Hydrophone calibration by laser interferometer in NMIJ

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1 Hydrophone calibration by laser intererometer in NMIJ Takeyoshi Uchida, Yoichi Matsuda, Masahiro Yoshioka National Metrology Institute o Japan National Institute o Advanced Industrial Science and Technology

2 Outline o the presentation.introduction.hydrophone sensitivity calibration using laser intererometry 3.Expansion o the calibration requency range up to 40 MHz 4.Measurement capability and validation 5.Summary

3 3.Introduction.Hydrophone sensitivity calibration using laser intererometry 3.Expansion o the calibration requency range up to 40 MHz 4.Measurement capability and validation 5.Summary

4 Ultrasonic power Hydrophone sensitivity Ultrasonic ield parameters Overview o NMIJ ultrasonic measurement standards Method Radiation orce balance Calorimetry Calibration range mw mw (5 MHz - 0 MHz) mw - 5 W (0.5 MHz - 5 MHz) 5 W - 00W ( MHz - 3 MHz) Expanded uncertainty (Level o conidence 95 %) 5 % - % 9 % Reciprocity 00 khz - MHz 0 % - 3 % Laser 0.5 MHz - 40 MHz intererometry 6. % - 7 % p R 7 % - 0 % Plane scan 0.5 MHz - 0 MHz I SPTA 4 % - 0 % I SATA 4 % - % 4

5 5 Hydrophone calibration systems in NMIJ Reciprocity Laser intererometry

6 6 Hydrophones Membrane Needle

7 Pulse-echo, Pulsed Doppler Lithotripsy Intravascular ultrasound Biomicroscopy Physiotherapy 3D Biomicroscopy Hydrophone sensitivity calibration in NMIJ Reciprocity Laser intererometry Ultrasonic requency (MHz) 7

8 8.Introduction.Hydrophone sensitivity calibration using laser intererometry 3.Expansion o the calibration requency range up to 40 MHz 4.Measurement capability and validation 5.Summary

9 9 Hydrophone sensitivity M() M V ( ) ( ) ( ) h Vh = = P( ) cu( ) V h ( ): Voltage amplitude rom hydrophone P ( ): Sound pressure amplitude U ( ): Particle displacement : Ultrasonic requency ρ: Water density c: Ultrasonic velocity in water

10 Laser intererometer Pelicle Hydrophone Tone burst ultrasonic wave Ultrasonic transducer Calibration procedure. Ultrasonic particle displacement U( ) measurement using laser intererometer. Derivation o sound pressure P( ) P( ) = πρcu( ) 3. Hydrophone output voltage V h ( ) measurement 4. Deviation o hydrophone sensitivity M ( ) M ( ) = V h ( ) / P( ) U( t ) Switch Ampliier Dizitizer V h ( t ) Termometer Trigger Block diagram o calibration system Power ampliier Signal generator 0

11 Normalized sensitivity (re..5 khz) Frequency response or optical intensity variation o intererometer Frequency (MHz)

12 Twice modulated light or requency response measurement Incident light (He-Ne Laser) Diracted light Diracted light To detector Diraction grating ormed by ultrasonic wave Transmitted light Acousto-optic modulator (AOM) Modulation requency Modulation depth m ( ) Transmitted light Acousto-optic modulator (AOM) Modulation requency Modulation depth m ( )

Optical intensity o twice modulated light ( ) ( ) t m m I t m m I t m t m I t m t m I t I 0 0 0 0

13 Optical intensity o twice modulated light ( ) ( ) t m m I t m m I t m t m I t m t m I t I cos ) ( ) ( cos ) ( ) ( ) )cos( ( ) )cos( ( ) )cos( ( ) )cos( ( ) ( = + + = Same amplitude 3

14 4.Introduction.Hydrophone sensitivity calibration using laser intererometry 3.Expansion o the calibration requency range up to 40 MHz 4.Measurement capability and validation 5.Summary

