New-Tech Europe Magazine | December 2018

sometimes the lower leg as well. “But with early detection and treatment, around 80% of amputations can be avoided.” The peak pressure value and impulse (pressure over time) are im-portant predictive parameters that may provide an indication con-nected to the risk of ulceration. Today, these parameters can be measured using sensor plates that the patient walks across. Howev- er, sensor soles in the shoe should enable far more accurate read-ings to be taken, plus they can also be used in combination with a corrective sole or shoe to check whether the problem has been rem-edied in this way. From sensor plate to sensor sole A sensor plate makes it possible to measure the pressure profile be-tween the plate and the foot (or shoe, if the person is wearing shoes). Typically, these readings will be taken at the doctor or in a store such as a runners’ lab or other location where the sensor plate is available. Sensor soles – which can just be inserted into some-one’s shoe – offer many new possibilities compared with sensor plates. In particular, sensor soles enable readings to be taken inside the shoe rather than underneath it. That way, one can obtain a very clear picture of the exact effect the shoe (and the corrective sole) is having on the foot movement. Also, with a sensor sole, you can track a person’s movement pattern over a longer period of time – days or weeks. The Belgian company RSscan had been playing around with this idea for some time. Then, when the EU InForMed project was launched, RSscan saw it as the ideal opportunity to get to work with research-ers from CMST/imec and Holst Centre on the topic. “In particular, sensor soles enable readings to be taken in-side the shoe rather than underneath it.”

Fig 1: Today, sensor plates are used to help people such as athletes to select the right shoes and soles for them, based on the pressure profile measured while walking or running.

Two potential technologies CMST/imec and Holst Centre each have their own area of expertise that may be of interest for the product that RSscan ultimately brings to market. CMST/imec uses polyimide as the carrier for its ‘flexible electronics’, with laminated copper on both sides. Sensors and inter-connections are then made by patterning the copper. Holst Centre works with thermoplastic polyurethane (TPU) and prints silver struc-tures on it using roll-to-roll techniques. Roll-to-roll printing is cheap-er, while copper etching allows to produce finer structures. Unique: multiple sensors and high measurement frequency The sensor sole is made up of two layers: one with sensors, while the other is a pressure-sensitive layer. When pressure is exerted on the pressure-sensitive layer, resistance is reduced and more current flows through the sensors. This makes it possible to measure differ-ences in pressure. Various sensor shapes have been trialed: square, round and finger-shaped structures. The interconnections have a unique winding structure that enables the sole to bend without losing function. The fact that this actually works can be seen from a test using a support

sole with a ‘deep liner’ at the heel. The sensors kept working while running the tests, despite the fact that the sensor sole was loaded in this curved position. The sensor layer has been designed in such a way that the custom-ized soles can be trimmed without losing the essential connections. Function was maintained in both size 39 and size 46. “The unique and most striking feature of the design is defi- nitely the sensor density: one sensor every 5 mm! The soles produced by most of RSscan’s competitors only have be-tween 10 and 13 sensors.” The high density is important for research purposes, as well as for the broad application of the sole. For certain medical problems, you need a high density of sensors at the heel, whereas for others it’s more on the front part of the sole. The measurement frequency that can be achieved with this sensor design and the supporting electronics is also unique. For example, speeds of 500 to 1000 Hz can be measured. Again, this is very im-portant for research and for doctors investigating specific com-plaints. On the market by 2020 The results from the InForMed

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