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Latest articles for Measurement Science and Technology

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  • PD sliding mode control of active suspension based on adaptive disturbance observer
    The control efficacy of active suspension systems is influenced by inherent nonlinearities, uncertainties in the sprung mass, and external disturbances. To address these challenges, this study proposes a proportional-derivative sliding mode controller integrated with an adaptive disturbance observer (ADO). The proposed ADO offers significant advantages, primarily due to its capability to significantly attenuate high-frequency oscillatory behavior commonly associated with conventional fixed-gain observers, while eliminating the need for a priori information regarding disturbance magnitude bounds or their rate of change. Furthermore, the robustness of the ADO is substantially improved, enabling it to effectively counteract a wide range of disturbances. Additionally, recognizing the dual nature of disturbances—where they can exhibit both advantageous and adverse effects—a disturbance effect indicator (DEI) is developed. By leveraging the adaptive estimation mechanism of the ADO in conjunction with the DEI, detrimental disturbances are actively mitigated, while beneficial components are preserved and utilized. The input-to-state stability of the developed active suspension control framework is analytically established via Lyapunov-based stability criteria. Experimental validation under standardized road excitation scenarios confirms the controller’s performance efficacy, with root-mean-square chassis acceleration reduced by 67.67% and 52.54% compared to passive configurations under bump and random road excitation profiles, respectively.

  • Design and experimental characterization of a small flexible TMR-based indentation probe for soft tissue hardness estimation
    The endoscopic transsphenoidal approach is a surgical method used to remove pituitary adenomas—benign tumors located near the pituitary gland. The success of this procedure depends heavily on assessing the tumor’s consistency, which is currently based on the surgeon’s tactile feedback and experience. This study presents the development of a novel sensor-based probe designed to provide real-time measurements of tissue hardness, supporting more objective surgical decision-making. The probe integrates a tunneling magneto resistance (TMR) sensor with a deformable, 3D-printed tip made of thermoplastic polyurethane. The tip features micro-beams that deform upon contact with tissue; the extent of deformation, measured by the TMR sensor, correlates with tissue stiffness. The flexible structure was fabricated using fused filament fabrication, and the process was characterized to control micro-beam dimensions by adjusting print parameters such as layer height, print speed, and nominal line width. A regression model was developed to predict beam width with high accuracy and repeatability. Eighteen probe designs, combining different beam widths (0.42 mm–0.63 mm) and numbers (3–5), were tested through indentation experiments on samples with Shore 000 hardness ranging from 51 to 83 (ASTM D2240), including a cooked egg white sample as a biological tissue analogue. Results revealed that probes with 4 and 5 beams printed at lower speeds offered superior sensitivity, linearity, and uniformity. In these configurations, the probe was able to estimate the hardness of adenoma-like materials with errors below 2%. These findings validate the proposed system’s potential for clinical use in evaluating soft to moderately firm tumors during surgery.

  • A semantic-aware measurement-driven autonomous target search framework for UGV in complex unknown environments
    Unmanned ground vehicles face numerous challenges when conducting target search in complex unknown environments, including insufficient target detection and localization capabilities, frequent repetitive paths during the search process, and low completion rates of target searches. To address these issues, we integrate target detection with autonomous exploration and propose a semantic-aware autonomous search strategy, which consists of three components: target detection and localization, local search, and global relocation. First, target detection and localization are achieved by employing YOLOv8 for object recognition and projecting the detected 2D bounding boxes onto 3D point clouds. Accurate target localization is ensured through depth histogram analysis and density-based spatial clustering of applications with noise (DBSCAN) clustering. In the following search task, we divide it into local and global stages for optimization. Second, the local search stage utilizes a semantic-aware information gain strategy within a dynamically expanded RRT framework, generating viewpoints around the robot to explore and ensuring efficient coverage of target regions in the local vicinity. Finally, in the global relocation stage, global frontiers are clustered, and a traveling salesman algorithm is applied to optimize the target visiting sequence. This ensures comprehensive target inspection on a global scale, improving search efficiency and accuracy. Comparative evaluations in various challenging simulation and real-world scenarios against state-of-the-art methods demonstrate that our approach achieves shorter search paths, reduced time, and higher target search integrity.

  • Miniaturization of optimal six-port reflectometer based on reduced-length coupled-line directional couplers
    Owing to their simple structure, six-port reflectometers (SPRs) are used as alternatives to vector network analyzers (VNAs) for reflection-coefficient sensing. However, the circuit areas of existing SPRs are generally too large for integration into microwave measurement systems, and most do not satisfy the optimal design criteria. In this paper, a miniaturized SPR with an optimal distribution of the circle center is proposed based on four directional couplers. The SPR comprises one codirectional coupler and three transdirectional couplers, and the coupling coefficients of the directional couplers are derived theoretically. The circuit area of the proposed SPR can be reduced by miniaturizing each directional coupler based on the tandem coupled lines. The proposed SPR was designed and fabricated at 2–3 GHz using strip lines. The measured S-parameters and circle center distributions were in good agreement with the theoretical derivations and electromagnetic simulations. Attenuators with different attenuation values were measured using the proposed SPR and a VNA, and the results showed good measurement consistency of the proposed SPR and VNA. Compared to other SPRs, the proposed SPR features the reliability of reflection coefficient measurements and flexibility in size.

  • Empowering smart measurement of digital infrastructures with self-sensing concrete