WO2015181172A1

WO2015181172A1 - A functionally radiolucent capacative pressure sensor

Info

Publication number: WO2015181172A1
Application number: PCT/EP2015/061593
Authority: WO
Inventors: Martin Bengtsson; Magnus DUSTLER; David BONDESSON; Amitoj DEO
Original assignee: Martin Bengtsson; Dustler Magnus; Bondesson David; Deo Amitoj
Priority date: 2014-05-28
Filing date: 2015-05-26
Publication date: 2015-12-03

Abstract

The invention relates to a pressure sensor comprising: at least an upper (101) and a lower (106) non-conductive layer; at least a first (102) and a second (105) conducting layer; and at least a first (103) and a second (104) spacing layer, wherein said upper non-conductive layer (101) is attached to said first conducting layer (102) which is attached to said first spacing layer (103) which is attached to said second spacing layer (104) which is attached to said second conducting layer (105) which is attached to said lower non-conductive layer (106) wherein said at least first (102) and second (105) conducting layers are connected to cables, and thereby forming a pressure sensor. The invention also relates to a pressure sensor array, a method of producing such pressure sensor and also the use of such pressure sensor array in an x-ray apparatus.

Description

A FUNCTIONALLY RADIOLUCENT CAPACATIVE PRESSURE SENSOR

TECHNICAL FIELD

The present invention relates to pressure sensors and specifically to capacitive pressure sensors that are radiolucent. The invention also relates to a pressure sensor array, a method of producing such pressure sensor and also the use of such pressure sensor array in an x-ray apparatus.

BACKGROUND

A medical x-ray examination involves the use of penetrating

electromagnetic radiation to image the internal anatomy of a patient. X-rays are attenuated by the matter they penetrate, with the resulting image being a function of the relative amount of absorption in each location, i.e. the intensity of the transmitted x-ray. X-ray attenuation is dependent mainly on the atomic number, Z, and the density of the traversed material.

For some medical applications it is important to be able to place sensors in such a way (e.g. on the patient) so that it is either necessary or preferable that they remain in the field-of-view during image acquisition. However, by placing the sensors in the field-of-view during image acquisition the sensor adversely affect the diagnostic quality of the x-ray image by obfuscating, due to absorption, the imaged organ.

In mammography, where you x-ray image a patient's breast, the examination may be experienced as being painful due to the fact that the breast has to be compressed to attain good image quality. One way of reducing the pain during the x-ray imaging is to monitor and adjust the compression of the breast and thereby reducing or completely eliminating the pain. The technique of monitoring and adjusting the compression of the breast has been disclosed in detail in the international patent application PCT/EP2014/057372. However, a drawback with this technique is that the pressure sensors that are used need to be in the field-of-view which, as discussed above, adversely affects the diagnostic quality of the x-ray image of the breast. Thus, having an x-ray transparent pressure sensor would therefore be highly sought after.

SUMMARY OF THE INVENTION

With the above description in mind, then, an object of the present invention is to provide a radiolucent pressure sensor, which seeks to mitigate, alleviate or eliminate one or more of the above-identified

deficiencies in the art and disadvantages singly or in any combination. More precisely, one object is to provide an x-ray transparent pressure sensor and a method of producing the same. The pressure sensor should especially be suitable to be used in mammography.

These and other objects are achieved by a pressure sensor comprising: at least an upper and a lower non-conductive layer; at least a first and a second conducting layer; and at least a first and a second spacing layer, wherein said upper non-conductive layer is attached to said first conducting layer which is attached to said first spacing layer which is attached to said second spacing layer which is attached to said second conducting layer which is attached to said lower non-conductive layer wherein said at least first and second conducting layers are connected to cables, and thereby forming a pressure sensor.

The pressure sensor described in this invention basically acts as a pressure sensitive capacitor, thus the input signal is pressure and the output signal is capacitance. The dielectric between the two capacitor plates consists of two layers: one elastic, deformable layer, and one mesh made of harder material preferably with air filled cavities. When the pressure on the pressure sensor increases the elastomeric layer is compressed. This results in a change in capacitance over the pressure sensor both due to a difference in dielectric thickness and a change in ratio between the air and the elastomeric layer. Thus, the pressure sensor can be described and modeled as a variable capacitor, where the variation depends on the deformation (strain) of the dielectric. A pressure sensor matrix with multiple individual pressure sensors can be created by using conductive layers to connect multiple sets of strain-variable capacitors.

