US2407643A

US2407643A - Apparatus for submarine signaling

Info

Publication number: US2407643A
Application number: US350326A
Authority: US
Inventors: Batchelder Laurence
Original assignee: Submarine Signal Co
Current assignee: Submarine Signal Co
Priority date: 1939-08-02
Filing date: 1940-08-03
Publication date: 1946-09-17
Anticipated expiration: 1963-09-17

Description

Sept 1946- L. BATCHELDER 2,407,643

APPARATUS FOR SUBMARINE SIGNALING Original Filed Aug. -2, 1950 3 Sheets-Sheet 1 L008 0.6.0.4 0.2 0 02 0.4 0.6 08 1.0

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2.422 2.0 L8 L6 L4 L2 I-.OO.8 0.60.402

' INVE TOR LAURENCE AT'CHEL. ER.

sfipt 17, 1946, BATQHELDER 2,4Q7fi43 APPARATUS FOR SUBMARINE SIGNALING Original Filed Aug. 2, 1939 3 Sheets-Sheet 3 v INVENTOR B I LAURENCE BATCHELDER.

' BY a ATTORNEY Patented Sept. 17, 19426 iiE stare A'll'hi FFEQE APPARATUS FGR SUBMAREWE SIGNALING Laurence Batchelder, Cambridge, Mass, assignor, by mesne assignments, to Submarine Signal Company, Boston, Mass, a corporation of Dela- Ware Claims. (Cl. 177386) The present application is a division of my copending application Serial No. 287,974, filed August 2, 1939.

The present invention relates to translating devices for converting compressional wave energy to electrical energy, and vice versa. More particularly the present invention relates to such devices as used for signaling under Water and is particularly concerned with the transmission and reception of compressional wave energy in a beam.

It has heretofore generally been understood that if a vibratable piston be made large in its dimensions in comparison with the wave length of the compressional waves at the signaling frequency, a concentration of energy along the axis perpendicular to the radiating surface will be obtained. However, such a concentration of energy in a main beam is accompanied by smaller concentrations of energy in directions at various angles with the axis of the main beam.

When the relative acoustic energy intensities in the free medium as produced by a sending device at a constant distance large compared to the dimensions of the device are plotted with respect to the angular directions from the axis perpendicular to the radiating surface, as on polar coordinated. graph paper, the main concentration of energy will appear as a large lobe representing the main beam, and a plurality of auxiliary lobes or ears representing the subsidiary energy concentrations in directions other than that of the main beam will also appear. These auxiliary lobes of the beam pattern are often objectionable particularly for signaling under water as in acoustic echo ranging for the determination of the distance and direction of remote objects. Such subsidiary energy concentrations can be reduced by not driving the plane radiating surface as a piston but by driving it at varying amplitudes over its surface.

It has been shown in the copending application of Harold M. Hart, Serial No. 285.902. filed July 22, 1933, that a good beam pattern with a main beam narrow enough to produce good directional effect and with the subsidiary maxima reduced to a very small value can be obtained by giving a circular radiating surface an amplitude varying in accordance with the followin equation:

A. 12 r 2 6 r 4 ZT)17(E) +7(E (1) where Ar represents the amplitude at any radial coordinate measured from the center of the ra- 2 diating surface; A0 is the amplitude at the center of the radiating surface; 1" is the radial distance of any point from the center of the radiating surface; and a is the maximum radius of the radiating surface. This equation can also be written:

A. 7 r 2 r 4 Amie- (5) z where Aav is the average amplitude of the surface and is obtained by integrating Ar from Equation 1 over the surface and dividing the integral by the area of the surface. This amplitude distribution is symmetrical with respect to the center of the radiating surfac and the maximum vibrational amplitude occurs at the center.

According to one feature of the present invention the amplitude distribution over the surface of a circular radiating surface is not made symmetrical about the center but is made symmetrical about a diameter. By this means more energy can be radiated into the medium, better efficiency can be obtained and for echo ranging purposes the noise level can be reduced.

According to another feature of the present invention the same improved beam pattern can be obtained in one or more planes by exciting the radiating surface at a uniform amplitude and suitably shaping the radiating surface.

