======================PIEZOELECTRIC_EFFECT====================================== piezoelectricity? some atomic lattice structures have as a "cell") a cubic or rhomboid cage made of atoms, this cage holds a single semi-mobile ion has several stable quantum position states inside cell ion's post ion state can be caused to shift by either deforming cage (applied strain) or by applying and electric field. coupling between central ion and cage provides the basis for transformation of mechanical strain to internal electric field shifts and vice versa. strain solid object like a rod of length (L) is stretched to a new length (L + delta L), the strain in the rod is defined as the ratio (delta L)/(L). This is a dimensionless measure of stretching or compression often stated as "inches per inch", "millimeters per meter", or "microns per meter (microstrain)" for convenience of visualization. elastic modulus (or Young's modulus) ? A. A material property of all elastic solids, Young's modulus (Y) is used to describe "stiffness" of materials. When rod or plate of cross section (A) and length (L) is pulled with force (F) resulting in an elongation (delta L), the Young's modulus can be computed as follows: Y = (L/A)*(F/deltaL) In piezo applications Y is frequently used to estimate the equivalent spring constant of a rod or a plate of material (i.e. that quantity (F/deltaF) that is in contact with a piezo actuator). tensile strength stress (measured in Newtons/m^2 or psi) at which a sample of solid material will break from tension. poling/depoling i n piezoceramic materials? A. The piezoelectric property of ceramics does not arise simply from its chemical composition. In addition to having the proper formulation the piezoceramics must be subjected to a high electric field for a short period of time to force the randomly oriented micro-dipoles into alignment. This alignment by application of high voltage is called "poling". At a later time, if an electric field is applied in the opposite direction it exerts a "dislodging stress" on the micro-dipoles. Low level applied fields result in no permanent change in the polarization (it bounces back upon removal). Medium fields result in partial degradation of the polarization (with partial loss of properties). High applied fields result in repolarization in the opposite direction. PIEZO_piezoceramic element is stressed by a voltage, stressed mechanically by force, generates electric charge. Piezoelectric coefficients with double subscripts link electrical and mechanical quantities. first subscript gives the direction of electrical field associated with voltage applied, or charge produced. second subscript gives the direction of mechanical stress or strain. Several piezoceramic material constants may be written with a "superscript" which specifies either a mechanical or electrical boundary condition. The superscripts are T, E, D, and S, signifying: T = constant stress = mechanically free E = constant field = short circuit D = constant electrical displacement = open circuit S = constant strain = mechanically clamped As an example, KT3 expresses the relative dielectric constant (K), measured in the polar direction (3) with no mechanical clamping applied. "d" CONSTANT The piezoelectric constants relating the mechanical strain produced by an applied electric field are termed the strain constants, or the "d" coefficients. The units may then be expressed as meters per meter, per volts per meter (meters per volt). PIEZO_MECHANICAL Qm) ratio of reactance to resistance in the equivalent series circuit representing the mechanical vibrating resonant systems. The shape of the part affects the value. PIEZO_CURIE TEMP temperature at which the crystal structure changes from a non-symmetrical (piezoelectric) to a symmetrical (non-piezoelectric) form, expresses in degrees Celsius. PIEZO_AGING RATE Aging is the attempt of the ceramic to change back to its original state prior to polarization. Aging of piezoelectric ceramics is a logarithmic function with time. The aging rate defines change in the material parameters per decade of time, i.e., 1-10 days, 5-50 days, etc. PYROELECTRICITY Piezoelectric materials are also pyroelectric. They produce electric charge as they undergo a temperature change. When their temperature is increased, a voltage develops having the same orientation as the polarization voltage. When their temperature is decreased, a voltage develops having an orientation opposite to the polarization voltage, creating a depolarizing field with the potential to degrade the state of polarization of the part. maximum electric field due to temperature shift is: where E (pyro) is the induced electric field in volts/meter, a is the pyroelectric coefficient in Coulomb/° C meter 2, DT is the temperature difference in °C, K3 is the dielectric constant, and e0 is the dielectric permittivity of free space. For PZT piezoceramic, a is typically ~ 400x10-6 coulomb/°C meter2. piezoceramic actuators be used at cryogenic temperatures? A. Yes. All piezo actuators continue to function right on