and 230, and are configured to expose the agricultural products to the electric field. The different electrical polarities of the parallel plates 220 and 230 allow for the electric field to be generated therebetween and for the agricultural products to be exposed to the electric field. The impedance matching circuit 190 is configured for dynamically adjusting an electrical impedance of the output stage or heating unit 200 as the agricultural products flow there through. More particularly, the structure of the impedance matching circuit 190 includes or is used for controlling elements of an LC matching circuit. Impedance can be automatically adjusted coactively based upon RF feedback from the heating unit 200 to the input of the impedance matching circuit 190. The impedance matching circuit 190 is used to adaptively control the combined impedance of the heating unit 200, which includes the impedance of the conductive elements 220 and 230 as well as the impedance(s) of the agricultural products flowing therethrough or passing therein / thereby. Because different types and sizes of the agricultural products can have different individual impedances, the impedance matching circuit 190 functions to maintain consistent overall impedance. The impedance matching circuit 190 also ensures a high efficiency of the transmission of radio frequency signals to the output stage 200 by minimizing unnecessary power losses. Additionally, the flow of agricultural products between the parallel plates 220 and 230 can cause dynamic changes to the overall load impedance in the adjustable output power unit 160. The impedance matching circuit 190 protects the high-power amplifier circuit 170 from encountering power losses due to such dynamic changes in load impedance.

The high-power radio frequency output signal received by the heating unit 200 creates an alternating electric field between the plates 220 and 230. When agricultural products such as rice containing rice weevils flow in between the plates 220 and 230, the alternating electric field agitates and excites the molecules in the rice. The rice contains polar molecules having an electrical dipole moment. The electric field causes the polar molecules in the rice to continuously reorient themselves in different directions. Molecular friction resulting from the molecular movement causes the rice to rapidly heat up throughout its entire mass. The agitated or excited molecules also move faster within the rice, thereby increasing the average kinetic energy of the molecules and thus the temperature of the rice. Therefore, because of the rapid oscillation of the molecules within the rice, heat is more uniformly generated from within the rice and conducted to the external surfaces of the rice, in or as a result of a process known as dielectric heating. The internal heat generated from within the rice kills the rice weevils living therein.

The agricultural products or rice is dielectrically heated to 55 °C, as prior research has shown that the temperature of 55 °C is sufficient to kill a substantial proportion of the parasites, insects, and pests that have contaminated and infested the agricultural products, including rice weevils that infest rice. At this temperature, the rice weevils can be more efficiently controlled or killed without damaging rice due to overheating. Moreover, any excess heat helps to reduce the moisture level in the rice and reduces the growth of mold therein. It should be noted that the viscosity, water content, and chemical composition of the rice may affect the dielectric properties and thus the efficiency and effectiveness of the adjustable output power unit 160. The efficiency and effectiveness may also be affected if different or other types of agricultural products are used as the dielectric material undergoing treatment, i.e. the materials flowing between the plates 220 and 230. Due to the use of radio frequency signals and radiation in the dielectric heating system 100, the various components of the system 100, including the adjustable output power unit 160, are made from materials that have a high resistance to radio frequency radiation. In particular, the heating unit 200 of the adjustable output power unit 160 requires materials with higher resistance to radio frequency signals and radiation in order to maintain continuous internal-to-external or dielectric heating of the agricultural products. An example of a suitable material is Teflon®. Additionally or alternatively, the components of the system 100 can be surrounded or coated with a layer of electromagnetic frequency shielding.

In the representative embodiment, the dielectric system 100 comprises a set of controls that can be used or operated to control one or multiple parameters of the system 100. Such parameters include, but are not limited to, the flow rate of the agricultural products between the parallel plates 220 and 230, the frequency of the source radio frequency signal from the oscillator 120, and/or the amplification power of the preamplifier 140 and the high-power amplifier circuit 170. Additionally, the dielectric system 100 is equipped with devices or accessories for automatic operating control, such as real-time temperature measurement. The real-time temperature can be detected or measured with fibre optic sensors, as they are able to endure the strong electric field, specifically in the heating unit 200. Further, such accessories can also comprise a proportional-integral-derivative (PID) controller, controls for computer displays, and/or recording devices or functionalities to monitor data derived during or associated with the usage of the dielectric heating system 100.

In an alternative embodiment of the present disclosure, the first radio frequency signal transmitted from the preamplifier 140 can be transmitted directly to the high-power amplifier circuit 170, without passing through the power splitter 150. The preamplifier 140 receives the source radio frequency signal from the oscillator 120 and outputs the first radio frequency signal to the high-power amplifier circuit 170. As there is a set of inputs for the high-power amplifier circuit 170, the high-power amplifier circuit 170 can receive the inputs from multiple sources in the absence of the power splitter 150. The multiple sources can come from a plurality of oscillators 120, wherein each oscillator 120 is coupled to a preamplifier 140. Alternatively, some of the oscillators 120 may not be coupled to the preamplifier 140 and are instead coupled directly to the high-power amplifier circuit 170. Each of the source radio frequency signals from the oscillators 120 will be transmitted, without going through any power splitter 150, to the set of inputs of the high-power amplifier circuit 170 for subsequent processing. The subsequent processing of the radio frequency signals will be apparent to a person having ordinary skill in the art based on the details disclosed herein.

In another alternative embodiment of the present disclosure, other than for killing rice weevils, the dielectric system 100 is usable for killing insects and insect eggs in crops such as corn, as well as insects / insect eggs in dried chilli. The dielectric system 100 is also usable for drying fruits and vegetables that are stored in non-metallic containers (e.g., from which water vapour can be released or vented). The drying is caused by the dielectric heating of the fruits and vegetables. Further, the dielectric system 100 can also be used for mitigating the growth of herbal mold and timber mold on materials by controlling the moisture levels of the materials by dielectrically heating the materials in order to keep them dry. It would be apparent to and understood by a person having ordinary skill in the art that a corresponding method of an application of the dielectric heating system 100 is derivable based on the details of the embodiments of the present disclosure.

In the foregoing detailed description, embodiments of the present disclosure in relation to a dielectric heating system and method for controlling rice weevils, mold, and/or moisture levels in agricultural products are described with reference to the figures. Although only some embodiments of the present invention are disclosed herein, it will be apparent to a person having ordinary skill in the art in view of this disclosure that numerous changes and/or modifications can be made to the disclosed embodiments without departing from the scope of the present invention. The scope of the disclosure as well as the scope of the following claims is not limited to embodiments described herein.