Three-axis Helmholtz Coil Research Articles

Far-Field Spatial Response of Off-Diagonal GMI Wire Magnetometers. Application to Magnetic Field Sources Sensing

Studying the spatial response of a single-axis magnetometer could be the key parameter to optimize the ultimate performances of magnetic heads of detection. Indeed, the problem of non-orthogonality, misalignment, and 3D spatial response could be improved based on the knowledge of the 3D sensor spatial response. In that way, we have investigated the latter for our giant magneto-impedance (GMI) magnetometer, as a far-field pattern, by using a three-axis Helmholtz coil system. Firstly, we calibrate our device and secondly, we apply a specific 3D magnetic field to obtain this pattern. The latter helps to observe the directional or angular dependence of the sensor sensitivity versus the applied magnetic field, as we exemplified. The results confirm the excellent directivity of our off-diagonal GMI magnetometer. The evaluation of the associated error compared to an ideal vector magnetometer is also given and discussed.

Simulation validation based on emission coil of three-axis square Helmholtz magnetic source

In electromagnetic detection, the received signal strength is largely determined by the transmitter’s signal strength. Therefore, it is necessary to select and design the transmitting coil to meet the requirements of the electromagnetic launching system. To obtain better-transmitting coils, Maxwell is used to establishing square and toroidal coil models for calculation and compare magnetic field intensity and uniformity. To cope with electromagnetic exploration in a complex environment, the electromagnetic field model of the three-axis toroidal coil and square Helmholtz coil is established. The magnetic field simulation results verify that the three-axis square Helmholtz coil has higher emission field intensity under the same excitation condition, which is suitable for electromagnetic exploration.

Design of A Three-axis Helmholtz Coil for Magnetic Sensor Calibration

Accurate measurement of magnetic sensor components is always an important issue in magnetic field applications, but there are unavoidable errors in the sensor system that need to be corrected before use. The common scalar correction method is difficult to effectively correct the sensor component because it requires a uniform and stable background magnetic field and depends on the magnetic field modulus. Therefore, a set of triaxial Helmholtz coils that can be used for sensor vector correction is designed to generate a controlled standard magnetic field. The design index of the coils, the size of the uniform zone, and the relationship between the magnetic field and the current were analyzed to provide a basis for the effective calibration of the sensor components. The measurement results show that the size of the uniform zone and the accuracy of the magnetic field of the coils designed in this paper meet the design requirements. Meanwhile, by using the coils in the calibration of the sensor array and the positioning of the magnetic target, the sensor error is reduced by three orders of magnitude, and the positioning accuracy of the magnetic target reaches 0.1 m with good practical effect.

Micromanipulation Using Reconfigurable Self-Assembled Magnetic Droplets With Needle Guidance

A dynamic self-assembly is a promising approach for inducing the collective behavior of agents to perform coordinated tasks at small scales. However, efficient pattern formation and navigation in environments with complex conditions remain a challenge. In this article, we propose a strategy for micromanipulation using dynamically self-assembled magnetic droplets with needle guidance. An iron needle was controlled by a three-degree-of-freedom (3-DoF) manipulator and magnetized by precessing magnetic fields. The process of self-assembly was optimized based on real-time vision feedback and a genetic algorithm. Affected by the locally induced field gradient near the needle, reconfigurable assembled magnetic droplets were formed beneath the air-liquid interface with high time efficiency, and the geometric center of the pattern was determined. Following the magnetized needle, assembled patterns were navigated along preplanned paths and exhibited reversible pattern expansion and shrinkage. Moreover, cargo can be trapped and caged by exploiting the induced fluid flow around the assembled droplets. To perform cargo transportation tasks in a multiple-obstacle environment, an optimal path planner with obstacle-avoidance capability was designed based on the particle swarm optimization (PSO) algorithm. Experiments demonstrated effective pattern formation, navigation, cargo trapping, and obstacle-avoidance transportation. The proposed method opens new prospects of using a dynamically self-assembled pattern as an untethered end-effector for micromanipulation. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —This article was motivated by the recent interest in utilizing the collective behavior of small-scale active agents to perform micromanipulation tasks. Driven by external magnetic fields, building blocks are gathered and assembled, yielding a dynamically stable pattern. To perform practical tasks, efficient pattern formation, control, and navigation are required. Besides, obstacles often exist in the working environment, challenging pattern navigation, and manipulation tasks. The strategy presented here is developed for micromanipulation using dynamically self-assembled magnetic droplets with needle guidance. The three-axis Helmholtz coil system is applied to rotate the droplets and magnetize the iron needle. Algorithms are designed to guide and optimize the pattern formation, navigation, and cargo trapping process. Magnetic droplets are real-time tracked, and ordered assembled patterns are formed in an optimized way. Following the needle, the pattern was navigated and performed cargo manipulation tasks with obstacle-avoidance capability. Experimental results have validated the proposed strategy in pattern formation, navigation, and cargo manipulation in a multiple-obstacle environment.

