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Ïîèñêîâûå ñëîâà: ionization front
RECENT DEVELOPEMENTS ON FIBER OPTIC AIR-BACKED MANDREL HYDROPHONES
· · · · · Introduction Possible aplications Prototype Preliminary results Future planning

M.Anghinolfi, A.Cotrufo, S.Cuneo, D.Piombo, A.Plotnikov, L.Repetto INFN Genova


Acoustic detection of pressure waves in water
Most interesting application: ·Military ·Tracking of mammals ·Detectionof shock waves reflected by the sea bed .... and possibly ·Detection of hadronic shower produced by UHE 's

Expected neutrino signal (a.u.)


First proposal

G.A Askarian: hydrodinamical emission in tracks of ionizing particles in stable liquids. 1957


and later....

G.A.Askarian, B.A.Dolgoshein, A.N.Kalinovsky, N.A.Mokhov: Acoustic detection of high energy particle showers in water. Nucl. Inst. and Meth., 164 (1979), 267. "... All this gives good reason to believe that the acoustical method of particle detection may find applications both at accelerators of the new generation and for detection of cosmic neutrinos in the Ocean" experimentally confirmed by L.Sulak, et al. : Experimental studies of the acoustic signature of proton beams traversing fluid media", Nucl. Inst. and Meth., 161 (1979),203


Neutrinos from where?
Production mechanism

1. Emission of jets 2. Fermi acceleration mechanism proton spectrum: dNp/dE ~E-2 3. p+p decay 4. Another mechanism: from decay produced in the interaction of p with CMB at energies above ~ 10
19

Cosmic source

p+N+

Neutrinos from succcesive and µ

eV


An exemple: the `cosmogenic neutrino flux'
created by decaying charged pions produced in interaction of primary nucleons of energy above 5x1019 eV with CMB photons, the GreisenZatsepin-Kuzmin effect(D.Semikoz, G. Sigl, hep-ph/0309328 29 sep 2003)


Why acoustic detection ?
·High energy neutrinos interact via DIS with matter (1% probability in 1 km of water at 1020eV ). ·Energy is shared between a quark ad a lepton; on the average 80% to the lepton and 20% to the hadronic shower ( Joule for 1020eV neutrinos) . ·The hadronic shower is confined (typically a 2 cm. Radiux x 20 m length cylinder) and produces detectable pressure waves. · the acoustic front has a typical disk shape('pancake'), the pressure wave is bipolar, 50 s period, amplitude mPa or higher depending on the initial energy and distance ·The signal propagates for several km (attenuation lenght of 1km at 20 kHz)


at high energies ( 1018eV) the acoustic detection may be an alternative to Cerenkov light detection (attenuation lenght 50 m)


The production mechanism


T.Karg

U.Erlangen

ARENA 2005


The acoustic signal


~1mPa @1000m distance from a 1018 eV shower T.Karg U.Erlangen ARENA 2005


The air backed mandrel hydrophone

coupler

·An optic fiber is wrapped outside a thin walled hallow cylinder ·The cylinder is mounted outside a passive inner tube with sufficient clearance to provide air backing. ·This air gap allow the cylinder to deform in response to incident acoustic waves. ·This deformation, proportional to the pressure, is measured by sensing the corresponding fiber length variation. ·To this purpose a Michelson interferometer is used; Bragg gratings embedded in the core of the fibre reflect the light from a laser


Main advantages
·Quite easy to fabricate ·Not expensive ·Driven by a laser source on shore ·Immune from electrical noise ·Do not require local power supply nor ADC conversion ·Can be arranged in large arrays by using multiplexing technique Present acheavement ·high sensityvity: below Sea State Zero at 5 kHz ·Brandwidth up to 5-10 kHz ·Our purpose ·Increase upper limit of the bandwidth (20 kHz ?) ·Increase operational depth (1500 m ?)


Modeling.....
1. Materials Young modulus E and Poissons' ratio
Material Young modulus ( GPa) Aluminum Ultem1000 Ultem2400 Core/cladding coating 70 3.3 11.7 72 1.1 0.33 0.44 0.37 0.17 0.45 Poissons' ratio

are the leading parameters in the design

For a composite material effective elastic parameters are obtained according to their cross sectional area e.g.: 0.5 mm thick Ultem1000 mandrel +5 layers 80/135 m fibres: Eeff=13.4 GPa

2. Geometry Responsitivity mostly depends on: · Radius, length, thickness, of the cylinder, · number of optic fibre layers, type of optic fibre (80/135 ­ 80/165 m) · Effective Young modulus, Poissons' ratio and density


3. Responsitivity relates the response of the hydrophone to its geometry and the external pressure;

L L



1 - E

2

R P t

Ultem 2400 2R=40 mm t = 1mm 5 layers of fibres

= -303 dB re Pa

Ultem 1000 2R=15 mm t=0.5 mm 5 layers of fibres

= -308 dB re Pa

Must be corrected for the finite length of the cylinder !!