These and other features and objects of the present invention will more fully appear and best be understood from the following description taken in connection with the accompanying drawings in which Fig. 1 is a graphical illustration of amplitude distributions and other features of the present invention; Fig. 2 is a polar diagram of certain beam patterns; Fig. 3 is a horizontal section of a magnetostriction oscillator; Fig. V4: is a vertical section of the oscillator shown in Fig. 3; Fig. 5 shows a different type of magnetostriction oscillator Within a streamlined housing partly in section; and Fig. 6 is a fragmentary enlarged section of Fig. 5 taken along the line VI-VI.

If a circular plane radiating surface having a diameter greater than the wave length at the signaling frequency be vibrated with an amplitude uniform over its surface, a beam pattern in the medium. will be obtained similar to that shown by the dotted curve in Fig. 2. This curve shows the relative compressional wave intensities in a plane perpendicular to the radiating surface at a constant distance from the surface large compared to the surface dimensions. The curve shows a maximum energy concentration along an axis 1/ perpendicular to the radiating surface which is assumed to have no rear radiation in the medium. At some angles from the axis. y the energy decreases as indicated by the dotted line en. At some larger angle from the axis y the radiated energy will fall to zero, and at a still greater angle again build up to a lower but still significant maximum value, then again fall to zero as the angle is further increased, and so on throughout the hemisphere facing the radiating piston. Thus, there will appear successive lobes of energy concentration at various angular distances from the axis y as indicated in Fig. 2 by the lobes e1, c2 and c3 of the beam pattern diagram. Where the radiating surface is circular, it will be understood that these subsidiary lobes are in the form of hollow cones so that the beam pattern graph in an plane perpendicular to the radiating surface will be the same as that shown in Fig. 2. The largest subsidiary maximum for such a uniformly excited circular radiating surface is approximately 1'7 db. below the maximum intensity of the main beam. Since the large subsidiary maxima e1, e2 and (23 are often objectionable, particularly for echo ranging purposes, the radiating surface may be given a non-uniform amplitude which, if suitably chosen, will reduce these subsidiary maxima. If the radiating surface be vibrated with an amplitude distribution like that determined by Equation 2 above, the beam pattern represented by the solid curve in Fig. 2 will be obtained. The main lobe E representing the main beam has a somewhat greater width than the main lobe e0 produced by uniform amplitude of the radiating surface but the auxiliary lobes E1, E2 and E3 are very much reduced in intensity. In fact, the largest subsidiary maxima can in this way be reduced more than 34 db. below the maximum intensit of the main beam.

One form of device which may be used to obtain the beam patterns of Fig. 2 is shown in Figs. 3 and 4. In this device a radiating member I having a radiating surface 2 adapted to contact the signaling medium-for example, water-has a plurality of magnetostriction tubes 3 firmly fixed to its inner surface. Each of the tubes 3 is driven by an electromagnetic coil i which surrounds it. While only relatively few nickel tubes have been shown, it will be understood that in practice a great many tubes may be used, often as many as several hundred. Each of the tubes together with its associated portion of the memher 5 forms a one-half wave length vibrating system. When the coils of all the tubes have the same number of turns and are excited with the same current, that is, have the same number of ampere turns, substantially uniform iston vibration of the surface tube is obtained. On the other hand, when the coil surrounding the tubes nearest the center of the element l are given a greater number of ampere turns than the coils surrounding the tubes nearer the edge of the member I, the surface 2 will have a greater amplitude at the center. If the ampere turns for the coils from center to edge of the radiating member be varied in accordance with Equation 1 above, a beam pattern substantially like that of the solid curve in Fig. 2 will be obtained. Such an amplitude distribution is generally obtained in practice by grouping the several coils in circular groups or substantially circular groups, all the coils in each group being given the same number of ampere turns. Such circular symmetry involves a rather complicated coil construction which can be considerably simplified in accordance with the present invention in which the amplitude distribution is made symmetrical about a diameter of the radiating member.

If it be assumed that the beam pattern represented by the solid curve in Fig. 2 is desired in one plane, the proper amplitude distribution for the circular radiating surface, symmetrical about the diameter perpendicular to the said plane is where Ax is the amplitude of the surface along any chord parallel to the diameter of symmetry, Aav is the average amplitude, a: is the radial distance of the chord from. the diameter of symmetry and a is the total radius of the radiating surface. This amplitude distribution can be obtained b calculation or by the method shown graphically in Fig. 1.

