What is the reason for harmonics in dc-dc converter?

[Tom.G]

That car radio video says to use a Dremel to open the Vibrator can. That's not needed. The can is crimped around the bottom phenolic wafer tht holds the pins. A pair of 6-inch diagonal cutters can be used to sttraighten out the crimp, allownig the can to be pulled off. After the repairs are made, replace and recrimp the can. Of course for testing in the radio, you don't want the vibrator flopping around, so pull out the cup of foam rubber that is lining the can and slip it over the vibrator.

 

[sophiecentaur]

It is possible to make a sinusoidal inverter to a suitable AC voltage with as low harmonics as you could want and then pass the sine wave to a rectifier / smoother. Problem is that the inverter either going to get HOT (inefficient), if you use a Class A amplifying device or it will be needlessly complicated, if you used a switch mode device. Either way would be poor Engineering when, in any case, you are going to rectify that power signal and be producing harmonics in any case.
I guess the reason that DC DC converter waveforms have 'measurable' harmonics is that it doesn't matter. Good Engineering doesn't spend resources on higher specs than needed.