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The square beyond compare!

Husain Shekhani • Jun 17, 2021

Sine waves are great for driving ultrasonic transducers. The resulting current waveform, more or less, will have pristine harmonic contents which will be great for analysis and feedback control. You also therefore avoid driving other harmonics which will create heat and cause unwanted oscillatory behavior. Sine waves can also be properly and easily amplified (or reduced) by a transformer in order to deliver maximum power to the transducer. Digital amplitude control is also a common feature of sine wave drive circuits.

So why would be drive our transducer with a square wave, which by its very nature consists of many harmonics and can be quite rigid with regards to amplitude control? There are two aspects of square waves which are awesome:

(1) Square waves drive signals are easy to generate.

(2) The half bridge and full bridge drivers used to generate square wave drive signal have an extremely low output impedance. This means that the drive voltage will not change at all due to changes in impedance of the transducer during operation. You cannot say that for almost all sine wave drive circuits, where such impedance change can cause instability.

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