The change in capacitance of the pressure sensor may, with proper calibration to known reference values, be employed to measure different physical quantities. In one embodiment, a force is applied to the pressure sensor, causing a deformation of the variable capacitor which is proportional to the applied force. Pressure, force per unit area, can be similarly measured if the contact area of the applied force is known.

According to (the international patent application WO 2014022641 A1 ) a wide range of materials can be used to create a similar pressure sensor for multitude of related applications. However, in the present application a requirement is that the combination of materials used for the construction of the sensor must be radiolucent so that it can be used in the field-of-view during for instance a mammography screening without adversely affecting the diagnostic quality of the x-ray image.

The main functionality of the pressure sensor is to respond to a physical input, and produce a corresponding output signal. The pressure sensor shall function in combination with machines that use electromagnetic radiation without the pressure sensor absorbing, scattering or disturbing such electromagnetic radiation in an appreciable manner. The pressure sensor shall thus be considered functionally radiolucent.

The present invention has shown to represent a pressure sensors meeting at least these requirements.

The upper and lower non-conductive layers may be comprised of Polymethyl methacrylate (PMMA) or any kind of non-conductive polymer having a low x-ray absorbance and no harmful effect on the skin of a person, such as cyclic olefin copolymers like Zeonor® or Topas®.

PMMA has shown to be a suitable material since it exhibits good surface properties when forming a base for the conductive layer to be applied thereto. Further, these materials are frequently used in x-ray applications and exhibit an equal and low absorption. This facilitates integration in an x- ray system as a whole. The first and second conducting layers may be comprised of Poly(3,4- ethyleneddioxythiophene) (PEDT) or any other conductive polymer such as polypyrrole or any 3,4,-ethylenedioxythiophene- (EDT-) based oligomer or copolymer.

Conductive polymers have shown to have a much lower absorbance in the x-ray spectrum compared to metal conductors. Also, EDT-based conductive polymers are among the most conductive polymers available today and the radiolucency is very close to that of PMMA.

The first spacing layer may be comprised of Polydimethysiloxane (PDMS) or any other similar elastomeric material. PDMS is a material that exhibits a favorable dielectric constant and that also exhibits favorable elastic properties for pressures used during e.g. mammography.

The second spacing layer may be comprised of Polyimide or any other photoresists such as SU-8®. The second spacing layer may be applied with a thickness adapted to fine tune the sensibility of the pressures to be applied.

The upper non-conductive layer may be thinner than or have the same thickness as said lower non-conductive layer. A thinner upper non-conductive layer has showed to give the sensor a finer spatial resolution.

Said first conductive layer and said second conductive layer may each comprise stripes of Poly(3,4-ethyleneddioxythiophene) (PEDT) or any other conductive polymer such as polypyrrole or any 3,4,-ethylenedioxythiophene- (EDT-) based oligomer or copolymer, wherein the stripes of the first and second conductive layers may be cross-aligned to each other. The point of intersection between the stripes in the resulting layered structure will form a pressure sensor. It goes without saying that there is no physical intersection between the stripes.

The first conductive layer may be arranged in a first specific pattern and said second conductive layer may be arranged in a second specific pattern, wherein the first and the second specific patterns of the first and second conductive layers respectively correspond to each other, whereby they together form a staggered pattern one on top of the other in said pressure sensor. Each point of intersection between the first and second patterns in the resulting layered structure will form a pressure sensor. The first and second patterns may in principle be any patterns, such as e.g.

separate squares, dots or other non-connected shapes. In the following such patterns are identified as specific patterns. It goes without saying that there is no physical intersection between the specific patterns in the different layers.

The second spacing layer may be arranged with through holes and/or cavities such that material from the first spacing layer is allowed to expand into said trough holes and/or cavities in said second spacing layer during a compression of said pressure sensor. The arrangement and size of the through holes and/or cavities may be used for focusing the deformation of PDMS to the individual sensors and thus increase the signal.

According to another aspect, the invention relates to a pressure sensor array comprising a plurality of pressure sensors of a design as given above.

According to yet another aspect, the invention relates to a method for forming a pressure sensor, the method comprising: - forming a first part by attaching at least a first conducting layer having cables to at least an upper non-conductive layer and at least a first spacing layer; - forming a second part by attaching at least a second conducting layer having cables to at least a lower non-conductive layer and at least a second spacing layer; and

- attaching the first spacing layer of the first part to the second spacing layer of the second part, thereby forming a pressure sensor.

