Sebastian Böser [email protected] Acoustic sensor and transmitter development Amanda/IceCube Collaboration Meeting Berkeley March 2005.

Sebastian Bö[email protected]

Acoustic sensor and transmitter development

Amanda/IceCube Collaboration Meeting

Berkeley

March 2005

Acoustic sensors and transmitters – 2 [email protected]

Overview

Motivation

Sensors calibration Methods Results Equivalent noise level

Transmitters Ringtransmitter HV signal generator

Acoustic sensors and transmitters – 3 [email protected]

Motivation

This talk

Acoustic sensors and transmitters – 4 [email protected]

Calibration

Problem interesting frequency ≈ 20 kHz

λwater = 7.5 cm λice = 20 cm

Oscillating signal reflections distort signal need container with xcont » λ

Setup at HSVA water tank 12m × 3m × 70m deep section 12m × 5m × 10m

Sensors Reference Hydrophone

Sensortech SA03

-163.3±0.3 dB re 1 V/µPa (5 to 65 kHz) Glass Ball, Iron Ball

Transmitter piezoceramic in epoxy

arbitrary signal generator

Acoustic sensors and transmitters – 5 [email protected]

Speed of sound

Method compare arrival times of

direct signal reflection at the surface reflection at the walls

Result vwater = 1409.7 ± 4.5 m/s

Theory vwater = 1411.2 m/s

good agreement

Acoustic sensors and transmitters – 6 [email protected]

Sensitivity: Method

Method transmit same signal to

reference sensor to calibrate

compare response relative calibration

Transmitted signals gated burst

precisely measuresingle frequency limited by

system relaxation time reflections

pulse in one shot measure full spectrum limited by

noise level

Acoustic sensors and transmitters – 7 [email protected]

Sensitivity: Gated burst

Time window start: after initial excitation stop: before 1st reflection

Fit

A(t) = A0sin(2πf·t + φ) + bt +c free phase and amplitude fixed frequency linear offset term

very good χ2

But: low-f and DC background

large error for small signals

probably overerstimated

Acoustic sensors and transmitters – 8 [email protected]

Sensitivity: pulse method

Transmitted signal

P ∞ ∂2Uin/ ∂t2 “soft” step function

Received signal

Fourier transform compare spectral components

Errors and noise

A(t) = Σf s(f)ei (2πft + φs) + n(f)ei (2πft + φn)

coherent signal: φs(f) = const

random noise: φs(f) = random

Noise spectrum from

average fourier transform

fourier transform average

define signal dominated regions

Acoustic sensors and transmitters – 9 [email protected]

Comparison of methods

Results high sensitivity and S/N

Glass ball: factor ≈ 20 Iron ball: factor ≈ 50

very good agreement strongly structured

many different resonance modes only valid for water

Acoustic sensors and transmitters – 10 [email protected]

Equivalent noise level

Method fourier transform

scaling, frequency range

backward transform

Problem noise recording from water tank lab self noise higher due to EM coupling

Equivalent Noise Level [mPa]

Frequency range [kHz]

5 - 120 5 - 65

Hydrophone 50.1± 0.7 40.3 ± 8.3

Glass Ball 17.1 ± 1.7 15.9 ± 1.7

Iron Ball 6.6 ± 0.6 4.7 ± 0.7

Acoustic sensors and transmitters – 11 [email protected]

How to do it for ice ?

Theoretical use formula for transmission in media

Problem temperature dependence

resonance modes amplifier gain× bandwidth

solid state vs. liquid

Practical use large ice volume (glacier, pole) use small ice block with changing boundary conditions

(e.g. air, water) determine reflections from comparison

Acoustic sensors and transmitters – 12 [email protected]

Transmitters

Large absorption length

Need high power transmitter

Piezoceramics can be driven with kV signals easy to handle cheap well understood

Ring-shaped piezo ceramic azimuthal symmetry larger signals than cylinders more expensive

Acoustic sensors and transmitters – 13 [email protected]

Transmitter: Ringtransmitter

Linearity tested from 100 mV to 300 V

perfect linearity

Frequency response three resonance modes

width, thickness and diameter

wide resonance at lower frequencies

Testing frequency sweep

dominated by reflections

resonance modes of container

white noise signal

reflections not in phase

resonance modes of transmitter

Acoustic sensors and transmitters – 14 [email protected]

Power supply

Problem build a HV generator for

arbitrary signals

Imax = 2πf Ctot Umax

Cring = 16 nF f = 100 kHz Umax = 1kV k33 = 0.34

Imax = 16 A, P ≈ 5.4 kW too large

Solution large capacity at low duty cycles

100 cycle burst 1ms 16 W large inductivity

discharge via capacitance shortcut after N cycles

Acoustic sensors and transmitters – 15 [email protected]

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