External Electromagnetic Coils Research Articles

Mitigating Singularities in Control of Magnetic Capsule Endoscopes Using a Novel Nested Electromagnetic Coil System

Magnetic actuation systems that utilize external electromagnetic coils present a promising approach for controlling untethered small-scale robots, notably in medical applications. However, these systems frequently experience actuation singularities at which robotic control over the agent is lost or severely diminished. Such singularities may lead to excessively large current or rapid current changes that significantly affect the robots’ stability in specific areas of the workspace. In order to effectively mitigate these actuation singularities, this paper introduces a closed-loop control method using a novel nested electromagnetic coil system, leveraging finite element analysis-based magnetic field data and a novel controller combining a singularity solver and optimal current control method. The electromagnetic system has 12 coils nested in four coil units, each having three concentric coils with different outer radius, surrounding a central workspace. We call the 12-coil system Variable Outer Radius Individually Addressable Coil Stacks (VORIACS). Here, we experimentally evaluate the method for closed-loop trajectory tracking of a soft magnetic capsule endoscope (PillCam™) and a permanent magnet robot inside the VORIACS system at different magnetic field orientations. The results demonstrate that the VORIACS system with a singularity solver reduces root mean square (RMS) position tracking errors of the PillCam™by 46% to 50% and orientation tracking errors by 41% to 42% compared to a standard 4-coil system. Moreover, the system can achieve a notable 60.73% reduction in RMS position error, with sub-millimeter precision control when controlling the permanent magnet robot. We further manipulate the PillCam™for tracking a medical application-inspired complex trajectory, showcasing the system’s potential in precise control of magnetic devices for medical use.

Investigation of the torque transmission time constant of a multi-disc magnetorheological clutch in the case of ramp function excitation

In this work the torque transmission time constant of a multi-disc magnetorheological (MR) fluid clutch is presented. The self-built clutch contains six layers of MR fluid and it is excited by an external electromagnetic coil. The transmitted torque is measured by a torque sensor using a self-developed LabVIEW software. Torque transmission is measured using ramp excitation with different slopes. The time constant of the clutch is derived from the time delay of the torque response. Our measurements showed the time constants as a hyperbolic function of the slope of the ramp excitation.

Non-invasive measurement of floating–sinking motion of a large object in a gas–solid fluidized bed

A Lagrangian sensor system has been established to non-invasively measure both the vertical position and dynamic force acting on itself. It consists of a 3-axis acceleration sensor, a 3-axis magnetometer, a microcontroller, a wireless module, batteries, and external electromagnetic coils. In this study, we applied the system to a free-moving coarse object in a gas–solid fluidized bed. The floating and sinking motions of the object in the fluidized bed are essentially caused by differences between its density and the apparent density of the fluidized media. However, the object sometimes shows strange behavior under the influence of variance in the fluidization state. We measured the temporal change of the upward force acting on the object as well as the vertical position, which is invisible from the outside. The experimental results indicate that the force acting on the object differs significantly between the floating and sinking states and is greatly complicated by interference with rising bubbles in the fluidized bed. The probability density of the vertical position of the object shows that its motion is explained not only by hydrostatic effects, but also by inhomogeneity of the fluidization state in the bed.

Growing Without Pain: The Noninvasive Expandable Prosthesis is Boon for Children with Bone Cancer, as well as Their Surgeons!

Background:Orthopedic oncology has evolved over the past few decades to favor limb salvage over amputations. The noninvasive expandable prosthesis can be lengthened with an externally applied magnetic field eliminating the pain, stiffness, as well as the risk of infection. We present the largest series in Indian experience with this implant over the last 8 years while analyzing its benefit to the surgeons and the patients, but are we able to justify the cost effectiveness?Materials and Methods:Eighteen implants were used in 16 patients with nonmetastatic primary bone sarcoma from May 2006 to June 2015. All implants were manufactured by Stanmore implants worldwide based in London, UK. Lengthening was done in the outpatient department during the followup visits using an external electromagnetic coil. The function was assessed using the musculoskeletal tumor society (MSTS) score.Results:The patients had a mean age of 10.25 years at the time of surgery. The mean followup was 49.56 months. Twelve patients are alive at a followup after surgery. The prostheses were lengthened by a mean of 31.64 mm and average lengthening per session was 4.18 mm. The mean MSTS score was 28.83. Two revisions for jammed mechanism and two patients had a successful two-stage revision for delayed infection.Conclusion:The noninvasive expandable prosthesis is an ideal implant for children undergoing limb salvage surgery for bone sarcoma who are expected to have more than 3 cm of limb length discrepancy at maturity. The initial high cost compared to a minimally invasive expandable implant can be recovered as there is no additional cost of lengthening. The small amounts of lengthening at more frequent intervals is more physiological as compared with the minimally invasive type where more lengthening is done to minimize the number of procedures. While the functional and oncological outcomes are comparable, this implant allows limb lengths to be maintained without pain, functional compromise or risk of infection.

