122, piezoceramic metallic

Fine-scale arrays (< 50/mr) have been produced by first making a metal master by hard X-ray lithography. This constitutes the mould from which a polymer negative array is made. The piezoceramic powder slurry or paste is formed in the sacrificial polymer mould which is subsequently burnt away in a presintering heating stage. 

Fig. 6.33 Hi-fi tweeter showing ceramic bimorph plate element. Inset, cross-section of element showing piezoceramic plates sandwiched between metallized glass fibre mesh.

The developed methods of metallization of different materials are widely used in the enterprises of the Commonwealth of Independent States (CIS) for production of quartz resonators and filters (several tens of min. were produced), monolithic piezoquartz filters, photomasks, piezoceramic devices for hydroacoustics and delay lines of colour TV sets (several hundreds of min. were produced), casings of integrated circuits and semiconducting apparatus, ceramic microplates, precise microwire resistors and other devices. 

Piezoelectric transducers are the most common devices employed for the generation of ultrasound and utilise ceramics containing piezoelectric materials such as barium titanate or lead metaniobate. The piezoceramic element commonly used in ultrasonic cleaners and for probe systems is produced in the form of a disk with a central hole. Ceramic transducers are potentially brittle and so it is normal practice to clamp them between metal blocks. This serves both to protect the delicate crystalline material and to prevent it from overheating by acting as a heat sink. Usually two elements are combined so that their overall mechanical motion is additive (Figure 10.4). Piezoelectric transducers are better than 95% electrically efficient and can operate over the whole ultrasonic range. 

Fine scaled composites can be prepared starting with molded and sintered ceramic arrays made by the soft mold process. Once the piezoceramic pillars have been formed, the remaining spaces are filled with a polymer matrix material. Next the base is removed by grinding. Metal electrodes are then bonded to the ends of the fibers and first used to polarize the piezoceramic at an elevated temperamre and then to apply an electric field or collect developed charges from the material. At this point, the active elements are ready to be used as piezoelectric transducer element. Experiments have shown that high-performance composites can be prepared . 

For speakers or buzzers, audible by humans, devices with a rather low resonance frequency are used (kilohertz range). Examples are a bimorph consisting of two piezoceramic plates bonded together, and a piezoelectric fork consisting of a piezodevice and a metal fork. A piezoelectric buzzer is shown in Figure 4.1.12, which has merits such as high electric power efficiency, compact size and long life. 

It is important to note that the unimorph (a piezoceramic plate and a metal plate bonded together) bending actuation cannot provide high efficiency theoretically, because the electromechanical coupling factor k is usually less than 10%. Therefore, instead of the unimorph structure, a simple disk was... 

One approach to optimize weight and acoustic emission is to actively influence sheet metals via ASAC. A corresponding project example is an actively damped car roof structure which was part of the German Leitprojekt Adap-tronik [165]. Several distributed piezoceramic actuators have been attached... 

The generic demonstrator shown in Fig. 7.15B consists of a glass fiber-reinforced polyamide 6 (GF-PA 6) component. Additionally, especially developed matrix identical thermoplastic compatible piezoceramic modules (TPM) were embedded in the demonstrator structure during its manufacturing process. In Fig. 7.14 the built up of different TPM configurations are shown, consisting of thermoplastic carrier films, metallized with electrode structures and piezoelectric functional layers (eg, piezoceramic plates, fiber composites, or printing pastes) in the middle. 

Farlow R, Hayward G (1994) Real-time ultrasonic techniques suitable for implementing non-contact NDT systems employing piezoceramic composite transducers. Brit J NDT 36 926-935 Gupta V, Yuan J (1993) Measurement of interface strength by the modified laser spallation technique, II Applications to metal/ceramic interfaces. J Appl Phys 74 2397-2404... 

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