Embedded Singularity Chipless RFID Tags

Every structure scatters an impulse plane wave in a unique fashion. The structural information of an object can be extracted by analyzing the late-time scattered field as the impulse-response of the structure. The late-time scattered field, which represents the source-free response of the structure, contains a summation of damped sinusoids. The frequency and damping factor of these damped sinusoids are uniquely associated with the structural information, and can be used to identify an unknown object. We propose to create uniquely identifiable scattered fields from an object by incorporating "notches" in the structure giving rise to specific damped sinusoids in the source-free scattered field of the structure. In this manner, data can be embedded into the structure of an object which is detectable using electromagnetic waves, allowing a metallic object to serve as a chipless radio-frequency identification tag (RFID). Data is encoded as complex natural resonant frequencies (referred to as poles) in the structure and is retrieved from the scattered field. Data retrieval is based on Singularity Expansion Method (SEM) analysis using target identification techniques. Each complex-frequency pole provides two-dimensional data (real and imaginary) which can be extracted from the late-time impulse response of the structure using a numerical technique such as the Matrix Pencil Method. We have designed and prototyped a 6-bit (3-pole) tag. The tag is analyzed using simulations and measurements. The tag is successfully read remotely via its scattered fields. The measured data are compared with simulation, and are in close agreement.