Towards Wireless Detection of Surface Modification of Silicon Nanowires by an RF Approach.

This paper shows the possibility to detect the presence of grafted molecules on the surface of silicon nanowires with a wireless RF radar approach based on the measurement of the backscattered signal of a resonant structure on which the nanowires are deposited. The measured resonance frequency allows the determination of the intrinsic properties related to temperature and humidity variations, which can be related to the presence of the grafted molecules. Several functionalizations of nanowires have been realized and characterized. For the first time, an RF approach is used to detect significant differences related to the presence of grafted molecules on the surface of nanowires. In addition to detecting their presence, the obtained results show the potential of the radar approach to identify the type of functionalization of nanowires. A set of six different grafted molecules (including octadecyltrichlorosilane, ethynylpyrene, N3) was tested and correctly separated with the proposed approach. Various measurements of the same samples showed a good repeatability which made the approach compatible with the possibility of differentiating the molecules with each other by radar reading. Moreover, discussions about the application of such functionalizations are made to increase the sensibility of sensors using a radar approach.

Directional amplitude backscatter modulation with suppressed Doppler based on rotating resonant loop.

The directional amplitude backscatter modulation with suppressed Doppler is demonstrated based on the scattering from a symmetrically rotating resonant loop. The concept is studied theoretically and experimentally with perfectly compatible results. The symmetrical rotation of the scatterer and the effect of radial resonance, as the two crucial points to realize the idea, are highlighted through the comparison between the symmetric and non-symmetric cases, and the results obtained for scatterers with and without radial resonance. The presented backscattering modulation technique provides an amplitude modulating waveform which is uniquely linked to the directional reradiation pattern of the rotating loop scatterer in a definite resonant mode. With the pure directional amplitude modulation (DAM) induced on the backscattered wave, the envelope waveform can be accurately retrieved form the received signal using the In-phase and Quadrature (IQ) representation. The contribution of the background in a real environment can be detected and removed to obtain the exact modulating waveform. This property of the proposed backscattering modulation method can be applied for sensing, localization, and identification purposes with high sensitivity, read range, and robustness.

CBRAM technology: transition from a memory cell to a programmable and non-volatile impedance for new radiofrequency applications.

Electrical resistance control programming of conductive bridging random access memory (CBRAM) radio frequency (RF) switches could benefit the development of electronically controlled non-volatile RF attenuators and other reconfigurable devices. The object of this study is to adapt a conventional CBRAM based memory cell to be used as an RF switch, and to demonstrate the feasibility of programming non-volatile RF CBRAM switches to achieve specific target resistances within a range of continuous values. The memory-RF technologic transition implies a drastic increase of the geometry in order to handle a much higher power, a decrease of the transition capacitance in order to operate at much higher frequencies, and a decrease of the LRS to a few ohms, which is critical for RF applications. These studies are initially performed on an in-house made RF CBRAM cell array at DC frequency, and then extended successfully to a co-planar waveguide (CPW) based shunt mode RF switch with an integrated CBRAM cell. Reliability of the proposed technique is validated through detailed analysis of factors like repeatability of the process, time stability of programmed states, and statistics of time taken to converge to a desired resistance value for an arbitrary RF CBRAM switch.

Chipless RFID Label with Identification and Touch-Sensing Capabilities.

This article presents a 14-bit chipless RFID label which, in addition to classical identification feature, can be used as decimal numeric keypad, allowing the deployment of secure access control applications. A low-cost single layer label comprising 10 RF loop scatterers is used to code information in the frequency domain. In addition, each resonator is associated to a digit in the decimal number system, and the difference in the spectrum caused by the touch event is exploited for the detection of each key pressing. The shape of the resonators has been carefully selected to be both highly resonant and to show high sensitivity to the presence or absence of the human finger. The concept is validated by measurements in an office environment using an FCC compliant low-cost chipless reader and microstrip vivaldi antennas. Simple detection algorithms are proposed for both identification and touch sensing in real environment.

Video-Rate Identification of High-Capacity Low-Cost Tags in the Terahertz Domain.

