rus
Issue #2/2024
A.A.Terentyev, A.V.Smirnov
STUDY OF POSSIBILITY OF FLEXIBLE VARIABLE VESSELS FOR REMOTE PRESSURE MEASUREMENT SYSTEMS
STUDY OF POSSIBILITY OF FLEXIBLE VARIABLE VESSELS FOR REMOTE PRESSURE MEASUREMENT SYSTEMS
The technology of silicon deposition has been developed, and it has been possible to obtain a durable polycrystalline silicon film with good adhesion on a PET substrate with a thickness of 150...200 nm. Using this technology, a prototype of a flexible variable capacitance was prepared. The study of capacitance changes due to changes in pressure acting on it has a linear form, which makes it possible to use this technology for the manufacture of a pressure sensor.
INTRODUCTION
Nowadays there is a wide and intensive application of automation means both in domestic and industrial spheres. In this regard, the task of developing various sensors, or, as it is often called, sensors in measurement and automation systems becomes very relevant. The application of flexible electrical circuits in electronics is the technology of assembling electronic circuits by mounting its elements on a flexible plastic pad made of polyimides, polyetheretherketone (PEEK) or transparent conductive polyester film – makes it possible to significantly expand possibility of applying electronics and automation based on flexible electronic elements in various fields. For example, RFID technology is widely used because the current-carrying elements such as an inductive circuit, microchip or other electronic elements are applied to a flexible plastic pad. This technology, better known as RF tags, is used, for example, to create anti-theft systems – when a flexible tag is glued on the goods in supermarkets, as well as in various identification systems, such as passes, bank cards, etc. There are examples of such technology development, for example, and for anti-theft systems. There are examples of development and application of such technology, for example, for rapid remote diagnostics and monitoring of patient’s health. For this purpose, a specially manufactured tag with sensors is glued on certain areas of the human body, and a reader device, which is located nearby (e.g. in a pocket of the patient’s clothes or in a handbag carried by the patient), promptly monitors the patient’s condition and promptly informs the patient in case of deviations from normal values.
Figure 1 shows some typical samples of various electronic circuits fabricated on a flexible and polymer base [1].
Our team is developing a system for remote monitoring of air pressure in car tyres, allowing to monitor tyre pressure both while driving in real time and while parked. Currently there is only one remote pressure monitoring system on the market with direct measurement of current tyre pressure, the TPMS ("tire pressure monitoring system"). However, this system has a rather complex electronic filling of the sensor itself, which measures pressure in the wheel and transmits the data via radio channel to a central unit, which processes the data and displays the values on the display. In this system, the key element is the sensor itself with a rather complex electronic stuffing, moreover, requiring electrical power supply, which is carried out from galvanic cells or a miniature battery. With all the convenience of the system itself, presence of expensive sensors that require periodic replacement of batteries makes developers look for alternative solutions in which the sensors would be cheap, without the use of batteries.
RESEARCH METHODS
The main difference is that our development uses a passive oscillating circuit as a pressure sensor, the resonant frequency of which depends on pressure applied to the linings of oscillating circuit capacitance. In this case, capacitance is a variable capacitor with electrically conductive material (copper, silver, etc.) sprayed on both sides of the elastic-plastic material. In this case, the sensor itself is very simple and cheap (containing sputtered inductance and variable capacitance), it will be a flexible structure (e.g. film-based or other flexible) like a sticker that can be simply stuck inside a tyre. As a passive oscillating circuit, this sensor does not require any batteries.
During operation of such a system, a short packet of modulated electromagnetic radiation is sent to the sensor, frequency varies within a certain range. When frequency of the electromagnetic radiation coincides with the resonant frequency of the passive oscillating circuit of the sensor, it re-emits a signal, which is perceived by the transmitter antenna and frequency of this signal determines the pressure value when the sensor response is maximum. The maximum response occurs when transmitter frequency coincides with the resonant frequency of the oscillating circuit of the sensor. Modelling of film materials deformation in COMSOL [2], study of film parameters on a Fei Phenom scanning microscope, and measurement of pressure-capacitance dependence on a mock-up sample were carried out.
RESULTS AND DISCUSSION
The main difference is that our development uses a passive oscillating circuit as a pressure sensor, and the resonant frequency depends on pressure exerted on the linings of the oscillating circuit capacitance. In this case, capacitance is a variable capacitor with an electrically conductive material (copper, silver, etc.) sprayed on both sides of the elastic-plastic material. In this case, the sensor itself becomes very simple and cheap (containing the sputtered inductance and variable capacitance), and is a flexible construction (e.g., film-based or other flexible), similar to a sticker, which can be glued inside a tyre. As a passive oscillating circuit, such a sensor does not require any batteries.
