In the proposed work, the dynamic performances of a miniature soft Magneto-Rheological (MR) shock absorber are analyzed. The final application for which the damper has been designed and in which it will be embedded is a variable stiffness insole for patients with foot neuropathy and undergoing plantar ulcerations. Considering that the common design methodology used to dimension MR devices merely defines the maximum ratings of the sustainable efforts (i.e. maximum sustainable load for MR dampers, pressure drop for MR valves and braking torque for MR brakes or clutches), the relevance of their dynamics involved (respectively the impact velocity of the loading body for shock absorbers, the imposed flow rate and the rotating speed for MR valves and brakes) is often neglected in the dimensioning phase although it may assume a fundamental relevance. The understanding of the dynamic behavior of MR devices become even more important if these latter are part of a element or a more complex system in which all the elements differently affect its final behavior. With this respect, test sessions are conducted to experimentally evaluate the contribution that the different elements composing the damper in order have on the overall performances of the final systems.

Magneto-Rheological (MR) fluids consist in a suspension of ferromagnetic particles dispersed in a fluid carrier. If excited by a magnetic source, the nearby magnetic field induces the particles magnetization with the formation of chainlike structures aligned parallel to the field direction. This phenomenon is responsible of the rise of a magnetic field dependent yield stress required to counteract the interactions between adjacent particles and break the ferromagnetic clusters. Thus, in the case of an external effort applied to the fluid, chain-like structures are stretched and the increased distance among adjacent particles results in an augmentation in the reluctance of the gap in which the MR fluid flows. The consequent variation in the magnetic flux produced by an exciting magnetic source can be detected as an induced voltage appearing in the system. The presented work proposes and discusses experimental sessions intended to underline the possibility to employ the aforementioned phenomenon in order to detect pressure or flow variation in MR valves.

The incidence of diabetic foot ulcerations and lower extremity amputations remains very high and inacceptable. The high risk of ulceration and consequent amputation is strongly related to difficulties to obtain foot off-loading, particularly on long term. Due to the complexity of their utilization, the available foot off-loading devices are underused both by health care providers and patients with very low therapeutic adherence. This article summarizes the foot off-loading in diabetic patients and describes the concept of intelligent footwear we developed, based on continuous measurements and permanent and automatic adaptations of the shoe insole's rigidity.

Les taux d’ulceration et d’amputation des membres inferieurs chez des patients diabetiques demeurent tres eleves et sont donc inacceptables. Les recidives d’ulceres plantaires qui augmentent le risque d’amputation sont fortement liees a la difficulte d’obtenir une decharge d’une zone a risque du pied et surtout le maintien de cette decharge sur le long terme. Vu leur complexite d’utilisation au quotidien, les dispositifs de decharges disponibles actuellement sont tres peu prescrits par les specialistes et tres peu portes par les patients, avec une adherence therapeutique tres basse.Cet article resume la problematique de decharge du pied diabetique et decrit le concept de chaussures intelligentes que nous avons developpees, base sur la mesure et l’adaptation permanente et automatique de la raideur de la semelle en fonction de la vie quotidienne des patients.

The proposed paper discusses the design and characterization of a soft miniature Magneto-Rheological (MR) shock absorber. In particular, the final application considered for the insertion of the designed devices is a controllable variable stiffness sole for patients with foot neuropathy. Such application imposes particularly challenging constraints in terms of miniaturization (cross-sectional area ≤ 1.5 cm2, height ≤ 25 mm) and high sustainable loads (normal loads up to 60 N and shear stresses at the foot/device interface up to 80 kPa) while ensuring moderate to low level of power consumption. Initial design considerations are done to introduce and justify the chosen novel configuration of soft shock absorber embedding a MR valve as the core control element. Successively, the dimensioning of two different MR valves typologies is discussed. In particular, for each configuration two design scenarios are evaluated and consequently two sets of valves satisfying different specifications are manufactured. The obtained prototypes result in miniature modules (external diam. ≤ 15 mm, overall height ≤ 30 mm) with low power consumption (from a minimum of 63 mW to a max. of 110 mW) and able to sustain a load up to 65 N. Finally, experimental sessions are performed to test the behaviour of the realized shock absorbers and results are presented.

The proposed work discusses and compares different typologies of Magneto-Rheological (MR) valves. The analysis is performed following a design methodology which imposes the magnetic induction over the MR fluid surface and the maximum induction crossing the iron cores. Coil dimensioning is also considered as an important design factor. An analytical model is developed for each of the studied MR valve geometries and evaluation criteria as the volume to maximum sustainable pressure ratio, the dynamic range, the efficiency and the reactivity are used to compare the different valve designs. Annular configurations, radial valves and valves combining radial and annular channels are discussed and their performances are compared. As a final step, finite element analysis are performed for the different typologies considered in order to validate the results obtained from the derived analytical models.

Magneto-Rheological Elastomers (MREs) represent emerging composite materials consisting of small magnetic particles dispersed in a highly elastic polymeric matrix. Particles interactions with external fields (magnetic and electric) and external stresses result in a variation of rheological and physical properties of the material. In particular, MRE samples exhibit piezoresistivity, i.e. a change in the intrinsic material resistivity if subjected to an external stress. While literature reports experimental sessions aimed to establish the MREs piezoresistive characteristics and sensing capabilities, tests assessing the presences of hysteresis and cyclic drifts for multiple loading/unloading cycles of the MREs are not diffused. Nevertheless, these information are crucial to establish the quality and reliability of a sensing system. The presented work addresses the investigation of such parasitic phenomena for different MRE samples in order to assess their existence and relevance, to provide a more detailed and comprehensive description of the MRE piezoresistive effect as well as to enlighten further important elements useful to determine the possibility of using such materials for the realization of force or pressure sensors.

Magneto-Rheological Fluids (MRFs) are smart materials whose physical properties can be controlled by an exciting magnetic field. MRFs are described as Bingham plastics with variable magnetic field dependent yield stress. Thanks to their particular features, MRFs have been largely employed to realize controllable power dissipating devices and, among them, regulable valves without moving parts. The most commonly configuration used for MRF based valves consists on fluid flow through an annular duct. The conception of such valves implies to deal with different physics. In particular, the magnetic circuit is usually designed and verified by mean of FE (Finite Element) analysis, while the duct geometry is usually dimensioned using an approximated formula based on fluid flow between parallel plates.In the presented work, a complete and detailed derivation of the analytical model is discussed in order to describe the flow of MRFs through an annulus using an approximate parallel plate geometry. Successively, the Bingham-Papanastasiou regularization is chosen as the mean to accurately describe the continuous non-linear yield stress and shear dependent viscosity of a commercially available MRF and it is then implemented into a FE software. This step allows to built a complete multiphysics problem for the design of MRFs based devices.Results obtained from the analytical model and FE analysis are then compared and the different steps in the proposed approaches are validated.