Field Sense: help benchmark sensitivity and/or range

vicky_molokh · 07-15-2013, 04:00 AM

Greetings, all!

Yes, I know that the standard Scanning Sense: Field Sense has a range of 200 in water and 20 in air/vacuum for purposes of active electrolocation (unless the range changed by modifiers) of various objects. But I'm trying to:

Figure the modifiers to Per rolls depending on size and strength of various fields, particularly for passive electrolocation (which acts as the Detect by RAW).
Assign sense levels to various animals. E.g. I've read that goblin sharks detect fields down to 5 nanovolts per centimetre. I know that an AA battery is 1½V and is 5 cm long. What do I do with those numbers? How far away can this sensitivity be used to detect such a battery? What would the sense levels and modifiers be?
How powerful is an electric field of various animals and appliances anyway? Both when physically active, and when static?

I must admit that I've forgotten almost everything about electric fields from my school days, and the potential complications for moving fields aren't making anything easier.

Thanks in advance!

lwcamp · 07-16-2013, 08:14 AM

An electric field due to flowing currents or an electric dipole (like that of batteries) falls off as the inverse cube of the distance. This is a significantly faster falloff than the inverse square die-away of radiated intensity. You could account for this by using the following for passive electrolocation of animals in water - make a Per roll with a bonus equal to the animal's SM and a penatly equal to 3/2 the range penalty on the Speed/Range table.

The AA battery would have a field that is initially somewhere around 1.5 V / 5 cm = 0.3 V/cm in the immediate vicinity of the battery. This will fall off as the inverse cube, so at 50 cm distance it would be 0.0003 V/cm, and at 5 m it would be 0.0000003 V/cm.

Luke

vicky_molokh · 07-16-2013, 08:28 AM

Quote:

Originally Posted by lwcamp

An electric field due to flowing currents or an electric dipole (like that of batteries) falls off as the inverse cube of the distance. This is a significantly faster falloff than the inverse square die-away of radiated intensity. You could account for this by using the following for passive electrolocation of animals in water - make a Per roll with a bonus equal to the animal's SM and a penatly equal to 3/2 the range penalty on the Speed/Range table.

The AA battery would have a field that is initially somewhere around 1.5 V / 5 cm = 0.3 V/cm in the immediate vicinity of the battery. This will fall off as the inverse cube, so at 50 cm distance it would be 0.0003 V/cm, and at 5 m it would be 0.0000003 V/cm.

Luke

Thanks!

Would 'immediate vicinity' in this context actually mean 'at a distance of 5 cm from the line between the poles'? Because it seems as if you multiplied distance by 10 and divided the field by 10³ based on that interpretation. If I understood correctly.

As figuring the base sensitivity of Detect that is bundled with Field Sense, I'm guessing the +0 detection should be centred around a human field at 2 yards distance (i.e. no modifiers for size, no modifiers for distance). The problem is . . . where can I find the value of the typical human electric field?

lwcamp · 07-16-2013, 08:48 PM

Quote:

Originally Posted by vicky_molokh

Would 'immediate vicinity' in this context actually mean 'at a distance of 5 cm from the line between the poles'? Because it seems as if you multiplied distance by 10 and divided the field by 10³ based on that interpretation. If I understood correctly.

Immediate vicinity means a sort of average field you would get about 5 cm or less from the center of the battery. Right near one of the terminals it would probably be considerably higher, for example, but at that point the dipole approximation I was using will start to break down.

Quote:

Originally Posted by vicky_molokh

As figuring the base sensitivity of Detect that is bundled with Field Sense, I'm guessing the +0 detection should be centred around a human field at 2 yards distance (i.e. no modifiers for size, no modifiers for distance). The problem is . . . where can I find the value of the typical human electric field?

If Google can't find it, you could take a volt-meter and measure how much voltage you generate when just standing there, and when flexing a muscle. Then divide by the distance between the probes to get the field. For best effect you might try placing the probes directly on your skin, but try with the probes away from your skin too, because - well, hey! Science! Might as well experiment. If you really get into this, you could try it underwater, in both fresh and salty water.

Luke

Anaraxes · 07-16-2013, 10:34 PM

Abstract

"Due to the transepidermal potential of 15-50 mV, inside positive, an injury current is driven out of all human skin wounds. The flow of this current generates a lateral electric field within the epidermis that is more negative at the wound edge than at regions more lateral from the wound edge. Electric fields in this region could be as large as 40 mV/mm, and electric fields of this magnitude have been shown to stimulate human keratinocyte migration toward the wounded region. After flowing out of the wound, the current returns through the space between the epidermis and stratum corneum, generating a lateral field above the epidermis in the opposite direction. Here, we report the results from the first clinical trial designed to measure this lateral electric field adjacent to human skin wounds noninvasively. Using a new instrument, the Dermacorder®, we found that the mean lateral electric field in the space between the epidermis and stratum corneum adjacent to a lancet wound in 18-25-year-olds is 107-148 mV/mm, 48% larger on average than that in 65-80-year-olds. We also conducted extensive measurements of the lateral electric field adjacent to mouse wounds as they healed and compared this field with histological sections through the wound to determine the correlation between the electric field and the rate of epithelial wound closure. Immediately after wounding, the average lateral electric field was 122 ± 9 mV/mm. When the wound is filled in with a thick, disorganized epidermal layer, the mean field falls to 79 ± 4 mV/mm. Once this epidermis forms a compact structure with only three cell layers, the mean field is 59 ± 5 mV/mm. Thus, the peak-to-peak spatial variation in surface potential is largest in fresh wounds and slowly declines as the wound closes. The rate of wound healing is slightly greater when wounds are kept moist as expected, but we could find no correlation between the amplitude of the electric field and the rate of wound healing."