- The curve F in Fig. 1 shows the amplitude distribution over the radiating surface in accordance with Equation 2 above plotted with respect to the average amplitude of the surface. Thus, the center of the radiating surface is given an amplitude 2.33 times that of the average amplitude of the surface while the edge of the surface is vibrated with an amplitude of 0.33 times the average amplitude of the surface. This amplitude distribution is the same for all diameters. The curve F, therefore, can be deemed to represent the outline of a solid figure symmetrical about its axis.

To produce the same beam pattern in one plane I vary the amplitude of the radiating surface symmetrically with respect to the diameter perpendicular to that plane in accordance with Equation 3 plotted in Fig. 1 as the curve G; that is all portions of the radiating surface lying along a chord parallel to the diameter are given the same amplitude, the amplitude for the various chords decreasing from the diameter outwards. Thus, in curve G the abscissae represent the per pendicular distances :1: of the several chords from the diameter relative to the total radius of the radiating surface, and the ordinates represent the amplitude of each chord relative to the average amplitude. The amplitude at each chord is the average of the various amplitudes which the several portions of the radiating surface along the chord would have if the radiating surface were excited with an amplitude distribution in accordance with the curve F circularly symmetrical about the center. Thus, at the diameter the radiating surface is given an amplitude of 1.4 whereas at the chord farthest removed from the diameter, the amplitude is 0.33. The curve G can be obtained from the curve F in the following manner.

Let the circle H represent the radiating surface having a vertical diameter JK about which the amplitude distribution is to be symmetrical to produce a beam pattern in th horizontal plane similar to that shown by the solid curve in Fig. 2. Then assume, for example, that it is desired to obtain the surface amplitude at the chord represented by the dotted line L. Since this amplitude is to be the average of the amplitude which would occur along this chord for circularly symmetrical amplitude distribution, it is first necessary to determin what amplitude'the various points on this chord would have for circularly symmetrical amplitude distribution. Take any point A on the chord at a distance OB from the center of the radiating surface. The amplitude of such points for circular symmetry is found from the curve F to be at B. This amplitude may then be plotted as the point A. Similarly, for other points on the chord L the amplitud can be determined which such points would have for circular symmetrical amplitude distribution whereby the curve M i obtained. Averaging all the amplitudes represented by the curve M gives the average amplitude represented by the line CC which for the particular chord chosen will be seen to lie at approximately 0.95 of the total average amplitude of the radiating surface. Transferring this point to a new graph, the point C' of the curve G is obtained. By making similar graphical constructions for other chords of the radiating surface the curve G will be obtained. As before stated, this curve gives the amplitude of successive elemental strips of the radiating surface parallel to a diameter.

In practice with, for example, a device of the type shown in Figs. 3 and 4 a close approximation to this amplitude distribution can be ob tained by dividing the driving elements into vertical rows symmetrical about the vertical diameter and giving the coils in each row the same number of ampere turns and those in successive rows the ampere turns indicated by the relative desired vibrational amplitudes as determined from the curve G. Thus the two rows of coils 5 and 6 which are at the distance 0.35/a from the diameter will be given the amplitude indicated by the points N and P on the curve G. With this amplitude distribution the device will produce a beam pattern in the horizontal plane similar to that of the solid curv shown in Fig. 2. planes the beam pattern will, of course, vary, the subsidiary maxima becoming greater.

It will be noted from a comparison of the curve G with the curve F that the maximum amplitude of any point on the radiating surface, that is the amplitude along the vertical diameter, is considerably less than the maximum amplitude required for circularly symmetrical amplitude distribution. Thi means that the peak amplitude is nearer the average amplitud for diametral symmetry. By the latter arrangement, therefore, more energy can be radiated into the water, for the peak amplitude is always limited by the amplitude at which cavitation takes place. Moreover, with diametral symmetry better efficiency is obtained because the different portions of th radiating surface are working more nearly at the same amplitude. The construction of the device is also simpler in the case particularly of an oscillator of the type shown in Figs. 3 and 4 where the radiating surface is driven by a great many individual elements distributed over it.

