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What is the best frequency for the job?

What is the best frequency for the job?

What is the best frequency for the job?

(OP)
The project I am looking into is to detect small inexpensive tags when placed inside a panelled delivery van when it passes a fixed reader, assuming worst case that the van is mostly metal sides, bottom, roof and doors with no windows what would be the best frequency to use if it was possible to receive a signal through the small ammount of minimal RF leakage that will occur through door seals, air vents etc etc?

The frequency must be license free.

From what I remember about wave theory the smaller the wavelength the better for effectively squeezing through small gaps. Do glass and most plastics have any particular frequencies that they are particulary absorbant to RF?

The tags will be self powered.

The readers can be placed about 5m from the van.

About 95% success rate or better is needed.

RE: What is the best frequency for the job?

Another factor that you haven't mentioned is that the tags on the bottom of the pile may be blocked by the boxes stacked above.

In the other thread you replied that the tags will be battery powered.  This will help immensely, but I'm not sure how that fits in with being inexpensive.

According to simple theory, the lower frequencies are blocked by the metal structure of the van.  In practice it is less of an issue (try it with a portable AM radio).

Your requirement that the frequency be license free may drive the solution.  Perhaps you should consider using the frequency band that permits the highest possible power output (EIRP) including consideration of antenna gain and practical size (probably not 27MHz CB).  Simply "blast" the van with as much power as possible and then have the tags pulse their response with as much power as they can muster.

I would fire the signal in through the front windshield and any other windows that might be consistent across your fleet.

Good luck.

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