The two types of antiresonance

Blog Layout

The two types of antiresonance

Husain Shekhani • October 19, 2020

This is a subtitle for your new post

A colleague on my recent post on LinkedIn regarding antiresonance in piezoelectric devices call attention to the “mechanical antiresonance”.

Indeed, there are two types of antiresonances:

1. Electrical – Parallel resonance between the motional (LCR) and the capacitive current (Co). This is where current is the lowest level, i.e., the highest impedance

2. Mechanical antiresonance – frequency at which the displacement output is at a local minimum

Just like you can quickly identify the antiresonance frequency from an impedance graph (impedance peak) you can identify the mechanical antiresonance by a displacement “valley”. You can find this most easily by using an FEA program and plotting displacement of a free end vs frequency. Below you can find a plot of displacement amplitude (y axis) vs frequency (x-axis). This may look like a piezo admittance plot, but it is actually a displacement plot. The “valleys” are the mechanical antiresonance.

Displacement vs. Frequency - the valleys are the mechanical antiresonance

Frequencies where sections of your piezoelectric element or transducer are vibrating out of phase, the net displacement as seen at the end is close to zero – however, there is still vibration occurring in your structure. Mechanical antiresonances cannot be discerned from impedance analysis, because they are masked by the parallel capacitance of the other LRC branches.

Notice that the mechanical antiresonance is typically more than 20% higher than the resonance frequency. Mechanical antiresonance comes about, in on sense, by interaction of different resonance modes, thus causing maximum destructive interference at the free ends of a transducer. Electrical antiresonance is a single mode phenomenon arising from the local resonant mode and the parallel capacitance.

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

< Older Post Newer Post >