Piezoceramic

Piezocomposite transducers are an advancement of piezoelectric ceramics. Instead of the classic piezoceramic material, a compound of polymer and piezoceramic is used for the composite element to improve specific properties. The 1-3 structure, which is nowadays mostly used as transducer material, refers to parallel ceramic rods incorporated in an epoxy-resin matrix (see Fig. 1). 

Piezocomposite ceramic can be tailored to our needs in contrast to conventional piezoceramic. The first parameter we can modify is the ceramic volume fraction. Fig. 2 indicates that the thickness coupling factor of the 1-3 composite is higher over a wide range of ceramic volume fraction between 15% and 95% than the coupling factor for PZT of about 0.52. Between 25% and 70% of volume fraction it is nearly constant at a high level of approximately 0.65. 

Historically, the first and most important capacitance method is the vibrating capacitor approach implemented by Lord Kelvin in 1897. In this technique (now called the Kelvin probe), the reference plate moves relative to the sample surface at some constant frequency and tlie capacitance changes as tlie interelectrode separation changes. An AC current thus flows in the external circuit. Upon reduction of the electric field to zero, the AC current is also reduced to zero. Originally, Kelvin detected the zero point manually using his quadrant electrometer. Nowadays, there are many elegant and sensitive versions of this technique. A piezoceramic foil can be used to vibrate the reference plate. To minimize noise and maximize sensitivity, a phase-locked... 

Since discovering and making use of the piezoelectric effect in naturally occurring crystals such as quartz and Rochelle salts, scientists have produced a wide range of piezoelectric materials in the laboratoi y. An early example is barium titanate, used in an electrical component called a capacitor. Currently, most piezoelectric materials are oxide materials based on lead oxide, zirconate oxide, and titanium. These very hard piezoelectric materials are termed piezoceramics. 

Piezoelectric fans are small, low-power, relatively low-noise, solid-state devices that provide viable thermal management solutions for a variety of portable electronic appliances, including laptop computers and cellular phones. In these fans piezoceramic patches are bonded onto thin, low-frequency flexible blades driven at resonance frequency, thereby creating an air stream directed at the electronics components. Thereby, up to 100% improvement over natural convective heat transfer can be achieved (Acikalin et al. 2004). 

Kymissis et al. have examined the possibility of generation of electrical power parasitically from devices built in a shoe, a wearable subsystem for the soldier. Merits of three different types of piezoelectric devices are compared. They are a unimorph strip piezoceramic composite, a stave of multilayer laminate of PVDF foil, and a shoe-mounted rotary magnetic generator as a part of technology demonstration a piezoelectric embedded shoe has also been postulated to periodically broadcast a digital radio frequency identification (RFID) signal as the wearer walks. 

For polycr5rstalline piezoceramics to work, the electrically charged dipoles within the entire piezoelectric component must be aligned by placing the piezoceramic within a high electric field—a process known as poling. The ability of piezoceramics to almost instantaneously convert electrical... 

Fig. 7. Schematic view of an acoustic cell filter [127]. P piezoceramic, C carrier (glass), F polysulfone foU, AV active volume, R reflector, CA cell aggregates, CS cell suspension, H harvest (clarified fluid). The nodal planes (pressure nodes) of the standing acoustic field are schematically indicated by dashed lines...

Aerogels are used in diermal insulation, catalysis, detection of high energy particles, piezoceramic, ultrasound transducers, integrated circuits, and as dehydrating agents. 

There are two principal types of materials that can function as piezoelectrics the ceramics and polymers. The piezoelectric materials most widely used are the piezoceramics based upon the lead zirconate titanate, FZT. The advantages of these piczoccramics arc that they have a high piezoelectric activity and they can be fabricated in many different shapes. 

Before the phenomenon piezoceramics can be discussed, some attention should be paid to ferroelectric ceramics. 

P = piezoceramic C = glass F = polysulfone foil AV = active volume R = reflector CA = cell aggregates CS = cell suspension H = harvest (clarified fluid)... 

Dielectric hysteresis in the commercially important ferrolectric piezoceramics (e.g. PZT c.f. Section 6.3.1) is comprehensively reviewed by D. Hall [15]. 

Recently injection-moulding has been exploited by L.J. Bowen [10] to fabricate a range of piezoceramic-polymer composites (see Section 6.4.6) for the active elements of sonar devices. 

The discussion is now restricted to matters relevant to the technology of piezoceramics. If it is assumed that the quantities d, g, s, and s are constants and, furthermore, the tensor nature of the various parameters (see below) is not taken into account, then equations of state can be written as follows. 

The first piezoceramic to be developed commercially was BaTi03, the model ferroelectric discussed earlier (see Section 2.7.3). By the 1950s the solid solution system Pb(Ti,Zr)03 (PZT), which also has the perovskite structure, was found to be ferroelectric and PZT compositions are now the most widely exploited of all piezoelectric ceramics. The following outline description of their properties and fabrication introduces important ideas for the following discussion of the tailoring of piezoceramics, including PZT, for specific applications. It is assumed that the reader has studied Sections 2.3 and 2.7.3. 

Compositions, composites and devices have been developed for the four main uses of piezoceramics ... 

BaTi03 was the first material to be developed as a piezoceramic and was used on a large scale for application 4 above. For most commercial purposes it has been... 

The search for piezoceramics having optimum electromechanical properties has been extended to cover MPB compositions of PbTi03 with various relaxors. The search is assisted by using a relationship established between the Curie point of the MPB composition and the tolerance factor (see Section 2.7.3) for the relaxor component [10]. 

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