This article focuses on the actual building of the parabolic antenna (the reflector) for the ultrasonic sensor. For this part of the project, I needed a little help with programming the CNC machine to
create the wood mold. So, I turned to my son, Max. Max
provided the Python programming that accomplished that
task and co-authored this installment with me.
Last time, when the subject of parabolic antennas was
introduced, it was mentioned that we currently use a mold
carved from wood by a CNC machine to create the
antenna. A sheet of heated plastic is then vacuum formed
over the mold, and the resulting antenna just needs a hole
cut in its bottom to allow the ultrasonic transducer through.
So, the first thing that needs to happen is to create the
Creating the Antenna
A paraboloid-shaped antenna will produce an almost
perfectly collimated beam of the ultrasonic transducer’s
energy. We don’t need a full paraboloid (Figure 1). A half
paraboloid (Figure 2) with the ultrasonic transducer pointed
up will still capture virtually all the transducer’s energy
(because the transducer emits most of its energy in a ± 30°
We know from last time that this half paraboloid is the
result of rotating a parabola (like the one in Figure 3)
through 180° about the horizontal axis.
However, to generate the paraboloid shape on the
CNC, we’ll be working with the shape turned 90° clockwise
as shown in Figure 4.
52 SERVO 07/08.2018
Figure 1. Full paraboloid with backfiring
Figure 2. Half-paraboloid with transducer firing up.
Figure 3. Parabola