A Compensation Method for Magnetic Localization on Capsule Robot in Medical Application

Aiming at the magnetic positioning accuracy of capsule robot and the magnetic coupling between capsule robot and external driving magnetic field, according to the requirements of capsule robot for position and attitude information, a magnetic positioning compensation method of capsule robot based on magnetic driving system is proposed. This method deduces the error formula according to the magnetic dipole model, optimizes the formula, reduces the number of unknowns, optimizes the calculation process and improves the positioning accuracy. At the same time, a compensation is added to solve the magnetic coupling problem between the external driving magnetic field three-axis Helmholtz coil and the capsule robot. Finally, several groups of experiments verify the effectiveness of the algorithm.

Design and implementation of a novel wireless modular capsule robotic system in pipe

Capsule endoscopy is a new type of technology in the diagnosis and treatment of digestive diseases, with painless and low invasive features. However, current capsule robots have many problems, such as over-sized, single function and lack of active locomotion control. This study proposed and designed a new wireless modular capsule robotic system in pipe. The modular capsule robots could move forward and backward in the pipe in the axial direction, turn in a bending environment, and achieve the rendezvous and separation action through the three-dimensional rotating magnetic field generated by the three-axis Helmholtz coils. In this paper, the drive system of the three-axis Helmholtz coils, the power supply control system, and the modular capsule robot structure were analyzed and designed respectively. Finally, a series of characterization experiments were carried out to evaluate the motion characteristics of the modular capsule robots, including the influence of the flow environment imitated to human body's gastrointestinal motility, the frequency of the input signal, and the different structure of the robots on the movement characteristics of the modular capsule robot in this study. The study also evaluated the turning characteristics of robots. Experimental results showed that under different circumstances, modular capsule robots had good motion characteristics, and the effectiveness of the modular functionality had also been verified.

3-D Magnetic Orientation Control of Ferromagnetic Film/Guanine Crystal Hybrid Plate

The light reflection intensity from a biogenic guanine crystal that shows strong light scattering on the broadest surface of the crystal can be modulated by the magnetic field switching due to the dynamic motion of magnetic orientation caused by the diamagnetic anisotropy. Magnetic field amplitudes required for magnetic orientation are drastically decreased by hybridizing the guanine crystal with a ferromagnetic thin film, which is one of the important factors for device application from the viewpoint of power consumption and field generation method. In this paper, we present the 3-D magnetic orientation control of the guanine crystal hybridized with the 5 nm thick permalloy film by applying the magnetic field with a three-axis Helmholtz coil. Vertical magnetic field dependences of the tilt angle of (102) plane of the guanine crystal from the substrate for various in-plane magnetic fields are investigated. It is clarified that the hybrid plate can be controlled three-dimensionally with the magnetic field less than several milliteslas by applying the suitable in-plane field. It is shown that the hybrid plate floating under water is transported by the magnetic field gradient using the permanent magnet, which is effective for carrying it to the target position. The 3-D magnetic orientation characteristics of the hybrid plate that shows the similar behavior to the biogenic guanine crystal for the vertical magnetic field are also mentioned.

