水曜日, 1月 25, 2006

Transverse dipolar chaining in binary suspensions induced by rf fields

It is demonstrated that, in certain frequency ranges of the applied field, the dipole interaction leads to patterns whereby particles of different types are connected across field lines. By applying a Monte Carlo simulation, the main characteristics of the chaining process in a mixture of polystyrene beads and yeast cells are analysed. A good correlation between the theoretical model applied and experimental data is achieved. The data show that different aggregation patterns occur as a function of frequency.

Hmmmmm, well since that didn't make much sence lets go back to basics, how about a little 'Understanding Propagation' now thats something more my speed. You ever wonder what planet these guys are from, and if we sound that alien to someone else?

--The process of transmitting signals into the air is called signal propagation. Understanding the concepts involved in taking a useful signal and sending it down a transmit path to an antenna and out into the air is an essential aspect of a techs position. A useful analogy to this process is a water hose. If we turn the faucet on for a moment we hope that all the water will get to the nozel and spray on our ganja garden, of coarse all the water will usually not make it. A small leak in the hose might send some water where we do not want it. A kink in the line might slow the water down. If it is a large kink it might stop the water altogether, and in fact send it back to the faucet (backwash), maybe causing more problems. Of coarse the best way to make sure everything works well is to use the right diameter hose for the preasure you want.(This could be said about other things in life...)

RF is much the same (except that after a while of effecient watering, we do not end up with big buds, but rather happy customers, of coarse the big buds would make happy customers--but now I'm digressing). We generally have an amplifier , our faucet, on which we attach a cable leading to the antenna, our nozzle. As we send our signal down the cable to the antenna, we hope that all our power makes it through the route and out the antenna, but there are reasons why this often does not occur: a bad cable that isn't shielded eneough, a connector that is not tightened near eneough, some sort of break in the transmission line, or a flaw in the antenna.

One advantage in the RF world is that by using what is called an RF bridge, we can seperate what we are transmitting down the cable and whats coming back the other way (the reflected power)

It is also important to understand is that different frequencies propagate differently. Generally lower frequencies will travel much greater distances, but they are also much more susceptabble to physical obsticles, such as a wall. Also lower frequencies will propagate with a much wider footprint then will higher frequencies; in other words higher frequencies have more propagation loss than lower frequencies. Higher frequencies are much more directional (hence the use of microwave signals for lie-of-sight point-to-point transmission systems). Thus transmitting 50W at 570 kHz is quite different than transmitting 50 W at 800 MHz. In cellular systems, we take advantage of this directionality when we divide cells into sectors.

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