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Gordon Couger writes to the sowacs list: ===8<============== You are working with what is referred to as a difficult problem. One that there is no obvious solution to and no good starting place. A capacitance sensor is a good idea but it needs to be scanned some way and the resolution needed calls for very high frequency and extremely rigid equipment. Unless someone has a material that will fluoresce using very low power radio frequency so the loss due to the interfering water at 2.3?? GHz can be mapped visually I can see no way to do it. You might build an RF sensor with a small aperture and illuminate a cylinder containing the seed with 2.3 GHZ microwaves I am not sure the exact frequency but it is the one that is absorbed by water and rotate the cylinder and move it in the Z axis and repeat and use the Radon transform that is used to reconstruct CAT scans from X ray images and do it but you need a really sensitive detector and really low RF source because you will be cooking it in a microwave oven so it will have to be done slowly so you don't disturb the distribution of the water. You might to the same thing with an infra red beam and a transparent or translucent soil substitute that is vastly more transparent to the band if infra red you pick than water. You could get higher resolution. If you elect to attempt one of these solutions I know where you might be able to get some help with the software and mechanical approach. Gordon Couger Stillwater, OK www.couger.com/gcouger ----- Original Message ----- From: "Bruce Metelerkamp" <brooz@pobox.com> To: "Bruce at Findasensor" <brooz@pobox.com> Sent: Monday, June 16, 2003 4:09 AM Subject: SOWACS: SEEDS as sensors - interesting! : Marty Grogan writes to the sowacs list: : ===8<============== : : How about using some wire mesh on either side of the seed arranged to : act a plates of a capacitor? A capacitance bridge could be used for : calibration and to monitor moisture. : : M. G. : : >Mark Bloomberg writes to the sowacs list: : >===8<============== : > : >My query relates to measuring moisture availability in the very small : >space around a germinating pine seed. This environment has a : >diameter ca 1cm, is close to the soil surface and therefore moisture : >levels fluctuate rapidly in relation to time of day, changes in : >atmospheric RH etc. : > : >Oleskog & Sahlen (Oleskog,G and Sahlen K. 1999. Determination of : >moisture conditions using Pinus sylvestris (L.) seeds as biosensors. : >Scandinavian journal of Forest Research.) stated that conventional : >methods of soil moisture measurement are not suitable because they : >may influence moisture levels in the seed's immediate environment, : >which is very small. There are also steep vertical gradients in : >moisture in the surface soil zone. Oleskog opted for a bioassay : >approach, using changes in seed fresh weight as an indicator of : >moisture availability. : > : >Does anyone have alternative views on this problem? : > : >Yours sincerely, Mark : > : >Mark Bloomberg : >Lecturer in Forestry : >SPES Division, Lincoln University : >Ph (64) (3) 325 2811 Ext 8437 : > ===8<============== NOTE: To get off this list, send an email to list@sowacs.com with the subject line: unsubscribe_sowacs For full instructions see this page: <http://www.sowacs.com/subscribe/index.html>