BIG DD COIL

[shila]

I want to build a transmiter/reciever coil by these caracters.

1)A big transmeter coil ,for ex. 40" diameter.
2)A small reciever coil at the center of the transmeter coil. for ex. 10"

I think this design produces stronger field and more sensitive reciever.

What you think about this idea theoretically& practically??

[Nexus]

Big coil design

I want to build a transmiter/reciever coil by these caracters.

1)A big transmeter coil ,for ex. 40" diameter.
2)A small reciever coil at the center of the transmeter coil. for ex. 10"

I think this design produces stronger field and more sensitive reciever.

What you think about this idea theoretically& practically??

It will be better if you go in this size for DD configuration. DD is in average 25% more sensitive that concentric type.
The field will not be stronger compared to a smaller TX coil unless the dencity of the transmitted field is equal to the dencity of the smaller coil.
Let me explain.
If two TX coils are working at the same conditions; voltage accross the windings, frquency and have equal Q, but one has diameter 2 time bigger than the other the result in the electromagnetic field density will be that the bigger coil will have as much less density in the transmitted field as the difference between the surface area of the two coils.
If we run some calculation just for round coils the result will be;
The surface area of a circle is pi by square R where R is the radius, pi is the constant 3.14... So if the small coil has for example R of 10" then the surface area will be 314"square inches
Now if the bigger coil is twice bigger then the R will be 20" which will mean 20"square x 3.14 = 400 x 3.14= 1256" square inches
If we divide 1256 by 314 the result will be 4 times difference between the surface area of two coils.
Now that efectively means if the conditions are equal that the larger coil will have 4 times lower density of the transmitted electromagnetic field.

Of cource the coils could be design in any way, not nesessary twice bigger or twice smaller.
However the most substantial advantage a big coil can offer is better ground penetration which commes from the larger surface area on which the field is transmitted. That gives longer way for the occuarance of electromagnetic decay.
Never the less there is a lot of wieght to be considered. Large coils are difficult to get light.

[Bojidar]

Hi Shila

You can build coil but first must to determine type of
spatial location on coils
You have 4 choices:
-type "wide scan"
-type "pin-point"
-type "coax"
-type "double D"
-type "double O"
Types DD and DO derivates from wide-scan coil.Difference between all types are in area of scan and form on field under coil.Very importance is how to connect (start and end) of wire!In any case you will have penetration from TX coil in RX coil when don't have a target under coil.You can use next equation:
To determine L:

2,54.10 000
L=-------------
Fres.Fres.C

where
L - in micro H,
C - in micro F;

To determine number of turns:

1 L.177
L=----- .R.n.n [micro H] or n=SQRT(---------)
177 R
Where:
L - in microH,
n - number of turns,
R - radius of bobbine;
Now,You can choose freq,C,R,.... You have all
Remember: Ground penetraition dependent from FREQ !!!! Big F->low depth.Characterization of Ground is like ferrite,but more complex.
Sorry for my bad Eng. and all the best

[fairdinkum]

gudday fella's when making DD coils for PI detectors such as the SD2200D does the 2 coils have to be set on the null points where they cross as in the past type of TR detectors?

One eye says to the other Eye hey something smells between us.
turu FDinkum

[rajesh]

You can build coil but first must to coil calculator thats >here...chemelec > www.telus.com/inductanc >calculator >...rajesh