Understanding Microwave Heating Systems: How Electromagnetic Waves Affect Dielectric Materials
When handling non-metallics or materials with non-conducting properties, a viable approach for how to best apply microwave (MW) heating technology is essential — allowing production facilities to develop and refine central processes around the world. Utilizing tailor-made, professional resources marks a clear difference in terms of yielding both stronger efficiency as well as elevated quality; where access to cutting-edge equipment supports manufacturers in meeting critical high demand at accelerated speeds. Specialized products call for custom thermal solutions. That’s why operating with a comprehensive grasp of the latest tools and techniques of the trade is business-critical. This is how thriving factories drive top-tier production — and simultaneously sharpen it.
Engineering and building high-powered industrial microwaves, systems, and dryers, customized to advance productivity and lower emissions, Thermex-Thermatron has cultivated a trusted background; leveraging competitive insights rooted in over 80 years of dielectric heating experience. In Thermex-Thermatron’s newest installment of our series, created to share the benefits of decades of global MW expertise, we provide a deep dive into the science of dielectric heating. Gain an industry-leading understanding of the innovative technologies that will help you yield greater versatility in process heating; and along with it, better-made, more profitable products.
Determining the Value of Impedance:
Gauging Wavelengths and Waveguides
When navigating the world of Industrial Microwave Heating Systems, utilizing premier equipment that optimizes the dielectric properties of your materials, intelligently designed and powerfully made, can safeguard production processes — facilitating high performance along with safer working conditions. Leveraging technologies that were built to maximize the power of the electromagnetic spectrum allows production facilities the key to harness the unique characteristics of MW heating technologies.
First, let’s define impedance (Z) as the ratio of the electric field to the magnetic field. Here, the Electric Field Strength (E) is measured in Volts / meters (V/m); and the Magnetic Field Strength (H) is measured in Amps / meters (A/m).
Z = E / H
Notably, Maxwell’s equations help break down electric and magnetic field behavior and movement, taking a close lens to electric charges and currents to better understand how they operate. In free space, the impedance of an electromagnetic wave is 377 Ω (Ohms); according to Maxwell’s law, determined from the units chosen to express the given fields. A material’s distinct dimensions and dielectric properties will go on to determine the impedance of the electromagnetic waves transmitted in a specific material other than free space.
If the dimensions of the transmission line and the material used as the dielectric shift, the wavelength and the impedance of the electromagnetic wave will likewise vary. Consider these three factors all part of the transmission line for the electromagnetic energy: the coaxial conductors, the waveguide, or the MW oven walls. The impedance of a waveguide can be expressed in two ways: 1) in relation to the voltage and current within the waveguide, or 2) in relation to the MW power transmitted through the waveguide as follows:
ZVI = (π/2) x Kz x (b/a)
Where, ZVI is the impedance expressed as a function of voltage and current
ZPI = (π/8)2 x Kz x (b/a)
Where, ZPI is the impedance expressed as a function of power and current
ZVP = 2 x Kz x (b/a)
Where, ZVP is the impedance expressed as a function of voltage and power
In all of the above formulas:
Kz = 377 λg/λ 0
In every formula listed, λg marks the wavelength inside the waveguide; and λ 0 denotes the wavelength of the free space.
When calculating, dimensions a and b will define the inside cross section of the waveguide; where, a signifies the large dimension of the waveguide and b indicates the small dimension of the waveguide. Reference the chart below to take a closer look at exploring values of typical waveguide impedance:
A Guide to Assessing Any Electric Phase:
There Must Be Two Waves
Engineers understand phase (ϕ) through the time difference traveling between two electrical signals of the same frequency. Consider that frequency, wavelength, impedance, and power density all characterize a single electromagnetic wave. However, to be able to specify a phase, two variables must exist: a pair of waves. After all, the phase of one wave is relative to the other wave; or to the same electromagnetic wave at another instant in time. Expressing phase in degrees, 360° stands equal to a time difference of one period. Phase is especially significant when we are looking into the results of two or more waves affecting a dielectric material in a given space and time. For instance, when wood is placed inside an RF press or microwave oven.
The drawing below illustrates two different types of phase shifting. With the first one, a phase shift occurs when signal B leads signal A by 90 degrees. In the case of the second phase, the incident or direct wave stands 180 degrees out of phase; with an oven wall bouncing the reflected wave.
Observing the Electrical Variables:
What Impacts Direction When Applying Microwave Heating
The other key quality of the fields mentioned above is direction. Because direction is relative, there are a number of items which can be cited as directional references; from the metallic surfaces of the applicator structure and process material supporting structures to the surfaces and internal structure of the process material. Other crucial directional references include the direction of travel of the microwave as well as the direction of the electric field itself.
Consider that the direction of travel of the microwave and the direction of the electrical field itself can be positioned uniquely from one another; so even though both variables indicate direction, they operate differently. In fact, they are typically found at right angles to each other; except in the case of so-called TM waves inside waveguides. Similarly to the motion of a boat — rocking up and down as waves travel past it; parallel to the horizontal.
The directional aspects of microwave electric fields may be single-dimensional, two-dimensional, or even three-dimensional. The various directional components of multidimensional fields may exist simultaneously or sequentially. In the next installment of our Microwave Heating series, diving into a comprehensive understanding of the industrial systems that can help you ramp up throughput on the production floor, we’ll explore the value of this quality of fields; illuminating further facets of microwave applicators.
The robust technology you leverage is only as effective as your knowledge in how to optimize it. With the high-performing resources to tailor solutions that empower your facility’s capabilities, you can leverage the support of our in-house laboratory, ThermaLab — engaging in a discovery process, where you can test cutting-edge technologies and find what’s most suitable for the application you’re seeking. In a dynamic industrial arena, where every day, manufacturing pressures, demands, and needs can shift, assembly lines rely on value-added insights; you can utilize industry-trusted tools to eliminate anything that holds processes backward. With breakthrough technology, created by skilled engineers dedicated to simplifying and strengthening production processes throughout the world, you can wield the versatility to transform the way you fast-track production.