Stray Field Management in Surgical Robotics
Mitigating Interference and Performance Issues
Uncontrolled magnetic fields can interfere with sensitive medical instruments. This paper outlines best practices for stray field management, shielding solutions, and design techniques to minimize interference in medical applications such as surgical robotics.
In the delicate dance of surgical robotics, precision is paramount. But what if an invisible force could disrupt this intricate ballet, compromising accuracy and patient safety? Uncontrolled magnetic fields, often a byproduct of powerful magnetic components, pose a significant threat to sensitive medical instruments. As a medical device design engineer, you understand that every millisecond and millimeter counts. This is where stray field management becomes not just a best practice, but a critical imperative.
The increasing integration of magnetic technology into medical devices, particularly in surgical robotics, brings remarkable capabilities but also introduces the challenge of managing stray magnetic fields. These uncontrolled fields can interfere with sensitive instruments, leading to performance issues and potentially compromising patient safety.
Understanding Stray Fields in Medical Devices
Stray fields are primarily driven by the net magnetic moment of magnets or magnetic assemblies. For a single magnet, the magnetic moment is a product of its intrinsic flux density and volume. In a magnetic assembly, the net magnetic moment is the vector sum of all individual magnetic components.
The near field of a magnet or assembly is highly dependent on both its overall magnetic moment and its geometry. As you move further away from the magnet, the impact of its geometry lessens, and the magnet can be approximated as a point source with a defined magnetic moment.
The Impact on Surgical Robotics
Surgical robotics relies on a sophisticated array of magnetic sensors, holding magnets, and motors for precise control and operation. These sensors typically measure the presence of a tool or linear and rotary positions. Stray magnetic fields, whether static (from permanent magnets or DC electromagnets) or alternating, can interfere with these critical magnetic sensing devices and sensitive electronics. For instance, electromagnetic interference can pose a danger to patients with active medical implants like pacemakers and implantable cardioverter-defibrillators (ICDs), which are typically designed to operate safely in fields less than 5 Gauss.
Consider a poorly designed torque coupler: while a properly designed 125 NM torque coupler might have a peak stray field of only 4.668 Gauss at 25mm distance, a poorly designed one within the same envelope dimensions could exhibit a peak stray field of 30 Gauss at the same distance, while also dropping torque to 100 NM. This demonstrates that proper design not only enhances performance but also significantly reduces stray fields and minimizes interference with surrounding instruments.
Best Practices for Stray Field Management
Effective stray field management is crucial for the reliable operation of surgical robotics. Here are key strategies:
- Design for Minimized Magnetic Moment: A fundamental approach to reducing stray fields is to minimize the net magnetic moment of your magnetic assemblies. For example, torque couplers are often designed with alternating poles and back iron, which allows the magnetic moments of individual components to cancel each other out, resulting in very low stray fields when efficiently designed.
- Strategic Magnet Orientation and Assembly: The geometry of the magnet or assembly significantly impacts the near field. Careful consideration of how magnets are oriented and assembled can help direct the useful magnetic field to the working part of the magnetic circuit while minimizing or containing unused fields.
- Magnetic Field Shaping: While magnetic flux lines are closed loops and cannot be stopped, they can be redirected. Magnetic field shaping techniques can generate a high magnetic field in the work zone while reducing the stray field. This can be achieved using highly permeable soft ferromagnetic materials to direct stray magnetic flux and focus the field.
- Superposition of Magnets: Another common method is the superposition of magnets, where magnetic fields from segments combine in the work zone but cancel each other on the outside, minimizing stray fields. This can produce a magnetic field approximately three times stronger than a similar structure with only two magnets. Depending on the application, combining soft magnetic materials and magnet superposition can maximize the magnetic field in the work zone and minimize wasted stray fields.
- Shielding Solutions: Selecting appropriate shielding materials is crucial to contain stray magnetic fields. High permeability materials can be used to redirect the magnetic flux away from sensitive areas, effectively creating a “magnetic shield.”
- Reverse Magnetic Moment Design: Another method to reduce the net magnetic moment and thus the stray field is to design in a reverse magnetic moment. For example, adding a redundant magnet outside a Halbach ring with an opposite magnetic moment can significantly reduce the net magnetic moment and, consequently, the stray field.
Partnering for Success
Developing magnetic solutions that meet the stringent requirements of surgical robotics demands expertise. Collaborating with a magnetic component partner like Dexter Magnetic Technologies, a part of Permag, who understands the intricacies of magnetic moment, stray field calculations, and shielding techniques, is essential. Our experience in magnetic design ensures that the useful magnetic field is directed precisely where needed, while unwanted interference is effectively minimized.
By meticulously managing stray magnetic fields, medical device design engineers can ensure the robust performance and reliability of surgical robots, ultimately contributing to safer and more effective patient outcomes.
Managing Stray Fields In Your Robotic System
Innovation in surgical robotics doesn’t just happen at the system level. It starts at the core, with magnetics that are custom-designed, purpose-built, and compliant with your quality systems.
With Dexter, you get more than a magnet. You get stray field management expertise in surgical robotics innovation.
Ready to Prototype Your Next-Gen Surgical Robotics Magnetic Assembly?
Let’s co-engineer a custom solution that manages your stray fields, meets your specs and exceeds your performance goals.
Speak with our medical device magnet design team
Additional Resources
Magnetic Stray Field Considerations for Medical Products: https://www.dextermag.com/wp-content/uploads/2023/07/Magnetic-Stray-Field-with-Biosrevised-6-6-2023-2-1.pdf