Greg Kaduchak - kaduchak@lanl.gov
Christopher Kwiatkowski and Dipen Sinha
Electronics and Electrochemical Materials and Devices Group
Los Alamos National Laboratory
Los Alamos, NM 87545
Popular version of paper 3aPA5
Presented Wednesday morning, November 12, 2003
146th ASA Meeting, Austin, TX
Today the detection, identification, and separation of aerosols have potential applications in a wide variety of fields ranging from environmental science to homeland security. Information about airborne particle sizes, particle distribution, and particle composition is important, and sometimes even critical, to researchers studying the environmental impact of industrial smog, or to military specialists and emergency responders trying to detect chemical or biological agents in the air. Unfortunately, the efficiency of detectors has been limited by their sensitivity to only relatively high aerosol concentrations.
Scientists at Los Alamos National Laboratory have recently created a simple device that quickly and inexpensively concentrates aerosols using sound waves created inside a piezoelectric (PZT) tube. The solid-state device requires very little power to operate and has the potential to greatly increase the efficacy of current generation aerosol detection devices (particle sizers, optical classifiers, etc.) by significantly increasing aerosol concentrations.
Figure 1 - close up of acoustic aerosol concentrator
Constructed from a commercially available PZT tube, the device works by rapidly expanding and contracting the approximately 2-mm-thick tube wall. These vacillations produce minute vibrations inside the tube that create pressure nodes in the form of lines along the axis of the tube. Aerosols drawn into the open-ended, air-filled tube concentrate in these pressure nodes and modifications to the tube can reduce the pressure nodes down to a single line. Once concentrated, the aerosols can be directed into a detection device, or simply held suspended against gravity in a form of acoustic levitation. In tests of a 19-mm diameter device, Los Alamos researchers have levitated 1-mm diameter drops of water using only 0.1 watts of electrical power. Acoustic levitation provides a means for isolating small samples without a containment vessel for a variety of analyses.
Figure 2 - Acoustic aerosol concentrator with aerosol stream passing through the acoustic cavity. (arrow indicates direction of aerosol stream) The acoustic field is OFF.
Figure 3 - Once the acoustic field is activated, the aerosol is instantly driven to three nodal positions. The high concentration causes the aerosol particles to agglomerate.
This new class of acoustic aerosol concentration devices will alleviate many of the alignment and power consumption requirements found in traditional acoustic levitators/concentrators, such as those using parallel plate transducer assemblies. The new devices are not only inexpensive to produce, but they also never need alignment.
The PZT tube may be most useful when coupled to the current array of aerosol detection devices on the market. Because aerosol detectors are more sensitive at higher aerosol concentrations, the device will greatly increase their sensitivity. In addition, the device's low power requirements make it especially advantageous for use in battery-operated, hand-held detectors. The Los Alamos scientists are currently implementing this device into various aerosol monitoring systems in conjunction with other teams and laboratories for homeland security and environmental applications.