EP0135426B1 - Pyroelectric pick-up tube - Google Patents

Description

The present invention relates to a pyroelectric target shooting tube. It also relates to a method for determining the axes of least expansion of the target.

Pyroelectric target shooting tubes are well known in the prior art. They are used for taking pictures in thermal television, and in particular in the infrared field.

The present invention relates more particularly to pyroelectric targets.

Figure 1 is a sectional view showing a pyroelectric target 1, and an assembly which is used according to the prior art to support this target, to polarize and read it.

The pyroelectric target 1 is fixed on a thin blade 2 which is itself stretched over a thick ring 3.

This type of support allows the target, which is very fragile, to be removed as much as possible from the vibrations to which it can be subjected in the tube in which it is mounted.

An electrode 4, transparent to the radiation to be detected, is deposited on one of the faces of the pyroelectric target.

This electrode 4 is deposited on the face of the target which does not receive the electron beam, symbolized by a right arrow in the figure, and which is used to read the charges created on the target by the variation in temperature.

Similarly, an electrode 5 is deposited on the face of the thin blade 2 which does not receive the radiation to be detected. This radiation is symbolized by a wavy arrow in Figure 1.

The target 1 covered with the electrode 4 is assembled on the one hand and the ring 3 and the thin blade 2 covered with the electrode 5 by a layer of adhesive 6 on the other hand.

The target read signal is collected on the electrode 5, which also ensures the polarization of the target.

There is no connection between the two electrodes 4 and 5 but only a capacitive coupling.

The problem which arises is that the capacity which is seen by the electron beam which is used to read the target 1 is constituted by the result of the capacity of the target and the layer of glue 6 mounted in series. The electrical signal read by the beam is multiplied by the ratio of these capacitances C _co ue / Cci _b te and the sensitivity of the target is reduced.

To avoid this decrease in sensitivity, it has been thought to directly connect the two electrodes 4 and 5. Thus, the capacity due to the layer of glue 6 is eliminated. In addition, we can then afford to use an electrode 5 of annular shape which further increases the sensitivity because the radiation to be detected does not have to pass through the electrode 5 which is not perfectly transparent.

The Applicant has shown that this solution is not satisfactory for the following reasons. The electrical contact made between the two electrodes 4 and 5 produces a mechanical disturbance which most often causes the pyroelectric target to rupture during temperature variations. Indeed, the thin blade 2 is made of an elastic material such as a film of mylar, registered trademark; in the same way, an adhesive having elastic properties is chosen for layer 6, to allow the pyroelectric target 1 to expand. The introduction into this assembly of an electrical contact, hard from the mechanical point of view, tends to cause rupture .

The present invention makes it possible to solve in a simple and effective manner the problem which arises when a direct connection is made between the electrodes 4 and 5.

According to claim 1, the present invention relates to a film tube, comprising a pyroelectric target, fixed on a thin blade stretched over a thick ring, an electrode being deposited on the pyroelectric target, and another electrode of annular shape being deposited. on the thin blade, a connection connecting these two electrodes separated by a layer of adhesive, the point of contact of this connection with the electrodes being situated towards the periphery of the electrodes, characterized in that the point of contact of this connection with the electrode deposited on the target is located in an angular sector of approximately 30 ° admitting for bisector one of the axes of least expansion of the target.

The invention makes it possible to obtain a gain of 50% on the average sensitivity of the tubes. A sensitivity of 8.5 uA / W was thus obtained with a target in triglyceride sulfate at 25 ° C. In addition, what is very important we have a solid assembly, which does not break.

• - la figure 1, une vue en coupe montrant une cible pyroélectrique et le montage utilisé selon l'art antérieur;
• - les figures 2 et 4, deux vues en coupe montrant une cible pyroélectrique et le montage utilisé selon deux modes de réalisation de l'invention;
• - la figure 3, une vue de dessus de la figure 2.

Other objects, characteristics and results of the invention will emerge from the following description, given by way of nonlimiting example and illustrated by the appended figures which represent:

• - Figure 1, a sectional view showing a pyroelectric target and the assembly used according to the prior art;
• - Figures 2 and 4, two sectional views showing a pyroelectric target and the assembly used according to two embodiments of the invention;
• - Figure 3, a top view of Figure 2.

In the different figures, the same references designate the same elements, but, for reasons of clarity, the dimensions and proportions of various elements are not observed.

Figure 1 has been described in the introduction to the description.

FIGS. 2 and 3 show a target assembled according to an embodiment of the invention, seen in section in FIG. 2 and seen from above in FIG. 3.

According to the invention, it is sought to position the point of contact with the electrode 4 deposited on the target of the connection between the two electrodes 4 and 5, near one of the axes of least expansion of the target.

It should be known that the pyroelectric target consists of a monocrystalline plate made of insulating material having a spontaneous electrical polarization which depends on its temperature.

Triglycocolle sulphate is generally used, designated by the letters TGS. or its fluorinated or deuterated derivatives, such as, for example, triglyceride fluoroberyllate or TGFB, or DTGS, or DTGFB.

The section of the pyroelectric blade is generally perpendicular to the pyroelectric axis. It can also be oblique to this axis.

The bodies used to make the pyroelectric target are very anisotropic and have two perpendicular axes of high expansion, corresponding to expansion in the opposite direction. Between these two axes, there are two other axes corresponding to zero expansion.

According to the invention, there is the point of contact of the connection between the two electrodes 4 and 5, with the electrode 4 deposited on the target, near one of the axes of least expansion.

Thus, there will be no rupture of the pyroelectric target.

