# Presentation: 572207

## Acoustic sensor and transmitter development

- Amanda/IceCube Collaboration Meeting
- Berkeley
- March 2005

## Overview

**Motivation**
**Sensors calibration**
- Methods
- Results
- Equivalent noise level
**Transmitters**
- Ringtransmitter
- HV signal generator

## Motivation

**Motivation**

**This**** ****talk**

## 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/****μ****Pa (5 to 65 kHz)**
- Glass Ball, Iron Ball
**Transmitter**
- piezoceramic in epoxy arbitrary signal generator

## 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**

## 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

## Sensitivity: Gated burst

**Time window**
- start: after initial excitation
- stop: before 1st reflection
**Fit **
**A(t) = ****A****0****sin(2****π****f****·****t + ****φ****) + ****b****t +****c**
- free phase and amplitude
- fixed frequency
- linear offset term
****** ****very good ****χ****2**
**But: low-f and DC background**
****** ****large error for small signals**
****** ****probably overerstimated **

## Sensitivity: pulse method

**Transmitted signal**
- P *∞* ∂2Uin/ ∂t2  “soft” step function
**Received signal**
- Fourier transform compare spectral components
**Errors and noise**
**A(t) = **Σ**f**** s(f)e****i (2****π****ft + ****φ****s****)**** + n(f)e****i (2****π****ft + ****φ****n****)**
- coherent signal: φs(f) = const
- random noise: φs(f) = random
**Noise spectrum from**
- average  fourier transform
- fourier transform  average
****** ****define signal dominated regions**

## 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

## 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 |

## 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

## 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

## Transmitter: Ringtransmitter

**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

## Power supply

**Power supply**

**Problem**
- build a HV generator forarbitrary signals
**I****max**** = 2****π****f C****tot**** U****max**
- Cring = 16 nF
- f = 100 kHz
- Umax = 1kV
- k33 = 0.34
**I****max**** = 16 A, P ****≈**** 5.4 kW**
-  too large
**Solution**
- large capacity at low duty cycles100 cycle burst  1ms  **16 W**
- large inductivity discharge via capacitance
-  shortcut after N cycles

## Next talk

**Next**** ****talk**