S.H. Choy

Highly durable all-fiber nanogenerator for mechanical energy harvesting

Future generations of wearable electronic systems and mobile communication place a great demand for harvesting energy from ambient environments or human movements. Soft fiber-based electric power generators are attractive in meeting the requirements of wearable devices because of efficient energy conversion performance, high durability and comfort. In this paper, we present a novel all-fiber wearable electric power nanogenerator, which consists of a PVDF–NaNbO3 nanofiber nonwoven fabric as an active piezoelectric component, and an elastic conducting knitted fabric, made from segmented polyurethane and silver coated polyamide multifilament yarns, as the top and bottom electrodes. The non-uniform deformation distribution in a compressed nanogenerator device determines the complex operating modes in the piezoelectric nanofiber nonwoven fabric. The nanogenerator consistently produces a peak open-circuit voltage of 3.4 V and a peak current of 4.4 μA in cyclic compression tests at 1 Hz and a maximum pressure of 0.2 MPa, which is comparable to normal human walking motion. More importantly, the all-fiber nanogenerator retains its performance after 1 000 000 compression cycles, demonstrating great promise as a wearable energy harvester that converts the mechanical energy of human movement into electricity.

Lead-free ceramics for pyroelectric applications

The use of lead-free materials has recently become a very important issue in environmental protection of the earth. Two groups of lead-free ceramics, (K0.5,Na0.5)NbO3 based (KNN) and Bi1−y(NaxK1−x)yTiO3 based (BNKT), were studied for their thermal, dielectric, and pyroelectric properties as candidates for pyroelectric sensor applications. The BNKT-based ceramic, [Bi0.5(Na0.94K0.05Li0.016)0.5]0.95Ba0.05TiO3 (BNKLBT), shows excellent pyroelectric properties when compared with KNN-based ceramic and lead zirconate titanate. Its properties were measured as follows: pyroelectric coefficient p=360μC∕m2K, pyroelectric figure of merit of current, voltage, and detectivity Fi=221pm∕V, Fv=0.030m2∕C, and Fd=14.8μPa−1∕2. With these outstanding pyroelectric properties, the BNKLBT ceramic can be a promising material for pyroelectric sensor applications. The BNKLBT ceramic with different thicknesses (i.e., 0.3, 0.5, and 0.7mm) have been used as the sensing element for fabricating infrared detectors. The current responsivi...

Enhanced ferroelectric and piezoelectric properties in doped lead-free (Bi0.5Na0.5)0.94Ba0.06TiO3 thin films

Doping effects with respect to the electrical properties of morphotropic phase boundary (Bi0.5Na0.5)0.94Ba0.06TiO3 thin films epitaxially grown on CaRuO3 electroded (LaAlO3)0.3(Sr2AlTaO6)0.35 (001) substrates were investigated. Substantial enhancement of ferroelectricity and piezoelectricity has been achieved in La+Ce codoped films with a remanent polarization Pr of 29.5 μC/cm2 and a remanent piezoelectric coefficient d33,f of 31 pm/V, whereas Mn doping seems more favorite to reduce the leakage current by two order of magnitude. Both doped films exhibited diodelike I-V characteristics, which are correlated with resistance switching effect.

Dielectric behavior and microstructure of (Bi1∕2Na1∕2)TiO3–(Bi1∕2K1∕2)TiO3–BaTiO3 lead-free piezoelectric ceramics

(0.95−x)(Bi1∕2Na1∕2)TiO3–x(Bi1∕2K1∕2)TiO3–0.05BaTiO3 lead-free piezoelectric ceramics (abbreviated as BNT–BKT–BT100x with x varying from 0 to 20 mol %) are prepared by a solid-state reaction process. Variation of the dielectric properties and microstructure of BNT–BKT–BT100x ceramics with BKT content is studied. The results indicate that the relative permittivity er and loss tangent tanδ vary with the BKT amount. Scanning electron microscope observation also indicates that BKT in high amount affects the microstructure. X-ray diffraction analysis shows that the incorporated BKT diffuses into the BNT–BT lattice to form a solid solution during sintering.

Study of BNKLBT-1.5 lead-free ceramic/epoxy 1-3 composites

Bismuth sodium titanate based lead-free ceramic fiber with the chemical formula of 0.885(Bi0.5Na0.5)TiO3–0.05(Bi0.5K0.5)TiO3–0.015(Bi0.5Li0.5)TiO3–0.05BaTiO3, BNKLBT-1.5, has been fabricated by a powder-based extrusion method. The ceramic fibers with 400μm diameter were well crystallized after being calcined at 800°C and sintered at 1170°C. The piezoelectric and ferroelectric properties of the single fiber were found to be 155pC∕N and ∼34.5μC∕cm2, respectively, which is comparable with that in bulk sample. 1-3 ceramic/polymer composites were fabricated by two routes, including dice and filled method and fiber pick-and-place method. Theoretical models were used to calculate the piezoelectric properties of the composites and compared with experimental results.

