WO2021107884A1

WO2021107884A1 - Pressure sensor and a method of sensing pressure

Info

Publication number: WO2021107884A1
Application number: PCT/SG2020/050703
Authority: WO
Inventors: Suryakanta Nayak; Aaron Voon-Yew THEAN; Yida Li
Original assignee: National University Of Singapore
Priority date: 2019-11-28
Filing date: 2020-11-27
Publication date: 2021-06-03

Abstract

A pressure sensor and a method of sensing pressure using the pressure sensor. the pressure sensor comprises a sensor element array, each sensor element comprising two opposing electrode elements; and a porous mat disposed between the two opposing electrode elements of the sensor element; wherein the porous mat exhibits a different capacitance in a compressed state with a force applied to the opposing electrode elements compared to a relaxed state with no force applied to the opposing electrode elements.

Description

PRESSURE SENSOR AND A METHOD OF SENSING PRESSURE

FIELD OF INVENTION

The present invention relates broadly to a pressure sensor and a method of sensing pressure, in particular the use of porous soft composite material as pressure/weight measurement sensor, specifically in the insole of a shoe for healthcare applications.

BACKGROUND

Any mention and/or discussion of prior art throughout the specification should not be considered, in any way, as an admission that this prior art is well known or forms part of common general knowledge in the field.

A pressure sensor is a device for pressure measurement in different applications. Pressure sensors have many applications in day-to-day life for controlling and monitoring different components, with great importance in healthcare and robotics for human machine interaction. Capacitive based pressure sensors have high sensitivity and robust structure, and are less sensitive to side stress and other environmental effects. However, their output is nonlinear with respect to input changes and the sensitivity in the near-linear region is not high enough to ignore many stray capacitance effects. Usually, pressure sensors are based on static mode of measuring the pressure. For example, existing weighing devices can only measure a person’s weight statically. Also, current smart watches usually use accelerometer/gyroscope for step count monitoring, and can give the step count even when the watch moves due to some physical disturbance instead of a person’s walk. So, most of the time the readings obtained are inaccurate.

As an application example, foot ulceration is a common complication due to diabetes. The structural foot deformities, limited mobility of joints, and muscle weakness/atrophy occur in both type 1 and type 2 diabetes. The above complications may occur due to hyperglycemia and play a significant role in increasing plantar pressures. The measurement of plantar pressure is frequently used to assess the gait conditions associated with diabetes as excessive pressure in specific areas may cause foot ulceration. The excessive pressure in feet, which lacks protective sensation, is considered as a major risk factor for plantar ulceration. Therefore, it is desired to implement effective diabetic foot care protocols in primary care settings to prevent the above complications [1, 2].

Gnanasundaram et. al. [2] have investigated the dynamic plantar pressure profile of persons with diabetes without neuropathy and the diabetic neuropathy without any foot deformity and morphological changes. They also compared the above result with a healthy control group to identify the initial risk factor leading to abnormal plantar pressure profile in persons with diabetes. In their study, subjects walked on a two-meter length BTS-P walk, which is a system to measure both static and dynamic plantar pressure. Gerlach et. al. [3] have used a low cost multi-walled carbon nanotube (MWCNT)-polydimethylsiloxane (PDMS)-composite as a sensor material for plantar pressure monitoring in ulcer prevention. They used six different printed sensors situated on characteristic points of the insole of a shoe to detect the unhealthy rollover patterns. Robles et. al. [4] have developed a monitoring system for plantar pressure distribution during walking. Their sensor is based on piezoresistive material sandwiched between two pieces of polyester and they used eight piezoresistive force sensors distributed in areas with the highest plantar pressure during walking. The above device is used on the shoe insole. Their device also has wireless communication for the continuous acquisition of signals and a graphical interface for viewing and storing data.

Currently, diabetic foot screening is static. The manufacturing cost of the sensing systems are also very high.

Embodiments of the present invention seek to address one or more of the above problems.

