J.A. Martínez-Mora

Acoustic Transmitters for Underwater Neutrino Telescopes

In this paper acoustic transmitters that were developed for use in underwater neutrino telescopes are presented. Firstly, an acoustic transceiver has been developed as part of the acoustic positioning system of neutrino telescopes. These infrastructures are not completely rigid and require a positioning system in order to monitor the position of the optical sensors which move due to sea currents. To guarantee a reliable and versatile system, the transceiver has the requirements of reduced cost, low power consumption, high pressure withstanding (up to 500 bars), high intensity for emission, low intrinsic noise, arbitrary signals for emission and the capacity of acquiring and processing received signals. Secondly, a compact acoustic transmitter array has been developed for the calibration of acoustic neutrino detection systems. The array is able to mimic the signature of ultra-high-energy neutrino interaction in emission directivity and signal shape. The technique of parametric acoustic sources has been used to achieve the proposed aim. The developed compact array has practical features such as easy manageability and operation. The prototype designs and the results of different tests are described. The techniques applied for these two acoustic systems are so powerful and versatile that may be of interest in other marine applications using acoustic transmitters.

The sound emission board of the KM3NeT acoustic positioning system

We describe the sound emission board proposed for installation in the acoustic positioning system of the future KM3NeT underwater neutrino telescope. The KM3NeT European consortium aims to build a multi-cubic kilometre underwater neutrino telescope in the deep Mediterranean Sea. In this kind of telescope the mechanical structures holding the optical sensors, which detect the Cherenkov radiation produced by muons emanating from neutrino interactions, are not completely rigid and can move up to dozens of meters in undersea currents. Knowledge of the position of the optical sensors to an accuracy of about 10 cm is needed for adequate muon track reconstruction. A positioning system based on the acoustic triangulation of sound transit time differences between fixed seabed emitters and receiving hydrophones attached to the kilometre-scale vertical flexible structures carrying the optical sensors is being developed. In this paper, we describe the sound emission board developed in the framework of KM3NeT project, which is totally adapted to the chosen FFR SX30 ultrasonic transducer and fulfils the requirements imposed by the collaboration in terms of cost, high reliability, low power consumption, high acoustic emission power for short signals, low intrinsic noise and capacity to use arbitrary signals in emission mode.

R&D studies for the development of a compact transmitter able to mimic the acoustic signature of a UHE neutrino interaction

Abstract Calibration of acoustic neutrino telescopes with neutrino-like signals is essential to evaluate the feasibility of the technique and to know the efficiency of the detectors. However, it is not straightforward to have acoustic transmitters that, on one hand, are able to mimic the signature of a UHE neutrino interaction, that is, a bipolar acoustic pulse with the ‘pancake’ directivity, and on the other hand, fulfil practical issues such as ease of deployment and operation. This is a non-trivial problem since it requires directive transducer with cylindrical symmetry for a broadband frequency range. Classical solutions using linear arrays of acoustic transducers result in long arrays with many elements, which increase the cost and the complexity for deployment and operation. In this paper we present the extension of our previous R&D studies using the parametric acoustic source technique by dealing with the cylindrical symmetry and demonstrating that it is possible to use this technique for having a compact solution that could be much more easily included in neutrino telescope infrastructures or used in specific sea campaigns for calibration.

Acoustic Sensor Design for Dark Matter Bubble Chamber Detectors

Dark matter bubble chamber detectors use piezoelectric sensors in order to detect and discriminate the acoustic signals emitted by the bubbles grown within the superheated fluid from a nuclear recoil produced by a particle interaction. These sensors are attached to the outside walls of the vessel containing the fluid. The acoustic discrimination depends strongly on the properties of the sensor attached to the outer wall of the vessel that has to meet the requirements of radiopurity and size. With the aim of optimizing the sensor system, a test bench for the characterization of the sensors has been developed. The sensor response for different piezoelectric materials, geometries, matching layers, and backing layers have been measured and contrasted with FEM simulations and analytical models. The results of these studies lead us to have a design criterion for the construction of specific sensors for the next generation of dark matter bubble chamber detectors (250 L).

Acoustic signal detection through the cross-correlation method in experiments with different signal to noise ratio and reverberation conditions

The study and application of signal detection techniques based on cross-correlation method for acoustic transient signals in noisy and reverberant environments are presented. These techniques are shown to provide high signal to noise ratio, good signal discernment from very close echoes and accurate detection of signal arrival time. The proposed methodology has been tested on real data collected in environments and conditions where its benefits can be shown. This work focuses on the acoustic detection applied to tasks of positioning in underwater structures and calibration such those as ANTARES and KM3NeT deep-sea neutrino telescopes, as well as, in particle detection through acoustic events for the COUPP/PICO detectors. Moreover, a method for obtaining the real amplitude of the signal in time (voltage) by using cross correlation has been developed and tested and is described in this work.

