Pulsed electric field is considered a "non-thermal" method for food processing that involves the application of short high-voltage pulses to create pores in cell membranes. However, since I am not familiar with the physics of the phenomenon I wonder if it is possible that at high frequencies (say 50 KHz) and using nanosecond-pulses this technology can be used to generate heat for other applications?
Yes
Non-thermal applications are when a useful effect can be generated with less power, or without generating heat.
In the same way, a useful way to use a hammer is to hit a nail into a wall. If you hit the nail often enough with a hammer it will get hot, but that might not be so useful or the best way to make the nail hot.
RF heating is used a lot. Often it is more economical to use continuous heating at a lower level rather than turning a more powerful source on and off. In some cases it is easier and cheaper to generate pulses, but I don't think that is usually the case.
By switching a electric field on and off, a theoretical current (the so called displacement current density, which James Clerk Maxwell introduced to amend Amperes Law) seems to flow. By a closer look what's happening there, it's a change in electric flux - no charges flow through, but interact within their fields. As electric flux "travels" through electrical isolating material, the polarisation of the molecules of the material change. I can imagine that there is some friction due to restraint in a isolator, which will heat the molecules when aligning with the electric field vector.
Thanks Stefan Ciba and Malcolm White for your answers. If my physics is right, the fact that the field is changing with time should lead to the generation of an alternating magnetic field and, therefore, I would expect the appearance of an electromagnetic field. So, I wonder how strong this field could be? Is there any way to model this phenomenon using simple equations rather than complex software?
Based on the geometry, it can, indeed, be the electric field, which can be utilized, without the influence of magnetic field. In the case of a electromagnetic wave or pulse, it is the principle of a microwave antenna, which will resonate with the molecules (they may work as an antenna for certain frequencies, which they absorb best).
Stefan Ciba , 50 kHz lies within the radiofrequency range which is used for induction heating using AC fields. I wonder if a squared pulse can also have the same effect especially if there were no induction coils in the system.
Dear Oscar Marin-Flores,
the nanosecond pulse will show broadband spectrum. This might be adventageous for different materials with different resonace frequencies to respond within the stimulus at once, but more effort hast to be done to satisfy EMC-safety. A sine wave instead, will show more efficient energy conversion when frequency is matched to a certain impedance. I'd recommend the second approach and maybe sweep the frequency until a optimum is reached.
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