In this article, we report on video-rate identification of very low-cost tags in the terahertz (THz) domain. Contrary to barcodes, Radio Frequency Identification (RFID) tags, or even chipless RFID tags, operate in the Ultra-Wide Band (UWB). These THz labels are not based on a planar surface pattern but are instead embedded, thus hidden, in the volume of the product to identify. The tag is entirely made of dielectric materials and is based on a 1D photonic bandgap structure, made of a quasi-periodic stack of two different polyethylene-based materials presenting different refractive indices. The thickness of each layer is of the order of the THz wavelength, leading to an overall tag thickness in the millimetre range. More particularly, we show in this article that the binary information coded within these tags can be rapidly and reliably identified using a commercial terahertz Time Domain Spectroscopy (THz-TDS) system as a reader. More precisely, a bit error rate smaller than 1% is experimentally reached for a reading duration as short as a few tens of milliseconds on an 8 bits (~40 bits/cm2) THID tag. The performance limits of such a tag structure are explored in terms of both dielectric material properties (losses) and angular acceptance. Finally, realistic coding capacities of about 60 bits (~300 bits/cm2) can be envisaged with such tags.

Functionalization and Characterization of Silicon Nanowires for Sensing Applications: A Review.

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 New Method of Secure Authentication Based on Electromagnetic Signatures of Chipless RFID Tags and Machine Learning Approaches.

In this study, we present the implementation of a neural network model capable of classifying radio frequency identification (RFID) tags based on their electromagnetic (EM) signature for authentication applications. One important application of the chipless RFID addresses the counterfeiting threat for manufacturers. The goal is to design and implement chipless RFID tags that possess a unique and unclonable fingerprint to authenticate objects. As EM characteristics are employed, these fingerprints cannot be easily spoofed. A set of 18 tags operating in V band (65-72 GHz) was designed and measured. V band is more sensitive to dimensional variations compared to other applications at lower frequencies, thus it is suitable to highlight the differences between the EM signatures. Machine learning (ML) approaches are used to characterize and classify the 18 EM responses in order to validate the authentication method. The proposed supervised method reached a maximum recognition rate of 100%, surpassing in terms of accuracy most of RFID fingerprinting related work. To determine the best network configuration, we used a random search algorithm. Further tuning was conducted by comparing the results of different learning algorithms in terms of accuracy and loss.

Guided Electromagnetic Wave Technique for IC Authentication.

Counterfeiting of an Integrated Circuit (IC) has become a significant concern for electronics manufacturers, system integrators, and end users. It is necessary to find a robust implementation that is efficient, low cost, and noninvasive in detection and avoidance of ICs counterfeiting. In this paper, we introduce the concept of using a guided radiofrequency (RF) wave technique to authenticate ICs. The approach discussed in this work highlights the use of electromagnetic (EM)/radiofrequency (RF) response that has been further evaluated to assign fingerprint or signature of ICs for the purpose of authentication. Our approach is to use EM/RF guided wave to sense the response of the ICs, extract the manufacturing-based process variation of an IC and finally generate identifier or signature of that IC. As a proof-of-concept, we performed experiments over different field-programmable gate array (FPGA) boards of the same family. The post-processing technique was applied on the measurement results to statistically quantify the error probability of the authentication technique.

Accurate Positioning System Based on Chipless Technology.

In this paper, we present an accurate method to localize an object on a 2D plan using the chipless technology. This method requires a single antenna and a chipless tag. Phase difference between a reference position and an unknown position is used to estimate the distances between each resonator and the antenna. Then, multi-lateration is used to determine the position of the chipless tag in the plan. This method provides a better accuracy compared to classical ones based on received signal strength indicator (RSSI) or round-trip time-of-flight. In a square of 10 cm side above the antenna, error over distance determination between each resonators and the antenna is less than 2 mm and localization error on the tag coordinates in the 2D plan is lower than 1 cm. To increase the robustness of this method, we propose also a selection of a subset of the resonators used by the multi-lateration process. This method permits to increase the localization area by more than 20%. All the results have been obtained in real environment, and at different heights to show the robustness of the proposed approach. Finally, localization sensors based on this method can also be used as classical chipless RFID tag for identification with the same coding capacity.

Terahertz encoding approach for secured chipless radio frequency identification.

In this article, we present a new family of chipless tags, which permit encoding of digital data in the terahertz domain. These devices consist of stacked dielectric media whose thicknesses are of the same order as terahertz wavelengths. Since the information is encoded in the volume of these multilayer terahertz tags, they can easily be associated with classical identification techniques (e.g., barcode, radio frequency identification), where information is encoded at the surface of the tag, to provide higher data security. The principle of this encoding approach is studied and experimentally demonstrated in this paper. A 2 bit tag prototype has been realized and measured for validation purposes.