I have found, however, that theoretically a beam pattern in the horizontal plane, the same as that obtained by the diametrically symmetrical amplitude distribution just described, can be obtained by driving the entire radiating surface at a uniform amplitude and suitably shaping the surface in accordance with the beam pattern desired. If we take, for example, the beam pattern represented by the solid curve in Fig. 2 which is produced in the horizontal plane by a vertical surface energized with the circularly symmetrical amplitude distribution represented by Equation 1 and the curve F in Fig. 1, or with my diametrically symmetrical amplitude distribution represented by the curve G in Fig. l, the same beam pattern in the horizontal plane can be obtained by a surface vibrating with a uniform amplitude,

In other 6 the surface being shaped as shown by the curve Q in Fig. l. The equation of this curve is h x 732x 16x F x/(2) (515(2) c t (4) where h is any ordinate,

ill

is the corresponding abscissal coordinate and a is the maximum width from the center line. This shape of radiating surface is derived directly from the curve G by multiplying the height of any point of the curve above the horizontal zero axis by the height of the corresponding point on the circle H. The entire surface Q so obtained is energized uniformly with the average amplitude of the curve G, but any uniform amplitude may be used.

Since the boundary of the surface Q is substantially diamond shaped, a satisfactory approximation, insofar as the reduction of secondary maxima is concerned, is obtained by making the radiating surface diamond shaped as, for example, in Fig. 1. For many practical purposes it may moreover be desirable to make the radiating surface in the form of a square as indicated by R in Fig. 1. This shape of surface is the equivalent of the diamond S in respect of the reduction of secondary maxirna in the horizontal plane. In fact, not only is the height of the apex of the figure entirely arbitrary, but also any quadrilaterally shaped radiating surface having two corners on the vertical center line and its other two corners equidistant from the center line and the same distance apart will produce the same horizontal beam pattern as the diamond shape S. For the quadrilateral oscillator vertically supported in this way the horizontal beam pattern has its maximum subsidiary energy concentration theoretically 26 db. below the main maximum as contrasted with the value of 34 db. for the largest subsidiary maximum of the non-uniform amplitude diametrically symmetrical circular oscillator and for the uniform amplitude oscillator shaped like Q in Fig. 1. While the beam pattern of the quadrilateral oscillator thus is not quite so good as that of the two last mentioned, it is much superior to square oscillators heretofore used with sides vertical and horizontal, in which case the largest subsidiary maximum is only 13 db. below the maximum of the main. beam.

For the square unit any type of oscillator having a square radiating surface can be used. For example, a multi-tube magnetostriction oscillator of the type shown in Figs. 3 and 4 can be employed by making the member I and the radiating surface 2 in the form of a square.

Another form of oscillator which conveniently lends itself to design with a square radiating surface is shown Figs. 5 and 6. oscillator is made up of laminations of magnetcstrictive material closely stacked together, each lamination being one-half a wave length in height. The laminations are assembled into a square block by means of the end plates 8 and the bolts 9 so that they will vibrate as a unit. The block so formed is supported at its vibrational node by means of the nodal orojections 26 formed on both sides of each lamina and is suitably held in position as by means of the elements If and 52 secured together by screws it, a piece of rubher 25 being interposed between the clamping members and the laminations. The laminations are perforated, as shown, through which perforations an exciting winding M can be wound. When this winding is excited with suitable current, the laminations will be set into vibration, and conversely when the laminations are vibrated by a compressional wave, an electric current will be set up in the winding it. In order to obtain the desired beam pattern in the horizontal plane the oscillator must be mounted with its radiating surface and one of its diagonals vertical as shown in Fig. 5. Such a mounting may be made in streamlined form, for example, in the form of a spherical housing E5. The spherical housing 55 may be clamped to a shaft it which may be projected from a ship and arranged for rotation into any desired direction. The portion of the housing l which covers one of the surfaces presented by the ends of the assembled laminations and which is to act as a radiating surface, say the surface I! in Fig. 6, is made of a thin material as at it which preferably does not offer any appreciable obstruction to the passage of sound waves in water. This may be fastened by means of screws 2% to a thickened equatorial section it? formed integrally with one of the lamination supporting members, for example, H. The rest of the spherical housing as represented by the portion i5 is also made relatively thick and fastened to the equatorial section 89 by screws 2!. The section [B may also have made integral with it or fastened to it a plate 22 parallel to the end surfaces 23 of the block of laminations which is opposite the radiating surface. To avoid radiation from the surface 23, a sponge rubber pad 2 or other sound absorbing material may be interposed between the plate 22 and the surface 23. The front portion 25 of the spherical casing which is opposite the radiating surface if is filled with a liquid such as water which can enter this portion of the casing through apertures 21. The device so formed is relatively simple in construction and provides a rectangular radiating surface mounted in a vertical plane with one of its diagonals vertical so that a beam pattern is obtained which is approximately as good a that represented by the solid curve in Fig. 2. Since, moreover, the oscillator is mounted in a streamlined housing, it can readily be used for acoustic echo ranging.

