Magnetic continuum robots offer flexibility and controllability, making them promising for minimally invasive surgery (MIS). However, the clinical application of these robots is relatively limited due to the difficulty of integrating miniaturized triaxial force sensors and their single functionality. This paper proposes a multifunctional magnetic catheter robot with magnetic actuation steering and triaxial force-sensing capabilities. The robot features 3 channels at its tip that integrate multi-segmented magnets, a novel triaxial force sensor, and various functional instruments. The sensor is calibrated, demonstrating high sensitivity and accuracy. The steering characterization of the robot confirms that the catheter tip exhibits effective flexibility and force sensing. Palpation experiments involving various hard lumps are performed on porcine kidney, with results verifying that the robot can reliably detect abnormal hard lumps within tissues. Additionally, palpation experiments in bronchial phantom demonstrate the robot’s imaging and palpation capabilities for lung nodules with an integrated endoscope. Further, the robot, equipped with biopsy forceps, successfully performs palpation and biopsy functions on simulated stomach polyps, demonstrating its capability for effective tissue manipulation. By leveraging force-sensing capabilities and integrating multifunctional instruments, the robot shows potential for expanded applications in MIS, paving the way for important advancements in clinical procedures.

A photonic crystal fiber (PCF) with high relative sensitivity was designed and investigated for the detection of chemical analytes in the terahertz (THz) regime. To ease the complexity, an extremely simple cladding employing four struts is adopted, which forms a rectangular shaped core area for filling with analytes. Results of enormous simulations indicate that a minimum 87.8% relative chemical sensitivity with low confinement and effective material absorption losses can be obtained for any kind of analyte, e.g., HCN (1.26), water (1.33), ethanol (1.35), KCN (1.41), or cocaine (1.50), whose refractive index falls in the range of 1.2 to 1.5. Besides, the PCF can also achieve high birefringence (∼0.01), low and flat dispersion, a large effective modal area, and a large numerical aperture within the investigated frequency range from 0.5 to 1.5 THz. We believe that the proposed PCF can be applied to chemical sensing of liquid and THz systems requiring wide-band polarization-maintaining transmission and low attenuation.

A novel fiber extrinsic Fabry-Pérot interferometric ultrasonic sensor for detecting high-frequency ultrasonic signals is proposed and fabricated. The diaphragm structure features an anti-outer-ring clover design. Finite element simulation is employed to determine optimal parameters before directly printing the sensor onto the fiber tip using two-photon 3D printing technique. Experimental results indicate that the sensor achieves a signal-to-noise ratio of 67 dB@300 kHz, a mechanical sensitivity of 1362 nm/kPa, and a noise equivalent acoustic signal level of 3.98 $\mu$Pa/Hz$^{1/2}$ @300 kHz. The proposed fiber sensor offers a new approach for sensing weak ultrasonic signals and is expected to be applied in various ultrasonic detection fields.

This paper develops a high-precision miniature three-dimensional Fiber Bragg Grating (FBG) force sensor designed for detecting and locating hard masses within tissues during Minimally Invasive Surgery (MIS) and robotic-assisted MIS palpation processes. The prototype consists of three FBG-etched optical fibers and an integrated elastomer. The fibers are suspended and parallel to each other within the elastomer, allowing each FBG to be directly compressed or stretched under stress. A novel model, combining segment-by-segment sensitivity and differential decoupling, is adopted for decoupling three-dimensional forces. This approach significantly reduces the crosstalk error caused by spatial forces, avoids the complexity of assembling multiple fibers in previous designs, and reduces the sensor's size, facilitating its integration into MIS procedures. Calibration experiments are conducted to determine the sensor's force sensitivity coefficients, achieving resolutions of 4.35 mN, 3.99 mN, and 3.30 mN in the X, Y, and Z directions, respectively. Through discrete and drag palpation tests on silicone with different types of hard inclusions, the results demonstrate that the proposed prototype has the ability to effectively identify the size, hardness, and depth of hard objects from the contact force information. Additionally, ex vivo porcine kidney palpation experiments are conducted to further verify the feasibility of locating hard masses during MIS palpation.

Objective: To accurately achieve distal contact force, a novel temperature-compensated sensor is developed and integrated into an atrial fibrillation (AF) ablation catheter. Methods: A dual elastomer-based dual FBGs structure is used to differentiate the strain on the two FBGs to achieve temperature compensation, and the design is optimized and validated by finite element simulation. Results: The designed sensor has a sensitivity of 90.5 pm/N, resolution of 0.01 N, and root–mean–square error (RMSE) of 0.02 N and 0.04 N for dynamic force loading and temperature compensation, respectively, and can stably measure distal contact forces with temperature disturbances. Conclusion: Due to the advantages, i.e., simple structure, easy assembly, low cost, and good robustness, the proposed sensor is suitable for industrial mass production.

A broadband single-polarization single-mode (SPSM) hollow core anti-resonant photonic crystal fiber (HC-ARPCF) is proposed and analyzed by the finite element method in this paper. The HC-ARPCF design consisted of outer semicircular cladding tubes and inner circular cladding tubes. The SPSM behavior is achieved through controlling the effective material absorption loss (EML) by loading epsilon negative (ENG) material in the selected semicircular cladding tubes. Optimization of the configuration parameters is conducted to yield a large loss difference (LD) between one of the two orthogonally polarized fundamental modes and all the other unwanted modes. Therefore, only one desired mode will exist after a proper propagation distance, i.e., SPSM guidance. Specially, the optimal design provides a 288 nm (from 1408 nm to 1676 nm and from 1680 nm to 1700 nm) bandwidth in terms of 40 dB/m minimum LD (MLD) and 168 nm (from 1452 nm to 1620 nm) bandwidth in terms of 100 dB/m MLD. Furthermore, this fiber also exhibits a large effective mode area and near-zero dispersion properties over the entire operation bandwidth. The proposed HC-ARPCF may find its applications in polarization maintaining and high-power laser systems.