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Electrical Requirements for Piezo Operation

Heat Generation in a Piezo at Dynamic Operation
As mentioned before, PZTs are reactive loads and therefore require charge and discharge currents that increase with operating frequency. The thermal heat, P, generated in the actuator can be estimated with the following equation:

P » tan d * f * C * U_p-p²       (4-23)

Heat generation in a Piezo.

Where
P = power converted to heat [W]

tan d = tangent of the loss angle (ratio of parallel resistance to parallel reactance)

f = operating frequency [Hz]

C = Piezo actuator capacitance [Farad (As/V)]

U_p-p = peak-peak drive voltage [V]

For standard actuator Piezo ceramics the loss factor is on the order of 0.01 to 0.02 (large signal conditions, smaller for small signal conditions). This means that up to 2% of the electrical power pumped into the actuator is converted to heat. Therefore, the maximum operating temperature can limit the Piezo dynamics. For large amplitude and high frequency, operation cooling measures may be necessary. A temperature sensor mounted on the ceramics is suggested for monitoring purposes.

PI is currently investigating the design of new Piezo materials showing extremely low loss angles while still displaying a large d₃₃ effect. These types of ceramics will allow high-frequency, long-term operation without cooling measures.

In addition, a new generation of amplifiers employing energy recovery technology has been developed for high power applications. shows the block diagram of such an amplifier. Instead of dissipating the reactive power at the heat sinks, only the active power used by the piezo actuator has to be delivered. The energy not used in the actuator is returned to the amplifier and reused as supply voltage by a step-up transforming process. The combination of low loss, high energy Piezo ceramics and amplifiers with energy recovery are the key to new high-dynamic piezo actuator applications in the near future.

Block diagram of an amplifier with power recovery.

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