GB2597105A

GB2597105A - Wireless sensor

Info

Publication number: GB2597105A
Application number: GB2010925.2A
Authority: GB
Inventors: Zhong Chenghuan
Original assignee: Inductosense Ltd
Current assignee: Inductosense Ltd
Priority date: 2020-07-15
Filing date: 2020-07-15
Publication date: 2022-01-19
Anticipated expiration: 2040-07-15
Also published as: GB202010925D0; GB2597105B

Abstract

A wireless ultrasound non-destructive testing (NDT) sensor 404 which emits a pulse of ultrasound energy into a test object and receives an echo signal. The sensor comprises an ultrasound transducer 406 and an induction coil 408. The internal diameter of the induction coil is smaller than the outer diameter of the ultrasound transducer, which provides an improved inductive coupling between the sensor and a remote energising device. The sensor is arranged for the coil to be positioned in parallel with the ultrasound transducer. The induction coil and ultrasound transducer are positioned side by side in a non-overlapping arrangement, which inhibits interference in use.

Description

WIRELESS SENSOR

Technical Field

The invention relates to a wireless sensor for non-destructive testing.

Background to the Invention

Non-destructive testing (NDT) is used extensively across a range of industries to evaluate the properties of a test object without causing damage to the test object. Examples of test objects include composite aircraft panels, gas-turbine engine components, pipelines and pressure vessels.

It is known to integrate an NDT sensor into a test object in order to provide, for example, reliable repeatable measurement and/or in situ monitoring while the test object is in service. For example, it is known to integrate an ultrasound sensor in or on a test object.

Furthermore, it is known to provide wireless integrated NDT sensors that can be inductively coupled to a remote device. The inductive coupling enables power to be provided to the integrated sensor from the remote device in a similar manner to known radio-frequency identification (RFID) modules. The inductive coupling can also be used for the transfer of measurement information from the integrated sensor back to the remote device.

However, the present inventors have identified that the operable distance or range between the NDT sensor and the remote device required for inductive coupling is limited in known systems, particularly for sensors operated at high frequency such as ultrasound sensors.

Summary of Invention

In accordance with a first aspect of the invention, there is provided a wireless ultrasound non-destructive testing (NDT) sensor for emitting a pulse of ultrasound energy into a test object and receiving an echo signal from the emitted pulse, the sensor comprising: an ultrasound transducer having an outer diameter; and an induction coil having an internal diameter, the induction coil being electrically coupled to the ultrasound transducer; wherein the internal diameter of the induction coil is smaller the outer diameter of the ultrasound transducer and the sensor is arranged for the coil to be positioned, in use, in parallel with the ultrasound transducer.

Thus, a wireless ultrasound NDT sensor according to the first aspect has a coil having an inner diameter which is smaller than the outer diameter of the transducer. The present inventors were surprised to discover that this provides an improved inductive coupling between the sensor and a remote energising device such as an inspection wand. Moreover, the sensor is arranged such that the coil is positioned at the side of the transducer, rather than on top of it, which the inventors have found to inhibit interference in use.

The term "in parallel" can mean that the sensor is arranged for the coil to be positioned on a test object next to the transducer in a side by side, non-overlapping arrangement. In some cases the sensor can be arranged for the coil to be positioned on a test object next to the transducer a spaced arrangement. The faces of the coil and transducer which are arranged to be closest to the test object can be positioned in the same plane for ease of attachment to the test object.

The outer diameter of the ultrasound transducer can be no greater than twice the internal diameter of the induction coil. This arrangement can maximise the coupling range between the sensor and a remote energising device such as an inspection wand. The inner diameter of the induction coil can be smaller than the outer diameter of the transducer by a factor of at least 1.01 and preferably by a factor of at least 2.

The inner diameter of the induction coil can be at least 10% smaller than the outer diameter of the ultrasound transducer. This arrangement can maximise the inductive coupling between the sensor and a remote energising device such as an inspection wand.