4.Correction due to the finite length and to the end-constraints

P
mandrel air gap support free to move = (1-C1) C1,C2 are a complicated function of E, , r ,t, L (dB re Pa)
type `old' `slim' `fat 1' `fat 2' material Ultem1000 Ultem1000 Ultem2400 Ultem2400 r (mm) 10 7.5 18 18 L (mm) 40 26 10 10 T (mm) 0.5 0.5 0.5 1 #layer 3 5 5 5 No edge effects -302 -308 -302 -304

P

fixed (glued) = (1-C2)

free -303 -309 -307 -311

glued <-330 -326 <-330 <-330


5.Response in frequency

Obtained from the normal modes of vibration of a cylindrical shell in vacuum Solutions expressed in terms of the displacements u,v,w in the axial, circumferential and radial directions. u=U
m,n(x)cos(n

)cos(t)

v=Vm,n(x)sin(n)cos(t) w=Wm,n(x)cos(n)cos(t)

0
n, number of circumferential waves, m number of axial half periods The radial "breathing mode" (m,n)=(1,0) gives the major contribution to the fiber length change i.e. to the frequency responsitivity of the idrophone


Behaviour in air
The frequency associated to the fundamental mode with n=0,m=1 · Increase with shell thikness t · decrease with radius R · decrease with length L



radial

t 2 4 R 2 1 + = 2 2 4 12 L (1 - ) R E
L (mm) 40 26 10 10 T (mm) 0.5 0.5 0.5 1 #layer 3 5 5 5

type `old' `slim' `fat 1' `fat 2'

r (mm) 10 7.5 18 18

radial
(kHz) 50 63 38 41


Behaviour in water
·The fluid lower the frequency of the resonance due to the added mass ·The fluid lower the amplitude of the resonance due to re-radiation of the acoustic wave ·See detailed analysis J.M.Scott: J. Sound and Vibration 125 (1988) 241 For the lowest radial `breathing mode' the displacement W1,0()

R 2 (1 - 2 ) W1,0 ( ) = p Et
where

1
shell

(1 - 2 ) R 2 2 1 + E t

fluid shell

K 0 (R ) K1 (R )

t 2 4 R -1- 12 L4

2

2 =


L

2 2

-



2

Vs

Vs is the sound velocity in water

K 0 ( R ), K 1 ( R

)

Modified Bessel functions, may be complex


Response in water vs air

ALENIA

`slim'


Response in water vs air

`fat'

`slim and long'


Directionality
Sound wave at frequency and angle : p=p0exp(-ik.r), k=/vs

Calculate the mean pressure

over the cylinder surface of radiur R andlength L:

1 1 = P0 L 2R


0

L

2

0

exp(-i ( KR sin cos + Kx cos ) Rddx

L sin cos R 2v

J s sin = 0 v L P0 s cos 2vs


Response in water (vs=1500m/s)
1 0.8 0.6 0.4 0.2

/p

0

10 kHz 20 kHz 30 kHz `

Alenia'

type: R=10mm, L=40 mm

0.2

0.4

0.6

0.8

1

1.2

1.4

1 0.8 0.6 0.4 0.2

/p

0

`

slim

': R=7.5 mm, L=26 mm


0.2 0.4 0.6 0.8 1 1.2 1.4


1 0.8 0.6 0.4 0.2

10 kHz

/p
0

`fat': R=20 mm, L=10 mm directionality more pronounced

20 kHz
0.2 0.4 0.6 0.8 1 1.2 1.4

30 kHz

Exemples of directionality in air: vs 1500m/s 340 m/s air 1/4 water directionality much more pronounced
1 0.8 0.6 0.4 0.2

5 kHz 10 kHz 15 kHz
0.2 0.4 0.6 0.8 1 1.2 1.4

1 0.8 0.6 0.4 0.2

0.2

0.4

`

slim

'

`

fat'

0.6

0.8

1

1.2

1.4


Modeling the `fat' hydrophone

5 layers of optic fibre mandrel in Ultem 2400 40x10x1 mm

air gap o-ring to support the mandrel


Winding the optic fibre


Some tests performed to define the winding procedure
Pre-tensioning of the fibre

Different diameters of the hydrophone


One prototype already realized
The hydrophone without the polyurathane coating Record of a phone ring The frequency response in air


comparison with piezo hydrophone


Work is just started... a lot of things ahead

·Complete the present prototype: polyurathane coating. ·Possible alternative : `fat' vs `slim' . Main advantages: less attenuation in the fibres, directionality (?), resistent to deeper depth. Detailed FEA calculations needed. ·Extend the present read out system from 10 to 20 kHz. ·Perform accurate calibration in air and water at different frequencies. ·Realize an hydrophone array. ·Start to calculate optimum geometry configuration and reconstruction tools for a large volume neutrino detector based on hydrophone arrays ·. . . . .






10 m


DWDM Cable with optic fibres 1000 m