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modeling dielectric heating with a pulsed microwave (square wave)

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I am having trouble modeling a pulsed power operation of microwave (2.45GHz) inside rectangular waveguide.

The model simulates dielectric heating of a packed beads inside the waveguide with microwave, similar to a 'RF heating' example model (RF + heat transfer modules). The rectangular waveguide has two ports on its side where microwave power can be introduced. Packed beads are located at the center of the waveguide. A pulsed microwave power at a fixed magnitude is incident from either side of the waveguide at a time. Microwave power can be modeled with a square wave with a period of 120s and 50% of duty cycle. Microwave is introduced such that alternating pulses from both side of the waveguide heat both side of the packed beads.

Here, I am having trouble modeling a pulsed microwave operation. Below is a list of methods I tried that did not work as COMSOL failed to find consistent initial values.

  1. using a built-in rectangular function with and without smoothing
  2. using a built-in waveform function (square type) with and without smoothing
  3. using explicit events to indicate when microwave was turned on/off

Even suing a high-degree of smoothing that made it look almost like a sine wave failed. Instead, I found that using sine function as a proxy of square wave works. These successful examples include

  1. Pwr0 * (sin(2pi/120t)+1)
  2. (Pwr0/2/atan(1/delta))atan(sin(2pi/Tpwr*t)/delta)+Pwr0/2

where Pwr0 = 50W delta = 0.01 TPwr = 120s

Currently an option (5) is the closest working option that I found but I wonder if there's a better approach as this method still creates the same error message when used with Pwr0 >= 100W. I also need to introduce more pronounced smoothing (by adjusting delta) to get the moel work.

Thank you!

0 Replies Last Post Aug 8, 2021, 9:47 p.m. EDT
COMSOL Moderator

Hello Tae Lim

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