The induction coil can be a planar induction coil having a plurality of turns, each turn being electrically coupled to other turns of the coil.. A planar coil can provide the senor with a low profile which can result in it being easily mounted within a test object. The coil can be arranged with a plurality of generally concentric turns, electrically coupled in series, An innermost turn of the induction coil can define the internal diameter and an outermost turn of the coil can define an outer diameter of the coil. The outer diameter of the coil can be greater than the outer diameter of the ultrasound transducer. This arrangement can maximise the coupling range between the sensor and a remote energising device such as an inspection wand.

The induction coil can have an inductance such that the induction coil and the ultrasound transducer form a circuit with a resonant frequency that matches a first operating frequency of the ultrasound transducer. This can results in an efficient production of ultrasound waves. The first operating frequency can be an optimal operating frequency of the ultrasound transducer, such as between 1 and 10 MHz.

The induction coil can have an inductance between 0.05 pH and 10 pH. The present inventor has found that by keeping the inductance in this low range, the resonant frequency of the LC circuit can be optimised for the first operating frequency of the ultrasound transducer. Preferably, the induction coil may have an inductance between 0.2 pH to 5 pH.

The wireless ultrasound NDT sensor can further comprise a support structure to which the transducer and coil are mounted. The coil can be mounted in a parallel, spaced relationship with respect to the transducer. This can result in the inner diameter of the inductance coil being smaller than the outer diameter of the transducer which results in a larger operating range between the sensor and a remote energising device in comparison to an embodiment with the transducer and inductor coil arranged coaxially. Moreover, the inductive coupling interference induced by eddy currents in the ultrasound transducer can be reduced with the ultrasound transducer outside of the induction coil.

The transducer and the induction coil can be mounted in substantially the same plane. This gives rise to a sensor with a low profile, which can be easily mounted within a test object.

In accordance with a second aspect of the invention, there is provided a wireless nondestructive testing system comprising a wireless ultrasound NDT sensor according to the first aspect and an inspection wand arranged to inductively operate the wireless ultrasound NDT sensor. This can enable the sensor to be remotely operated when it is mounted within a test object.

In accordance with a third aspect of the invention, there is provided a method of producing a wireless ultrasound NDT sensor, the method comprising: providing an ultrasound transducer; providing an induction coil having an inner diameter smaller than the outer diameter of the transducer; mounting the ultrasound transducer outside of the induction coil; and electrically coupling the induction coil to the ultrasound transducer.

This method can result in the production of a sensor with an increased coupling range in comparison to known sensors. The method can improve the likelihood of the inductance of the ultrasound sensor being optimised for an operating frequency of the transducer in comparison to known methods.

The method can further include the step of calculating the inductance value required to operate the ultrasound transducer at an operating frequency; and whereby the step of providing the induction coils comprise providing a capacitance of the ultrasound transducer providing an induction coil having an inner diameter which is smaller than the ultrasound transducer diameter, and having the required inductance value. This method can result in the inductance of the ultrasound sensor being optimised for an operating frequency of the transducer.

Optional features of the first aspect can be applied to the third aspect in an analogous manner.

Brief Description of the Drawings

Embodiments of the invention will now be described, strictly by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a schematic representation of a known wireless NDT system; Figure 2 is circuit diagram of the wireless ultrasound sensor of Figure 1; Figure 3 is a simplified circuit diagram of the wireless ultrasound sensor of Figure 1; Figure 4 is a schematic representation of a wireless ultrasound sensor according to an embodiment of the invention; and Figure 5 is a schematic representation of a wireless NDT system including the sensor of Figure 4.

Description of Embodiments

Referring first to Figure 1, a known wireless NDT system is shown generally at 100. The NDT system is arranged for testing of a test object 102 and comprises a wireless ultrasound sensor 104 which is embedded in or attached to the test object 102 and a remote device comprising an inspection wand 106. The wireless ultrasound sensor 104 comprises a piezoelectric ultrasound transducer 108, electrically coupled to an induction coil 110. The induction coil 110 enables the wireless ultrasound sensor 104 to be remotely powered by the inspection wand 106 by inductive coupling. The induction coil 110 is connected to a negative electrode of the transducer 108 by a first connection 112 and to a positive electrode of the transducer 108 by a second connection 114.

