Micrometer-scale displacement and thickness sensing using a single terahertz resonant-tunneling diode
This work provides a compact, cost-effective THz sensing solution for industrial applications requiring micrometer precision.
A single resonant-tunneling diode operating at 280 GHz is used as a self-mixing radar to detect micrometer-scale displacements (~5 μm resolution) and thin-film thicknesses (12.5, 25, 50 μm) at room temperature.
Resonant tunneling diodes (RTDs) support room-temperature terahertz (THz) oscillation and simultaneous THz-band detection, enabling compact monostatic THz sensors for practical and cost-effective sensing applications. In this paper, we present a highly integrated 280 GHz-band radar system based on a single RTD that exploits the self-mixing effect to generate a low-frequency interferometric signal. The resulting self-mixing signal is further analyzed from a radar perspective and processed to extract micrometer-scale displacement and thin-film thickness variations. Experimentally, the proposed system demonstrates a minimum detectable displacement of approximately 5 um and quantitatively resolves polymer film thicknesses of 12.5, 25, and 50 um.