Sea Technology

JUN 2014

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www.sea-technology.com June 2014 / st 23 T he rapid improvements in high-speed digi- tal components, substantially advanced by the medical ultrasound industry, are providing new op- portunities in digital signal processing for acoustic instrumentation development. The improvements in digital signal processing mean that acoustic instrument manufacturers are investing a lot of effort in development to make products more competitive and offer customers improved measurement capabilities. Nortek Piezo Ltd. (Ab- erdeen, Scotland) has collaborated with many acoustic in- strument manufacturers to design innovative composite transducers that provide increased bandwidth, more effcient energy transmis- sion and greater receiver sensitivity. These im- provements allow instrument manufacturers to implement more sophisticated broadband transmissions and reduce power output, while realizing gains in measurement range and resolution. The Signature55 acoustic Doppler dual current profler with a 1,000-meter range is an example of how composite transducers can enable innovations in instrument devel- opment. Piezo Composite Transducers Acquiring the highest quality data from the front-end transducers is a prerequisite for im- proving signal processing. Piezo composite transducers offer many performance improve- ments over traditional single-element piezo transducers and are being more widely adopted to provide improved capa- bilities to underwater instrument manufacturers. Composite Production. A piezo composite transducer is typically a combination of an active piezoelectric ceramic and a passive polymer to create a composite structure. Most piezo composite transducers start as a solid block or circu- lar disk of piezoelectric ceramic, and then deep groves of the active material are removed through cutting processes to create a pattern of gaps that are flled with a passive poly- mer. The specifc pattern of the active material, ratio be- tween active and passive materials, and material properties of the passive fll matrix all impact the acoustic characteris- tics of the fnal piezo composite transducer assembly. Improved Performance Increased Sensitivity. Active acoustic instruments trans- mit acoustic energy and then listen for the return echo from the seafoor or objects and particles within the water column. These echoes are often very weak, therefore the measurement range is inherently reduced. Piezo composite construction greatly improves the sensitivity of the receiv- ing capability of the transducer, improving the measurement range of acoustic products. Instinctively, cutting away por- Composite Transducers Enable Acoustic Instrumentation Innovation Improving Bandwidth, Sensitivity to Foster New Product Development By Eric Siegel • Mark Walsh • Atle Lohrmann (Top) Illustration of a composite transducer. (Bottom) The Signature55 was frst deployed offshore Toulon, France. JUN2014.indd 23 6/4/14 1:04 PM

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