The induction coil 110 and the ultrasound transducer 108 together form an LC circuit with a particular resonant frequency. For NDT applications using an ultrasound transducer, this frequency is generally in the range of 1 to 10 MHz. In use, the inspection wand 106 is brought towards the sensor 104 which induces a current in the LC circuit at the resonant frequency. This causes the transducer 108 to output an ultrasound pulse. The ultrasound pulse can reflect off a surface of the test object 102 and the reflected signal is received by the transducer 108, producing a current in the sensor 104 that can be transmitted to the inspection wand 106 via inductive coupling.

In order for inductive coupling to take place between the inspection wand 106 and the sensor 104, the inspection wand 106 must be held within a distance x of the ultrasound sensor 104. Outside of this range, the inductive coupling is too weak to enable the inspection wand 106 to operate. In one example, operation means 'pulse echo' operation in which a signal is sent from the wand 106 to the transducer 108 for emission into the test object 102 and the received echo is sent back to the wand 106. The maximum operating distance is determined by a number of factors including the resonant frequency of sensor 104, the resonant frequency of the inspection wand 106, material between the inspection wand and sensor and the outer diameter d of the coil.

Figure 2 shows a circuit diagram of the wireless NDT sensor 104 of Figure 1. The induction coil 110 can be represented as an inductance L parasitic resistance Rd and capacitance Cd, which are electrically coupled in parallel with the piezoelectric ultrasound transducer 108, which can be represented as an impedance Zp7.

For high frequency (approximately 1 to 10MHz) applications such as in an ultrasound sensor, a coil with a small number of turns (generally 1 to 10) is typically used and therefore the perfect inductor assumption may be made and the parasitic resistance and capacitance of the induction coil 110 can be neglected. Therefore, the electrical circuit can be simplified as shown in Figure 3 to an inductance associated with the coil L, and a capacitance associated with the transducer C. The frequency fo is then given by:

_ h -

and the required inductance of an induction coil can be estimated as: f2 r It is known to design a coil to achieve this value of inductance by adjusting the parameters of the coil such as coil diameter, number of turns and turn density. An equation for inductance of a circular loop of number of turns N and circle radius R, with wire radius a, and medium relative permeability pr is given by: IR\ Ni'Rpop4 2.0 a In order to design a coil with the required inductance to achieve a high frequency fo required to operate the ultrasound transducer, the coil will necessarily have a small diameter, particularly for a coil having a small number of turns, which in turn limits the distance at which the sensor 104 can be operated by the inspection wand 106, as the inductive coupling range is reduced for a smaller diameter coil or less number of turns.

In Figure 4, a wireless ultrasound sensor according to a first embodiment is shown generally at 404. The sensor is arranged for pulse echo operation as describe above.

The sensor 404 comprises a piezoelectric ultrasound transducer 406 and a planar induction coil 408. The induction coil 408 is connected to a negative electrode of the transducer 406 with a first connection 410 and to a positive electrode of the transducer 406 with a second connection 412. The induction coil has internal diameter di which is smaller than the outer diameter dz of the ultrasound transducer The transducer 406 is positioned such that, in use, it is outside of the induction coil 408. In the illustrated embodiment the transducer 406 is spaced from the induction coil 408 by roughly the diameter of the transducer 406, but in other embodiments other suitable distances can be provided.

The transducer 406 is a small transducer; for example the outer diameter of the ultrasound transducer is no greater than twice the internal diameter of the induction coil. The maximum diameter of the transducer can for example be 20 mm. By providing a small transducer 406, the capacitance associated with the transducer Cpz can be relatively small and the inductance of coil L can be relatively large. Consequently, the outer diameter d and the number of turns of the induction coil can be made large, which leads to an increased inductive coupling range.

By positioning the transducer 406 outside the induction coil 408 and the inner diameter di of the induction coil 408 being smaller than the outer diameter d2 of the transducer, the inventors have found that the inductive coupling can be improved relative to known sensors.

In addition, situating the transducer 406 outside of induction coil 408 can, in use, minimise inductive coupling interference induced by eddy currents formed on the top of the ultrasound transducer 406 when the sensor 404 is inductively coupled to a remote device such as an inspection wand.

