Engineering Smart Technologies

Frequently Asked Questions

1. How does a QuickPack piezoelectric actuator create motion?
Some materials exhibit what is called the piezoelectric effect, which literally means that electric charge is generated when the material is pressed (or squeezed or stretched). The reverse is also true: an applied electric field will cause a change in dimensions of the piece of material. For a positive voltage applied in the z-direction, a solid rectangular piece will expand in one direction (z) and contract in the other two (x and y); if the voltage is reversed, the piece will contract in the z-direction and expand in the x- and y-directions. This is somewhat like thermal expansion and contraction, but since electric field is used instead of temperature, a quick reaction is achieved in response to commands easily generated with electronic circuits.

Top

2. How can a QuickPack actuator be used?
There are two basic operating modes for QuickPack actuators:

• Strain actuator - The QuickPack device is bonded to the surface of a structure, and expands and contracts in the planar direction in response to drive voltage. This imparts strain on the surface of the structure, causing the structure to bend or flex.

• Bimorph actuator - In this configuration, the actuator has two flat, thin layers permanently bonded together and wired "out-of-phase." When one layer expands, the other layer contracts, causing the actuator to bend, much like a bi-metal strip. For more information, click here and see Tech Note 2

These two types of piezoelectric actuators can be used in a variety of applications. Mide's core application area is active vibration control of structures in precision machinery.

Top

3. How do I attach a QuickPack strain actuator to a structure?
For complete bonding instructions, click here and see Tech Note 1

Top

4. How do I hold a QuickPack bimorph actuator securely?
For a complete description of how to use bimorph actuators, click here and see Tech Note 2

Top

5. How much current is required to drive a QuickPack actuator?
For many purposes, the electrical behavior of a QuickPack actuator can be approximated by that of a simple capacitor. When the actuator is driven with a sinusoidal voltage, the required current can be found from the equation

Where I is peak current in amperes, C is capacitance in farads, V is peak drive voltage in volts, and f is frequency in hertz.

The capacitance for each model of QuickPack actuator is listed in the specifications.

Top

6. What is the maximum frequency at which a QuickPack actuator can operate?
When the actuator is being operated as a strain actuator (e.g., bonded to a surface) it can operate over a very broad frequency range, from zero to at least 20 kHz. However, it is recommended that the standard QuickPack actuators not be operated with more than 20 Wrms of input power (power consumption is related to drive frequency). For a sinusoidal input, the power can be calculated by multiplying the required rms current (see equation above and divide result by the square root of 2) by the rms input voltage (peak voltage divided by the square root of 2).

In a cantilevered bimorph configuration, a QuickPack actuator is typically specified to operate in the quasi-static frequency range, from 0 Hz up to about 1/2 the frequency of its first bending mode. The actuator can be operated at frequencies above this range, but the deflections are greatly influenced by the structural dynamics of the actuator and do not respond linearly to the input voltage. In some cases, driving the actuators at resonance can cause high enough strains to crack the piezo elements, so care should be taken when driving a bimorph at higher frequencies.

Top

7. Can piezoelectrics be used to control very small amplitude vibrations?
In active systems, there is no inherent lower-limit on the amplitude of vibration which can be controlled (other than that it must be large enough to measure so feedback can be sent to the controller).

Top

8. What is the maximum operating temperature for a QuickPack actuator?
All of the standard products are rated up to 212°F (100°C). Because the QuickPack actuator is not 100% efficient, some of the electrical energy it consumes turns into heat, increasing the temperature of the actuator. This is not a concern in most applications, but if the actuator is exposed to high environmental temperatures or will be driven at high power levels (often associated with high frequencies), you should try to monitor the actuator temperature to avoid overheating.

Top

9. Can I get a special size or shape of QuickPack actuator?
Midé can design custom sized and shaped actuators at your request. This includes rectangles, disks, rings and curved piezos. Please contact Midé to learn more about how we can design a QuickPack actuator to meet your dimensional requirements.

Top

10. What kind of piezo is used in QuickPack actuators?
For standard QuickPack strain actuators, the material is industry type PZT-5A. QuickPack bimorph actuators are constructed with PZT-5H. The material properties for both types can be found on the piezo properties (PDF) Page.

Top

11. What kind of electrodes do QuickPack actuators have?
Currently, all of our standard products use nickel electrodes.

Top

12. Can QuickPack actuators also be used as sensors?
Yes, since QuickPack actuators are made with piezoelectric material, they can be used for sensing strain as well as producing it. In general, piezoceramic has non-linearities and hysteresis that make it difficult to use in "instrumentation grade" sensors. But for typical closed-loop active structural control systems, these factors can be effectively ignored.

Top

13. Can I use one layer of a two-layer QuickPack for sensing and the other layer for actuation?
This technique is usually not effective. The reason is mainly that the sensing layer will mostly sense strain that is being induced by the actuating layer, instead of measuring the natural dynamics of the structure. This problem is often called feed-through, because the actuator output is fed directly through the sensor to the controller. In general, we have found that a separate QuickPack device placed next to the actuator works much better than having one on top of the other.

Top

14. When performing structural control, are there some structural materials that are better suited for control than others?
There is a lot of theory behind the importance of mechanical impedance matching. The ideal, is to have a base material with the exact same bending properties as the piece of piezo that is attached. In reality, this is usually not possible; however even mismatched base materials can be effectively controlled. Some materials to avoid are very soft materials like rubber or most woods; in such cases, the QuickPack actuator will serve more to locally stiffen the structure than to control vibration. It is also important to keep in mind that you must bond the actuator to the base material, so make sure it is something that epoxy will adhere to. Midé has successfully bonded QuickPack actuator to steel, aluminum, carbon-fiber composites, and many plastics.

Top

15. Can QuickPack devices be embedded in laminated composites or injection molded plastics?
Midé has done some preliminary investigation in both of the areas and has had promising results with both methods.

Top

For more information:
Please Contact Conor Clery (Products), or call: 781-306-0609 x292