Philippe Talbot

Detection of micro-cracks on metal surfaces using near-field microwave dual-behavior resonator filters

The aim of this paper is to demonstrate that micro-cracks at the surface of metals can be detected and imaged by using near-field micro-wave resonators. It deals with two novel sensors: a first-order dual-behaviour resonator (DBR) filter and a first-order DBR filter with an open-ing in the ground plane. Measurements were mainly carried out on a stainless steel mock-up with several EDM (i.e. manufactured by Electron Discharge Machining) rectangular surface notches presenting widths between 0.1 and 0.3 mm and depths between 0.5 and 3 mm. The results presented here show the high sensitivity of the DBR probes and their ability to differentiate between notches of different depths and notches of different widths.

Microwave characterization of filled polymers

Interest in filled polymers has expanded in recent years as investigators have recognized the great flexibility allowed by these materials to suit particular properties such as electrical, mechanical, and/or coupling between these properties. This article describes the work undertaken to investigate the microwave response of two different types of samples: one with carbon black or silica particles embedded in a linear low-density polyethylene, and the other with carbon black particles or carbon fibers embedded in an epoxy resin. We report broad-band (30 MHz–14 GHz) measurements of the complex permittivity of these materials obtained by measuring the scattering parameters (S parameters) of a microstrip line loaded with a rectangular sample of the test material. The experimental results presented give access to data which can be rationalized in terms of a combination of Bruggeman’s self-consistent model with Jonscher’s phenomenological analysis. This analytical approach yields data that are in good correspo...

Electromagnetic and magnetic properties of multicomponent metal oxides heterostructures: Nanometer versus micrometer-sized particles

We have measured the composition and frequency-dependent complex effective permittivities and permeabilities in zero applied field of a series of ZnO and ferrimagnetic γ-Fe2 O3 composites prepared by powder pressing. The overall features of the room temperature electromagnetic properties of these diluted magnetic semiconductor composites exhibit a strong dependence on the powder size of the starting materials. For instance, electromagnetic spectroscopy over the frequency range (300 MHz–10 GHz) shows that composites made of nanoparticles (N-type samples) display a strong increase of the real and imaginary parts of the permeability compared to composites made of micron-sized particles (M-type samples). The observed dielectric behavior as a function of composition is manifestly at odds with the predictions from the simple property-averaging continuum model of Bruggeman. Additionally, a gyromagnetic resonance in the gigahertz region of frequency has been established for N-type samples which is not observable ...

Effective magnetic permeability of Ni and Co micro- and nanoparticles embedded in a ZnO matrix

Current trends in the miniaturization of microwave devices have prompted considerable interest in studying electromagnetic transport in nanoscale systems. Understanding the effect of physical structure and the role of interfaces is critical for gaining insight into the electromagnetic and magnetic properties of nanostructures and their behavior in microwave devices such as circulators and isolators. Previously, we have described the electromagnetic characteristics at microwave frequencies and the static magnetic properties of γ–Fe2O3∕ZnO micro- and nanocomposites fabricated via powder processing. Here we present systematic effective permeability measurements of magnetically structured granular systems composed of magnetic grains embedded in a nonmagnetic matrix using broadband microwave spectroscopy. Using the transmission∕reflection waveguide method, the effective complex permeability was measured in the frequency range of 0.01–10GHz. The results were compared for composites consisting of micrometer-size...

