Miniature FBG force sensor capable of effectively resisting lateral forces

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This paper presents a high-precision miniature force sensor based on fiber Bragg grating (FBG) for measuring axial contact force (CF) between a medical instrument tip and tissue during minimally invasive surgery (MIS) palpation. The newly designed FBG force sensor, with a reduced diameter of 1.5 mm and a total length of 12 mm, is easier to integrate into miniature medical instruments compared to existing 3 mm diameter sensors. The sensor consists of a tubular elastomer structure and two optical fibers. A unique staggered inclined notch design on the elastomer surface enhances sensitivity to axial forces and mitigates lateral force-induced strains. The central axial optical fiber has FBG1 inscribed to detect strains from axial forces and temperature changes, while the adjacent fiber has FBG2 to measure only temperature-induced strains. Calibration and temperature compensation experiments confirmed the sensor's accuracy in measuring CF and decoupling temperature effects. The sensor has an axial force sensitivity range of 0 to 1.4 N with a sensitivity of 270.809 pm/N and a dynamic measurement error of less than 0.2 g. The post-temperature compensation error is less than 0.08 N. Simulation palpation experiments, using silicone embedded with hard blocks to mimic pathological tissues, validated the sensor's effectiveness in detecting tissue abnormalities and distinguishing the hardness of different blocks during MIS palpation. A comparative experiment was conducted with a traditional helical-structured sensor to assess lateral force resistance, confirming that the designed sensor exhibits excellent lateral force resistance.