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Energy in an ultrasonic resonator
Husain Shekhani • October 27, 2020
Energy in an ultrasonic resonator
Losses in piezoelectric/ultrasonic devices are an interesting topic both from scientific and engineering perspectives. Here, I will touch on the most important loss parameter – the mechanical quality factor.
This discussion makes some generalization for the sake of simplicity.
The root definition of the mechanical quality factor is:
Q = 2Pi (energy stored per cycle) / energy lost
Or in terms of frequency:
Q= 2Pi *f *energy stored per cycle/power loss
If we assume that the system is a first order resonator (linear-“ish”), Q can be determined from the 3db bandwidth of impedance or from the half power bandwidth considering real admittance.
The awesome thing you can do if you measure both power (with voltage, current and phase) and the Q factor using the bandwidth method is that you can back calculate the mechanical energy stored in the system
Energy stored = Q *power loss /(2 Pi* f)
However, you must measure the Q factor using a constant current sweep, which can be accomplished by providing a sufficiently large resistor in between your driver and transducer or by using a closed loop control to maintain constant current.
What’s the benefit of knowing your mechanical energy?
It tells you how much energy is stored in your system, which is closely related to how much energy can be delivered per cycle. It also tells you how robust your transducer is to loading.
Please let me know if you have questions and comments on this topic at husain@ultrasonicadvisors.com. Also please send your colleagues this email and ask them to subscribe if you think they would benefit from these emails. This is the subscription link: [Link to subscribe]
Regards,
Husain Shekhani, PhD
Ultrasonic Advisors
husain@ultrasonicadvisors.com