Q:What adhesives do you recommend to bond MFCs to a structure?
We recommend two component adhesives like 3M's DP 460 Epoxy or Loctite's E120 HP Epoxy. Best results are obtained if the adhesive is cured at 50°-60°C for 2 hours and the MFC is pressed against the structure with a fixture during curing.
Q: What is the best way to bond an MFC to a Host Structure?
Please watch our video tutorial How to Bond and Cure the MFC on our YouTube channel!
We would like to discourage simple clamping techniques to bond the MFC to a host structures. Clamping techniques, if not used properly, can damage the outer Kapton shell of the MFC which will lead to early failures of the MFC
In general vacuum bagging is a safe method to bond the MFC to structures and can be done using the following steps:
Q: I want to use the MFC as a strain sensor, but it seems I’m not getting any readings.
Make sure you have attached the MFC to a structure which actually is inducing a strain into the patch, i.e. stretching or compressing the fibers.
Q: What is the max force that an MFC can produce?
The MFC will expand at 1800 ppm over the length of the actuator (free strain). The blocking force is about 4kN/cm² for the active cross section of the MFC.
Q: Is the MFC porous or non-porous?
The MFC is non-porous due to its environmentally sealed packaging.
Q: What amount of force is a standard MFC generating, displacement?
The M8557P1 is generating about 900N blocking force and ~150µm displacement (free strain).
Q: Can the MFC be operated at frequencies higher than 10kHz?
Yes. The published 10kHz is in general the upper limit of operating the MFC as an actuator using a high electric field (i.e. voltages in excess of one third of the maximum operating voltage). Piezo ceramic can operate at much higher frequencies of up to 10-20 MHz.
Q: What is the typical density of an MFC?
Typical areal density is 0.16g/cm² or volume density of 5.44 g/cm³.
Q: What is the mechanical efficiency of an MFC, meaning electrical energy transformed into mechanical energy?
This question requires a little more in-depth analysis:
Q: How tight a radius of curvature can you bend the MFC before cracking? For example the standard size 3.4" x 2.2" MFC M8557P1.
For the 12-mil (0.3mm) thick, standard MFC package the minimum curvature diameter of the actuator is about 4.7 inches (120mm) curled in fiber direction and 4 inches (100mm) curled perpendicular to the fiber direction.
Please download the following publication for additional information about the tensile strain behavior of the MFC: Nonlinear Tensile and Shear Behavior of Macro Fiber Composite Actuators
Q: What type of electrodes are available for 1-3 Piezo Composite?
We offer Copper-Tin (CuSn), Gold (Au) or Silver (Ag) electrodes for our 1-3 composites. All electrodes are applied using a vacuum deposition process and range between 700nm and 1.2 µm in thickness.
Q: How do I connect wires to electroded 1-3 composites?
Most of our customers solder wires to the 1-3 composites using a low temperature solder. Soldering on a 1-3 composite requires experience due to the fact that a considerable area of the composite under the electrode is made of plastic. If the solder iron is too hot or applied too long, the plastic will become soft and the bonding with the sputtered electrode material will fail causing the electrode to come off.
Q: What solders should I use? What is a good solder procedure?
Skin the wire from its insulation, then plate the stripped length with tin. Use some flux, e.g. "Fludor" to cover the wire tip, take a drop of liquid tin with the solder bit, and then hold the wire to the solder bit. After this contact the electrode with both solder bit and wire, remove the solder bit, and keep the wire on electrode. Do not apply any loads until the tin has cooled.
Q: Can I glue wires to an electroded 1-3 composites?
Yes, you can - by using a conductive glue for attaching wires to the composites. Conductive glues allow for a reliable way to connect wires to our 1-3 composites, with comparable and better adhesion as standard soldering. We recommend the following glues from Epoxy Technology (www.epotek.com): Epo-Tek 430, Epo-Tek H20E, Epo-Tek EE 129-4.
Q: What is the difference between “dice-and-fill” and “arrange-and-fill” manufacturing methods?
Dice-and-fill technique has been around for many years and is more expensive than the arrange-and-fill method used by Smart Material. Essentially, dice-and-fill begins with a bulk block of PZT, wherein many grooves are diced using a diamond saw, and the grooves are filled with polymer. The extensive cutting is the primary factor in the higher manufacturing costs. With arrange-and-fill, long strands of fibers are arranged randomly on end, and polymer is poured around them, forming a large block of piezo composite. This block can then be diced into different length pieces according to the frequency desired. This translates into a faster, more cost-effective process.
Q: What is a PEH?
PEH is the abbreviation for Piezo Electric Harvester. Sometimes a Piezo Electric Harvester is also referred to as PEG, Piezo Electric Generator.
Q: What is a Cantilever and its function in a PEH?
A Cantilever is a rigid structural element that extends horizontally and is supported or clamped at one end only. Cantilevers used as PEHs are typically made from glass fiber composites, like FR4, sheet metal or plastic. A piezo electric device, like a monolithic piezo ceramic plate or a MFC, is normally bonded close to the supported/clamped side of the cantilever. Bending the cantilever strains the attached piezo ceramic device, either compressing or stretching it, and causes the piezo electric device to generate an electric charge. The amount of generated electric charge, measured in Coulomb, is a function of the amount of strain imposed on the piezo electric device. The amount of strain is, in simple terms a function of how much the cantilever is bent and the distance of the piezo ceramic device from the middle (neutral) layer of the assembly.
Q: What is a Piezo Electric Harvesting Circuit?
A Piezo Harvesting Circuit or PHC is an electronic device which accepts the generated electric energy of a PEH/PEG as input and generates a stabilized DC (Direct Current) output.
A Piezo Harvesting Circuit is often also referred to as Conditioner, PMC (Power Management Controller) or Electronic Piezo Harvesting Module.
Q: What is a unimorph, bimorph or trimorph PEH?
A unimorph or monomorph is a cantilever that consists of one active layer and one inactive layer.
Q: Are electrical energy and electrical power the same?
Electrical energy and electrical power are often used in a way suggesting that they are interchangeable. They are not! Energy and Power are closely related but they are not the same. This is an important fact to understand if designing energy harvesting applications.
Energy is defined as the capacity to do work. Work can be in the form of kinetic energy, potential energy and thermal energy. It is also correct to say, if you are doing work to an object, you give the object energy. Furthermore you can add energy to an object by transferring heat. This is the first law of thermodynamics: The total energy of a system can be increased by doing work on it or by adding heat.
Power is the rate of doing work or the rate at which energy is used, produced, or transferred.
It is important to understand that it is the same amount of energy if you are using 1kW for one hour or 1W for one thousand hours. Or, it is the same amount of potential energy, as when a crane is lifting a 1 ton stone block 20 m up in 1 min or 1 hour. But the required power for the motor of the crane is higher if you lift the block in 1min instead of 1 hour because the time interval is different.