A coaxial-waveguide composite resonant microwave heating device with multiple feeds and a control method

Abstract

The application discloses a coaxial-waveguide composite resonance microwave heating device with multiple feed sources and a control method, which comprises a waveguide cavity and multiple coaxial coupling structures. The top surface of the waveguide cavity is open. The multiple coaxial coupling structures are integrated in the cavity wall of the waveguide cavity. Each coaxial coupling structure comprises a coaxial port and a coaxial coupling spiral which are connected with each other. The coaxial port serves as an input end of the feed source. Microwave signals are sequentially input into the waveguide cavity through the coaxial port and the coaxial coupling spiral. The object to be heated in the waveguide cavity is heated. The embedded spiral structure is arranged to construct a coaxial-waveguide composite resonance mode. In combination with a gradually changing spiral parameter design and a multiple-source heating control method, impedance matching and heating uniformity are further optimized. The application is suitable for industrial heating and precise material processing fields with extremely high requirements on temperature uniformity.

Description

Technical Field

[0001] This invention belongs to the field of microwave heating technology, specifically relating to a multi-feed coaxial-waveguide composite resonant microwave heating device and its control method. Background Technology

[0002] Microwave heating technology has demonstrated enormous application potential in various industries in recent years, particularly in food processing, chemical processing, pharmaceutical preparation, and tobacco production. Microwave heating, through the direct action of electromagnetic waves on the interior of an object, enables more efficient and uniform heat transfer, significantly improving heating efficiency and reducing energy consumption. Furthermore, microwave heating allows for precise temperature control by adjusting frequency and power, meeting the heating requirements of different materials. Compared to traditional methods, microwave heating is faster and more energy-efficient, improving production efficiency and reducing energy waste. Despite its wide application, existing technologies still face significant challenges in terms of precision control and uniformity, primarily in the following aspects:

[0003] Current industrial microwave ovens and early microwave heating equipment primarily rely on magnetrons as microwave generators, with fixed output frequencies and random, uncontrollable phases. When multiple magnetrons operate simultaneously, chaotic and fixed standing wave interference patterns form within the cavity, resulting in noticeable "hot spots" and "cold spots" inside the heated object. In industrial heating scenarios, this non-uniformity can lead to localized overheating and damage to materials, low chemical reaction yields, or incomplete drying. Traditional resistance wire heating or electromagnetic induction heating relies mainly on heat conduction, which suffers from long preheating times, low utilization of the central area, and easy carbonization and charring at the edges. Regarding coupling structures, existing microwave heating devices typically use simple electric field probes or magnetic field loops for coupling. These traditional structures struggle to achieve impedance matching with high-Q cavities over a wide frequency range, especially when the dielectric constant of the load changes drastically with temperature, causing a sharp drop in coupling efficiency, leading to significant energy reflection and even damage to the microwave source. Furthermore, existing microwave heating technologies lack effective dynamic control methods; to improve heating uniformity, current technologies often employ mechanical stirring. However, mechanical stirring can only improve the distribution over time average; it cannot eliminate instantaneous strong field points, nor can it perform targeted heating of specific areas. More importantly, traditional equipment lacks depth-direction control capabilities, making it impossible to deliver energy differently based on the object's state along the wave propagation direction.

[0004] In conclusion, although microwave heating technology has shown great potential in improving heating efficiency and product quality, it still faces many challenges in terms of heating uniformity, multi-channel collaborative control capabilities, and energy efficiency. Summary of the Invention

[0005] The purpose of this invention is to provide a multi-feed coaxial-waveguide composite resonant microwave heating device to improve heating uniformity and multi-channel collaborative control capability.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: The first objective of the present invention is to provide a multi-feed coaxial-waveguide composite resonant microwave heating device, comprising a waveguide cavity and multiple coaxial coupling structures. The top surface of the waveguide cavity is open, and the multiple coaxial coupling structures are integrated within the cavity wall of the waveguide cavity. Each coaxial coupling structure includes an interconnected coaxial port and a coaxial coupling screw. The coaxial port serves as the input end of the feed source. Microwave signals are sequentially input into the waveguide cavity through the coaxial port and the coaxial coupling screw to heat the object to be heated within the waveguide cavity.

[0007] The coaxial port is inserted into the cavity wall of the waveguide cavity at one end along its own axial direction and extends out of the waveguide cavity at the other end. The coaxial port includes a port coaxial core and a port outer conductor. The port outer conductor is sleeved on the outside of the port coaxial core and the two are arranged coaxially. An insulating medium is filled between the port outer conductor and the port coaxial core.

[0008] The coaxial coupling helix includes a helical groove recessed in the inner wall of the waveguide cavity and a helical coaxial core suspended in the helical groove. No insulating medium is filled between the helical coaxial core and the helical groove. The groove surface of the helical groove is a metal surface. The helical coaxial core is electrically connected to the port coaxial core in the coaxial port for transmitting microwave signals.

[0009] In one specific implementation, the coaxial coupling spiral is either a uniform spiral or a non-uniform spiral. When the coaxial coupling spiral is a uniform spiral, the pitch between adjacent threads on the coaxial core and the depth of the spiral groove are constant. When the coaxial coupling spiral is a non-uniform spiral, the pitch between adjacent threads on the coaxial core and the depth of the spiral groove are not constant.

