An ABO3-type perovskite solid-solution, (K0.5Na0.5)NbO3 (KNN) doped with 2 mol.% Ba(Ni0.5Nb0.5)O3-δ (BNNO) is reported in this communication. Such a composition yields a much narrower bandgap (~1.6 eV) compared to the parental composition -pure KNN -and other widely used piezoelectric and pyroelectric materials (e.g. Pb(Zr,Ti)O3, BaTiO3).Meanwhile, it exhibits the same large piezoelectric coefficient as that of KNN (~100 pC N -1 ) and a much larger pyroelectric coefficient (~130 µC m -2 K -1 ) compared to the previously reported narrow bandgap material (KNbO3)1-x-BNNOx. The unique combination of these excellent ferroelectric and optical properties opens the door to the development of multi-source energy harvesting or multi-functional sensing devices for the simultaneous and efficient conversion of solar, thermal and kinetic energies into electricity simultaneously and efficiently in a single material. Individual and comprehensive characterizations of the optical, ferroelectric, piezoelectric, pyroelectric and photovoltaic properties are investigated with single and co-existing energy sources. No degrading interaction between ferroelectric and photovoltaic behaviors was observed. This composition may fundamentally change the working principles of state of the art hybrid energy harvesters and sensors, and thus significantly increase the unit 2 volume energy conversion efficiency and reliability of energy harvesters in ambient environments.Various energy harvesting (EH) techniques have been investigated in recent decades in order to overcome the shortcomings of batteries in terms of lifespan, overall cost-effectiveness and chemical safety. [1] However, the power level and stability provided by a single-source energy harvester are often insufficient for practical applications. In order to address this issue, various hybrid energy harvesters have been developed and investigated. [2][3][4] However, as such hybrid energy harvesters have mostly been simple physical combinations of individual harvesters made from different materials/structures, the effective size of the entire system can become much larger than its individual counterparts. [2,3] In such a case one has to compromise either on the number of simultaneously harvested energy sources or on the space taken by different energy harvesting components. [5] This compromise usually leads to the loss of the advantage of energy harvesters over batteries. A similar situation may occur in hybrid sensors.One method to solve the problem is to design or discover a single composition/material which enables the simultaneous harvesting/detection of multiple energy sources. At the same time the individual conversion efficiency of the material for each energy source should be neither reduced nor interrupted in this multi-task performance. This requires different energy conversion effects exhibited by the same material to be independent of each other, or coupled but working in the same direction, and to be functional simultaneously. This communication reports a perovski...

Sliding electrical contacts are ubiquitous in electric motors and various forms of monolithic metal -carbon composite brushes and filamentous precious metal brushes represent the highest performance materials available. There is a tremendous opportunity to develop a whole new class of high-performance brush contacts using aligned films of carbon nanotubes, possessing super-compressibility, [1] high electrical and thermal conductivity, [2][3] mechanical strength, [4] tunable friction behavior, [5] and environmental insensitivity. Here, we demonstrate the feasibility of aligned multiwalled carbon nanotube (MWCNT) brushes as a new and superior alternative to the traditional high-performance brushes for electrical contacts. These brushes have been shown to provide stable low-noise operation for extended sliding durations. We investigate both the direct-current (DC) and alternating-current (AC) properties of these nanotube brush contacts and demonstrate their reliable low-noise electrical performance as rotating axels as well as sliding contacts in motors. Our results demonstrate a new materials approach to produce stable, intimate, and ultralight electrical brush contacts at moving interfaces.Both the DC and AC current-carrying properties of macroscopic CNT contacts were investigated. The most common applications for sliding contacts are brushes that carry electrical current in motors and generators.[6] Solid brushed-type electric motors are still widely used and desirable because of their intrinsically low magnetic fields and noise and potential for high power density applications. The low cost, ease of controlling the speed, and demonstrated operation over a range of challenging conditions make brushes popular choices for electric motors. In most applications the brushes are fixed on flexible cantilevers that are designed ideally to provide compliance and low applied normal load, yet to follow the rotational error motions of the shaft without bouncing (an extremely detrimental process that leads to arcing and rapid brush deterioration). [6,7] The relatively high rigidity and high mass of solid brushes causes a paradoxical situation in brush design, where low loads are desirable for low frictional losses and long life, but high loads are desirable for stable and low contact resistance.[6]Carbon nanotubes (CNTs) [2,8] are interesting materials with high electrical conductivity and mechanical compliance and these properties have been exploited in nanoelectromechanical systems and nanoelectronic devices. [9][10][11] Various applications for nanotube brushes have been suggested [12] but the use of nanotube brushes as contacts has not yet been exploited. Large blocks of ordered CNT films (or brushes) can today be synthesized directly by catalytic chemical vapor-phase deposition (CCVD) methods. [13,14] Brushes with a large foot-print area of up to several square centimeters and with thicknesses beyond several millimeters have already been reported.[15] The attractive mechanical and electrical properties of these CNT brush...

In this paper a piezoelectric energy harvester based on a Cymbal type structure is presented. A piezoelectric disc ∅35 mm was confined between two convex steel discs ∅35 mm acting as a force amplifier delivering stress to the PZT and protecting the harvester. Optimization was performed and generated voltage and power of the harvester were measured as functions of resistive load and applied force. At 1.19 Hz compression frequency with 24.8 N force a Cymbal type harvester with 250 μm thick steel discs delivered an average power of 0.66 mW. Maximum power densities of 1.37 mW/cm 3 and 0.31 mW/cm 3 were measured for the piezo element and the whole component, respectively. The measured power levels reported in this article are able to satisfy the demands of some monitoring electronics or extend the battery life of a portable device.

This paper presents the results of a piezoelectric circular diaphragm harvester utilising a unique measurement setup with tailored input force (walk profile), adjustable mechanical pre-stress, and simultaneous measurement of the harvested energy output and input force pressure. The harvester, incorporating the pre-stressing mechanism, consisted of a 191 μm thick PZ-5A piezoelectric disc (Ø 34.5 mm) and a 100 μm thick steel plate (Ø 45.5 mm). Its performance was measured with pressure cycles at a frequency of 0.96 Hz. Harvested energy was measured as a function of the pre-stressing state, the applied force, and the pressure profile. The optimal bending pre-stress was found to improve the efficiency of harvesting by ∼141% compared to the case without pre-stress. The maximum obtained efficiency was 14.7%, and the maximum average power density of 6.06 mW cm−3 was measured for a unimorph diaphragm energy harvester. The results show that the pre-stressing technique is an effective method to improve the efficiency and generated power in this type of piezoelectric harvester, potentially enabling it to power different portable devices and sensors in future applications.

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