Abstract
This study describes a novel fiber optic extrinsic Fabry–Perot interferometric (EFPI) ultrasonic sensor comprising a low-cost and high-performance silicon diaphragm. A vibrating diaphragm, 5 μm thick, was fabricated by using the Microelectromechanical Systems (MEMS) processing technology on a silicon-on-insulator (SOI) wafer. The Fabry–Perot (FP) cavity length was solely determined during the manufacturing process of the diaphragm by defining a specific stepped hole on the handling layer of the SOI wafer, which made the assembly of the sensor easier. In addition, the use of cheap and commercially available components and MEMS processing technology in the development of the sensing system, limited the cost of the sensor. The experimental tests showed that the minimum detectable ultrasonic pressure was 1.5 mPa/sqrt(Hz) −0.625 mPa/sqrt(Hz) between 20 kHz and 40 kHz. As a result, this sensor has the potential to successfully detect weak ultrasonic signals.
Highlights
Ultrasonic waves have extensive applications in diverse areas, such as detection of defects in various materials and structures, sonar detection, medical diagnostics, etc.In these applications, ultrasonic sensors always play a vital role in acquiring ultrasonic wave information
The fiber optic extrinsic Fabry–Perot interferometric (EFPI) sensors have a number of inherent advantages such as; high-frequency response, immunity to electromagnetic interference (EMI), remote sensing capability, small size, light weight and easy construction; they have become an ideal candidate for ultrasonic detection [1,2,3,4,5]
To ensure that it has an efficient frequency response to ultrasonic waves, the diaphragm is generally designed to have a high natural frequency, which results in a low sensitivity
Summary
Ultrasonic waves (frequency >20 kHz) have extensive applications in diverse areas, such as detection of defects in various materials and structures, sonar detection, medical diagnostics, etc. An air cavity on the fiber was formed firstly by an etching process, proposed a new all-glass fiber EFPI pressure sensor. EFPI acoustic sensor, where length optical fiber controlled by attaching thin spacers to the two fixedthin fiber capillary [11] These and the diaphragm was two controlled by attaching spacers to the fixed fibermethods capillarycan [11].realize. It is urgent further facilitate sensor methods realize of thethe precise assembly of the FP cavity on optical fiber.toHowever, it is urgent to assembly and simplify the process. In most of the reported work, the optical fiber must be further facilitate sensor assembly and simplify the process.
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