During the system operation a short packet of modulated electromagnetic radiation is sent to the sensor, and frequency varies within a certain range. When electromagnetic radiation frequency coincides with the resonant frequency of the passive oscillating circuit of the sensor, it re-emits a signal, which is perceived by the transmitter antenna and the signal frequency determines pressure value at which the sensor response is maximum. The maximum response occurs when transmitter frequency coincides with the resonant frequency of the oscillating circuit of the transducer. In the development of this pressure monitoring system, an important task becomes the design of a variable capacitance, which must be flexible. All currently available technologies for manufacturing flexible electronic structures (RFID-technologies) do not imply the use of flexible variable capacitance, and there are no applications where it would be necessary. When developing a flexible variable capacitance, the value of which would depend on air pressure, it was decided to use parallel electrically conductive linings with an elastic-plastic dielectric between them. In this case, the electrically conductive linings simultaneously play the role of a membrane on which an external pressure, e.g. air pressure, acts. In this case, the distance between the linings is reduced, which increases the capacitance of the capacitor. When connected to the linings of such an inductance capacitor, an oscillating circuit with a resonant frequency varying depending on the external pressure is obtained. When choosing an elastic-plastic material, it was decided to use a dielectric with drilled holes containing air, which is known to be isotropic and elastic when pressurised to a certain volume. Thus, the problem was reduced to the task of applying a conductive layer to a polymer base to form shells of variable capacitance, placing between the shells a dielectric with holes for air bubbles, and providing sealing of the inter-cladding space to prevent air leakage from the holes in which it, in the form of bubbles, is disposed.
A 23 μm thick lavsan film with one-sided metallisation (Al film) was chosen as the base of the capacitor. A nanoscale silicon film was deposited on the non-metallised surface by laser ablation, which serves as an elastic element (membrane) of the capacitor.
Laser ablation is a method of removing substance from a surface by a laser pulse. At low laser power the substance vaporises or sublimates in the form of free molecules, atoms and ions, i.e. a weak plasma is formed above the irradiated surface. At laser pulse power density exceeding threshold of the ablation mode, a microexplosion occurs with formation of a crater on the sample surface and luminous plasma together with flying solid and liquid particles (aerosol), which are deposited on the cooled substrate.
The film parameters were studied using a Fei Phenom scanning electron microscope (Fig.2).
As a result of silicon sputtering it was possible to obtain a strong polycrystalline silicon film with good adhesion on a PET substrate with a thickness of 150...200 nm.
Figs.3–4 shows photos of the sample with silicon film, however, when the sample is cut, the silicon layer in the place of cut is destroyed, which should be taken into account when manufacturing elements based on sputtered silicon film.
According to the results of COMSOL Multyphysics modelling of the condenser membrane deformation, which is a multilayer structure – Al-polyethylene terephthalate-Si, the design of the pressure sensor (Fig.5) was calculated and selected (sketch version), and a mock-up sample was made.
Metallised glass-textolite with thickness of 0.25 mm was taken as the base of the prototype sensor. Topology of the sensor was created on a CNC engraving and milling machine according to technology of creating mock-up printed circuit boards. A 12 µm thick polyethylene terephthalate was chosen as the dielectric. The upper lining of the capacitor was made of metallised polyethylene terephthalate with the thickness of 23 microns. Thickness of the metalised Al layer was less than 100 nm.
All adhesive joints are prepared with epoxy two-component adhesive. To ensure tightness of internal volume of the condenser during curing of the adhesive joints, the sensor was placed in a vacuum chamber (pressure 10–1 Pa) to remove gas bubbles from the adhesive joints.
Figure 6 shows a mock-up of the pressure sensor assembly glued to a rigid base.
A specialised test bench was assembled for testing on a mock-up sample. The overpressure was changed in the range of 0...1 atm.
The results of the test are shown in Fig.7.
It can be seen that variation of the capacitance of the variable capacitor is almost linear depending on variation of the air pressure in a chamber. Which is quite a satisfactory result for use as a pressure sensor in car wheels.
CONCLUSIONS
The silicon sputtering technology has been worked out, it was possible to obtain a strong polycrystalline silicon film with good adhesion on PET substrate with thickness of 150...200 nm. Using this technique, a prototype of flexible variable capacitance was prepared. The study of capacitance change from the pressure changes acting on it has a linear form, which allows to use this technology for manufacturing a pressure sensor for solving problems of remote control of pressure in car wheels. In this case, the sensor will be similar to a flexible sticker that can be stuck on the inner surface of the tyre.
