Stealth nanobeacons consisting of irregular-shaped aggregates of gold colloidal nanoparticles are promising anti-counterfeiting taggants due to their surface-enhanced Raman scattering (SERS) signals and high resistance to imitation as chemical physical unclonable functions (PUFs). Inkjet printing enables flexible placement of such taggants but suffers from unstable droplet ejection caused by particle aggregation arising from their irregular and anisotropic structures.

In this study, fundamental aspects of inkjet printing for stealth nanobeacons were investigated using polystyrene nanoparticles of comparable size as model particles. Inkjet ejection behavior was analyzed from the perspective of solid-liquid multiphase flow, and particle concentration distributions in the ink and printed films were evaluated. The results clarify particle-size-dependent ejection behavior and concentration distribution mechanisms, providing guidelines for stable inkjet printing of functional inks containing irregular nanostructured aggregates.

Silicon piezoresistive (PZR) sensors have been widely used for stress and strain detection in MEMS applications, but further improvements in sensitivity and miniaturization are required for emerging uses. This study presents a piezo-Zener (PZZ) sensor utilizing a Zener diode, designed and fabricated for detecting micro-strains in MEMS actuators, offering superior temperature characteristics and potential for low-power operation. A silicon cantilever integrated with the PZZ sensor was prototyped. The PZZ sensor achieved a sensitivity of 0.671 µA/MPa under constant voltage bias (-21.2 V, initial current -1 mA), surpassing the low-doping PZR sensor’s 0.428 µA/MPa in similar conditions (1.45 V, initial current 1 mA). The sensor showed a temperature coefficient of 0.086%/°C, slightly lower than the high-doping PZR sensor's at 0.103%/°C. Noise characteristics revealed noise density floor of approximately 0.01 nV²/Hz both for PZZ and high-doping PZR in the 10 Hz to 5 kHz band. The Allan deviation revealed that the bias instability of the PZZ sensor is about two orders of magnitude lower than for the high-doping PZR sensor (0.027 mV/√s vs 1.79 mV/√s). These results highlight the PZZ sensor’s promise for combining high sensitivity with stable temperature and noise performance, avoiding the trade-off inherent in conventional PZRs.

This study evaluates the ignition risk of hydrogen-oxygen mixtures exposed to high-temperature microheaters used for hydrogen sensors by means of thermo-fluid simulations incorporating chemical kinetics. To reproduce the known ignition temperature of 833 K for hydrogen-oxygen mixtures, the activation energy in the Arrhenius rate expression was calibrated. Simulations were carried out for (i) a microheater with a 0.2 mm × 0.2 mm heated zone and (ii) a rotationally symmetric ellipsoidal coil heater 1 mm long with a mid-radius of 0.25 mm. Ignition occurred at 1173 K for the microheater, which is higher than the 923 K predicted for the coil heater. This difference is attributed to the microheater's very narrow hot zone: radicals generated there readily diffuse into the surrounding cooler gas and are quenched, thereby suppressing the chain reactions required for ignition.

It is important to measure water content and electric conductivity in agricultural soil. This study presents a four-terminal soil impedance measurement system for wide-area sensor-to-sensor measurement. While conventional two-terminal methods suffer from accuracy degradation due to parasitic components in long cables, the proposed system achieves accurate measurement by separating current supply and voltage measurement paths. A digital signal processing-based lock-in amplifier was implemented on a microcontroller with a compact 50-mm square board. Performance verification demonstrated significant improvement in capacitance measurement errors, particularly in low-resistance and low-capacitance regions, generally achieving the target relative error of within 10% and showing the feasibility of wide-area soil measurement.

Furthermore, measurements with laboratory-prepared soil samples showed that the proposed system’s capacitance values agreed to within ±10% of those obtained using a commercial impedance analyzer (4294A). Moisture estimation was achieved within ±5% error for medium-moisture ranges (20-40%), whereas drier soil (∼10%) yielded larger deviations due to the small capacitance shift of 74.6 fF per 1% moisture change. This indicates that improving electrode geometry to amplify moisture-dependent impedance variation is a promising direction for enhancing accuracy in practical deployments.