Sami Hage-Ali

A Millimeter-Wave Microstrip Antenna Array on Ultra-Flexible Micromachined Polydimethylsiloxane (PDMS) Polymer

The use of polydimethylsiloxane (PDMS), an ultra flexible polymer, as a substrate for the realization of reconfigurable microwave devices in the 60-GHz band is presented. As bulk PDMS is demonstrated to be lossy at millimeter waves, membrane-supported devices are considered. A new reliable and robust technological process has been developed to micromachine membrane-supported transmission lines and microstrip antenna arrays. It is shown that transmission lines printed on 20-¿m-thick membranes exhibit similar performances as bulk substrates commonly used at millimeter-wave frequencies. A microstrip antenna array has been also designed and fabricated to demonstrate the feasibility of directive antennas supported by large membranes. Promising applications for mechanical beam-steering, beam-forming, and frequency-tunable antennas are expected.

A Millimeter-Wave Inflatable Frequency-Agile Elastomeric Antenna

This letter reports a millimeter-wave frequency-agile microstrip antenna printed on an ultrasoft elastomeric polydimethylsiloxane (PDMS) substrate. The microstrip patch antenna is supported by a PDMS membrane suspended over an air cavity. The distance H between the patch and the ground plane, and thus the resonant frequency of the antenna, are tuned using pneumatic actuation, taking advantage of the extreme softness of the PDMS membrane. A continuous frequency shift varying from 55.35 to 51 GHz (≈8%) has been obtained for a tuning range of H between 200 and 575 μm. In all configurations, the antenna remains matched and its radiation characteristics are very satisfactory.

Packageless acoustic wave sensors for wireless body-centric applications

This paper describes the investigation of the potential of packageless structures for body-centric acoustic wave sensor applications based on Al2O3/ZnO/Lithium Niobate structures, which are investigated numerically and experimentally.

AlN/GaN/spphire as promising structure for wireless, batteryless and packageless acoustic wave sensors for high temperature applications

Waveguiding layer acoustic waves (WLAW) technology is considered as a packageless solution for extreme miniaturization of acoustic wave devices. WLAW solution is also original and suitable for high-temperature applications. Indeed, the achievement of a stable high-temperature packaging still constitutes a technological lock, in particular regarding sealing performance. In this context, we consider AlN/GaN/Sapphire as a promising WLAW structure for high-temperature applications. Indeed, the high-temperature stability of these three materials was previously demonstrated. However, in order to develop fully operational WLAW sensors based on this layered structure, it is necessary to have a better knowledge of the behaviour of each constitutive material with respect to the temperature. Consequently, the aim of this work is to experimentally validate GaN and AlN elastic constants sets in a large temperature range, which is a prerequisite to make the design of WLAW sensors according to the targeted performance.

AlN/ZnO/LiNbO 3 packageless structure as a low-profile sensor for on-body applications

This paper describes the potential of the AlN/ZnO/LiNbO3 structure for packageless surface acoustic wave sensors. This structure, based on the waveguiding acoustic wave principle, is studied numerically and experimentally.

SAW resonators for magnetic field sensing with (TbCo 2 /FeCo) multilayered IDTs as sensitive layer

In previous studies [1,2] we have shown the possibility to realize wireless magnetic SAW sensors with a delay line configuration using layered structures. SAW devices in resonator configuration with Ni interdigital transducers (IDT) on the substrate were also investigated by Kadota et al. [3]. The physical phenomena behind sensor behavior is still unclear and the interpretation of the results is not fully in line with the proposed theoretical models. This work aims to understand the physics and the interaction between acoustic waves and magnetostrictive layers under magnetic fields. Here, we investigate multilayer (LiNbO3/(TbCo2/FeCo)) SAW structures with different geometries and configurations.

Theoretical and experimental study of ScAlN/Sapphire structure based SAW sensor

Several SAW devices based on Sco.1Alo.9N/Sapphire bilayer structures were fabricated using various wavelengths and film thicknesses. The acoustic velocity, electromechanical coupling coefficient and temperature coefficient of frequency (TCF) of each device was then measured and the results were compared with calculations using several sets of elastic, piezoelectric and dielectric constants available in the literature. We have shown that the accuracy of available constants is not enough to permit a reliable optimization and design of SAW devices for signal processing and sensors applications.

Dynamic light scattering study of the ultrasonication of P(VDF-TrFE): A new model

ABSTRACT The purpose of this paper is to understand the mechanisms occurring during the ultrasonication of the copolymer poly(vinylidenedifluoride-trifluoroethylene). In these experimental conditions, the polymer adopts a core–shell structure and its hydrodynamic diameter is measured by dynamic light scattering. The results show that, without covalent bonds breakage, the hydrodynamic diameter decreases with ultrasonication time and a smaller size population appears. This evolution is reversible in a matter of days. A new two-step mechanism is proposed to describe this phenomenon: first the erosion of a core–shell structure and second the contraction of the core. Beyond shedding a new light on the phenomena occurring during the sonication of polymers used in nanocomposites elaboration, this work also strongly questions the traditional techniques used to study the degradation of polymers, which use the hydrodynamic diameter measurement to determine the molecular weight.

Potential of Al2O3/GaN/Sapphire layered structure for high temperature SAW sensors

This paper describes the investigation of the potential of packageless structures for acoustic wave sensor applications based on Al2O3/IDT/GaN/Sapphire structure. The finite elements modeling predicts the possibility of acoustically isolated waveguiding layer acoustic wave (WLAW) to propagate inside this structure with very low displacement at the top surface of the topmost Al2O3 layer. This layer serves as a protecting layer against oxidation of internal layers as well as an acoustically isolating layer, providing a mean for packageless packaging of this structure. The modeling results get confirmation in experiments with the precursor IDT/GaN/Sapphire structure thus supporting hopes on the predicted correct operation of the final Al2O3/IDT/GaN/Sapphire structure.