Ultra‐Low‐Noise Seismic Accelerometers for Earthquake Prediction and Monitoring

The design of ultra‐low‐noise seismic piezoelectric accelerometers (PEs) with integral electronics (IEPE) is presented. They feature probably the lowest noise floor (for their size and weight) and the lowest operating frequencies (near‐dc) ever reported to date among these types of vibration sensors. These highly sensitive sensors can be used for earthquake monitoring and in the earthquake prediction system by detecting and monitoring microseismic fluctuations. The warning system using these sensors would be fundamentally different from current warning systems using the network of hundreds of seismometers across seismically active regions and recording only seismic events. Two Meggitt (OC) IEPE seismic accelerometers, models 86 and 87‐10 having sensitivity of 10 V/G, are described. The model 86 has a weight of about 770 g and a frequency range from 0.003 to 200 Hz at the ±3 dB level. Its noise floor in terms of the equivalent input noise acceleration spectral density is about 37, 7, and 3 nG/ Hz at at frequencies 1, 10, and 100 Hz, respectively. The model 87‐10 is a compact sensor with a weight of about 170 g and a frequency range from 0.02 to 500 Hz at the ±3 dB level. It has noise of about 90, 25, and 10 nG/ Hz at at frequencies 1, 10, and 100 Hz, respectively

On the design of a MEMS piezoelectric accelerometer coupled to the middle ear as an implantable sensor for hearing devices

Abstract The presence of external elements is a major limitation of current hearing aids and cochlear implants, as they lead to discomfort and inconvenience. Totally implantable hearing devices have been proposed as a solution to mitigate these constraints, which has led to challenges in designing implantable sensors. This work presents a feasibility analysis of a MEMS piezoelectric accelerometer coupled to the ossicular chain as an alternative sensor. The main requirements of the sensor include small size, low internal noise, low power consumption, and large bandwidth. Different designs of MEMS piezoelectric accelerometers were modeled using Finite Element (FE) method, as well as optimized for high net charge sensitivity. The best design, a 2 × 2 mm2 annular configuration with a 500 nm thick Aluminum Nitride (AlN) layer was selected for fabrication. The prototype was characterized, and its charge sensitivity and spectral acceleration noise were found to be with good agreement to the FE model predictions. Weak coupling between a middle ear FE model and the prototype was considered, resulting in equivalent input noise (EIN) lower than 60 dB sound pressure level between 600 Hz and 10 kHz. These results are an encouraging proof of concept for the development of MEMS piezoelectric accelerometers as implantable sensors for hearing devices