ECE332 Lab 1 Spring 2008
Week 1. a. Wind a ten-turn solenoid inductor using magnet wire on a cardboard form. Hold the wire
in place with fingernail polish or tape. After the inductor is constructed, carefully measure its dimen-
sions.
b. Use at least two different formulas to calculate its inductance. Do a web search to find a formula
that you think might be better than the two we used in class.
c. Run an LTSpice simulation of a simple RL circuit using 50 ohms for R and the range of values you
obtained in step b to obtain a plot of frequency response from 10 kHz to 10 MHz.
d. Connect a 50 ohm signal generator and >1 M oscilloscope probe and measure the frequency re-
sponse of the RL circuit you simulated in step c. Record the amplitude across the inductor at a num-
ber of points, including 10 kHz 10 MHz, the -3dB (half power) point, and the -20 dB point.
e. Calculate the value of your inductor using the measurements in step d.
f. Connect a 470 pF capacitor in parallel with your inductor to make a resonant circuit. Connect the
scope probe across the inductor-capacitor, and magnetically couple a little energy into the inductor
using a two-turn loop made from a clip-lead cable. Find the resonant frequency of the tuned circuit by
sweeping the signal generator and noting the frequency at the peak. Use the resonant circuit formula
to calculate the inductance, and compare this value with what you obtained in step e.
g. Plot the shape of the resonant circuit response between the -20 dB points. Estimate the Q of the
resonant circuit from the half-power bandwidth.
Week 2. a. Wind a second inductor on a different sized cardboard form so that one will slip over the
other.
b. Using the methods from week 1, measure the inductance of the series, coupled, and anti-coupled
inductors.
c. Plot the series inductance as a function of axial and lateral separation. Record at least 20 points,
and over enough distance that coupling decreases to nearly zero. How do you define “nearly zero?”
Week 3. Using the data you collected in week 2, calculate the magnetic coupling coefficient k as a
function of separation distance. Now simulate the RL response for the inductor pair in LT Spice with k
as a stepped parameter.
Inductance and Coupled Magnetic Fields
Lab Report You may bring your checked lab reports to each of the exams in class, so make sure they
are clear and complete. For this lab, you should have: a derivation of inductance using Ampere’s law
and the magnetic energy formula; sketches of your inductors with dimensions; calculations of induc-
tance; LT Spice plot of RL frequency response using your calculated inductance and your measured
values; a sketch of the resonant circuit (LC) method of measuring inductance; you measured value
using the LC method; a plot of the resonant response; a calculation of Q; measurements of the 2nd
inductor and series combinations with various degrees of coupling; A plot of k versus separation; LT
Spice plot of RL frequency response as k varies.
