Thin single-layer textile-based matrix-type pressure sensor for protective clothing

The research focuses on the development of an ultra-thin, single-layer, matrix-type textile pressure sensor for the field of smart textiles, which can record the location of pressure application and determine the applied force. The sensor possesses the tactile characteristics of a textile, and its design incorporates only textile-based materials, ensuring greater flexibility and improved integration with textile materials. The research describes the study of piezo-resistive electro-conductive textiles and identifies the most suitable materials for creating the sensor. Testing was performed using a Zwick/Roell Z2.5 compression/strain test column and an Agilent A34970A ohmmeter. Testing focused on the sensor’s electrical resistance changes under cyclic loading, sensitivity, measurement hysteresis, and repeatability. From the experiments can summarise that for the Sefar Carbotex 03-120CF sensor load cycling repeatability varies significantly depending on the pressure point and it is difficult to summarize an approximate range of changes in the load and resistance values and hysteresis values changes in most cases from 0,44 to 0,94. The best results showed the EeonTex LTT-SLPA 60 kOhm sensor with better cycling repeatability in the low, middle and high range, and the values at different pressure points are comparable and hysteresis values changes in most cases from 0,83 to 0,94. It was found that the sensitivity values of the Sefar Carbotex 03-120CF sensor are in range of 0,004–0,05 KPa but values of the EeonTex LTT-SLPA 60 kOhm sensor–in range of 0,002–0,005 kPa. For the Carbotex fabric sensor with the increase in pressure resistance decreases, but for the Eontex fabric sensor, it increases. This can be explained by the elasticity of the Eontex fabric, as it is made of knitted fabric. A design for sensor electrodes is created using embroidery software, and electrodes made of electroconductive thread are produced using automated embroidery technology. To visually display the sensor’s operation on screen, a serial interface is used with tailor-made software. The development of this type of textile sensor would contribute to various wearable applications for protective clothing, such as in fencing equipment for sports or in the field of bullet impact detection in soft armor and protective clothing for operators working in environments with a risk of injury from impact with moving parts or falling objects, such as heavy agricultural machinery operators and first responders as well in medical application in mattress toppers to monitor body impressions.

Wearable pressure sensors can be designed in several ways, each with its own advantages and disadvantages. Capacitive sensors are based on changes in capacitance due to external forces acting on the sensor, usually in a perpendicular direction (Samarentsis et al., 2022; Aqueveque et al., 2020). Although such sensors have high accuracy and repeatability, their main drawback is their low sampling rate, which makes them suitable only for monitoring slower processes. Microcontroller manufacturer Microchip (previously named Atmel) cited 20–250 ms as a typical measurement period for its Q-Touch hardware acceleration capacitive sensor controller (Atmel, 2016). Other options for pressure sensors are piezo-electric sensors (Tahir et al., 2020) and piezo-resistive sensors (Melnykowycz et al., 2014; Fortunato et al., 2020; Pang et al., 2021; De Fazio et al., 2021). The first were used in gait monitoring and were well-suited for insole sensors. They are not the best solution where a large area of a 3D anatomical structure should be covered and monitored. Triboelectric sensors are the latest development of wearable pressure sensors (Nguyen and Lee, 2022). These sensors may present disadvantages in terms of frequencies and operating range (Yao et al., 2022), so they were not included in this study. This paper focused on piezo-resistive sensors. These sensors are based on a piezo-resistive material, so by measuring the change in electrical resistance, it is assumed that the applied force can be determined. The researchers use two main approaches to designing pressure sensor arrays: individual sensors and matrix sensors. Individual sensor arrays with a relatively small number of sensors are mostly used because each sensor must have at least one individual contact, and an array of n sensors has at least n + 1 conductive trace (Okss et al., 2020). Currently, such matrices with a large number of individual sensors can be produced mainly using printing technologies that do not have sufficient wear resistance when printing on fabrics subject to bending and tensile deformation, typical for the use of protective clothing. The use of a matrix pressure sensor makes it possible to create large sensor surfaces with a significantly smaller number of conductive paths compared to the case of individual sensors (Cheng et al., 2016). Most pressure sensors consist of three layers: a middle piezo-resistive pressure-sensitive layer is sandwiched between two outer layers with embedded parallel conductive tracks (hereafter, the outer layers are referred to as conductive layers). Such fully textile-based arrays have been developed and successively tested in several applications: a smart bed (Laurino et al., 2019), a sitting posture control device (Xu et al., 2013), a smart mat (Sundholm et al., 2014a), and others.

