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Advances In Piezoelectric Transducers.iso

The vibrations are generated using piezoelectric elements which are capacitors that change shape when charged and discharged. The vibration frequency corresponds to the resonant frequency of the structure and uses the mechanical Q (amplification) to multiply piezo element movements of 10 to 100 nanometers to motor movements of 1 to 10 micrometers. For most piezo motors, two orthogonal vibrations are generated that combine to produce Lissajous motions with a preferred direction that is changed by changing the drive frequency or phase.

Advances in Piezoelectric Transducers.iso

Co-fired multi-layer piezoelectric elements are now available that operate efficiently at ultrasonic frequencies with the drive voltage supplied directly from a battery. This motor innovation eliminates the need for a DC-DC voltage boost to 40 or 200 volts, and enables small, efficient and smart drive circuits which are similar in size and cost to stepper and DC motor drive solutions. Two examples of piezo motor driver ICs are the NSD2101 from ams (figure 1) and the LT3572 from Linear Technologies.

The first experimental demonstration of a connection between macroscopic piezoelectric phenomena and crystallographic structure was published in 1880 by Pierre and Jacques Curie. Their experiment consisted of a conclusive measurement of surface charges appearing on specially prepared crystals (tourmaline, quartz, topaz, cane sugar and Rochelle salt among them) which were subjected to mechanical stress. These results were a credit to the Curies' imagination and perseverance, considering that they were obtained with nothing more than tinfoil, glue, wire, magnets and a jeweler's saw.

In the scientific circles of the 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 did not, however, predict that crystals exhibiting the direct piezoelectric effect (electricity from applied stress) would also exhibit the 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 the existence of the "converse effect," and continued on to obtain quantitative proof of the complete reversibility of electro-elasto-mechanical deformations in piezoelectric crystals.

At this point in time, after only two years of interactive work within the European scientific community, the core of piezoelectric applications science was established: the identification of piezoelectric crystals on the basis of asymmetric crystal structure, the reversible exchange of electrical and mechanical energy, and the usefulness of thermodynamics in quantifying complex relationships among mechanical, thermal and electrical variables.

In the following 25 years (leading up to 1910), much more work was done to make this core grow into a versatile and complete framework which defined completely the 20 natural crystal classes in which piezoelectric effects occur, and defined all 18 possible macroscopic piezoelectric coefficients accompanying a rigorous thermodynamic treatment of crystal solids using appropriate tensorial analysis. In 1910 Voigt's "Lerbuch der Kristallphysik" was published, and it became the standard reference work embodying the understanding which had been reached.

During the 25 years that it took to reach Voigt's benchmark, however, the world was not holding its breath for piezoelectricity. A science of such subtlety as to require tensorial analysis just to define relevant measurable quantities paled by comparison to electro-magnetism, which at the time was maturing from a science to a technology, producing highly visible and amazing machines. Piezoelectricity was obscure even among crystallographers; the mathematics required to understand it was complicated; and no publicly visible applications had been found for any of the piezoelectric crystals.

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 the end of the war, they did achieve their goal of emitting a high frequency "chirp" underwater and measuring depth by timing the return echo. The strategic importance of their achievement was not overlooked by any industrial nation, however, and since that time the development of sonar transducers, circuits, systems, and materials has never ceased.

In fact, during this revival following World War I, most of the 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 the materials available at the time often limited device performance and certainly limited commercial exploitation.

During World War II, in the U.S., Japan and the 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, the 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.

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 the other way around.

From a business perspective, the market development for piezoelectric devices lagged behind the technical development by a considerable margin. Even though all the 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 the growth of this industry was severely hampered.

The Pz1200 Piezoelectric Valve can be configured as a non-contact jet or precise high-speed contact dispensing valve. The advanced piezoelectric ceramic actuation technology achieves exceptional levels of dispense accuracy and superior process control.

Alpinion Medical Systems believes that technology is only meaningfulwhen it delivers value to health care providers. Guided by this philosophyAlpinion focuses on the development and production of ultrasoundincluding diagnostic ultrasound and advanced piezoelectric and single-crystal transducer technology

EBL Products Inc. provides standard and application specific andindustrial piezoceramic transducer elements to researchers as well asmanufacturers of piezoelectric transducers according to their terms andspecifications

SIMetris support ultrasonic product development using our finite elementsimulation tool NACS. We provide analysis of piezoelectric,vibroacoustic, and magneto-mechanical interactions as well as productoptimization.

The goal of TRS Technologies, Inc. is to utilize cutting edge R&Dcombined with extensive manufacturing knowledge to build and growlasting and profitable business relationships making us the preferredsupplier of high quality, specialty piezoelectrics and dielectrics to OEMsin the medical, sensor, and military markets.

Acoustic waves are mechanical waves generated by the high-frequency vibration of piezoelectric materials (e.g., lithium niobate, lithium tantalite, quartz) when alternating current (AC) electrical signals act on them24. Depending on whether the entire body or just the surface of the material vibrates, acoustic waves can be divided into bulk acoustic waves (BAWs) and surface acoustic waves (SAWs). Additionally, acoustic waves are also distinguished as traveling waves or standing waves in the field of acoustics. Traveling waves are unidirectional waves with regular propagation, whereas standing waves are composite waves that transmit bilaterally.

Blood serves as a circulating carrier that provides the body with various nutrients and oxygen and removes waste. The numerous cells in the blood characterize the physiological state of the body. Changes in the number and state of blood cells often lead to diseases. The isolation of specific cells from blood can help to diagnose and treat health problems. Petersson et al. demonstrated the separation of RBCs and platelets using a BAW-based device59. Cells were added through the side inlets. Cesium chloride solution was added through the middle inlet to manipulate the relative density between the cells and fluid to enhance the separation efficiency. However, whether the added solution has an irreversible negative impact on the cells needs to be further studied. Cells were separated and flowed out of different outlets based on their sizes and densities. The separation of RBCs, platelets, and leukocytes in the buffy coat was also investigated using this device. While the efficiency of separating multiple cells simultaneously was not high, this early BAW-based microfluidic device was instrumental in promoting the use of similar systems in blood cell isolation. Liu et al. demonstrated that bubble-driven acoustic microstreaming can be used to separate cells and plasma in whole blood samples with a plasma purity of 99.9%89. Rectangular lateral cavities were positioned at a 15 angle from the channel to trap air bubbles. An acoustic microstreaming vortex was generated by the trapped bubbles with the vibration of the piezoelectric substrate. The size- and density-dependent trapping principle contained the larger blood cells in the vortex, allowing the blood plasma to flow downstream. Meanwhile, the fluid vortex acted as a micropump, which facilitated the continuous flow of fluid without integrating other pump equipment. Furthermore, the device utilized a similar bubble-driven microstreaming effect to enhance the mixing of the antigen-conjugated PS beads and HIV-p24 antibodies in plasma and trap the complexes for fluorescent detection to assess the concentration of HIV-p24 antibodies. This multifunctional device shows its ability to rapidly separate and detect biomarkers in blood samples.


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