The method results in the provision of a pressure sensor having the same advantages as previously discussed.

The first and second conducting layers may be provided by spin- coating on the upper non-conductive layer and lower non-conductive layer respectively. Spin-coating as such is a well established technology in thin film technology and is advantageous since it allows creation of layers of well defined thicknesses.

The first conducting layer may be provided by spin-coating on the upper non-conductive layer in a pattern forming stripes, and wherein the second conducting layer may be provided by spin-coating on the lower non- conductive layer in a pattern forming stripes with a 90 degree angle compared to the stripes on the first conducting layer. Accordingly, the stripes will form a rectilinear staggered pattern within the resulting layered structure. Each staggered point of intersection will constitute a pressure sensor in a pressure sensor array.

Alternatively, the first conducting layer may be provided by spin- coating on the upper non-conductive layer forming a specific pattern, and wherein the second conducting layer may be provided by spin-coating on the lower non-conductive layer in a specific pattern, whereby the specific patterns on the upper and lower non-conductive layers correspond to each other, whereby the specific patterns together form a staggered pattern one on top of the other in said pressure sensor.

According to yet another aspect, the invention relates to the use of a pressure sensor array of the type described above in an x-ray apparatus. The x-ray apparatus may by way of example be a mammographic apparatus used for mammography screening. The imaging steps in such apparatus consist of positioning the breast on a table. A compression plate in which a pressure sensor array of the inventive type is then lowered until a desired position and compression is acquired. The plate may e.g. have three speed settings. Before the breast is reached, the compression may be performed quickly until resistance is met. Next the compression velocity may be lowered partly for the patients comfort and partly for a possibility to optimize compression. The optimization may for instance be performed through specific settings in the machine that compares compression to applied force and stops when added force does not result in sufficient reduction of thickness. Also, the settings may be made to stop compression if the applied pressure on part of the breast reaches a pre-set level. The current force over the compression plate, as detected by said pressure sensors, may by way of example be measured with +/- 5 N accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

Further objects, features and advantages of the present invention will appear from the following detailed description of the invention, wherein embodiments of the invention will be described in more detail with reference to the accompanying drawings, in which:

FIG. 1 shows a block diagram of a pressure sensor array. The top part of the figure shows a separated view of the pressure sensor while the bottom part shows the complete pressure sensor according to an embodiment of the present invention; FIG. 2 shows an image of a pressure sensor array, according to an embodiment of the present invention, that was imaged using a

mammography system; and

FIG. 3a-d shows an image of a pressure sensor array, according to another embodiment of the present invention, which was imaged using a mammography system.

DETAILED DESCRIPTION

In the following one embodiment of the present invention relating to a pressure sensor will be described. The pressure sensor is composed as a layered structure having a cross section disclosed by Fig. 1 . For clarity, layers are not shown to scale. When describing the layered structure, reference is made to upper and lower to facilitate the understanding. It goes without saying that the layered structure during use may be oriented in any suitable manner.

The below specifics describe the construction of a pressure sensor array 100 suitable for measuring force or pressure. It should not be constructed as the only way in which such a pressure sensor array, or a pressure sensor array equivalent to it, can be constructed but merely as one possible embodiment. The pressure sensor array 100 may preferably be fabricated in thin film polymer layers. Polymers are in general more transparent to x-ray radiation compared to metals, and with the development of conductive polymers with high enough conductivity it has been shown to be possible to make the pressure sensor array 100 with a uniform absorbance, i.e. across its surface area. A single pressure sensor is not shown in any figure, however, a skilled person would understand that a single pressure sensor follows the same construction principles as discussed in conjunction with the pressure sensor array 100 in figure 1 .

The pressure sensor array 100 to be described in detail below comprises the following layered structure: an upper non-conductive layer 101 , a first conductive layer 102, a first spacing layer 103, a second spacing layer 104, a second conductive layer 105, and a lower non-conducting layer 106.

