DEVICE FOR DETECTING STRAINS AND TRANSMITTING DETECTED DATA

Abstract

A device for detecting strains and transmitting detected data that can be applied to the surface of a structure to be monitored or incorporated in the structure is provided. The device allows to reliably acquire and transmit data concerning the strains undergone by the structure. The device comprises a matrix made of an electrically insulating material, in which at least one or more strain sensors, an electronic circuit and an antenna electrically connected to one another are embedded. One or more strain sensors are made of a material selected from metals and metal alloys, electrically conductive resins and electrically conductive inks.

Claims

1. A device for detecting strains and transmitting detected data, which device comprises an electrically insulating matrix in which there are embedded at least: one or more strain sensors, made as resistive conductive elements, the dimensional variations of which bring about variations of electrical resistance; an electronic circuit electrically connected to the one or more sensors and adapted to detect the variations of electrical resistance; an antenna electrically connected to said electronic circuit, wherein the one or more strain sensors are made of a material selected from the group consisting of metals and metal alloys, electrically conductive resins and electrically conductive inks.

2. The device according to claim 1, wherein the one or more strain sensors are made of an electrically conductive resin.

3. The device according to claim 1, wherein the one or more strain sensors are made of an electrically conductive ink.

4. The device according to claim 1, wherein the electronic circuit and the antenna are made on one and the same printed circuit board.

5. The device according to claim 4, wherein the printed circuit board is made as a flexible printed circuit board.

6. The device according to claim 1, wherein a shielding layer is further embedded in said electrically insulating matrix.

7. The device according to claim 6, wherein the shielding layer is made of a ferritic material.

8. The device according to claim 6, wherein a further conductive layer is associated to the shielding layer.

9. The device according to claim 1, further comprising, within the electrically insulating matrix, one or more sensors adapted to detect environmental conditions of the environment surrounding the device.

10. The device according to claim 1, comprising two strain sensors arranged at 90 relative to each other.

11. The device according to claim 1, comprising three strain sensors arranged at 120 relative to one another.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Characteristics and advantages of the invention will become more apparent from the following detailed description of a preferred embodiment of the invention, given by way of non-limiting example with reference to the annexed drawings, in which:

[0044] FIG. 1 is a cross-sectional schematic view of a device for detecting strains and transmitting detected data according to the invention;

[0045] FIG. 2 is a sectional schematic view taken along the plane II-II of the device of FIG. 1.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

[0046] Referring to FIGS. 1 and 2, there is illustrated a device 1 according to the invention for detecting strains and transmitting detected data.

[0047] According to the invention, said device comprises an electrically insulating matrix 3, in which there are embedded at least: [0048] a strain sensor 5, made as a resistive conductive element, the dimensional variations of which (caused by an applied load) bring about variations of its electrical resistance; [0049] an electronic circuit 7 comprising means for detecting said electrical resistance variations of said strain sensor 5; [0050] an antenna 9;
wherein said strain sensor 5 is made of a material selected from the group comprising metals and metal alloys, electrically conductive resins and electrically conductive inks.

[0051] It is apparent that said strain sensor 5 and said electronic circuit 7 will be electrically connected to each other, for example at corresponding contacts or pads 11, and also said electronic circuit 7 and said antenna 9 will be electrically connected to each other, for example at corresponding contacts or pads 13.

[0052] The strain sensor 5 can have the desired size and shape. More particularly, the use of electrically conductive resins and electrically conductive inks allows high versatility, increasing the degrees of freedom in choosing the size and shape of the sensor; advantageously, the sensor can have a large size, much larger than that of strain sensors used in prior art, and its geometry can follow complex patterns.

[0053] The electronic circuit 7 and the antenna 9 can be made according to any suitable technology within the reach of those skilled in the art.

[0054] In the embodiment shown in the Figures, said electronic circuit 7 and said antenna 9 can be made on one and the same printed circuit board (PCB) 15.

[0055] More particularly, said printed circuit board 15 is preferably made as a flexible printed circuit board, obtained for instance from a film of polyamide or a PEEK-type synthetic fabric, whereby the corresponding device 1 as a whole will exhibit some flexibility, which will allow it to adapt to structures having complex surfaces.

[0056] The device 1 according to the invention may further comprise one or more sensors (not illustrated) adapted to detect the environmental conditions of the environment surrounding the device itself, such as temperature and humidity.

[0057] If provided, said additional sensors too will be electrically connected to the electronic circuit 7 by means of corresponding contacts or pads.

[0058] The electronic circuit 7 may further comprise a memory unit allowing to store information about the device 1 and about the data detected by said device during its operation. More particularly, said memory device allows to permanently store in the sensor all the information necessary to interpret the effected detections (including the parameters for calibration of the sensor) and to identify the sensor. When a complex structure is to be monitored, requiring use of large number of devices 1, this considerably simplifies management by eliminating the need to maintain specific external documentations, which are complex to manage and potentially subject to becoming detached or lost.

[0059] Still referring to the embodiment shown in the Figures, the device 1 further comprises a shielding layer 17 associated to the printed circuit board 15.

[0060] Said shielding layer 17 is preferably made of a ferritic material and its function will become apparent from the description of the operation of the device 1 according to the invention provided here below.

[0061] As anticipate above, said device 1 can be applied to a newly built structure as well as to an already existing structure.

[0062] The sensing part of the device, consisting of the strain sensor 5 and the electronic circuit 7 connected thereto, is protected from external agents by the matrix 3.

[0063] Said matrix 3 not only protects the strain sensor and its electronic circuit from atmospheric agents, but it also electrically isolates them, owing to the fact that it is made of an electrically insulating material.

