Wanan Yang

A Cubic 3-Axis Magnetic Sensor Array for Wirelessly Tracking Magnet Position and Orientation

In medical diagnoses and treatments, e.g., endoscopy, dosage transition monitoring, it is often desirable to wirelessly track an object that moves through the human GI tract. In this paper, we propose a magnetic localization and orientation system for such applications. This system uses a small magnet enclosed in the object to serve as excitation source, so it does not require the connection wire and power supply for the excitation signal. When the magnet moves, it establishes a static magnetic field around, whose intensity is related to the magnets position and orientation. With the magnetic sensors, the magnetic intensities in some predetermined spatial positions can be detected, and the magnets position and orientation parameters can be computed based on an appropriate algorithm. Here, we propose a real-time tracking system developed by a cubic magnetic sensor array made of Honeywell 3-axis magnetic sensors, HMC1043. Using some efficient software modules and calibration methods, the system can achieve satisfactory tracking accuracy if the cubic sensor array has enough number of 3-axis magnetic sensors. The experimental results show that the average localization error is 1.8 mm.

A Six-Dimensional Magnetic Localization Algorithm for a Rectangular Magnet Objective Based on a Particle Swarm Optimizer

To build a wireless capsule endoscope with active external guidance for controllable and interactive diagnosis on the gastrointestinal tract, it is necessary to track the capsules 3-D position and 3-D orientation. An approach to tracking is to enclose a small rectangular permanent magnet in the capsule. The magnetic field produced around the body by the rectangular magnet can be detected by magnetic sensors outside the patients body. With these detected magnetic sensor data, the 3-D localization and 3-D orientation parameters can be computed by an appropriate algorithm based on the mathematical model of the rectangular magnets magnetic field. We tried several nonlinear optimization algorithms, and simulation experiments show that the particle swarm optimization algorithm can work effectively with good accuracy when the magnet moves within a predetermined range.

A New Tracking System for Three Magnetic Objectives

We have implemented a new noninvasive multiobjective tracking system, which can be used for localization of an endoscope and monitoring of heart valve prostheses and gastrointestinal transit of solid oral dosage forms or nutrients. The marker is modeled as a magnetic dipole, and the magnetic field at some point is regarded as summation of those from three dipoles. By minimizing the squared errors of magnetic field values between measurements and calculation using a hybrid of the particle swarm optimization (PSO) algorithm and the clone algorithm, an iterative result can be obtained, which is taken as the initial guess of the Levenberg-Marquardt (L-M) optimization method, and the first point can be determined. Subsequently, the previous computed point is used as the next initial guess of L-M algorithm, and the successive points are calculated. The tracking results demonstrate that the average position error for three objectives is 3.7 mm and the average orientation error is 1.8 when the objectives move randomly in the space surrounded by the sensor array.

An improved magnetic localization and orientation algorithm for wireless capsule endoscope

In this paper, we propose a novel localization algorithm for tracking a magnet inside the capsule endoscope by 3-axis magnetic sensors array. In the algorithm, we first use an improved linear algorithm to obtain the localization parameters by finding the eigenvector corresponding to the minimum eigenvalue of the objective matrix. These parameters are used as the initial guess of the localization parameters in the nonlinear localization algorithm, and the nonlinear algorithm searches for more appropriate parameters that can minimize the objective error function. As the results, we obtain more robust and accurate localization results than those by using linear algorithm only. Nevertheless, the time efficiency of the nonlinear algorithm is enhanced. The real experimental data show that the average localization accuracy is about 2mm and the average orientation accuracy is about 1.6° when the magnet moves within the sensing area of 240mm ×240mm square.

Real time algorithm for magnet's localization in capsule endoscope

To track the movement of a wireless capsule, a magnetic localization and orientation system is designed. In this system, a permanent magnet is enclosed in the capsule, which generates a magnetic field around. With the magnetic sensor array arranged out of the human body, we can measure the magnets magnetic signals, and compute the capsules 3D localization and 2D orientation parameters by applying an appropriate algorithm. In this paper, we presented a real time localization algorithm that consists of the Levenberg-Marquardt (LM) algorithm and the Least Squares Curve Fitting Method. The experimental results show that this algorithm has good accuracy, high speed and high robustness.