Simulation of DNA extraction and separation from salivary fluid by superparamagnetic beads and electromagnetic field in microfluidic platform

The conceptual simulation study of DNA extraction and separation from salivary fluid sample are mainly divided into two parts. The initial study covered microfluidic channel design and effective DNA extraction by using mobilizing superparamagnetic (SPM) beads in COMSOL Multiphysics® software. The subsequent part presented simulation work for DNA separation from SPM beads in electromagnetization field. The main objective of this study in microfluidic platform in presence of electromagnetic field was to achieve higher and uncontaminated yield of DNA as sample preparation step which can be applied for clinical analysis. COMSOL Multiphysics® simulation software was used to study the entire work and presented in this paper with complete study steps. The attached DNA onto SPM beads was separated by specifying computational fluid dynamics in laminar flow, particle tracing module and electromagnetic field by using external electromagnetic coil as magnet array. Most of the SPM beads were captured and held by magnetic field when 100 mT/min was generated by electromagnetic coil. 82.01% of uncontaminated DNA yield from salivary fluid was able to separate from SPM beads after DNA extraction in microfluidic channel. In the absence of external magnetic field, the produced superparamagnetism enable SPM beads to flip in an isotropy provide efficient separation. The mechanical and chemical stability of silica surface of SPM beads provide an excellent chromatography separation medium for DNA sample preparation for further downstream analysis.

Polymer filament–based in situ microrobot fabrication using magnetic guidance

In this article, we present a new three-dimensional printing inspired method for in situ fabrication of mobile magnetic microrobots with complex topology by bending a polymer filament on demand directly inside an enclosed operational environment. Compared with current microrobot fabrication methods that typically involve multiple microfabrication steps and complex equipment, the proposed method is simply and fast. The target shape is formed as the filament is fed through a hot needle inserted into the workspace, and the filament bending moment is induced by attaching a tip magnet at the end of the filament and projecting magnetic fields wirelessly from external electromagnetic coils. The filament bending mechanics and the behavior of the bending zone are analyzed and verified through bending experiment. A shape planner is developed for automatically controlling the fabrication process of any desired planar shapes, and the shape creation potential of this method is also studied. Magnetically active millimeter-scale robotic devices of different planar shapes are fabricated using polylactic acid filament with diameter as small as 100 μm. As demonstrations of the in situ formation of functional microrobotic devices, a micro-gripper is fabricated and controlled to assemble a cell cage. A micro-spring is created as a manipulating tool with force sensing capability. We, thus, show the utility of the fabrication method for creating complex microrobot shapes remotely in enclosed environments for advanced microrobotic applications, with the potential for scaled down applications in health care and microfluidics.

Note: On-chip multifunctional fluorescent-magnetic Janus helical microswimmers.

Microswimmers integrated into microfluidic devices that are capable of self-illumination through fluorescence could revolutionize many aspects of technology, especially for biological applications. Few illumination and propulsion techniques of helical microswimmers inside microfluidic channels have been demonstrated. This paper presents the fabrication, detachment, and magnetic propulsions of multifunctional fluorescent-magnetic helical microswimmers integrated inside microfluidics. The fabrication process is based on two-photon laser lithography to pattern 3-D nanostructures from fluorescent photoresist coupled with conventional microfabrication techniques for magnetic thin film deposition by shadowing. After direct integration inside a microfluidic device, injected gas bubble allows gentle detachment of the integrated helical microswimmers whose magnetic propulsion can then be directly applied inside the microfluidic channel using external electromagnetic coil setup. With their small scale, fluorescence, excellent resistance to liquid/gas surface tension, and robust propulsion capability inside the microfluidic channel, the microswimmers can be used as high-resolution and large-range mobile micromanipulators inside microfluidic channels.