For this purpose the oscillator is mounted, as just described, on a normally vertical shaft rotatable about its axi and projected beneath a vessel the water. By supplying the oscillators winding with a suitable direct polarizing current and an alternating current of suitable frequency, a compressional wave impulse can be emitted. A reflection from a distant object may be received by the same oscillator and after suitable arnplification be used to actuate an indicator. If a timing device be associated with the impulse transmitting key and with the indicator, the time interval between the emitted and reflected impulses can be measured, thus determining the distance of the remote object. The direction of the reflecting object is determined by the direction in which the oscillator is facing during the signal transmission and receipt. It is important, therefore, that the oscillator have a beam pattern in the horizontal plane which is not only sharply directional in its main beam, but which also ha its subsidiary maxima small compared to the main maximum. This is obtained with a simple construction by my square oscillator mounted with two of its corners on a vertical line.

The square oscillating surface mounted with one diagonal vertical, of course, produces the same beam pattern in both horizontal and vertical planes. Where the beam pattern in the vertical plane is not particularly important, the upper (or lower) half of the square can be omitted, the resulting beam pattern in the horizontal plane not being affected. Thus I can use any triangularly shaped uniformly active radiating surface having one corner on the vertical center line and the other two corners equidistant from the center line, without change in the horizontal beam pattern for a given sum of the distances of the last-mentioned two corners from the center line.

A. triangularly shaped oscillator of this type is particularly useful for collision prevention and other forward signaling on ships. For this purpose the oscillator having a triangularly shaped radiating surface, preferably isosceles or equilateral, is mounted on the outside of the skin of a ship, preferably well forward, with its base line horizontal and its apex on the vertical center line and projecting downwards. The entire structure is covered with a housing streamlined in the forward direction. The housing material is such that it does not appreciably interfere with the passage of compressional waves through it. The housing itself is filled with a compressional wave conducting liquid such as oil or water. A still better beam pattern will, of course, be obtained if the radiating surface is not exactly triangular, but is shaped like the lower half of the figure Q in Fig. 1. In this case the beam pattern in the horizontal plane will be the same as that of the solid curve in Fig. 2.

For collision prevention the oscillator is keyed periodically to transmit a compressional wave impulse in synchronism with the zero position of an indicator. Reflected impulses may be received by the same oscillator or a separate unit and utilized to actuate the indicator. The indicator may be arranged in the usual manner for time interval measurement whereby the distance of the reflecting object can be ascertained. A keying and indicating mechanism of the type shown in U. S. Patent 1,678,560, issued July 24, 1928, to H. G. Dorsey and R. L. Williams, may, for example, be used.

The triangularly shaped oscillator or that of half the surface Q is particularly adapted for collision prevention because by virtue of its shape, it is readily mounted on the ships hull and is easily streamlined without the use of an undesirably large housing. Moreover, the beam pattern in. the horizontal plane, which for collision prevention is th only plane of interest, is very good.

Having now described my invention, I claim:

1. In a system for collision prevention for ships of the type wherein compressional wave signals are transmitted and signals reflected from a distant object are received, the combination with the hull of a vessel of a compressional wave device having a continuous, plane, active surface area having a horizontal dimension greater than the wave length of the waves at the signaling frequency in the signaling medium and whose vertical height decreases substantially linearly from a finite value at a center line to zero at both sides thereof, means for vibrating said surface with a uniform amplitude and for uniformly responding to vibrations of said surface and means for mounting said device on said vessel with said center line and said surface vertical and orthogonal to the fore and aft line of the vessel.

2. A compressional wave sending and receiving device having a continuous, plane, transmitting and receiving surface shaped symmetrically with respect to two perpendicular coordinate axes substantially in accordance with the equation h a; 2 7 32 x 2 16 a; 4 a- (i) (5 EC) r5 i where h and .r are the coordinates of any point on the surface boundary with respect to said axes and a is the maximum value of :r and is larger than half a wave length of the waves at the signaling frequency in the signaling medium and means for driving said surface with a uniform amplitude and for uniformly responding to vibrations of said surface.

