Control of objects using remotely generated magnetic fields has established itself as a viable option for 3D position control, though the objects being manipulated to date have largely been limited to soft and hard-magnetic objects that react to a static magnetic field. This limits the application to a small subset of materials. This work presents the first analytically derived model for 3D position control of any electrically conductive material subject to a time-varying magnetic field. By leveraging the induced eddy current and subsequent induced dipole, this model shows that conductive materials behave equivalently to diamagnetic materials and are therefore not subject to the limitations of Earnshaw's theorem, making stable, open-loop levitation possible. This is demonstrated by open-loop position control of a semi-buoyant aluminum sphere.

Deep Brain Stimulation is used to treat Parkinson's disease and other neurological disorders by implanting an electrode into the brain via a straight-path needle insertion. Enabling course correction and curved trajectories by using a steerable needle has the potential to improve operative outcomes. In this work, a physically motivated dynamic model for an actively steered magnetic-tipped needle is derived. Process and measurement noise covariances and model parameter curvature gain are identified using an expectation-maximization (EM) algorithm. Parameter convergence and accuracy are evaluated, and an RMS position trajectory accuracy of 0. 81 mm is calculated for expected conditions. The EM algorithm converged for expected parameter variations in simulation, which supports the EM implementation's use in identifying the parameters of the model in a physical system.

Underground environments present their unique challenges for wireless communication. This paper presents an empirical study of WiFi performance where aerial-ground robots are used to map, navigate, and search in an unknown underground environment. While wireless signal attenuates significantly around corners, WiFi's overall performance is encouraging.

Shape shifting soft microrobots are generated from self-folding hydrogel bilayer structures. The folding conditions are analyzed to develop an optimal strategy for producing desired three-dimensional shapes. We present two different methods for programming magnetization in these microrobots that are variant and invariant to folding. The microrobots can be navigated through user-defined trajectories using rotating magnetic fields, and the morphing in response to temperature changes can be tuned for adaptive behavior. On-demand modulation of the mobility of individual microrobots is demonstrated by morphing their shape using selective near infrared light (NIR) exposure.

A magnetic-tip steerable needle is presented with application to aiding deep brain stimulation electrode placement. The magnetic needle is 1.3mm in diameter at the tip with a 0.7mm diameter shaft, which is selected to match the size of a deep brain stimulation electrode. The tip orientation is controlled by applying torques to the embedded neodymium-iron-boron permanent magnets with a clinically-sized magnetic-manipulation system. The prototype design is capable of following trajectories under human-in-the-loop control with minimum bend radii of 100mm without inducing tissue damage and down to 30mm if some tissue damage is tolerable. The device can be retracted and redirected to reach multiple targets with a single insertion point.

This paper presents a method to localize a magnetically guided catheter using a single rotating C-Arm. Because the three dimensional position of the catheter tip, when extracted from a single view, contains large uncertainties, we propose to combine multiple views by rotating the C-Arm and using a Kalman filter. The proposed approach yields good tracking performance for several catheter poses and reduces the maximum estimated standard deviation to 0.3 cm after incorporating six views. This represents a 62 percent reduction in three dimensional position uncertainty.

This is the first demonstration of a modular and reconfigurable magnetic-manipulation system with integral ferromagnetic material. This system-which includes multiple Omnimagnets, each comprising three orthogonal solenoids and a spherical ferromagnetic core-is capable of dexterous manipulation of a magnetic tool. The magnetization coupling of an arbitrary arrangement of spherical ferromagnetic cores is solved, enabling an analytical solution for the magnetic forces and torques. Thus, the system does not require extensive field maps or in situ field characterization. If the positions and orientations of the Omnimagnets are sensed, the Omnimagnets can be actively rearranged during manipulation while maintaining control of the tool. This could enable new capabilities in medical procedures because the manipulation system can be modified to accommodate the imaging systems and enable physician access without loss of control. The capabilities of this system are demonstrated through five-degree-of-freedom manipulation (position and heading) of a permanent-magnetic tool with several arbitrary Omnimagnet configurations.

Numerous magnetic-manipulation systems have been developed to control objects in relatively large workspaces. These systems vary in their number of electromagnets, their configuration, and their limitations. To date, no attempt has been made to rigorously quantify how many electromagnets are required to perform a given magnetic manipulation task. For some tasks, such as controlling the field at a point, the answer is clear: the same number as dimension of control. For tasks that apply magnetic forces on an object, the answer is less clear, and some systems, which have more control magnets than kinematic degrees of freedom (DOFs), have demonstrated unexpected singularities that only arise at specific object orientations. This paper provides a general analysis for static electromagnetic systems rooted in the governing magnetic equations and proves an unintuitive result. That is, if only magnetic fields and forces are used to control an unconstrained magnetic object, four magnetic sources are required for 3-DOF force control and eight magnetic sources are required for orientation-independent 5-DOF force and heading control.

In this paper, we examine several magnetic control methods that utilize the fully controllable dipole field generated by the single stationary dipole source. Since the magnetic field generated by a dipole source is nonuniform, it applies both forces and torques to magnetic objects and can be used to manipulate magnetic tools. Recently, the Omnimagnet, a computer-controlled magnetic dipole source capable of varying both its dipole-moment direction and magnitude, was developed to perform magnetic manipulation. The equations and methods are developed generally; therefore, they can be applied to any omnidirectional dipole source, but their effectiveness is demonstrated using the Omnimagnet.

An Omnimagnet is an omnidirectional electromagnet comprised of a ferromagnetic core inside of three orthogonal nested solenoids. It generates a magnetic dipole-field with both a variable dipole-moment magnitude and orientation with no moving parts. The design of an Omnimagnet, in which each solenoid has the same dipole moment and minimizes the differences between each of the solenoid's fields, is provided and optimized for strength by tailoring the size of the spherical core used to amplify the solenoids' field. This design is then analyzed using FEA tools and shown to be dipole-like in nature. Various magnetic control methods are then motivated by providing the necessary equations relating the three applied currents to applied field, torque, or force on an adjacent magnetic device. Finally, the optimal design is constructed and its utility is demonstrated by driving a helical capsule endoscope mockup through a transparent lumen.

A method for estimating limb orientation, during static, quasi-static, and dynamic motions, by using a combination of gyroscopes and accelerometers is presented. The method uses two tri-axis accelerometers and one single axis rate gyro to calculate an estimate of angle relative to the gravitational vector independently from the rotational accelerations. This unbiased inclination estimate is blended with the angular velocity and acceleration measurements using a Kalman filter to obtain the final estimated orientation. Initially developed for implementation in a feedback control loop for control of sit-to-stand transitions in felines during direct electrical stimulation of the sciatic nerve, the method can be directly applied to other limb angle measurement tasks such as human gait analysis. The algorithm and sensor is tested on a rotational linkage with a predefined trajectory and compared to an encoder measurement with good agreement.