R&D towards the acoustic positioning system of KM3NeT

M. Ardid, M. Bou-Cabo, F. Camarena, V. Espinosa, G. Larosa, C.D. Llorens, and J.A. Martínez-Mora (IGIC –UPV),

representing the KM3NeT consortium

VLVNT’09 – Athens - October 2009

Introduction

• In undersea neutrino telescopes, sea currents result on drifts of the top of the detection units and Optical Modules (OMs) by several meters

• However, muon track reconstruction is based on:

– precise arrival time of Cherenkov photons to the OMs(< 2 ns)

– Monitor the OM position with the corresponding resolution (< 40 cm)

• An acoustic triangulation system is needed for monitoring the OM positions, so as to provide the tracking precision and angular resolution required for astronomical neutrino source searches.

• We present our effort in R&D towards this system for KM3NeT– Activities, solutions proposed, prototype systems and tests– We have focused in the transceiver design

Specifications for the system

• Difficulties of the system:– Deep water, large volume, number of elements, integration in the

telescope. – Combined in a system with reasonable cost and complexity

• Large uncertainty in the description of the detector:– mechanics, optical modules, distances between elements, etc.?

• General specifications:– Acoustic range > 1 km– Cost: of the order of 1% of the total cost– Reliable– Redundancy

Solution proposed

• Acoustic transducer:– We have selected the commercial available SX30 Free Flooded Ring

from Sensortech, Canada, since it fulfils all the requirements:• It can operate as emmiter and receiver with good efficiencies (20-40 kHz)• It can stand high power signals• It can stand high pressures• It can be affordable in the large number of units required by KM3NeT

• Electronics– Worth to do R&D in the electronics to::

• Fulfil the special requirements of the system: low-power consumption, configurable from shore, etc.

• Optimise to the transducer chosen• Reduce costs

Acoustic transducer: Specifications

• Info from the supplier

Tests to transducers: Transmit Voltage Response

Preamplifier

Generator Signal

Recorded Board

PC

Acoustic Board

Power Supply 5 V

ITC 1042 FFR10 cm

10 cm

10 cmReson

EMITTER

RECEIVER

TRIGGER

Osciloscope

Tests to transducers: Transmit Voltage Response

Calibration from the supplier

• Small variations with respect to the supplier calibration

Tests to transducers: Received Voltage Response

Preamplifier

Generator Signal

Recorded BoardPC

Acoustic Board

Power Supply 5 V

TRIGGER

ITC 1042 FFR10 cm

10 cm

10 cmReson

EMITTERRECEIVER

Tests to transducers: Received Voltage Response

Calibration from the supplier

• Larger variations observed: possible effect of the preamplifier used • Need deeper investigation

Tests to transducers: Transmiting Directivity

Calibration from the supplier

• We will check in the following months

Tests to transducers: Pressure dependence

• Tests performed at the large hyperbaric tank at IFREMER-Brest– Small variations with pressure

Electronics: Requirements

• To handle emission and reception– Protect reception from high tension

• All-data-to-shore approach– Increase reliability, easier tuning, and versatility

• Configurable from shore – Communication using Slow Control (RS232)

• Low power consumption– Less than 1 W at 5 V– Store energy to have very high electric power in short time

Electronics: solution proposed

• Design of the 1st electronic board:– Blue: Communication and control– Red: Emission part

• Digital feeding + transducer response – Green: Reception part

• Limiter to protect from emission• Analogic, see G. Riccobene’s talk for

ADC and rest of the electronic chain

Performance of the first electronic board• Low consumption

– Less than 1 W at 5 V• Easy configuration and control by RS232

– Possible to handle arbitrary signals for emission, but could be improved• Fast synchronisation using a TTL signal

– A few s delay for emission, stability better than 1 s• High power for emission

– Transducer feeded with 300 Vpp, but probably not enough for KM3NeT• Low intrinsic noise• Good matching between the electronics and the transducer and

response according to the designAlmost ready a 2nd version of the electronic board, which overcomes the limitations observed and improves performance.Tests before the end of the year.

Tests to electronics + transducers: Signals emmitted

• Arbitrary signal emission not implemented in the first version of the board.

• Some examples of tone bursts at 30 kHz are shown.

• 2nd version of the board, possible to use arbitrary signals easily. Take advantage of signal processing techniques.

1 cycle

5 cycles 10 cycles100 cycles

Fluctuations in received amplitude due to reflections in the tank

Tests to board + transducers: Receiving response and transmitting power

Tests to board + transducers: Intrinsic noise• Measurement done in the anechoic chamber• Singular frequencies appear, most probable due to

electromagnetic contamination of our lab• Need confirmation in a cleaner environment• For the rest, noise below 120 dB (~ ≤Sea State 1)

Preliminary

Tests to board + transducers: Whole process (echo)

• Whole performance of the system can be studied in a pool looking at echoes.

• Measurements from last week:– Analyses are going on to study

the stability in amplitude and time.

Amplitude limited during emission

Floor echo

Wall echoes

Red :with reflectorBlue: w/o reflector

Tests to board + transducers: Summary

• We have designed and tested a system that can be used in the acoustic positioning system fulfilling most of the requirements: – Low cost, Low power, stability, etc.– We have acquired an important know-how

• Improvements are needed in some aspects:– Transmitting power (or sensitivity) is not enough:

• We are in the 0-10 dB Signal-to-Noise ratio.• 2nd Electronic Board will provide about 185 dB ref 1 Pa at 1 m

– Arbitrary signals for emission very helpful for KM3:• Possible in the 2nd version

• More checks needed in some aspects: – Intrinsic noise, stability.

2nd Electronic board

• More accurate arbitrary signal: using a more powerful microcontroller and the PWM technique

• Power up the signal more than four times: using an H-Bridge• Capacity of acquiring and processing the received signal in the

board

Conclusions

• We have the know-how and are in the way to have a solution for the transceivers of the acoustic positioning system of KM3NeT

• In principle, t is compatible with the different options for the receiver hydros:– Good sensitive hydrophones that can be used in acoustic detection of

neutrinos or bioacoustic monitoring– Acoustic modules: piezos glued inside the glass spheres– And of course with the free flooded ring transducers.