Deformable Structure Shape Sensing Using EIT and FDM
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Solution Overview
Problem
Current shape sensing methods for soft robotic devices in minimally invasive surgery are limited by inaccuracy, robustness, and deformability, and existing techniques like EM tracking, imaging, and optical tracking are impractical or unsuitable due to interference from other equipment or line-of-sight requirements.
Innovation Solution
A sensor system using electrical impedance tomography (EIT) with frequency division multiplexing (FDM) to inject multiple frequencies simultaneously through different electrode pairs, allowing real-time shape and position sensing of deformable structures, suitable for unstructured environments like the operating theater.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If electromagnetic tracking is used to track single points in space, then tracking capability is provided, but measurements are influenced by stray EM fields from other equipment making shape reconstruction impossible
Solution Approach 1:
The patent introduces an intermediary conductive medium (conductive fluid or conductive polymer) that fills the soft robotic device and couples electrodes to the device structure. This intermediary enables electrical impedance measurements to be made through the device material itself, eliminating the need for external EM fields and stray field interference while maintaining tracking capability through impedance tomography reconstruction.
Solution Approach 2:
The patent replaces electromagnetic tracking with electrical impedance tomography. Instead of using external EM fields to track positions, the system injects electrical current through electrodes and measures voltage responses to reconstruct shape and position. This substitution eliminates sensitivity to stray EM fields while providing comprehensive shape measurement capability.
2Measurement precision
If imaging techniques such as fluoroscopy are used, then shape information can be obtained, but large doses of radiation or contrast agents are required
Solution Approach 1:
The patent replaces ionizing radiation-based imaging (fluoroscopy, X-ray) with electrical impedance tomography. By injecting low-level electrical currents through electrodes and measuring voltage responses, the system reconstructs shape information without requiring radiation or contrast agents, thereby eliminating harmful radiation exposure while maintaining measurement precision.
Solution Approach 2:
The patent changes the physical parameter used for measurement from electromagnetic radiation (X-rays, fluoroscopy) to electrical impedance. By measuring changes in electrical resistance and conductance through the soft robotic device, the system obtains shape information without the harmful effects of radiation, using instead the device's own electrical properties as the measurement parameter.
3Difficulty of detecting and measuring
If optical tracking methods are used to track objects, then tracking is possible, but line of sight is required making them impractical in MIS applications
Solution Approach 1:
The patent uses the soft robotic device itself as the intermediary medium for measurement. By embedding electrodes within the conductive material of the device, the system can measure shape and position through electrical impedance without requiring external line-of-sight access. The device's own structure serves as the measurement pathway, eliminating the need for optical line-of-sight.
Solution Approach 2:
The patent replaces optical tracking with electrical impedance tomography. Instead of using light-based methods that require line-of-sight, the system uses electrical current injection and voltage measurement through the device material. This substitution enables tracking capability without line-of-sight requirements, making the system suitable for minimally invasive applications where optical access is limited.
4Measurement precision
If fibre Bragg gratings are used to measure strain, then strain measurement is possible, but the location of localized deflection cannot be determined requiring large numbers of sensor elements
Solution Approach 1:
The patent merges multiple measurement functions into a single integrated system. By distributing electrodes throughout the conductive material of the soft robotic device, the system simultaneously measures strain, determines location of deflection, and reconstructs three-dimensional shape all through a single electrical impedance tomography process. This eliminates the need for multiple separate sensor elements while maintaining measurement precision.
Solution Approach 2:
The patent transitions from one-dimensional strain measurement (single point measurement) to three-dimensional shape reconstruction. By injecting current through multiple electrodes distributed in space and measuring voltage responses, the system reconstructs the complete three-dimensional shape and location of deflection, adding spatial dimensionality to the measurements without requiring proportional increases in sensor elements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate, real-time shape and position sensing of soft robotic devices, suitable for minimally invasive surgery, without line-of-sight requirements and interference from other equipment, providing proprioceptive capabilities and biocompatibility.
Implementation Method 1
an electrical conductor operably connected to the deformable structure and electrically couplable to each of the electrodes
Implementation Method 2
Electrical Impedance Tomography (EIT) is a sensing technique that infers variations in electrical impedance of electrically conductive media within a certain domain from voltage measurements made by electrodes positioned at the boundary of that domain
Data Source
Figure 1~2c
Figure 3a~4c
Figure 5~9
AI summary
A sensor system comprising: a deformable structure; a plurality of electrodes operably connectable to the deformable structure; an electrical conductor operably connected to the deformable structure and electrically couplable to each of the electrodes; a current source connectable to predetermined electrodes; a current injector for injecting current from the current source through predetermined electrodes; a voltage recorder for recording the voltage between predetermined pairs of electrodes; and an analyser for analysing voltage recordings to thereby determine the shape of the deformable structure.