SAW-RFID System For Detection Of Underground Heating Pipes

Informatization of heating pipes is the key part of building smart city,which is a trend in the world.Currently,detection technologies are only available on exposed heating pipes,and temperature is the key information to determine whether heating pipes leak or not.SAW-RFID(Radio Frequency Identification)system has many excellent properties: passive wireless,strong penetrability,temperature sensing capability,etc.As a result,it is particularly applicable for the detection of underground heating pipes.This article contains three main parts: algorithm,tag and reader.It could not only to detect the location of heating pipes,but also to get the its temperature,which could be used to monitor the working status of heating pipes for preventing leakage accidents.As a wireless passive detection system,SAW-RFID is highly similar to radar system in mechanism,constraints of its operating range could be seen through the radar equation.In the algorithm section,the principle and implementation of time reverse method were introduced.Meanwhile,the modulation and demodulation scheme of pulse compression method were also introduced,combined with simulations.Contradiction between resolution and range could be solved by these method.Heating pipes are working in the high-temperature environment,which requires SAW tags could operate normally at 150 ℃,and temperature measurement can be achieved within the operating temperature range.Structure of SAW tag was redesigned to achieve high resolution and wide range of temperature measurement,including three temperature reflectors and multi-pulse position encoding(Multi-Pulse Position Modulation referred MPPM)technology.In order to facilitate the inspection of underground heating pipes,IF digitization was used to realize the miniaturization of reader.Analog modules,digital modules,FPGA control module,data acquisition module were separately introduced,and the reader with 10 MHz bandwidth,70 MHz IF,922.5MHz carrier frequency was achieved,which could transmit query signals flexibly.Finally,reader testing,temperature measurement experiment,time reversal experiment and chirp query experiment were conducted,all results met design requirements,which showed that the design of the SAW-RFID system could detect underground heating pipes successfully.