Effect of mechanical loading on the tuning of acoustic resonances in Ba<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>TiO<Subscript>3</Subscript> thin films

The effect of mechanical loading on the tuning performance of a tunable Thin Film Bulk Acoustic Wave Resonator (TFBAR) based on a Ba_0.3Sr_0.7TiO₃ (BST) thin film has been investigated experimentally and theoretically. A membrane-type TFBAR was fabricated by means of micromachining. The mechanical load on the device was increased stepwise by evaporating SiO₂ on the backside of the membrane. The device was electrically characterized after each evaporation step and the results were compared to those obtained from modeling. The device with the smallest mechanical load exhibited a tuning of − 2.4% and − 0.6% for the resonance and antiresonance frequencies at a dc electric field of 615 kV/cm, respectively. With increasing mechanical load a decrease in the tuning performance was observed. This decrease was rather weak if the thickness of the mechanical load was smaller or comparable to the thickness of the active BST film. If the thickness of the mechanical load was larger than the thickness of the active BST layer, a significant reduction in the tuning performance was observed. The weaker tuning of the antiresonance frequency was due to a reduced tuning of the sound velocity of the BST layer with increasing dc bias. The resonance frequency showed a reduced tuning due to a decrease in the effective electromechanical coupling factor of the device with increasing mechanical load. With the help of the modeling we could de-embed the intrinsic tuning performance of a single, non-loaded BST thin film. We show that the tuning performance of the device with the smallest mechanical load we fabricated is close to the intrinsic tuning characteristics of the BST layer.     

Detection of vascular alterations by in vivo magnetic resonance angiography and histology in APP/PS1 mouse model of Alzheimer’s disease

Object

The brain of patients with Alzheimer’s disease (AD) is characterized by the presence of amyloid plaques and neurofibrillary tangles. Vascular alterations such as amyloid angiopathy are also commonly reported in patients with AD and participate in mechanisms involved in disease onset and progression. Transgenic mouse models of AD have been engineered to evaluate the pathophysiology and new treatments of the disease. Our study evaluated vascular alterations in APP_SweLon/PS1_M146L mouse model of AD.

Materials and methods

Histological analysis and in vivo magnetic resonance angiography protocols based on time of flight (TOF) and contrast-enhanced (CE) angiography were applied to evaluate cerebrovascular alterations.

Results

Histological analysis showed that cerebrovascular amyloid deposition starts by the same time as extracellular amyloid plaques. However, unlike plaques deposition, severity of cerebrovascular alterations is stabilized in older animals. Alteration of the middle cerebral artery was detected in old APP_SweLon/PS1_M146L mice with respect to adult ones by evaluating the severity of vessel voids and the reduction of vessel length on TOF- and CE-angiograms. Age-related alterations in control PS1 mice were only detected as a reduced vessel length on CE-angiograms.

Conclusion

These results show that macroscopic vascular abnormalities are part of the pathological alterations developed by APP_SweLon/PS1_M146L mouse models of AD.