FIG. 2 differs from FIG. 1 by the fact that the electrode 5 is of annular shape and by the presence of the connection 7 between the two electrodes 4 and 5.

In the embodiment of Figure 2, the connection 7 is made by inclusion in the adhesive layer 6 of a conductive material. This material can be for example metallic lacquer, graphite or conductive adhesive. The introduction of a hard product into the glue could cause the connection to break if care was not taken to position the contact point 8 of the connection 7 with the electrode 4 near one of the axes of least expansion of the target.

In Figure 2, the connection 7 is vertical.

In Figure 3, there is partially shown the target of Figure 2 and its assembly, seen from above. The two circles 10 and 11 corresponding to the internal diameter of the electrode 5 and to the internal diameter of the ring 3.

We have represented the two axes A, and A ₂ of strong expansion of the target which are perpendicular and the axes of least expansion of the target A ₃ and A ₄ . In FIG. 3, by way of example, the contact point 8 is placed near the axis A ₄ .

In fact, it is considered satisfactory to place the contact point 8, and generally also the entire connection 7, in an interval of approximately 30 ° centered on one of the axes of least expansion of the target.

It is necessary to place the contact point 8 as much as possible towards the periphery of the electrodes 4 and 5 so that it does not disturb the useful zone of the target.

The axes of least expansion can be determined using X-rays, from the determination of the crystal axes.

The axes of least expansion can also be determined by locating the crystal axes during the growth of the pyroelectric target.

The invention provides a method for determining these axes.

In the following description, the method according to the invention will be described in the case of a pyroelectric target consisting of a thin blade of TGS cut perpendicular to the pyroelectric axis.

This target is placed under a hot spring. One can for example use an incandescent lamp. The target is carried for example around 40 or 50 ° C.

Under the action of heat, the target bulges along an axis, for example the axis A, and becomes for example concave. One of the axes of strong expansion was thus determined.

If we continue to heat, for a few more minutes for example, the target bulges in the opposite direction and along an axis perpendicular to the first. For example, it becomes convex along the axis A ₂ .

By calculations well known to those skilled in the art, the angle 8 is determined between the axis of high positive expansion and the two axes of least expansion A ₃ and A ₄ . This angle depends in particular on the material used for the target.

In FIG. 3, the axis A ₂ is the axis of strong positive expansion and there is an angle θ of 63 ° between the axis A ₂ and the two axes A ₃ and A ₄ . These two axes are symmetrical with respect to axis A ₃ .

To determine which of the axes of strong dilation is the axis of positive dilation, one uses the crystalline axes of the target. These crystal axes can for example be indicated by the manufacturer of the targets.

The precision in determining the axes A ₃ and A ₄ is sufficient for the intended use.

It is of course sufficient to determine one of the axes Ai and A ₂ to obtain the axes A ₃ and A ₄ .

The determination of axes A ₃ and A ₄ can be used for something other than to position connection 7.

• - 1°) la cible est placée sous une source chaude;
• ­ 2°) on relève au moins l'un des axes perpendiculaires entre eux selon lesquels elle se déforme successivement et qui constituent ses axes de forte dilatation A₂, A₂;
• - 3°) on calcule l'angle θ entre l'axe de forte dilatation positive A2,qui est déterminé à partir de ses axes cristallins, et chacun des axes de moindre dilatation A₃, A₄.

In summary, the process for determining the axes of least expansion is as follows:

• - 1 °) the target is placed under a hot spring;
• 2) there is at least one of the axes perpendicular to each other along which it deforms successively and which constitute its axes of high expansion A ₂ , A ₂ ;
• - 3 °) the angle θ is calculated between the axis of strong positive expansion A2, which is determined from its crystalline axes, and each of the axes of least expansion A ₃ , A ₄ .

In Figure 4, there is shown in section another embodiment of the invention.

In this embodiment, the connection 7 is external. An orifice 9 is made on the target to connect the connection 7 to the electrode 4. The electrode 5, as can be seen in the figures, is easily accessible thanks to its large diameter. The orifice 9 must be produced without damaging the electrode 4 since contact must be resumed at this location.

The attack can be carried out by local dissolution of the crystal of the target, or also for example, by ionic attack or plasma attack, with masking.

The connection 7 can be as in the case of FIG. 2 produced by metallic lacquer or conductive paste.

Claims (4)

1. Picture taking tube comprising a pyroelectric target (1) fixed onto a thin lamella (2) stretched on a thick ring (3), an electrode (4) being deposited on the pyroelectric target-(1), and a further, annular electrode (5) being deposited on the thin lamella, a connection (7) connecting these two electrodes separated by a layer of adhesive (6), the contact point (8) of this connection (7) with the electrodes (4, 5) lying towards the periphery of the electrodes, characterized in that the contact point (8) of this connection (7) with the electrode (4) deposited on the target (1) is located within an angular sector of about 30°, admitting as a bisector one of the axes (A3, A4) of smaller expansion of the target.

2. Tube according to claim 1, characterized in that the pyroelectric target (1) is of triglycine sulfate or one of its fluorinated or deuterated derivatives.

3. Tube according to any of claims 1 and 2, characterized in that this connection (7) comprises an inclusion of conductive material within the adhesive layer (6) separating the two electrodes (4, 5).

4. Tube according to any of claims 1 to 3, characterized in thatthis connection (7) is external to the adhesive layer (6) separating the two electrodes (4, 5) and in that the connection with the electrode (4) covering the pyroelectric target (1) is provided through an orifice formed on this target.

Images