.PS
cct_init

# Usual defs...
qrt=dimen_/4;
hlf=dimen_/2;
dim=dimen_;

Org: Here
# Half ellipse of half height, bottom.
hEmaj=30mm__
HEcentre:Here+(hEmaj/2,0)
for theta = pi_ to 2*pi_ by pi_/30 do {
  line to HEcentre+(hEmaj*cos(theta)/2, hEmaj/2*sin(theta)/2)
}
line -> up_ 3mm__ left_ 1mm__
"$\underset{\sim}{B}$" at Here+(3mm__,0)

move to Org+(15mm__,15mm__)
E1:ellipse wid 10mm__ ht 5mm__ with .c at Here
line from E1.e down_ 30mm__
line from E1.w down_ 30mm__
Bot:Here

# Half ellipse of half height, bottom.
hEmaj=10mm__
HEcentre:Here+(hEmaj/2,0)
for theta = pi_ to 2*pi_ by pi_/20 do {
  line to HEcentre+(hEmaj*cos(theta)/2, hEmaj/2*sin(theta)/2)
}

line -> from Org+(15mm__,-10mm__) up_ 20mm__
right_
"$I$" at last line.center ljust_

line -> from Bot+(5mm__,15mm__) to Bot+(-5mm__,9.25mm__)
"$r$ " rjust_ above_ at last line.center

dimension_(from Bot to Bot+(10mm__,0), -7mm__, 2a, 4mm__, 3mm__)

"{\tiny biot}" at Org+(30mm__,-20mm__)
.PE