A real-time tracking method for the rectangular magnet based on parallel Levenberg-Marquardt algorithm

magnetic flux intensity of the rectangular magnet is the function of its location and orientation. With the measured magnetic flux intensities at two points around the rectangular magnet by 3-axis magnetic sensors, a non-linear equation group is established, and the location and orientation of the rectangular magnet can be determined by seeking the solution of the equation group by using general Levenberg-Marquardt (L-M) algorithm. However, the time occupied by general L-M algorithm is too long to realize real-time tracking for the rectangular magnet. We propose an improved method which computes Jacobin Matrix in L-M algorithm in parallel. Making use of the Open Multi-Processing (OpenMP) model, the parallel operation is implemented on the dual-core personal computer. As a result, the real-time tracking for the rectangular magnet is realized, and the tracking curve is smooth.

A new calibration method for magnetic sensor array for tracking capsule endoscope

To track the movement of wireless capsule endoscope in the human body, we design a magnetic localization and orientation system. In this system, capsule contains a permanent magnet as the movable object. A wearable magnetic sensor array is arranged out of the human body to capture the magnetic signal. This sensor array is composed of magnetic sensors, Honeywell product HMC1043. The variations of magnet field intensity and direction are related to the capsule position and orientation. Therefore, the 3D localization information and 2D orientation parameters of capsule can be computed based on the captured magnetic signals and by applying an appropriate algorithm. In order to initialize the system and improve the tracking accuracy, we propose a calibration technique based on high-accurate localization equipment, FASTRAK. The calibration method includes two steps. Firstly, we acquire the accurate reference data from FASTRAK tracking equipment, and transform them into the position and orientation parameters of the magnet. Secondly, we calculate three important parameters for the sensor calibration: the sensitivity, the center position, and the orientation. Based on the calibration, we can adjust the magnetic localization and orientation system quickly and accurately. The experimental results prove that the calibration method used in our system can improve the system with satisfactory tracking accuracy.

Locating Intra-Body Capsule Object by Three-Magnet Sensing System

Magnetic localization is an appropriate method for tracing an intra-body capsule object because of its satisfactory accuracy and efficiency. In this method, the capsule is enclosed in a ring magnet, which establishes a magnetic field around the human body. By using a sensor array system with a number of triaxial magnetic sensors, the magnetic flux densities can be measured, and the magnet can be localized by an appropriate algorithm. However, a problem for such a system is that the movements of the human body have interferences on the localization. Therefore, in order to compensate the interferences, we propose a three-magnet localization method. Here, in addition to the capsule object magnet, two other magnets are fixed on the surface of the human body to serve as reference objects. The position and orientation parameters of all the three magnets are determined by applying the optimal algorithm on the sensing data from the sensor array. Then, a reference coordinate system is built based on the two reference objects, and the capsule magnet is relatively tracked with respect to this reference system in human body. The experimental results show that the average localization error caused by the body movement interference is reduced from 30.1 mm (in the original coordinate system) to 3.82 mm (in reference coordinate system) and the average direction error reduced from 17.7° to 2.2°.

A wireless actuation system for micro-robot moving inside pipeline

We propose an external actuation technique for wireless micro-robot in pipeline. In this technique, the external magnetic field is used to rotate the micro-robot by applying a force on the magnet which is enclosed in the robot. With the help of the spiral structure on the outer surface of the robot, the rotation of robot can be converted to axial motion through liquid such as water or oil of the pipeline. The motion principles of the micro robot is discussed in this paper. The real experimental results show this actuation method is realizable and feasible.

Investigation of the Relationship Between Tracking Accuracy and Tracking Distance of a Novel Magnetic Tracking System

The position and orientation of an object embedding with a permanent magnet can be acquired in real time via a magnetic tracking system. However, one characteristic of the magnetic tracking technique is its varied tracking accuracy along with the tracking distance. Hence, this paper tends to investigate the relationship between the tracking accuracy and the distance from the magnet to the sensor array by both simulations and experiments. Results show that the relationship is expressed as a cubic polynomial equation, and that the equation coefficients are related to the properties of the magnet and the signal-to-noise ratio of the sensor outputs. When the magnet is located at a distance from 36 to 96 mm above the sensor array, the system had the best performance, while average localization and orientation errors were 0.70 mm and 1.22°, respectively. Thus, this system achieved the best tracking accuracy compared with the state-of-the-art of magnetic tracking systems. This paper is helpful to the researchers who want to implement a magnetic tracking system or need to know clearly the valid tracking distance of a magnetic tracking system.