Optimization of the Coupling Coefficient of the Inductive Link for Wireless Power Transfer to Biomedical Implants

This work focuses on the optimization of coupling coefficient (k) of the inductive link for the wireless power transfer (WPT) system to be used in implantable medical devices (IMDs) of centimeter size. The analytic expression of k is presented. Simulations are conducted by using the high-frequency structure simulator (HFSS). Analytic results are verified with simulations. The receiving (Rx) coil is implanted in the body and set as a circular coil with a radius of 5 millimeters for reducing the risk of tissue inflammation. The inductive link under misalignment scenarios is optimized to improve k. When the distance between the transmitting (Tx) and Rx coils is fixed at 20 mm, it is found that, to maximize k, the Tx coil in a planar spiral configuration with an average radius of 20 mm is preferred, and the Rx coil in a solenoid configuration with a wire pitch of 0.7 mm is recommended. Based on these optimization results, an inductive link WPT system is proposed; the coupling coefficient k, the power transfer efficiency (PTE), and the maximum power delivered to the load (MPDL) of the system are obtained with both simulation and experiment. Different media of air, muscle, and bone separating the Tx and Rx coils are tested. For the muscle (bone) medium, PTE is 44.14% (43.07%) and MPDL is 145.38 mW (128.13 mW), respectively.

A TLM Formulation Based on Fractional Derivatives for Dispersive Cole-Cole Media

An auxiliary differential equation (ADE) transmission line method (TLM) is proposed for broadband modeling of electromagnetic (EM) wave propagation in biological tissues with the Cole-Cole dispersion Model. The fractional derivative problem is surmounted by assuming a linear behavior of the polarization current when the time discretization is short enough. The polarization current density is approached using Lagrange extrapolation polynomial and the fractional derivation is obtained according to Riemann definition of a fractional α -order derivative. Reflection coefficients at an air/muscle and air/fat tissues interfaces simulated in a 1-D domain are found to be in good agreement with those obtained from the analytic model over a broad frequency range, demonstrating the validity of the proposed approach.

Soft robot development: Air muscle for rehabilitation robotic application

Physiotherapy is a science which acts in the area of biomechanical and functional disorder, establishing diagnostics and supporting the locomotor system rehabilitation. These procedures require assistance of a physiotherapist, however they are insufficient for the country´s demand. Usually such procedures use devices with the newest technology, in order to enable recovery and avoid possible permanent trauma. In order to face this reality, we have committed to develop an air muscle, based on the McKibben´s model, with the purpose of proposing a new low-cost parallel robot to physiotherapy (Soft Robot) for the rehabilitation of patients with ankle injuries. This robot is responsible for moving three degrees of freedom platform, therefore acting directly in the rehabilitation of the patient through the execution of soft and accurate therapeutic movements that stimulate the recovery of operated tissues. First, it is build an air muscle that will be used as actuator in parallel platform. Then is raised a curve of behavior to shift versus pressure on proposed muscle. In conjunction with these data to actuator behavior is modelled and simulated the new parallel robot. This air muscle was build using a latex tube covered by a braided fibred mesh and fuelled by a pneumatic tire valve, therefore obtaining a nonlinear behavior of contraction to each pressure value admitted on muscle. By means of this prototype building purpose, we obtained satisfactory results, such as a contraction of 25% of the nominal length for pressures up to six bars. Considering such a result and the low cost involved building actuator as this one, the advantage in using this model is perceptible.

Myoelectric Prosthetic Hand with Air Muscles

Prosthesis development was historically been done in order to find a matching replacement for a human hand which is unique in exhibiting its dexterous properties. Prosthesis controls that are established with the help of heavy motors make it a very complex actuation mechanism with relatively less power and efficiency. This paper describes an EMG – activated, tendon-driven, air muscle mechanism which delivers, relatively high power to weight ratio with higher efficiency by mimicking human muscle motion. The EMG signal is acquired from the skin surface by surface EMG electrodes and is conditioned using the basic techniques. Using a spring-loaded mechanism the weight of the hand prosthesis is kept to a minimum. Air muscles are used in for better control and to improve power to weight ratio. The flexion movements are achieved with a nylon string (tendon).