In order to maximise the inductive coupling between the induction coil 408 and a remote device such as the inspection wand, the inner diameter di of the induction coil 408 should be made small. In the embodiment shown in Figure 4, the induction coil 408 has an internal diameter di of between lmm and 10 mm and the ultrasound transducer 406 has an outer diameter d2 of between 2 mm and 11 mm. However, in some embodiments, the induction coil can have an inner diameter di of between 1 mm and 20 mm and the ultrasound transducer can have an outer diameter d2 of between 2 mm and 40 mm, with the diameter of the transducer 406 being at least 1.1 times that of the inner diameter di of the induction coil 408.

Figure 5 shows a wireless NDT system 500 including the wireless ultrasound sensor 404 of Figure 4 embedded in or attached to a test object 502 and a remote device, in this case an inspection wand 504. The wireless ultrasound sensor 404 can be inductively operated by the inspection wand 504 in a similar manner to the wireless NDT system of Figure 1. However, because the transducer is small and outside of coil, and the inner diameter of induction coil is smaller than the outer diameter of the transducer, the NDT system 500 of Figure 5 can be operated with a greater distance x2 between the inspection wand 504 and the wireless ultrasound sensor 404 than would be possible for the NDT system of Figure 1.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be capable of designing many alternative embodiments without departing from the scope of the invention as defined by the appended claims.

Claims

CLAIMS1. A wireless ultrasound non-destructive testing (NDT) sensor for emitting a pulse of ultrasound energy into a test object and receiving an echo signal, the sensor comprising: an ultrasound transducer having an outer diameter; and an induction coil having an internal diameter, the induction coil being electrically coupled to the ultrasound transducer; wherein the internal diameter of the induction coil is smaller the outer diameter of the ultrasound transducer and the sensor is arranged for the coil to be positioned, in use, in parallel with the ultrasound transducer.
2. A wireless ultrasound NDT sensor according to claim 1 wherein the outer diameter of the ultrasound transducer is no greater than twice the internal diameter of the induction coil.
3. A wireless ultrasound NDT sensor according to claim 1 or 2 wherein the inner diameter of the induction coil is at least 10% smaller than the outer diameter of the ultrasound transducer.
4. A wireless ultrasound NDT sensor according to any preceding claim wherein the induction coil is a planar induction coil having a plurality of turns.
5. A wireless ultrasound NDT sensor according to claim 4, wherein an innermost turn of the induction coil defines the internal diameter and an outermost turn of the coil defines an outer diameter of the coil, wherein the outer diameter of the coil is greater than the outer diameter of the ultrasound transducer.
6. A wireless ultrasound NDT sensor according to any preceding claim wherein the induction coil has an inductance such that the induction coil and the ultrasound transducer form a circuit with a resonant frequency that matches an optimal operating frequency of the ultrasound transducer.
7. A wireless ultrasound NDT sensor according to any preceding claim wherein the induction coil has an inductance between 0.05 pH and 10 pH.
8. A wireless ultrasound NDT sensor according to any preceding claim, further comprising a support structure to which the transducer and coil are mounted, the coil being mounted in a parallel, spaced relationship with respect to the transducer.
9. A wireless ultrasound NDT sensor according to any preceding claim, wherein the transducer and the induction coil are mounted in substantially the same plane.
10.A wireless non-destructive testing system comprising a wireless ultrasound NDT sensor according to any of claims 1 to 9 and an inspection wand arranged to inductively operate the wireless ultrasound NDT sensor.
11.A method of producing wireless ultrasound NDT sensor according to any preceding claim, the method comprising: providing an ultrasound transducer; providing an induction coil having an inner diameter smaller than the outer diameter of the transducer; mounting the ultrasound transducer outside of the induction coil; and electrically coupling the induction coil to the ultrasound transducer.
12.A method according to claim 11, further comprising: calculating the inductance value required to operate the ultrasound transducer at an operating frequency; and whereby the step of providing the induction coils comprise providing a capacitance of the ultrasound transducer providing an induction coil having a inner diameter which is smaller than the ultrasound transducer diameter, and having the required inductance value.