Development of a micro seismometer based on molecular electronic transducer technology for planetary exploration

Abstract

Molecular Electronic Transducer (MET) is a recent technology applied in seismic instrumentation that proves highly beneficial to planetary seismology. MET is an electrochemical cell that senses the movement of liquid electrolyte between electrodes by converting it to the output current. Seismometers based on MET technology are attractive for planetary applications due to their high sensitivity, low noise floor, small size, lack of fragile moving parts and independence on the direction of sensitivity axis. This paper reports an approach to build a micro MET seismometer using Micro-Electro-Mechanical Systems (MEMS) techniques. We have reduced the MET cell size, resulting in internal dimensions close to 1 micrometer (µm). The employment of MEMS improves the sensitivity up to and reproducibility of the device, and has reached 1 micro Gee ( √ ) noise level at 1 Hz.

Molecular Electric Transducers as Motion Sensors: A Review

“…Meanwhile making sizes of elements of the cell smaller expands the frequency range and decreases convection produced noise inside the sensitive cell. An alternative approach to build the sensing element is to use (MEMS) techniques, which have reduced the internal dimensions of MET electrodes close to 1 μm, improved the sensitivity and reproducibility [18]. …”

“…These shortcomings can be overcome by introducing MEMS microfabrication techniques to build the MET sensing element, as shown in Figure 6 [18], which reduces the MET cell size and produced the internal dimensions close to 1 μm. The use of MEMS allows batch fabrication, thereby lower the cost, improves the sensitivity and reproducibility of the device, and has reached 1 micro Gee noise level.…”

“…The self-noise spectrum density achieves $1.0\times {10}^{-5 }m/s^2/\sqrt{Hz}$ at 1 Hz for the current device, and the sensitivity achieves 400 V/(m/s 2 ) [18]. Figure 8 shows the spectrum density of a fabricated single-50 μm diameter-channel MEMS MET seismometer in comparison with a commercialized seismometer CMG-40T (Guralp Systems Ltd.).…”

“…Significant work on Solion motion detectors was continued in Russia, where the term “Molecular Electronic Transducer” was introduced to describe such a device [8]. Inspired by the exceptionally high rate of mechanical signal conversion to electric current in MET involving mass and charge transport, pioneering MET studies [9–15] provide an alternative paradigm in the development of motion sensors in wide variety of applications including nuclear explosion monitoring and seismic sensing in planetary exploration [16–18]. The advantages of MET motion sensors include their small size, lack of fragile moving parts (thus high shock tolerance), high sensitivity and low noise especially at low frequencies, and independence of the response on installation angle.…”

AC Equivalent Circuit Model of an Electrochemical Accelerometer for 3D Numerical Simulation in the Low-Frequency Range

“…The interaction of the chemical reaction and fluid motion in the form of the proportional ion concentration gradient ∇C generated by acceleration a causes the current between the anodes and cathodes to change. The differential current from the two cathodes, which is the output of the sensing element, also forms the input to the signal conditioning circuit for the next process [6][7][8][9][10][11][12][13][14][15].…”