Biomedical subjects
Publications and source records attributed to T Kikas.
It is shown experimentally that chemical information can be encoded and preserved in flowing liquid streams. It can be retrieved by chemical sensing arrays using correlation analysis. This finding is important for understanding of the mechanism of chemotaxis as practiced by some aquatic animals and also is a necessary prerequisite for construction of chemical plume tracking robots.
The purpose of this research is to estimate the effect of turbulent mixing on the information content in a chemically encoded signal, to investigate the effect of the presence of multiple encoded frequencies, and to evaluate the information contained in the higher harmonics of the coherence spectra. The virtual plume instrument is used to mimic the flow conditions and signal patterns in a real chemical plume. Two-frequency modulation experiments are performed using solenoid valves to introduce concentration plugs of a marker into the carrier flows at certain constant frequencies. In our experiments, the length of the delay elements and the dispersion were varied to mimic different characteristics of the turbulent plume. In addition, an artificial but uncorrelated white noise was added to the raw amperometric signals in order to simulate the "noisy" conditions existing in a real plume. Our experiments reveal that the introduced turbulence has only a marginal effect on the coherence spectra. Moreover, it is shown that when the second frequency is present in the plume, both fundamental frequencies can be unambiguously assigned. Higher harmonics in the coherence spectra have been found to depend on the distance from the source. These findings are important for understanding of the mechanism of chemotaxis and may also lead to the design of optimized search algorithms for chemical plume tracking robots.
Many animals have the ability to search for odor sources by tracking their plumes. Some of the key features of this search behavior have been successfully transferred to robot platforms, although the capabilities of animals are still beyond the current level of sensor technologies. The examples described in this paper are (1) incorporating into a wheeled robot the upwind surges and casting used by moths in tracking pheromone plumes, (2) extracting useful information from the response patterns of a chemical sensor array patterned after the spatially distributed chemoreceptors of some animals, and (3) mimicking the fanning behavior of silkworm moths to enhance the reception of chemical signals by drawing molecules from one direction. The achievements so far and current efforts are reviewed to illustrate the steps to be taken toward future development of this technology.