Valérie Vigneras

A 900MHz RF energy harvesting module

This paper presents a guideline to design and optimize a RF energy harvester operating in ISM Band at 902 MHz. The circuit is implemented on a standard FR4 board with commercially available off-the-shelf devices. The topology of the impedance transformation block is selected to reduce the losses which improves the overall performances of the system. The characterization of the harvesting module shows sensitivity of -22.5 dBm for a dc output voltage of 200 mV up to -11 dBm for 1.08 V. A wireless power transmission in an indoor environment is measured with a radiated source power of 16.8 dBm. The harvester exhibits a DC rectified voltage of 1.25 V at 0.5 meter and still 500 mV at 1.5 meter.

Light trapping efficiency of organic solar cells with large period photonic crystals

We study the optical properties of a 2D Photonic Crystal (PC) inserted in the upper ITO electrode of a classical P3HT:PCBM solar architecture with an ultra-thin active layer. First, we analyze the optical response of the system when only the active layer is supposed to absorb light. This allows us to observe clear photonic crystal resonances in the absorption spectrum, which increase the cell efficiency even if the period of the PC is higher than the wavelength. This is in apparent contradiction with the common belief that PC should work in subwavelength regime. Then, by turning to a real system (with optical losses in all the layers), an optimized PC design is proposed, where the maximum of efficiency is obtained for a PC period of 1200 nm, much larger than visible wavelength.

NON DESTRUCTIVE DIELECTRIC CHARACTERIZATION OF THIN FERROELECTRIC FILMS MATERIALS USING COPLANAR LINE STRUCTURE

ABSTRACT This paper presents a nouvelle and non-destructive Broadband characterization method which uses a coplanar line for the measurement of the complex permittivity of linear dielectric materials and precisely, that of ferroelectric thin films. The method uses the transmission coefficient and the quasi-TEM analysis to find the effective permittivity of the multilayer system, and then the coplanar conformal mapping technique is employed to extract the relative permittivity of the thin layer. Comparing our results to those of cavity resonator method at 12 GHz shows a good agreement. The measurement is done in the microwave frequency band (45 MHz–20 GHz).

LaTiO x N y Thin Films, Measurement and Application to Microwave Device

This paper reports about three issues: a non-destructive method for dielectric measurement of materials; the first microwave dielectric measurement of a new birth dielectric LaTiOxNy material, and a topology for X-band phase shifter based on tuneable ferroelectric thin films interdigital capacitors.

Non-destructive measurements of dielectric constant of thin dielectric films with metallic backing using coplanar transmission line

This paper introduces a new characterization method of measurement for the permittivity of dielectric material in thin films deposited on metallic/semiconductor substrate. The method uses the conformal mapping technique to extract the relative permittivity and loss tangent is a non-destructive way. After measuring the S-parameters of the material when placed on a coplanar transmission line, an inverse problem is applied to extract the dielectric constant. The permittivity measurement is done for thin film of 5 micrometer thickness. The obtained results are satisfying and encouraging and the method is validated using standard FEM simulation software.

A concurrent 915/2440 MHz RF energy harvester

This paper presents the development of two dual-band radio-frequency (RF) harvesters optimized to convert far-field RF energy to DC voltage at very low received power. The first one is based on a patch antenna and the second on a dipole antenna. They are both implemented on a standard FR4 substrate with commercially off-the-shelf devices. The two RF harvesters provide a rectified voltage of 1 V for a combined power, respectively, of −19.5 dBm at 915 MHz, −25 dBm at 2.44 GHz, of −20 dBm at 915 MHz, and −15 dBm at 2.44 GHz. The remote powering of a clock consuming 1 V/5 µA is demonstrated, and the rectenna yields a power efficiency of 12%.

Concise formulation of the three-dimensional multiple-scattering theory

The scattering of an electromagnetic wave by a set of dielectric and metallic spheres is a well-known physical problem. We show a mathematical simplification of the multiple-scattering theory. In this paper, we will establish the multiple-scattering equation in two different ways. Through the study of the equation form, we can choose the simplest spherical wave expansion for calculations. Then, we propose concise expressions of the Mie scattering coefficients and translation coefficients for both polarizations. With these simplified expressions, large spheres are studied without loss of accuracy. Far-field expressions, cross-sections, and the scattering matrix are also simplified. Thus, we obtain formulas that can be easily understood from a physical point of view.

Tunable photonic crystals controlled by spin-crossover material in Terahertz range

We use a spin crossover material as active defect inserted into a periodic structure of alternating layers of glass and air. By inducing the spin transition of the defect, a single defect mode of this Bragg filter designed for the submillimeter wavelength can be tuned over 15 GHz. This shows prospective applications of spin crossover materials at terahertz frequencies.