down to zero degrees Kelvin. This may seem counter-intuitive at first; however, you must remember that the basis for the piezoelectric effect is inter-atomic electric fields, and electric fields are not affected by temperature at all. Quantitatively, the piezo coupling of most common piezoceramics does decrease as temperature drops. At liquid helium temperatures, the motion of most materials drops to about half that measured at room temperature. static applications? A. Piezo transducers are not suitable for static force measurements. They can be used effectively for transient force measurements lasting less than 0.1 second. PIEZOELECTRIC EFFECT certain dielectric materials converts an Input voltage to a mechanical motion or vice versa. important uses include filters, beepers, sonar, ultrasonics, micropositioners, gyros, microphones, miniature fans, strain gauges, accelerometers, and furnace igniters. + _______|_______ __|_______________|____ ____---- ----___ | _______________________ | |____---- |_______________| ----___| | - 0 _______|_______ ________|_______________|_____________ | | |______________________________________| |_______________| | 0 - ____ _______|_______ ___ | ----__|_______________|____---- | |____ ___| ----_______________________---- |_______________| | + fatigue life of piezoelectric Why piezoelectricity some atomic lattice structures have as an a cubic or rhomboid cage made of atoms, this cage holds a single semi-mobile ion which has several stable quantum position states inside cell. The ion's post ion state can be caused to shift by either deforming cage (applied strain) or by applying and electric field. The coupling between central ion and cage provides basis for transformation of mechanical strain to internal electric field shifts and vice versa. electric field small known charge (Q) placed near a charge will experience an accelerating force (F) electric field (E) is ratio F/Q (a vector). strain? rod of length (L) stretched to length (L + delta L), strain defined as ratio (delta L)/(L). elastic modulus (or Young's modulus) "stiffness" of materials. Young's modulus can be computed as follows: Y = (L/A)*(F/deltaL) tensile strength is stress (measured in Newtons/m^2 or psi) at which a solid material will break from tension. poling/depoling piezoceramic materials? A. The piezoelectric property of ceramics does not arise simply from its chemical composition. In addition to having proper formulation piezoceramics must be subjected to a high electric field for a short period of time to force randomly oriented micro-dipoles into alignment. This alignment by application of high voltage is called "poling". At a later time, if an electric field is applied in opposite direction it exerts a "dislodging stress" on micro-dipoles. Low level applied fields result in no permanent change in polarization (it bounces back upon removal). Medium fields result in partial degradation of polarization (with partial loss of properties). High applied fields result in repolarization in opposite direction. Damping is term used for general tendency of vibrating materials or structures to lose some elastic energy to internal heating or external friction. cryogenic temperatures? A. Yes. All piezo actuators continue to function right on down to zero degrees Kelvin. This may seem counter-intuitive at first; however, you must remember that basis for piezoelectric effect is inter-atomic electric fields, and electric fields are not affected by temperature at all. Quantitatively, piezo coupling of most common piezoceramics does decrease as temperature drops. At liquid helium temperatures, motion of most materials drops to about half that measured at room temperature. pyroelectric effect a voltage will arise between electrodes in response to temperature shifts. static applications can be used effectively for transient force measurements lasting less than 0.1 second. fatigue life of piezoelectric material? A.The "fatigue life" is pretty difficult to estimate; although we've had a piezo fan running constantly here since 1982, no conclusive tests have been done. It would depend on mounting, voltages, etc. cut up a sheet of piezoceramic into size I want? best cut using a special diamond saw. Small prototype parts can be cut from piezoceramic sheet stock by using a razor blade and a straight edge to score piezo surface and then making a controlled break. Even with practice this method does not yield straight-sided parts or repeatable cuts. Use at your own risk. bond/attach piezoceramic sheet to a structure like an aluminum beam? We suggest that you contact several epoxy manufacturer discuss application, being sure to include: 1. The metal surfaces to be joined 2. Temperature of operation 3. Any unusual shear stress requirements Note: University of Missouri at Rolla has a very helpful section on this. superglue' Good quality temporary bonds may be made with cyanoacrylate (e.g. "super glue"). An added benefit of cyanoacrylate bonds is that bond easily achieves electrical contact. The length of time bond will last