Multi-Physics Field Computation for Microwave Heating of Multi-Mobile Components Based on Transformation Optics and Implicit Function

It is popular to use moving elements to improve heating uniformity during microwave heating under some situations. However, it is still a challenge to simulate moving elements during microwave heating due to the complexity of mathematical modeling. In this paper, a novel continuous algorithm based on implicit function and level set methods is developed to compute this heating process. By introducing the implicit function and level set methods, the moving region's properties are set as a function of space coordinate and time, which means that the movement of the elements is represented by the variation of the parameters. In addition, with the coordinate transformation, the coupling process of electromagnetic field and heat transfer in microwave heating can be performed. A 2-D applicator model and a 3-D applicator model with a rotating turntable are used to illustrate the proposed method in detail. Experiments are also conducted to testify the validity of the proposed method. The results obtained by the proposed method are in accordance with those obtained by experiments. Moreover, compared with conventional methods, the proposed method is more accurate and efficient.

Aiming at the intercoupling of multiple physics and the time-varying characteristics of boundary conditions in the microwave heating process, how to optimize the temperature uniformity of materials with a cooperative-mode stirrer is focused in this paper. First, the formation of standing waves can be effectively avoided by introducing the mode stirrer, thereby improving the heating efficiency of the material. Description of pattern stirrer motion processes using implicit functions and level set methods. Second, in order to optimize the temperature uniformity of the material, the stirrer is made intelligent, and the electromagnetic field distribution can be optimized by using different stirrer positions and directions, and the temperature uniformity is improved through intelligent coordination of stirrers in different positions. Finally, the finite element method is used to perform numerical simulation calculations on integer and continuous variables. The results show that the proposed method can improve the temperature uniformity of the conventional microwave heating model by 28.2%–81.44% and 23.2%∼63.91% at each level and lead hammer section respectively, and can improve the heating efficiency by 14.8%∼36.4%. According to its performance when heating different shapes and different materials, the proposed method is efficient and feasible.

Decoupling microwave heating efficiency from food property variations: A reduced-gradient index metamaterial strategy for superior efficiency and uniformity

Traditional microwave heating requires the heated object to be placed in a metal cavity, which limits its flexibility. Moreover, the microwave heating efficiency is affected by the shape, size, and permittivity of the load. This paper proposes a direct-insertion microwave heating device based on a dielectric wedge. It offers flexible and efficient heating for different loads. Firstly, a dielectric wedge with a gradient refractive index was designed, which can convert electromagnetic waves into surface waves propagating along the dielectric. Secondly, efficient heating of materials with permittivity ranging from 10 to 80, regardless of their shape, is achieved by inserting the dielectric wedge into the load. Microwave heating efficiencies above 90 % were consistently observed in heating tests with beverages, mashed potatoes, and minced fish of varying shapes. Finally, A high-power continuous flow heating scheme was introduced, utilizing the device as a heating module and scaling up by adding more modules to boost microwave power. Multi-physics simulations confirmed the device's efficiency and versatility in microwave continuous flow heating, with minimal energy interference between microwave sources.

The level set method is a mathematical and computational, technique for tracking a moving interface over time. It can naturally handle topological changes such as merging or breaking interfaces. Intrinsic geometric properties of the interface, such as curvature and normal direction, are easily determined from the level set function p. There are many applications of the level set method, including kinetic crystal growth, epitaxial growth of thin films, image restoration, vortex dominated flows, and so forth. Most applications described in the growing literature on the applications of level sets advance the level set equation with explicit time integration. Hence, small CFL-respecting time steps are needed to maintain stability. In this thesis, an implicit level set method is introduced and applied to wildland firespread models, removing vulnerability to instability.

Variations in load shape, volume, and permittivity significantly impact microwave energy conversion efficiency within multimode heating cavities. This study introduces a wedge dielectric plate that enables asymmetric microwave propagation when being in contact with a load, thereby enhancing heating efficiency and robustness under load variations. First, based on the transformation optics theory, an asymmetric waveguide is established by the wedge dielectric plate. Experimental results show varying microwave transmission efficiencies in both forward and reverse directions. Second, a microwave multimode cavity with a dielectric substrate is designed. When the dielectric wedge, dielectric substrate, and load are in physical contact, an efficient microwave transmission path will be formed to enable directed propagation toward the load via surface waves. Simulation results show over 90% heating efficiency with loads of varying volumes, dielectric properties, and shapes. Finally, microwave heating experiments are conducted and compared with a domestic oven using different loads. The proposed method achieves approximately 40% higher temperature increase at 750 W. This method is advantageous due to its low manufacturing cost, high power, robustness, and versatility, making it highly suitable for industrial applications.

In the past decades, a large amount of research was conducted to investigate the application prospect of microwave heating technology in improving the efficiency of asphalt pavement self-healing and de-icing. This paper reviewed the achievements in this area. Firstly, the properties of asphalt concrete after microwave heating were summarized, including microwave sensitivity and heating uniformity. Then, the evaluation indicators and influence factors of the self-healing properties of the asphalt mixtures heated by microwave were reviewed. Finally, the application of microwave heating in asphalt pavement de-icing was explored. In addition, asphalt pavement aging due to microwave heating was also reviewed. It was found that microwave heating technology has good prospects in promoting asphalt pavement self-healing and de-icing. There are also some problems that should be studied in depth, such as the cost-effectiveness of microwave-sensitive additives (MSAs), the performance of the pavement with MSAs, mechanism-based self-healing performance indicators, and the aging of asphalt pavements under cycling microwave heating.