[0064] The antenna 9 allows to communicate wirelesslyfor example through radio-frequencywith an external instrument 100.

[0065] In a particularly simple variant of the invention, the instrument 100 is able to receive the transmitted data from the antenna 9. In this case, the device 1 must be provided with its own power supply means (batteries) for exciting the strain sensor 5 and supplying the electronic circuit 7.

[0066] However, in the preferred embodiment of the invention, the wireless communication between the device 1 and the tool 100 takes place in both directions, as also shown in FIG. 1. In this way, it is possible to avoid equipping the device 1 with an internal power supply source, as the energy necessary for its operation comes from the external instrument 100, via radio-frequency or similar wireless mode.

[0067] Therefore, when it is desired to detect strains undergone by the structure to which the device 1 is applied, the external instrument 100 supplies the device 1 with the energy required to excite the strain sensor 5.

[0068] The dimensional variation undergone by the strain sensor due to the load (stress) to which it is subjected results in a corresponding variation of its electrical resistance; said electrical resistance variation is detected by the electronic circuit 7 and transmitted to the external instrument 100 through the antenna 9.

[0069] In the case in which additional sensors suitable for the detection of environmental conditions (temperature, humidity, etc.) are provided, also the data detected by said additional sensors are processed by the electronic circuit 7 and transmitted to the external instrument 100 through the antenna 9.

[0070] It is to be noted that the excitation energy can be supplied to the strain sensor 5 simultaneously with the interrogation thereof; alternatively, it is possible to provide for supplying power to the strain sensor 5 and interrogating it at different times, while equipping it at the same time with means for storing power (either wirelessly rechargeable from the outside or disposable).

[0071] It will be evident that the operations of detection and transmission of data described above may take place continuously or discretely, and in the latter case they may take place at regular and predetermined time intervals or upon the user's input.

[0072] The importance of providing the shielding layer 17 associated to the printed circuit board 15 of the device 1 according to the invention will also be evident from the foregoing description.

[0073] Since the radio-frequency communication between the device 1 and the external instrument 100 is a short distance communication, the magnetic component of the radio-frequency emission is the one of greatest importance. The presence of conductive materials in the structure to which the device 1 is applied (carbon, reinforced concrete, metals and so on) near the antenna 9 disturbs or cancels the communication, because of eddy currents that the radio-frequency emission generates in such materials. These eddy currents in turn generate a magnetic field symmetrical and opposite to the field of the radio-frequency emission, which is thus attenuated or canceled.

[0074] In the case of the device according to the invention, the problem posed by eddy currents is even more serious, since not only must the radio-frequency communication from the antenna 9 to the external instrument 100 be preserved from the influence of said eddy currents in order to correspondingly preserve the accuracy of the transmitted data, but it is also necessary that the external instrument 100 transmits to said device 1 sufficient energy to properly excite the strain sensor 5 without any negative influence by said eddy currents. Hence the importance of the shielding layer 17.

[0075] As mentioned above, said shielding layer is made of a ferritic material.

[0076] In this regard it is to be noted that said ferritic material should preferably be chosen depending on the conductive materials in the structure to which the device 1 is applied, so that the shielding effect is optimized according to the specific characteristics of the magnetic field generated by the eddy currents. This is possible when the final destination of the device 1that is, the type of structure to which the device will be applied and the materials that compose itis already known at the production stage.

[0077] However, there are cases in which a universal device for detecting strains is desired, i.e. a device having a behaviour which is effective whatever its final destination may be. In these cases it is possible to provide for associating to the shielding layer 17 a further conductive layer (not shown) with known characteristics on the basis of which the choice of the ferritic material of the shielding layer 17 has been calibrated. This further conductive layer can be made (for example) of carbon. Since said conductive layer is closer than the conductive materials of the structure to be monitored to the shielding layer 17, the magnetic field generated in said conductive layer is much stronger than that generated in said structure. It follows thatbeing the ferritic material chosen on the basis of the characteristics of said conductive layerthe device 1 according to the invention is effectively shielded whatever the characteristics of the structure to which it is associated may be.

[0078] It is clear from the above that thanks to the structure of the device 1 according to the invention it is therefore possible to correctly detect the strains undergone by the associated structure and transmit the detected distance data to an external instrument 100.

[0079] The absence of wire connections allows to apply, to the same structure, a large number of devices for strain detection according to the invention and ensures a considerable freedom in the choice of the positions in which said devices can be applied.

[0080] It also ensures a great flexibility, since the number and the position of the devices for strain detection according to the invention can be varied over time depending on the specific needs that may arise from time to time.

[0081] It is possible to provide for associating to each of the devices according to the invention a corresponding external instrument (for example in the case of applications where strain detection should take place in a continuous manner), or using only one external instrument in association with all the devices according to the invention (for example in the case of applications in which such devices are interrogated only at discrete time intervals).

[0082] Therefore, it is evident that the invention achieves the objects set forth above, as it provides a device which allows to detect strains and transmit detected data with great accuracy and reliability, while at the same time showing great simplicity and versatility in terms of practical application.

[0083] It will also be evident that the embodiment described above with reference to the accompanying drawings has been given merely by way of non-limiting example, and that modifications and variations within the reach of those skilled in the art may be made without departing from the scope of protection defined by the appended claims.

[0084] For example, although in the illustrated embodiment the device includes only one strain sensor, it is also possible to use multiple strain sensors, for example two strain sensors arranged at 90 relative to each another, three strain sensors arranged at 120 relative to one another, and so on.