Q: What adhesives are you recommending 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: I want to use the MFC as a strain sensor but it seems I can not get any reading?
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 type 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 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.
As a sensor the MFC is currently used in applications to detect strain of up to several MHz. In low electric field operations it is also used as an actuator to generate ultrasound of up to 700kHz (i.e. SHM applications). Major criteria for operating the MFC as an actuator at higher frequencies is the heat built-up in the device due to dielectric and parasitic losses. Monitoring the device temperature is a good way to determine the upper frequency/voltage limit in the specific application. In general the temperature during operation should not exceed 80°C.
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 mor in depth analysis:
a) In general a PZT 5A material used in the MFC has an effective coupling coefficient (k33) of about 0.69. That is it's first order electrical-to-mechanical energy conversion efficiency. k33 is a measure of efficiency, but not the actual efficiency.
b) k33² is the ratio of stored mechanical energy to input electrical energy (= 0.48), but this is not the same as output work energy efficiency, since one can not actually use all of the stored energy to do useful work.
c) Max. output work energy efficiency (under optimum loading condition) for the MFC will work out to about 0.16, so max 16% of input electrical energy can be converted into useful output work with an MFC.
d) Max. output-work energy efficiency is not the same as output-work to consumed electrical energy efficiency! Most (may be 97-99%, depending on dielectric loss of the package) of the electrical energy not converted to work is actually stored electrostatically, i.e., like in a capacitor. You can recover that energy, in principal, with a clever drive electronic design.
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.
Max. mechanical tensile strain for the MFC is approx. 4500 ppm, before fracture. This applies to a MFC without an electric field applied. The package might be still functional, although elastic properties will change. For the 12-mil (0.3mm) thick, standard MFC package, this works out to a minimum curvature diameter of the actuator of about 4.7 inches (120mm) curled in fiber direction and 4 inches (100mm) curled perpendicular to the fiber direction.
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 usind a vacuum deposition process and range between 700nm and 1.2 µm in thickness.
Our standard electrode is the copper-tin electrode which combines cost effectivness with electrical properties similar to gold. Soldering wires to CuSn is much easier compared to gold. Our CuSn-electrode is about 1µm thick with a 500 nm tin-coating as passivation layer to prevent the copper from corroding.
Q: How do I connect wires to electroded 1-3 composites?
Most of our customers are soldering wires to the 1-3 composites using a low temperature solder. Soldering on a 1-3 composites 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.
While soldering please pay attention to minimize the contact time between composite and solder bit as short as possible. We use a lead-free solder wire with temperatures around 270°C and a contact time less than 0.5 seconds. If you can not attach the wire to the composite in the first attempt, please give the composite some time to cool down, otherwise this spot will become over-heated and the elctrode will fail.
Q: What solders should I use? What is a good solder procedure?
Skin the wire from its insulation, 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, hold the wire to the solder bit contact the electrode with both solder bit and wire, remove solder bit, keep wire on electrode, do not apply any loads until the tin has cooled.
Flux: Alpha-Grillo "Fludor" Wires:
stranded, 0,06...0,14 sq.mm or enameled copper wire
solder wire: leadfree FLUITIN 1532 per ISO 12224-1/1.12,
alloy SAC305 of Cookson Electronics/Alphametals
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, many grooves are diced using a diamond saw, and the grooves are filled with polymer. The extensive cutting is the primary factor in driving up manufacturing cost. 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.