S. Capdevila

Electromagnetic Modeling of RFID-Modulated Scattering Mechanism. Application to Tag Performance Evaluation

Radio-frequency identification (RFID) technology relies on the modulated scattering technique (MST) as a means to convey the information from the tag to the reader. The interaction mechanism between the reader and the tag is described in a physically meaningful way by the reciprocity theorem which is deeply rooted into Maxwell equations. This approach provides a simple and yet complete formulation that allows to fully describe the interaction between the reader and the tag, even in complex environments. From this formulation, a clear understanding is derived on how the different design tradeoffs affect system performance. Based on this approach, the paper is focused on several issues of practical relevance for antenna tag design such as maximum power transfer, maximum sensitivity, and nonlinearity effects.

Terahertz graphene optics

AbstractThe magnitude of the optical sheet conductance of single-layer graphene is universal, and equal to e2/4ħ (where 2πħ = h (the Planck constant)). As the optical frequency decreases, the conductivity decreases. However, at some frequency in the THz range, the conductivity increases again, eventually reaching the DC value, where the magnitude of the DC sheet conductance generally displays a sample- and doping-dependent value between ∼e2/h and 100 e2/h. Thus, the THz range is predicted to be a non-trivial region of the spectrum for electron transport in graphene, and may have interesting technological applications. In this paper, we present the first frequency domain measurements of the absolute value of multilayer graphene (MLG) and single-layer graphene (SLG) sheet conductivity and transparency from DC to 1 THz, and establish a firm foundation for future THz applications of graphene.

RFID Multiprobe Impedance-Based Sensors

In this paper, a passive multiprobe sensor using conventional UHF radio frequency identification (RFID) tags is presented. The RFID link between the reader and the tag is analyzed from a general point of view by means of reciprocity principle, to obtain a compact and explicit expression of the response of RFID tags that can be exploited in sensing measurements. A calibration scheme to remove nonlinearities in the response of RFID tags, which are due to the scavenging powering mechanism of passive tags, is also presented along with measurements. Finally, experimental results and discussion of a complete multiprobe sensing scenario are used to show the different challenges involved and how to overcome them.

UWB high-contrast robust tomographic imaging for medical applications

In this paper a complete UWB Circular Tomographic System robust to high contrast or large objects, applied to Breast Tumor Detection, is presented. The main contribution of this paper is to focus on the implementation of a two degrees of freedom imaging setup in order to deal with non-symmetric objects and to demonstrate its functionality with realistic breast phantoms.

Multi-Loaded Modulated Scatterer Technique for Sensing Applications

Modulated scatterer technique (MST) probes have been commonly used for near-field mapping application in antenna measurements as well as in imaging applications. Although they can be used as a general sensor, they present limitations in the amount of information that can be obtained. The paper proposes a new configuration for MST probes that can be used for sensing applications, which consists in using a set of impedances (at least three different impedances) instead of the conventional two impedance loads. Additional sensitive loads, such as thermistors, can be added to the multi-load MST sensor, in order to remotely sense their variation and perform further sensing of parameters which could not always be sensed by conventional MST. The paper presents the formulation and approaches that can be used to exploit the sensing capabilities of such multi-loaded MST sensor, as well as experimental validations through the measurement of the temperature in the neighborhood of the sensor.

3-D Microwave Magnitude Combined Tomography for Breast Cancer Detection Using Realistic Breast Models

Microwave imaging (MWI) is a feasible tool for medical imaging driven by its capability to discriminate between different types of tissues and abnormalities. Nowadays, a variety of reconstruction algorithms are investigated, mainly based on complex and time-consuming iterative schemes. Considering a future patient use, an algorithm requiring tens of hours seems unrealistic. In this letter, a 3-D quasi real-time algorithm, inspired in a computationally efficient modified-Born method, is assessed for early-stage breast cancer detection using 3-D anthropomorphic breast phantoms. The algorithm uses multifrequency information over a portion of the UWB range to produce robust images with a fair tradeoff between resolution and penetration.

Passive RFID based sensing

The principle of communication of passive RFID, which relies on the Modulated Scattering Technique (MST) to transmit the information from the tag to the reader, opens a way to enable conventional RFID for sensing purposes, without any additional circuitry. In this paper a short description of the physical principle behind the sensing is presented along with measurements of RFID tags used for sensing in multiple applications, such as electromagnetic field measurement temperature or presence detection.

Broadband conductivity of graphene from DC to THz

In this paper for the first time we have studied the broadband sheet conductance of few-layer graphene on single-crystal quartz substrate. Few-layer graphene was grown on Nickel coated Si wafers and transferred to the target substrate, which is single crystal quartz. High frequency measurements at X-band (8–12 GHz), using WR90 waveguide were performed. In addition, sheet resistance at W-band (75–100 GHz) and 1 THz range is also measured providing a comprehensive frequency sheet conductance calculation. The sheet resistance is extracted form the transmission coefficient (S21). The results present small variation at different frequency bands, and are quite stable within the bands.

RFID-based flexible low-cost EM field probe

The capability of the RFID tags as a low cost flexible device to measure the EM complex field distribution has been presented and some preliminary results presented. The devices do not need any kind of electrical connexion giving them a high versatility to act as a remote EM probing device under different conditions of positioning and accessibility. Sensitivity and dynamic range are aspects that need to be further investigated in order to have systems capable of exploring large areas in terms of spatial dimensions and amplitude levels.

Propagation measurements and simulations in tunnel environment at 5.8GHz

After the measurement campaign the simulation tool has been validated at mean values. Adjusting the input parameters the fast fading has been considered and new parameters have emerged in order to correct the mean values (see figure 8b). After that, a curved shaped tunnel and other frequencies must be studied to develop a statistical behavior model and use the simulator in radio-deployment.