Sniffers: Fluid-Dynamic Sampling for Olfactory Trace Detection in Nature and Homeland Security—The 2004 Freeman Scholar Lecture

[+] Author and Article Information
Gary S. Settles

gss2@psu.edu Department of Mechanical and Nuclear Engineering,  Penn State University, University Park, PA 16802.

J. Fluids Eng 127(2), 189-218 (Feb 10, 2005) (30 pages) doi:10.1115/1.1891146 History: Received February 10, 2005

Vertebrates aim their noses at regions of interest and sniff in order to acquire olfactory trace signals that carry information on food, reproduction, kinship, danger, etc. Invertebrates likewise position antennae in the surrounding fluid to acquire such signals. Some of the fluid dynamics of these natural sensing processes has been examined piecemeal, but the overall topic of sniffing is not well investigated or understood. It is, however, important for several human purposes, especially sampling schemes for sensors to detect chemical and biological traces in the environment. After establishing some background, a general appraisal is given of nature’s accomplishments in the fluid dynamics of sniffing. Opportunities are found for innovation through biomimicry. Since few artificial (“electronic”) noses can currently sniff in the natural sense, ways are considered to help them sniff effectively. Security issues such as explosive trace detection, landmine detection, chemical and biological sniffing, and people sampling are examined. Other sniffing applications including medical diagnosis and leak detection are also considered. Several research opportunities are identified in order to advance this topic of biofluid dynamics. Though written from a fluid dynamics perspective, this review is intended for a broad audience.

Copyright © 2005 by American Society of Mechanical Engineers
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Figure 1

Examples of olfactory flow visualization in nature. (a) condensed moisture traces of a rat sniffing on a Zwaardemaker mirror, a form of surface flow visualization, courtesy F. Bojsen-Møller, and (b) tracer particles disturbed by a dog sniffing a horizontal surface, and (c) schlieren image of the exhalation from a dog’s nose (47)

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Figure 2

Diagram of a basic sniffing process (the actual interior of a dog’s nose is much more complicated than this)

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Figure 3

Streamlines (arrowed) and equipotential lines (solid) for (a) a flanged, sharp-edged inlet and (b) a bulbous “natural” bellmouth inlet. (These planar 2D potential flow solutions are shown only for illustration purposes)

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Figure 4

Portal results of liberated RDX particle mass as a function of impinging-jet stagnation pressure (83)

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Figure 5

Inlet vortex into a vacuum cleaner hose with a cross breeze, visualized by coating the ground plane with talcum powder

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Figure 6

(a) Schlieren image of the rising boundary layer and thermal plume from a human being (L. J. Dodson) (46) and (b) scanning electron microscopy image of a desquamated human skin flake, H. A. Gowadia (123-124). According to Syrotuck (125), “They are cornflake in shape which gives them an aerodynamic characteristic.”

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Figure 7

Sampling inlet probes on the NASA-Dryden DC-8, (a) heated, Teflon-lined PANAK probe, (b) U. Hawaii shrouded probe (147), (c) nacelle-mounted ATHOS probe (146), (d) wing-tip mounted aerosol scattering spectrometer probes, and (e) shrouded POPS probe (NASA photos)

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Figure 8

Schlieren images of high-Rayleigh-number thermal convection from a suddenly heated horizontal surface, simulating the earth at sunup on a windless day, courtesy J. C. Mollendorf (167). (a) Early thermals, (b) a forest of starting thermal plumes develops, with both their crowns and stalks visible, and (c) fully developed thermal convection field. These pictures compliment those in the literature using tracer-particle visualization. Here an integrated view is shown, though one can imagine the depth effect

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Figure 9

Satellite photo of the ash plume from the eruption of Mount Etna on October 29, 2002. The plume direction is SSE over eastern Sicily, the city of Siracusa, and the Mediterranean Sea. The lateral scale is roughly 200km, and the scale of the largest visible eddy (i.e., the plume width) is perhaps 10km. Photo PIA03733 by the NASA GSFC/LaRC/JPL MISR Team

