## 2 State of the Art
### Application of RFID in a Simulated Production Line for an Industrial Context  
A third experimental case study is the implementation and testing of RFID technologies in the context of a suitably simulated industrial production environment within a learning factory (as an educational unit within an engineering faculty at a university in Canada), to demonstrate the potential of digitising production processes from an I4.0 perspective and optimising the activities of companies and organisations in engineering and industry. In this context, four different products were designed and manufactured in this learning factory, namely, a pneumatic linear actuator, an internet of things board (essentially the basic hardware and software components on which IoT applications can run and function), an electronic screwdriver, and a solenoid valve (an electromechanical control valve normally used to control the flow of a liquid or gas). The implementation of an RFID system within a production line for one or more of the products considered, to improve the traceability process, was the subject of research and analysis in the case study in question [31]. The components that make up the solenoid valve are as follows: the valve body with inlet and outlet ports, a solenoid coil with housing, a plunger, and a spring. In this context of characterising the product in question, the valve body is manufactured using a metal powder laser sintering process (carried out by additive manufacturing) and then finished using a CNC machine tool. The piston, on the other hand, is produced using additive manufacturing on a metal 3D printer or cut using a CNC machine. In addition, the solenoid coil housing is manufactured using a plastic 3D printer or an injection moulding process. Indeed, this flexibility of the learning factory in question to demonstrate the production of a product using multiple manufacturing technologies can demonstrate the reality of flexible manufacturing processes in an appropriate way [31]. Figure 4 shows an image of the inside of the learning factory (which is relevant to the present study because the internal environment visualised in the factory in question largely resembles the internal industrial environment of the company where the case study was carried out, particularly along various sections of the shop floor). The case study was developed at Dinefer S.A., a company specialising in cable test equipment production. Continuing with the content of interest about the application of RFID and digitisation of the production process in the case study, each of the above-mentioned production stations along the manufacturing line has access to RFID and QR code or barcode technologies. Thus, each component produced can be associated with an RFID tag, a QR code, or a barcode (or both), and, in turn, the information related to the completion of the processesassociated with the respective workstation in question can be developed in two ways, namely [31]:  
* By properly tracking the system, keeping the product's RFID tag unchanged, and storing the data related to the process in the respective production execution system;
* By changing the data stored on the label when the manufactured components leave the production plant. Both approaches provide adequate information on the stage of the production process that has been completed for the respective components in question. Therefore, since the system installed in the learning factory can implement both methods considered, the relevant approach to analyse (and the one that was applied in the experimental study) corresponds to that of the traceability system [31]. Following the production flow under study, the solenoid valve components need to be assembled.