Field Sensor
From BEAM Robotics Wiki
A device or circuit that when acted upon, or stimulated by, an electric or magnetic field of some type, will produce an electrical signal in some proportion to that field. There are two types of field sensors:
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[edit] Active Field Sensors
These are circuits that produce their own sensing field (typically an electric field and respond to disruptions of, or changes in, that field. The changes are usually the result of an object entering or moving through the field.
[edit] Passive Field Sensors
These circuits are usually passive only in that they do not produce a sensing field of thier own. Instead they respond to the presents of, or changes in electric or magnetic fields that exist in the surounding environment. A typically passive field sensor will produced an output signal that varies proportional to the field it is designed to detect.
[edit] Active vs Passive Field Sensors
(From a post (message #52801) to the BEAM email list) from Wilf Rigter,
"Everything should be made simple as possible, but not more so." -- Einstein
Beam is all about simplicity but the Efield detector is a case of simplicity run amuk.
Static Efields are the density contours of electron distribution. Efields do not identify objects as such, just the differences in trapped charges. Like motion detectors they are not easy to use for anything other than detecting change.
Even aerosols like thunder clouds can have very large trapped electron charges. These charges are transported by various mechanisms and fluctuate wildly (can you say lightning?) Move one Efield and they all move. Like a weather barometer, detecting natural E fields is like using an electron barometer, measuring one point you can detect change but there is no information on direction.
By generating a large fluctuating local field, its interaction ( capcitive coupling ) with the environment can be measured.
This is the method used in capaciflectors and capacitive sensors which are practical for obstacle detection (solid state push buttons, liquid level, etc.)
Also see http://www.physicsmathforums.com/showthread.php?t=114
[edit] BEAM E-Field Sensors
Field sensors have not been widely used BEAMers. This is principally due to three things.
- The complexity of many of the existing designs
- The amount of power needed, especially for active field sensors
- The difficulty involve in interfacing them with typical BEAM robot circuits
Thankfully there have been a few field sensors developed by BEAMers specifically for use with BEAM robots. These include:
