Acoustic Transducer Design Application of Advanced Acoustic Technology

Acoustic Transducer Design: Application of Advanced Acoustic Technology to Oceanographic Measurements Dezhang Chu Woods Hole Oceanographic Institution, MA 02543

Transducer Design: ? Physical Process Range? Sample Volume? ? Targets Biological Process

Active Sonar Equation SL = Source Level (d. B re 1 m. Pa @ 1 m) TL = Transmission Loss ( 40 log r + 2 ar) NL = Noise Level (d. B) DIR= Receiving Directivity ( ) TS = Target strength (d. B) SV = Volume Backscattering Strength (d. B) V = Insonified Sample Volume (m 3) Example: Typical parameters for a Simrad EK 500, 120 k. Hz transducer at T = 5 o C TS = -70 d. B, r = 67 m SNR = 10 d. B FREQUENCY (Hz)

Characteristics of Scattering Targets siphonophore fish pteropod T-microstructure (Intense ) euphausiid copepod T-microstructure (Background )

Fluid Sphere - ka Resonance Scattering Geometric Scattering Rayleigh Scattering

Application Objective: • Detection – Resonance frequency, geometric scattering region ( ) • Classification – two or more frequencies, or broadband signals ( ) Resonance Scattering Geometric Scattering Rayleigh Scattering

Angular Resolution - Beampattern main lobe side lobes Disk

Linear Array (more complicated system) b Aperture Angular Resolution: Field of View Array Gain:

beampattern of individual element Linear array grating lobe main lobe

Lost City 2003 (Kelley, Karson, Yoerger, Bradley)

Range Resolution Narrow-band: Broadband: (Chirp) Pulse Compression

Sidelobe Reduction mechanical shading Chebyshev Weighting slightly broader main lobe electronic shading

Objective Detection Classification Geometry Application Range Sample Volume SNR Frequency Bandwidth Beampattern Spatial Resolution Array Parameters etc. Sensor Parameters Target Physical/Biological Charactristics