In previous research, commercially available pressure-sensitive piezo-resistive textile materials were analyzed for use in multilayer sandwich-type pressure sensors (Vališevskis et al., 2023a; Vališevskis et al., 2023b; Vališevskis et al., 2023c). Authors’ research in the field of textile materials structure and sensitivity characteristics (Vališevskis et al., 2023a) showed that polyester knitted fabrics with a piezo-resistive polymer coating and carbon-polyester fabrics are most suitable for pressure sensor needs. The experiments were done using conductive textiles EeonTex LTT-SLPA 60 kOhm polymer-coated knitted fabric and carbon/polyester Sefar Carbotex 03-120CF, 03-160CF, 03-205CF woven fabrics according to datasheets and availability on the market. In these experiments for conductive layers and traces, hot melt adhesive and self-adhesive electrically conductive textile fabrics/tapes with conductive adhesives (Holland Shielding Systems B.V.) were used.

The author’s previous research (Vališevskis et al., 2023b) explored the methods by which the dynamic range of commercially available piezo-resistive fabrics can be extended. These materials performed well in instances of slowly changing loads. However, in instances where the dynamic load resistance of these materials decreased significantly, it reached 60–70 Ω in the case of 3,5 J impacts and 10–30 Ω in the case of 7 J impacts. This made it impossible to measure the impacts of higher energy. The primary objective of this paper was to study methods for increasing the resistance of these materials to make them suitable for measuring high-energy impacts.

In these experiments (Vališevskis et al., 2023b), pressure sensor sensing conductive electrodes were made with embroidered traces with conductive threads instead of hot melt adhesive and self-adhesive electrically conductive textile fabrics/tapes, to ensure more stable operation of the sensor and automation sensor-producing process with machine embroidery.

In the authors’ previous research, a matrix-type multi-layer textile pressure sensor to determine the point of impact of the bullet (Kukle et al., 2024) was developed, where the matrix sensor consists of 5 × 5 electrodes embroidered with electroconductive thread on layers of outer cotton fabric (horizontally and vertically). The middle layer consists of a combination of electrically conductive fabrics (EeonTex LTT-SLPA 60 kOhm and Sefar Carbotex) with fiberglass mesh.

In the market, there are some commercially available solutions for pressure sensors: company Datasoft offers the Automatic Injury Detection (AID) sensor from printed plastic for the price of more than 400 USD, which is relatively expensive and not soft and flexible (not human body friendly). Conventional (non-textile) pressure sensors are used in commercial smart (top) mattress solutions with pressure monitoring- Novel.de Pliance, Tekscan BPMS, BodiTrak2, Tactilus Bodyfitter, X-sensor Reveal, Body Pressure Mapping (BPM) etc. After analyzing the available products, it can be concluded that the sensor technology is intended for specialized use (medical or sports products). The prices of the technologies are very high, which forces us to look for a more reasonably priced solution.

Analyzing the research of scientists on textile pressure sensors can be distinguished from the research and experiments of capacitive pressure carried out by scientists, D. Sofronov, R. A. Angelove, and Y. Soforonov for developing a sensor pad prototype. The sensors were embroidered on 100% cotton fabric using HC12 Madeira conductive thread (Sofanova et al., 2021).

They developed a pressure sensor mattress covered with 64 pressure-sensitive sensors, which are located in the full width of the mattress, in 3 zones - according to the risk zones of the body, which are exposed to the risk of sleeping. Using customized software, the output data of the sensor was displayed visually on a display.

