A DIY question / handlebar / build

I think your sketch is great. However use slots instead of holes for the screws, so you can tune the length, to aim for a resonant frequency at the speed you want to ride.

Simplify it by using two saddle clamps instead of the pictured round thing. Saddle clamps are often used for securing pipe to a wall.

One of your main problems will be rotation over time - the front will drop down like a cheap headlight. If your handlebars are steel, then consider drilling into them and using one additional bolt to prevent rotation. You could also weigh as much behind the bars as you do in front, so they are "balanced".

You can hang the beam below the bars too - it doesn't have to be on top. Mind out for knee-strike though if its off to the side.

Lastly does this need to be on the bars? You could secure the device to the stem so it points straight out the front in the middle, which gives more material to buttress the unsupported arm out the front. This might help with cable snagging while turning.