Research
Thermal-Piezoresistive resonators
Thermal-actuation and piezoresistive-detection effects have been employed to pump the effective quality factor of MEMS resonators, targeting better mass sensing performance in air. A variety of mass sensors based on thermal-piezoresistive resonators (TPR) have been reported. Increasing the bias direct current (Idc) is the typical way of pumping Qeff, in such resonators, and a self-oscillation can even be achieved when Idc is set in a proper range. However, pumping Qeff does not suppress the thermomechanical noise, which is in contrast with that of enlarging the inherent mechanical Q, according to the detailed analysis on the difference between Q and Qeff. The influences of the thermal-piezoresistive pumping effect on the dynamic range, frequency stability and sensor resolution of a TPR are experimentally investigated in this project.
Mode localized resonant sensors
Mode localized accelerometers
This paper reports an acceleration sensing method based on two weakly coupled resonators (WCRs) using the phenomenon of mode localization. When acceleration acts on the proof masses, differential electrostatic stiffness perturbations will be applied to the WCRs, leading to mode localization and thus mode shape changes. Therefore, acceleration can be sensed by measuring the amplitude ratio shift. The proposed mode localization with differential perturbation method leads to a sensitivity enhancement of a factor of 2 than the common single perturbation method. The theoretical model of the sensitivity, bandwidth, and linearity of the accelerometer are established and verified. The measured relative shift in amplitude ratio (~312162 ppm/g) is 302 times higher than the shift in resonance frequency (~1035 ppm/g) within the measurement range of ±1g. The measured resolution based on amplitude ratio is 0.619mg and the nonlinearity is ~3.5% in the open-loop measurement operation.
Mode localized electrometers
This work reports a high-sensitivity resonant electrometer based on the mode localization of two degreeof-freedom weakly coupled resonators (WCRs). When charges are applied to the input electrodes, the effective stiffness of a specific resonator of the WCRs will be perturbed, leading to a drastic change in mode shape owing to the mode localization phenomenon. By measuring the shift of the amplitude ratio, the small charge fluctuation can be accurately sensed. The theoretical mode of the electrometer is established based on the transfer functions of the WCRs. In particular, we establish the design rules of the coupling factor according to the -3-dB bandwidth, amplitude ratio measurement errors, and frequency misalignment between the resonators. The experimental results show that the amplitude ratio-based sensitivity is ∼2151 times higher than the frequency-based sensitivity. The amplitude ratio-based resolution of the electrometer is approximately 1.269 fC
Triboelectric nanogenerator (TENG)
Conductive Polyurethane Foam based TENG
Scavenging the energy of human motions has attracted widespread attentions with the development of wearable electronics. This paper for the first time proposed a progressive triboelectric nanogenerator based on macro-triangle-prism-shaped conductive polyurethane (PU) foam and polytetrafluoroethylene (PTFE) film, which occupy the top and bottom spots of the triboelectric table respectively. The proposed macro-structured conductive PU foam also integrates the functions of spring, spacer and electrode. Thanks to the innovative structures and chosen of the materials, an extended current peak width is obtained. A maximum RMS power density of 100 nJ/cm²/tap was obtained with a 60 MΩ resistive load and press force of 10 N @ 5 Hz. By regulating the TENG with a Bennet doubler conditioning circuit, the ubiquitous voltage saturation phenomenon when charging a storage capacitor using full-wave rectifiers is avoided. Moreover, the energy per cycle, charging efficiency and totally stored energy can be exponentially pumped up. With a Bennet circuit charging a 5 nF capacitor, a harvested energy density of ~710 nJ/cm2/tap was obtained when voltage across the capacitor was 400 V. Putting the device under sole within 25 human steps, the totally stored energy was 0.43 mJ with a Bennet circuit, 2.9 times higher than that using a full-wave rectifier. At the 25th step, the charging efficiency with a Bennet circuit was 20.3 times better than that with a full-wave rectifier, with the proposed charging-efficiency criterion. The Bennet was proven better for regulating the triboelectric nanogenerators with long operation-time compared to the classical full-wave rectifier.