The impregnated active carbon used in air purification systems degrades over time due to exposure to contamination and
mechanical effects (packing, settling, flow channeling, etc.). A novel approach is proposed to detect contamination in
active carbon filters by combining the electromechanical impedance spectroscopy (EMIS) and electrochemical
impedance spectroscopy (ECIS). ECIS is currently being used to evaluate active carbon filtration material; however, it
cannot differentiate the impedance changes due to chemical contamination from those due to mechanical changes. EMIS
can detect impedance changes due to mechanical changes. For the research work presented in this paper, Piezoelectric
wafer active sensor (PWAS) was used for the EMIS method. Some remarkable new phenomena were unveiled in the
detection of carbon filter status.
1. PWAS EMIS can detect the presence of contaminants, such as water and kerosene in the carbon bed
2. PWAS EMIS can monitor changes in mechanical pressure that may be associated with carbon bed packing,
settling and flow channeling
3. EMIS and ECIS measurements are consistent with each other and complimentary
A tentative simplified impedance model was created to simulate the PWAS-carbon bed system under increasing
pressure. Similar impedance change pattern was observed when comparing the simulation results with experimental
A remote atmospheric breakdown (RAB) is a very rich source of ultraviolet (UV) and broadband visible light that could provide the early warning to the presence of CW/BW agents through spectroscopic detection, identification and quantification at extended standoff distances. A low-intensity negatively chirped laser pulse propagating in air compresses in time due to linear group velocity dispersion and focuses transversely due to non-linear effects resulting in rapid laser intensity increase and ionization near the focal region that can be located kilometers away from the laser system. Proof of principle laboratory experiments are being performed at the Naval Research Laboratory on the generation of RAB and the spectroscopic detection of mock BW agents. We have demonstrated pulse compression and focusing up to 105 meters in the laboratory using femtosecond pulses generated by a high power Ti:Sapphire laser. We observed nonlinear modifications to the temporal frequency chirp of the laser pulse and their effects on the laser compression and the positions of the final focus. We have generated third harmonics at 267 nm and white light in air from the compressed pulse. We have observed fluorescence emission from albumin aerosols as they were illuminated by the compressed femtosecond laser pulse.