Starting with the upper most layer of the pressure sensor array 100, this is made of a non-conductive layer 101 forming a base material. The non- conductive layer 101 may be formed by any kind of polymer with low x-ray absorbance and without having any harmful effect on the skin of a person. In the disclosed embodiment, the non-conductive layer 101 is formed by Polymethyl methacrylate (PMMA). This material is advantageous since it is already used to fabricate compression plates in several mammographic setups. This material has also shown to exhibit good adhesion to the first conductive layer comprising Poly(3,4-ethyleneddioxythiophene) (PEDT) 102 to be attached thereto. Other examples of materials with the same properties are materials such as cyclic olefin copolymers like Zeonor^® or Topas^®.

The non-conductive layer 101 has a thickness within the range of 200 μιτι-3 mm and more preferred 250 μηη-400 μιτι.

A first conductive layer 102 is attached to the lower side of the first non-conductive layer 101 . In the disclosed embodiment the first conductive layer 102 is formed by PEDT, i.e. Poly(3,4-ethyleneddioxythiophene). PEDT is one of the most conductive polymers available today but may be

exchanged to another conductive polymer with equal attributes in conductivity such as polypyrrole or any 3,4,-ethylenedioxythiophene- (EDT-) based oligomer or be combined with any other material for stability or processing purposes, like in the commonly used combination PEDT/PSS (polystyrensulphonate) or PEDT in combination with carbon nanotubes or graphene.

The first conductive layer 102 is in the disclosed embodiment arranged as a plurality of parallel stripes of uniform width and thickness extending across the surface of the non-conductive layer 101 . It goes without saying that the invention should not be restricted to a pattern of parallel stripes. Other specific patterns, such as separate squares, dots or other non- connected shapes may by way of example be used. It goes without saying that there is no physical intersection between the specific patterns in the different layers.

The first conductive layer 102 has a thickness within the range of 1 -10 μιτι and more preferred 5-7 μιτι.

The first conductive layer 102 is connected to a first spacing layer 103 comprised of Polydimethysiloxane (PDMS) which is a type of silicone rubber that has many applications. PDMS is very elastic and has unique flexibility properties. The elasticity has shown to be important in the functionality of the pressure sensor array 100. During operation of the pressure sensor array 100, the material of the first spacing layer 103 deforms when a pressure is applied to the pressure sensor array 100 and then returns to its initial state, i.e. thickness, when pressure is no longer applied to it. It is biocompatible due to its relatively inert characteristics and is even used in breast implants which make it suitable for applications where the human body is involved. The first conductive layer 102 can be replaced with any other similar elastomeric material. However, PDMS has been shown to be favorable since it exhibits a relatively high dielectric constant, 2.3-2.8. A high value is favorable when used as a dielectric in a capacitor since it results in a higher capacitance. High in this context relates to air where the dielectric constant is around 1 .

The first spacing layer 103 has a thickness within the range of 30-120 μιτι and more preferred 50-100 μιτι. Now turning to the second spacing layer 104, this is in the disclosed embodiment formed by Polyimide. Polyimide has shown to be suitable due to its photolithographic properties and its rigidity. Like the first spacing layer, the second spacing layer 105 acts as a dielectric. In case of a Polyimide

Durimide ^® 7520, the dielectric constant is 3.2-3.3.

It is however possible to use most of the thick photoresists available on the market, such as, in one embodiment, SU-8^®.

The second spacing layer 104 has a thickness within the range of 2-50 μιτι and more preferred 15-20 μιτι.

The second spacing layer 104 is connected to a second conductive layer 105. In the disclosed embodiment the second conductive layer 105 is formed by PEDT, i.e. Poly(3,4-ethyleneddioxythiophene). PEDT is one of the most conductive polymers available today but may be exchanged to another conductive polymer with equal attributes in conductivity, such as polypyrrole or any 3,4,-ethylenedioxythiophene- (EDT-) based oligomer or be combined with any other material for stability or processing purposes, like in the commonly used combination PEDT/PSS (polystyrensulphonate) or PEDT in combination with carbon nanotubes or graphene.

Like the first conductive layer 102, the second conductive layer 105 is in the disclosed embodiment arranged as a plurality of parallel stripes of uniform width and thickness extending across the surface of the lower second non-conductive layer 106 to be disclosed. It goes without saying that the invention should not be restricted to a pattern of parallel stripes. Other specific patterns such as separate squares, dots or other non-connected shapes are possible. It goes without saying that there is no physical intersection between the specific patterns in the different layers

In the disclosed embodiment the stripes of the first and second conductive layers 102, 105 are cross-aligned to each other forming a rectilinear pattern.

