At Full Matrix we are very excited to be working adjacent to the Fusion Power industry, where fascinating scientific and engineering problems go hand-in-hand with environmentally positive technologies.
Our Technology uses ultrasound to monitor the condition of pipes (meaning to be constantly checking for damage/faults) and other critical infrastructure. Currently, ultrasound condition monitoring equipment available in the market works well on straight pipes (for which there are analytical solutions) in non-extreme environments. This equipment is not designed to work on any geometries more complex than a straight pipe. This is why Full Matrix’s technology is so key. Using electromagnetic transducers (EMATs) and advanced signal processing, we will be able to use ultrasound to, not just, monitor the condition of complex structures, but at extreme conditions.
Within and around a fusion power reactor, the conditions are very hostile. There are high temperatures, high levels of neutron and gamma radiation and a soup of electromagnetic noise. This makes the design of sensors for condition monitoring particularly challenging.
To quickly give a bit of context:
The technology that Full Matrix is currently developing uses EMATs to monitor the condition of pipes and other conducting structures. An EMAT is a very simple structure involving a coil of wire wrapped around a permanent magnet. This is then placed just above the surface of the structure to be monitored. When a current flows in the coil it interacts with the static magnetic field and creates a force in the surface of the structure (Figure 1). This can be imagined using Fleming’s left hand rule! When the current being generated in the coil of wire is alternating, travelling acoustic waves can be created in the structure (Figure 2). It is these travelling acoustic waves (in constrained geometries, like a pipe) that we use to identify faults.
Fig.1: Image of an EMAT on a pipe. Orthogonal vectors are shown representing current flow, the static magnetic field and the induced force in the pipe.
The EMATs work very similarly in receiver mode. When the pipe surface under them moves due to a travelling wave, this motion of conducting material in a static magnetic field results in an induced current flowing in the coil. This is the mechanism by which the signal is received.
The use of EMATs (over other types of transducers) makes it possible for our equipment to work at very high temperatures as the EMATs do not have to be in contact with the structure being monitored.
Fig.2: A visualisation of a travelling acoustic wave in a pipe produced by two EMATs placed opposite one another.
In order to identify a developing crack, fault, or area of corrosion in a structure it is essential that the received acoustic signals of a healthy pipe in the same environmental conditions (temperature, humidity, etc.) are the same. This is known as a “baseline”. It is important to have a repeatable baseline for an experimental set-up otherwise you won’t notice small changes in the received signal that would be indicative of a crack, fault, or area of corrosion. Damage will manifest itself as small changes to amplitude, form, or arrival time of received signals.
An example of a received signal in a pipe may look like can be seen in figure 3.
Fig.3: The blue trace shows the generated pulse (10kHz, 5 cycles) that flows through the coil. The red trace shows the received signal detected by a ring of receiver EMATs. You can see the initial peak in the received trace due to the pulse going into the pipe. There is then a ‘quiet zone’ of lower amplitude peaks, which is followed by the reflection of the pulse from the end of the pipe at about 6.5ms.
Much of the primary experimental work to be done over the next few months at Full Matrix will be to work on baseline repeatability. This will also involve the quantitative assessment of the effects of different environmental factors on the signals transmitted and received using our set-up of transmitter and receiver EMATs.
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