RESUMO
A type of hollow gold nanoparticle (HGNP)-modified fiber optic long-range surface plasmon resonance (LRSPR) sensor with sensing self-reference is proposed and demonstrated. HGNPs have a stronger plasmonic field compared to solid GNPs because of the coupling between the inner and outer walls of HGNPs. The intense near-field electronic coupling between long-range surface plasmon polaritons associated with the LRSPR gold layer and localized surface plasmon polaritons of HGNPs leads to localized electromagnetic-field enhancement and LRSPR response signal amplification. Therefore, the HGNP-modified LRSPR sensor possesses a more excellent sensing property compared with the unmodified LRSPR sensor. The long-range resonance dip in the transmission spectrum is shown to shift in response to ambient refractivity change, and the characteristic absorption peak is fixed, allowing to regard it as a reference to improve detection accuracy of the sensors. The mode-field distribution of the sensors is simulated by using the finite element method, and the simulation results show that the electric-field intensity on the HGNP surface is significantly enhanced compared with that of the gold layer surface of the unmodified LRSPR sensor. 1874.79 nm/RIU improvement in sensitivity, 1.42 times improvement in figure of merit (FOM), and approximately 50% reduction in limit of detection (LOD) are achieved for the refractivity measurement of a low-concentration biological solution with the employment of HGNPs in LRSPR sensing experiments. The HGNP-modified LRSPR sensor proposed in this paper has high detection accuracy and FOM and low LOD, and can realize remote real-time online monitoring. Therefore, it has important research value and broad application prospects in the field of biochemical detection.
RESUMO
Cam mechanism is widely applied in industry because it can help achieve various complex motions of the follower via the cam contour design. However, its performance is significantly affected by the wear condition. This study proposes a load distribution measurement instrument to assist the study on friction and wear regularities of oscillating follower cam mechanisms through obtaining the normal pressure (F) and friction force (Ff) distributions along the cam profile. In the instrument, F and Ff are automatically calculated via a MATLAB program based on the geometry and the measured rotary resistance torque and rotary angle of the cam. The latter two parameters are obtained through a static torque sensor and a rotary encoder built in servo motor in real time, respectively. An experimental test was conducted and the cam morphology after service was observed using scanning electron microscopy. Results show that the wear condition of the cam is significantly related to the corresponding F and Ff. Complex load parameters of oscillating follower cam mechanisms can be provided by this instrument, which is crucial in understanding the friction and wear behaviors of cams and finding the vulnerable position.