Is there an RFID system available by which inexpensive RFID tags placed on water utility pipes, laid beneath ground level at a depth of 2 to 3 meters (6.6 to 9.8 feet), could be tracked via a drone flying 50 meters (164 feet) in the air?
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No passive UHF RFID system would enable tags to be read from 50 meters in the air. A low-cost passive UHF RFID system has a range of up to 10 meters (33 feet). It might be possible to read tags 2 to 3 meters underground, but it would depend on soil conditions. Dry, loose, sandy soil might allow enough RF energy to reach a tag that it could power up and reflect back a signal to a reader. Water absorbs RF energy in the UHF spectrum, however, so it is highly unlikely that dense, moist soil would allow enough energy to reach the tag—or, if it did, for the energy from the tag to reach the reader.
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I conducted a test some months ago by digging a hole 2′ deep into dry soil and placing a Tag at the bottom. The Tag could only be read if the Reader were placed at ground level using a handheld Reader of 4W (30dBm). I then buried the Tag and it was unable to be read at all. This was a large ABS Tag capable of reading 30 feet+ in free air.
A BLE tag may meet your demand, put a Bluetooth Low Energy Beacon on the water pipe, even covered with soil, the singal can go through since it is an active tag of which the power is much stronger than passive system, a low cost BLE beacon/tag price can be lower to USD 3.0 for a good volume.
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