SUMMARY

In accordance with a first aspect of the present invention, there is provided a pressure sensor comprising: a sensor element array, each sensor element comprising two opposing electrode elements; and a porous mat disposed between the two opposing electrode elements of the sensor element; wherein the porous mat exhibits a different capacitance in a compressed state with a force applied to the opposing electrode elements compared to a relaxed state with no force applied to the opposing electrode elements.

In accordance with a second aspect of the present invention there is provided a method of sensing pressure using the pressure sensor of the first aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be better understood and readily apparent to one of ordinary skill in the art from the following written description, by way of example only, and in conjunction with the drawings, in which:

Figure 1(a) shows a schematic representation of a porous mat based pressure sensor according to an example embodiment.

Figure 1(b) shows a schematic representation of a porous mat based pressure sensor according to another example embodiment,

Figure 2(a) shows a schematic representation of main pressure points of a foot. Figure 2(b) shows a photograph of pressure sensor in the form of an insole with eight sensors at different locations, according to an example embodiment.

Figure 2(c) shows a bar-chart illustrating capacitance values corresponding to the applied pressure at different locations of a foot applied to the pressure sensor of Figure 2(b).

Figure 3 [Nayak, Suryakanta, et al. "Liquid-metal-elastomer foam for moldable multi functional triboelectric energy harvesting and force sensing." Nano Energy 64 (2019): 103912.] is used to illustrate the general concept of smart footwear with energy harvesting, force sensing capabilities, and wireless data connectivity as an example application field for example embodiments.

Figure 4 [Nayak, Suryakanta, et al. "Liquid-metal-elastomer foam for moldable multi functional triboelectric energy harvesting and force sensing." Nano Energy 64 (2019): 103912.] shows the schematic representation of testing conditions of one single sensor element for use in a sensor element array according to example embodiments with porous composite sandwiched between upper and lower electrodes.

Figure 5(a) and (b) [Nayak, Suryakanta, et al. "Liquid-metal-elastomer foam for moldable multi-functional triboelectric energy harvesting and force sensing." Nano Energy 64 (2019): 103912.] show the output current (Isc) and voltage (Voc), respectively, with respect to different types of motion of one single sensor element for use in a sensor element array according to example embodiments.

Figure 6(a) (b) [Nayak, Suryakanta, et al. "Liquid-metal-elastomer foam for moldable multi functional triboelectric energy harvesting and force sensing." Nano Energy 64 (2019): 103912.] show, respectively, the variation of Capacitance with applied force for composite with optimum composition and single sensor element samples of three different thicknesses (1, 2, and 3 cm) and area of 5 cm x 5 cm for use in a sensor element array according to example embodiment, and the dynamic capacitance as a function of time at two different cyclic compressive forces (700 N and 2000 N) for two of the single sensor elements samples with thicknesses 1 and 3 cm. Ecoflex-LMA composite in the form of an insole was used as the porous material between the opposing electrodes.

Figure 7 shows a schematic presentation for the preparation of porous LMA-Ecoflex composites for use in example embodiments. [Nayak, Suryakanta, et al. "Liquid-metal- elastomer foam for moldable multi-functional triboelectric energy harvesting and force sensing." Nano Energy 64 (2019): 103912.]

Figure 8 shows a schematic representation of energy harvesting mechanism involved during compression-relaxation cycles of a single cavity. [Nayak, Suryakanta, et al. "Liquid-metal- elastomer foam for moldable multi-functional triboelectric energy harvesting and force sensing." Nano Energy 64 (2019): 103912.]

Figure 9 shows a schematic representation of energy harvesting mechanism involved during contact- separation between top copper electrode and the porous composite. [Nayak, Suryakanta, et al. "Liquid-metal-elastomer foam for moldable multi-functional triboelectric energy harvesting and force sensing." Nano Energy 64 (2019): 103912.]

DETAILED DESCRIPTION

Embodiments of the present invention provide a pressure sensor based on soft porous composite material, which can have a range of applications including in the field of healthcare monitoring, robotics, and human-machine interaction.

