Current submersible structural health monitoring techniques suffer from poor positioning accuracy and insensitive perception of structural defects. The existing structural health detection techniques are investigated to address these problems, this paper presents an acoustic measurement system with passive listening triggering active detection is proposed. In this paper, a spherical receiver transducer array and a forked finger transducer are fabricated using polyvinylidene fluoride (PVDF) piezoelectric film as the core device. The system uses the receiver transducer array to receive acoustic signals and determine the location of structural damage based on the acoustic signals, and then actively triggers the fork-finger transducer at the corresponding location to generate acoustic surface waves to detect structural defects in titanium alloys. The feasibility of the designed system is verified through experiments, which show that the device can determine the orientation of the noise and whether a fracture has occurred in the structure.
This paper describes the fabrication method of a PVDF interdigital transducer (PVDF-IDT) suitable for the underwater environments and conducts experiments on the detection of structural defects of underwater structures based on the IDT Rayleigh wave technology. The micro-sized and soft material property of PVDF-IDT has the characteristic of being permanently adhered to the surface of the inspected structure and shows great potential for the construction of lightweight structural health monitoring systems. Therefore, this paper has carried out the Rayleigh wave-structure damage experiment to obtain the empirical formula of surface wave and structural damage, and the empirical formula shows that the surface wave can achieve sub-millimeter precision detection of structural damage.
Absorption-based optical sensors have been developed for the determination of water pH. In this paper, based on the preparation of a transparent sol–gel thin film with a phenol red (PR) indicator, several calculation methods, including simple linear regression analysis, quadratic regression analysis and dual-wavelength absorbance ratio analysis, were used to calculate water pH. Results of MSSRR show that dual-wavelength absorbance ratio analysis can improve the calculation accuracy of water pH in long-term measurement.
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