A magnetoelectric ͑ME͒ laminate configuration was fabricated using a flextensional cymbal located between two magnetostrictive Terfenol-D ͑Tb 1−x Dy x Fe 2 ͒ plates. The laminate, operating in transverse magnetized/transverse polarized mode, has a ME voltage coefficient of 56.8 mV/ Oe under a magnetic bias field of 1 kOe, which is larger than that of conventional Terfenol-D/PZT/ Terfenol-D configuration. It is believed that the enhancement of ME effect is due to the coupling between the magnetostriction of Terfenol-D and the high piezoelectric response of cymbal. Recently the magnetoelectric ͑ME͒ effect has been intensively studied in single-phase materials that simultaneously reveal ferromagnetic and ferroelectric properties and in multiphase materials that are composed of ferromagnetic and ferroelectric phases in laminate and composite configurations, due to their potential applications as current and magnetic sensors and magnetic-electric transformers.
This paper describes the modeling of magnetoelectric (ME) effects for disk-type Terfenol-D (Tb0.3Dy0.7Fe1.92)/PZT (Pb(Zr,Ti)O3) laminate composite at low frequency by combining the advantages of the static elastic model and the equivalent circuit model, aiming at providing a guidance for the design and fabrication of the sensors based on magnetoelectric laminate composite. Considering that the strains of the magnetostrictive and piezoelectric layers are not equal in actual operating due to the epoxy resin adhesive bonding condition, the magnetostrictive and piezoelectric layers were first modeled through the equation of motion separately, and then coupled together with a new interface coupling factor kc, which physically reflects the strain transfer between the phases. Furthermore, a theoretical expression containing kc for the transverse ME voltage coefficient αv and the optimum thickness ratio noptim to which the maximum ME voltage coefficient corresponds were derived from the modified equivalent circuit of ME laminate, where the interface coupling factor acted as an ideal transformer. To explore the influence of mechanical load on the interface coupling factor kc, two sets of weights, i.e., 100 g and 500 g, were placed on the top of the ME laminates with the same thickness ratio n in the sample fabrication. A total of 22 T-T mode disk-type ME laminate samples with different configurations were fabricated. The interface coupling factors determined from the measured αv and the DC bias magnetic field Hbias were 0.11 for 500 g pre-mechanical load and 0.08 for 100 g pre-mechanical load. Furthermore, the measured optimum thickness ratios were 0.61 for kc = 0.11 and 0.56 for kc = 0.08. Both the theoretical ME voltage coefficient αv and optimum thickness ratio noptim containing kc agreed well with the measured data, verifying the reasonability and correctness for the introduction of kc in the modified equivalent circuit model.
This study presents a large displacement, piezoceramic and metal composite-based actuator, named drum piezoceramic-actuator. The drum actuator consists of a short, thick-walled steel cylinder sandwiched by two thin composite disks, which are fabricated from a brass disk bonded with one piezoceramic disk. The piezoceramic disk polarized in its thickness direction is of a large diameter to thickness ratio, thus, produces a large radial displacement under an applied voltage in the thickness direction, and consequently results in a large transverse deflection of the composite disks in the drum. Some original results are obtained in the drums with the geometrical changes in the short, thick-walled steel cylinder. The drum (outer diameter: 12.0 mm) demonstrates displacement output 7 times as large as that of a cymbal actuator with the same ceramic material and comparable dimensions under the same DC driving voltage of 78 V. The effective piezoelectric charge coefficient d 0 33 of the drum is measured and is about 3 times as large as that reported for the cymbal. The drums also showed first resonance frequency of the transducer from 15.68 to 32.57 kHz and faster response time of about tens microseconds which are mainly based on the dimensions of the short, thick-walled steel cylinder.
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