material between the plates as an example the return surface area may be about 8000 mm 2 the standoff may be about 3 mm and the mud dielectric permittivity may be about 5 u03b5 0 leading to a return formation capacitance of about 120 pf the impedances zli and zlr can be determined during the design of the tool but due to spatial restrictions at least one of the two impedances can have a large capacitive component of the order of about several tens or hundreds of pico farads by altering the design of the tool or by adding one or more electric components it is possible to balance the two capacitances if the standoff in to fm and rt to fm vary in the same way then the ratio zmi zmr may not change and one can use a fixed ratio zli zlr however if with standoff they do not vary in the same way one may rely on zli or zlr being sufficiently high to prevent the waveguide effect or one may apply some actively regulated balancing technique s to obtain the correct ratio likewise if the mud permittivity changes zmi zmr may not change and one may use a fixed ratio of zli zlr fig3 shows an alternative view of the equivalent circuit scheme of fig1 fig3 shows that by properly choosing the ratio zli zlr it is possible to make the potential difference between tm and fm substantially equal to zero or at an acceptable level fig3 is equivalent to fig2 where the zim has been replaced by the two borehole coaxial transmission lines where uc is the upward coaxial line formed by tm borehole annulus and fm dc is the downward coaxial line formed by tm.