The composite capacitive sensor is a mixture of highly elastic material, in one embodiment Ecoflex and liquid metal alloy (LMA_Galinstan_Liquid at room temperature_Melting point = -19 °C) is used. Sodium chloride (NaCl) has been used as a sacrificial template during fabrication of the sensors according to example embodiments described herein, which are removed to get the porous matrix. The detailed description of the fabrication process for LMA-Ecoflex composites according to a non-limiting example embodiment is given below with reference to Figure 7.

As illustrated in Figure 7, the mixing of Ecoflex 700A, B (Ecoflex 0030 Part A/B, Smooth on) and other ingredients [liquid-metal- alloy 702 (LMA-Galinstan, Ga62hi22Sni6, Good fellow, UK) and NaCl particles 704 (Sigma Aldrich)] was done by a high-speed blender with a micro-container 706. Initially, the micro-container 706 was kept inside a refrigerator for 15- 45 minutes to avoid excess heating during the ingredients mixing/blending process. Then, Ecoflex 0030 (Part A) 700A was placed in the micro-container 706 followed by the addition of LMA 702 and anhydrous sodium chloride particles 704. The mixing was done for 4-15 minutes at 2, 000 - 30, 000 rpm and the above mixed mass with the container 706 was kept inside refrigerator for 5 - 60 minutes to cool down to the room temperature. Finally, equal weight part of Ecoflex 0030 (Part B) 700B [Part A:Part B = 1:1] was added to the above mixture and mixed for another 1 - 10 minutes at 2, 000 - 30, 000 rpm. The above composite mixtures were casted into different acrylic molds and cured at 90 ⁰ - 150 °C for 15 - 45 minutes. The cured composites were immersed in hot deionized (DI) water (heated at 100 - 250 °C) for 1 - 3 h followed by 24 - 48 h in cold water and this step was repeated three times. Fresh DI water was used after every 24 - 48 h to ensure that all the salt dissolved completely. After the above process, the samples with DI water were kept in furnace at 90 °C for 72 h, where fresh DI water was used after every 24 h. The NaCl particles 704 were used as a sacrificial template, i.e. dissolving in the process leaving pores e.g. 708. The mass ratio between the NaCl particles 704 and Ecoflex 700A,B in LMA-Ecoflex composites was adjusted to control the porosity.

In the example composites, 10 g (parts) of Ecoflex 700A,B is used as the base matrix. The concentration (by weight parts) of LMA 702 and NaCl particles 704 is varied with respect to the above base matrix (Ecoflex 700A,B).

It is noted that the present invention is not limited to the use of LMA. Other nanomaterials such as carbon black powder, carbon fibers, graphene, CNTs, and metal nanoparticles can be utilized. In example embodiments, sensing shoe insoles are provided based on Ecoflex-LMA and Ecoflex-carbon black composites. In different embodiments, PDMS, Polyurethane (PU) and other rubbers may be used.

The operation principle of Ecoflex-Galinstan based insoles according to example embodiments was tested with respect to different types of human motion and the output was in the form of capacitance change with respect to the applied force given by different types of human motion. The operation principle of insoles according to example embodiments was also tested with persons of different weight and it was found that different signals are generated as the person’s weight changed. The measurement method according to example embodiments can also be helpful to get the calories loss information during any physical activities by a person. The composite porous material can be readily molded into any shape, including a desired insole shape, demonstrating ease of fabrication as well as the ability to conform well to the foot as well as in shoes so that it can sense force at any place of the foot. By monitoring the foot pressure at eight different locations according to an example embodiment, diabetic patients can monitor their walking habit by measuring the plantar pressure.

The porous material according to example embodiments, e.g. made up of Ecoflex and carbon black, is cheap and can be easily commercialized. The present invention is also not limited to the insole. In other embodiments, the sensor can also be made in the form of a door mat or room mat with an array of sensors. Sensors according to example embodiments, e.g. based on shoe insole or pressure mat, can be useful in the healthcare industry to monitor plantar pressure in diabetic patients and also to measure person’s weight both statically and dynamically. In addition, in the field of robotics, sensors according to example embodiments can be used on a robotic hand or other parts of a robot to provide better safety of a robot to avoid any mechanical hazard/damage. Also, the pressure sensors according to example embodiments can be placed on gloves’ surface and can be used for human-machine interface applications. The devices according to example embodiments, e.g. the insole/pressure-mat, can be used both as a capacitive sensor and for motion-based energy harvesting.

