R&D towards the acoustic positioning system of KM3NeT

1. 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

2. Introduction • In undersea neutrino telescopes, sea currents result on drifts of the top of the detection unitsand 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

3. Specificationsforthesystem • 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

4. Solutionproposed • Acoustictransducer: • Wehaveselectedthecommercialavailable SX30 Free Flooded Ring fromSensortech, Canada, sinceitfulfilsalltherequirements: • It can operate as emmiter and receiver withgoodefficiencies (20-40 kHz) • It can stand highpowersignals • It can stand highpressures • It can beaffordable in thelargenumber of unitsrequiredby KM3NeT • Electronics • Worth to do R&D in theelectronicsto:: • Fulfilthespecialrequirements of thesystem: low-powerconsumption, configurable from shore, etc. • Optimisetothetransducerchosen • Reduce costs

5. Acoustictransducer: Specifications • Infofromthesupplier

6. Acoustic Board Preamplifier Osciloscope Power Supply 5 V Recorded Board TRIGGER PC Generator Signal 10 cm ITC 1042 10 cm 10 cm FFR EMITTER Reson RECEIVER Teststotransducers: TransmitVoltage Response

7. Teststotransducers: TransmitVoltage Response • Small variationswithrespecttothesuppliercalibration Calibration from the supplier

8. Acoustic Board Preamplifier Power Supply 5 V Recorded Board TRIGGER PC Generator Signal 10 cm ITC 1042 10 cm 10 cm FFR Reson RECEIVER EMITTER Teststotransducers: ReceivedVoltage Response

9. Teststotransducers: ReceivedVoltage Response • Largervariationsobserved: possibleeffect of thepreamplifierused • Needdeeperinvestigation Calibration from the supplier

10. Teststotransducers: TransmitingDirectivity • Wewillcheck in thefollowingmonths Calibration from the supplier

11. Teststotransducers: Pressuredependence • Testsperformed at thelargehyperbarictank at IFREMER-Brest • Small variationswithpressure

12. 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

13. Electronics: solutionproposed • 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

14. Performance of thefirstelectronicboard • 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 ms delay for emission, stability better than 1 ms • 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 design Almost ready a 2nd version of the electronic board, which overcomes the limitations observed and improves performance. Tests before the end of the year.

15. 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 100 cycles 10 cycles 5 cycles Fluctuations in received amplitude due to reflections in the tank

16. Tests to board + transducers: Receiving response and transmitting power

17. 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

18. 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. Wall echoes Floor echo Red :with reflector Blue: w/o reflector Amplitude limited during emission

19. 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 mPa 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.

20. 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

21. 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.