Microwave analog experiments on optically soft spheroidal scatterers with weak electromagnetic signature

Saleh, Hassan; Charon, Julien; Dauchet, Jérémi; Tortel, Hervé; Geffrin, Jean-Michel

doi:10.1016/j.jqsrt.2017.03.024

Cited by 7 publications

(3 citation statements)

References 34 publications

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“…In Merchiers et al (2010) measurements and models like the superposition Tmatrix method, DDA and MoM were compared in amplitude and phase of the scattered field of an aggregate, giving comparable results for different frequencies or wavelengths. Later, in Saleh et al (2017), measurements and simulations of the scattered field of spheroids made in T-matrix and FEM also gave equivalent results in terms of intensity and phase. These results proved the validation of our simulation methods compared to other models and our measurements.…”

Section: Simulationmentioning

confidence: 93%

Scattering properties of protoplanetary dust analogs with microwave analogy: Aggregates of fractal dimensions from 1.5 to 2.8

Valencia

Geffrin

Ménard

et al. 2022

A&A

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Context. The growth of dust grains in protoplanetary disks is not understood in detail. Several studies have proposed the presence of aggregates and irregular grains to overcome the physical barriers in grain growth models. In order to understand the scattering properties of these aggregates, laboratory measurements of light scattering and microwave scattering have been developed over the last 50 years. Aims. We aim to measure the scattering properties of different protoplanetary analog aggregates with fractal dimensions of 1.5, 1.7, 2.0, 2.5, and 2.8. Methods. We used the microwave scattering technique (microwave analogy) for the measurements. The analog particles were virtually generated and fabricated by 3D printing with a controlled size (scaling factor), geometry, and refractive index. The seven analogs were measured at wavelengths ranging from 16.7 mm to 100 mm, leading to aggregate size parameters ranging from X agg = 1 to X agg = 20. The results were compared to finite element method calculations of the same analogs for cross-validation. Results. The phase function and the degree of linear polarization were deduced from the scattered field measurements of the different aggregates. These scattering properties are compared and discussed as a function of the fractal dimension. Conclusions. The scattering properties of aggregates with different fractal dimensions are different. Three different realizations of aggregates with the same fractal dimension but different monomer configurations yield the same phase functions. We verified that the maximum degree of linear polarization is higher for porous aggregates than for compact aggregates. Furthermore, the maximum polarization occurs at larger scattering angles for high fractal dimensions, while the half width at half maximum of the phase functions present larger values for small fractal dimensions.

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Section: Simulationmentioning

confidence: 93%

Scattering properties of protoplanetary dust analogs with microwave analogy: Aggregates of fractal dimensions from 1.5 to 2.8

Valencia

Geffrin

Ménard

et al. 2022

A&A

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“…Numerical calculations of the scattering properties of the AgC181, AgC185, AgC186, AgC187, AgC232, AgC233 and GravelLike have been conducted using the Finite Element Method presented in [30] and using the same files to describe the geometry of the objects than the one used to print them. The scattering properties are computed considering the similar orientations and inclinations of the sample as during the measurements, by steps of 10°.…”

Section: Numerical Calculationsmentioning

confidence: 99%

Number of independent measurements required to obtain reliable mean scattering properties of irregular particles having a small size parameter, using microwave analogy measurements

Renard

Geffrin

Valencia

et al. 2021

Journal of Quantitative Spectroscopy and Radiative Transfer

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“…An interest has been shown recently toward the manufacturing of analogs with low permittivity (between 1 and 3) to mimic the electromagnetic response of photosynthetic microalgae particles. In [17] this question has been investigated on analogs of spheroidal particles machined from rigid polyurethane foams with permittivities ranging from 1.3 to 1.45. Due to machining difficulties and a request for lower prmittivity, we have been led to derive a simple and "user friendly" method capable of producing objects of any shape and size while controlling their permittivity spatial distribution in a one-shot manufacturing process.…”

mentioning

confidence: 99%

Approach to Control Permittivity and Shape of Centimeter-Sized Additive Manufactured Objects: Application to Microwave Scattering Experiments

Saleh

Tortel

Leroux

et al. 2021

IEEE Trans. Antennas Propagat.

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Controlling the electromagnetic properties of dielectric objects is demanded in microwave applications such as radar cross section studies, metamaterial design and antennas prototyping. Additive manufacturing has made the fabrication of desired shapes easier, but there is still room for improvement in controlling the permittivity. This paper proposes a novel approach to control the permittivity of 3D printed objects, in particular the ones with low permittivity contrasts. The effective permittivity is set by locally varying the material density. The object is first meshed using tetrahedral meshing software. Then its air percentage is controlled by adjusting the diameter of cylinders, which are positioned at each edge of the mesh. By tuning the volume fraction, one can achieve the required effective permittivity. Design, manufacturing and characterization steps are discussed while considering the specific case of spheres. With such a canonical shape, the effective permittivity can be directly retrieved by comparing far field electromagnetic scattering measurements with Mie computations. Bistatic Radar Cross Section measurements and simulations are provided and discussed. They enable us to assess the validity of the proposed methodology, in particular the good adequacy between the adequately chosen unstructured air/material distribution, the desired relative permittivity and the good homogenization of the object.

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Microwave analog experiments on optically soft spheroidal scatterers with weak electromagnetic signature

Cited by 7 publications

References 34 publications

Scattering properties of protoplanetary dust analogs with microwave analogy: Aggregates of fractal dimensions from 1.5 to 2.8

Scattering properties of protoplanetary dust analogs with microwave analogy: Aggregates of fractal dimensions from 1.5 to 2.8

Number of independent measurements required to obtain reliable mean scattering properties of irregular particles having a small size parameter, using microwave analogy measurements

Approach to Control Permittivity and Shape of Centimeter-Sized Additive Manufactured Objects: Application to Microwave Scattering Experiments

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