An eddyingized sensor made of carboxylated multi-walled carbon nanotube@dodecyl benzene sulfonic acid-doped polyaniline for dual-function detection of ammonia concentration and gap

In the confined, curved spaces of high-precision equipment, single-function sensors cannot monitor multiple parameters like gas concentration and gap. This study prepared an eddyingized sensor based on flexible thermoplastic polyurethane (TPU) fibers for the detection of ammonia concentration and gap, by optimizing the compounding ratio of dodecylbenzenesulfonic acid-doped polyaniline (DBSA-PANI) and carboxylated multi-walled carbon nanotubes (MWCNT-COOH). The TPU-MWCNT-PANI-0.1 sensor enables the detection of ammonia within the concentration range of 0–30 ppm, with a relative resistance change of 11.62% at 30 ppm and good selectivity. The response and recovery time to 24 ppm NH 3 are 21 s and 240 s, respectively. For gap detection (0–5 mm), the maximum sensitivities are 0.2619 mm −1 (impedance magnitude) and 0.1095 mm −1 (impedance angle) within the 1–0 mm range. The repeatability and stability of the sensor are evaluated: after 20 cycles in 24 ppm NH 3 , the relative standard deviations (RSD) for the relative change in resistance, impedance magnitude, and angle are 0.59%, 1.16%, and 1.38%, respectively. Over 30 repeated gap tests (0–5 mm), the RSD for the relative change in impedance magnitude and angle are 0.13% and 0.32%, respectively. A 31-day test confirms long-term stability, with all RSD below 2.28% for NH 3 tests and 0.08% for gap tests. The sensor also maintains mechanical stability after eight bending cycles at 30°, 60°, and 90°. A signal-separation strategy using direct current resistance and alternating current impedance enables dual-parameter detection of ammonia (0–30 ppm) and gap (0–5 mm), providing a simple and reliable solution.