In one example embodiment of the present invention, porous soft composite material as capacitive pressure/weight measurement sensor built in the insole of a shoe is provided for healthcare applications. However, as described above other embodiments of the present invention can also be used, for example, on robot hands as pressure sensor, for human- machine interaction, for motion-based energy harvesting, and in the form of door/room mat.

In the example embodiments described below, copper is used for the construction of a metal electrode array. However, the present invention is not limited to the use of copper, i.e. other conducting materials, including other conducting metals, can be used in different embodiments.

Figure 1(a) shows a schematic representation of a porous mat 100 based pressure sensor 101 according to an example embodiment, with upper electrodes e.g. 102, 104 and lower electrodes e.g. 106, 108 forming an array of copper electrodes. The electrodes e.g. 102, 104, 106, 108 are used on both (top and bottom) sides of the porous mat 100. The electrodes e.g. 102, 104, 106, 108 and porous mat 100 are covered by pure PDMS layers 110, 112 in this embodiment from both top and bottom sides in order to avoid moisture and impurities, which may affect the sensor performance. The testing can be done, for example, over a frequency, f, range from 100 Hz to 1 MHz at an AC bias voltage of 1 V between the upper and lower electrodes e.g. 102, 104, 106, 108 to get capacitance (C) using a E4980AL LCR meter. Accordingly, the sensor 101 according to an example embodiment incorporates an array of individual sensor elements e.g. 114 between opposing portions of the upper electrodes e.g. 102 and the lower electrodes e.g. 106, respectively. As will be appreciated by a person skilled in the art, the individual sensor elements e.g. 114 are addressable for measurements using measurement lines connected to the respective upper and lower electrodes e.g. 102, 104, 106, 108.

Figure 1(b) shows a schematic representation of a porous mat 150 based pressure sensor 151 according to another embodiment, with electrodes e.g. 152, 154 on one side (e.g. top side) of the porous mat 150 and a single electrode 156 on the other side (e.g. bottom side) of the porous mat 150 forming an array of electrodes, e.g. made from copper. The electrodes e.g. 152, 154, 156 and porous mat 150 are covered/embedded for protection, e.g. by pure Polydimethylsiloxane, PDMS, layers 160, 162 in this embodiment from both top and bottom sides in order to avoid moisture and impurities, which may affect the sensor performance. In a different example embodiment, unloaded Ecoflex rubber may be used instead of PDMS. The testing can again be done, for example, over a frequency, f, range from 100 Hz to 1 MHz at an AC bias voltage of 1 V between the electrodes e.g. 152, 154 and the single electrode 156 to get capacitance (C) using the E4980AL LCR meter. Accordingly, the sensor 151 according to an example embodiment incorporates an array of individual sensor elements e.g. 164 between the respective electrodes e.g. 152 and the opposing portions of the single electrode 156. As will be appreciated by a person skilled in the art, the individual sensor elements e.g. 164 are addressable for measurements using measurement lines connected to the respective electrodes e.g. 152, 154 and the single electrode 156.

Figure 2(a) shows a schematic representation of main pressure points of a foot. Figure 2(b) shows a photograph of pressure sensor 200 in the form of an insole with eight sensors (l)-(8) at different locations, with the electrode pairs comprising one of the eight sensors (l)-(8) and different respective opposing portions of a single electrode sheet 202, according to an embodiment as broadly described above with reference to Figure 1(b). Figure 2(c) shows a bar-chart illustrating capacitance values corresponding to the applied pressure at different locations of a foot applied to the pressure sensor 200. Ecoflex-LMA composite was used for the porous shoe insole in the sensor 200 of Figure 2(b).

