Portable, Integrated Microscale Sensors (PIMS) for Explosives Detection
Overview and Significance
To successfully deter and detect explosives threats, a multimodal technical approach based upon an array of orthogonal or near-orthogonal sensing technologies (e.g. spectroscopic systems, imaging systems, swab-based sensors, etc.) is essential. The present effort seeks to develop a sensing system that can address one such detection vector, namely portable, integrated, microscale sensors (PIMS) that are suitable for vapor-phase explosives detection. These small-scale, cost-effective sensing systems are ideally suited for integration into existing baggage, cargo, and passenger screening portals, building ventilation systems or handheld portable devices, and, as subsequently described, exhibit performance metrics (e.g. false positive/ negative rates, sensitivities, and power consumption metrics) that are expected to compare very favorably when integrated in operational environments. The PIMS devices being developed within the context of ALERT are based on so-called bifurcation-based mass sensing principles, wherein vapor-phase target analytes chemomechanically interact with a functional layer (typically a polymer) deposited upon the oscillating surface of a microscale electromechanical resonator. This interaction renders a change in the resonator’s effective mass, eliciting a shift in natural frequency and, given that the system is driven into a nonlinear response regime with two stable response branches, a marked change in amplitude. Because this approach utilizes a nonlinear mechanism and a threshold technique for sensing, the associated control electronics can be greatly simplified (in comparison to sensors based solely on resonance-shift principles), which significantly aids the development of portable sensors with reduced form factors and favorable power consumption metrics. In addition, the sensitivity of the system can be widely tuned, as it is not based solely on the underlying physics of the device. In prior work by the investigators, which focused on vapor-phase alcohol sensing, bifurcation-based mass sensors were shown to yield superior performance metrics (i.e. false positive/negative rates, sensitivity and power consumption metrics) in laboratory environments and compared favorably to their more conventional counterparts.
The antithesis of a feedback linearization system, this controller ensured that any quartz or MEMS resonator, designed to exhibit a linear frequency response structure, exhibits the softening nonlinear frequency response structure required for bifurcation-based sensing (additional details can be found above).Phase 2 Year 2 Annual Report
Students Currently Involved in Project
- Nikhil Bajaj