A Wideband, Low-Noise Accelerometer for Sonar Wave Detection

Abstract

Abstract-This paper presents the development of a highperformance micromachined capacitive accelerometer for detection of sonar waves. The device is intended to replace existing hydrophones in towed array sonar systems, and thus, needs to meet stringent performance requirements on noise, bandwidth, and dynamic range, among others. The in-plane, single-axis accelerometer is designed based on a mode-tuning structural platform. A frame was used instead of a solid plate for the proof-mass of the device, allowing us to push undesired vibration modes beyond the operating bandwidth of the device while enabling us to employ a portion of the area for capacitive sensing elements. The designed accelerometer was fabricated on a silicon-on-insulator wafer with 100µm device layer with capacitive gaps of ~2.2µm. The sensitivity of the accelerometer is 4.0V/g with a noise spectral density of better than /√ . The fundamental resonant frequency of the device is 4.4kHz. The open loop dynamic range of the accelerometer, while operating at atmospheric pressure, is better than 135dB with a cross-axis sensitivity of less than 30dB.

Micromachined Accelerometers with Sub-µg/√Hz Noise Floor: A Review

“…Boom and Kamp et al [16] 2 ng/ √ Hz (at 28.1 Hz) -3-28.1 Hz #+M iddlemiss et al [18] 8 ng/ √ Hz (at 1 Hz) -2.31 Hz #+Ẑ hang et al [22] 51.8 ng/ √ Hz (at 1 Hz) -158 Hz #T ang et al [24] 8 ng/ √ Hz (at 1 Hz) +8 mg 0.5-3 Hz #+P ike et al [31] 0.25 ng/ √ Hz (at 0.1-10 Hz) -6 Hz + Wu et al [39] 10-50 ng/ √ Hz (at 1 Hz) ±1.4 g 13.2 Hz + Edalatfar et al [44] 350 ng/ √ Hz (at 1-5 kHz) 135 dB 4500 Hz + Yazdi and Najafi [45] 160 ng/ √ Hz -<1000 Hz + Aaltonen et al [9] 300 ng/ √ Hz (at 30 Hz) ±1.5 g 300 Hz +X u et al [11] 200 ng/…”

“…Edalatfar et al [ 43 ] (2016) developed a capacitive MEMS accelerometer with a resonant frequency of 2 kHz and a thermal noise floor of 193 ng/√Hz. In 2018, a capacitive MEMS accelerometer for the detection of sonar waves was developed based on a mode-tuning structural platform, which had a noise floor of lower than 350 ng/√Hz (at 1–5 kHz) and a dynamic range of 135 dB [ 44 ]. To achieve a high sensitivity, the accelerometers were designed with a large number of capacitive combs with small gaps (2.2 μm) and a large proof masse.…”

“…"+" refers to large proof mass, "#" refers to low spring constant, "-" refers to low noise interface circuit and "^" refers to high Q. [39] 10-50 ng/√Hz (at 1 Hz) ±1.4 g 13.2 Hz + Edalatfar et al [44] 350 ng/√Hz (at 1-5 kHz) 135 dB 4500 Hz + Yazdi and Najafi [45] 160 ng/√Hz --<1000 Hz + Aaltonen et al [9] 300 ng/√Hz (at 30 Hz) ±1.5 g 300 Hz +^ Xu et al [11] 200 ng/√Hz (at 100 Hz) ±1.2 g 700 Hz ^ Utz and Kraft et al [55] 216 ng/√Hz (at 30-40 Hz) ±1. 25 [100] 144 ng/√Hz (at <1-50 Hz) ±0.05 g 1-50 Hz +^& Pandit and Seshia et al [102] 17.8 ng/√Hz (at 0.25-4 Hz) ±1 g 5 Hz +^& Zhao and Seshia et al [103] 98 ng/√Hz (at 1 Hz) ±1 g 5 Hz +^& Yin et al [104] 380 ng/√Hz ±15 g 2.7 Hz +^& Zhao and Seshia et al [116] 680 ng/√Hz (at 0.5-3 Hz) --3 Hz ^& Figure 24.…”

Fabrication of MEMS Directional Acoustic Sensors for Underwater Operation

“…These sensors have evolved over the years, from relatively heavy and complex systems that required significant space onboard ships to thin light linear arrays easily handled by relatively small autonomous platforms [3,4]. An alternative approach is the use of vector sensors, which are designed to acquire vector quantities associated with the sound field [5][6][7][8][9][10][11]. The most common method to determine the direction of sound is the measurement of pressure gradient [8] or particle velocity due to the volumetric motion of the medium [9].…”

“…An alternative approach is the use of vector sensors, which are designed to acquire vector quantities associated with the sound field [5][6][7][8][9][10][11]. The most common method to determine the direction of sound is the measurement of pressure gradient [8] or particle velocity due to the volumetric motion of the medium [9]. These variables carry the directional information of the acoustic energy propagation, which helps to identify the direction of the source.…”