[0010] As one specific implementation, the coaxial coupling helix satisfies the following physical relationship:

[0011] ,

[0012] Where Z0 represents the characteristic impedance of the coaxially coupled helix, P represents the pitch of the coaxial helix core, and d represents the diameter of the coaxial helix core. μ 0 Represents the permeability of free space. ε The dielectric constant of the medium between the spiral groove and the coaxial spiral core is represented by , and D represents the depth of the spiral groove.

[0013] As a specific implementation, when the coaxial coupling spiral is a non-uniform spiral, the pitch of the spiral coaxial core satisfies the following: the pitch at the end closer to the coaxial port is greater than the pitch at the end farther from the coaxial port.

[0014] In one specific implementation, when the coaxial coupling spiral is a non-uniform spiral, the depth of the spiral groove varies with a gradient along the spiral extension direction, that is, the depth of the spiral groove increases gradually from the coaxial port to the spiral end.

[0015] In one specific implementation, the coaxial ports in the multiple coaxial coupling structures are evenly spaced along the outer wall of the waveguide cavity in the axial or circumferential direction, and each coaxial port is connected to an independent phase and amplitude control channel.

[0016] As a specific implementation, a transmit RF power source system that provides power to multiple coaxial ports includes: a microwave excitation source, a power distribution network, a multi-channel phase control network, a distributed power amplifier module, a distributed power matching network, a controller, and a DC power supply module, wherein...

[0017] The microwave excitation source generates an initial radio frequency signal, which is divided into multiple microwave signals by the power distribution network, and then enters the multi-channel phase control network respectively.

[0018] The multi-channel phase control network includes multiple independently adjustable phase shifting units, which are used to independently modulate the phase of each microwave signal under the command of the controller.

[0019] The distributed power amplifier module includes multiple power amplifiers that correspond one-to-one with the coaxial ports, used to receive multiple signals after phase modulation by a multi-channel phase control network;

[0020] The controller independently controls the output power amplitude of each microwave signal by adjusting the DC bias voltage or drain voltage provided by the DC power supply module to each power amplifier. After being amplified, the multiple microwave signals are impedance matched by a distributed power matching network and then coupled into the waveguide cavity through the coaxial port.

[0021] In one specific implementation, the insulating medium is made of polyethylene, Teflon, or foamed plastic.

[0022] Another objective of this invention is to provide a microwave heating control method for a coaxial-waveguide composite resonant microwave heating device based on the aforementioned multi-feed source. The multi-feed source coaxial-waveguide composite resonant microwave heating device has a zoned independent heating mode and a multi-source coordinated heating mode. Specifically,

[0023] In the zoned independent heating mode, a single or partial coaxial port is excited, and the corresponding coaxial coupling spiral couples microwave energy to a set coverage area inside the waveguide cavity, thereby achieving zoned independent heating of the internal area of ​​the waveguide cavity.

[0024] In the multi-source coordinated heating mode, all coaxial ports are simultaneously excited. By adjusting the relative phase and amplitude relationship between the coaxial ports, a controllable electromagnetic field interference pattern is synthesized in the waveguide cavity. The specific steps are as follows:

[0025] 1) Initialization: Start the microwave excitation source to generate a reference signal;

[0026] 2) Phase scanning: Under the premise of maintaining a constant microwave signal operating frequency, a rotating vector phase scanning strategy is executed. Specifically, one coaxial port is set as the reference phase, and the phases of the other coaxial ports are controlled to form a preset phase gradient sequence. The overall offset of the phase gradient sequence or the phase vector combination is changed periodically over time, thereby exciting a rotating electromagnetic field mode in the waveguide cavity, so that the electric field interference peak region formed by the superposition of multiple signals is scanned traversally in space.

[0027] 3) Frequency scanning: Within the preset working bandwidth, the carrier frequency of the microwave signal is periodically changed according to the set scanning rate; utilizing the frequency dispersion characteristics of the coaxial coupling spiral as a slow wave structure, the axial angle and coverage of microwave energy radiated from the spiral structure into the waveguide cavity are changed with the frequency, driving the radiation beam to perform dynamic scanning in the longitudinal depth direction of the waveguide cavity.

[0028] As a specific implementation method, when the object to be heated is unevenly distributed or needs to be heated at a fixed point, a zoned independent heating mode is adopted to increase the power amplitude of the coaxial port in the corresponding area; when uniform heating of the entire cavity is required, a multi-source collaborative heating mode is adopted, and steps 2) and 3) are executed cyclically to reduce heating dead zones by using multi-dimensional electromagnetic field scanning.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] 1) The microwave heating device of this invention innovatively adopts a coaxial helical slow-wave structure embedded in the waveguide cavity wall. This design utilizes the air dielectric transmission line formed by the helical groove and the suspended coaxial core to achieve efficient mode conversion and impedance matching from coaxial feeding to waveguide resonance within an extremely compact space. This integrated design not only significantly reduces the device size and eliminates dielectric loss, but also extends the interaction path between the electromagnetic wave and the load through the slow-wave effect of the helical structure, greatly improving the heating coverage volume and energy conversion efficiency.

