Shoaling vibration amplifier with flattened transfer function and suppressed spurious modes

J. Micromech. Microeng.

Thiele

et al. 2018

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A micromechanical broadband vibration amplitude-amplifier for low power detection of acoustic emission signals is presented. It is based on a coupled mass-spring system and was fabricated in a two-level bulk microfabrication process. The device consists of ten resonators coupled in series, which decrease in mass by a factor of three each, to achieve a high amplification over a broad bandwidth. The fabrication process for this multiscale device is based on front- and backside etching of a silicon-on-insulator wafer. It enables coupling MEMS resonators of two different thicknesses with a weight ratio from largest to smallest mass of 26’244 and reduces die size by resonator stacking. The first ten eigenmodes of the device are in-plane and unidirectional. Steady-state and transient response of the device in comparison to a 1D lumped element model is presented. An average amplitude amplification of 295 over a bandwidth of 10.7 kHz (4.4–15.1 kHz) is achieved and can be reached in less than 1 ms. Applications are low-power detection of short broadband vibration signals e.g. for structural health monitoring (cliffs, pipelines, bridges).

Section: Structural Designmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

Two-level bulk microfabrication of a mechanical broadband vibration amplitude-amplifier with ten coupled resonators

J. Micromech. Microeng.

Thiele

et al. 2018

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“…Recently, there has been increased interest in the detection of lower frequency AE signals from a few kHz upward with the purpose of increasing the measurement radius in high attenuation materials such as granular media, rock or concrete or in systems with limited accessibility [1]- [3]. This paper builds on the preliminary data presented in [4] on a broadband, in-plane MEMS amplifier for the detection of very low frequency AE.…”

Section: Introductionmentioning

confidence: 99%

Off-Resonant Vibration Amplifier With Flattened Band-Pass Characteristic and Improved Axis Selectivity

J. Microelectromech. Syst.

Ritz

et al. 2017

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We present the design, fabrication, and characterization of an in-plane vibration sensor with frequency selective displacement amplification and differential capacitive read-out. The mechanical structure is based on six resonators with decreasing stiffness coupled in-plane. A differential capacitance attached to the last mass serves as electrical read out. Finite element and lumped element models are both presented. The devices were fabricated in a single mask silicon on insulatorbased process. The mechanical, as well as the capacitive transfer function and the pressure dependence, have been investigated experimentally and compared with simulations. The measured mean (minimum) amplification was 24 dB (16 dB) over a bandwidth of 10 kHz (3-13 kHz). While the mean amplification is pressure dependent, the minimum amplification and bandwidth show a less than 10% decrease over a wide pressure range from 6.3 to 64 mbar. The pressure dependent measurements also show that the minimum amplification is independent of the Q factor of the modes down to values of Q∼10. Both simulation and experiment show that the off-axis modes occur outside the bandwidth of the device. Along with the low cross-sensitivity of the capacitive readout (0.06%), this provides good axis selectivity despite the high number of degrees of freedom. The device can be used for detection of broadband vibration signals, e.g., for structural monitoring of infrastructure such as bridges and pipelines.

“…Previously we have shown that shoaling amplitude amplification by a coupled mass-spring chain is an effective way to achieve quasi band-pass zero power mechanical amplification of vibrations [1,2]. The approach does not rely on resonance like many acoustic emission sensors (e.g., [3]) and does not amplify low frequencies-which may contain environmental noise-in contrast to lever mechanisms [4].…”

Section: Introductionmentioning

confidence: 99%

“…The approach does not rely on resonance like many acoustic emission sensors (e.g., [3]) and does not amplify low frequencies-which may contain environmental noise-in contrast to lever mechanisms [4]. Building upon the results in [1,2] which either suffer from spurious modes (out-of-plane design) or can only be read out at the last mass (in-plane design), we present an in-plane shoaling amplifier with small mirrors on top of each resonator for full optical characterization.…”

Section: Introductionmentioning

confidence: 99%

Steady-State and Transient Response of a Micromechanical Broadband Shoaling Amplifier

Proceedings of Eurosensors 2017, Paris, France, 3–6 September 2017

Roman

et al. 2017

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An in-plane MEMS broadband shoaling motion amplitude amplifier based on a coupled mass-spring system is presented. It is shown how the amplification amplitude can be traded for the operational bandwidth by design. Three devices with different numbers of masses (three, five and seven), but all of them with the same total mass, were fabricated in silicon. The achieved baseline-amplification × bandwidth product ranges from 18.0 dB × 11.5 kHz for the seven mass device to 27.7 dB × 3.9 kHz for the three mass device. Transient recordings show amplification along the mass-spring-chain. The response time to reach the baseline amplification was found to be in the order of 10 −4 s. This passive device can be used for ultra-low power structural and environmental monitoring (e.g., bridges, pipelines or rock-faces).