Emerging technology design: smart bio-sensing clothing
The fabric-embedded fibre-like biometric sensor that is being described in this case study provides a continuous and simultaneous measure of a large plurality of biomedical parameters including heart-beat rhythm and phonocardiogram-like signal, breathing (rhythm and respiration sound), blood pressure and blood-pulse velocity.
Author(s): Talia Sirkis, Sergey Agdarov, Yafim Beiderman, Ronen Rozenshtein, Yevgeny Beiderman, Zeev Zalevsky
This sensor is a touch-less device targeting the multiple sectors not just sport wear. It does not have any electrical contact, therefore can be used in wet environment without degradation in its performance. It was integrated into a shirt and tested before and after being washed and ironed. The operation principle of the fibre-like sensor includes insertion of special artefacts into the core of the fibre and measuring the back reflected light.
Introduction and challenge
The current competitors to the technology described in this case study are operating in the smart clothing market aiming the sportsmen market while their solutions always require tight contact with the sensor. Their clothing embedded sensors are capable of monitoring only one biomedical parameter (usually the heart beats or rhythm) per sensor. Examples of existing companies involve Sensoria fitness  which develops smart socks (required tight contact and monitor only heart beats), Athos  smart clothes (measure only heart beats and require tight contact while aimed only for sportsmen) and the smart shirt or bra of OMsignal . The most common technology to perform this tight contact bio-sensing is the insertion of an electrical wire/stripe into the clothing that when is being stretched changes its electrical resistivity. Sweating many times affects the precision of such measurement and the tight contact is not always pleasant to the tissue in case of long lasting sport exercises. Fibres have been used before to sense biomedical parameters as well . However, it was done in a way requiring tight contact between the fibre and the body of the wearer in a way similar to the electronic stripes currently being integrated into the sport wear . There, as appears in , an optical fibre-based sensor was used in order to detect photo-plethysmography and from that the heart beats by inspecting ratio of absorption between different wavelengths and then measuring the respiratory rate by computing the relation between bending radius and attenuation of the optical fibre. Both parameters were measured by injecting a single beam light traveling along a bended fibre. Besides that a good overview of the technical and commercial activity in the field of bio-sensing textiles appears in  as well as in [6,7].
The main challenges still existing in this new field of application of biosensor in wearable clothing involve lack of industrial supply chain products, lack of manufacturing technology for efficient production on industrial scale, lack of quality, performance and safety standards.
Technology and solution
In the study case we present, we have developed a fabric with an integrated sensor that can measure many (rather than a single) biomedical parameters simultaneously (via a single sensor) and it does not require any contact between the fibre-like sensor and the body of the wearer. It is a fibre-like sensor that so far was experimentally tested for measuring several biomedical parameters as heart-beat rhythm, breathing, blood-pulse pressure and blood-pulse velocity (one sensor for all parameters). All this is obtained without having full contact between the fibre and the skin of the wearer. The operation principle of our patented technology  is based on unique methods for measuring reflection of light going through the fabric-integrated optical fibre. Special artefacts are inserted into the core of the fibre and cause two things:
- Realisation of in-fibre interferometer that can measure with high precision movements and deformations caused to the fibre itself . This is obtained as the artefacts cause to photons going through the fibre to be back reflected and to interact with the reference photons coming from the light source. This interaction is called interference and it extracts the relative change in the phase and in the polarisation state caused to those affected photons with respect to the reference photons.
- Interaction of the light with the wearer's tissue is due to the artefacts that cause some of the light to escape from the fibre (the total reflection condition is no longer preserved) and then some of the photons that are back reflected from the tissue are also coupled into the fibre again. The escaped photons interact with the nearby tissue while its time varying movements modulate those photons (Doppler shifts). This modulation, which is expressed in changing the relative phase and the polarisation state of the interacting photons in time, is extracted by interfering them with the reference photons coming from the light source.
A schematic sketch of the operation principle is depicted in Fig 1.
Fig 1: Schematic sketch of the operation principle of the proposed sensor
We experimentally demonstrated the capability to sense the above-mentioned biomedical parameters being vital life signals at elderly population. We performed large variety of experiments in which the measurements performed with our fibre-like sensor were compared with the medical reference measurement and deviation error of <10% was observed for all measured bio-parameters.
In addition to its capability to monitor bio-parameters, our smart clothing can also hear the voice of the wearer  as the pressure waves propagating from the voice source cause to a time changing deformation to the special fibre sensor. This deformation is measured by the fibre interferometer. Thus, we can monitor not only the medical condition of the elderly subject but also hear him calling for help.