Self-organization of ultrasound in viscous fluids

We report the theoretical and experimental demonstration of pattern formation in acoustics. The system is an acoustic resonator containing a viscous fluid. When the system is driven by an external periodic force, the ultrasonic field inside the cavity experiences different pattern-forming instabilities leading to the emergence of periodic structures. The system is also shown to possess bistable regimes, in which localized states of the ultrasonic field develop. The thermal nonlinearity in the viscous fluid, together with the far-from-equilibrium conditions, are responsible of the observed effects.

Constraining Secluded Dark Matter models with the public data from the 79-string IceCube search for dark matter in the Sun

We acknowledge the financial support of Plan Estatal de Investigacion, ref. FPA2015-65150C3-2-P (MINECO/FEDER), Consolider MultiDark CSD2009-00064 (MINECO) and of the Generalitat Valenciana, Grant Prometeoll/2014/079. We would like to thank the colleagues J.D. Zornoza, C. Rott, J.L. Feng, J. Smolinsky and P. Tanedo for the fruitful discussions and comments about this work.The 79-string IceCube search for dark matter in the Sun public data is used to test Secluded Dark Matter models. No significant excess over background is observed and constraints on the parameters of the models are derived. Moreover, the search is also used to constrain the dark photon model in the region of the parameter space with dark photon masses between 0.22 and ~ 1 GeV and a kinetic mixing parameter e ~ 10−9, which remains unconstrained. These are the first constraints of dark photons from neutrino telescopes. It is expected that neutrino telescopes will be efficient tools to test dark photons by means of different searches in the Sun, Earth and Galactic Center, which could complement constraints from direct detection, accelerators, astrophysics and indirect detection with other messengers, such as gamma rays or antiparticles.

Transducer Development and Characterization for Underwater Acoustic Neutrino Detection Calibration.

A short bipolar pressure pulse with “pancake” directivity is produced and propagated when an Ultra-High Energy (UHE) neutrino interacts with a nucleus in water. Nowadays, acoustic sensor networks are being deployed in deep seas to detect this phenomenon as a first step toward building a neutrino telescope. In order to study the feasibility of the method, it is critical to have a calibrator that is able to mimic the neutrino signature. In previous works the possibility of using the acoustic parametric technique for this aim was proven. In this study, the array is operated at a high frequency and, by means of the parametric effect, the emission of the low-frequency acoustic bipolar pulse is generated mimicking the UHE neutrino acoustic pulse. To this end, the development of the transducer to be used in the parametric array is described in all its phases. The transducer design process, the characterization tests for the bare piezoelectric ceramic, and the addition of backing and matching layers are presented. The efficiencies and directivity patterns obtained for both primary and parametric beams confirm that the design of the proposed calibrator meets all the requirements for the emitter.

Optimization of Dimensions of Cylindrical Piezoceramics as Radio-Clean Low Frequency Acoustic Sensors

Circular piezoelectric transducers with axial polarization are proposed as low frequency acoustic sensors for dark matter bubble chamber detectors. The axial vibration behaviour of the transducer is studied by three different methods: analytical models, FEM simulation, and experimental setup. To optimize disk geometry for this application, the dependence of the vibrational modes in function of the diameter-to-thickness ratio from 0.5 (a tall cylinder) to 20.0 (a thin disk) has been studied. Resonant and antiresonant frequencies for each of the lowest modes are determined and electromechanical coupling coefficients are calculated. From this analysis, due to the requirements of radiopurity and little volume, optimal diameter-to-thickness ratios for good transducer performance are discussed.

System of Reciprocal Acoustic Sensors for Monitoring Sea Currents

In this paper we propose to monitor sea currents over a large region by using few acoustic sensors distributed in the contour of the region. The method is based on the measurement of the travel time of the acoustic wave between sensors in communication. The travel time difference of the forward and backward propagations between acoustic transducers depends on the sea current. From the information of a set of sensors, it is possible to determine the sea current. Here, the basis of the technique is described and different considerations for the design of the system are discussed. Finally, we show the application and validation of the proposed method with data from a set of acoustic sensors in the deep sea ANTARES neutrino telescope.