The second conductive layer 105 has a thickness within the range of

1 -10 m and more preferred 5-7 μιτι. The second conductive layer 105 is attached to a lower most layer 106 of the pressure sensor array 100. During operation, the lower most layer 106 is intended to be in contact with the body part to be examined under compression.

The lower most layer 106 is made of a non-conductive layer 106 forming a base material. The non-conductive layer 106 may be formed by any kind of polymer with low x-ray absorbance and without having any harmful effect on the skin of a person. In the disclosed embodiment, the non- conductive layer 106 is formed by Polymethyl methacrylate (PMMA). This material is advantageous since it is already used to fabricate compression plates in several mammographic setups. This material has also shown to exhibit good adhesion to the second conductive layer comprising Poly(3,4- ethyleneddioxythiophene) (PEDT) 105 to be attached thereto. Other examples of materials with the same properties are materials such as cyclic olefin copolymers like Zeonor^® or Topas^®.

The lower non-conductive layer 106 has a thickness within the range of 200 μιτι-3 mm and more preferred 1 -3 mm.

During operation, such as during mammography, the lower non- conductive layer 106 will be arranged in contact with the stand whereas the upper non-conductive layer 101 will be in contact with the breast. It is preferred that the two layers differ in thickness, although it is possible to have the same thickness. The upper non-conducting layer 101 is preferably much thinner than the lower non-conducting layer 106. The reason for this is that a higher resolution is achieved, since a pressure at one point will not affect other areas on the upper non-conducting layer 101 . The lower nonconducting layer 106 is preferably much thicker than the upper nonconducting layer 101 . A higher thickness has shown to provide structural stability to the pressure sensor array 100.

In the following one method of manufacturing the pressure sensor array will be described.

The lower non-conducting layer 106 of PMMA is in contact with the second conducting layer 105 of PEDT which is a polymer with very robust characteristics. The second conducting layer 105 of PEDT material is also highly conductive and is for that reason used in the pressure sensor. This polymer can be coated onto several materials by either spin-coating or by a printing technique. In the pressure sensor array 100, the first and second conducting layers 102,105 of PEDT are spin-coated as stripes, see figure 1 .

To create a pressure sensor array 100, the first and second

conducting layers 102,105 of e.g. PEDT stripes are cross-aligned (see figure 1 ) to create a matrix. Alternatively the first and second conducting layers 102,105 can be coated on as separate capacitor areas, individually connected and addressed or in a combination with one large bottom capacitor plate and smaller individual top plates.

In the fabrication of the pressure sensor array 100, spin-coating with in-situ polymerization to form the first and second conducting layers 102,105 films may be used but it is possible to use any off-the-shelf pre-polymerized solutions from several vendors. The patterning of the polymerized films may be achieved by lift off, laser ablation, Reactive Ion Etching, screen printing, or any similar technique.

On the second conductive layer 105 of PEDT, a second spacing layer 104 of polyimide (Durimide^®) is spin-coated. A pattern is created in this layer (see figure 1 ) through photolithography processes. The reason for this material to be patterned has to do with the fact that the first spacing layer 103 of PDMS that is in contact with the second spacing layer 104 has to have somewhere "to go" , i.e. expand into, when pressure is applied over the sensor, resulting in an improvement in the resolution of the pressure sensor. Thus, the second spacing layer 104 is arranged with through holes and/or cavities such that material from the first spacing layer 103 can expand into said holes and/or cavities in said second spacing layer 104 when pressure is applied to the pressure sensor array 100.

On the first spacing layer 103 of PDMS, the structures of the first conductive layer 102 are created by spin-coating, as can be seen in figure 1 . In one embodiment, if the first conducting layer 102 of PEDT is spin-coated on the upper non-conductive layer 101 as stripes (see above), this layer is spin-coated with a 90 degree angle compared to the second conducting layer 105 of PEDT that is spin-coated on the lower non-conductive layer 106 of PMMA. The result of all this is that a pressure sensor matrix is achieved, where each crossing of the first and second conductive layers 102,105 of PEDT creates one pressure sensor each. Accordingly, by such matrix, a pressure sensor array 100 may be formed comprising a plurality of pressure sensors. It goes without saying that there is no physical contact between the conducting layers in said crossings.

