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We use vibration localization as a sensitive means of detecting small perturbations in stiffness in a pair of weakly coupled micromechanical resonators. For the first time, the variation in the eigenstates is studied by electrostatically coupling nearly identical resonators to allow for stronger localization of vibrational energy due to perturbations in stiffness. Eigenstate variations that are orders of magnitude greater than corresponding shifts in resonant frequency for an induced stiffness perturbation are experimentally demonstrated. Such high, voltagetunable parametric sensitivities together with the added advantage of intrinsic common mode rejection pave the way to a new paradigm of mechanical sensing.

A frequency comb consists of a series of equally spaced discrete frequencies. In recent years, optical frequency combs [1][2][3][4][5][6][7][8] have emerged as a potential toolset spanning diverse applications ranging from frequency metrology [1-4] to molecular fingerprinting [8]. Specifically the ability to precisely define the frequency spacing between frequency markers and align these measurements with microwave sources through the comb generation process has led to a number of physical measurements [4] requiring very high accuracy including the observation of gravitational waves [9].Optical frequency combs have been generated by using the comb-like mode structure of modelocked lasers and more recently through the interaction of continuous-waver lasers with high Q toroidal optical microresonators mediated via the Kerr non-linearity [10].Despite the analogies between phonons and photons, a direct analogue for an optical comb in the phononic domain has not been observed and comb generation process is thought to be largely limited by the nonlinear dispersion relations of phonons. However, theoretical work [11] has recently demonstrated the possibility for generation of frequency combs in a phononic system represented by Fermi-Pasta-Ulam α (FPU-α) chains [15] where the dispersion relationship does not play a role. In this letter, we report the first experimental confirmation of a phononic frequency comb in a microfabricated structure bearing similar traits predicted by numerical simulations performed on a FPU-α chain [11]. Additionally, our resonator also captures the onset of Duffing nonlinear mechanism [12][13][14] and its interference with the nominal phononic comb.The non-linear three wave mixing mechanism resulting in the generation of frequency combs is theoretically facilitated through the excitation of non-linear resonances of various orders.Specifically, in Direct Nonlinear Resonance (DNR) as termed in [11], the interaction between the eigenmode and driven phonon mode in a non-linear lattice results in the formation of equi-spaced spectral lines at a characteristic frequency ∆ set by the drive frequency and the intrinsic phonon mode frequencies. Mathematically, the DNR phenomenon can be modelled through the coupled dynamics. Figure 1A) upon the drive level crossing a specific threshold value. Here, the displacement profile corresponding to the sub-harmonic mode can be conceived as a pre-stressed framework for the level of coupling between drive frequency and intrinsic resonance mode ( Figure 1B). That being said, the propensity for comb generation is higher at the antinodes of sub-harmonic mode. Additionally, figure 1b1 provides an evidence for the phase coherency of equidistant comb lines. In this letter, we systematically report the experimental results carried out in the extensional resonator based test bed to understand the frequency comb generation and discuss the opportunities for active tuning of comb structure.The drive amplitude dependence on the phononic comb for an off-resonant drive frequenc...

Piezoelectric vibration energy harvesters have drawn much interest for powering self-sustained electronic devices. Furthermore, the continuous push towards miniaturization and higher levels of integration continue to form key drivers for autonomous sensor systems being developed as parts of the emerging Internet of Things paradigm. The synchronized switch harvesting on inductor (SSHI) and synchronous electrical charge extraction (SECE) are two of the most efficient interface circuits for piezoelectric energy harvesters; however, inductors are indispensable components in these interfaces. The required inductor values can be up to 10 mH to achieve high efficiencies, which significantly increase overall system volume, counter to the requirement for miniaturized self-power systems for IoT. An inductorless bias-flip rectifier is proposed in this paper to perform residual charge inversion using capacitors instead of inductors. The voltage flip efficiency goes up to 80% while 8 switched capacitors are employed. The proposed SSHC (Synchronized Switch Harvesting on Capacitors) circuit is designed and fabricated in a 0.35 µm CMOS process. The performance is experimentally measured and it shows a 9.7× performance improvement compared to a full-bridge rectifier for the case of a 2.5 V open-circuit zero-peak voltage amplitude generated by the piezoelectric harvester. This performance improvement is higher than most of reported state-of-theart inductor-based interface circuits while the proposed circuit has a significantly smaller overall volume enabling system miniaturization.

In recent years, the concept of utilizing the phenomenon of vibration mode-localization as a paradigm of mechanical sensing has made profound impact in the design and development of highly sensitive micro-and nanomechanical sensors. Unprecedented enhancements in sensor response exceeding three orders of magnitude relative to the more conventional resonant frequency shift based technique have been both theoretically and experimentally demonstrated using this new sensing approach. However, the ultimate limits of detection and in consequence, the minimum attainable resolution in such mode-localized sensors still remain uncertain. This paper aims to fill this gap by investigating the limits to sensitivity enhancement imposed on such sensors, by some of the fundamental physical noise processes, the bandwidth of operation and the noise from the electronic interfacial circuits. Our analyses indicate that such mode-localized sensors offer tremendous potential for highly sensitive mass and stiffness detection with ultimate resolutions that may be orders of magnitude better than most conventional micro-and nanomechanical resonant sensors.