###### Abstract  
Using a sample coated with three types of carbon-based paints, namely single-wall carbon nanotube (SWCNTs), carbon black, and graphite, the amount of radio wave absorption for each was measured. SWCNTs proved to have the superior radio wave absorption effect in the millimeter band. Considering the change in the amount of radio wave absorption depending on the coating amount, three different coating thicknesses were prepared for each test material. The measurement frequency was set to two frequency bands of 28 GHz and 75 GHz, and the measurement method was carried out based on Japanese Industrial Standard (JIS) R1679 \"Radio wave absorption characteristic measurement method in the millimeter wave band of the radio wave absorber.\" As for the amount of radio wave absorption in the 28 GHz band, a maximum amount of radio wave absorption of about 6 dB was obtained when 35 m of CNT spray paint was applied. It was confirmed that the carbon black paint came to about 60% that of the SWCNT, and the graphite paint did not obtain much radio wave absorption even when the coating thickness was changed. Furthermore, even in the 75 GHz band, the radio wave absorption was about 7 dB when 16 \(\upmu\)m of CNT spray paint was applied, showing the maximum value. Within these experimental results, the CNT spray paint has a higher amount of radio wave absorption in the millimeter wave band than paints using general carbon materials. Its effectiveness could be confirmed even with a very thin coating thickness of 35 \(\upmu\)m or less. It was also confirmed that even with the same paint, the radio wave absorption effect changes depending on the difference in coating thickness and the condition of the coated surface.  
ememailment wave; millimeter wave; radio wave absorber; electromagnetic wave shielding; 5G; in-vehicle radar; IoT; stealth; EMC (electromagnetic compatibility); EMI (electromagnetic interference); EMS (electromagnetic susceptibility); SWCNT +
Footnote †: journal: Applied Sciences  
environment will deteriorate due to interference. Thus, there is an urgent need to develop technology to control the radio wave environment.  
In recent years, attention has been focused on various shapes of micro/nanostructures, such as rods, tubes, beams, plates, and shells, and their mechanical behaviors [2]. In particular, carbon nanotubes are attracting attention. CNTs are tubular, fibrous, one-dimensional materials consisting only of carbon with a diameter of nanometers [3]. CNTs are extremely lightweight because their constituents are only carbon atoms. CNTs can be classified into single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) according to their structure (see Figure 1).  
Reinforced composites such as carbon nanotubes are new nanomaterials, and their mechanical behavior has recently been attention-grabbing in materials science and engineering science due to their excellent mechanical and electrical properties after fusion with a matrix [4; 5].  
The radio wave absorption effect of SWCNTs (single-walled carbon nanotubes) is attracting attention as a technology for controlling the radio wave environment, but its specific characteristics have not yet been fully studied.  
By comparing the radio wave absorption effect in the millimeter wave band within conventionally used carbon-based material and SWCNTs in this paper, the purpose of the study is to verify the possibility of using SWCNTs as radio wave absorbers for the millimeter wave band.