A group of scientists M. Sundholm, J. Cheng, B. Zhou, A. Sethi et al. created a multilayer piezo-resistive pressure sensor using textile materials (Sundholm et al., 2014b). Piezo-resistive fabric is placed between two layers of electrically conductive fabric. This sensor was developed in different sizes, depending on the purpose of the application. For example, for controlling sitting posture by placing the sensor on a chair, for tracking sports activities by placing the sensor under an exercise mat. The analyzed pressure sensor senses the pressure load over the entire surface of the sensor, instead of, as in the previous study, where the sensors were placed only in specific areas. The output data of the sensor is visible on the computer screen in a matrix layout. Points with the highest-pressure load are colored in yellow/red, but with less pressure, in blue/green. The sensor is connected to the computer using Bluetooth wireless technology.

J. Tabor et al. describe a capacitive pressure-sensitive sensor made of textile materials (Tabor et al., 2021), to use it in leg and arm prostheses to ensure the most comfortable conditions for the person wearing it. The sensor consists of 9 capacitive sensors, which are embroidered on a dielectric non-woven fabric - “Kraton md 1,653”, made of copolymer “SEBS”. The silver-coated textile thread of the manufacturer “Shieldtex” 235/36 was used as an electroconductive embroidery thread. 3 parallel seams, each 1 cm apart, were dried on the dielectric cloth using a straight lockstitch sewing machine with electroconductive thread wrapped around the needle and sewing thread in a boat thread. On the other side of the fabric, three parallel seams are sewn perpendicular to the ones previously sewn, forming a single-layer capacitive pressure-sensitive sensor. The stitches were connected to a chip that transmits data to a smart device via Bluetooth or via a USB connecting cable, where the data is displayed visually in a 3 × 3 large matrix.

The novelty of the method, in contrast to previous studies, is that the pressure sensor consists of one piezo-resistive textile layer, on both sides of which electrodes are embroidered in the form of a matrix.

Materials

From the previous research (Vališevskis et al., 2023b; Vališevskis et al., 2023c; Kukle et al., 2024), it was found that piezo-resistive textile Sefar Carbotex line made by Sefar AG (Heiden, Switzerland)- Sefar Carbotex 03-120CF, 03-160CF, 03- 205CF, and EeonTex LTT-SLPA 60 kOhm (Eeonyx Corp., Pinole, CA 94564) are suitable for the development of a single-layer pressure sensor. Carbotex line textiles are classified by mesh opening (120 μm, 160 μm, and 205 µm), and they have carbon threads with different sizes and configurations. These are woven fabrics, composed of polyester threads in warp direction and unidirectional weft threads, made of carbon-loaded composite material, which alternate with non-conductive polyester threads. According to surface density (0,85 g/m 2) and thickness (225 µm) for the experiments, Sefar Carbotex 03-205CF fabric was chosen as the most suitable for embroidery. This conductive textile has carbon-impregnated composite threads interwoven in a warp direction with alternating polyester threads. Warp threads are exclusively made of polyester.

EeonTex LTT-SLPA 60 kOhm is a bi-directionally stretchable elastic knitted fabric containing 72% nylon and 28% spandex, and is coated with a proprietary conductive formulation, based on conductive polymers. Its area density is 163 g/m2, and it has a thickness of 0.38 mm. It is made by Eeonyx Corp. (Pinole, CA, United States).

The choice of electroconductive thread for embroidery is based on the authors’ research (Briedis et al., 2016; Briedis et al., 2022; Briedis et al., 2017), where it was used in the production of Al-air battery and textile moisture sensor constructions. Although previous studies used Madeira HC 12 (Madeira Garnfabrik, Freiburg, Germany) (electrical resistance is <100 Ω/m) electroconductive embroidery thread to achieve the best electrical conductivity performance and stability for the sensor in this study, the authors chose to use Thermotech N-30 (Tibtech Innovations, Parc d’Activités Pierre Mauroy, France 59223 RONCQT) which is a non-insulated multifilament steel yarn with 30 Ω/m electrical resistance and has previously shown excellent performance in providing electrical connections when used as bobbin thread in embroidery. The electrical conductivity of a closed-circuit embroidery element was investigated in previous research (Juchnevičienė et al., 2018).

