Marco Soares dos Santos

Magnetic levitation-based electromagnetic energy harvesting: a semi-analytical non-linear model for energy transduction.

Magnetic levitation has been used to implement low-cost and maintenance-free electromagnetic energy harvesting. The ability of levitation-based harvesting systems to operate autonomously for long periods of time makes them well-suited for self-powering a broad range of technologies. In this paper, a combined theoretical and experimental study is presented of a harvester configuration that utilizes the motion of a levitated hard-magnetic element to generate electrical power. A semi-analytical, non-linear model is introduced that enables accurate and efficient analysis of energy transduction. The model predicts the transient and steady-state response of the harvester a function of its motion (amplitude and frequency) and load impedance. Very good agreement is obtained between simulation and experiment with energy errors lower than 14.15% (mean absolute percentage error of 6.02%) and cross-correlations higher than 86%. The model provides unique insight into fundamental mechanisms of energy transduction and enables the geometric optimization of harvesters prior to fabrication and the rational design of intelligent energy harvesters.

Novel intelligent real-time position tracking system using FPGA and fuzzy logic

The main aim of this paper is to test if FPGAs are able to achieve better position tracking performance than software-based soft real-time platforms. For comparison purposes, the same controller design was implemented in these architectures. A Multi-state Fuzzy Logic controller (FLC) was implemented both in a Xilinx(®) Virtex-II FPGA (XC2v1000) and in a soft real-time platform NI CompactRIO(®)-9002. The same sampling time was used. The comparative tests were conducted using a servo-pneumatic actuation system. Steady-state errors lower than 4 μm were reached for an arbitrary vertical positioning of a 6.2 kg mass when the controller was embedded into the FPGA platform. Performance gains up to 16 times in the steady-state error, up to 27 times in the overshoot and up to 19.5 times in the settling time were achieved by using the FPGA-based controller over the software-based FLC controller.

Instrumented hip implants: Electric supply systems

Instrumented hip implants were proposed as a method to monitor and predict the biomechanical and thermal environment surrounding such implants. Nowadays, they are being developed as active implants with the ability to prevent failures by loosening. The generation of electric energy to power active mechanisms of instrumented hip implants remains a question. Instrumented implants cannot be implemented without effective electric power systems. This paper surveys the power supply systems of seventeen implant architectures already implanted in-vivo, namely from instrumented hip joint replacements and instrumented fracture stabilizers. Only inductive power links and batteries were used in-vivo to power the implants. The energy harvesting systems, which were already designed to power instrumented hip implants, were also analyzed focusing their potential to overcome the disadvantages of both inductive-based and battery-based power supply systems. From comparative and critical analyses of the methods to power instrumented implants, one can conclude that: inductive powering and batteries constrain the full operation of instrumented implants; motion-driven electromagnetic energy harvesting is a promising method to power instrumented passive and active hip implants.

Active orthopaedic implants: Towards optimality

Abstract Although everlasting life span is a primary requirement for orthopaedic implants, their current rate of failure is relatively high. The fundamental problem of implementing optimal implants remains a top research topic. No methodology to ensure everlasting life span of orthopaedic implants has ever been proved. Joint prostheses are only being designed to operate passively, only restoring joint function. Instrumented implants have not been designed as full interactive mechanisms with the surrounding physiological environment. The purpose of this paper is twofold: (1) to prove that non-instrumented passive implants and instrumented passive implants are not able to optimize the minimization of the failures throughout the lifetime of the implants, whatever the optimization level of the implants, rehabilitation protocols or surgical procedures; and (2) to prove that active implants ensure performance optimality preventing failures. Research in the design of active implants is thus proposed as an effective methodology to characterize failures and to perform therapeutic actuations in real-time, ensuring optimal trajectories from states of failure to states of without-failure.

Instrumented hip joint replacements, femoral replacements and femoral fracture stabilizers

This paper reviews instrumented hip joint replacements, instrumented femoral replacements and instrumented femoral fracture stabilizers. Examination of the evolution of such implants was carried out, including the detailed analysis of 16 architectures, designed by 8 research teams and implanted in 32 patients. Their power supply, measurement, communication, processing and actuation systems were reviewed, as were the tests carried out to evaluate their performance and safety. These instrumented implants were only designed to measure biomechanical and thermodynamic quantities in vivo, in order to use such data to conduct research projects and optimize rehabilitation processes. The most promising trend is to minimize aseptic loosening and/or infection following hip or femoral replacements or femoral stabilization procedures by using therapeutic actuators inside instrumented implants to apply controlled stimuli in the bone–implant interface.