[0031] 2) Distributed Power Architecture Based on Spatial Synthesis within Waveguide Cavity: This invention abandons the traditional single high-power magnetron and its high-voltage power supply system, instead employing distributed feeding via multiple coaxial ports. Through spatial power synthesis within the resonant cavity using multiple independent coaxial ports, an equivalent high-power microwave output is obtained by superimposing multiple low-voltage, low-power signals. This architecture effectively solves the problems of heat dissipation bottlenecks, short lifespan, and low reliability faced by single high-power sources, while significantly reducing system maintenance costs. It provides a feasible hardware path for the miniaturization and solid-state development of industrial-grade microwave heating devices.

[0032] 3) Dynamically Controlled Heating Strategy: Addressing the drawback of fixed field distribution in traditional microwave heating, this invention proposes a heating strategy based on amplitude-phase decoupling control. The device can dynamically adjust the phase and amplitude combination of each channel according to load characteristics: utilizing rotating vector phase scanning and the frequency dispersion characteristics of the spiral structure, energy scanning is achieved to eliminate heating dead zones. This multi-dimensional dynamic field shaping capability enables the device to achieve uniform heating covering the entire cavity for loads of different materials, shapes, and locations, significantly improving heating quality. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the axial cross-sectional structure of a multi-feed coaxial-waveguide composite resonant microwave heating device according to the present invention.

[0034] Figure 2 This is a diagram of the transmitting radio frequency power source system that provides energy to the multiple coaxial ports of the coaxial-waveguide composite resonant microwave heating device in this invention;

[0035] Figure 3 This is a front view of a multi-feed coaxial-waveguide composite resonant microwave heating device according to the present invention;

[0036] Figure 4 This is a three-dimensional schematic diagram of a multi-feed coaxial-waveguide composite resonant microwave heating device according to the present invention;

[0037] Figure 5 This is a top-view cross-sectional view of a multi-feed coaxial-waveguide composite resonant microwave heating device according to the present invention.

[0038] Figure 6 This is a three-dimensional structural diagram of the port coaxial core and the spiral coaxial core in this invention;

[0039] Figure 7 This is a partially enlarged schematic diagram of the coaxial port in this invention;

[0040] Figure 8 This is an electric field distribution diagram of the in-phase feeding of the multi-feed coaxial-waveguide composite resonant cavity in Embodiment 1 of the present invention;

[0041] Figure 9 This is an electric field distribution diagram of a multi-feed coaxial-waveguide composite resonant cavity fed with a 90° phase difference in Embodiment 1 of the present invention;

[0042] Figure 10 This is an electric field distribution diagram of the four ports of the multi-feed coaxial-waveguide composite resonant cavity in Embodiment 1 of the present invention, each individually fed;

[0043] Wherein: 1. Waveguide cavity; 11. Internal region of the cavity; 12. Cavity wall; 122. Inner wall; 123. Outer wall; 13. Cavity bottom;

[0044] 2. Coaxial coupling structure; 21. Coaxial port; 211. Port coaxial core; 212. Port outer conductor; 213. Insulating medium; 22. Coaxial coupling helix; 221. Helical groove; 222. Helical coaxial core;

[0045] 3. Microwave excitation source; 4. Power distribution network; 5. Multi-channel phase control network; 6. Distributed power amplifier module; 7. Distributed power matching network; 8. Controller; 9. DC power supply module. Detailed Implementation

[0046] To make the objectives, technical solutions, and effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. However, the scope of protection of the present invention is not limited to these embodiments.

[0047] See Figure 1 , 3 As shown in Figure 4, this invention provides a multi-feed coaxial-waveguide composite resonant microwave heating device, including a waveguide cavity 1 and multiple coaxial coupling structures 2. The top surface of the waveguide cavity 1 is open, and the multiple coaxial coupling structures 2 are integrated within the cavity wall 12 of the waveguide cavity 1. Each coaxial coupling structure 2 includes an interconnected coaxial port 21 and a coaxial coupling screw 22. The coaxial port 21 serves as the input end of the feed source. Microwave signals are sequentially input into the waveguide cavity 1 through the coaxial port 21 and the coaxial coupling screw 22 to heat the object to be heated within the waveguide cavity 1. See [reference needed]. Figure 5-7 As shown.

[0048] Specifically, the waveguide cavity 1 is a hollow cylindrical shape with one end open, including a cavity wall 12, a cavity bottom 13, and an internal cavity region 11 enclosed by the two, which is used to place the object to be heated. The cavity wall 12 of the waveguide cavity 1 has a certain thickness, including an outer wall 123 and an inner wall 122.

[0049] The coaxial port 21 is inserted into the cavity wall 12 of the waveguide cavity 1 at one end along its own axial direction and extends out of the waveguide cavity 1 at the other end to receive microwave transmission signals from the radio frequency power source. It includes a port coaxial core 211 and a port outer conductor 212. The port outer conductor 212 is sleeved on the outside of the port coaxial core 211 and is arranged coaxially with the port coaxial core 211. An insulating medium 213 is filled between the port outer conductor 212 and the port coaxial core 211. The insulating medium 213 is made of polyethylene (PE), Teflon (FEP) or foamed plastic. The insulating medium 213 surrounds the port coaxial core 211 to achieve electrical isolation and mechanical support between the port coaxial core 211 and the port outer conductor 212, and can fix the position of the port coaxial core 211 and the spiral coaxial core 222 connected to it.

