ABSTRACT
A new spherical vibrational energy harvesting device with an additional low power management circuit for optimizing the power transfer from the mechanical vibrations to a storage capacitor is presented. The device is devoted to underwater wireless sensor network applications due to its broadband vibrational energy harvesting, sensing, and communicating facilities. The sensing node container consists of two acrylic glass (PMMA) half-spherical shells and a Pz26 piezoelectric ring clamped between the shells. The energy harvesting, the management circuit, and communication electronics were fitted within the hollow portion of the sphere. A simulation model of the energy extraction and management system using spice has been developed. This simulation shows the feasibility and efficiency of the low power extraction circuit; a level of the necessary stored voltage was set at 3 V. The numerical model was validated by underwater experimental measurements; a voltage of 3 V was obtained at the terminals of a storage capacitor (47 µF) which was sufficient to supply the communication electronics. Power harvesting performances were measured relative to the transmitter/sensor distance and the incident acoustical field excitation voltage. Finally, 175 µW of harvested power has been measured with an excitation voltage of 8 Vpp at 5 cm distance from the emitter.
ABSTRACT
The novel dimeric silicotungstates [[SiM2W9O34(H2O)]2]12- (M = Mn2+, Cu2+, Zn2+) have been synthesized and characterized by IR spectroscopy, elemental analysis, and magnetic measurements. X-ray single-crystal analyses were carried out on K4Na6Mn[[SiMn2W9O34(H2O)]2].33H2O (1), which crystallizes in the triclinic system, space group P1, with a = 12.2376(7) A, b = 13.6764(8) A, c = 15.6177(9) A, alpha = 70.2860(10) degrees, beta = 79.9150(10) degrees, gamma = 70.2760(10) degrees, and Z = 1; K3Na5[[SiCu2W9O34(H2O)]2].26H2O (2) crystallizes in the triclinic system, space group P1, with a = 11.4271(12) A, b = 12.5956(13) A, c = 15.3223(16) A, alpha = 80.456(2)degrees, beta = 76.383(2) degrees, gamma = 76.968(2) degrees, and Z = 1; K4Na6[[SiZn2W9O34(H2O)]2].34H2O (3) crystallizes also in the triclinic system, space group P1, with a = 12.2596(14) A, b = 13.2555(15) A, c = 16.2892(18) A, alpha = 96.431(2) degrees, beta = 100.944(2) degrees, gamma = 110.404(2) degrees, and Z = 1. The polyanions consist of two lacunary B-alpha-[SiW9O34]10- Keggin moieties linked via a rhomblike M4O16 (M = Mn, Cu, Zn) group leading to a sandwich-type structure. Magnetic measurements show that the central Mn4 unit in 1 exhibits antiferromagnetic (J = -1.77(5) cm(-1)) as well as weak ferromagnetic (J' = 0.08(2) cm(-1)) Mn-Mn exchange interactions. In 2 the Cu-Cu exchange interactions are antiferromagnetic (J = -0.10(2) cm(-1), J' = -0.29(2) cm(-1)).
