Tunable Chipless RFID Pressure Sensor Utilizing Additive Manufacturing—Model, Simulation, and Measurement

Each sensing application has its own set of unique requirements and constraints that must be satisfied by its sensor. These requirements can include being wireless, passive, noncontact, customizable, multifunctional, and/or minimally invasive, depending on the application. Chipless radio frequency identification (RFID) tags are a type of microwave sensor that has the potential to meet many of these requirements, especially when additive manufacturing (AM) is employed to create customizable substrates that are sensitive to different ranges of environmental measurands. This work examines the potential efficacy of a proposed chipless RFID pressure sensor design approach that utilizes polymer AM substrates. Complex permittivity and stress–strain measurements were conducted to develop a model that relates the resonant frequency of the chipless RFID sensor to pressure, which in turn allows for the design of sensors with customized sensing ranges and sensitivities. This model is based around a standard rectilinear 3-D polymer-printed infill pattern. Custom-infill patterns can be developed to further tune the sensor performance based on a desired application. Electromagnetic (EM) simulations and measurements of fabricated tags, including one design based on the model with a rectilinear infill pattern and two designs that utilize custom-infill patterns, were conducted to illustrate the efficacy of the developed model and sensor design approach. Several possible sources of inconsistency between measurement and simulation are also investigated.