As part of the development procedure of our sensor, we have successfully incorporated our fibre into a fabric and even showed its operability also after washing and ironing. We performed one cycle of washing the fabric at temperature of 40° in regular washing machine and then ironed it for about 10 min. After that another set of measurements was performed and there was detected no degradation in performance with respect to the precision of results obtained prior to the washing and ironing cycle.
After performing the biomedical sensing of vital signals and in case that a problematic deviation is observed, the output of our sensor may be wirelessly transmitted (via special connector having a wireless Blue-tooth transmitter and which is connected to the fibre sensor and is also embedded in the clothing) to a smart phone for processing and displaying the obtained measurement and for further transmitting it to a telemedicine centre for alerting the medical staff or the relatives of the elderly subject. Our smart clothing communicates with other smart devices and allows performing the desired elderly care from a distance.
The sensor is composed out of two components. The first is the fibre-like sensor itself through which we inject photons and measure the photons returning back. The fibre is very thin having diameter of about 0.1 mm. The fibre is connected to a connector which includes the light source, the detector, the power supply as well as a wireless unit that transmits the obtained results to a smart phone or to a laptop for display purposes, for further processing the data and for further transmitting it to a telemedicine centre. At the moment the connector module is not yet miniaturised but the final volume that will include all of its components will be <1 cm 3. In case of elderly care, the proposed smart clothing allows the person positioned in the telemedicine centre to constantly monitor the vital life signals of the smart cloths wearer. Schematic sketch of the overall integrated system is seen in Fig 2 a. A schematic description of the structure of our future product is seen in Fig 2 b.
Fig 2: Schematic sketch of the overall integrated system and the future product
a Schematic sketch of the overall integrated system
b Schematic description of the product
Testing and validation
The fibre-like sensor was integrated into a shirt. It was done by fabric gluing technology. However, it was also checked and found suitable to be integrated into the fabric via weaving machinery which can be done also in mass production, fabric-manufacturing facilities. Note that the fibre-like sensor we use can be made out of PMMA (poly(methyl methacrylate)) polymer or out of glass. In the case of polymer it is very flexible in sense of bending radius. In the case of glass the bending radius should not be smaller than 5 mm. The fibre used in our experimental validation was made out of glass.
In Fig 3 a, we show one of our research and development engineer who is wearing our smart shirt in which our fibre-like sensor was integrated, while the output of the measurement which was in this case the heart beats is displayed on the laptop screen that is positioned near by the wearer. As indicated before, our fibre-like sensor does not require tight contact between the fibre and the body of the wearer. In Fig 3 b, we present an image of another research and development engineer who is wearing our sensor being loosely connected to the external part of his shirt and yet capable of performing the measurement of several biomedical parameters simultaneously. In the right lower part of Fig 3 b, we show an example of the heart beating (the rate and the shape of the signal) measurement performed by our fibre-like sensor.
Fig 3: Research and development engineer wearing our smart shirt
a Our research and development engineer wearing our smart shirt
b Way our sensing fibre looks like when connected externally to a shirt
The proposed technological concept that was briefly described in this case study can be used for large variety of applications not only related to elderly care or to the sport market segments. Given the fact that the smart clothing market is rapidly growing, the incorporation of such technology can go much beyond those segments. For instance, it can be incorporated into diapers or into mattress of babies in order to constantly monitor their breathing and their vital signals similarly to what EarlySense Ltd tries to do , while in our case we will monitor simultaneously many life vital bio-parameters.
Note that as indicated before, in all of our experiments we have performed measurements with our sensor and in parallel with an independent reference sensor. In the case of blood pressure, the reference was the manual sleeve device. The SPO2 sensor put on the finger of the subject was a reference device to measure heart beats and oximetry. The number of respirations per minute was counted by two independent individuals as a reference. As an outcome, all the results extracted from our fibre-like device could be compared with the reference measurements.
In this case study, we have briefly introduced a new fibre-based sensing technology capable of being integrated into any type of fabric and which can perform continuous biomedical monitoring of vital life signals of the person that wears the fabric with the sensor. All this is obtained without the need of a tight contact between the fabric-integrated sensor and the body of the wearer. We have been able to measure several biomedical parameters simultaneously with the same single fibre-based sensor. Future dissemination of this technology can be very useful in elderly care related applications as well as in monitoring of vital life signal especially of breathing of babies.
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