The Effect of pulsed Microwaves on Bacteria

[uncle albert]

We are interested in looking at the effect of the pulsing of microwaves subjected to power and time of eg 50W for 10 seconds at 2.45GHz but pulsing the microwaves as well to investigate the added kill effect that the pulsing adds, comparing plate counts before irradiation, after non pulsed irradiation and then after pulsed irradiation.

Does anyone have any suggestions/recommendations or does anyone know of any literature or papers and where we could get some pointers about the mechanism of action of the pulsing?

Cheers for nowAndy/Uncle Albert

 

[alxm]

Well, http://dx.doi.org/10.1006/jtbi.2000.2123" .

As for the mechanism, I think it's safe to say the exact effects in living things are unknown. But to sketch out the general "physical chemistry of microwaves for biologists":

Microwaves correspond to dipole moment excitations in molecules; i.e. increased vibration and rotation of molecular bonds in polar molecules.
In a simple molecule (e.g. water) this quickly degrades into heat (vibration/rotation/bumping around in general), but in a delicate macromolecule (read: proteins, DNA, etc) the local 'heating up' of a single bond or two can lead to conformal changes/denaturation as the bond(s) could suddenly rotate well outside its 'usual' range. Which is also what's been observed.

The short answer is: 'heat'. But of course, usually when we talk heat we mean bulk heat which is evenly distributed. Whereas with microwaves, especially if you pulse them, you're more-or-less making specific spots very 'hot' very quickly; and things might occur before they 'cool down' again. (quotes because heat is really a macroscopic property) So you could view it as thermal shock, or partial thermal shock. (which may be worse, given that we're probably evolved to cope better with even heating)

Obviously both bulk heat itself and denaturation are capable of killing things, and in many different ways. But as a chemical physicist, figuring that bit out is not my department. But there's no single mechanism for sure, any more than there is for say, how cancer is caused.

(Note for layfolks: I'm not saying here that I believe microwave ovens/cellphones/wifi/etc are a significant health hazard. I do not. There's simply too little power. Suntanning is far worse)

 

[microwaveguru]

There have been many papers on killing bacteria with microwaves i.e. Olsen, C.M. et. al., J. Microwave Power, Vol 1, # 1 (1966) is a very early paper. It and following research indicates that all bacterial destruction is thermal. In my own case I have a number of patents using low levels of microwave energy to destroy bacteria on medical and dental instruments.

There is a more fundamental question: how to generate 50 watts of microwave energy. You cannot use a domestic oven to do this. It takes research equipment, and that's not cheap. Think $ 5,000 and higher. I have such an oven that sells for about $ 20,000. Pulsing is not difficult and the oven manufacturer can likely provide you with such a system.

 

[uncle albert]

There have been many papers on killing bacteria with microwaves i.e. Olsen, C.M. et. al., J. Microwave Power, Vol 1, # 1 (1966) is a very early paper. It and following research indicates that all bacterial destruction is thermal. In my own case I have a number of patents using low levels of microwave energy to destroy bacteria on medical and dental instruments.

There is a more fundamental question: how to generate 50 watts of microwave energy. You cannot use a domestic oven to do this. It takes research equipment, and that's not cheap. Think $ 5,000 and higher. I have such an oven that sells for about $ 20,000. Pulsing is not difficult and the oven manufacturer can likely provide you with such a system.

We have just bought equipment that will allow us to vary the power setting from 0 to 300 W and have been playing around to find out what we can do with it. The problem we have at present is the reflected power but we are working on that aspect.
Thanks guys for your help. It has been really productive.

Andy

 

[microwaveguru]

Andy
Good luck. This sort of experimenting is difficult - I've been doing it for 50 years. If you need help list your problems.