skip to main content

This content will become publicly available on March 1, 2025

Title: High Signal‐to‐Noise Ratio Event‐Driven MEMS Motion Sensing
Two solutions for improving MEMS triboelectric vibration sensors performance in contact‐separation mode are reported experimentally and analytically. Triboelectric sensors have mostly been studied in the mesoscale. The gap variation between the electrodes induces a potential difference that represents the external vibration. Miniaturizing the device limits the sensor output because of the limited gap. This work offers a warped MEMS diaphragm constrained on its edges. The dome‐shaped structure provides one order of magnitude larger displacement after contact‐separation than standard designs resulting in one order of magnitude greater voltage and signal‐to‐noise‐ratio. Second, micro triboelectric sensors do not operate unless the external vibration is sufficiently forceful to initiate contact between layers. The proposed constraints on the edge of the diaphragm provide friction during periodic motion and generate charges. The combination of the warped diaphragm and boundary constraints instead of serpentine springs increases the charge density and voltage generation. The mechanical properties and electrical output are thoroughly investigated including nonlinearity, sensitivity, and signal‐to‐noise ratio. A sensitivity of 250 mV/g and signal‐to‐noise‐ratio of 32 dB is provided by the presented device at resonance, which is very promising for event‐driven motion sensors because it does not require signal conditioning and therefore simplifies the sensing circuitry.  more » « less
Award ID(s):
Author(s) / Creator(s):
; ; ;
Publisher / Repository:
Date Published:
Journal Name:
Page Range / eLocation ID:
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. We present a MEMS microphone that converts the mechanical motion of a diaphragm, generated by acoustic waves, to an electrical output voltage by capacitive fingers. The sensitivity of a microphone is one of the most important properties of its design. The sensitivity is proportional to the applied bias voltage. However, it is limited by the pull-in voltage, which causes the parallel plates to collapse and prevents the device from functioning properly. The presented MEMS microphone is biased by repulsive force instead of attractive force to avoid pull-in instability. A unit module of the repulsive force sensor consists of a grounded moving finger directly above a grounded fixed finger placed between two horizontally seperated voltage fixed fingers. The moving finger experiences an asymmetric electrostatic field that generates repulsive force that pushes it away from the substrate. Because of the repulsive nature of the force, the applied voltage can be increased for better sensitivity without the risk of pull-in failure. To date, the repulsive force has been used to engage a MEMS actuator such as a micro-mirror, but we now apply it for a capacitive sensor. Using the repulsive force can revolutionize capacitive sensors in many applications because they will achieve better sensitivity. Our simulations show that the repulsive force allows us to improve the sensitivity by increasing the bias voltage. The applied voltage and the back volume of a standard microphone have stiffening effects that significantly reduce its sensitivity. We find that proper design of the back volume and capacitive fingers yield promising results without pull-in instability. 
    more » « less
    more » « less
  3. In this paper, a multi-frequency MEMS acoustic emission (AE) sensor is designed, characterized, and tested. The sensor includes sixteen individual resonators tuned in the range of 100 kHz to 700 kHz. The resonator frequencies are selected to form constructive interference when they are connected in parallel to increase the signal-to-noise ratio. Each resonator is comprised of a membrane that forms the mass and four beams that provide stiffness. The membrane size is kept the same for each resonator to have approximately the same sensitivity per frequency. The influence of spring elements on the resonant frequency and the sensitivity is numerically demonstrated. The sensor is manufactured using MEMSCAP PiezoMUMPs. The characterization experiments show a slight shift in the resonant frequency of individual resonators compared to the design values. The MEMS sensor is packaged using a custom-designed printed circuit board to improve the signal-to-noise ratio. The sensor performance is compared with a conventional AE sensor. The sensitivity and frequency bandwidth of the MEMS AE device is brought to a comparable level to bulky AE sensors. 
    more » « less
  4. null (Ed.)
    This paper presents a review of state-of-the-art micro-electro-mechanical-systems (MEMS) acoustic emission (AE) sensors. MEMS AE sensors are designed to detect active defects in materials with the transduction mechanisms of piezoresistivity, capacitance or piezoelectricity. The majority of MEMS AE sensors are designed as resonators to improve the signal-to-noise ratio. The fundamental design variables of MEMS AE sensors include resonant frequency, bandwidth/quality factor and sensitivity. Micromachining methods have the flexibility to tune the sensor frequency to a particular range, which is important, as the frequency of AE signal depends on defect modes, constitutive properties and structural composition. This paper summarizes the properties of MEMS AE sensors, their design specifications and applications for detecting the simulated and real AE sources and discusses the future outlook. 
    more » « less
  5. Abstract

    Contact electrification in a gas medium is usually followed by partial surface charge dissipation caused by dielectric breakdown of the gas triggered during separation of the surfaces. It is widely assumed that such discharge obeys the classical Paschen’s law, which describes the general dependence of the breakdown voltage on the product of gas pressure and gap distance. However, quantification of this relationship in contact electrification involving insulators is impeded by challenges in nondestructive in situ measurement of the gap voltage. The present work implements an electrode-free strategy for capturing discrete discharge events by monitoring the gap voltage via Coulomb force, providing experimental evidence of Paschen curves governing nitrogen breakdown in silicone-acrylic and copper-nylon contact electrification. It offers an alternative approach for characterizing either the ionization energies of gases or the secondary-electron-emission properties of surfaces without the requirement of a power supply, which can potentially benefit applications ranging from the design of insulative materials to the development of triboelectric sensors and generators.

    more » « less