An alternative embodiment of the first conductive layer 102 of PEDT is to be made into a number of separate squares, dots or other non-connected shapes, i.e. specific patterns, and matching identical squares, dots or non- connected shapes, on the second conductive layer 105 of PEDT in such a way that they line-up with each other in a staggered fashion in the layered pressure sensor array 100 forming a sandwich construction.

In one embodiment, the three top layers 101 , 102, 103 in the sandwich construction in figure 1 of the pressure sensor array 100 may be created separately, forming a first part, and the three bottom layers 104, 105, 106 of the pressure sensor array 100 may also be created separately, forming a second part. The first and the second part are then aligned and put together, either manually or automatically, thereby completing the pressure sensor array 100 as seen in figure 1 . Since the adhesion of PDMS 103 on polyimide 104 is sufficiently strong, no process of construction is necessary to fasten them.

It goes without saying that all layers 101 -106 may be created in a single process.

The pressure sensor array 100 read-out may be accomplished by attaching connecting cables to the first and second conductive layers

102,105 of each individual pressure sensor and measuring capacitance.

If the conductive layers 102, 105 of the pressure sensor array 100 consist of connected stripes as described above, an alternative embodiment of the invention is to have only one connecting cable attached to each stripe, whereby capacitance may be measured separately between each pair of stripes. Capacitance for individual pressure sensors may then be calculated through solving the resulting system of equations, with the number of equations and number of variables both equal to the square of half the number of stripes.

A pressure sensor arrayl 00 of the type exemplified above was successfully tested for pressures between 0-40kPa. Pressure sensors with only one PEDT stripe (resulting in a single pressure sensor) were also fabricated. These sensors were successfully tested in the range of 0-60kPa.

A pressure sensor array 200 according figure 1 was imaged with an existing mammography system with a cesium-Iodine detector as shown in figure 2, where the image was taken at a setting of 28 kV at 56mAs, which are close to those used in regular breast screening. This is not to be construed as that the pressure sensor array 100,200 is suitable only for use on such systems at such energies, but is included for illustrative purposes only.

Through the image seen in figure 2, statistical information was extracted from the circumscribed areas seen in figure 3a to figure 3d. The mean value and standard deviation of pixel values in the images, converted to grayscale images, were the basis of analysis. Figure 2 shows an x-ray image of the sensor where the PEDT material in the pressure sensor cannot be seen in the image. The thinner PMMA layer is 201 , the thicker PMMA layer is 202. Number 203 represents a conductive epoxy used to attach the cables 204.

Figure 3a shows an image with only PEDT on one of the halves of the pressure sensor in stressed area 301 . This is called No PEDT1 in table 1 . Figure 3b shows an image with only PEDT on one of the halves of the pressure sensor in stressed area 303. This is called no PEDT2 in table 1 . Figure 3c 400 shows an image with PEDT on both halves of the sensor in stressed area 401 . This is called PEDT1 in table. Figure 3d shows an image with PEDT on both halves of the pressure sensor in the stressed area 403. This is called PEDT2 in table 1 . 301 , 303, 401 and 403 are the pixilated areas chosen for statistical evaluation. Since no visual effect can be seen comparing the areas, argument can be made that the layer seems to be radiolucent.

In figure 2 the image of the pressure sensor can be seen. The pressure sensor is placed on top of a slab of PMMA to protect the detector. The visible sensor backing material, PMMA in this case, is equivalent in absorption to the compression plate that would be used in a breast examination, and as in one embodiment of the invention, the pressure sensor may be integrated directly with this compression plate. This does not impair imaging. The only other visible parts in the image are cables and the conductive epoxy that is used to attach the cables. Looking at the parts that are covered with more PEDT (the sensor elements) no statistically significant difference is noticed compared to other parts of image. This must be construed to mean that the pressure sensor's absorption is too low for it to register on an x-ray image, thus strengthening previous claim of the pressure sensors radiolucent characteristics.

Measurement show the average pixel values and standard deviation in specified regions. Regions are shown in figure 3a to figure 3d.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" "comprising," "includes" and/or "including" when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. The foregoing has described the principles, preferred embodiments and modes of operation of the present invention. However, the invention should be regarded as illustrative rather than restrictive, and not as being limited to the particular embodiments discussed above.

The different features of the various embodiments of the invention can be combined in other combinations than those explicitly described. It should therefore be appreciated that variations may be made in those embodiments by those skilled in the art without departing from the scope of the present invention as defined by the following claims.