Methods

Automated embroidery technology was chosen for the production of pressure sensor electro-conductive electrode traces from conductive embroidery thread on both sides of the electro-conductive fabric. The choice of embroidery technology is based on its applicability to ready-made piezo-resistive fabrics (compared to the time-consuming use of knitting or weaving), easy programming with an embroidery computer program, and rapid electrode production with automated embroidery.

An electronic system based on a SAM D21 32-bit microcontroller was built for signal recording and pre-processing. The system measures resistance with a sampling rate of around 80 kHz and has a built-in threshold for impact detection. Upon detection of the impact, the data points right before and after the impact were transferred to a computer via a serial communication port. Threshold activation ensured automatic data alignment and simplified further data analysis.

To test the pressure sensitivity of the selected matrix pressure sensor, the sensors fabricated with embroidery were tested using a Zwick/Roell Z2.5 (ZwickRoell GmbH & Co. KG, August-Nagel-Straße 11, 89079 Ulm, Germany) compression/strain test column by pressing the sensors between 20 × 20 mm polyimide plates directly connected to Zwick clamps with an initial preload of 0.5 N in three pressing force ranges: 0.5–5.0 N, 0.5–50.0 N, and 0.5–100.0 N, corresponding to pressure levels of 15 kPa, 125 kPa, and 250 kPa (Figure 1).

An Agilent A34970A (Agilent Technologies, Inc. Headquarters. 5301 Stevens Creek Blvd, Santa Clara, CA 95051, USA) ohmmeter was used to measure the resistance during the experiments. This device has a high declared accuracy of 0.008% of reading plus 0.001% of range (according to the manufacturer’s accuracy specifications). This has a minimal effect on the experiments due to the nature of the materials subjected to testing, due to the drift and hysteresis observed during experiments.

Pressure sensor construction

As a result, two matrix-type (6 × 4 rows and columns) pressure sensors were created. One sensor uses Sefar Carbotex 03–205 CF piezo-resistive fabric, but another sensor uses EeonTex LTT-SLPA 60 kOhm knitted fabric. The constructions of both sensors are identical; both consist of 6 electrode lines horizontally and 4 electrode lines vertically. Each of the electrode lines is located on different sides of the piezo-resistive fabric.

Fabric Sefar Carbotex 03–205 CF has woven carbon and nylon 6.6 composite material in the weft direction, but in the warp direction - nylon 6.6 threads, which means that its electrical conductivity can be observed only in the weft direction. This fabric has piezo-resistive properties, which are one of the most important properties for the development of such a sensor. The fabric is stiff enough to embroider with an embroidery sewing machine, yet flexible and thin enough to accommodate deformation caused by pressure.

Fabric EeonTex LTT-SLPA 60 kOhm is a knitted fabric, which means more elasticity and a possible greater response to the recognition of the imposed load, as confirmed in previous studies (Vališevskis et al., 2023b; Vališevskis et al., 2023c).

One type of conductive thread was used to embroider the sensor electrodes: Thermotech N-30 (Tibtech) thread.

Use of embroidery software for sensor electrode designing.

The embroidery design of the sensor electrode was designed in the embroidery computer program Brother PE-DESIGN V8. The “snake” shape pattern of the sensor electrode was created by three-step zig-zag stitches based on previous studies (Cheng et al., 2016; Laurino et al., 2019). The zig-zag pattern was chosen so that the conductive thread forming the electrode is positioned at a 45-degree angle to the warp and weft threads of the fabric, which prevents possible penetration between them and a possible short circuit.