http://www.ncbi.nlm.nih.gov/pubmed/22092802

whswhs · 07-16-2013, 10:40 PM

I haven't figured that particular function, but a long time ago I worked out the field strength relations for a magnetic dipole, which is essentially the same geometry. It's a messy function of distance, but once you get a few multiples of the separation between the poles as a range, it does get close to an inverse cube. I don't know if I could still do the integral, though. I'd have to drag down Halliday & Resnick and struggle with it for an evening, I think.

Bill Stoddard

07-15-2013, 04:00 AM	#1
vicky_molokh GURPS FAQ Keeper Join Date: Mar 2006 Location: Kyïv, Ukraine	Field Sense: help benchmark sensitivity and/or range Greetings, all! Yes, I know that the standard Scanning Sense: Field Sense has a range of 200 in water and 20 in air/vacuum for purposes of active electrolocation (unless the range changed by modifiers) of various objects. But I'm trying to: Figure the modifiers to Per rolls depending on size and strength of various fields, particularly for passive electrolocation (which acts as the Detect by RAW). Assign sense levels to various animals. E.g. I've read that goblin sharks detect fields down to 5 nanovolts per centimetre. I know that an AA battery is 1½V and is 5 cm long. What do I do with those numbers? How far away can this sensitivity be used to detect such a battery? What would the sense levels and modifiers be? How powerful is an electric field of various animals and appliances anyway? Both when physically active, and when static? I must admit that I've forgotten almost everything about electric fields from my school days, and the potential complications for moving fields aren't making anything easier. Thanks in advance! __________________ Vicky 'Molokh', GURPS FAQ and uFAQ Keeper

07-16-2013, 08:14 AM	#2
lwcamp Join Date: Nov 2004 Location: The plutonium rich regions of Washington State	Re: Field Sense: help benchmark sensitivity and/or range An electric field due to flowing currents or an electric dipole (like that of batteries) falls off as the inverse cube of the distance. This is a significantly faster falloff than the inverse square die-away of radiated intensity. You could account for this by using the following for passive electrolocation of animals in water - make a Per roll with a bonus equal to the animal's SM and a penatly equal to 3/2 the range penalty on the Speed/Range table. The AA battery would have a field that is initially somewhere around 1.5 V / 5 cm = 0.3 V/cm in the immediate vicinity of the battery. This will fall off as the inverse cube, so at 50 cm distance it would be 0.0003 V/cm, and at 5 m it would be 0.0000003 V/cm. Luke

07-16-2013, 10:34 PM	#5
Anaraxes Join Date: Sep 2007	Re: Field Sense: help benchmark sensitivity and/or range Abstract "Due to the transepidermal potential of 15-50 mV, inside positive, an injury current is driven out of all human skin wounds. The flow of this current generates a lateral electric field within the epidermis that is more negative at the wound edge than at regions more lateral from the wound edge. Electric fields in this region could be as large as 40 mV/mm, and electric fields of this magnitude have been shown to stimulate human keratinocyte migration toward the wounded region. After flowing out of the wound, the current returns through the space between the epidermis and stratum corneum, generating a lateral field above the epidermis in the opposite direction. Here, we report the results from the first clinical trial designed to measure this lateral electric field adjacent to human skin wounds noninvasively. Using a new instrument, the Dermacorder®, we found that the mean lateral electric field in the space between the epidermis and stratum corneum adjacent to a lancet wound in 18-25-year-olds is 107-148 mV/mm, 48% larger on average than that in 65-80-year-olds. We also conducted extensive measurements of the lateral electric field adjacent to mouse wounds as they healed and compared this field with histological sections through the wound to determine the correlation between the electric field and the rate of epithelial wound closure. Immediately after wounding, the average lateral electric field was 122 ± 9 mV/mm. When the wound is filled in with a thick, disorganized epidermal layer, the mean field falls to 79 ± 4 mV/mm. Once this epidermis forms a compact structure with only three cell layers, the mean field is 59 ± 5 mV/mm. Thus, the peak-to-peak spatial variation in surface potential is largest in fresh wounds and slowly declines as the wound closes. The rate of wound healing is slightly greater when wounds are kept moist as expected, but we could find no correlation between the amplitude of the electric field and the rate of wound healing." http://www.ncbi.nlm.nih.gov/pubmed/22092802

07-16-2013, 10:40 PM	#6
whswhs Join Date: Jun 2005 Location: Lawrence, KS	Re: Field Sense: help benchmark sensitivity and/or range I haven't figured that particular function, but a long time ago I worked out the field strength relations for a magnetic dipole, which is essentially the same geometry. It's a messy function of distance, but once you get a few multiples of the separation between the poles as a range, it does get close to an inverse cube. I don't know if I could still do the integral, though. I'd have to drag down Halliday & Resnick and struggle with it for an evening, I think. Bill Stoddard