Instrumented knee joint implants: innovations and promising concepts

This article focuses on in vivo implementations of instrumented knee implants and recent prototypes with highly innovative potential. An in-depth analysis of the evolution of these systems was conducted, including three architectures developed by two research teams for in vivo operation that were implanted in 13 patients. The specifications of their various subsystems: sensor/transducers, power management, communication and processing/control units are presented, and their features are compared. These systems were designed to measure biomechanical quantities to further assist in rehabilitation and physical therapy, to access proper implant placement and joint function and to help predicting aseptic loosening. Five prototype systems that aim to improve their operation, as well as include new abilities, are also featured. They include technology to assist proper ligament tensioning and ensure self-powering. One can conclude that the concept of instrumented active knee implant seems the most promising trend for improving the outcomes of knee replacements.

Multi-source Harvesting Systems for Electric Energy Generation on Smart Hip Prostheses

The development of smart orthopaedic implants is being considered as an effective solution to ensure their everlasting life span. The availability of electric power to supply active mechanisms of smart prostheses has remained a critical problem. This paper reports the first implementation of a new concept of energy harvesting systems applied to hip prostheses: the multi-source generation of electric energy. The reliability of the power supply mechanisms is strongly increased with the application of this new concept. Three vibration-based harvesters, operating in true parallel to harvest energy during human gait, were implemented on a Metabloc TM hip prosthesis to validate the concept. They were designed to use the angular movements on the flexion-extension, abduction-adduction and inward-outward rotation axes, over the femoral component, to generate electric power. The performance of each generator was tested for different amplitudes and frequencies of operation. Electric power up to 55 μJ/s was harvested. The overall function of smart hip prostheses can remain performing even if two of the generators get damaged. Furthermore, they are safe and autonomous throughout the life span of the implant.

New cosurface capacitive stimulators for the development of active osseointegrative implantable devices

Non-drug strategies based on biophysical stimulation have been emphasized for the treatment and prevention of musculoskeletal conditions. However, to date, an effective stimulation system for intracorporeal therapies has not been proposed. This is particularly true for active intramedullary implants that aim to optimize osseointegration. The increasing demand for these implants, particularly for hip and knee replacements, has driven the design of innovative stimulation systems that are effective in bone-implant integration. In this paper, a new cosurface-based capacitive system concept is proposed for the design of implantable devices that deliver controllable and personalized electric field stimuli to target tissues. A prototype architecture of this system was constructed for in vitro tests, and its ability to deliver controllable stimuli was numerically analyzed. Successful results were obtained for osteoblastic proliferation and differentiation in the in vitro tests. This work provides, for the first time, a design of a stimulation system that can be embedded in active implantable devices for controllable bone-implant integration and regeneration. The proposed cosurface design holds potential for the implementation of novel and innovative personalized stimulatory therapies based on the delivery of electric fields to bone cells.

Improvement on control performance using FPGAs over software-based platforms

No studies about the evaluation of the performances achieved by FPGAs over software-based controllers have been reported. The main aim of this paper is to identify which of the FPGA-based or software-based soft real-time platforms is able to achieve better position tracking performance of servo-pneumatic systems. A Fuzzy Logic controller was implemented both in a Xilinx® Virtex-II FPGA and in a soft real-time platform NI CompactRIO®-9002. The tracking response of 20 step trajectories was analysed. The FPGA-based controller achieved up to 16 times lower steady-state errors and up to 27 times lower overshoots. These experimental results have shown performance gains associated with the use of FPGA technologies over software-based soft real-time platforms.

Bridging the gap between advanced control methods and industrial control applications: Shortcomings of the current nonlinear PID Method and new research lines to its enhancing

As the performance requirements become more demanding and the plants become more and more complex, control designers were naturally forced to look beyond traditional linear control theory and attempt to find more advanced nonlinear methods. However, it has been very difficult to overcome the huge gap between the current knowledge, researched by the scientific automatic control community, and its application in the industrial environment. In this paper, it is proposed to consider the nonlinear PID as the method to deal with this hitch. The current nonlinear PID methodologies were reviewed and their shortcomings presented. The main aim is to objectify new research lines that may enhance it, in order to ensure that the evolution of industrial control systems is strongly linked to that of the control techniques.