Magnetoelectric effect in lead-free BNKLBT ceramic/terfenol-D continue fiber composite laminates

A magnetostrictive-piezoelectric laminated composite has been developed by sandwiching a lead-free BNKLBT ceramic plate polarized in the thickness direction between two terfenol-D continuous fiber composite plates. This lead-free magnetoelectric (ME) laminated composite has a large ME voltage sensitivity of 2.5 V/Oe at the resonance frequency of 130.9 kHz under a low magnetic bias field (HBias) of 0.6 kOe. This work shows the potential of BNKLBT lead-free ceramics in ME sensing application.

Study of 1–3 PZT Fibre/Epoxy Composites with Low Volume Fraction of Ceramics

Lead zirconate titanate (PZT) fibres were prepared by the viscous suspension spinning process (VSSP). Pre-sintered PZT powder mixed with poly (acrylic acid) was spun in a spinnerette to form fibres. The diameter of the fibre was 0.4 mm. The piezoelectric and ferroelectric properties of the single fibre were studied. The piezoelectric coefficient (d33) and the remnant polarization Pr for a single fibre were found to be 490 pC/N and 26 μC/cm2, respectively, which are comparable with that in the bulk sample. The fibres were used to fabricate 1–3 PZT fibre/epoxy composites with low volume fraction of PZT (<0.2). Different theoretical models were used to calculate the piezoelectric coefficient (d33) of the composites and compared with experimental results.

0.75(Bi1/2Na1/2)TiO3-0.20(Bi1/2K1/2)TiO3-0.05BaTiO3 Lead-Free Ceramics with Addition of CeO2

Lead-free piezoelectric 0.75(Bi 1/2 Na 1/2 )TiO 3 -0.20(Bi 1/2 K 1/2 )TiO 3 -0.05BaTiO 3 ceramics(abbreviated as BNKBT-20) with addition of 0.2, 0.4, 0.6 and 0.8 wt% of CeO 2 , respectively, were prepared by a conventional mixed oxide method. The addition of CeO 2 can reduce the dissipation factor and enhance the mechanical quality factor significantly. The composition with 0.4 wt% CeO 2 has a piezoelectric d 33 constant of 129 × 10− 12 C/N and a relatively low dissipation factor (tan δ = 1.8%) at 1 kHz which shows a 50% reduction in the dissipation factor when compared with BNKBT-20 before doping (tan δ = 3.74%).

Lead-Free Piezoelectric Transducers for Microelectronic Wirebonding Applications

Lead-free piezoelectric ceramics have been extensively studied recently for replacing the widely used lead-based piezoelectric materials for environmental protection reasons. Among various candidates, potassium sodium niobate-based and bismuth titanate-based ceramics are the two most promising alternatives. In this chapter, the use of (K0.475Na0.475Li0.05)(Nb0.92Ta0.05Sb0.03)O3 added with 0.4wt% CeO2 and 0.4wt% MnO2 (abbreviated KNLNTS) and 0.885(Bi0.5Na0.5)TiO3-0.05(Bi0.5K0.5)TiO3-0.015(Bi0.5Li0.5)TiO30.05BaTiO3 (abbreviated as BNKLBT) lead-free piezoelectric ceramics as the driving elements of ultrasonic wirebonding transducers is reported. The fabrication and characterization of the ceramics, in the form of ring, and the wirebonding transducers are presented. The ceramic rings are fastened and pre-stressed through a pair of titanium alloy plates in the transducers. The vibration characteristics of the ceramic rings and the transducers are analyzed using a finite-element method (FEM). On the basis of the simulation results, the dimensions of the rings and the titanium alloy plates are determined. The lead-free transducers, operating at a frequency of ~65 kHz, exhibit comparable voltage rise and fall times as the commercial lead zirconate titanate (PZT) transducers. Because of the better matching of the acoustic impedances between the ceramic and titanium alloy, an effective transfer of vibration energy is achieved in the transducers, leading to a large axial vibration (~1.7 m at 0.1 W). Moreover, the lead-free transducers exhibit a small lateral vibration (0.05 m at 0.1 W), which is essential for producing a small or narrow bond. The transducers have successfully bonded the aluminum wire on the standard die and gold-plated PCB. The bonds are of good quality, having a smaller deformation ratio (as compared to the commercial PZT transducer) and high bond strength (exceeding the industrial requirement). These clearly show that the lead-free piezoelectric ceramics are promising candidates for replacing the lead-based ceramics as a driving element in the future generation of wire bonders.

High sensitivity cymbal-based accelerometer

A high sensitivity piezoelectric accelerometer has been developed by replacing the conventional piezoelectric rings with a cymbal transducer. The sensitivity of the cymbal-based accelerometers containing cymbal transducers with different endcap thicknesses and different seismic masses has been measured as a function of driving frequency. Due to the high d33′ coefficient of the cymbal transducers, the cymbal-based accelerometers have a high sensitivity of ∼97pC∕ms−2 with the amplitude rise of 2.85% (<1dB) at one-third of the mounted resonance frequency (3.38kHz). The effect of the seismic mass, the resonance frequency, and d33′ coefficient of the cymbal transducers on the sensitivity and the frequency range of the cymbal-based accelerometers are reported.