ACKNOWLEDGMENTS
This work was supported by the grant of the Russian Science Foundation № 23-29-10211 and the Chuvash Republic of Russia, https://rscf.ru/project/23-29-10211/
PEER REVIEW INFO
Editorial board thanks the anonymous reviewer(s) for their contribution to the peer review of this work. It is also grateful for their consent to publish papers on the journal’s website and SEL eLibrary eLIBRARY.RU.
Declaration of Competing Interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Nowadays there is a wide and intensive application of automation means both in domestic and industrial spheres. In this regard, the task of developing various sensors, or, as it is often called, sensors in measurement and automation systems becomes very relevant. The application of flexible electrical circuits in electronics is the technology of assembling electronic circuits by mounting its elements on a flexible plastic pad made of polyimides, polyetheretherketone (PEEK) or transparent conductive polyester film – makes it possible to significantly expand possibility of applying electronics and automation based on flexible electronic elements in various fields. For example, RFID technology is widely used because the current-carrying elements such as an inductive circuit, microchip or other electronic elements are applied to a flexible plastic pad. This technology, better known as RF tags, is used, for example, to create anti-theft systems – when a flexible tag is glued on the goods in supermarkets, as well as in various identification systems, such as passes, bank cards, etc. There are examples of such technology development, for example, and for anti-theft systems. There are examples of development and application of such technology, for example, for rapid remote diagnostics and monitoring of patient’s health. For this purpose, a specially manufactured tag with sensors is glued on certain areas of the human body, and a reader device, which is located nearby (e.g. in a pocket of the patient’s clothes or in a handbag carried by the patient), promptly monitors the patient’s condition and promptly informs the patient in case of deviations from normal values.
Figure 1 shows some typical samples of various electronic circuits fabricated on a flexible and polymer base [1].
Our team is developing a system for remote monitoring of air pressure in car tyres, allowing to monitor tyre pressure both while driving in real time and while parked. Currently there is only one remote pressure monitoring system on the market with direct measurement of current tyre pressure, the TPMS ("tire pressure monitoring system"). However, this system has a rather complex electronic filling of the sensor itself, which measures pressure in the wheel and transmits the data via radio channel to a central unit, which processes the data and displays the values on the display. In this system, the key element is the sensor itself with a rather complex electronic stuffing, moreover, requiring electrical power supply, which is carried out from galvanic cells or a miniature battery. With all the convenience of the system itself, presence of expensive sensors that require periodic replacement of batteries makes developers look for alternative solutions in which the sensors would be cheap, without the use of batteries.
RESEARCH METHODS
The main difference is that our development uses a passive oscillating circuit as a pressure sensor, the resonant frequency of which depends on pressure applied to the linings of oscillating circuit capacitance. In this case, capacitance is a variable capacitor with electrically conductive material (copper, silver, etc.) sprayed on both sides of the elastic-plastic material. In this case, the sensor itself is very simple and cheap (containing sputtered inductance and variable capacitance), it will be a flexible structure (e.g. film-based or other flexible) like a sticker that can be simply stuck inside a tyre. As a passive oscillating circuit, this sensor does not require any batteries.
During operation of such a system, a short packet of modulated electromagnetic radiation is sent to the sensor, frequency varies within a certain range. When frequency of the electromagnetic radiation coincides with the resonant frequency of the passive oscillating circuit of the sensor, it re-emits a signal, which is perceived by the transmitter antenna and frequency of this signal determines the pressure value when the sensor response is maximum. The maximum response occurs when transmitter frequency coincides with the resonant frequency of the oscillating circuit of the sensor. Modelling of film materials deformation in COMSOL [2], study of film parameters on a Fei Phenom scanning microscope, and measurement of pressure-capacitance dependence on a mock-up sample were carried out.
RESULTS AND DISCUSSION
The main difference is that our development uses a passive oscillating circuit as a pressure sensor, and the resonant frequency depends on pressure exerted on the linings of the oscillating circuit capacitance. In this case, capacitance is a variable capacitor with an electrically conductive material (copper, silver, etc.) sprayed on both sides of the elastic-plastic material. In this case, the sensor itself becomes very simple and cheap (containing the sputtered inductance and variable capacitance), and is a flexible construction (e.g., film-based or other flexible), similar to a sticker, which can be glued inside a tyre. As a passive oscillating circuit, such a sensor does not require any batteries.
