Tao Deng

A MEMS Based Electrochemical Vibration Sensor for Seismic Motion Monitoring

This paper presents a micro-electro-mechanical system (MEMS) based electrochemical vibration sensor for seismic detection. Simulations were conducted to analyze the effect of the insulating spacers thickness on the sensitivity of the devices. Then, devices with different insulating spacers thicknesses were fabricated based on MEMS processes. The devices sensitivity was confirmed by a customized experimental platform, verifying the simulation results. In addition, the device performance was characterized with a quantified bandwidth of 0.2-5 Hz with sensitivity of 30.2 V/(m/s2) and a linear voltage output as a function of the input vibration amplitude (up to 10 mg). The devices noise was determined as -140 dB at 1 Hz. A random-vibration testing in the laboratory environment was conducted, where response correlations among seven devices were calculated as 0.976±0.017, suggesting high device repeatability. A field test was conducted right above a subway line to detect the seismic motion caused by the train and test results showed that the performance of the proposed devices was comparable with that of the commercial product MET-1001. A field test was also conducted in a prairie to monitor natural seismic motions and experimental results indicated that the proposed electrochemical sensors can detect seismic motions in a lower frequency domain with an energy peak at around 0.3 Hz compared with conventional moving-coil seismic sensors with an energy peak at 3 Hz. This newly proposed vibration sensor may function as a promising seismic motion detecting device in the field of geophysical prospecting where low-frequency seismic motion detection is requested.

Microelectromechanical Systems-Based Electrochemical Seismic Sensors With Insulating Spacers Integrated Electrodes for Planetary Exploration

This paper presents a microelectromechanical system (MEMS)-based electrochemical seismic sensor for a planetary exploration. An insulating spacer and an electrode of the device are fabricated on one silicon wafer, thus decreasing the number of wafers, facilitating wafer-level alignment and enabling the fabrication of thin insulating spacers (50 μm). The proposed device achieves a sensitivity of 1978.2 V/(m/s) ( f = 1 Hz) and a noise level of 100 (nm/s)/Hz1/2 (3.2 ng/Hz1/2, f = 0.02 Hz). Side-by-side random vibration experiment shows that the prosed devices have a correlation coefficient of 0.955±0.029 (n = 7), indicating a high repeatability. Moreover, the proposed devices located in Beijing can effectively record the seismic motion signal of the Nepal earthquake (over 3000 km away), suggesting a capability of detecting remote quake events.

Extending upper cutoff frequency of electrochemical seismometer by using extremely thin Su8 insulating spacers

Here we presented a scheme based on MEMS technology to manufacture electrochemical seismometers and improved the seismometers high-frequency property. This device contained 2 pairs of perforated electrodes and 3 pieces of insulating spacers. Numerical simulations indicated the upper cutoff frequency fc of the devices was related not just to the radium of holes in electrodes but to insulating spacers thickness. A thin layer of Su8 torn off from the substrate by a special craft was chosen to fabricate insulating spacer, and to ensure proper size of hole in electrodes and good consistency of electrodes, silicon wafers covered with platinum were applied to fabricate electrodes. Through this method we could obtain insulating spacers 300-5μm thick. Finally, we demonstrated, the upper cutoff frequency of the devices was expend to 50Hz by reducing the spacers thickness to 30μm, without any circuit compensation. Meanwhile, devices low frequency properties werent affected.

The Characteristics of MEMS Based Seismic Sensors Using the Electrochemical Approach

The characteristics of MEMS based electrochemical seismic sensors (EC seismic sensors) are presented in this paper. A numerical model is set up, and a series of vibration test is established. The numerical simulation and vibration test results are illustrated and the difference between them is discussed.

Temperature effects on characteristics of MEMS based electrochemical seismic sensors for linear motion detecting

This paper first investigates the mechanism of the temperature effects on characteristics of MEMS based electrochemical seismic sensors for linear motion detecting both by numerical simulation and experimental methods. Both the simulation and experimental results indicates that the device sensitivity increases with temperature and the tendency of the device frequency response remains the same under different temperatures, providing crucial information for further electronic compensation. The average device temperature sensitivity at different frequency points obtained by the simulation and the experiment is 1.30%/°C and 1.88%/°C (compared with the device sensitivity), respectively, indicating that the intensified electrochemical reaction caused by the increasing temperature is the primary factor (69%) for the increasing device sensitivity and the thermal effects on the electrolyte solution flow and the ion transfer are the secondary factors.

Microelectromechanical system-based electrochemical seismic sensors with an anode and a cathode integrated on one chip

This paper presents a microelectromechanical system (MEMS)-based electrochemical seismic sensor with an anode and a cathode integrated on a single chip. The proposed approach decreases the number of requested wafers as the sensing unit from seven to two. In addition, no alignment and no bonding among the electrodes are needed, significantly simplifying the fabrication process. The experimental results indicate that the proposed device produced a sensitivity of 5771.7 V (m s−1)−1 at 1.4 Hz and a noise level of −163 dB (i.e. 7.1 (nm s−1)/Hz1/2) at 1 Hz. Moreover, the proposed device effectively responds to random ground motions, enabling the detection of low-frequency seismic motions caused by earthquake events.

A MEMS based electrochemical seismometer with a novel integrated sensing unit

This study proposed a new process to fabricate the sensing unit of an electrochemical seismometer using only one silicon wafer. Based on this new fabrication process, the effective area of electrodes and the fabrication efficiency were significantly improved. In this study, the SU-8 negative photoresist was utilized as both the substrate (exposed SU-8) and the sacrificial layer (unexposed SU-8) on top of which the suspended platinum electrodes were fabricated using the positive-photoresist lift-off technology. The performances of the proposed devices were characterized experimentally where compared to the commercially available counterpart CME6011, significant improvements in 3 dB working bandwidth (0.11 Hz ~21.50 Hz vs. 0.47 Hz ~18.24 Hz) and device sensitivity (1592V/(m/s) vs. 820 V/(m/s)) were located.

Effect of the cathodes on the characteristics of the MEMS based electrochemical seismometer

The effects of the cathodes on the characteristics of the electrochemical seismometer were first studied in this paper. By utilizing the proposed MEMS fabrication process, four types of devices with cathodes of different structures were carefully designed and fabricated for comparison. The experimental results indicated that the sidewall cathodes mainly affected the attenuation rate in the high frequency domain and the surface cathodes per unit area had more effects on the device sensitivity than the sidewall cathodes per unit area. Moreover, the proposed electrochemical seismometers only with surface cathodes were featured with central working frequency less than 1 Hz.