15 5 Expansion o calibration requency range or hydrophone sensitivity developed rom 0.5 MHz - 0 MHz in 005 expanded up to 40 MHz in 04

16 Issue or the expansion up to 40 MHz Decreasing S/N on ultrasonic signal with increasing ultrasonic requency Because o increasing ultrasonic attenuation ( 0.8 db / cm at 0 MHz 3.3 db / cm at 40 MHz ) However ultrasonic ar ield is used in NMIJ to reduce uncertainty by dierence rom plane wave 6

17 Reduction o ultrasonic attenuation by shortening ultrasonic propagation distance Propagation distance to orm ar ield: increasing proportional to. ultrasonic requency (inevitable). square o aperture radius o sound source Ultrasonic transducer with small aperture is developed in NMIJ 7

18 Transducer or calibration beyond 0 MHz Shape : Circular plane with mm radius Center requency c : 40.3 MHz -6 db bandwidth : 8 MHz ( 70 % ) 8

19 Evaluation o eective radius o the transducer Directivity o the transducer Normalized amplitude 0.5 ( c ) 40 MHz Rotation angle, /deg. Fitting D ( ) = Directivity unction J ( ka sin ) t sin Far ield is ormed at propagation distance 50 mm (Propagation distance 70 mm is used below 0 MHz) ka Deriving transducer radius t a t = 0.88 mm at 40 MHz at 9

20 Sound pressure amplitude, p / kpa 0 Sound pressure o the transducer at propagation distance o 50 mm : Current system : This study Frequency, / MHz High enough to calibrate rom 0 MHz to 40 MHz

21 .Introduction.Hydrophone sensitivity calibration using laser intererometry 3.Expansion o the calibration requency range up to 40 MHz 4.Measurement capability and validation 5.Summary

22 Factor Voltage measurement Ultrasonic ield Intererometer Eective reractive index Pellicle Characteristic impedance Reproducibility Uncertainty actors Item Linearity o digitizer Quantization error o digitizer Impedance matching Frequency response o moving average ilter Speciication o digital voltmeter Propagation distance Direction dierence between hydrophone and ultrasonic propagation Spatial averaging on hydrophone active element Frequency response o intererometer Acousto-optic eect Transmission actor o sound pressure Dependence on water temperature Stability o hydrophone sensitivity

23 Uncertainty o laser intererometry calibration Uncertainty actor Frequecy (MHz) Voltage measurement Ultrasonic ield Intererometer Eective reractive index Pellicle Characteristic impedance Reproducibility Relative Expanded uncertainty [k = ] (%)

24 Sensitivity ( nv / Pa) En 数 Validation Comparison with sensitivities calibrated in NPL 0 : NMIJ : NPL Reerence hydrophone Frequency (MHz) Frequency (MHz) 4

25 5 Key comparison CCAUV.U-K4 or hydrophone calibration Participants: NPL, PTB, NMIJ, NIM, INMETRO Frequency: 0.5 MHz ~ 0 MHz (8 requencies) Operation term: Mar. 04 ~ Sep. 05 Calibration results in NMIJ: Agree with KCRVs in the range o expanded uncertainty

26 6.Introduction.Hydrophone sensitivity calibration using laser intererometry 3.Expansion o the calibration requency range up to 40 MHz 4.Measurement capability and validation 5.Summary

27 7 Summary Hydrophone sensitivity calibration rom 0.5 MHz to 40 MHz has been provided using laser intererometry in NMIJ. Intererometer calibration using twice modulated light and broadband ultrasonic transducer with small aperture used or the calibration system.

28 Issue or urther expansion o higher calibration requency range Increasing ultrasonic attenuation ( 3.3 db / cm at 40 MHz 7.5 db / cm at 60 MHz) ]] Solutions under consideration. Further downsizing o transducer to keep short propagation distance to orm ar ield. Multi-layer transducer to enhance radiated sound pressure amplitude 8

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