[0050] The coaxial coupling helix 22 includes a helical groove 221 recessed in the inner wall 122 of the waveguide cavity 1 and a helical coaxial core 222 suspended in the helical groove 221. No insulating medium is filled between the helical coaxial core 222 and the helical groove 221. Because the port coaxial core 211 is fixedly connected to the helical coaxial core 222, the helical coaxial core 222 is suspended in the helical groove 221. The spiral groove 221 is a groove structure with three metal sides and one open side. The spiral coaxial core 222 is a circular coaxial core that is also spirally distributed like the spiral groove 221. The spiral coaxial core 222 is electrically connected to the port coaxial core 211 in the coaxial port 21 for transmitting microwave signals. At the same time, the position is fixed by the insulating medium 213 of the coaxial port 21. The spiral groove 221 of the coaxial coupling spiral 22 is not filled with the insulating medium 213, so as to improve the efficiency of microwave coupling and heating. Meanwhile, the coaxial coupling spiral 22 is evenly distributed on the inner wall 122, covering the main area inside the waveguide cavity 1.

[0051] The coaxial coupling screw 22 can be a uniform screw or a non-uniform screw. When the coaxial coupling screw 22 is a uniform screw, the pitch between adjacent threads on the coaxial core 222 and the depth of the screw groove 221 are constant. When the coaxial coupling screw 22 is a non-uniform screw, the pitch between adjacent threads on the coaxial core 222 and the depth of the screw groove 221 are not constant. By adopting a non-uniform screw structure, power attenuation can be compensated at the end of the screw where the energy is weaker.

[0052] The gradient spiral, or non-uniform spiral structure, specifically achieves the matching of the microwave source output impedance and the load impedance through the structural parameter configuration of the coaxially coupled spiral 22. The specific matching method satisfies the following physical relationship:

[0053] ,

[0054] Where Z0 represents the characteristic impedance of the coaxial coupling screw 22, P represents the pitch of the coaxial screw core 222, and d represents the diameter of the coaxial screw core 222. μ 0 Represents the permeability of free space. ε The dielectric constant of the medium between the spiral groove 221 and the spiral coaxial core 222 is represented by D, and the depth of the spiral groove 221 is represented by D.

[0055] The characteristic impedance Z0 of the coaxial coupling screw 22 is inversely proportional to the pitch P of the coaxial core 222 and directly proportional to the logarithmic function of the outer diameter D determined by the equivalent depth of the spiral groove 221. The diameter d of the coaxial core 222 is fixed to carry current. The coaxial coupling screw 22 constructs a transition section with gradually changing impedance by gradually decreasing the pitch P or increasing the depth D of the spiral groove 221 along the microwave propagation direction, thereby transforming the standard impedance of the coaxial port 21 to a high impedance state in the waveguide cavity 1.

[0056] The specific derivation process of the above physical relationship is as follows: the coaxial coupling spiral 22 is essentially a slow-wave coaxial transmission line, and the characteristic impedance of this structure... Z0 Through unit length inductance L' and capacitor C' The derivation leads to:

[0057] ,

[0058] Inductance per unit length L' Mainly composed of the pitch of coaxially coupled screw 22 P Coaxial core with spiral diameter 222 d Decide, μ 0 The permeability of free space is expressed by the formula for the inductance of a long straight solenoid: .

[0059] Unit length capacitor C' Mainly determined by the depth of the spiral groove 221 D The diameter of the coaxial spiral core 222 d Decision, that is , ε The dielectric constant of the medium between the spiral groove 221 and the spiral coaxial core 222 is generally air.

[0060] Combining the above two points, the characteristic impedance of coaxially coupled screw 22 is obtained. Z0 Formula relating to structural parameter configuration:

[0061] .

[0062] When the coaxial coupling screw 22 is a non-uniform screw, the pitch of the coaxial core 222 satisfies the following: the pitch P1 at the end closer to the coaxial port 21 is greater than the pitch P2 at the end farther from the coaxial port 21. The smaller pitch P1 corresponds to a lower characteristic impedance, and the pitch P2 > P1 corresponds to a higher characteristic impedance, thus forming a broadband impedance transformer.

[0063] Furthermore, when the coaxial coupling screw 22 is a non-uniform screw, the depth of the screw groove 221 varies with gradient along the screw extension direction. That is, the depth D1 of the screw groove 221 increases from the coaxial port 21 to the screw end with gradient D2. This setting allows the characteristic impedance to gradually increase with the screw extension direction to achieve impedance matching.

[0064] In this invention, the coaxial ports 21 in the multiple coaxial coupling structures 2 are arranged in an array along the outer wall 123 of the waveguide cavity 1, and can be evenly spaced in the axial or circumferential direction. Each coaxial port 21 is connected to an independent phase and amplitude control channel and is configured with an independently adjustable feed unit.

[0065] See Figure 2 As shown, the transmit RF power source system that provides power to multiple coaxial ports 21 includes: a microwave excitation source 3, a power distribution network 4, a multi-channel phase control network 5, a distributed power amplifier module 6, a distributed power matching network 7, a controller 8, and a DC power supply module 9.

[0066] The signal link configuration is as follows:

[0067] The microwave excitation source 3 generates an initial radio frequency signal, which is divided into multiple microwave signals by the power distribution network 4, and then enters the multi-channel phase control network 5 respectively.

[0068] The multi-channel phase control network 5 contains multiple independently adjustable phase shifting units, which are used to independently modulate the phase of each microwave signal under the command of the controller 8.