will be application dependent, from seconds to years. electrical contact to side of piezoceramic that is bonded down? most common method is to make a conductive bond between a metal substrate and piezo part. attach wire leads to piezoceramic? All of PSI piezoceramic parts come with a thin metallic electrode already on ceramic. Wire leads can be soldered (use ordinary 60/40 resin core solder) anywhere on electrode to suit application/experiment. Most PSI ceramics have nickel electrodes and require use of an additional liquid flux for uniform results. Q. How can I access center shim? stretch a sheet before it breaks? approximately 500 microstrain ( micrometers per meter) in regular use. If sheet loses some properties, can it be repoled? A. Yes. For 5H material, an electric field of 40 - 50 volts/mil will restore nearly all lost polarization. For 5A, use 50 - 100 volts/mil. frequency limit of piezoceramic sheet? material has a thickness mode vibration in neighborhood of 13 MHz and a planar dilatation mode at around 14 KHz. highest voltage that I can drive a piezoceramic sheet to? low frequency operation (0 to 5 KHz) a conservative recommendation for applied bi-polar voltage for a single sheet of PSI-5A ceramic is ±90 volts. Voltage applied in poling direction only can be raised up to 250 volts. Use caution! mechanical power can I get out of one sheet? A. In theory, one standard PSI-5A sheet (1.5" x 2.5" x .0075") used as an "extender" can do .00035 joules of work on outside world in a quasistatic cycle (i.e. a slowly executed sinusoidal cycle). When operated just under its first longitudinal resonance of 15 KHz, theoretically available output power from sheet would be around 5 watts. In practice it is difficult to collect more than 100f this work. Resonant designs can be considerably more efficient. electrical power can I get out of one piezo sheet in principle? A. Assuming that we stretch a PSI-5A 1.5" x 2.5" x .0075" sheet to ±500 microstrains quasistatically at a frequency just below its fundamental longitudinal resonance of 15 KHz, and that we collect 1000f stored electrical energy at its height twice per cycle we would get approximately 9 watts of electrical power from sheet. The mechanical energy input under these assumptions would be in excess of 100 watts. Resonant designs can be considerably more efficient. However, mechanical apparatus for achieving above mentioned 15 KHz high strain excitation is not available, and there is no known electronic method for extracting 1000f available energy. electrical power can be extracted from a typical piezo bender element in practice? A. A "Double Quick Mount" bending element bolted to a rigid surface provides a convenient demonstration of a cantilever mount generator. Applying 80 gram force to its tip at a frequency of 60 Hz produces an open circuit voltage of 15V peak between its two electrical leads. When leads are connected to a 8 Kohm resistive load, output to load is 5.3 Vrms, representing a power output of 3.6 mW. effects temperature on piezoceramic transducers? A. Temperature changes cause a voltage to appear across electrodes of any piezo transducer. This is due to pyroelectric properties of piezoceramic. Temperature also affects every property of piezoceramics (elastic, dielectric and piezoelectric coupling). There is no general trend. Each dependence must be looked up or better yet measured in context of your experiment. ( find piezo devices? 'watch beepers' are piezoceramic audio transducers, most battery operated smoke detector alarms, fish finders, some cigarette lighters, many gas grill igniters. USA 617-547-1777 Fax: 617-354-2200 email: sales@piezo.com first demonstration of piezoelectric phenomena and Piezo crystallographic structure was published in 1880 by Education Pierre and Jacques Curie. In scientific circles of day, this effect was considered quite a "discovery," and was quickly dubbed as "piezoelectricity" in order to distinguish it from other areas of scientific phenomenological experience such as "contact electricity" (friction generated static electricity) and "pyroelectricity" (electricity generated from crystals by heating). The Curie brothers asserted, however, that there was a one-to-one correspondence between electrical effects of temperature change and mechanical stress in a given crystal, and that they had used this correspondence not only to pick crystals for experiment, but also to determine cuts of those crystals. To them, their demonstration was a confirmation of predictions which followed naturally from their understanding of microscopic crystallographic origins of pyroelectricity (i.e., from certain crystal asymmetries). The Curie brothers did not, however, predict that crystals exhibiting direct piezoelectric effect (electricity from applied stress) would also exhibit converse piezoelectric effect (stress in response to applied electric field). This property was mathematically deduced from fundamental thermodynamic principles by Lippmann in 1881. The Curies immediately confirmed existence of "converse effect," and