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It is introduced that the mass sensitivity (Sm) of an acoustic wave (AW) device with a concentrated mass can be simply determined using its mode shape function: the Sm is proportional to the square of its mode shape. By using the Sm of an AW device with a uniform mass, which is known for almost all AW devices, the Sm of an AW device with a concentrated mass at different locations can be determined. The method is confirmed by numerical simulation for one type of AW device and the results from two other types of AW devices.

Magnetoelastic sensors as an important type of acoustic wave sensors have shown great promise for a variety of applications. Mass sensitivity is a key parameter to characterize its performance. In this work, the effects of mass load distribution on the mass sensitivity of a magnetoelastic sensor under different resonance modes were theoretically investigated using the modal analysis method. The results show that the mass sensitivity and “nodal point” positions are related to the point displacement, which is determined by the motion patterns. The motion patterns are affected by resonance modes and mass load distribution. Asymmetrical mass load distribution causes the motion patterns lose symmetry and leads to the shift of “nodal point”. The mass sensitivity changing with mass load distribution behaves like a sine wave with decaying amplitude and the minimum mass sensitivity appears at the first valley. This study provides certain theoretical guidance for optimizing the mass sensitivity of a magnetoelastic sensor or other acoustic wave based sensors.

Ta/Nd/NdFeB/Nd/Ta films were deposited by magnetron sputtering on Si (100) substrates and subsequently annealed for 30 min at 923 K in vacuum. It was found that the microstructure and magnetic properties of Ta/Nd/NdFeB/Nd/Ta films strongly depend on the NdFeB layer thickness. With NdFeB layer thickness increasing, both the grain size and the strain firstly reduce and then increase. When NdFeB layer thickness is 750 nm, the strain reaches the minimum value. Meanwhile, both the in-plane and perpendicular coercivities firstly drastically increase and then slowly decrease with NdFeB layer thickness increasing. The highest in-plane and perpendicular coercivities can be obtained at NdFeB layer thickness of 750 nm, which are 21.2 kOe and 19.5 kOe, respectively. In addition, the high remanence ratio (remanent magnetization/saturation magnetization) of 0.87 can also be achieved in Ta/Nd/NdFeB (750 nm)/Nd/Ta film.

Resonant-mode based cantilevers are an important type of acoustic wave based mass-sensing devices. In this work, the governing vibration equation of a bi-layer resonant-mode based cantilever attached with concentrated mass is established by using a modal analysis method. The effects of resonance modes and mass loading conditions on nodes and mass sensitivity of the cantilever were theoretically studied. The results suggested that the node did not shift when concentrated mass was loaded on a specific position. Mass sensitivity of the cantilever was linearly proportional to the square of the point displacement at the mass loading position for all the resonance modes. For the first resonance mode, when mass loading position xc satisfied 0 < xc < ∼ 0.3l (l is the cantilever beam length and 0 represents the rigid end), mass sensitivity decreased as the mass increasing while the opposite trend was obtained when mass loading satisfied ∼0.3l ≤ xc ≤ l. Mass sensitivity did not change when concentrated mass was loaded at the rigid end. This work can provide scientific guidance to optimize the mass sensitivity of a resonant-mode based cantilever.

The existence of “blind point” lowers the mass sensitivity and reliability of magnetostrictive particle (MSP) based biosensors. In addition, asymmetric distribution of mass loading (e.g. bacteria) will cause the shift of “blind point” and change of mass sensitivity of an MSP based biosensor. In this work, a modal analysis method was introduced and conducted to derive the governing vibration equation for an MSP biosensor with asymmetric mass loading. The effects of asymmetric mass loading on the “blind point” shift and mass sensitivity were unveiled by solving the governing vibration equation. It was found that the plot of “blind point” shift showed an “M” shape with the valley located at a/l ∼ 0.5 and two peaks located at a/l ∼ 0.25 and a/l ∼ 0.75. In addition, the theoretical results showed that the resonance frequency shift (Δf) depends on the value of a/l (i.e. both the attached mass and mass distribution) and their relationship is nonlinear. Based on the definition of mass sensitivity (Sm), the values of Sm were derived for the selected values of a/l. The results showed that Sm decreased initially with increasing a/l, reaching the minimum, and then increased until a/l = 1. That is, the maximum mass sensitivity is obtained when a/l equals to a critical value Xc (0 < Xc < l). Based on the result, an optimal mass loading distribution design criterion for developing a more sensitive MSP based biosensor was proposed.

In this work, we propose a novel wireless actuator which is composed of magnetostrictive material/copper bi-layer film. The actuator can be controlled to move like a snake bi-directionally along a pipe by tuning the frequency of external magnetic field near its first order resonant frequency. The governing equation for the actuator is established and the vibration mode shape function is derived. Theoretical analysis shows that motion of the actuator is achieved by asymmetric vibration mode shape, specific vibration bending deformation, and effective net total impacting force. The simulation and experimental results well confirm the theoretical analysis. This work provides contribution to the development of wireless micro robots and autonomous magnetostrictive sensors. [ABSTRACT FROM AUTHOR]

Abstract: The detailed preparation process of Eu2+ and Dy3+ ion co-doped Sr3Al2O6 flower-like phosphor powders with red long afterglow by a sol–gel method in the reducing atmosphere is reported. X-ray diffraction (XRD), scanning electron microscopy (SEM) and fluorescence spectrophotometer are employed to characterize the phosphor powders. The results reveal that Sr3Al2O6:xEu2+,yDy3+ (x=4, 8, 10, 20mol%, y =10mol %) phosphor powders calcined at 1200°C for 2h possess a Sr3Al2O6 single cubic phase. The Sr3Al2O6:Eu2+, Dy3+ crystallites show a new flower-like morphology. The excitation and emission spectra indicate that a broad excitation band chiefly lies in the visible range and that Sr3Al2O6:Eu2+, Dy3+ phosphor powders exhibit a broad red emission band with emission peak at 612nm under 472nm excitation. Sr3Al2O6:Eu2+, Dy3+ at the Eu2+concentration of 8mol% shows the strongest luminescent intensity. Red long-afterglow phosphorescence is observed in the dark with naked eye after the removal of the excitation source. [Copyright &y& Elsevier]