Hitoshi Hamasaki

Past studies have reported that carbon dioxide emissions during combustion vary depending on the tree species used as fuel. It has also been reported that the moisture content of wood affects combustion efficiency. From this perspective, identifying the tree species and moisture content is crucial for utilizing waste wood as a resource. Therefore, this study verified the effectiveness of non-destructive diagnosis using terahertz waves. Samples with adjusted moisture content were prepared for eight types of wood. Each wood sample was irradiated with multiple broadband terahertz electromagnetic waves, and their transmission characteristics were compared. Experimental results revealed a strong negative correlation (Pearson Correlation coefficient: −0.98~−0.71 square meter/gram) between the sample’s specific gravity and transmittance when irradiated with 65 GHz and 90 GHz sub-terahertz waves. This trend was particularly pronounced during 90 GHz sub-terahertz irradiation. Furthermore, it was found that the trend in transmittance variation differed depending on the wood’s moisture content. These results indicate that terahertz waves are effective as a wood identification method capable of distinguishing between coniferous and broadleaf trees. Furthermore, they are considered effective for predicting wood moisture content. This research is expected to contribute to promoting wood recycling and the sustainable use of wood resources.

The application of sub-terahertz waves is being considered as a method to view the corrosion status of internal steel bars. In this study, reflectance intensities were measured for six specimens with different moisture contents using electromagnetic waves from 7.5 to 17.5 GHz. The results showed that the differential reflectance intensity decreased with increasing water content. An equation for estimating the water content at a cover thickness of 10 mm was also calculated. Regarding chloride ion content, no common trend was observed, and it was confirmed that there was a trend in the amount of chloride ions at each cover thickness.

A feasibility study was conducted on the detection of corroded rebars inside concrete using sub-THz waves. In this study, spectral measurements were performed with a reflection-type system in the 20–50 GHz frequency range. Measurements were conducted on steel plates corroded in salt water and on concrete specimens containing these corroded plates. The results confirmed that reflectance decreases as corrosion progresses. Furthermore, it was demonstrated that the presence or absence of internal steel plates and corrosion can be detected up to a cover thickness of 20 mm. The frequency spectral peaks and their periodicity also provided a means to estimate the cover thickness.

Many of Japan’s infrastructures are more than 50 years old, and more old infrastructures are expected in the future. Therefore, the challenge is to inspect the deteriorated condition of those infrastructures. This study focuses on the use of electromagnetic waves in NDT as an inspection method for infrastructure. One issue with this method is that the device is not suitable for actual infrastructure inspections. We constructed a portable reflection measurement system that utilizes sub-terahertz waves among electromagnetic waves. Reflection measurements were conducted on corroded and uncorroded steel plates using this compact system. It may be possible to identify samples using peak shift with a horn antenna. With a probe antenna, identification is based on reflectance.