[0069] The distributed power amplifier module 6 includes multiple power amplifiers corresponding one-to-one with the coaxial port 21, used to receive multiple signals after phase modulation by the multi-channel phase control network 5;

[0070] The controller 8 independently controls the output power amplitude of each microwave signal by adjusting the DC bias voltage or drain voltage provided by the DC power supply module 9 to each power amplifier. After the amplified multi-channel microwave signals are impedance matched by the distributed power matching network 7, they are coupled into the waveguide cavity 1 through the coaxial port 21.

[0071] This invention also provides a microwave heating control method for a coaxial-waveguide composite resonant microwave heating device employing multiple feed sources. The multi-feed coaxial-waveguide composite resonant microwave heating device has a zoned independent heating mode and a multi-source coordinated heating mode. Specifically,

[0072] In the zoned independent heating mode, a single or partial coaxial port 21 is excited, and the corresponding coaxial coupling spiral 22 couples microwave energy to a set coverage area inside the waveguide cavity 1, thereby realizing zoned independent heating of the internal area of ​​the waveguide cavity 1.

[0073] In the multi-source coordinated heating mode, all coaxial ports 21 are simultaneously excited. By adjusting the relative phase and amplitude relationship between each coaxial port 21, a controllable electromagnetic field interference pattern is synthesized in the waveguide cavity 1. The specific steps are as follows:

[0074] 1) Initialization: Start microwave excitation source 3 to generate a reference signal;

[0075] 2) Phase scanning: Under the premise of maintaining a constant microwave signal operating frequency, a rotating vector phase scanning strategy is executed. Specifically, one of the coaxial ports 21 is set as the reference phase, and the phases of the other coaxial ports 21 are controlled to form a preset phase gradient sequence (for example, maintaining a constant phase difference ΔΦ between adjacent ports). The overall offset of the phase gradient sequence or the phase vector combination is changed periodically over time, thereby exciting a rotating electromagnetic field mode in the waveguide cavity 1, so that the electric field interference peak region formed by the superposition of multiple signals can be scanned in space.

[0076] 3) Frequency scanning: Within the preset working bandwidth, the carrier frequency of the microwave signal is periodically changed according to the set scanning rate; the frequency dispersion characteristics of the coaxial coupling spiral 22 as a slow wave structure are used to change the axial angle and coverage of microwave energy radiated from the spiral structure into the waveguide cavity 1 as the frequency changes, driving the radiation beam to perform dynamic scanning in the longitudinal depth direction of the waveguide cavity 1.

[0077] When the object to be heated is unevenly distributed or needs to be heated at a fixed point, a zoned independent heating mode is adopted to increase the power amplitude of the coaxial port 21 in the corresponding area; when uniform heating of the entire cavity is required, a multi-source collaborative heating mode is adopted, and steps 2) and 3) are executed cyclically to reduce heating dead zones by using multi-dimensional electromagnetic field scanning.

[0078] The following provides specific examples.

[0079] Example 1

[0080] This embodiment provides a microwave tobacco heating device with a multi-feed coaxial-waveguide composite resonance. See also... Figure 1 , 2As shown, the heating device is a hollow cylindrical metal structure open at one end. The waveguide cavity has a height of 40mm and includes an internal region 11 and a cavity wall 12. The cavity wall 12 is 2mm thick, the outer wall 123 has a diameter of 11mm, and the inner wall 122 has a diameter of 7mm. The inner diameter is designed so that the internal region 11 can accommodate a tobacco stick with a diameter of 6.8-7.0mm. The cavity bottom 13 is sealed to the bottom surface of the waveguide cavity 1, and the top surface of the waveguide cavity 1 is open for placing the tobacco to be heated. The cavity bottom 13 is 2mm thick and serves as an electromagnetic shielding short circuit. The waveguide cavity 1 is made of oxygen-free copper (C10100), and the inner wall 122 is silver-plated with a thickness of 5μm.

[0081] To efficiently feed microwave energy into the high-impedance tobacco load, this device integrates four coaxial coupling structures 2 within the cavity wall 12. Each coaxial coupling structure 2 includes a coaxial port 21 and a coaxial coupling screw 22, which are connected together. The coaxial port 21 serves as the input end of the feed source, and the microwave signal is input into the waveguide cavity 1 for heating through the coaxial port 21 and the coaxial coupling screw 22.

[0082] Four coaxial ports 21 are evenly distributed on the outer wall 123. Each coaxial port 21 is 3 mm long and passes through the cavity wall 12 of the waveguide cavity 1. The coaxial core 211 of the port extends inward and is embedded in the cavity wall 12 to a depth of 1.2 mm, and is smoothly welded to the spiral coaxial core 222 of the coaxial coupling spiral 22. The insulating medium 213 and the outer conductor 212 of the port are removed at the connection point to form an exposed feed probe structure. The other end protrudes 1.8 mm outside the outer wall 123 and is configured to receive microwave transmission signals from the radio frequency power source. The axes of the four coaxial ports 1, 2, 3, and 4 are located at four points 3.5 mm, 13.5 mm, 23.5 mm, and 33.5 mm away from the bottom surface of the cavity bottom 13, respectively.