Discrete-Time Optimal Control of Electromagnetic Coil Systems for Generation of Dynamic Magnetic Fields With High Accuracy

Electromagnetic coil systems (ECSs) have been widely used for actuation and motion control of magnetic micro/nanorobots. In this paper, two typical ECSs with different system configurations are developed: One is computer-based and uses servoamplifiers for driving the coils and the other adopts an embedded control system with home-designed circuit boards for driving the coils. For dynamic control of the two types of ECSs, a unified control scheme is proposed with two objectives: 1) to make the output magnetic field converge to the reference without steady-state error; 2) to achieve optimal transient response under tunable requirement of control effort. In the scheme, dynamic models of the two systems are described by a unified state-space form with different dimensions, which are obtained by system identification. Then, a discrete-time optimal controller is designed based on the linear quadratic with integral action method to realize the control objectives. Finally, in order to make the controller applicable to the real ECSs, the time-delayed system states are estimated by utilizing a Kalman filter, and a Smith predictor inspired compensator is designed to compensate for time delay and modeling error. Simulations and experiments using the proposed control scheme are conducted for the two ECSs with three-axis Helmholtz coils, which show the easy adaption of the control approach to different coils. Experimental results validate the significantly improved dynamic performances of the two ECSs, and tracking a three-dimensional dynamic magnetic field with high accuracy is also demonstrated.

High-Sensitivity Three-Axis Vector Magnetometry Using Electron Spin Ensembles in Single-Crystal Diamond

We demonstrate a three-axis vector magnetometer based on ensembles of negatively charged nitrogen vacancy centers in single-crystal diamond. A diamond with $\text{C}_{3v}$ symmetry was used to establish the coordinate system for vector magnetic field sensing. We control the external static magnetic field with three-axis Helmholtz coils. Four pairs of magnetic resonance peaks were obtained, which were used to calculate the three Cartesian components of the magnetic field with sensitivity of $\sim5\;\text{nT}/ \sqrt{\text{Hz}}$ for each Cartesian component, free of interaxis error. The magnetometer is suitable for single-chip manufacturing.

3D Helmholtz Coil-based Hybrid Manipulation for Active Locomotion of Magnetic Micro/Nano Robots

This study presents hybrid control based on three-axis Helmholtz coil for manipulation of magnetic micro/nano robots. In general, magnetic force and torque control requires both Maxwell and Helmholtz coils. Therefore, the configuration of the magnetic manipulation system is complex and requires many power supplies. The hybrid method controls the three-axis Helmholtz coil and three power supplies through mechanical switch control to generate magnetic force and torque. Magnetic torque is controlled by the three-axis Helmholtz coil with a rotating magnetic field, and magnetic force is controlled by generating gradient magnetic field through the separated coils by the switch control. Three switches separate each Helmholtz coil and six switches control the separated six coil with the three power supplies. The hybrid control can provide simple configuration of coil system, various active locomotion, and precision control in complex environments. To verify the proposed method, we conducted magnetic simulation with various experimental tests.

Fabrication of Biogenic Guanine Crystal/Ferromagnetic Film Hybrid Plate for Micro-Optical Micro-Electromechanical Systems

In micro-optical device and micro-electromechanical systems applications, the driving power and response time are the important factors for their performance. In this paper, a diamagnetic guanine crystal/ferromagnetic film hybrid plate is fabricated by the sputtering method in order to decrease the magnetic field amplitude required for the guanine crystal orientation. The behavior of the hybrid plate having a 5 nm-thick permalloy film in water under magnetic fields is investigated by using a three-axis Helmholtz coil. The hybrid plate rotates according to the horizontal magnetic field so that the length of (102) plane of guanine crystal is parallel to the field direction. For the vertical magnetic field, the hybrid plate easily stands up. These behaviors are attributed to the large shape anisotropy of ferromagnetic film of hybrid plate. Magnetic field amplitudes required for magnetic orientation drastically decrease compared to those for diamagnetic orientation of the pure guanine crystal. It has been demonstrated that LED lights which are simultaneously irradiated from different directions can be selectively introduced into the microscope by using the reflection of hybrid plate which is controlled with external magnetic fields.

Preliminary Validation of Robotic Control of Magnetic Particles for Targeted Hyperthermia

In this paper, we present a new method for targeted hyperthermia using an electromagnetic navigation system. Typically, Fe₃O₄ magnetic nanoparticles (MNPs) are utilized by injection methods. However, the study demonstrated that the proposed method provides active locomotion for targeting a destination within a three-axis Helmholtz coil, and generates heat through a high-frequency heating coil. To realize these two functions, the entire system combined the electromagnetic navigation system and a high-frequency heating system. The Fe₃O₄ MNPs were prepared via chemical synthesis. Using vibrating sample magnetometer (VSM) and X-ray diffraction (XRD), we observed the magnetic properties and structure of the crystals. Through various experimental tests, we investigated the controllability, mobility, and steering ability of the MNPs. In particular, we confirmed the heating characteristics of the fabricated MNPs according to the changes in the magnetic field strength at 205 kHz. On average, the particle cluster generated a temperature of 73.12 °C at 58 kA/m.

