In surgical navigation, electromagnetic (EM) tracking is only as reliable as the sensor inside the device. Strong signal quality and minimal interference are critical, and they depend on three key design choices: coil design, core shape, and placement. Here, we’ll explore how each of these factors helps OEMs develop highly accurate EM sensors for surgical navigation.
How to Optimize EM Sensor Performance & Efficiency
Coil Design
Signal strength and integrity are critical for EM sensor performance, but so is sensitivity, which directly influences localization accuracy. There are two ways to increase EM sensor sensitivity:
- Add more winds to the coil
- Increase coil size
Because EM sensors are typically confined to compact footprints, increasing coil size is often impractical. That makes additional winds the most effective way to boost sensitivity – and therefore accuracy.
However, increasing the number of winds alone isn’t always sufficient. That’s when it’s time to consider adding a core, which also has a direct impact on accuracy.
Core Shape
A core is essentially a magnetic funnel, and its efficacy is measured as permeability – the degree to which a material amplifies a local magnetic field when exposed to an external one.
There are two types of permeability:
- Intrinsic permeability: The theoretical maximum amplification
- Shape permeability: The realistic amplification level, which is orders of magnitude lower than intrinsic permeability
So, while intrinsic permeability might look promising in theory, shape permeability is what ultimately governs performance. Long, slender, cylindrical cores are often best because they maximize aspect ratio, enhancing sensitivity and accuracy.
Other factors also influence performance, including material selection, heat treatment, and magnetic response across all three regions: initial, peak, and saturation. Read our white paper for an in-depth discussion of how these variables impact core performance.
Placement
Sensor placement is likewise critical to surgical navigation accuracy. Sensors are often integrated into shafts, PCBs, or components to reduce labor costs and improve durability. Thus, it’s important to understand how placing a sensor inside a device impacts performance, as accuracy might differ between standalone testing and real-world application.
Adjacent components can also affect sensor accuracy. Consider, for example, an interventional device with multiple metallic components made from 304 or 316 stainless steel (braids, compression coils, and pull wires). Although these alloys are nonmagnetic in the heat-treated austenitic phase, cold-working and machining processes can induce magnetic crystalline phases. These changes can amplify or attenuate sensor sensitivity, reducing localization accuracy.
Best practice dictates accounting for sensor placement early in the design process to ensure accuracy in the surgical suite.
Next Steps
With deep expertise in both EM sensor design and high-value subassemblies, Intricon is uniquely positioned to guide OEMs through the entire product lifecycle. Our team can partner with you to develop a sensor that delivers superior localization accuracy in critical surgical navigation applications – ultimately fostering market success.