continued on to obtain quantitative proof of complete reversibility of electro-elasto-mechanical deformations in piezoelectric crystals. LABORATORY CURIOSITY MATHEMATICAL CHALLENGE 1882 - 1917 The first serious applications work on piezoelectric devices took place during World War I. In 1917, P. Langevin and French co-workers began to perfect an ultrasonic submarine detector. Their transducer was a mosaic of thin quartz crystals glued between two steel plates (the composite having a resonant frequency of about 50 KHz), mounted in a housing suitable for submersion. Working on past end of war, they did achieve their goal of emitting a high frequency "chirp" underwater and measuring depth by timing return echo. The strategic importance of their achievement was not overlooked by any industrial nation, however, and since that time development of sonar transducers, circuits, systems, and materials has never ceased. FIRST GENERATION APPLICATIONS WITH NATURAL CRYSTALS 1920 - 1940 The success of sonar stimulated intense development activity on all kinds of piezoelectric devices, both resonating and non-resonating. Some examples of this activity include: * Megacycle quartz resonators were developed as frequency stabilizers for vacuum-tube oscillators, resulting in a ten-fold increase in stability. * A new class of materials testing methods was developed based on propagation of ultrasonic waves. For first time, elastic and viscous properties of liquids and gases could be determined with comparative ease, and previously invisible flaws in solid metal structural members could be detected. Even acoustic holographic techniques were successfully demonstrated. * Also, new ranges of transient pressure measurement were opened up permitting study of explosives and internal combustion engines, along with a host of other previously unmeasurable vibrations, accelerations, and impacts. In fact, during this revival following World War I, most of classic piezoelectric applications with which we are now familiar (microphones, accelerometers, ultrasonic transducers, bender element actuators, phonograph pick-ups, signal filters, etc.) were conceived and reduced to practice. It is important to remember, however, that materials available at time often limited device performance and certainly limited commercial exploitation. SECOND GENERATION APPLICATIONS WITH PIEZOELECTRIC CERAMICS 1940 - 1965 During World War II, in U.S., Japan and Soviet Union, isolated research groups working on improved capacitor materials discovered that certain ceramic materials (prepared by sintering metallic oxide powders) exhibited dielectric constants up to 100 times higher than common cut crystals. Furthermore, same class of materials (called ferroelectrics) were made to exhibit similar improvements in piezoelectric properties. The discovery of easily manufactured piezoelectric ceramics with astonishing performance characteristics naturally touched off a revival of intense research and development into piezoelectric devices. The advances in materials science that were made during this phase fall into three categories: 1. Development of barium titanate family of piezoceramics and later lead zirconate titanate family 2. The development of an understanding of correspondence of perovskite crystal structure to electro-mechanical activity 3. The development of a rationale for doping both of these families with metallic impurities in order to achieve desired properties such as dielectric constant, stiffness, piezoelectric coupling coefficients, ease of poling, etc. All of these advances contributed to establishing an entirely new method of piezoelectric device development - namely, tailoring a material to a specific application. Historically speaking, it had always been other way around. This "lock-step" material and device development proceeded world over, but was dominated by industrial groups in U.S. who secured an early lead with strong patents. The number of applications worked on was staggering, including following highlights and curiosities: * Powerful sonar - based on new transducer geometries (such as spheres and cylinders) and sizes achieved with ceramic casting. * Ceramic phono cartridge - cheap, high signal elements simplified circuit design * Piezo ignition systems - single cylinder engine ignition systems which generated spark voltages by compressing a ceramic "pill" * Sonobouy - sensitive hydrophone listening/radio transmitting bouys for monitoring ocean vessel movement * Small, sensitive microphones - became rule rather than exception * Ceramic audio tone transducer - small, low power, low voltage, audio tone transducer consisting of a disc of ceramic laminated to a disc of sheet metal * Relays - snap action relays were constructed and studied, at least one piezo relay was manufactured It is worth noting that during this revival, especially in U.S., device development was conducted along with piezo material development within individual companies. As a matter of policy, these companies did not communicate. The reasons for this were