Three-Axial Helmholtz Coil Design and Validation for Aerospace Applications

This paper presents the detailed design, construction, and validation of a three-axis square Helmholtz coil. It also describes the methodology used to drive each pair of coils as well as the setup to operate it in a closed-loop system using a digital PID controller. The coil will be mainly used for aerospace applications, especially to aid the development and testing of attitude determination and control systems that use the earth's magnetic field as a reference vector. Most of the system was built using commercial components, reducing cost, and complexity compared to similar commercial systems. The assembled Helmholtz coil has approximately one cubic meter and can generate magnetic fields up to 2 G/ axis, keeping a uniformity of 0.04% around 11 cm of the center, in each axis. A custom-designed voltage-controlled current source, based on the Howland current pump, was employed, requiring no complex electronic circuits. The coil was designed to be part of a hardware-in-the-loop (HiL) system, which is controlled by a dSPACE modular simulation hardware and uses a commercial fluxgate magnetometer as the reference. This setup reduces the complexity of the proposed system when compared to similar ones. This paper presents two distinct results: first, there is the validation and results of the uniformity regarding the generated field around the system's center; second, results of the setup with the closed-loop HiL simulation are shown, which includes tests of the coil when generating a dynamic magnetic field.

Multifunctional Robotic Guidewire System using Spiral-type Magnetic Microrobot with Magnetic Manipulation

This paper presents a new multifunctional active guidewire system for medical applications that uses a magnetic microrobot. The study demonstrated that the proposed microrobot system could swim and be controlled under Low-Reynolds-number (Re) environments in blood vessel models. The prototype of the robotic guidewire, which is driven within a three-axis Helmholtz coil system, consists of a guide-wire, spiral blade, drilling tip, and permanent magnet. The spiral-type microrobot showed stable active locomotion between 3 kA/m and 9.1 kA/m under driving frequency up to 70 Hz in a silicone oil (of viscosity 1000 cst). The microrobot produced a maximum moving velocity of 8.08 × 10 −3 m/s at 70 Hz and 9.1 kA/m. In particular, the robotic guidewire produced 3D locomotion with drilling in the three-axis Helmholtz coil system. We verified active locomotion, towing of guidewire, steering, and drilling of the proposed robotic guidewire system through experimental analyses.

Marsh frogs, Pelophylax ridibundus, determine migratory direction by magnetic field.

Orientation by magnetic cues appears to be adaptive during animal migrations. Whereas the magnetic orientation in birds, mammals, and urodele amphibians is being investigated intensively, the data about anurans are still scarce. This study tests whether marsh frogs could determine migratory direction between the breeding pond and the wintering site by magnetic cues in the laboratory. Adult frogs (N=32) were individually tested in the T-maze 127cm long inside the three-axis Helmholtz coil system (diameter 3m). The arms of the maze were positioned parallel to the natural migratory route of this population when measured in accordance with magnetic field. The frogs were tested under two-motivational conditions mediated by temperature/light regime: the breeding migratory state and the wintering state. The frogs' choice in a T-maze was evident only when analyzed in accordance with the direction of the magnetic field: they moved along the migratory route to the breeding pond and followed the reversion of the horizontal component of the magnetic field. This preference has been detected in both sexes only in the breeding migratory state. This suggests that adult ranid frogs can obtain directional information from the Earth's magnetic field as was shown earlier in urodeles and anuran larvae.

Study of Magnetic Field Measurement System for g-2/EDM Experiment at J-PARC

Two magnetic field monitoring systems for g-2/EDM experiment at J-PARC are developed. One is a continuous-wave NMR magnetometer, which is used to measure the field homogeneity in a muon storage region. The other is a Hall effect magnetometer, which is used to measure the magnetic field around the muon injection region and that for focusing the muon beam. In order to improve the accuracy of the commercial NMR magnetometer, a digital signal processing system was implemented instead of an analog one. As for the Hall probe system, a three-axis Helmholtz coil system was fabricated to measure tilt angles of Hall sensors in a three-axis Hall probe. The field homogeneity of each Helmholtz coil was measured, and the result agreed well with the design values.

