Magnetomotive drive and detection of clamped-clamped mechanical resonators in water

We demonstrate magnetomotive drive and detection of doubly clamped string resonators in water. A compact 1.9 T permanent magnet is used to detect the fundamental and higher flexural modes of $\mathrm{200 \mu m}$ long resonators. Good agreement is found between the magnetomotive measurements and optical measurements performed on the same resonator. The magnetomotive detection scheme can be used to simultaneously drive and detect multiple sensors or scanning probes in viscous fluids without alignment of detector beams.Comment: 4 pages, 3 figure

Nonlinear modal interactions in clamped-clamped mechanical resonators

A theoretical and experimental investigation is presented on the intermodal coupling between the flexural vibration modes of a single clamped-clamped beam. Nonlinear coupling allows an arbitrary flexural mode to be used as a self-detector for the amplitude of another mode, presenting a method to measure the energy stored in a specific resonance mode. Experimentally observed complex nonlinear dynamics of the coupled modes are quantitatively captured by a model which couples the modes via the beam extension; the same mechanism is responsible for the well-known Duffing nonlinearity in clamped-clamped beams.Comment: 5 pages, 3 figure

Interactions between directly and parametrically driven vibration modes in a micromechanical resonator

The interactions between parametrically and directly driven vibration modes of a clamped-clamped beam resonator are studied. An integrated piezoelectric transducer is used for direct and parametric excitation. First, the parametric amplification and oscillation of a single mode are analyzed by the power and phase dependence below and above the threshold for parametric oscillation. Then, the motion of a parametrically driven mode is detected by the induced change in resonance frequency in another mode of the same resonator. The resonance frequency shift is the result of the nonlinear coupling between the modes by the displacement-induced tension in the beam. These nonlinear modal interactions result in the quadratic relation between the resonance frequency of one mode and the amplitude of another mode. The amplitude of a parametrically oscillating mode depends on the square root of the pump frequency. Combining these dependencies yields a linear relation between the resonance frequency of the directly driven mode and the frequency of the parametrically oscillating mode.Comment: 5 pages, 4 figure

Q-factor control of a microcantilever by mechanical sideband excitation

We demonstrate the coupling between the fundamental and second flexural mode of a microcantilever. A mechanical analogue of cavity-optomechanics is then employed, where the mechanical cavity is formed by the second vibrational mode of the same cantilever, coupled to the fundamental mode via the geometric nonlinearity. By exciting the cantilever at the sum and difference frequencies between fundamental and second flexural mode, the motion of the fundamental mode of the cantilever is amplified and damped. This concept makes it possible to enhance or suppress the Q-factor over a wide range.Comment: 9 pages, 3 figure

[18F]Sodium Fluoride PET has the potential to identify active formation of calcinosis cutis in limited cutaneous systemic sclerosis

OBJECTIVES: Calcinosis cutis affects 20-40% of patients with systemic sclerosis (SSc). When calcinosis cutis becomes clinically apparent, it is irreversible in most cases. Detection of active calcification formation might allow early disease-modifying interventions. We assessed the feasibility of visualizing active calcifications using [18F]Sodium Fluoride ([18F]NaF) PET/low-dose CT (LDCT) in SSc patients with calcinosis cutis. METHODS: In this cross-sectional, observational pilot study patients underwent a whole body [18F]NaF PET/LDCT. All patients met the 2013 ACR/EULAR SSc criteria and had clinically detectable calcinosis cutis. (Sub)cutaneous calcifications were described by three investigators. RESULTS: Nine female patients were included (median age 59.0 years [IQR 51.5-70.5]). [18F]NaF uptake was mostly visible in the fingers (n=7) and knees (n=5). [18F]NaF PET showed calcifications in the fingers of 3 patients where calcifications were undetected on LDCT and in the clinic. Ninety-seven percent of [18F]NaF positive lesions was visible on LDCT. Of all lesions visible on LDCT, 70% was also visible on [18F]NaF PET. CONCLUSION: Imaging of active calcifications in SSc is feasible using [18F]NaF PET/LDCT. Seventy percent of calcifications on LDCT were [18F]NaF PET positive. Although these findings require replication, [18F]NaF PET/LDCT may detect active calcification formation, being potentially suitable for early disease-modifying interventions