At the end of each line of electrodes, there is a place to connect the wires that will connect the embroidery to the chip. Fine 1 mm copper wires covered with insulating material - polysilicon were used as connecting wires. The embroidery design was engineered to fit in the largest embroidery frame available, measuring (300 × 200) mm. Size of one vertical sensor electrode line (width x length) = (25 × 173) mm. Size of one horizontal sensor electrode line (width x length) = (25 × 257) mm. It is possible to place 6 vertical sensor electrode lines and 4 horizontal sensor electrode lines in the given area. 66 crossing points are formed between the horizontal and vertical sensor electrode lines. See screenshots from the embroidery computer program PE DESIG (Figure 2).

Thread tension experiments for sensor embroidery

The matrix pressure sensor consists of horizontal electrode (X) and vertical electrode (Y) lines. For it to be able to determine the location of the pressure, it is necessary to ensure that the vertical and horizontal electrode lines, which are made of electrically conductive threads, do not touch (connect) at rest. They are sewn on both sides of the piezo-resistive fabric-first, the horizontal electrode lines are created by embroidery on one side of the fabric, and then the vertical electrode lines are sewn on the other side of the fabric.

To produce the right electro-conductive thread placement, it is needed to get a lockstitch seam where this electro-conductive thread forms a line on one side of the fabric (see B thread in Figure 3).

Given the limitations that the lector-conductive thread Thermotech N-30 cannot be used as a needle thread, experiments were conducted to determine the tension of the thread to achieve an indicator that the Thermotech N-30 thread stretches in a line when used as a bobbin thread.

In the embroidery preparatory experiments both fabrics - Sefar Carbotex 03–205 CF and EeonTex LTT-SLPA 60 kOhm were used.

For the embroidery Brother PR-600 II lockstitch embroidery sewing machine was used.

To ensure that the electrically conductive thread is placed in the line, it is necessary to adjust the right tension of the needle and the bobbin threads. In the experiment, three 2-section “meander” patterns were embroidered onto the fabric scrap with the controlled pre-adjusted tension of the needle and the bobbin thread. They were measured in grams (g) and adjusted with a needle tension dial and bobbin thread tension screw. The both thread tension values were measured with a Sauter dynamometer. The needle thread by pulling the thread up from the thread tensioner, but the tension of the bobbin thread was measured by pulling the thread from the bobbin thread holder.

It is generally believed that for lockstitch sewing machines, in properly balanced seams, the needle thread and shuttle thread should be interlocked in the middle of the sewn fabric (thread consumption should be the same), and the recommended needle and bobbin thread tension varies according thread used between 15 and 30 g (Juki corporation, 1999). For the most commonly used lockstitch sewing, the needle thread tension is 20 g and the shuttle thread tension is 20 g. In embroidery, the tensions are different, because it must be ensured that the upper needle thread will be visible from the surface, but the lower bobbin thread can never appear on the surface. In this regard, the bobbin thread is tensioned more tightly and can reach a value of 40–50 g.

In experiments electro-conductive thread used in bobbin Thermotech N-30 is light brown. Red embroidery thread colors were chosen for the second (nonconductive 100% polyester embroidery No 40 thread) for more visibility.

After testing with conventional thread tension adjustments for embroidery (needle thread tension 20 g and bobbin thread tension 50 g) it was concluded although the electro-conductive thread is on the bottom of the fabric, it is also somewhere visible on the surface of the fabric, which can cause a short circuit with the other fabric side electrode (Figure 4).

To achieve the desired result, the tension of the bobbin thread was increased. The needle thread tension was also increased slightly to ensure stable seam formation. The following thread tensions were obtained, which ensure that no short circuits will occur between the sensor electrodes: Needle thread tension – 30 g

Bobbin thread tension – 70 g.

The obtained result is shown in Figure 5. No bobbin (electro-conductive) thread is visible anywhere on the surface of the fabric. This method allows for control of whether the embroidery thread is pulled to the other side of the embroidery while embroidering.

Sensors development

Sensor No 1 - Sefar Carbotex 03–205 CF with Thermotech N-30 thread.

The embroidery sequence was programmed with the Brother PE-Design V8 embroidery design software.