Magnetic Robot and Manipulation for Active-Locomotion With Targeted Drug Release

In this paper, we propose a new mechanism for targeted drug release based on active locomotion. The manipulating method is a magnetic torque control based on a rotating magnetic field using a three-axis Helmholtz coil system. The applied magnetic field creates two rolling (radial and longitudinal directions) and a rotating motion for active locomotion according to variations in the working space and robot posture. Two spiral components in the robot mechanism and the rotating motion completely conduct and control the drug release. Magnetic attractive force between the two spiral components prevents drug leakage during the movement for targeting. When the robot arrives at the destination, the robot switches the direction of the thrust force of the two spiral components to separate the robot body for the drug release. The thrust force for the drug release is higher than the magnetic attractive force. We verified the rapid active locomotion and targeted drug release using precise control through various experiments. In our assessment, the proposed robot mechanism can realize the role of a functional medical robot for therapy and diagnosis.

Three-dimensional swimming tadpole mini-robot using three-axis Helmholtz coils

Electromagnetic-actuated robotic systems have been studied recently for special purposes. Because these systems use external magnetic fields to control their robots, the robots can have simple structures and move with much freedom. In particular, these electromagnetic actuation (EMA) systems are being widely adopted for the actuation of biomedical mini-robots and microrobots for minimally invasive surgery (MIS) and diagnosis. We previously reported, as a feasible biomedical robot, the biomimetic swimming tadpole mini-robot, which can only swim above water. Indeed, the two-dimensional (D) plane swimming tadpole mini-robot is limited in its use because of its motility in the 2D plane. Therefore, this paper proposes a 3D swimming tadpole mini-robot that can move freely in water. First, in the proposed 3D swimming tadpole mini-robot, the buoyancy force was regulated for subaqueous swimming, and the permanent magnet was rearranged for precise movement. Second, to attain a 3D swimming motion, the actuation mechanism of the robot was developed using an EMA system. Finally, various experiments verified that the proposed 3D swimming tadpole mini-robot can swim freely in a 3D water environment.

20pm3-PM028 動的自己組織化のための複数区画化されたマイクロ粒子の作製

This paper describes dynamic self-assembly of hydrogel microparticles that can encapsulate various materials. Using a centrifuge-based microfluidic device, we fabricated multi-compartmentalized hydrogel microparticles that encapsulated magnet-responsive colloid particles in one compartment. The hydrogel microparticles made a periodic movement along externally-applied precessional magnetic field and interacted to each other using attractive magnetic force, resulting in the self-assembly of the microparticles in response to the magnetic field. According to the conditions of precessional magnetic field generated by three-axis Helmholtz coil, we succeeded in constructing a couple of different assembled structures (pearl chain and close packing), and in controlling the length of the assembled pearl chain. Our dynamic self-assembly system will be an effective platform for constructing functional structures including heterogeneous materials, for organizing biomimetic autonomous microrobots, and for understanding self-organization and complex systems observed in nature.

Control theorem of a universal uniform-rotating magnetic vector for capsule robot in curved environment

For realizing non-contact steering swimming of a capsule robot in curved environment filled with viscous liquid, based on spatial orthogonal superposition theorem of alternating magnetic vectors, an innovative physical method is proposed, which employs three-axis orthogonal square Helmholtz coils fed with three phase sine currents to create a universal uniform magnetic spin vector as energy source. According to the antiphase sine current superposition theorem generalized in this paper, an effective control method for successively adjusting the orientation and the rotating direction of the universal magnetic spin vector is proposed. For validating its feasibility and controllability, three-axis Helmholtz coils, power source and an innovative capsule robot prototype were manufactured, experiments were conducted in both spiral pipe and animal intestine. It was demonstrated that the orientation and the rotational direction of the universal uniform-magnetic spin vector can be adjusted successively through digital control and steering swimming of the capsule robot in spiral intestine can be achieved successfully. The breakthrough of the universal rotating uniform-magnetic vector will push forward the development of modern physics and biomedical engineering