Author: Dr Laetitia Marrot
STSM Period: 2020-03-06 – 2020-03-26
Hosting institution: Czech Technical University in Prague, UCEEB
From ITC: Yes
PURPOSE OF THE STSM
The STSM aims at developing an interactive pressure-sensitive textile flooring for active ageing and safety of older adults. Two applications are envisioned for the pressure-sensitive textile flooring.
- First, an active ageing application by encouraging the elderly to walk. The textile flooring would be able to react under the pressure of the walking user and to be used as individual or collaborative game-based rehabilitation tool.
- Second, a safety application by detecting the fall of the elderly. The smart textile flooring would be able to differentiate if the user is walking on the textile flooring or if the user fell and cannot get up anymore. In this case, the textile flooring would immediately send an alarm signal to caregivers.
Hence, the interactive pressure-sensitive textile flooring will provide both playful and comforting roles to encourage older adults to be more active.
The STSM will focus more specifically on the pressure-sensitive response of the main constituent of the textile flooring (textile coated with piezoresistive material). After successful completion of the STSM, the next step of the project will focus on the “interactivity” of the textile flooring. The signals from the developed pressure sensitive floor will be evaluated in prototyping phase.
DESCRIPTION OF WORK CARRIED OUT DURING THE STSMS
Prior to the STSM, textiles samples were coated with carbon particles to produce conductive textiles. Increasing carbon content was introduced in the coating, up to 70% of carbon relating to the matrix weight. Small size samples (60 x 25 mm2) were tested during the STSM. For this preliminary study, emphasis has been made on the assessment of the electrical properties of the small size coated samples. Several tasks were carried out:
- Meetings with the different key researchers for the project (researchers and head of the Laboratory of Electronic Systems) for the organization of the time on site and training on the testing equipment.
- Development of a labview block diagram to monitor the LCR meter and record the response data from the textile under solicitation at various frequencies.Measurement of capacitance and resistance of the unloaded coated textile under AC current for different frequencies from 20 Hz to 2 MHz and under DC current.
- Measurement of capacitance and resistance of coated textile with compression stress from 0.5 to 10 MPa under AC current for different frequencies from 100 Hz to 2 kHz and under DC current.
- Establishment of an action plan to move forward with the project
DESCRIPTION OF THE MAIN RESULTS OBTAINED
- The DC surface resistance of the coated fabrics decreases with increasing carbon content. On the electrical resistivity scale, the surface resistivity of the coated samples are typical for EMI shielding and semi-conductors.
- For AC measurement the sample was approximated as a simple paralele combination of Rp and Cp. For each carbon content, the values of AC resistance (Figure 1) are close to the values measured with DC current (only the values for 0 and 10% were over ranged when measured with DC current). Beside for 0 and 10% of graphite whose samples present negative resistance values from 20 kHz, the AC resistance is relatively stable with the variation in frequency. The percentage of resistance compared with the initial value at 20 Hz shows a decrease up to 8% with increasing frequency for the sample with 20% graphite. From 30% graphite, the resistance of the samples slightly increases with increasing frequency (up to 1%), which is a typical result for conductive materials.
- The AC surface capacitance Cp of the coated fabrics with increasing graphite content is presented in the Figure 2. From 30% of graphite, a discontinuous behaviour of the capacitance appears at a frequency of 20 kHz.
- The electrical properties of the textile fabrics under compression load from 0.5 to 10 MPa are measured with DC and AC current with a maximum frequency of 2 kHz (limited by the LCR equipment). With an increase of compression load, the change of AC surface resistance Rp for different frequencies is similar to the change of DC resistance R. The coated textiles show a piezoresistive behaviour with their DC resistance increasing when the compressive load increases. Moreover, the higher the carbon content, the lower the increase of resistance with the compressive load.
The piezoresistive behavior of the coated textile has been confirmed on small size samples. The collaboration is expected to continue on 1) up scaling the sample size and testing their electrical behavior before introduction in the intelligent flat at UCEEB and 2) conducting testing with compression produced by someone walking on large size samples. The results of this future collaboration are expected to be presented at the 19th European Conference on Composite Materials (ECCM19) in Nantes, France, initially planned on June 22-26, 2020.