3. In a system for collision prevention for ships of the type wherein compressional wave signals are transmitted and signals reflected from a distant object are received, the combination with the hull of a vessel of a compressional wave device having a continuous, plane, active surface area shaped with respect to a center line substantially in accordance with a straight line approximation to the curve defined by the equation in rectangular coordinates:

h 2 7 32 a: 2 16 x 4 rv (a)(r-rs(i) l-(2)) where h is any ordinate,

is the corresponding abscissal coordinate and a is the maximum value of a; and is larger than half a wave length of the waves at the signaling frequency in the signaling medium, means for mounting said device on said vessel with said center line and said surface vertical and the :1:- axis horizontal and in a plane perpendicular to the fore and aft line of the vessel and means for driving said surface with a uniform amplitude and for uniformly responding to vibrations of said surface.

4. A compressional wave sending and receiving device comprising a continuous, plane, radiating surface having an active parallelogramshaped area, means for supporting said surface in acoustic relation to the signaling medium and with one of its diagonals vertical, the other diagonal being horizontal and of a dimension larger than the Wave length of the waves at the signal ing frequency in the signaling medium, and means for driving said surface and responding to vibrations of said surface with a uniform amplitude over the entire surface.

5. A compressional Wave sending and receiving device comprising a radiating element having a square, continuous, plane, radiating surface, means for supporting said device with said surface in acoustic relation to the signaling me-' dium and with one of its diagonals vertical, the other diagonal being horizontal and of a dimension larger than the wave length of the waves at the signaling frequency in the signaling medium and means for vibrating said surface and responding to vibrations of said surface with a uniform amplitude over the entire surface.

6. A compressional wave sending and receiving device comprising a continuous, plane, radieting and receiving surface havin a quadrilateral shape with one pair of opposite corners located on a diagonal and the other pair of corners equidistant from said diagonal at a distance greater than half the wave length of the waves at the signaling frequency in the signaling medium, means mounting said surface in acoustic relation to the signaling medium with said diagonal vertical and means for vibrating said surface and responding to vibrations of the surface with uniform amplitude over the surface whereby the horizontal receiving and transmitting beam pattern in the medium will have a strong main maximum energy concentration in the direction at right angles to the surface and only relatively small subsidiary maximum energy concentrations in other horizontal directions.

7. A compressional wave sending and receiving device having a continuous, plane, substantially triangularly shaped active surface area having one corner located on a center line and the other two corners equidistant from said center line at a distance therefrom greater than half a wave length of the waves at the signaling frequency in the signaling medium, means mounting said device with said surface in acoustic relation to the signaling medium and with said center line vertical and means for driving said surface and responding to vibrations of said surface with a uniform amplitude over the surface.

8. A submarine signaling device comprising a compressional wave oscillator having a continuous, plane, square active surface, means mounting the same on a vessel with one of its diagonals vertical including a spherical housing having a section facing said surface formed of a substantially acoustically permeable material and having compressional wave absorbing means contained in the opposite section of said housing and in back of said surface and means for driving said surface and responding to vibrations of said surface with a uniform amplitude over the surface.

9. A submarine signaling device comprising a compressional wave oscillator having a continuous, plane, substantially square radiating surface forming one end of a laminated core of magnetostrictive material, said core being one half a wave length in thickness and a plurality of wave lengths on a side, means for supporting said core at a vibrational node and with one of the diagonals of its radiating surface Vertical and means for driving said surface and responding to vibrations of said surface with a uniform amplitude over the surface.

10. A submarine signaling device comprising a compressional wave oscillator having a continuous, plane, substantially square radiating surface forming one end of a laminated core of magnetostrictive material, said core being one half a wave length in thickness and a plurality of Wave lengths on a side, and means for supporting said core at a vibrational node, said means including a spherical housing having an equatorial section, means supporting the oscillator thereby with its nodal plane substantially at a diameter within said equatorial ection, means mounting said spherical housing on a vessel with a diagonal of said radiating surface vertical and means for driving said surface and responding to vibrations of said surface with a uniform amplitude over the surface.

LAURENCE BATCHELDER.