Nowadays, microwave heating has evolved into a common tool for chemists based on its numerous advantages over conventional conductive heating. Surprisingly, the efficiency of microwave-assisted heating is still rather unexplored. In this contribution, we report our investigations concerning the heating efficiency of a variety of solvents including polar and apolar substances. Moreover, the effects of adding salt or passive heating elements on the microwave heating efficiency will be addressed. Finally, the heating efficiency of demineralized water is discussed at different volumes and with different microwave power levels in both monomode and multimode microwave synthesizers, demonstrating maximum average heating efficiencies of 10% for small-scale vessels (5 mL), 20% for medium-scale (50 mL), and 30% for large-scale microwave heating (400 mL).

This paper deals with structural optimization for designing periodic structures in a hole array wavelength filter. The hole array wavelength filter that consists of metallic thin film and dielectric enables to transmit narrow bandwidth light. It is known that transmission spectrum can be changed not only by the periodicity of hole array but also by the shape of holes. For optimizing the hole shape, the level set method is used in this study. In the ordinary level set method, the boundaries are implicitly expressed by the zero level set of a scalar function, called the level set function, within a fixed mesh. Therefore, the material interpolation becomes numerically awkward within the elements across the implicit zero level set because those elements inevitably take on intermediate material properties even if the boundary of zero level set are mathematically clear. As the result, the optimization is likely to yield wrong solution. Here, a new level set optimization method incorporating Arbitrary Lagrangian Eulerian method is proposed to eliminate intermediate values on the interfaces perfectly. As a result, the proposed method can successfully perform the structural optimization of hole shape without intermediate values.

In this letter, the substrate of a microstrip antenna is chosen as the transformation medium. Using complex transformation optics, a standing-wave current distribution along the circumference of a circular patch is transformed into a uniform traveling current distribution instead, thus generating perfectly circularly polarized waves. This letter provides a novel way of designing the microstrip antenna whereby the traditional substrate is replaced by the transformation medium whose parameters can be readily derived from the theory of transformation optics. Furthermore, introducing complex transformation optics into antenna design is a new attempt. In terms of its flexibility of controlling the amplitude distribution of electromagnetic fields, it offers extra freedom of manipulating the radiation pattern of an antenna.

Based on the theory of transformation optics (TO), a new and simple method for generating multimodal orbital angular momentum (OAM) carrying beams in 3-D space is proposed in this letter. The proposed 3-D arbitrary-way multimodal OAM generator only requires an electric dipole as the source. It consists of a four-way plane waves converter and four multimodal OAM generators. Since this method only requires the operation of radial scaling map, different topological charge modes can be easily obtained by appropriately setting the sizes of the physical geometries.

In this chapter, we explore shape representation, registration, and modeling through implicit functions. To this end, we propose novel techniques for global and local registration of shapes through the alignment of the corresponding distance transforms by defining objective functions that minimize metrics between the implicit representations of shapes.Registration methods in the space of implicit functions like the sum of squares differences (SSD), which can account for primitive transformations (similarity), and more advanced methods like mutual information, which are able to handle more generic parametric transformations, are considered. To address local correspondences we also propose an objective function on the space of implicit representations where the displacement field is represented with a free form deformation that can guarantee one-to-one mapping. In order to address outliers as well as introduce confidence in the registration process, we extend our registration paradigm to estimate uncertainties through the formulation of local registration as a statistical inference problem in the space of implicit functions. Validation of the method through various applications is proposed: (i) parametric shape modeling and segmentation through active shapes for medical image analysis, (ii) variable bandwidth non-parametric shape modeling for recognition, and (iii) object extraction through a level set method. Promising results demonstrate the potentials of implicit shape representations.Key wordsDistance transformsimplicit representationssum of squares differencesmutual informationfree form deformationsgradient descent

ABSTRACTA pilot-scale process for continuous in-flow microwave processing of foods, designed and implemented at SP Food and Bioscience, was evaluated for heat treatment of a homogeneous model food for high-temperature short-time (HTST) conditions, at constant total input microwave power, at 2450 MHz. The microwave system has three consecutive cavities, one excited by the TM020 microwave mode that heats primarily in the tube centre, and two TM120 mode cavities that heat primarily in the tube periphery. The temperature uniformity of the homogeneous model food after microwave heating is here evaluated in terms of spatial distribution, for different set-ups of input microwave power in each cavity and for different order of the placement of the cavities, while maintaining the total input microwave power. The microwave heating uniformity is evaluated, based on measured and calculated radial temperature profiles. Combined TM020 and TM120 heating was found to result in more uniform heating by means of spatial temperature uniformity over the tube cross section. Furthermore, appropriately selected microwave power distribution between the centre and periphery heating cavities results in a stable heating profile in the studied food, that differs only about 10 °C or less between highest and lowest average values directly after microwave heating.

The contamination of soils by mineral oils presents a significant environmental challenge, particularly due to the widespread use of petroleum products in various industrial sectors. This study investigates the efficiency of microwave heating compared to conventional resistance heating for the thermal desorption of mineral oil from contaminated soils. The experimental results demonstrated that microwave heating offers superior performance in terms of pollutant removal efficiency, energy consumption, and the preservation of soil’s physical and chemical properties. This study further conducted a kinetic analysis of the desorption process, revealing that microwave heating follows a first-order kinetic model and requires lower activation energy than conventional methods. The findings suggest that microwave-assisted thermal desorption is a highly effective and energy-efficient technology for soil remediation, providing a potential alternative to conventional techniques. This research offers valuable insights into optimizing thermal desorption processes for environmental remediation, with implications for broader applications in soil treatment.

Microwave heating mechanism and Self-healing performance of scrap tire pyrolysis carbon black modified bitumen