Chun Zhao

The University of York · Department of Electronics

Phononic frequency combs represent the mechanical analog of optical frequency combs. Several independent experimental studies have demonstrated the onset and evolution frequency comb response in a variety of micro- and nanoelectromechanical devices in recent years. A theoretical basis for exploring and understanding the conditions for comb generati...

This work reports a multiple-parameter decoupling (MPD) method based on resonant MEMS sensors subject to blue-sideband excitation (BSE), thus enabling simultaneous separation of the cross-coupled physical quantities, e.g. acceleration and temperature, of a single MEMS sensor. Such a technique exploits the property of the BSE that multiple vibration...

Precision measurements of local gravitational acceleration variations are of great importance in geophysical surveys. With advantages such as cost-effectiveness and portability, Micro-Electro-Mechanical system (MEMS)-based gravimeters have shown the potential for long-term gravity measurements. In this paper, aiming to further improve the stability...

This study reports a closed-loop system (CLS) for resonant micro-electromechanical systems (MEMS) sensors subject to blue-sideband excitation (BSE) for the first time. Compared with the conventional excitation scheme, which uses an AC signal with a frequency that is very close to or equal to that of the desired MEMS resonator mode, the BSE scheme a...

This paper reports a miniaturized resonant Lorentz-force magnetometer that exploits blue-sideband actuation to attain a better sensitivity and resolution. The resonant magnetometer consists of a double-ended tuning fork (DETF) resonator with cavity slots to optimize thermoelastic dissipation, as well as a Lorentz-force generator structure to transd...

Mode-localized sensors have attracted attention because of their high parametric sensitivity and first-order common-mode rejection to temperature drift. The high-fidelity detection of resonator amplitude is critical to determining the resolution of mode-localized sensors where the measured amplitude ratio in a system of coupled resonators represent...

Magnetometers are ubiquitous in applications covering many aspects of modern life, such as navigation, smart devices, biomedical systems, geological surveying and aerospace. This work reports a resonant Lorentz-force magnetometer featuring structural topology, in which cavity slots are incorporated in the device structure to improve the thermoelast...

In this paper, the air buoyancy effect on Micro-Electro-Mechanical System (MEMS)-based gravity sensors for high-resolution gravity measurements is investigated. The MEMS gravimeter is operated in an atmospheric environment without any vacuum chamber; thus significantly simplifying the design, implementation and maintenance, and reducing the cost of...

In this paper, a new approach for enhancing the temperature sensitivity of a resonant MEMS thermometer, based on parametric modulation, is proposed. By periodically modulating the effective stiffness of a standard clamped-clamped beam (C-C beam), which is used as a proof-of-concept resonant MEMS thermometer, it is possible to create a virtual energ...

Silicon MEMS resonators are increasingly being adopted for applications in timing and frequency control, as well as precision sensing. It is well established that a key limitation to performance is associated with sensitivity to environmental variables such as temperature and pressure. As a result, technical approaches to address these factors such...

This paper reports a precision mode-localized accelerometer operating in a higher-order flexural mode. The accelerometer consists of two symmetric resonators coupled by a central rigid coupler to generate an ultra-weak coupling factor. A reduced noise floor is observed when the resonators operate in the higher-order flexural mode compared to the ba...

This paper describes a hybrid mass sensing system comprising a QCM (quartz crystal microbalance) mass sensor operating under atmospheric pressure and a 3-DOF mode localized coupled resonator operating in vacuum. Nanoparticles as consecutive mass perturbations are added onto the QCM, the output signals with respect to the amount of mass change are t...

Miniaturized physical transducers based on weakly coupled resonators have previously demonstrated the twin benefits of high parametric sensitivity and the first-order common-mode rejection of environmental effects. Current approaches to sensing based on coupled resonator transducers employ strong coupling where the modal overlap of the responses is...

The large-scale fabrication of high performance on-chip micro-supercapacitors (MSCs) is the foot-stone for the development of next generation miniaturized electronic devices. In practical applica-tions, however, MSCs may suffer from a low areal energy density as well as complicated fabrication strategy that is incompatible with semiconductor proces...

An ultra-sensitive mode-localized accelerometer is reported in this letter. In order to lower the coupling factor of the coupled resonators thus improving the parametric amplitude ratio sensitivity, a stiff anchor support is employed as a mechanical coupler between resonators. A coupling factor of 7.4×10−5 was obtained, which is so far the lowest m...