[0083] The coaxial port 21 is a multi-layered cylinder comprising three layers: a coaxial core 211, an outer conductor 212, and an insulating medium 213 filling the spaces between them. The coaxial port 21 uses an RG-405 standard semi-rigid coaxial structure to ensure a standard impedance matching of 50 ohms. The coaxial core 211 is made of silver-plated copper with a diameter of 0.5 mm, and the outer conductor 212 is made of seamless copper tubing with an inner diameter of 1.68 mm. The outer diameter is 2.2 mm. The outer conductor 212 of the port is tightly welded or crimped to the outer wall 123 of the waveguide cavity 1 to achieve good RF grounding and electromagnetic shielding. The port coaxial core 211 and the port outer conductor 212 are aligned at the center. The insulating medium 213 is Teflon. The insulating medium wraps around the port coaxial core 211 to achieve electrical isolation and mechanical support between the port coaxial core 211 and the port outer conductor 212, and can fix the position of the port coaxial core 211 and the spiral coaxial core 222 connected to it. Each coaxial port 21 is connected to an independent phase and amplitude control channel and is configured as an independently adjustable feed unit.

[0084] The coaxial coupling spiral 22 comprises a spiral groove 221 recessed within the inner wall 122 and a spiral coaxial core 222 suspended within the spiral groove 221. The four spiral grooves 221 are square slots with a depth of 1.68 mm and a width of 1.68 mm, arranged in a spiral pattern with a pitch of 2.5 mm. They are distributed in four regions at distances of 3.5 mm-8.5 mm, 13.5 mm-18.5 mm, 23.5 mm-28.5 mm, and 33.5 mm-38.5 mm from the bottom surface of the cavity bottom 13. Each spiral groove 221 encircles the inner wall 122 twice. The material of the metal surface within the spiral grooves 221 is the same as that of the waveguide cavity 1. The spiral coaxial core 222 is deployed within the spiral grooves 221. The spiral coaxial core 222 is also a circular coaxial core arranged in a spiral pattern. The four spiral coaxial cores 222 are made of silver-plated copper, each with a diameter of 0.5 mm and a pitch of 2.5 mm. The spiral coaxial core 222 and the port coaxial core 211 of the coaxial port 21 are connected as one unit to transmit microwave signals, while the position is fixed by the insulating medium 213 of the coaxial port 21; the spiral groove 221 of the coaxial coupling spiral 22 is not filled with insulating medium to improve the efficiency of microwave coupling and heating; the coaxial coupling spiral 22 is evenly distributed on the inner wall 122, covering the main area inside the waveguide cavity 1.

[0085] See Figure 1 , 2 As shown, the coaxial coupling spiral 22 is uniformly distributed, meaning that the diameter, pitch, and depth of the spiral groove 221 of its coaxial core 222 are constant. More preferably, it is a gradually varying non-uniform spiral to compensate for power attenuation at the weaker spiral end. Specifically, the coaxial core 222 adopts a non-uniform pitch design; at the end near the coaxial port 21, the pitch... P1=2.5mm, corresponding to a lower characteristic impedance; at one end extending into the waveguide cavity 1, the pitch is... P2 =1.8mm, corresponding to a high characteristic impedance, thus forming a broadband impedance transformer; the depth of the spiral groove 221 varies gradually along the spiral extension direction, from the depth at the coaxial port 21. D1 =1.68mm gradually transitions to the depth at the end. D2 =2.0mm, which increases the characteristic impedance to achieve the purpose of matching the cavity impedance.

[0086] The transmit RF power source system, which provides power to multiple coaxial ports 21, includes: a microwave excitation source 3, a power distribution network 4, a multi-channel phase control network 5, a distributed power amplifier module 6, a distributed power matching network 7, a controller 8, and a DC power supply module 9. The signal link configuration of the transmit RF power source system is as follows:

[0087] Microwave excitation source 3 generates an initial radio frequency signal, which is divided into multiple microwave signals by power distribution network 4 and then enters multi-channel phase control network 5. The phase-modulated multiple signals are input to distributed power amplifier module 6, which contains multiple power amplifiers corresponding one-to-one with coaxial port 21. Controller 8 independently controls the output power amplitude of each microwave signal by adjusting the DC bias voltage or drain voltage provided to each power amplifier by DC power supply module 9. The four microwave signals are then amplified by distributed power amplifier module 6 to a power of over 2.5W. After impedance matching by distributed power matching network 7, the amplified multiple microwave signals are coupled into waveguide cavity 1 through coaxial port 21, achieving cavity spatial synthesis. Distributed power matching network 7 is used to improve the VSWR of the output from distributed power amplifier module 6 to coaxial port 21, thereby improving signal output efficiency.

[0088] The microwave excitation source 3 is a frequency synthesizer using the Analog Devices ADF4360-1 integrated voltage-controlled oscillator, and its output frequency range covers the 2.40GHz-2.50GHz sweep frequency heating range required by this invention.

[0089] The power distribution network 4 adopts a tree topology consisting of three cascaded two-way Wilkinson power dividers. The first-stage power divider splits the signal from the microwave excitation source 3 into two, and the two power dividers in the second stage further split each signal into two, ultimately forming four equal-amplitude and in-phase radio frequency signals, providing isolation of better than 20dB between each signal.

[0090] The multi-channel phase control network 5 uses the MAPS-011019 digital phase shifter, which operates in the 2.4GHz-5.1GHz frequency band and has a 360° phase coverage and a minimum phase step of 5.625°. The controller 8 sends digital control words to the four phase shifters through a serial interface, thereby achieving precise phase difference and high-speed rotation between the four signals.

