A piezoelectric microvalve for compact high frequency high differential pressure micropumping systems

A piezoelectrically driven hydraulic amplification microvalve for use in compact high-performance hydraulic pumping systems was designed, fabricated, and experimentally characterized. High-frequency, high-force actuation capabilities were enabled through the incorporation of bulk piezoelectric material elements beneath a micromachined annular tethered-piston structure. Large valve stroke at the microscale was achieved with an hydraulic amplification mechanism that amplified (40/spl times/-50/spl times/) the limited stroke of the piezoelectric material into a significantly larger motion of a micromachined valve membrane with attached valve cap. These design features enabled the valve to meet simultaneously a set of high frequency (/spl ges/1 kHz), high pressure(/spl ges/300 kPa), and large stroke (20-30 /spl mu/m) requirements not previously satisfied by other hydraulic flow regulation microvalves. This paper details the design, modeling, fabrication, assembly, and experimental characterization of this valve device. Fabrication challenges are detailed

Spin tunnelling in mesoscopic systems

We study spin tunnelling in molecular magnets as an instance of a mesoscopic phenomenon, with special emphasis on the molecule Fe8. We show that the tunnel splitting between various pairs of Zeeman levels in this molecule oscillates as a function of applied magnetic field, vanishing completely at special points in the space of magnetic fields, known as diabolical points. This phenomena is explained in terms of two approaches, one based on spin-coherent-state path integrals, and the other on a generalization of the phase integral (or WKB) method to difference equations. Explicit formulas for the diabolical points are obtained for a model Hamiltonian.Comment: 13 pages, 5 figures, uses Pramana style files; conference proceedings articl

Lateral vibration attenuation of a beam with piezo-elastic supports subject to varying axial tensile and compressive loads

In this paper, vibration attenuation of a beam with circular cross-section by resonantly shunted piezo-elastic supports is experimentally investigated for varying axial tensile and compressive beam loads. Varying axial beam loads manipulate the effective lateral bending stiffness and, thus, lead to a detuning of the beams resonance frequencies. Furthermore, varying axial loads affect the general electromechanical coupling coefficient of transducer and beam, an important modal quantity for shunt-damping. The beam’s first mode resonance frequency and coupling coefficient are analyzed for varying axial loads. The values of the resonance frequency and the coupling coefficient are obtained from a transducer impedance measurement. Finally, frequency transfer functions of the beam with one piezo-elastic support either shunted to a RL-shunt or to a RL-shunt with negative capacitance, the RLC-shunt, are compared for varying axial loads. It is shown that the beam vibration attenuation with the RLC-shunt is less influenced by varying axial beam loads

Detectability of stress-induced martensite phase in ferromagnetic shape memory alloy Fe-30.2at.%Pd by Barkhausen noise method

The possibility to detect the phase transformation of stress-induced martensite in ferromagnetic shape memory alloy Fe–30.2at.%Pd thin foil was investigated by using Barkhausen noise (BHN) method. Stress-induced martensite twin was observed by laser microscope above loading stress of 25 MPa. BHN caused by grain boundaries appears in the lower frequency range and BHN by martensite twin in the higher frequency range. The envelope of the BHN voltage as a function of time of magnetization shows a peak due to austenite phase at weak magnetic field. The BHN envelope due to martensite twins creates additional two peaks at intermediate magnetic field. BHN method turns out to be a powerful technique for non-destructive evaluation of the phase transformation of ferromagnetic shape memory alloy