Precise Underwater Distance Measurement by Dual Acoustic Frequency Combs

Abstract

Underwater acoustics is of fundamental importance for marine science and technology. However, acoustic waves transmitted by state‐of‐the‐art underwater acoustic systems are not inherently phase locked, which hinders the development of underwater acoustic technology. For example, the precision of underwater distance measurement can only achieve centimeter level. As a versatile tool, optical frequency combs have enabled revolutionary progress in optical metrology and precision measurement. In parallel with optical frequency combs, here, the generation of fully stabilized, underwater acoustic frequency combs is reported, in which equidistant acoustic modes are produced via a hydroacoustic transducer. The precision of each individual acoustic mode is measured to be 10−9 at 1 s and 10−12 at 1000 s averaging times. Underwater distance measurements are carried out in an anechoic pool using a dual‐comb scheme. Comparison with reference values shows consistency within 50 µm (7 × 10−6 in relative). The relatively long‐duration experiments at 7 m distance yield an Allan deviation of 1.8 µm (2.6 × 10−7 in relative) at 1 s and further 480 nm (6.8 × 10−8 in relative) at 40 s averaging times. The approach to acoustic frequency comb generation offers a promising and powerful platform for future underwater distance measurement, positioning, and navigation.

Harmonic and subharmonic waves on the surface of a vibrated liquid drop

“…Our results can also find applications in the emergent field of acoustic frequency comb generation [55] and their application in underwater distance measurements [56]. Similar to an optical frequency comb, an acoustic frequency comb is a spectrum consisting of a series of discrete, equally spaced elements that have a well-defined phase relationship between each other (for a review see, e.g., [40]).…”

Acoustic frequency combs using gas bubble cluster oscillations in liquids: a proof of concept

“…Our current findings contribute to further development of an emergent field of AFC generation 11,[14][15][16][17] . They also extend our previous observation of frequency combs originating from the onset of Faraday waves in OPEN 1 Optical Sciences Centre, Swinburne University of Technology, Hawthorn, VIC 3122, Australia.…”

“…AFC technique is an emerging metrological approach that benefits from technological maturity of optical frequency combs. It opens up opportunities for accurate measurements in various physical, chemical and biological systems in situations, where using light poses technical and fundamental limitations, for example, when precise underwater distance measurement is required 15 .…”

“…Similar to optical frequency combs, acoustic (phononic) frequency combs (AFC)-purely acoustic signals with spectra containing equidistant coherent peaks-exploit the ability of acoustic waves to provide precision information about the medium in which they propagate [11][12][13][14][15][16][17] . In contrast to light, acoustic waves can propagate in water and opaque liquids over long distances, which underpins many acoustics-based technologies including sonar, underwater communication and sensing 15 and marine biology 18 . Yet, even though AFCs have already been used to accurately measure distances between underwater objects 15 , research on them remains under-established.…”

“…In contrast to light, acoustic waves can propagate in water and opaque liquids over long distances, which underpins many acoustics-based technologies including sonar, underwater communication and sensing 15 and marine biology 18 . Yet, even though AFCs have already been used to accurately measure distances between underwater objects 15 , research on them remains under-established. The development of new types of acoustic combs is needed for sensing and imaging systems 11,14 , in particular, biomedical imaging 16,19,20 .…”