This paper reviews the research and development of micromachined accelerometers with a noise floor lower than 1 µg/√Hz. Firstly, the basic working principle of micromachined accelerometers is introduced. Then, different methods of reducing the noise floor of micromachined accelerometers are analyzed. Different types of micromachined accelerometers...

Temperature sensors are one of the most important types of sensors, and are employed in many applications, including consumer electronics, automobiles and environmental monitoring. Due to the need to simultaneously measure temperature and other physical quantities, it is often desirable to integrate temperature sensors with other physical sensors,...

This paper introduces a differential vibrating beam MEMS accelerometer demonstrating excellent long-term stability for applications in gravimetry and seismology. The MEMS gravimeter module demonstrates an output Allan deviation of 9 μGal for a 1000 s integration time, a noise floor of 100 μGal/√ Hz, and measurement over the full±1 g dynamic range (...

Electromagnetic wave absorbers are essential devices in imaging, wireless communication and energy harvesting systems. In this paper, we propose and experimentally demonstrate a flexible and ultra-broadband terahertz (THz) wave absorber based on graphene-vertically aligned carbon nanotube (G-VACNT) hybrids. The THz absorber consists of Cu/PDMS/grap...

Resonant micro-electrometers have been the research interest to many groups around the world. Conventionally, the resonant electrometers rely on a frequency-shift based readout. In this chapter, a new type of resonant micro-electrometer based on mode-localization effect is introduced and discussed. This new electrometer implementation is one subset...

Flexible micro-supercapacitors (MSCs) are promising candidates as miniaturized power sources and energy storage components for next generation wearable electronic devices. Herein, we report a low-temperature-operated (~80∘C) direct fabrication method for the realization of flexible MSCs. To demonstrate the capability of the fabrication method, a fl...

Understanding and controlling modal coupling in micro/nanomechanical devices is integral to the design of high-accuracy timing references and inertial sensors. However, insight into specific physical mechanisms underlying modal coupling, and the ability to tune such interactions is limited. Here, we demonstrate that tuneable mode coupling can be ac...

Ultra-wideband absorbers have found wide applications in wireless communications, energy harvesting and stealth applications. Herein, with the combination of experimental and theoretical analyses, we develop a flexible ultra-wideband terahertz (THz) absorber based on vertically aligned carbon nanotubes (VACNTs). Measured results show that the propo...

Capacitive displacement transducers (CDTs) have been widely used in many physical sensors, attributing to high-resolution, simple electricity and easy manufacturing process. Gap-variation CDTs generally have higher displacement resolution due to small electrode gaps but suffer from the pull-in effect, the nonlinear effect and squeeze-film damping;...

Highly accurate microelectromechanical-systems inertial sensors have a wide range of potential applications, including inertial navigation and seismometry. Conventional approaches to the implementation of inertial sensors rely on transducers that convert the external acceleration into changes in displacement of a proof mass or shifts in resonant fr...

Piezoelectric vibration energy harvesting has drawn much interest to power distributed wireless sensor nodes for Internet of Things (IoT) applications where ambient kinetic energy is available. For certain applications, the harvesting system should be small and able to generate sufficient output power. Standard rectification topologies such as the...

A novel differential configuration of a high-resolution mode-localized resonant SOI-MEMS accelerometer is presented in this paper. An effective maximum scale factor of 11/g and a bias-stability of $2.96\mu g$ is demonstrated. A minimum noise floor of $3\mu g/\sqrt {Hz}$ is shown for device operation in an optimum working region. A large bandwid...

The amplitude ratio output metric in mode localized weakly coupled resonators has been established to show superior rejection of first order temperature and pressure variations over frequency shift output metric. This work for the first time documents a holistic study on the temperature dependence of amplitude ratio and frequency shift output metri...

Capacitive sensing is a key technique to measure the test mass movement with a high resolution for space-borne gravitational wave detectors, such as Laser Interferometer Space Antenna (LISA) and TianQin. The capacitance resolution requirement of TianQin is higher than that of LISA, as the arm length of TianQin is about 15 times shorter. In this pap...

This letter presents a high-performance resonant MEMS accelerometer comprising of a single force-sensitive vibrating beam element sandwiched between two inertial masses. The accelerometer demonstrates a noise floor of 98 ng/Hz1/2 and a bias stability of 56 ng under ambient conditions, corresponding to a frequency noise floor of 0.77 ppb/Hz1/2 and a...

In order to efficiently extract power from piezoelectric vibration energy harvesters, various active rectifiers have been proposed in the past decade, which include synchronized switch harvesting on inductor (SSHI), synchronous electric charge extraction (SECE), and so on. Although reported active rectifiers show good performance improvements compa...