During the system operation a short packet of modulated electromagnetic radiation is sent to the sensor, and frequency varies within a certain range. When electromagnetic radiation frequency coincides with the resonant frequency of the passive oscillating circuit of the sensor, it re-emits a signal, which is perceived by the transmitter antenna and the signal frequency determines pressure value at which the sensor response is maximum. The maximum response occurs when transmitter frequency coincides with the resonant frequency of the oscillating circuit of the transducer. In the development of this pressure monitoring system, an important task becomes the design of a variable capacitance, which must be flexible. All currently available technologies for manufacturing flexible electronic structures (RFID-technologies) do not imply the use of flexible variable capacitance, and there are no applications where it would be necessary. When developing a flexible variable capacitance, the value of which would depend on air pressure, it was decided to use parallel electrically conductive linings with an elastic-plastic dielectric between them. In this case, the electrically conductive linings simultaneously play the role of a membrane on which an external pressure, e.g. air pressure, acts. In this case, the distance between the linings is reduced, which increases the capacitance of the capacitor. When connected to the linings of such an inductance capacitor, an oscillating circuit with a resonant frequency varying depending on the external pressure is obtained. When choosing an elastic-plastic material, it was decided to use a dielectric with drilled holes containing air, which is known to be isotropic and elastic when pressurised to a certain volume. Thus, the problem was reduced to the task of applying a conductive layer to a polymer base to form shells of variable capacitance, placing between the shells a dielectric with holes for air bubbles, and providing sealing of the inter-cladding space to prevent air leakage from the holes in which it, in the form of bubbles, is disposed.
A 23 μm thick lavsan film with one-sided metallisation (Al film) was chosen as the base of the capacitor. A nanoscale silicon film was deposited on the non-metallised surface by laser ablation, which serves as an elastic element (membrane) of the capacitor.
Laser ablation is a method of removing substance from a surface by a laser pulse. At low laser power the substance vaporises or sublimates in the form of free molecules, atoms and ions, i.e. a weak plasma is formed above the irradiated surface. At laser pulse power density exceeding threshold of the ablation mode, a microexplosion occurs with formation of a crater on the sample surface and luminous plasma together with flying solid and liquid particles (aerosol), which are deposited on the cooled substrate.
The film parameters were studied using a Fei Phenom scanning electron microscope (Fig.2).
As a result of silicon sputtering it was possible to obtain a strong polycrystalline silicon film with good adhesion on a PET substrate with a thickness of 150...200 nm.
Figs.3–4 shows photos of the sample with silicon film, however, when the sample is cut, the silicon layer in the place of cut is destroyed, which should be taken into account when manufacturing elements based on sputtered silicon film.
According to the results of COMSOL Multyphysics modelling of the condenser membrane deformation, which is a multilayer structure – Al-polyethylene terephthalate-Si, the design of the pressure sensor (Fig.5) was calculated and selected (sketch version), and a mock-up sample was made.
Metallised glass-textolite with thickness of 0.25 mm was taken as the base of the prototype sensor. Topology of the sensor was created on a CNC engraving and milling machine according to technology of creating mock-up printed circuit boards. A 12 µm thick polyethylene terephthalate was chosen as the dielectric. The upper lining of the capacitor was made of metallised polyethylene terephthalate with the thickness of 23 microns. Thickness of the metalised Al layer was less than 100 nm.
All adhesive joints are prepared with epoxy two-component adhesive. To ensure tightness of internal volume of the condenser during curing of the adhesive joints, the sensor was placed in a vacuum chamber (pressure 10–1 Pa) to remove gas bubbles from the adhesive joints.
Figure 6 shows a mock-up of the pressure sensor assembly glued to a rigid base.
A specialised test bench was assembled for testing on a mock-up sample. The overpressure was changed in the range of 0...1 atm.
The results of the test are shown in Fig.7.
It can be seen that variation of the capacitance of the variable capacitor is almost linear depending on variation of the air pressure in a chamber. Which is quite a satisfactory result for use as a pressure sensor in car wheels.
CONCLUSIONS
The silicon sputtering technology has been worked out, it was possible to obtain a strong polycrystalline silicon film with good adhesion on PET substrate with thickness of 150...200 nm. Using this technique, a prototype of flexible variable capacitance was prepared. The study of capacitance change from the pressure changes acting on it has a linear form, which allows to use this technology for manufacturing a pressure sensor for solving problems of remote control of pressure in car wheels. In this case, the sensor will be similar to a flexible sticker that can be stuck on the inner surface of the tyre.
ACKNOWLEDGMENTS
This work was supported by the grant of the Russian Science Foundation № 23-29-10211 and the Chuvash Republic of Russia, https://rscf.ru/project/23-29-10211/
PEER REVIEW INFO
Editorial board thanks the anonymous reviewer(s) for their contribution to the peer review of this work. It is also grateful for their consent to publish papers on the journal’s website and SEL eLibrary eLIBRARY.RU.
Declaration of Competing Interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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