With reference to Figure 3 [Nayak, Suryakanta, et al. "Liquid-metal-elastomer foam for moldable multi-functional triboelectric energy harvesting and force sensing." Nano Energy 64 (2019): 103912.], the insole based sensor according to example embodiments with capacitive response to deformation, enables the sensor to perform in-motion pressure/weight measurement while worn by a user 300 using porous composite materials 302 with sensor element array (not shown in Figure 3, but compare Figure 1(a) and (b)). Figure 3 illustrates the general concept of smart footwear 304 with energy harvesting (triboelectric current flow indicated upon compression (numeral 306) and relaxing (numeral 308) of the porous composite material 302), force sensing capabilities (numeral 310), and wireless data connectivity (numerals 312, 314). Figure 4 [Nayak, Suryakanta, et al. "Liquid-metal- elastomer foam for moldable multi-functional triboelectric energy harvesting and force sensing." Nano Energy 64 (2019): 103912.] shows the schematic representation of testing conditions of one single sensor element 400 (only) for use in a sensor element array according to example embodiments with porous composite 402 sandwiched between upper and lower electrodes 404, 406, respectively. During testing, a shoe insole with the single embedded sensor element 400 is kept inside the shoe, for obtaining measurement results representative of measurement results obtainable from a of sensor element array for use according to example embodiments. The change in pressure information is collected from the change in capacitance data upon compressive cycles. The shoe insole with single sensor element was tested with different modes of human motion to check the person’s force/weight with respect to each type of motion. Ecoflex-LMA composite in the form of the insole was used as the porous material between the opposing electrodes.

Figure 5(a) and 5(b) [Nayak, Suryakanta, et al. "Liquid-metal-elastomer foam for moldable multi-functional triboelectric energy harvesting and force sensing." Nano Energy 64 (2019): 103912.] show the output current (Isc) and voltage (Voc) with respect to different types of motion, of one single sensor element for use in a sensor element array according to example embodiments. Figure 5(a) shows the short circuit current (Isc) and Figure 5(b) shows the open circuit voltage (Voc) profiles at different stages of human motion: foot pressing, tip toeing, bending, walking, stomping, and jogging (person’s weight = 73 kg). The output current (Isc) and voltage (Voc) are highest in case of jogging which are ~13 mA and -200 V respectively. The capacitance value with both static and dynamic forces was also measured and it was observed that there is increase in capacitance with more force applied, which is due to the thinning of the porous composite material. Ecoflex-LMA composite in the form of the insole was used as the porous material between the opposing electrodes.

Figure 6(a) and (b) [Nayak, Suryakanta, et al. "Liquid-metal-elastomer foam for moldable multi-functional triboelectric energy harvesting and force sensing." Nano Energy 64 (2019): 103912.] show, respectively, the variation of Capacitance with applied force for composite with optimum composition and samples of three different thicknesses (1, 2, and 3 cm) and area of 5 cm x 5 cm, and the dynamic capacitance as a function of time at two different cyclic compressive forces (700 N and 2000 N) for samples of two different thicknesses 1 and 3 cm. Ecoflex-LMA composite in the form of the insole was used as the porous material between the opposing electrodes.

According to example embodiments, a shoe insole or a pressure mat incorporating a sensor element array to investigate plantar pressure in case of diabetic patient can be provided, for example to detect force on the foot at eight different locations. The pressure mat can be helpful for patients, who are not using shoes at their home or using sandals. Embodiments of the present invention exploit a change in capacitance with loading of different static or cyclic forces, for providing pressure/weight measurement sensors incorporating a sensor element array for various applications such as in healthcare, robotics and human-machine interface.

In example embodiments, capacitance is used to check pressure/weight. Capacitance varies almost linearly with the applied pressure/weight. It is noted that while V/I can be measured when there is some motion and pressure/weight may be derived, capacitance can advantageously be measure in all cases (static/dynamic).

The pressure mat sensor according to one example embodiment can be useful to detect plantar pressure in diabetic patients.

The design of the electrodes of the sensor element array and the selection of operating conditions for frequency response analysis can be adapted to meet desired applications/specifications.

