Radio frequency identification technology (RFID)

Radio frequency identification technology was originally created to identify friendly aircraft from enemy aircraft during the Second World War. It eventually found its way  into civilian applications ranging from door access control to livestock tracking.

It is a wireless technology which is recently being used as a replacement for the traditional barcode system. An RFID system consists of two hardware components: the reader and the tag/transponder. The reader itself typically consists of a microcontroller alongside RF circuitry such as envelope detectors and filters which are required to transmit and receive RF energy.

The reader includes a coil or antenna which is used to transmit and receive. The functions of the reader include:
(1) Transfer enough power to the tag to energise it;
(2) receive the data stored in the tag’s memory via response signal from the tag;
(3) write data to tags memory.

The hardware of the tag comprises a microchip with memory which stores the tags unique identification code. The RF portion of the tag is made up of a wound or printed coil connected to a capacitance to form a tuned LC circuit.

One of the biggest challenges posed by CUI is the inaccessibility due to the large standoff distance introduced by thick insulation. Moisture in the insulation and high temperatures create a microclimate which can accelerate the development of corrosion.

The hidden nature of CUI may result in it going unnoticed for long periods of time leading to potentially catastrophic failures. A review of the literature on the most common NDT techniques for corrosion detection showed that the majority of techniques are limited when it comes to online in-situ monitoring of CUI primarily due to the thick insulation layer.

Solutions to overcome this problem typically involves either applying much higher input power using bulky,pensive equipment or the use of inspection holes in the insulation layer to send waves along the length of the pipe to another inspection hole. The passive RFID sensors identified in the literature demonstrate the potential of cheap, battery free wireless sensing. RFID tags have been adapted to sense a wide range of diverse phenomena.

Due to their battery-free operation, RFID tags have shown the potential to be embedded into structures such as concrete for long term condition monitoring. However, the sensing tags used in majority of the studies examined make use of either thin films or sacrificial elements added to the tag. The changes that occur to the thin films or the sacrificial elements may not represent the true condition of the structure on which the tag is embedded.

Furthermore, long term monitoring using RFID tags is limited if the sensing elements of a tag degrades faster than the structure it’s monitoring. Another challenge not addressed by existing studies is the resulting performance degradation when tags are placed onto metallic structures. To tackle the particular problem of thick insulation, the use of passive LF RFID tags as corrosion sensors is proposed in this study.

The developed system aims to address the following issues:

• Obtain corrosion measurements on steel through thick layers of insulation/ large standoff distances.
• Since the system is passive, a method needs to be developed to address the issue of varying displacement between the reader and the tag, i.e. obtain position independent corrosion measurements. 
• The system much be very low cost, and use off-the-shelf components. To minimise costs further, the tag should be unmodified. The interaction between the tag coil and the metal being the sensing mechanism. 
• Suitability for long term monitoring by not using any sacrificial elements. 

Source: https://theses.ncl.ac.uk/dspace/bitstream/10443/2348/1/Alamin%2014.pdf