In the first experiment, the sensor was built using Sefar Carbotex 03–205 CF with Thermotech N-30 multifilament steel electro conductive thread in bobbin was made. The piezo-resistive fabric was placed in an embroidery frame, which was then placed in an embroidery sewing machine. Initially, all the horizontal (4 pcs) lines of sensor electrodes were embroidered on one side of the piezo-resistive fabric. For this kind of fabric, no additional supporting material - stabilizer was used because of stability (no elasticity) of woven fabric.

Once they were embroidered, electrical wires (yellow) were manually attached to the end of each line of electrodes, which were then sewn together with a securing stitch (blue) using an embroidery machine. When the horizontal sensor electrode lines were completed, the piezo-resistive fabric was turned to the other side, and the vertical sensor electrode lines (6 pieces) were embroidered. Wires were sewn to the end of each electrode in the same way as for the horizontal electrodes. The Brother PR-600II embroidery machine available in the laboratory does not have a power cord holder and driver attachment, but TFP (tailored fiber placement) technology and appropriate equipment can be used for full process automation (https://www.tfp-tech.com). The result was an embroidered pressure sensor with connecting wires attached (see Figure 6).

Using connecting wires, the sensor lines were connected to the Seeeduino XIAO board with an SAMD21 series microcontroller integrated into the matrix-type sensor signal reading board. This sensor readout board was developed in project No VPP-AIPP-2021/1–0009 within the framework of “Prototype of lightweight ballistic protective vest enhanced with graphene and silicon aerogel with an integrated multi-zone pressure-sensitive layer for impact detection”. The sensor can be connected to a computer using the USB C type data transmission connecting cable. In the “Processing 4” software, the pre-built software will display the data in a 4 × 6 field matrix. The sensor was placed on a soft surface, connected to a computer, and its operation was tested. Pressure was applied by hand and observations were made on the computer screen. At rest, no changes are observed in the matrix, however, as a result of the pressure, the movement of the matrix squares is visible on the computer screen. When pressure was applied to the sensor, the specific square in the matrix moved on the computer screen (see Figure 11).

Sensor No 2 - EeonTex LTT-SLPA 60 kOhm with Thermotech N-30 thread.

The conditions of the embroidery process are different from the previous ones due to the specifics of embroidery of knitted fabric. To prevent the elasticity of the fabric during embroidery, a special support material was used - a stabilizer on the surface of the fabric. The stabilizer was attached to the surface of the fabric to achieve contact of the conductive thread of the bobbin with the piezo-resistive fabric. The stabilizer with an adhesive coating was used and attached to the fabric by ironing (see. Figure 7).

Once electrodes on one surface of fabric were embroidered, electrical wires (yellow) were manually attached to the end of each line of electrodes and connected together with a securing stitch (blue) using an embroidery machine. Adhesive tape (orange) was used to better secure the electrical wires to the fabric before sewing it on. After sewing, the stabilizer paper was teared off, but it remained under the threads, which does not affect the sensors operation.

Figure 8 show embroidered vertical electrodes on fabric surface and underside.

When the horizontal sensor electrode lines were completed, the piezo-resistive fabric was turned to the other side, stabilization attached to the other side of fabric, and the vertical sensor electrode lines (6 pieces) were embroidered. Wires were sewn to the end of each electrode in the same way as for the horizontal electrode. In the Figure 9 can see the finished sensor.

Sensors pressure sensitivity testing

Sensors pressure sensitivity were tested using a Zwick/Roell Z2.5 compression/strain test column by pressing the sensors between 20 × 25 mm polyimide plates directly connected to Zwick clamps with an initial preload of 0.5 N in three pressing force ranges: 0.5–5.0 N, 0.5–50.0 N, and 0.5–100.0 N, corresponding to pressure levels of 15 kPa, 125 kPa, and 250 kPa. Agilent A34970A ohmmeter was used to measure the resistance during the experiments. A total of 24 cyclic tests were performed. Each sensor was tested at 4 points, start load was set to 0,5 and equipment performed 7 cycles with testing speed 0.5 N/min or 5 N/min, depending on the testing range.

