5.1     Automatic frequency tuning

The automatic frequency tuning activates automatically if the software detects the band excitation for BHM scenario (Allow BHM option checked in Heating Details dialogue of QW-Editor). The algorithm of the proposed BHM regime with automatic frequency tuning can be summarised in the following steps:

A.     Analyse the scenario at its initial enthalpy distribution H₀(x,y,z) with pulse excitation and S-parameter postprocessing. When the |S11| curve is converged, detect and store the frequency f₀ of its deepest resonance.

B.      Analyse the scenario again at its initial temperature distribution H₀(x,y,z), but now with a sinusoidal source at f₀. Perform one BHM iteration (steps 1 through 8 in Philosophy behind QW-BHM). Save the enthalpy field H₁(x,y,z).

C.      Analyse the scenario with pulse excitation and S-parameters. As initial conditions, take zero electromagnetic fields (as usual) but initial enthalpy pattern H₁(x,y,z) instead of the previous H₀(x,y,z). Detect and store the frequency f₁ of the deepest resonance.

D.     Come back to the sinusoidally driven scenario. Maintain its enthalpy pattern H₁(x,y,z), the previously electromagnetic fields calculated in step B, and media parameters modified in step B. Change the frequency of the source to f₁. Continue until a new steady state (which will change due to both: change of media parameters and source frequency). Perform the second BHM iteration (steps 1 through 8 in Philosophy behind QW-BHM). Save the enthalpy field H₂(x,y,z).

E.      Perform a step analogous to C, but enthalpy pattern H₂(x,y,z), and detect frequency f₂.

F.      Come back to the simulation of step D, changing the frequency to f₂.

The above sequence of steps will be performed until the desired total heating time is covered by the BHM iterations in steps B, D, F, etc.

In QW-BHM implementation, switching between the pulsed and sinusoidal scenarios is accomplished with the use of freeze files. Two freeze files _ini.sfr and _sin.sfr with pulsed and sinusoidal source, respectively, are saved upon starting QW-Simulator. At this point, both contain zero initial electromagnetic condition. The initial enthalpy field H₀(x,y,z) is saved, too, in a *.vi3 file.

Then we run an iterative BHM process:

- In all odd steps (A, C, E,..) the RunFreeze command is performed on the ini.sfr file, for a specified number of FDTD iterations. The ini.sfr file itself remains constant throughout the BHM process. However, at the beginning of each odd step, before compilinglcsm matrices, a new initial enthalpy read from consecutive *.vi3 files, leading to the updated media parameters. A new RunFreezeIterEnth task has been implemented in version 6.5, covering this combination of actions. At the end of each odd step the deepest resonance is detected with a new FindResonance task.

- In even steps (B, D, F,...) the RunFreeze command is performed on the _sim.sfr file, for a specified number of FDTD iterations, and one BHM iteration is performed. The _sim.sfr file is saved (overwritten) at the end of each even step, so that it always contains the last calculated patterns of thermal quantities and electromagnetic fields. The current enthalpy is additionally saved in a *.vi3 file. At the beginning of each even step, before resuming the FDTD iterations, the source frequency is changed to the one detected by the last FindResonance task.