590 likes | 739 Views
User Constructed Sonar Equipment. Presented to PSUBS Convention 2004. Sonar Principles. Basic Concepts Transducers Ping generation Ping reception Post-ping processing Construction and testing. Sonar Principles. Basic Concepts Transducers Ping generation Ping reception
E N D
User Constructed Sonar Equipment Presented to PSUBS Convention 2004
Sonar Principles • Basic Concepts • Transducers • Ping generation • Ping reception • Post-ping processing • Construction and testing
Sonar Principles • Basic Concepts • Transducers • Ping generation • Ping reception • Post-ping processing • Construction and testing
Basic Sonar Concepts • Generate a signal at some frequency f0 • Drive an transducer at f0 for a short duration of time generating a “ping” • Allow the sound waves generated to propagate outward at the speed of the medium Vm • Receive the return echo signal measuring the time of flight from transmission to reception Tf • Calculate the distance to target, D = ( Tf · Vm ) / 2
Speeds of Sound vm0 Degrees Celsius [1] • Air 332 m/s 1,090 f/s • Fresh water 1,404 m/s 4,610 f/s • Sea water 1,440 m/s 4,730 f/s • Copper 3,560 m/s 11,680 f/s • Iron 5,130 m/s 16,830 f/s
Sonar Considerations • Attenuation of signal by water • Spherical radiators • Sonar patterns • Choice of frequency • Sensitivity of receiver • Types of transducers
Attenuation of Sound Through Water [2] • Absorption Roughly Related to frequency squared • Scattering Signal scatters use to foreign materials in the water
Sonar Considerations • Attenuation of signal by water • Spherical radiators • Sonar patterns • Choice of frequency • Sensitivity of receiver • Types of transducers
Spherical Sound Radiation • Sound intensity: I = Power / Area (W/m2) • Where area of a sphere = 4pr2 • Same power through any radius (r) we can imagine, with the source in the center • Let PT = Total power through any radius (r) • Therefore: I1 = PT / 4pr12 and I2 = PT / 4pr22 • Combining we have: I1 / r12 = I2 / r22 • We have: I2 = (r12 / r22) I1 or I2 = (r1/ r2) 2 I1 • Conclusion: Intensity of sound drops off with the square of the distance (r) from the source
Sonar Considerations • Attenuation of signal by water • Spherical radiators • Sonar patterns • Choice of frequency • Sensitivity of receiver • Types of transducers
Sonar Considerations • Attenuation of signal by water • Spherical radiators • Sonar patterns • Choice of frequency • Sensitivity of receiver • Types of transducers
Sonar Considerations • Attenuation of signal by water • Spherical radiators • Sonar patterns • Choice of frequency • Sensitivity of receiver • Types of transducers
Sonar Considerations • Attenuation of signal by water • Spherical radiators • Sonar patterns • Choice of frequency • Sensitivity of receiver • Types of transducers
Sonar Principles • Basic Concepts • Transducers • Ping generation • Ping reception • Post-ping processing • Construction and testing
Transducers • Sonar transducer facts • Beam Angle • Piezoelectric principles • Piezoelectric ceramics • Ring and disk transducers elements • Piezoelectric modes • Typical piezoelectric ceramics • Fish finder transducers • Available specialty transducers
Sonar Transducer Facts • Transducers convert electrical signals to sound. • Transducers convert sound into electrical signals. • Most transducers send and receive best at one characteristic frequency f0. • Most small sonar transducers are of a piezoelectric form. • Most piezoelectric materials for sonar application are ceramics.
Piezoelectric Principles [3] Voltage Creates DW DW Generates Voltage DW = Change in Thickness
Piezoelectric CeramicsManufactured in a Variety of Shapes [4]
Ring and Disk Transducer Elements Rings Helps Eliminate Lateral Resonance Modes Thin Discs Showing Conductive Coating
Typical Piezoelectric Ceramics [6] Channel Industries, Inc.
Relatively Inexpensive Encapsulated Wiring Attached Wide or Narrow Cone Locally Available Little Choice of Resonate Frequencies Unknown Piezoelectric Material Used Unknown Electrical Properties of Material Fish Finder Transducers Advantages Disadvantages
Fish Finder Transducers(Eagle [7]) Transom Mount Cylinder Thru Hull
Available Specialty Transducers [7] Thru Hull Bronze Thru Hull Plastic Trolling Motor Mount
Sonar Principles • Basic Concepts • Transducers • Ping generation • Ping reception • Post-ping processing • Construction and testing
Ping Driver Circuit • Amplifies 192-KHz Signal from Generator and Drives Transducer • Generates Drive Only when Ping Enable is Active • Multiplexes Sonar Transducers if System Requires
Sonar Principles • Basic Concepts • Transducers • Ping generation • Ping reception • Post-ping processing • Construction and testing
Sonar Principles • Basic Concepts • Transducers • Ping generation • Ping reception • Post-ping processing • Construction and testing
Post-ping Processing Options • Sample return analog for feed to computer or microcontroller. • Use analog means of measuring time between ping and the breaking of a return threshold level. • Be creative with your own methods of monitoring returned amplitude vs time!
Sonar Principles • Basic Concepts • Transducers • Ping generation • Ping reception • Post-ping processing • Constructionand testing
Construction and Testing • Pressure Housing • Electronic assembly • Modules • Transducer array • Testing
Electronics Assembly Microcontroller Board