This paper presents a chipless radio frequency identification (RFID) sensor tag having both identification and sensing capabilities. It is based on one resonant scatterer operating as a signal processing antenna in the 3-7.5 GHz band. The scatterer is used to monitor a physical parameter variation, as well as to identify the remote sensor. To make a resonator sensitive to the humidity, silicon nanowires are deposited on the tag surface using a simple process. The tag needs only one conductive layer so that it can be directly printed on the product to sense and to identify. Measurements done using a bistatic radar configuration in the frequency domain validate this concept. To demonstrate the reliability of such an application, two chipless RFID sensors placed in various environments are simultaneously detected using an anticollision technique based on spectral separation.

This article presents a comparison between the read range of classical radio frequency identification (RFID) and chipless RFID in free-space and real environments (REs). From the presented model, read range is derived using analytical formulation over nonisolated channels for both technologies. This article shows that the well-known bounds classically used in free space cannot be achieved in REs, i.e., subjected to leakage, coupling, and/or reflections) and therefore need to be modified. Although the introduced bound for semipassive tags is close to the one corresponding to free space, however, we show that for chipless tags, read range cannot be predicted by the radar equation and presents severe limitations since these tags are linear time-invariant systems. This new bound does not depend on the transmitted power or the reader sensitivity but relies on the concept of residual environment. We show that this quantity is the key parameter to evaluate the read range of a chipless RFID system. Moreover, the residual environment can easily be estimated or measured for any reading system. We show that the proposed bound can accurately predict the read range of a chipless system in different environments from anechoic chamber to nonstationary REs. Results are confirmed in simulation and measurements where the difference between the theoretical read range and the measured one is only 20 cm.

Silicon nanowires are attractive materials from the point of view of their electrical properties or high surface-to-volume ratio, which makes them interesting for sensing applications. However, they can achieve a better performance by adjusting their surface properties with organic/inorganic compounds. This review gives an overview of the main techniques used to modify silicon nanowire surfaces as well as characterization techniques. A comparison was performed with the functionalization method developed, and some applications of modified silicon nanowires and their advantages on those non-modified are subsequently presented. In the final words, the future opportunities of functionalized silicon nanowires for chipless tag radio frequency identification (RFID) have been depicted.

A temperature and humidity chipless RFID sensor is presented in this paper. The tag ID as well as the two physical parameters are extracted using a traditional chipless RFID tag and interrogation procedure. No specific material, i.e. particularly sensitive to the quantities to be measured, is used for ease of implementation. The method is based on a model which describes precisely the evolution of the scatterer’s resonance frequency as a function of temperature and humidity. The materials permittivity (impacted by these two quantities) and dilatation (impacted only by the temperature) are taken into consideration to estimate these two physical quantities independently and simultaneously using only the measurement of the resonance frequencies of two scatterers. Measurements in a controlled environment and in a real environment are achieved showing the potential of this approach for the sensor application. The sensing limitation as well as the possibility of this approach to characterize the temperature and humidity dependencies of unknown materials are also presented.

This work presents the designs of single-layer chipless radio frequency identification (RFID) tags based on the RF-encoding particles (REP) approach. These tags are the first realized for reading in cross-polarization resulting in a higher immunity against multipath, and thus, achieving robust readings in a practical environment. The proposed chipless tags are of credit-card size, with a frequency band of operation ranging from 3 to 6 GHz within the ultra-wideband (UWB), compliant with low-cost additive fabrication techniques, and realized with low-cost plastic and paper substrates. A study on reader-tag polarization and rotation angle is performed for the proposed designs and compared with the existing designs of two-layers. For the first time, it is presented that the low-cost single-layer tags can be read in realistic environments with only one measurement.

RFID is a widely employed wireless technology to identify items and animals (including humans). The reader, which is usually controlled by a computer, transmits an interrogating signal toward the tag. The backscattered signal is, in turn, modulated from the tag, mostly with either binary phase-shift keying or amplitude-shift keying. This is possible through the presence of an application-specific integrated circuit [1].