MEMS Sensors for Underwater Applications

Microelectromechanical system (MEMS)-based sensors for marine environment help to realize new systems that bring enhanced levels of perception, control, and performance to sonar systems and sensors related to marine environments. Processing, assembly, packaging, testing, and manufacturing methods are all highly dictated by the intended application of MEMS devices; hence, these disciplines are being honed up to meet the demands with new materials and performance requirements across a wide spectrum of underwater applications. Five basic parameters are measured in the ocean to define its physical state: temperature, salinity, pressure, density, and velocity of sound. These can be obtained using a pressure sensor, temperature detector, and a conductivity sensor. Biologically inspired MEMS shear stress sensors comprising a piezoresistive floating element offer the potential to make flow measurements in fluid with unprecedented sensitivity, and spatial and temporal resolution. In order to get finer resolution of underwater objects in turbid waters, it is imperative to work at MHz frequencies. Different types of transducers such as CMUT, PMUT, and Helmholtz resonator are also realized by MEMS fabrication and are readily scalable in size. In addition, multiplexing, pulsing, and pre-amplifying electronics can be easily integrated on the same chip with the transducers or on a separate chip via flip-chip bonding. This allows for 1D and 2D arrays of elements to be easily steered electronically. Thus, fabrication of a large number of transducers with built-in pre-amplifiers required in a planar array configuration is possible with MEMS-based technology.