Acoustic transmission loss in Hilbert fractal metamaterials.

Acoustic metamaterials are increasingly being considered as a viable technology for sound insulation. Fractal patterns constitute a potentially groundbreaking architecture for acoustic metamaterials. We describe in this work the behaviour of the transmission loss of Hilbert fractal metamaterials used for sound control purposes. The transmission loss of 3D printed metamaterials with Hilbert fractal patterns related to configurations from the zeroth to the fourth order is investigated here using impedance tube tests and Finite Element models. We evaluate, in particular, the impact of the equivalent porosity and the relative size of the cavity of the fractal pattern versus the overall dimensions of the metamaterial unit. We also provide an analytical formulation that relates the acoustic cavity resonances in the fractal patterns and the frequencies associated with the maxima of the transmission losses, providing opportunities to tune the sound insulation properties through control of the fractal architecture.

A Review of SMA-Based Actuators for Bidirectional Rotational Motion: Application to Origami Robots.

Shape memory alloys (SMAs) are a group of metallic alloys capable of sustaining large inelastic strains that can be recovered when subjected to a specific process between two distinct phases. Regarding their unique and outstanding properties, SMAs have drawn considerable attention in various domains and recently became appropriate candidates for origami robots, that require bi-directional rotational motion actuation with limited operational space. However, longitudinal motion-driven actuators are frequently investigated and commonly mentioned, whereas studies in SMA-based rotational motion actuation is still very limited in the literature. This work provides a review of different research efforts related to SMA-based actuators for bi-directional rotational motion (BRM), thus provides a survey and classification of current approaches and design tools that can be applied to origami robots in order to achieve shape-changing. For this purpose, analytical tools for description of actuator behaviour are presented, followed by characterisation and performance prediction. Afterward, the actuators' design methods, sensing, and controlling strategies are discussed. Finally, open challenges are discussed.

Toward Conductive Polymer-Based Soft Milli-Robots for Vacuum Applications.

For the last two decades, the development of conducting polymers (CP) as artificial muscles, by materials researchers and chemists, has made establishing a reliable and repeatable synthesis of such materials possible. CP-based milli-robots were mostly unknown in soft robotics, however, today, they play a vital role in robotics and smart materials forums. Indeed, this subclass of soft robots has reached a crucial moment in their history, a moment where they can display rather interesting features, based on established foundations in terms of modeling, control, sensing, and planning in various applications. The purpose of this paper is to present the potential of conductive polymer-based soft milli-robots as high-performance devices for vacuum applications. To that end, a trilayer polypyrrole-based actuator was first used inside a scanning electron microscope (SEM), characterized for different applied voltages, over a relatively long period. Additionally, the tip positioning of the cantilever was also controlled using a closed-loop control. Furthermore, as a proof of concept for more complex soft milli-robots, an S-shaped soft milli-robot was modeled, using a hybrid model comprised of two models; a multi-physics model and a kinematic model. It was then fabricated using laser machining and finally characterized using its tip displacement. polypyrrole-based soft milli-robots proved to have tremendous potential as high-performance soft robots at the microscale for a wide range of applications, including SEM micro-manipulation as well as biomedical applications.

Ultracompact reference ultralow expansion glass cavity.

We present the first experimental characterization of our ultracompact, ultrastable laser. The heart of the apparatus is an original Fabry-Perot cavity with 25 mm length and pyramidal geometry, equipped with highly reflective crystalline coatings. The cavity, along with its vacuum chamber and optical setup, fits inside a 30 L volume. We have measured the cavity's thermal and vibration sensitivities and present our first estimation of the cavity fractional frequency instability at σy(1 s)=7.5×10-15.

Developments and Control of Biocompatible Conducting Polymer for Intracorporeal Continuum Robots.

Dexterity of robots is highly required when it comes to integration for medical applications. Major efforts have been conducted to increase the dexterity at the distal parts of medical robots. This paper reports on developments toward integrating biocompatible conducting polymers (CP) into inherently dexterous concentric tube robot paradigm. In the form of tri-layer thin structures, CP micro-actuators produce high strains while requiring less than 1 V for actuation. Fabrication, characterization, and first integrations of such micro-actuators are presented. The integration is validated in a preliminary telescopic soft robot prototype with qualitative and quantitative performance assessment of accurate position control for trajectory tracking scenarios. Further, CP micro-actuators are integrated to a laser steering system in a closed-loop control scheme with displacements up to 5 mm. Our first developments aim toward intracorporeal medical robotics, with miniaturized actuators to be embedded into continuum robots.