[0091] The power amplifier in the distributed power amplifier module 6 uses an NXP MHT1008NLDMOS RF power transistor, achieving deep amplitude control through significant adjustment of the drain voltage, with a single transistor saturation power of 12.5W. This device is specifically designed for microwave heating, capable of withstanding a voltage standing wave ratio of 10:1, and is not easily damaged by drastic changes in load (tobacco) impedance, eliminating the need for expensive circulator protection circuits and further reducing costs. In this embodiment, by controlling its bias or drain voltage, the output power can be linearly adjusted to over 2.5W to meet rapid preheating requirements.

[0092] Controller 8 uses an STM32 series MCU.

[0093] The DC power supply module 9 includes an adjustable DC-DC boost converter TITPS61175. The controller (8) dynamically adjusts the feedback terminal of the DC-DC converter through the PWM signal, thereby changing the drain voltage supplied to the MHT1008N and realizing independent linear control of the output power of each microwave channel.

[0094] Implementation of Distributed Power Matching Network 7: To replace the expensive circulator, this embodiment employs a microstrip line-capacitor hybrid matching network at the amplifier output. This network consists of multiple PCB microstrip transmission lines connected in series, with high-Q RF chip capacitors (C0G dielectric) connected in parallel at specific nodes. This structure not only matches the low output impedance of the LDMOS to the standard impedance required by the coaxial port 21, but also forms a low-pass filter, effectively filtering out high-order harmonics and ensuring the purity of microwave energy entering the waveguide cavity 1.

[0095] The device's workflow and heating control are divided into three stages. The first stage, preheating, uses full-power mode: all four microwave sources are activated, set to be in phase (0° phase difference), and the frequency is fixed at 2.45GHz. At this time, the energy is maximized and focused on the central axis of the cigarette, achieving instantaneous burst heating from the inside out, with a heating time of 15-20 seconds. The second stage enters constant temperature mode, and controller 8 executes a rotating vector phase scanning strategy. The phases of ports 1, 2, 3, and 4 are set to 0°, 90°, 180°, and 270° respectively, and the phase vector rotates with time at a speed of 100Hz, i.e., cycling sequentially according to T0[0°, 90°, 180°, 270°], T1[90°, 180°, 270°, 0°], T2[180°, 270°, 0°, 90°], and T3[270°, 0°, 90°, 180°]. The microwave hotspots inside the cavity rotate rapidly around the cavity, preventing localized overheating and scorching of the tobacco while ensuring that tobacco near the tube wall at the edges is also fully heated and utilized, with a heating time of 200-250 seconds. In the third stage, controller 8 initiates a frequency scan, periodically changing the frequency within the range of 2.40GHz-2.50GHz. The frequency change alters the leakage angle of the spiral structure, and the system automatically scans the entire length of waveguide cavity 1, with a heating time of 100-150 seconds.

[0096] Furthermore, regarding the electromagnetic characteristics of this device, see [link to relevant documentation]. Figure 8-10 As shown, electromagnetic simulation is performed to analyze the electromagnetic distribution characteristics of the cavity. For example... Figure 8 The diagram shows the field division where each microwave input signal has the same phase, corresponding to the full-power mode where the four microwave sources operate in phase during the first stage of the device's heating process. Figure 9 The field distribution is a 90-degree phase difference between the four signals, corresponding to the rotating vector phase scanning strategy in the second stage. Figure 10 In the diagrams (a), (b), (c), and (d), the electric field distribution inside the cavity is shown when each of the four coaxial ports 1, 2, 3, and 4 is individually powered. The maximum electromagnetic energy inside the cavity is distributed at different locations when powered by different coaxial ports. This working model corresponds to a zoned independent heating mode, which can perform targeted zoned heating and reduce the energy consumption of the heating system.

[0097] This microwave smoking device example achieves uniform volume heating of the tobacco stick within a tiny space of 7mm in diameter by combining the aforementioned coaxial spiral-waveguide cavity composite resonant hardware with two-dimensional electronic scanning. Based on this, the easily damaged heating needle structure is eliminated, and energy utilization efficiency is significantly improved.

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A multi-feed coaxial-waveguide composite resonant microwave heating device, characterized in that, The device includes a waveguide cavity and multiple coaxial coupling structures. The top surface of the waveguide cavity is open. The multiple coaxial coupling structures are integrated within the cavity wall of the waveguide cavity. Each coaxial coupling structure includes an interconnected coaxial port and a coaxial coupling helix. The coaxial port serves as the input end of the feed source. Microwave signals are sequentially input into the waveguide cavity through the coaxial port and the coaxial coupling helix to heat the object to be heated within the waveguide cavity. The coaxial port is inserted into the cavity wall of the waveguide cavity at one end along its own axial direction and extends out of the waveguide cavity at the other end. The coaxial port includes a port coaxial core and a port outer conductor. The port outer conductor is sleeved on the outside of the port coaxial core and the two are arranged coaxially. An insulating medium is filled between the port outer conductor and the port coaxial core. The coaxial coupling helix includes a helical groove recessed in the inner wall of the waveguide cavity and a helical coaxial core suspended in the helical groove. No insulating medium is filled between the helical coaxial core and the helical groove. The groove surface of the helical groove is a metal surface. The helical coaxial core is electrically connected to the port coaxial core in the coaxial port for transmitting microwave signals.