In this paper, energy localization within weakly coupled nonlinear MEMS resonators has been utilized for sensing applications. The sensitivity and the noise floor of the weakly coupled resonators operating beyond the critical amplitude have been characterized at the boundaries of the unstable branch, termed as bifurcation points in this paper. The...

This paper presents results from the closed-loop characterization of an electrically coupled mode-localized sensor topology including measurements of amplitude ratios over long duration, stability, noise floor and the bandwidth of operation. The sensitivity of the prototype sensor is estimated to be -5250 in the linear operation regime. An input-re...

In this paper, for the first time, the mass sensitivity of a 3-DoF mode localized electrostatically coupled resonator is investigated and characterized under atmospheric pressure. A reversible method is used in which nanoparticles are added on and removed from one resonator of the 3-DOF coupled resonator system. Furthermore, a comparison of three m...

In this letter, we experimentally demonstrate the existence of an optimal operating region in a resonant microelectromechanical systems sensor utilizing the principle of vibration mode localization, to achieve ultra-high resolution amplitude ratio measurements. We have shown analytically that the coupling strength and stiffness mismatch between the...

Piezoelectric vibration energy harvesting is becoming a promising solution to power wireless sensors and portable electronics. While miniaturizing energy harvesting systems, rectified power efficiencies from miniaturized piezoelectric transducers (PT) are usually decreased due to insufficient voltage levels generated by the PTs. In this paper, a mo...

Piezoelectric vibration energy harvesting is becoming a promising solution to power wireless sensors and portable electronics. While miniaturizing energy harvesting systems, rectified power efficiencies from miniaturized piezoelectric transducers (PT) are usually decreased due to insufficient voltage levels generated by the PTs. In this paper, a mo...

Quality factor is one of the most important parameters for a MEMS resonator. Most MEMS resonators are dominated by thermoelastic dissipation (TED). This paper demonstrates that the TED in a disk resonator that is made of (111) single-crystal silicon is surpassed by clamping loss. The stiffness-mass decoupling design method, combined with reducing t...

In this paper, we present the strongly nonlinear behavior of a 2-degree-of-freedom weakly coupled microelectromechanical systems (MEMS) resonator system in a mixed nonlinear regime, using a closed-loop phase feedback oscillator approach. Three out of four nonlinear bifurcation points within a strongly nonlinear coupled resonator system, with both e...

In this paper, for the first time, the mass sensitivity of a 3-DoF mode localized electrostatic coupled resonator was characterized under atmospheric pressure. A reversible method was used in which nanoparticles are added on and removed from one resonator of the 3-DOF coupled resonator system. Besides, a comparison of three mass sensitivity charact...

An electrostatically actuated non-linear microelectromechanical systems (MEMS) resonator can describe double hysteresis behavior in the measured frequency response due to the interplay between electrical and mechanical non-linearities in the system. This paper provides the first experimental mapping of the stable and unstable branches of the freque...

UK Engineering and Physical Sciences Research Council (EPSRC) (Grant number: EP/L010917/1 and EP/N021614/1)

This paper presents an enhanced SSHI (synchronized switch harvesting on inductor) rectifier with startup circuit and representative environment validation using real world vibration data collected from a tram. Compared to a conventional SSHI rectifier, the proposed rectifier dynamically monitors the working status of the circuit and restarts it whe...

EPSRC (Grant EP/L010917/1)

A resonant vibration energy harvester typically comprises of a clamped anchor and a vibrating shuttle with a proof mass. Piezoelectric materials are embedded in locations of high strain in order to transduce mechanical deformation into electrical charge. Conventional design for piezoelectric vibration energy harvesters (PVEH) usually utilizes piezo...

This letter presents the first experimental results on the closed-loop characterization of a mode-localized microelectromechanical resonator system. Comparisons between the closed-loop oscillator approach and the open-loop frequency sweep approach show good agreement of output metrics including the amplitude ratios and mode frequencies. This new ap...

This letter presents the first experimental results on the closed-loop characterization of a mode-localized microelectromechanical resonator system. Comparisons between the closed-loop oscillator approach and the open-loop frequency sweep approach show good agreement of output metrics including the amplitude ratios and mode frequencies. This new ap...

We report a new class of MEMS resonant potential sensor based on the mode localization effect using a 3-degree-of-freedom (DoF) electrically weakly coupled resonator system. As opposed to previously reported electrically coupled 2DoF mode-localized resonant sensors, it can be shown in theory that the 3DoF structure has an improved sensitivity witho...