The charge generation mechanism according to example embodiments will now be described with reference to Figures 8 and 9. Figure 8 shows a single pore 800 structure which shows that negative charges e.g. 802 are gained by the Ecoflex 801 surface e.g. 803 of the pore 800 and compressing leaves positive charge e.g. 804 on the region with more FMA 805. Relaxing again leaves positive charge e.g. 806 below the Ecoflex surface e.g. 803 of the pore 800. Contact-separation mode happens between top electrode and the porous composite. With reference to Figure 9, initially, when the top electrode 900 touches the composite 902 surface it produces negative charges on the composite 902 surface and leaves positive charge on the top electrode 900. When the two surfaces are separated by a small gap 904, a potential drop is created. As both electrodes 900, 906 are connected by a load 908, free electrons (indicated at numeral 910) from bottom electrode 906 would flow to the top electrode 900 to build an opposite potential in order to balance the electrostatic field. Again, when the gap is closed, the triboelectric charges created potential disappears and electrons flow back (indicated at numeral 912) from the top electrode 900 to the bottom electrode 906.

In one embodiment, a pressure sensor is provided comprising a sensor element array, each sensor element comprising two opposing electrode elements; and a porous mat disposed between the two opposing electrode elements of the sensor element; wherein the porous mat exhibits a different capacitance in a compressed state with a force applied to the opposing electrode elements compared to a relaxed state with no force applied to the opposing electrode elements.

The porous mat may exhibit triboelectric properties for energy harvesting when changing between the compressed and relaxed states. The pressure sensor may be configured for harvesting the energy via the opposing electrode elements.

The pressure sensor may comprise multiple electrodes disposed on one side of the porous mat and a single second electrode disposed on another side of the porous mat, wherein each sensor element comprises one of the first electrodes and an opposing portion of the second electrode.

The pressure sensor may comprise multiple electrodes disposed on one side of the porous mat and multiple electrodes disposed on another side of the porous matt, wherein each sensor element comprises a portion of one of the multiple electrodes on the one side and an opposing portion of one of the multiple electrodes on the other side.

The pressure sensor may further comprise protective layers embedding the sensor element array and the porous mat.

The pressure sensor may be in the form of a shoe insole or a mat. In one embodiment, a method of sensing pressure using the pressure sensor of the above embodiment is provided.

The method may be applied to one or more of a group consisting of healthcare applications, monitoring plantar pressure in diabetic patients, measuring a person’s weight statically, measuring a person’s weight dynamically, robotic applications to provide better safety of a robot to avoid any mechanical hazard/damage, and human-machine interface applications.

The method may further comprise motion-based energy harvesting.

Embodiments of the present invention can have one or more of the following features and associated benefits/advantages:

Embodiments of the present invention can measure a person’s weight both statically and dynamically, and can hence be used as a fitness tracker and/or as a weighing scale.

Embodiments of the present invention can, for example, also solve the issues of: (i) providing both dynamic and static measurements of foot pressure, and (ii) confirming large-scale manufacturability of all device components at reasonable cost.

Aspects of the systems and methods described herein such as the signal measurement and processing may be implemented as functionality programmed into any of a variety of circuitry, including programmable logic devices (PLDs), such as field programmable gate arrays (FPGAs), programmable array logic (PAL) devices, electrically programmable logic and memory devices and standard cell -based devices, as well as application specific integrated circuits (ASICs). Some other possibilities for implementing aspects of the system include: microcontrollers with memory (such as electronically erasable programmable read only memory (EEPROM)), embedded microprocessors, firmware, software, etc. Furthermore, aspects of the system may be embodied in microprocessors having software- based circuit emulation, discrete logic (sequential and combinatorial), custom devices, fuzzy (neural) logic, quantum devices, and hybrids of any of the above device types. Of course, the underlying device technologies may be provided in a variety of component types, e.g., metal- oxide semiconductor field-effect transistor (MOSFET) technologies like complementary metal-oxide semiconductor (CMOS), bipolar technologies like emitter-coupled logic (ECL), polymer technologies (e.g., silicon-conjugated polymer and metal-conjugated polymer-metal structures), mixed analog and digital, etc.

