Design optimization of Miniature Magnetorheological Valves with Self-Sensing Capabilities Used for a Wearable Medical Application

Abstract

Magnetorheological (MR) fluids are materials characterized as "intelligent" since their rheological properties may be controlled by the excitation of an external magnetic field. The application of the latter brings the fluid from a liquid to a semi-solid state. Due to their properties, these materials are widely used, among others, in biomedical applications. In the present work, multiple MR valves are incorporated as pressure limiters in a smart biomedical insole for diabetic patients. The diabetics are affected by high plantar pressures that cause ulceration and frequently, as a consequence of ulceration, lower extremity amputation. This novel insole aims at the active plantar pressure offloading. Thus, considering the small size of the insole, the number of the valves, as well as the high plantar pressures that reach up to 1 MPa on diabetic feet, a study is performed on optimizing the design of the MR valve, exploiting the Design of Experiments (DoE) techniques. Moreover, a testbench is presented for the examination of pressure self-sensing capabilities of the valves, with a future goal to integrate them in the design optimization and acquire a sensorless system.

Optimization of Radial Magnetorheological Valves with Constraints of Volume, Pressure Drop and Power Consumption

“…Table II presents the optimal radial model parameters and compares them with an existing, not optimized radial valve prototype, fabricated based on previous studies [19]. In parallel, it shows, also, a comparison with the optimal annular valve model of our previous study [11] as well as with an annular valve prototype [19], in order to distinguish which configuration is more suitable for our wearable medical solution. In fact, the radial optimized model presents better characteristics compared to its corresponding prototype with regards to total volume, total pressure drop, flow rate, reactivity and power consumption, reducing total power consumption almost to half.…”

“…Table I includes the range of the above parameters. According to our previous study [11], the ratio hc/ht, where hc the height of the coil, does not have a significant effect on the optimal model and, thus, it is not taken into account as an optimization factor. The outer core external radius of the valve ro is set to the constant value 5.5 mm, in order to meet the constraints for sufficient pressure sensing resolution and system complexity [11].…”

“…1and (2) respectively. Then the pressure drop and the dynamic range of the valve were calculated using the following equations [14], [11]:…”

“…D is a figure of merit that indicates the operation range of the valve, ranging from free flow to a no flow. It is set to 5 in this case, leading to an approximation of c to 2.3 [11]. The volume V of the valve is calculated as:…”

“…As a consequence, ulcers are created on the plantar surface that can easily deteriorate and end up to a gangrene and an amputation. A first version of MR devices for this purpose, which act as pressure limiters has been designed [10], while the annular model of this version has already been optimized in our previous studies [11]. The pressure limiters appear in two states, the on-state, when the valve's coil is fed with current and the plantar load is sustained, and the off-state, when no Fig.…”