Bob Grimm - EFields
Electric-Field Sensors
Geophysical electric-field measurements are routinely made using grounded metal stakes or porous electrolyte pots (e.g., magnetotelluric and resistivity/IP systems in the Supporting Facilities page), but such galvanic ground contact will be impossible at the extremely cold and/or dry, electrically resistive surfaces of the Moon, Mars, and elsewhere.
Under PIDDP funding (R. Grimm, PI), we developed a prototype electrometer (TRL 4) that featured a shielded-plate electrode driven with the output of the first stage of the input amplifier. Input impedances up to 300 GOhm were therefore transformed to acceptable levels in a near-unity gain amplifier. Related methods have been used in resistive ground in Antarctica by others. Jeff Johnston of
Geometrics, Inc. (shown here pulling the capacitively coupled OhmMapper) built and tested this sensor.
I have been a co-investigator in NASA PIDDP and MIDP projects led by Greg Delory of the University of California, Berkeley, Space Sciences Lab in developing wideband, high-impedance, electric-field sensors. The overlying static shield in the Geometrics design isn't used and electrodes are "cleats" or simple spheres that adjust between galvanic and capacitive coupling as necessary.
Prototype deployable magnetotelluric package for Mars exploration (G. Delory, UCB and T. Nielsen, Quasar, Inc.) under test at the Snake River Plain, ID (TRL ~5). Electrodes are deployed at distance; detached unit contains magnetometers.