The above description of illustrated embodiments of the systems and methods is not intended to be exhaustive or to limit the systems and methods to the precise forms disclosed. While specific embodiments of, and examples for, the systems components and methods are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the systems, components and methods, as those skilled in the relevant art will recognize. The teachings of the systems and methods provided herein can be applied to other processing systems and methods, not only for the systems and methods described above.

It will be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive. Also, the invention includes any combination of features described for different embodiments, including in the claims, even if the feature or combination of features is not explicitly specified in the claims or the detailed description of the present embodiments. In general, in the following claims, the terms used should not be construed to limit the systems and methods to the specific embodiments disclosed in the specification and the claims, but should be construed to include all processing systems that operate under the claims. Accordingly, the systems and methods are not limited by the disclosure, but instead the scope of the systems and methods is to be determined entirely by the claims.

Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise," "comprising," and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in a sense of "including, but not limited to." Words using the singular or plural number also include the plural or singular number respectively. Additionally, the words "herein," "hereunder," "above," "below," and words of similar import refer to this application as a whole and not to any particular portions of this application. When the word "or" is used in reference to a list of two or more items, that word covers all of the following interpretations of the word: any of the items in the list, all of the items in the list and any combination of the items in the list.

References

1. Falzon, Brooke, et al. "Duration of Type 2 Diabetes is a Predictor of Elevated Plantar Foot Pressure." The review of diabetic studies: RDS 14.4 (2018): 372-380.

2. Gnanasundaram, Saraswathy, et al. "Gait changes in persons with diabetes: Early risk marker for diabetic foot ulcer." Foot and Ankle Surgery (2019).

3. Gerlach, Carina, et al. "Printed MWCNT-PDMS-composite pressure sensor system for plantar pressure monitoring in ulcer prevention." IEEE Sensors Journal 15.7 (2015): 3647-3656.

4. Robles, A., et al. "Development of a Monitoring System for Vertical Plantar Pressure Distribution during Human Walking." 2019 Global Medical Engineering Physics

Exchanges/Pan American Health Care Exchanges (GMEPE/PAHCE). IEEE, 2019.

Claims

1. A pressure sensor comprising: a sensor element array, each sensor element comprising two opposing electrode elements; and a porous mat disposed between the two opposing electrode elements of the sensor element; wherein the porous mat exhibits a different capacitance in a compressed state with a force applied to the opposing electrode elements compared to a relaxed state with no force applied to the opposing electrode elements.

2. The pressure sensor of claim 1, wherein the porous mat exhibits triboelectric properties for energy harvesting when changing between the compressed and relaxed states.

3. The pressure sensor of claim 2, configured for harvesting the energy via the opposing electrode elements.

4. The pressure sensor of any one of claims 1 to 3, comprising multiple electrodes disposed on one side of the porous mat and a single second electrode disposed on another side of the porous mat, wherein each sensor element comprises one of the first electrodes and an opposing portion of the second electrode.

5. The pressure sensor of any one of claims 1 to 3, comprising multiple electrodes disposed on one side of the porous mat and multiple electrodes disposed on another side of the porous matt, wherein each sensor element comprises a portion of one of the multiple electrodes on the one side and an opposing portion of one of the multiple electrodes on the other side.

6. The pressure sensor of any one of claims 1 to 5, further comprising protective layers embedding the sensor element array and the porous mat.

7. The pressure sensor of any one of claims 1 to 6, in the form of a shoe insole or a mat.

8. A method of sensing pressure using the pressure sensor as claimed in any one of claims 1 to 7.

9. The method of claim 8, applied to one or more of a group consisting of healthcare applications, monitoring plantar pressure in diabetic patients, measuring a person’s weight statically, measuring a person’s weight dynamically, robotic applications to provide better safety of a robot to avoid any mechanical hazard/damage, and human-machine interface applications.

10. The method of claim 8 or 9, further comprising motion-based energy harvesting.