There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

A large body of work has been reported in the last 5 years on the development of lead-free piezoceramics in the quest to replace lead–zirconate–titanate (PZT) as the main material for electromechanical devices such as actuators, sensors, and transducers. In specific but narrow application ranges the new materials appear adequate, but are not yet suited to replace PZT on a broader basis. In this paper, general guidelines for the development of lead-free piezoelectric ceramics are presented. Suitable chemical elements are selected first on the basis of cost and toxicity as well as ionic polarizability. Different crystal structures with these elements are then considered based on simple concepts, and a variety of phase diagrams are described with attractive morphotropic phase boundaries, yielding good piezoelectric properties. Finally, lessons from density functional theory are reviewed and used to adjust our understanding based on the simpler concepts. Equipped with these guidelines ranging from atom to phase diagram, the current development stage in lead-free piezoceramics is then critically assessed.

Perspective on the Development of Lead-free Piezoceramics

Recent developments of zinc oxide based photocatalyst in water treatment technology: A review

Progress in discovery and structural design of color conversion phosphors for LEDs

This review summarizes recent advances in the use of porphyrins, phthalocyanines, and related compounds as components of solar cells, including organic molecular solar cells, polymer cells, and dye-sensitized solar cells. The recent report of a porphyrin dye that achieves 11% power conversion efficiency in a dye-sensitized solar cell indicates that these classes of compounds can be as efficient as the more commonly used ruthenium bipyridyl derivatives.

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Porphyrins and phthalocyanines in solar photovoltaic cells

A new quad-band microstrip bandpass filter (BPF) using asymmetric stepped impedance resonators (SIRs) is proposed. The filter only employs two sets of the asymmetric SIRs. One set is designed to operate at the first and third passbands (2.4/5.2 GHz) and the other set is employed at second and fourth passbands (3.5/6.8 GHz). By tuning the impedance and length ratios of the asymmetric SIRs, a multi-band filter can be easily achieved. This study provides a simple and effective method to design a quad-band filter with low insertion loss and compact size. Experimental verification is provided and good agreement has been found between simulation and measurement.

A New Quad-Band Bandpass Filter Using Asymmetric Stepped Impedance Resonators

Preparation of TiO2/Nano-metal composite particles and their applications in dye-sensitized solar cells

Preparation of TiO2/NiO composite particles and their applications in dye-sensitized solar cells

Preparation of Sr2SiO4:Eu3+ phosphors by microwave-assisted sintering and their luminescent properties

In this letter, a novel compact dual-band bandpass filter (BPF) is designed to achieve the characteristic of low insertion loss and high isolation for global position system (GPS)/wireless local area network (WLAN) applications. This BPF is implemented by properly selecting the impedance ratio (R) and physical length ratio (alpha) of the asymmetric stepped-impedance resonator (SIR) with one step discontinuity. The coupling coefficient between the coupled asymmetric SIRs is calculated by using full-wave simulator IE3D. The proposed filter has very good measured characteristics including a low insertion loss of 1.1 dB for both passbands, a high isolation insertion loss of 55 dB between the two passbands and a wide stopband rejection of 38 dB from 2.7 to 5.3 GHz. Good agreement with responses of electromagnetic (EM) simulation and measurement is compared.

Ru-Yuan Yang

Papers

A New Quad-Band Bandpass Filter Using Asymmetric Stepped Impedance Resonators

Preparation of TiO2/Nano-metal composite particles and their applications in dye-sensitized solar cells

Preparation of TiO2/NiO composite particles and their applications in dye-sensitized solar cells

Preparation of Sr2SiO4:Eu3+ phosphors by microwave-assisted sintering and their luminescent properties

Design of the Compact Dual-Band Bandpass Filter With High Isolation for GPS/WLAN Applications