Patent Application
20180190897
This invention generally relates to the field of sensor technology.
A piezoelectric sensor can be used to measure pressure, force, acceleration, or strain by converting mechanical stress to electrical charge. It can also be used to generate sound by converting electrical charge to mechanical waves. In Structural Health Monitoring (SHM) applications, the piezoelectric sensors can be used to generate and receive ultrasonic waveforms to detect structural damages. The main component of a piezoelectric sensor is a two-sided piezo ceramic component. One side of the piezo ceramic component is bonded to the target structure permanently to send and receive ultrasonic signals. A typical piezoelectric sensor for SHM is thin, rigid, and very fragile. The sensor electrodes are can easily get electrically shorted when the sensor is mounted to the target structure if the surface of the target structure is electrically conductive. This can negatively affect the performance of the sensor. Similarly, when multiple sensors are mounted to the target structure, these sensors could be electrically shorted together. Therefore, it requires great care to bond the piezoelectric sensor to the target structure. One approach is to mount the piezoelectric sensor to a flexible circuit and glue the flexible circuit to the structure with epoxy. This approach provides better protection than bare piezoelectric sensors, but the piezoelectric sensors can still be damaged during the installation process if the flexible circuit is bent on the piezo disc area, and it is still very easy to short the sensor electrodes with the target structure. Installation of such flexible circuit piezoelectric sensors also requires extensive labor and special tools, such as vacuum bags and air pumps. After installation, the piezoelectric sensors, even protected by the flexible circuits, are still vulnerable to external impacts and strains. Therefore, it is desirable to have a mechanically strengthened piezoelectric sensor for SHM that is easy to install, resistant to external impacts, and more robust in operation.
The present invention discloses a mechanically strengthened piezoelectric sensor for SHM applications. In one embodiment, the sensor includes a two-sided piezo ceramic component, a sensor encapsulation, and at least two wires. The sensor encapsulation has an indented side that forms a recessed area. There is a supporting structure inside the recessed area. The supporting structure may be manufactured as an integral part of the encapsulation (e.g., through injection molding). Alternatively, the supporting structure may be manufactured separately and assembled inside the recessed area of the encapsulation. The two-sided piezo ceramic component has at least two electrodes. It is mounted into the recessed area of the encapsulation and is supported by the supporting structure inside the encapsulation with the side facing outwards slightly lower than the upper edge of the recessed area. The supporting structure of the encapsulation provides mechanical strength to the piezo ceramic component. The wires are attached to the electrodes of the piezo ceramic component and extend outside the encapsulation.
In another embodiment, the mechanically strengthened piezoelectric sensor further includes a Printed Circuit Board (PCB). The piezo ceramic component is soldered on the PCB. Then, the PCB is mounted into the recessed area of the encapsulation and is supported by the supporting structure. The supporting structure inside the encapsulation provides mechanical strength to the PCB. The wires are attached to the PCB and electrically connected to the electrodes of the piezo ceramic component. The wires also extend outside the encapsulation.
The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and also the advantages of the invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings. Additionally, the leftmost digit of a reference number identifies the drawing in which the reference number first appears.
This invention discloses a mechanically strengthened piezoelectric sensor for SHM applications. In one embodiment, the sensor includes a two-sided piezo ceramic component, a sensor encapsulation, and at least two wires. The two-sided piezo ceramic component is mounted into the encapsulation directly. There is a supporting structure inside the encapsulation to provide mechanical strength to the piezo ceramic component. The wires are attached to the electrodes of the piezo ceramic component and extend outside the encapsulation.
In another embodiment, the mechanically strengthened piezoelectric sensor further includes a PCB. The piezo ceramic component is soldered on the PCB. Then, the PCB is mounted into the encapsulation. There is a supporting structure inside the encapsulation to provide mechanical strength to the PCB. The wires are attached to the PCB and electrically connected to the electrodes of the piezo ceramic component. The wires also extend outside the encapsulation. The wires can be but are not limited to coaxial cable or twisted wire.
The encapsulation can be made of different materials to meet mechanical and environmental requirements. Typical materials include but are not limited to metal, plastic, ceramic, composite, rubber or a combination of the above. The shape of the encapsulation can be round, triangle, square, rectangular or others. The encapsulation is designed to improve strength, resist impacts, and simplify the installation process.
In one embodiment of the invention, the encapsulation has an indented side that forms a recessed area. The piezo ceramic component or the PCB is installed inside the recessed area with the side of the piezo ceramic component facing outwards slightly lower than the upper edge of the recessed area. This design allows maximal contact area between the piezo ceramic component and the target structure, while preventing short circuit between the piezoelectric sensor and the structure. Most environmental impacts, tensile forces, and vibrations are absorbed by the encapsulation, shielding the piezo ceramic component. To install the sensor to the target structure, one can apply pressure to the encapsulation, without touching the piezo ceramic component. Since the piezo ceramic component is slightly lower than the upper edge of the encapsulation, the encapsulation takes the pressing force and protects piezo ceramic component. Moreover, the small gap between the piezoelectric sensor and the target structure prevents potential electrical short circuit. The gap should be filled with epoxy or glue to allow the ultrasound wave transfer between the piezoelectric sensor and the structure. No special tools, such as vacuum bags and air pumps, are required during installations and this design significantly simplifies the installation.
In another embodiment of the invention, the encapsulation has an opening to allow the wires to extend outside the encapsulation. The opening can be on the sidewall of the encapsulation or on the bottom side of the encapsulation. When the opening is on the sidewall of the encapsulation, the opening can be large enough to be on the same level as the upper edge and the bottom edge of the encapsulation, or just a hole through the sidewall of the encapsulation. The encapsulation may have extensions around the opening to hold the wires in place to further protect the wire and the piezo ceramic component from external pushing or pulling forces. The wires can be further protected and/or held by adding an optional protection layer, such as a plastic tube or a heat shrinkable tube.
In one embodiment, glue, epoxy or other non-conductive material is used to fill the gap between the piezo ceramic component and the encapsulation as well as the gap between the wires coming out of the encapsulation and the encapsulation and/or the extension to add additional strength. Waterproof materials and wires may be used to make the piezoelectric sensor waterproof.
In another embodiment of the invention, multiple piezo ceramic components and/or PCBs are protected by a single encapsulation. The encapsulation is designed to support multiple piezo ceramic components and/or PCBs. In another embodiment of the invention, multiple piezo ceramic components are mounted to a single PCB. The PCB is designed to support multiple piezo ceramic components. When multiple piezo ceramic components and/or PCBs are protected by a single encapsulation, each piezo ceramic component and/or PCBs has its attached wires coming out of the encapsulation separately. Alternatively, the piezo ceramic component and/or PCBs can be connected in serial and the wires of the serial connection come out of the encapsulation.
Although specific embodiments of the invention have been disclosed, those having ordinary skill in the art will understand that changes can be made to the specific embodiments without departing from the spirit and scope of the invention. The scope of the invention is not to be restricted, therefore, to the specific embodiments. Furthermore, it is intended that the appended claims cover any and all such applications, modifications, and embodiments within the scope of the present invention.
This application claims priority to U.S. provisional patent application Ser. No. 62/442,049, filed Jan. 4, 2017, the entire content of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62442049 | Jan 2017 | US |