Low temperature magnetron sputter deposition of polycrystalline silicon thin films using high flux ion bombardment

We demonstrate that the microstructure of polycrystalline silicon thin films depends strongly on the flux of low energy ions that bombard the growth surface during magnetron sputter deposition. The deposition system is equipped with external electromagnetic coils which, through the unbalanced magnetron effect, provide direct control of the ion flux independent of the ion energy. We report the influence of low energy (<27eV) Ar+ on the low temperature (<450°C) growth of polycrystalline silicon thin films onto amorphous substrates. We use spectroscopic ellipsometry, Raman scattering, x-ray diffraction, and cross sectional transmission electron microscopy to analyze the film microstructure. We demonstrate that increasing the flux ratio of Ar+ ions to silicon neutrals (J+∕J0) during growth by an order of magnitude (from 3 to 30) enables the direct nucleation of polycrystalline Si on glass and SiO2 coated Si at temperatures below 400°C. We discuss possible mechanisms for this enhancement of crystalline microstructure, including the roles of enhanced adatom mobility and the formation of shallow, mobile defects.

Effects of assistant anode on planar inductively coupled magnetized argon plasma in plasma immersion ion implantation

The enhancement of planar radio frequency (RF) inductively coupled argon plasma is studied in the presence of an assistant anode and an external magnetic field at low pressure. The influence of the assistant anode and magnetic field on the efficiency of RF power absorption and plasma parameters is investigated. An external axial magnetic field is coupled into the plasma discharge region by an external electromagnetic coil outside the discharge chamber and an assistant cylindrical anode is inserted into the discharge chamber to enhance the plasma discharge. The plasma parameters and density profile are measured by an electrostatic Langmuir probe at different magnetic fields and anode voltages. The RF power absorption by the plasma can be effectively enhanced by the external magnetic field compared with the nonmagnetized discharge. The plasma density can be further increased by the application of a voltage to the assistant anode. Owing to the effective power absorption and enhanced plasma discharge by the assistant anode in a longitudinal magnetic field, the plasma density can be enhanced by more than a factor of two. Meanwhile, the nonuniformity of the plasma density is less than 10% and it can be achieved in a process chamber with a diameter of 600 mm.

Improved planar radio frequency inductively coupled plasma configuration in plasma immersion ion implantation

Plasmas with higher density and better uniformity are produced using an improved planar radio frequency (rf) inductively coupled plasma configuration in plasma immersion ion implantation (PIII). An axial magnetic field is produced by external electromagnetic coils outside the discharge chamber. The rf power can be effectively absorbed by the plasma in the vicinity of the electron gyrofrequency due to the enhanced resonant absorption of electromagnetic waves in the whistler wave range, which can propagate nearly along the magnetic field lines thus greatly increases the plasma density. The plasma is confined by a longitudinal multipolar cusp magnetic field made of permanent magnets outside the process chamber. It can improve the plasma uniformity without significantly affecting the ion density. The plasma density can be increased from 3×109 to 1×1010 cm−3 employing an axial magnetic field of several Gauss at 1000 W rf power and 5×10−4 Torr gas pressure. The nonuniformity of the plasma density is less than 10% and can be achieved in a process chamber with a diameter of 600 mm. Since the plasma generation and process chambers are separate, plasma extinction due to the plasma sheath touching the chamber wall in high-energy PIII can be avoided. Hence, low-pressure, high-energy, and high-uniformity ion implantation can be accomplished using this setup.

An Implantable Bone-Conduction Hearing Device

A new implantable hearing device that transmits an acoustical signal from an external electromagnetic coil to a small magnet implanted in the temporal bone has been developed and implanted in more than 350 patients. Animal research indicates that the device serves as a high-fidelity sound source throughout the audio range. Especially notable is its high-frequency performance. Human experiments using a body processor indicate that the device compares favorably with conventional bone conduction hearing aids, and patients report excellent sound quality as well as improved ability to understand conversational speech. Further development has resulted in an at-the-ear (ATE) processor. Extensive testing of the ATE unit has revealed that current models provide approximately 10 dB less output than the body processors. Further research and development are continuing to address the need for increased power output from the ATE processor and to eliminate other minor problems.