Airborne Particle Detection Based on a Spin Hall Effect Measurement

A particle detection approach that measures a change of a spin-dependent photocurrent caused by a particle is proposed. The concept is evaluated through step by step mathematical analysis of an airborne particle sensing process using an inverse spin Hall effect (ISHE) device and a circularly polarized incident light, and an equation is derived to reveal the key parameters that affect the particle detection. The theoretical model predicts that the detection signal of a submicron particle will be on the scale of nanovolts when using a large ISHE sensor of a 10^-4 V signal without the particle disturbance, indicating that some submicron particles are likely detectable with a commercially available nanovoltmeter if background noise can be suppressed. The derived model further shows that the detection sensitivity can be increased significantly by decreasing sensor pixel size. This contrasts from conventional approaches to increase sensitivity using expensive high-power short-wavelength lasers or bulky optical components, allowing this proposed sensor to be more compact, cost effective, and power efficient than existing photon counters. In addition, the theoretical model suggests that the sensor can have multiple controllable knobs in the same device, which could be utilized to suppress background noise and perform comprehensive particle analysis. Because the proposed approach is to detect changes in light intensity, degree of circular polarization, and helicity caused by a particle in the same device, the approach can potentially provide better detection capabilities than existing techniques and address challenges in mobile, wearable, and process equipment applications.