threefold: first, improved materials were developed under wartime research conditions, so experienced workers were accustomed to working in a "classified" atmosphere; second, post war entrepreneurs saw promise of high profits secured by both strong patents and secret processes; and third, fact that by nature piezoceramic materials are extraordinarily difficult to develop, yet easy to replicate once process is known. From a business perspective, market development for piezoelectric devices lagged behind technical development by a considerable margin. Even though all materials in common use today were developed by 1970, at that same point in time only a few high volume commercial applications had evolved (phono cartridges and filter elements, for instance). Considering this fact with hindsight, it is obvious that while new material and device developments thrived in an atmosphere of secrecy, new market development did not - and growth of this industry was severely hampered. JAPANESE DEVELOPMENTS 1965 - 1980 In contrast to "secrecy policy" practiced among U.S. piezoceramic manufacturers at outset of industry, several Japanese companies and universities formed a "competitively cooperative" association, established as Barium Titanate Application Research Committee, in 1951. This association set an organizational precedent for successfully surmounting not only technical challenges and manufacturing hurdles, but also for defining new market areas. Beginning in 1965 Japanese commercial enterprises began to reap benefits of steady applications and materials development work which began with a successful fish-finder test in 1951. From an international business perspective they were "carrying ball," i.e., developing new knowledge, new applications, new processes, and new commercial market areas in a coherent and profitable way. Persistent efforts in materials research had created new piezoceramic families which were competitive with Vernitron's PZT, but free of patent restrictions. With these materials available, Japanese manufacturers quickly developed several types of piezoceramic signal filters, which addressed needs arising in television, radio, and communications equipment markets; and piezoceramic igniters for natural gas/butane appliances. As time progressed, markets for these products continued to grow, and other similarly valuable ones were found. Most notable were audio buzzers (smoke alarms, TTL compatible tone generators), air ultrasonic transducers (television remote controls and intrusion alarms) and SAW filter devices (devices employing Surface Acoustic Wave effects to achieve high frequency signal filtering). By comparison to commercial activity in Japan, rest of world was slow, even declining. Globally, however, there was still much pioneering research work taking place as well as device invention and patenting. HIGH VOLUME MARKETS 1980 - Present The commercial success of Japanese efforts has attracted attention of industry in many other nations and spurred a new effort to develop successful piezoceramic products. If you have any doubts about this, just track number of piezo patents granted by U.S. Patent Office every year - there has been a phenomenal rise. Another measure of activity is rate and origin of article publication in piezo materials/applications area - there has been a large increase in publication rate in Russia, China and India. Solid state motion is presently single most important frontier. The technical goals of frontier are to obtain useful and reasonably priced actuators which are low in power and consumption and high in reliability and environmental ruggedness; or, more simply stated, "solenoid replacements," or "electrostatic muscles." The search for perfect piezo product opportunities is now in progress. Judging from increase in worldwide activity, and from successes encountered in last quarter of 20th century, important economic and technical developments seem certain. Typical electric squirrel cage motors generate AC voltage of purest sinewave.use no brushes and do not produce any RFI.(Radio Frequency Interference) A They can not be overloaded; if too much of a load is applied to generator, it simply quits generating. Removing load will usually cause generator to start again Speeding up motor will help if doesn't start right away. By adding capacitors in parallel with motor power leads, and driving it above nameplate RPM, 1725 RPM ones need to turn at approximately 1875 RPM,3450 RPM ones at 3700 RPM) motor will generate AC voltage!capacitance helps to induce currents into rotor conductors and causes it to produce AC current. 200 uf starting capacitor across permanent 160 uf running capacitor (Using Normally Closed contacts) to get it generating. When 120 volts was produced, relay contacts opened up and removed 200 uf from circuit. That worked, but it was not dependable. I just gave up on that one. capacitors used must be type designated as "running" capacitors ,NOT "starting" capacitors Starting capacitors are used for a very short time,less than a second or two,