Transcript Slide 1
Abstract
According to recent biology literature, Mustelus canis sharks localize odors based on the time delay between olfactory signals detected by each of their nares. This project replicates this process by implementing a LabVIEW GUI to collect voltage data from an array of three sensor pairs, in which each sensor in a pair functions as an individual nare in an “electronic nose.” This project investigates several methods of isopropyl alcohol exposure to simulate the dispersion of odor due to a chemical leak. Experimenters implemented a Dynamic-Time-Warp processing algorithm to compute the overall delay between signals in each sensor pair.
These delays were used in a voting system to localize the source relative to the sensor array. This approach presents some limitations because signals from individual sensors in each sensor pair do not have identical morphologies. While additional work is required to improve the system’s consistency, preliminary results are promising. This sensor system will eventually interface to a mobile robotic platform that will actively seek out a chemical source.
Overview Data Acquisition
• Voltage to sensor circuit controlled by the above LabVIEW data acquisition algorithm during exposure to isopropyl alcohol.
• Isopropyl alcohol placed on either Top or Bottom side of circuit, at varying distances (10, 20, 30, 40 and 50 cm) from the array.
• Presence of alcohol alters sensor conductivity, resulting in voltage outputs from each sensor.
Isopropyl Alcohol Exposure to Sensor Array Experimental Setup
Goal
: Develop a sensor array that distinguishes between two possible source locations: Top (above the sensor array) and Bottom (below the sensor array).
TOP “Electronic noses” Figaro sensor Isopropyl alcohol source BOTTOM Elvis Data Acquisition Circuit
Sensor array composed of 3 columns, each containing a pair of compatible sensors that functions as an “electronic nose” to detect isopropyl alcohol during data collection
PREVIOUS METHOD
• Alcohol diffuses from cap • Limitations - Concentration depends on airflow in the room - Delay computation difficult due to varied number and placement of peaks
OUR METHOD
• Alcohol evaporates from 2”x2” alcohol-soaked paper towel, reducing surface tension • Fan blows over odor source to standardize air flow • Odor introduced using impulse input rather than step input
The time delay between sensor pair signals, computed via Dynamic Time Warping, determines the odor source location detected by sensor array.
Data Processing
800 700 data1 data2 data3 600 500 400 300 200 100 0 0 100 200 300 400
Time
500 600 • Dynamic Time Warp algorithm computes the path that maximizes the local match between two signals in a pair and records the differences in time as area on either side of this best path.
- Best path between two signals from a sensor pair is linear.
700 800 - Positive deviations from best-fit path indicate positive time delays. Negative deviations indicate negative delays.
• Overall delay computed for each sensor pair. Matlab algorithm computes a vote of delays and localizes source based on the vote.
Results
Location of Alcohol Source
Bottom Top
Samples
25 25
Percent of Votes
Correct Incorrect Undecided 84 28 0 60 16 12
Location of Alcohol Source
Bottom Top
Samples
15 15 Correct 86.7
75
Percent of Votes
Incorrect 6.67
25 Undecided 6.67
0
Previous method provided extreme bias towards one side due to air currents in the room. Using controlled airflow and an impulse source, our new method seems to eliminate this bias. More data is required to confirm.
The differences in density and susceptibility to turbulence between air and water may account for the difficulty of localizing a source in air via the shark-inspired model.