Inspection of alien metal particles in electronic materials such as glass fibers and resins is a critical issue to control the quality and guarantee the safety of products. In this paper, we present a new detection technique using sub-millimeter wave for films as electric materials in product lines. The advantage of using sub-millimeter wave frequency is that it is easy to distinguish conductive particles from a nonconductive material such as plastic films. Scattering of a submillimeter wave by a metal particle is used as the detection principle. By simulation, it is observed that the scattering pattern varies intricately as the diameter varies from 10 to 700 μm at 300 GHz. The demonstration system is composed of a Keysight performance network analyzer (N5247A PNA-X) with 150–330 GHz VDI extension modules, transmitting and receiving antennas, and focusing dielectric lens. An output signal is radiated via an antenna and focused onto a metal particle on a film. The wave scattered by the metal particle is detected by an identical antenna through a lens. The signal scattered from a metal particle is evaluated from the insertion loss between antennas (S<sub>21</sub>). The result shows that a particle of diameter 300 μm is detectable at 150–330 GHz through S<sub>21</sub> in the experimental system that we prepared. Peaks calculated in simulation were detected in experimental data as well as in the curves of the particle diameter versus S<sub>21</sub>. It was shown that using this peak frequency could improve S<sub>21</sub> level without higher frequency.
This paper reviews the development of microwave carbon nanotube resonator sensors for gas sensing applications. The carbon nanotube sensor is a passive circuit that does not rely on battery for operation. Our experimental results demonstrate that the microwave carbon nanotube resonator sensor achieve a sensitivity of 8000 and 4000 Hz/ppm at 20 and 100 ppm respectively. This sensor platform has great potential for wireless sensing network applications.