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Homework Help: Print a circuit for measuring electrical impedance

  1. Sep 13, 2012 #1
    Hi there,
    I am supposed to measure the electrical impedance (which depends on conductivity) of an electrically conducting object by use of eddy current technique induced by an air core coil. for this purpose I need to print a circuit. would you please help me with the characteristics and out put of the circuit. what kind of electronics devices should I use and how to design the circuit.
    The coil has a few centimeter in diameter and less than 100 turns of very small cross sectional wire that should be loaded with frequency in range of 100kHz- 10MHz.
    Thank you in advance.
  2. jcsd
  3. Sep 14, 2012 #2


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    Staff: Mentor

    Welcome to the PF.

    Since this is your project, please tell us your initial thoughts on how to proceed. What are the relevant equations for eddy currents, resistivity, skin depth, etc.? How will you detect the eddy currents...?
  4. Sep 14, 2012 #3
    Thank you,
    Since I have to make a coil by hand, the number of turns, inner and outer coil radius and cross section of the wire is determined. I have to load the coil and examine it on a phantom (Al or Cu) to induce eddy current in them and then measure conductivity of the phantom.
    I have some equations to measure the quality factor of the coil and then if the coil is suitable to use I have to measure the coil on an LCR meter to collect data on L(x) and R(x) where X is stand-off and these data will be used to design the electronics. But still do not have any idea how to design the circuit.
    skin depth : δ= √(2/ωμσ), where ω is radian frequency (rad/s), μ is magnetic permeability (H/m), σ is conductivity (siemance/m).
    Unloaded inductance : L= 7.88(〖〖(R〗_0+R_i)〗^2 n^2 l^2)/(13R_0-7R_i )
    where R_0 is outer radius, R_i is inner radius, n is the number of turns and l is the number of layers.
    For self resonant frequency we have: SFR= 1/(2π√(L.C_cable )) where, L is unloaded inductance and (C_cable) is capacitance of the cable.
    Operating frequency : f_min=1/(2π√(L.C)), and
    f_max= 2 f_min
    DC and AC resistance of the coil: R_AC=2R_DC
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