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Nanda,

Are you providing some seperation from the metal?  If so, how much?  Metalcraft sells our inlays with a foam spacer attached to provide seperation from the metal and better read range. 

http://www.idplate.com/

With your set up that reads 14cm, is this the range with the tag mounted on metal?  What is the free space range?

Another option is to add a ferrite sheet shielding material to the back of the tag.  Ferrishield manufactures such material.   

http://www.ferrishield.com/html/RFIDShielding/RFIDabsorbershielding.html 

Hello Eddie

We tested the tags on metal, with spacing between the metal and tag , and just tag. The Following were observed:

1. Read range was 14cm  when internal antenna was used in open air ; read range was 18cm when extenal antenna was used of size 25x30cm at 200mw Power on TRF7960 in open air

2. No tags were read by reader when pasted on metal plate directly

3. Spacing of 3cm was given and tested and found the read range was 12cm

Want to know  the ideal free space range between metal and tag? What could be done to increase the range in metal surfaces???

Nanda,

Take a look at figure 3-1 in the app note below.  100% of the free space read range is attained at about 4.5cm spacing.

http://www.ti.com/lit/an/scba018/scba018.pdf

Adding a ferrite sheet to the back of the tag can allow you to place the tag directly to metal and still function but will be at a reduced range.  The best way to acheive optimal range is to provide seperation from the metal.

Thank you Eddie

I have observed that the closer the inlay near to metal the less inductive it is. 

I have tag which i got it when i bought TRF7960 development kit i.e ISO 15693 passive tag.  Will the read range depend on the size of the tag as well??? I have seen tags in different shapes with differnt read ranges. Will i have any improvement in read range if i find a tag bigger in size than the one i have?? Can i get bigger tags at TI ??

I have seen that with more power we can acheive longer distance but at 200mW i want to acheive 25cm using external antenna of size 25x30cm on metal with free space or using foam spacers or using ferrite sheet as u mentioned.

Thanks again

Regards

Nanda

Yes, you will see longer read range with a larger tag size.  The largest tag that TI offers is our 76mm x 45mm inlay.  You could work with a third party for larger tags.  I would recommend talking with Syrma.  They could offer a larger tag and also provide encapsulation to help work near metal.  Please make sure to specify to Syrma which TI tag IC you would like to use (Standard, Pro, Plus). 

http://www.syrmatech.com/rfid-products.html