It can be seen from the Figure 10, that Carbotex fabric sensor has low load cycling repeatability in the low range (0,5-5N), but it becomes better in middle (0,5–50N) and high range (0,5–100N), but it varies significantly depending on the pressure point and it is difficult to summarize an approximate range of changes in the load and resistance values of the Carbotex fabric sensor.

Figure 11 shows the change in sensor resistance made of Eontex fabric values depending on the applied load and hysteresis curves of the relevant areas. This sensor shows better cycling repeatability in the low, middle and high range, and the values at different pressure points are comparable.

The sensitivity of the resistive pressure sensor (S) is defined by Equation 1: where Δ R –change of resistance and.

R 0 – initial resistance without applied pressure,

P– pressure, kPa.

In Table 1, the sensitivity values for the sensors tested, calculated according to (1), can be found. For the Carbotex fabric sensor with the increase in pressure resistance decreases, but for the Eontex fabric sensor, it increases. This can be explained by the elasticity of the Eontex fabric, as it is made of knitted fabric.

Pressure sensor testing

The sensor was placed on a soft surface, connected to a computer, and its operation was tested. Pressure was applied by hand and observations were made on the computer screen.

(see Figure 12). At rest, no changes are observed in the matrix; however, as a result of the pressure, the movement of the matrix squares is visible on the computer screen. When pressure was applied to the sensor, the specific square in the matrix moved on the computer screen.

From the results obtained, it can be concluded that unlike previous studies where the authors used Madeira H-12 thread for electrodes, the Thermotech N-30 conductive thread used in this study shows good applicability with embroidery in a bobbin with experimentally obtained thread tension values, much better electrical conductivity values (30 Ω/m vs. 100 Ω/m) and provides better sensor sensitivity- 0,002–0,005 kPa (Eontex fabric sensor). In addition, it must be concluded that it is better to use a sensor made of Eontex fabric, as it has good pressure sensitivity properties, and the hysteresis values in most cases vary from 0.83 to 0.94, which are comparable to the values obtained for the 3-layer sensor in previous studies.

A thin matrix-type pressure sensor made of a single-layer textile was developed, which can record the location of pressure application and determine the force applied. The pressure sensor provides information on changes in the electrical resistance of the piezo-resistive textile at the moment of impact. The study concluded that Carbotex and Eontex fabrics are among the thinnest piezo-resistive fabrics for creating a thin pressure sensor. Still, sensor from Carbotex fabric does not have the best pressure sensitivity properties for determining pressure magnitude-it varies significantly depending on the pressure point and it is difficult to summarize an approximate range of changes in the load and resistance values and hysteresis values changes in most cases from 0,44 to 0,94 with sensitivity values in range of 0,004–0,05 kPa, but it is more durable. Sensor from Eontex fabric has good pressure sensitivity properties and hysteresis values changes in most cases from 0,83 to 0,94 with sensitivity values in range 0,002–0,005 kPa, it is more elastic and not as durable. Sensor from Eontex fabric has been proposed as having potential use in smart textiles.

The paper reported on research demonstrating that embroidery technology can be used to produce a single-layer thin-matrix type textile pressure sensor industrially. It has been experimentally proven that for the electrodes production with embroidery technology, steel multifilament conductive thread in a bobbin can be used, which solves the problems with the inefficient conductivity of electro-conductive threads. Depending on the application, the pressure sensor can be of different sizes; alternatively, it can be made with different numbers of vertical and horizontal electrodes. This type of sensor has a multi applications; it can be used in mattress toppers to monitor body print, as well as in fencers’ equipment or bullet impact detection in soft body armor and in the field of protective smart clothing for operators, working in environments with a risk of injury due to impact with moving parts or falling objects, e.g., operator of heavy agricultural machinery, first responders etc. Further research will include in-depth studies of sensor electrode configurations for various application areas, calibration and repeatability studies of specific sensors.