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Figure 10

An abridged phylogeny of mammals for the study of external nares evolution. For brevity the common name is given in place of the scientific species name. Time progresses nonlinearly from left to right for compactness, and branches indicate evolutionary divergences of a group (the lower arm) from the general mammalian stock

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Figure 11

External nares of a Golden Retriever (a) during inhale and (b) during exhale portions of sniffing cycle (47), and (c) solid cast of the nasal cavity of a dog reconstructed from CAT scans (62) (cast provided courtesy T. S. Denny Jr., Auburn University)

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Figure 12

(a) Schlieren image revealing the “ejector effect” of expired air jets during canine sniffing that draws in air from a warm forward scent source and (b) diagram illustrating the region of expired jet impact upon a ground plane (dotted line) and the induced airflow caused by jet entrainment (47). See also Fig. 1

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Figure 13

External nares of (a) a domestic shorthaired cat and (b) a burro, Equus asinus, photo by L. J. Dodson

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Figure 14

External nares of (a) a piglet and (b) a calf, photos by L. J. Dodson

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Figure 15

External nares of (a) cottontail rabbit, Sylvilagus obscurus and (b) human, Homo sapiens

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Figure 16

(a) CFD solution of airspeed in the F344 rat’s nasal cavity (53,247), courtesy J. S. Kimbell and (b) sectional anatomy of an albino rat’s nasal cavity with darkened olfactory epithelium (248), courtesy J. S. Kauer

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Figure 17

(a) External nares of a Sprague-Dawley lab rat provided by M. J. Kennett, Penn State University and (b) external nares of the opossum Didelphis virginiana

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Figure 18

(a) Close-up image of the Great Spotted Kiwi’s beak tip, copyright Chris Smuts-Kennedy, reproduced by permission. (b) The upper beak of the tube-nosed Dove Prion, Pachyptyla desolata, redrawn from (258)

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Figure 19

Lateral flagellum of one antennule of the clawed lobster Homarus americanus. Proximal diameter shown is 1.4mm. Hairlike projections are aesthetascs and guard hairs (out of water and in disarray). See (92) for electron microscopy images

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Figure 20

(a) Giant silkworm moth, Antheraea polyphemus, wingspan 8cm and (b) closeup of feathery antennae

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Figure 21

(a) Mosquito feeding on a human hand. Courtesy Philip Myers, http://animaldiversity.ummz.umich.edu. One antennal flagellum is visible. (b) Microgram of a mosquito antennal flagellum, about 20μm in diameter, showing two complete segments, the long sensilla chaetica, and the numerous shorter sensilla trichodea, photo by J. M. Listak

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Figure 22

The GE Infrastructure Security VaporTracer sniffing a briefcase

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Figure 23

2D potential-flow simulation of an Aaberg inlet

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Figure 24

Diagram of a cyclone sampling nozzle for an ion mobility spectrometer, from (96)

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Figure 25

Schlieren photos of a flanged inlet sampling a thermal boundary layer (a) in still air and (b) with a light lateral breeze from the right (47)

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Figure 26

The path of water through the olfaction chamber of an eel, top view, redrawn from illustrations in (40,253,325)

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Figure 27

Canine olfaction sensitivity curves measured at Auburn University, redrawn from http://www.vetmed.auburn.edu/ibds/. Except for methyl benzoate, a cocaine derivative, all trace chemicals shown are explosive-related

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Figure 28

(a) The author standing in a prototype version of the GE Infrastructure EntryScan3 explosive detection portal (Penn State photo by Greg Grieco) and (b) schlieren image of portal with subject (L.J. Dodson) and with air-jet puffers firing

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Figure 29

Diagrams of motion in the human aerodynamic wake from smoke flow visualization experiments (372,378), (a) median plane and (b) dorsal plane

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Figure 30

Corresponding to Fig. 2, computed instantaneous motion of a scalar contaminant in the aerodynamic wake of a simulated human (372), (a) median plane and (b) dorsal plane

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Figure 31

(a) Schlieren image of an acetone vapor leak cascading downward and being inhaled (arrow) by the snout of the Cogniscent artificial nose (b) a hand-held, wand-type sniffer probe is used to search for a natural gas leak, visualized by large-field schlieren optics (46,408,411)




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