Magneto-Oscillatory Localization for Small-Scale Robots

Engineering Electrical Engineering Information Science Electronic Information Automation Bioengineering Life Sciences
small-scale robots magneto-oscillatory wireless localization biomedical real-time control

Detailed Explanation of a New Small-scale Magneto-oscillatory Localization Method and Its Application in Robotics

Research Background and Motivation

Micro-robots have demonstrated immense potential in the medical field, especially in minimally invasive surgeries, targeted drug delivery, and in vivo sensing. Recently, significant progress has been made in driving and powering nano- to millimeter-scale robots wirelessly in biological environments. However, real-time localization of these micro-robots, particularly deep within biological tissues, remains a technical challenge that urgently needs to be addressed. Traditional medical imaging techniques, such as Magnetic Resonance Imaging (MRI), Computed Tomography (CT), and Positron Emission Tomography (PET), though advantageous in spatial resolution, are unsuitable for continuous tracking of moving robots due to low refresh rates or radiation issues. Additionally, existing static magnetic localization methods can achieve up to five degrees of freedom (DOF) in certain scenarios but cannot achieve full six degrees of freedom localization due to rotational symmetry around the magnetic axis. Therefore, developing a method for real-time, wireless localization with micrometer precision and six degrees of freedom within deep biological tissues has become the primary motivation for this study.

Source and Author Information

This paper was published in the journal npj Robotics, titled “Small-scale magneto-oscillatory localization for small-scale robots.” The DOI is 10.1038/s44182-024-00008-x. The main authors are F. Fischer (DKFZ), C. Gletter (University of Stuttgart), M. Jeong (University of Stuttgart), and T. Qiu (DKFZ). The article was published in 2024 in the Nature series journal npj Robotics.

Detailed Research Process

Research Process

This research proposes a Small-scale Magneto-Oscillatory Localization (SMOL) method that achieves six degrees of freedom for real-time wireless localization through a cantilever with a limited magnetic dipole. The SMOL method utilizes the mechanical oscillations of the magnetic dipole to break the traditional rotational symmetry of a single permanent magnet, thus achieving full six degrees of freedom localization.

  1. SMOL Device Design and Principle: The SMOL device consists of a cantilever structure with an attached magnetic dipole. The cantilever generates mechanical oscillations under an external magnetic field. These oscillations are captured by a multi-sensor array, and decoded through fitting a physical model to obtain position and orientation information.

  2. Excitation and Sensing Unit Design: The excitation unit consists of a pair of vertically arranged planar coils that generate alternating magnetic fields in orthogonal planes. The sensing unit is a magnetic sensor array that captures the complex magnetic signals generated by the oscillating magnet. The oscillating multiple frequency signals of the magnet are captured by the sensors, and six degrees of freedom information of the SMOL device is obtained by fitting a magnetic field model.

  3. Oscillation Mode and Signal Processing: The mechanical oscillation frequency of the cantilever is determined by the material and geometric properties of the cantilever. Reliable oscillation signals are extracted using Fourier Transform (DFT) and signal filtering, and decoded under a physical model using the Levenberg-Marquardt optimization algorithm.

  4. Precision and Localization Depth Experiment: Simulations and experiments comparing positions and orientations validate the localization precision and applicable depth of the SMOL method. Actual measurements are conducted in different environments to evaluate its performance under varying damping coefficients.

Research Results

  1. Full Six Degrees of Freedom Localization: The SMOL method accurately decodes the device’s three degrees of freedom position (x, y, z) and three degrees of freedom orientation (pitch, yaw, roll) by combining multi-sensor data. Experimental results show that position accuracy reaches sub-millimeter level within 80 mm from the sensor array, even refining down to 100 micrometers; orientation accuracy reaches sub-1 degree.

  2. Wide Application Range and Environmental Compatibility: This method is applicable under various physical boundary conditions, including solid boundaries, viscoelastic media, and liquid boundaries. Compared to traditional methods, SMOL exhibits significantly improved performance in high damping environments such as biological soft tissues.

  3. Real-time Closed-loop Control: The SMOL device can be quickly integrated with micro-robots to achieve real-time closed-loop control. In experiments, micro-robots are driven by gradient and rotating magnetic fields in viscoelastic media, with SMOL achieving precise path tracking and directional control.

Research Value and Significance

Scientific Value: The SMOL method enables wireless, real-time, full six degrees of freedom localization for small-sized robots, addressing the limitations in precision and degrees of freedom of traditional localization methods, thereby advancing the application of micro-robots in biomedicine.

Application Value: This method holds significant practical potential and can be widely applied in tool navigation for minimally invasive surgery, targeted drug delivery, and in vivo monitoring. Due to its high precision and real-time performance, the SMOL method has broad application prospects in clinical medical applications.

Research Highlights

  1. Small Size with High Precision: Achieving sub-millimeter level position and sub-degree level orientation in six degrees of freedom through mechanical oscillations, suitable for integration in micro-robots and medical instruments.

  2. Wide Applicability: Simple design of the SMOL method allows stable operation under various boundary conditions, adapting to multiple biomedical scenarios.

  3. Real-time Performance: Utilizing unique frequency response characteristics, avoiding low-frequency interference, and achieving high signal-to-noise ratio localization, enabling real-time closed-loop control with micro-robots and surgical tools.

Other Important Information

The paper provides detailed information on the mathematical model, experimental equipment design, and experimental procedures of the SMOL method. The design and validation processes, including coil design, sensor placement, and data processing algorithms, are further elaborated in supplementary materials. Additionally, the research team conducted actual biological sample tests, verifying the effectiveness and applicability of the SMOL method in real biological tissues.

Conclusion

The SMOL method achieves full six degrees of freedom localization for small-scale robots within deep biological tissues through innovative magneto-oscillatory localization technology. This method not only has high exploratory value in scientific research but also provides a new technical path for practical medical applications. Research results indicate that the SMOL method holds significant application prospects and development potential in real-time localization and navigation of diagnostic and therapeutic devices.