Claims

1 . A pressure sensor comprising:

at least an upper (101 ) and a lower (106) non-conductive layer;

at least a first (102) and a second (105) conducting layer; and at least a first (103) and a second (104) spacing layer, wherein said upper non-conductive layer (101 ) is attached to said first conducting layer (102) which is attached to said first spacing layer (103) which is attached to said second spacing layer (104) which is attached to said second conducting layer (105) which is attached to said lower non-conductive layer (106), wherein said at least first (102) and second (105) conducting layers are connected to cables, and thereby forming a pressure sensor.

2. The pressure sensor according to claim 1 , wherein the upper (101 ) and lower (106) non-conductive layers are comprised of Polymethyl methacrylate (PMMA) or any kind of non-conductive polymer having a low x- ray absorbance and no harmful effect on the skin of a person such as cyclic olefin copolymers like Zeonor® or Topas®.

3. The pressure sensor according to claim 1 or 2, wherein the first (102) and second (105) conducting layers are comprised of Poly(3,4- ethyleneddioxythiophene) (PEDT) or any other conductive polymer such as polypyrrole or any 3,4,-ethylenedioxythiophene- (EDT-) based oligomer or copolymer.

4. The pressure sensor according to any of claims 1 -3, wherein said first spacing layer (103) is comprised of Polydimethysiloxane (PDMS) or any other similar elastomeric material.

5. The pressure sensor according to any of claims 1 -4, wherein said second spacing layer (104) is comprised of Polyimide or any other photoresists such as SU-8®.

6. The pressure sensor according to any of claims 1 -5, wherein said upper non-conductive layer (101 ) is thinner than or has the same thickness as said lower non-conductive layer (105).

7. The pressure sensor according to any of claims 1 -6, wherein said first conductive layer (102) and said second conductive layer (105) each comprises stripes of Poly(3,4-ethyleneddioxythiophene) (PEDT) or any other conductive polymer such as polypyrrole or any 3,4,-ethylenedioxythiophene- (EDT-) based oligomer or copolymer, wherein the stripes of the first and second conductive layers (102, 105) are cross-aligned to each other.

8. The pressure sensor according to any of claims 1 -6, wherein said first conductive layer (102) is arranged in a first specific pattern and said second conductive layer (105) is arranged in a second specific pattern, wherein the first and the second specific patterns of the first and second conductive layers(102, 105) respectively correspond to each other, whereby they together form a staggered pattern one on top of the other in said pressure sensor.

9. The pressure sensor according to any of claims 1 -8, wherein said second spacing layer (104) is arranged with through holes and/or cavities such that material from the first spacing layer (103) is allowed to expand into said trough holes and/or cavities in said second spacing layer (104) during a compression of said pressure sensor.

10. A pressure sensor array (100) comprising a plurality of pressure sensors according to claims 1 -9.

1 1 . A method for forming a pressure sensor, the method comprising: - forming a first part by attaching at least a first conducting layer

(102) having cables to at least an upper non-conductive layer (101 ) and at least a first spacing layer (103) ; - forming a second part by attaching at least a second conducting layer (105) having cables to at least a lower non-conductive layer (106) and at least a second spacing layer (104) ; and

- attaching the first spacing layer (103) of the first part to the second spacing layer (104) of the second part, thereby forming a pressure sensor.

12. The method of claim 1 1 , wherein said first and second conducting layers (102, 105) are provided by spin-coating on the upper non-conductive layer (101 ) and lower non-conductive layer (106) respectively.

13. The method of any of claims 1 1 -12, wherein the first conducting layer (102) is provided by spin-coating on the upper non-conductive layer (101 ) in a pattern forming stripes, and wherein the second conducting layer (105) is provided by spin-coating on the lower non-conductive layer (106) in a pattern forming stripes with a 90 degree angle compared to the stripes on the first conducting layer (102).

14. The method of any of claims 1 1 -12, wherein the first conducting layer (102) is provided by spin-coating on the upper non-conductive layer (101 ) forming a specific pattern, and wherein the second conducting layer (105) is provided by spin-coating on the lower non-conductive layer (106) in a specific pattern, whereby the specific patterns on the upper and lower non- conductive layers (101 , 106) correspond to each other, whereby the specific patterns together form a staggered pattern one on top of the other in said pressure sensor.

15. Use of a pressure sensor array (100) according to any of clams 1 -

10 in an x-ray apparatus.