Effective permittivity of nanocomposite powder compacts

Advances in nanotechnology have led to a variety of new materials with strong potential applications to microwave and millimeter-wave components, e.g. dispersions of nanoscale particles, nanoparticle-filled polymers, self-assembled nanolattices of magnetic particles. More specifically, the properties of nanocomposites can be tailored for operation as insulators, ferro- and ferrimagnetic materials, highly conductive materials as well, for specific applications. In this study, we have investigated the electromagnetic response at microwave frequencies, using frequency domain network analysis, of cold-pressed powder compacts made of Ni, /spl gamma/-Fe/sub 2/O/sub 3/, Co, and ZnO nanosized powders. Effective complex permittivities of composites over the frequency range (100 MHz-10 GHz) as a function of composition were studied. Within the frequency range of measurements the real and imaginary parts of the effective permittivity of nanocomposites exhibit spectra which can be analytically well represented by power laws. The associated power law exponents, which are similar for the real and imaginary parts of the permittivity, are in the range 0.05-0.20 in agreement with data in the published literature. The dependences of the effective permittivity vs. composition are compared to those obtained from the effective medium theory of Bruggeman, which is found not to be adequate for all nanocomposites studied.

Electromagnetic characterization of fine-scale particulate composite materials

Abstract We report the results of the composition and frequency-dependent complex permittivity and permeability of ZnO and γ-Fe 2 O 3 composites prepared by powder pressing. The electromagnetic properties of these materials exhibit a strong dependence on the powder size of the starting materials. In the microwave frequency range, the permittivity and permeability show nonlinear variations with volume fraction of Fe 2 O 3 . As the particle size decreases from a few micrometers to a few tens of nanometers, the data indicate that local mesostructural factors such as shape anisotropy, porosity and possible effect of the binder are likely to be intertwined in the understanding of electromagnetic properties of fine-scale particulate composite materials.

Instrumentation for microwave frequency-domain spectroscopy of filled polymers under uniaxial tension

Artificially engineered multiphase heterostructures with high permittivity, high permeability and low dielectric and magnetic losses are desired for microwave applications. In addition, the direct conversion of electrical (and/or magnetic) energy to mechanical work through a material response is important for many practical applications. Thus, there is a need for sensitive and quantifiable techniques to probe how uniaxial strain affects the complex effective permittivity or magnetic permeability of particulate-filled polymers. We describe an apparatus for in situ studies of the effective electromagnetic properties of filled polymers under elongation. As currently configured, our new system will already be of significance to a wide variety of research, and in particular in the materials, automotive as well as aeronautical science. In this paper, we describe the design and operation of the measurement system. Two examples of preliminary observations of electromagnetic properties of filler reinforced polymeric materials under axial strain have been obtained and are presented to illustrate the utility of this instrumentation. On one hand, the effective permittivity of carbon-black-filled SBR (styrene-butadiene rubber) is discussed as a function of the carbon black volume fraction, frequency and extension ratio. On the other hand, we also show how the effective permeability of plasto-ferrite at microwave frequency changes due to external stress. This paper concludes with suggestions for possible research topics of current interest where the knowledge of material parameters under stress would be beneficial to the basic understanding of physical processes.

Study of relaxation and spin resonance in magnetic liquids

Abstract The complex susceptibility of magnetic liquids is investigated in a wide frequency range (10 Hz-2 GHz) with a microwave-type technique. Three loss mechanisms can be identified: Brownian relaxation, Neel relaxation and natural spin resonance. The effect of the temperature on Neel relaxation and natural spin resonance is confirmed theoretically.

DETECTION OF MICRO‐CRACKS ON METAL SURFACES USING NEAR‐FIELD MICROWAVE RESONATORS

This paper demonstrates how micro‐cracks at the surface of metals can be detected and imaged by using near‐field microwave resonators. It deals with two novel sensors: a first‐order dual‐behavior resonator (DBR) band‐pass filter probe and a first‐order DBR filter with an opening in the ground plane. Measurements results carried out on a stainless steel mock‐up with several 200 μm wide EDM rectangular surface notches are presented showing the high sensitivity of the DBR probes and their ability to differentiate between notches of different depths.

Theoretical and experimental demonstration of the feasibility of metallic surface cracks detection using microwaves techniques

In this paper, we describe how microwaves can be used to detect surface micro-cracks on metallic surface. We propose a resonant probe based on the excitation of evanescent waves. We investigate the electromagnetic analysis of the probe when interacting with cracks and demonstrate its sensitivity to cracks. This theoretical demonstration is confirmed by experiment