Implementation of Pneumatic Air Muscle for Actuating Knee Exoskeleton Using Four-Bar Linkage

The knee exoskeleton is a device that assists users with weak knees to walk. It consists of a mechanical construction put around the human knee which is equipped with an actuator for movement. One mechanism that can be used to mimic movement of the real knee is the four-bar linkage. This research explores the possibility of using pneumatic air muscles as actuators for a knee exoskeleton with four-bar linkage implementation. A pneumatic air muscle is a single-acting linear actuator that contracts when filled with pressurized air, mimicking muscle contraction. It is much lighter than electrical motors, but—according to characterization done in this research—is difficult to control due to its inconsistent torque output. Nevertheless, this research shows that simple gait movements can be simulated using a knee exoskeleton actuated by pneumatic air muscles with an on-off control scheme.

A McKibben Type Sleeve Pneumatic Muscle and Integrated Mechanism for Improved Stroke Length

Sleeve pneumatic muscles have shown significant performance improvements over conventional air muscle design, offering increased energy efficiency, force output, and stroke length, while allowing the actuator to become a structural component. However, there remain comparatively few studies involving sleeve muscles, and current applications have not focused on their potential advantages for joints actuated antagonistically with two muscles or their application to a more general class of pneumatic artificial muscle. This research presents a modular sleeve muscle design using the McKibben type construction, with a separate membrane and braid. To further increase stroke length, an internal pulley mechanism is implemented. The performance of the sleeve muscle is compared to an equivalent unaltered muscle and shows substantial improvements in force output, stroke length, and energy efficiency. Further testing shows that the internal pulley mechanism increased the effective stroke length by 82%, albeit at the cost of reduced maximum force output.

Design of a Soft Multi-Degree of Freedom Tool Positioner With Variable Stiffness Integrating Molded Air Muscles Actuation, Granular Jamming and Dielectric Elastomer Sensing

Soft technology is more and more present in robotics allowing safe interaction with humans, high dexterity in constrained environments, and safe manipulation of fragile or undefined objects. However, soft robotics is limited by a fundamental trade-off between available workspace and stiffness. Position feedback is also challenging as soft robots generally use deformable mechanisms instead of discrete joints. Here, the design of a soft four-degree-of-freedom tool positioner integrating a brake system and a soft sensor is proposed to address these issues. The design integrates molded air muscle actuators, granular jamming brakes, and Dielectric Elastomer Sensors (DES). The design is experimentally validated based on the requirements of a manipulator for liver cancer treatment, which is a representative application of soft robotics. The use of granular jamming mitigates the fundamental trade-off of soft robotics as it allows the manipulator to reach a large workspace (1500 cm3) while having the capacity to provide a high stiffness (up to19 times the initial stiffness). DES provides satisfactory position feedback, demonstrating a 0.69 mm accuracy that is lower than the 1 mm requirement. The proposed design using granular jamming and DES could greatly benefit human-safe and medical robotics.

Design of a Durable Air-Muscle With Integrated Sensor for Soft Robotics

Soft robotics integrates compliant actuators and sensors that expand design possibilities beyond classic robotics based on rigid modular components. In particular, deformable elastomer-based actuators used in soft robots, such as air-muscles, offer the possibility of having large numbers of embedded degrees of freedom. However, air-muscles fatigue life and strain capability call for a tradeoff, limiting their practical use in demanding applications such as physical rehabilitation, medical robotics, and mobile robots. This paper presents the design of a durable high-strain air-muscle composed of a silicone tube and an axially elastic sleeve (radially rigid), which integrates a flexible Dielectric Elastomer (DE) position sensor. The uniformity of the sleeve, by opposition to usual braids, makes for a reinforcement without local stresses that cause membrane failure. Designed based on fatigue failure principles, this air-muscle withstands 145 000 cycles at 50 % elongation, which demonstrates its potential as a durable high-strain actuator. Performance maps of the air-muscle confirm good linearity between force, pressure and strain and demonstrate bi-directional force capability. Furthermore, the integration of a DE sensor allows for accurate position control of the air-muscle (0.17 mm), making the air-muscle/sensor unit a relevant building block for complex soft robotics systems. The all-polymer high-strain actuator/sensor unit proves to be accurate and durable as well as cost-effective, thus making it ideal for soft robotics applications requiring large numbers of actuators and integrated sensing.