Quality factor control of mechanical resonators using variable phononic bandgap on periodic microstructures

The quality factor (Q-factor) is an important parameter for mechanical resonant sensors, and the optimal values depend on its application. Therefore, Q-factor control is essential for microelectromechanical systems (MEMS). Conventional methods have some restrictions, such as additional and complicated equipment or nanoscale dimensions; thus, structural methods are one of the reasonable solutions for simplifying the system. In this study, we demonstrate Q-factor control using a variable phononic bandgap by changing the length of the periodic microstructure. For this, silicon microstructure is used because it has both periodicity and a spring structure. The bandgap change is experimentally confirmed by measuring the Q-factors of mechanical resonators with different resonant frequencies. The bandgap range varies depending on the extended structure length, followed by a change in the Q-factor value. In addition, the effects of the periodic structure on the Q-factor enhancement and the influence of stress on the structural length were evaluated. Although microstructures can improve the Q-factors irrespective of periodicity; the result of the periodic microstructure is found to be efficient. The proposed method is feasible as the novel Q-factor control technique has good compatibility with conventional MEMS.

Mode coupling and locking of a Π-shaped cantilever resonator using laser-induced asymmetric modulation

Mechanical resonators, such as microcantilevers, demonstrate significant potential for use in information technology. Cantilevered beams of various geometries clamped at one end form the most ubiquitous structures in microelectromechanical systems (MEMSs) that support multimode vibration for the detection, conversion, and processing of small signals. In this study, we demonstrate that the potential of these devices can be further extended by utilizing a strategy based on mode coupling and locking induced by asymmetric photothermal modulation. A cantilever was designed to have a Π-shape with a specific geometry such that the resonant frequencies of the two orthogonal modes are close to one another. Additionally, we show that mode coupling between the two modes, which are originally orthogonal to one another, can be achieved through laser-induced photothermal modulation. In particular, the two modes can be parametrically tuned to become degenerate through mode coupling with a significant increase in the quality factor from 112 to 839. This approach is universal and can be extended to improve the detection limits of microresonators in high-dissipation environments with enhanced signal-to-noise ratios.

A fast insight into the nonlinear oscillation of nano-electro mechanical resonators considering the size effect and the van der Waals force

Nano/micro actuators are widely used in micro/ nano electro mechanical systems (NEMS/MEMS) and the study on its nonlinear oscillation is of great significance. This paper begins with a wrong variational principle ([19] Appl Nanosci, 2016, 6: 309-317) of the reduced governing partial differential equation of the resonator which is used to describe the nonlinear oscillation of nano-electro mechanical resonators that takes into account the size effect and the van der Waals force. By using the Semi-inverse method, we establish the genuine variational principle. Then a simple method so called He’s frequency formulation is applied to solve the problem, where it only needs one-step to get the approximate amplitude-frequency relationship. Comparing with the existing method, it shows that the proposed method is simple but effective, which is helpful to be of significance to the study of the nonlinear oscillation in micro/nano electro mechanical systems.

Ultra-coherent nanomechanical resonators based on inverse design

Engineered micro- and nanomechanical resonators with ultra-low dissipation constitute a promising platform for various quantum technologies and foundational research. Traditionally, the improvement of the resonator’s performance through nanomechanical structural engineering has been driven by human intuition and insight. Such an approach is inefficient and leaves aside a plethora of unexplored mechanical designs that potentially achieve better performance. Here, we use a computer-aided inverse design approach known as topology optimization to structurally design mechanical resonators with optimized performance of the fundamental mechanical mode. Using the outcomes of this approach, we fabricate and characterize ultra-coherent nanomechanical resonators with, to the best of our knowledge, record-high Q ⋅ f products for their fundamental mode (where Q is the quality factor and f is the frequency). The proposed approach - which can also be used to improve phononic crystals and coupled-mode resonators - opens up a new paradigm for designing ultra-coherent micro- and nanomechanical resonators, enabling e.g. novel experiments in fundamental physics and extreme sensing.

Ground-state cooling of mechanical resonators by quantum reservoir engineering

Ground-state cooling of multiple mechanical resonators becomes vital to employ them in various applications ranging from ultra-precise sensing to quantum information processing. Here we propose a scheme for simultaneous cooling of multiple degenerate or near-degenerate mechanical resonators to their quantum ground-state, which is otherwise a challenging goal to achieve. As opposed to standard laser cooling schemes where coherence renders the motion of a resonator to its ground-state, we consider an incoherent thermal source to achieve the same aim. The underlying physical mechanism of cooling is explained by investigating a direct connection between the laser sideband cooling and “cooling by heating”. Our advantageous scheme of cooling enabled by quantum reservoir engineering can be realized in various setups, employing parametric coupling of a cooling agent with the target systems. We also discuss using non-thermal baths to simulate ultra-high temperature thermal baths for cooling.