Ultralow-frequency ultranarrow-bandwidth coherent terahertz imaging for nondestructive testing of mortar material.

Nondestructive testing of concrete materials is essential in civil engineering to maintain social infrastructure such as buildings or bridges. In this study, we constructed an ultralow-frequency, ultranarrow-bandwidth, coherent terahertz (THz) imaging system based on THz time-domain spectroscopy (THz-TDS). Based on its ultralow-frequency-localized THz wave and coherent detection, the present system achieved a wide dynamic range of THz power over 100 dB at 0.046 THz, which is appropriate to measure the mortar material. The achieved dynamic range of the THz power was 59 dB larger than that of a commercialized THz-TDS system and 49 dB larger than that of an ultralow-frequency noncoherent THz imaging system equipped with a high-power electric THz source. Ultimately, the proposed system could visualize the inner structure of a mortar sample with a thickness of 10 mm, and the present system can investigate a mortar sample with a thickness of over 130 mm. The proposed method is an attractive tool for non-destructive testing of thick concrete structures characterized by non-invasiveness and non-contact remoteness.

Design-of-experiment analysis of non-destructive detachment of electric parts from printed circuit boards of mobile phones using a cross-flow shredder.

For minor metal recycling from electric parts, detachment without breakage (non-destructive detachment) of the electric parts from printed circuit boards (PCBs) is required. A cross-flow shredder (CFS), a drum-type chain mill, is often used in PCB recycling, but the effects of its individual features (e.g., chain thickness) on the non-destructive detachment of the PCB parts have yet to be understood. In this study, a CFS suited to the design-of-experiment (DoE) approach was developed; 27 different experimental conditions were evaluated, with three repetitions under each condition for a single PCB crushing, and the effect of nine CFS factors on the non-destructive detachment of parts from the PCBs of mobile phones was investigated. It was revealed that two factors (rotation rate and vent screen) have a statistically significant influence on such non-destructive detachment, and two other factors (chain-wall distance and crushing time) have a significant influence on related results such as the overcrushing of boards (PCBs after parts detachment) and powder generation. Based on these results, a future perspective on CFS improvement is presented.

Experimental validation of a 2D-3D conversion method for estimation of multiple 3D characteristics of discrete elements.

Accurate assessment of three-dimensional (3D) characteristics, such as the shape and size distribution, of discrete elements (e.g. particles, granules, grains, voids, crystals, cells and fibers) is required in various fields. But generally, in practice, two-dimensional (2D) instead of 3D assessment is conducted due to limitations in time, cost or measurement technology (as in microscopic observation of discrete elements). In this study, experimental validation was conducted for a 2D-3D conversion method, developed in 2018, which estimates multiple 3D parameters based on 2D counterparts, using an x-ray computed tomography analysis of silica sand. Six 3D parameters (volume, surface area, long-axis length, sphericity and long/middle and long/short axis ratios) were successfully estimated based on five measured 2D parameters (sectional area, perimeter, long-axis length, circularity and long/short axis ratio).