2. The multi-feed coaxial-waveguide composite resonant microwave heating device according to claim 1, characterized in that, The coaxial coupling spiral can be a uniform spiral or a non-uniform spiral. When the coaxial coupling spiral is a uniform spiral, the pitch between adjacent threads on the coaxial core and the depth of the spiral groove are constant. When the coaxial coupling spiral is a non-uniform spiral, the pitch between adjacent threads on the coaxial core and the depth of the spiral groove are non-constant.

3. The multi-feed coaxial-waveguide composite resonant microwave heating device according to claim 2, characterized in that, The coaxial coupling helix satisfies the following physical relationship: ， Where Z0 represents the characteristic impedance of the coaxially coupled helix, P represents the pitch of the coaxial helix core, and d represents the diameter of the coaxial helix core. μ 0 Represents the permeability of free space. ε The dielectric constant of the medium between the spiral groove and the coaxial spiral core is represented by , and D represents the depth of the spiral groove.

4. The multi-feed coaxial-waveguide composite resonant microwave heating device according to claim 2, characterized in that, When the coaxial coupling helix is ​​a non-uniform helix, the pitch of the coaxial core of the helix satisfies the following condition: the pitch at the end closer to the coaxial port is greater than the pitch at the end farther from the coaxial port.

5. A multi-feed coaxial-waveguide composite resonant microwave heating device according to claim 2, characterized in that, When the coaxial coupling spiral is a non-uniform spiral, the depth of the spiral groove changes in a gradient along the spiral extension direction, that is, the depth of the spiral groove increases in a gradient from the coaxial port to the spiral end.

6. A multi-feed coaxial-waveguide composite resonant microwave heating device according to claim 1, characterized in that, In multiple coaxial coupling structures, the coaxial ports are evenly distributed axially or circumferentially along the outer wall of the waveguide cavity, and each coaxial port is connected to an independent phase and amplitude control channel.

7. A multi-feed coaxial-waveguide composite resonant microwave heating device according to claim 1, characterized in that, A transmit RF power source system that provides power to multiple coaxial ports includes: a microwave excitation source, a power distribution network, a multi-channel phase control network, a distributed power amplifier module, a distributed power matching network, a controller, and a DC power supply module. The microwave excitation source generates an initial radio frequency signal, which is divided into multiple microwave signals by the power distribution network, and then enters the multi-channel phase control network respectively. The multi-channel phase control network includes multiple independently adjustable phase shifting units, which are used to independently modulate the phase of each microwave signal under the command of the controller. The distributed power amplifier module includes multiple power amplifiers that correspond one-to-one with the coaxial ports, used to receive multiple signals after phase modulation by a multi-channel phase control network; The controller independently controls the output power amplitude of each microwave signal by adjusting the DC bias voltage or drain voltage provided by the DC power supply module to each power amplifier. After being amplified, the multiple microwave signals are impedance matched by a distributed power matching network and then coupled into the waveguide cavity through the coaxial port.

8. A multi-feed coaxial-waveguide composite resonant microwave heating device according to claim 1, characterized in that, The insulating medium is made of polyethylene, Teflon, or foamed plastic.

9. A microwave heating control method for a multi-feed coaxial-waveguide composite resonant microwave heating device according to any one of claims 1-8, characterized in that, The multi-feed coaxial-waveguide composite resonant microwave heating device has a zoned independent heating mode and a multi-source coordinated heating mode. Specifically, In the zoned independent heating mode, a single or partial coaxial port is excited, and the corresponding coaxial coupling spiral couples microwave energy to a set coverage area inside the waveguide cavity, thereby achieving zoned independent heating of the internal area of ​​the waveguide cavity. In the multi-source coordinated heating mode, all coaxial ports are simultaneously excited. By adjusting the relative phase and amplitude relationship between the coaxial ports, a controllable electromagnetic field interference pattern is synthesized in the waveguide cavity. The specific steps are as follows: 1) Initialization: Start the microwave excitation source to generate a reference signal; 2) Phase scanning: Under the premise of maintaining a constant microwave signal operating frequency, a rotating vector phase scanning strategy is executed. Specifically, one coaxial port is set as the reference phase, and the phases of the other coaxial ports are controlled to form a preset phase gradient sequence. The overall offset of the phase gradient sequence or the phase vector combination is changed periodically over time, thereby exciting a rotating electromagnetic field mode in the waveguide cavity, so that the electric field interference peak region formed by the superposition of multiple signals is scanned traversally in space. 3) Frequency scanning: Within the preset working bandwidth, the carrier frequency of the microwave signal is periodically changed according to the set scanning rate; utilizing the frequency dispersion characteristics of the coaxial coupling spiral as a slow wave structure, the axial angle and coverage of microwave energy radiated from the spiral structure into the waveguide cavity are changed with the frequency, driving the radiation beam to perform dynamic scanning in the longitudinal depth direction of the waveguide cavity.

10. The microwave heating control method according to claim 9, characterized in that, When the object to be heated is unevenly distributed or requires fixed-point heating, a zoned independent heating mode is adopted to increase the power amplitude of the coaxial port in the corresponding area; when uniform heating of the entire cavity is required, a multi-source collaborative heating mode is adopted, and steps 2) and 3) are executed cyclically to reduce heating dead zones by using multi-dimensional electromagnetic field scanning.

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