Cavity ring-down spectroscopy (CRDS) is an ultra-sensitive direct absorption technique that offers unique advantages compared to other spectroscopic techniques. It can measure cooperative enhanced absorption for weakly absorbing species at ultra-low concentrations. This is achieved by leveraging the concept of a stable optical cavity, which allows for an effective optical path length of several kilometers within a small physical sample length. One advantage of CRDS technology is that it is unaffected by fluctuations in the intensity of the light source. Another advantage is its applicability to the detection of atoms, molecules, and radicals in the atmosphere. Additionally, the equipment associated with this technology is compact and robust. This paper will first introduce the fundamental principles and setup of CRDS technology. It will then provide an overview of the characteristics of the fabrication equipment and the high reflectivity mirror coating process used in cavity ring-down spectroscopy.

Inertial navigation technology originally designed for precise guidance of missiles is widely used in weapon systems. Guided missiles have become supersonic and high maneuverability with advancement of science and technology. Antivibration performance against high vibration and shock energy is accordingly required. Sensors of an Inertial Navigation System (INS) have a high sensitivity. Conversion coefficients for acceleration values and bias errors in signals must be minimized. A vibration isolator is generally applied to protect INS by attenuating the vibration and shock energy transmitted from dynamic disturbances. The stiffness and damping are changed using highly damped materials such as elastomers that must be protected from disturbances. A vibration isolator is widely used in various fields. However, it is important to understand characteristics of a vibration isolator composed of elastomer because it has nonlinearities such as hyperelasticity and viscoelastic as well as damping characteristics. In this study, a COTS vibration isolator suitable for INS was selected through theoretical approach. Response characteristics of the system in a vibration and shock environment were analyzed through FEM analysis and vibration and shock test. In addition, through repeated excitation test, reproducibility and structural stability were confirmed when the vibration isolator was installed in the system.

To develop a technology to diagnose the fault of dampers applied to railway vehicles and to set criteria, test runs were performed to measure damping force and displacement acting on a lateral damper during vehicle operation. Normal damper and fault damper were installed on a test train. Damper force and velocity of the lateral damper during test running were measured. Distributions of damper force and velocity representing the state of the damper had the same distribution in repeated tests. Distribution of the damper force and velocity was consistently uniform regardless of the train driving direction. Thus, the effect of train driving direction on damper force and velocity distribution was insignificant. The fault of the damper appeared to have a direct effect on the distribution of the damper force, suggesting that the fault of the damper could be sufficiently diagnosed just by monitoring the force of the damper. Especially, when comparing the velocity-force distribution, the fault damper showed a clear difference from a normal damper. Results of this paper could be used for developing a technology for diagnosing damper fault for railway vehicles in the future.

In this paper, we propose acoustophoretic microfluidic devices with an acoustic transparent polymer wall using a simple and low-cost fabrication method followed by MEMS (Micro-Electromechanical Systems) processes. Generally, due to the acoustic standing wave between two opposing walls in microfluidic channel, the particle focusing lines are fixed according to the applied frequency. In the proposed device, however, it is possible to place the particle focusing lines in the arbitrary position within the fluidic domain through the optimized width of polymer wall. The PDMS (Polydimethylsiloxane) mold with thin layer was used as the sealing layer between the Si substrate and cover glass, as well as the decoupling layer between the acoustic boundary and fluidic boundary. The thickness of PDMS mold needed to be minimized to decrease the heating by the acoustic energy absorption of PDMS layer, which was successfully made using the spin-coating of PDMS and the UV tape transfer method. The acoustophoretic device with thin PDMS layer and optimized width of PDMS wall can be applied, for biotechnological applications such as the separation of blood cells and micro-particles.

In an environment where ultra-high-precision equipment is used, vibration inevitably occurs due to various factors. These vibrations generate fatal effects, such as defect generation and reduced production yield, on ultra-high-precision production equipment. Among the multiple methods for solving vibration problems, a Tuned Mass Damper (TMD) is a useful technique that reduces vibration without changing the existing structure by attaching a passive dynamic system consisting of additional mass, spring, and damper. However, it is difficult to realize fine-tuning of the system parameters for optimal performance because the passive elements have structural limitations. An active TMD, which has a form wherein sensors, actuators, and a control device are added to the passive TMD structure, was introduced. It has higher performance than passive TMD because dynamic characteristics can be induced to stable and highly damped by a well-designed control algorithm realized by software in the control device. In this study, an active TMD was developed utilizing passive TMD with a voice coil actuator and attached to the center of both end fixed beam that assumed a single-degree-of-freedom structure. A dual-loop control algorithm using a non-minimum phase system was designed for a high-damped response while retaining stability. The modal test was performed for experimental evaluation and excellent performance of active TMD was verified.