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

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

3. Active Sonar Equation SL = Source Level (dB re 1mPa @ 1m)
FREQUENCY (Hz)
SL = Source Level (dB re 1m)
TL = Transmission Loss ( 40 log r + 2ar)
NL = Noise Level (dB)
DIR= Receiving Directivity ( )
TS = Target strength (dB)
SV = Volume Backscattering Strength (dB)
V = Insonified Sample Volume (m3)
Typical parameters for a Simrad EK500, 120 kHz transducer at T = 5o C
TS = -70 dB, r = 67m SNR = 10 dB
Example:

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

5. Fluid Sphere - ka
Resonance
Scattering
Geometric
Scattering
Rayleigh
Scattering

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

7. Angular Resolution - Beampattern
main lobe
Disk
side lobes

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

9. beampattern of individual element
Linear array
beampattern of individual element
grating lobe
main lobe

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

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

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

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