WO2021250683A1

WO2021250683A1 - A method for depositing layer of zinc oxide nanoparticles over a substrate of hygroscopic material as a dielectric substrate and a sensor containing the substrate for detecting moisture

Info

Publication number: WO2021250683A1
Application number: PCT/IN2020/050648
Authority: WO
Inventors: Jayant Rajaram Pawar; Manish Shinde; Amit PATWARDHAN; E.A. Singh; Rabinder Henry
Original assignee: Jayant Rajaram Pawar
Priority date: 2020-06-12
Filing date: 2020-07-27
Publication date: 2021-12-16
Also published as: ZA202300357B

Abstract

Disclosed is a method of depositing layer of zinc oxide nanoparticles over a substrate of hygroscopic material as a dielectric substrate. Also, provided a sensor containing the zinc oxide nanoparticles deposited dielectric substrate for detecting moisture of a tertiary packaging system.

Description

FIELD OF THE INVENTION The present invention relates to a method for depositing layer of zinc oxide nanoparticles (hereinafter referred ZnO-NP) over a substrate of hygroscopic material. More particularly the present invention relates to a method for depositing layer of ZnO-NP over a substrate of hygroscopic material as a dielectric substrate and a sensor containing such dielectric substrate for detecting moisture seepage in packets of industrial products during transport and storage. The ZnONP deposited dielectric substrate based sensor of the present invention is highly sensitive towards moisture. BACKGROUND ART The safe transport and storage of moisture sensitive products is mandatory to avoid huge economic losses due to unnoticed moisture seepage into packets more particularly tertiary packaging system. Nowadays, diverse humidity and moisture sensors available for assorted applications (Matko, V. and Donlagic, D., 1997. Sensor for high-air-humidity measurement. Sensors and Actuators A: Physical, 61(1), pp.331-334.; Rittersma, Z.M., 2002. Recent achievements in miniaturised humidity sensors—a review of transduction techniques. Sensors and Actuators A: Physical, 96(2), pp.196- 210.; Huang, T.H., Chou, J.C., Sun, T.P. and Hsiung, S.K., 2008. A device for skin moisture and environment humidity detection. Sensors and Actuators B: Chemical, 134(1), pp.206-212). Many moisture and humidity sensors have followed comb-type finger copper electrodes pattern on printed circuit board (PCB) (Dokmeci, M. and Najafi, K., 2001. A high-sensitivity polyimide capacitive relative humidity sensor for monitoring anodically bonded hermetic micropackages. Journal of Microelectromechanical Systems, 10(2), pp.197-204.; Huang, T.H., Chou, J.C., Sun, T.P. and Hsiung, S.K., 2008. A device for skin moisture and environment humidity detection. Sensors and Actuators B: Chemical, 134(1), pp.206-212.; Chetpattananondh, K., Tapoanoi, T., Phukpattaranont, P. and Jindapetch, N., 2014. A self-calibration water level measurement using an interdigital capacitive sensor. Sensors and Actuators A: Physical, 209, pp.175-182.; & Rukavina, A.V., 2015. Non-invasive liquid recognition based on interdigital capacitor. Sensors and Actuators A: Physical, 228, pp.145- 150). However, these existing sensors are not sensitive towards absolute moisture in the industrial packets, in particular tertiary packets. In environmental science, there is a difference between relative humidity and absolute humidity. The term “Relative moisture or humidity” is the measure of water vapor relative to the temperature of the air. It is expressed as the amount of water vapor in the air as a percentage of the total amount that could be held at its current temperature. It does not give the exact quantity of water vapor in the air whereas the term “Absolute moisture or humidity” is the measure of water vapor or moisture in the air, regardless of the temperature which is usually expressed in amount of moisture per cubic meter (g/m³) of air and could also be converted to µL using the standard conversion known in the art. In existing art, few capacitive sensors are working on the principle of parallelly arranged metal electrode, for instance Chetpattananondh K et al, 2014 (Chetpattananondh, K., Tapoanoi, T., Phukpattaranont, P. and Jindapetch, N., 2014. A self-calibration water level measurement using an interdigital capacitive sensor. Sensors and Actuators A: Physical, 209, pp.175-182; and Homayoonnai S. et al, 2016 (Homayoonnia et al., Design and Fabrication of Capacitive Nanosensor based on MOF Nanoparticles as Sensing Layer for VOCs Detection, Sensors and Antuators B. Chemical, 2016, Vol.237, Page No. 776-786). However, the existing sensors are not sensitive towards absolute moisture determination (µL) which might be due to the sensing material as used, the arrangement of the sensing material in the device and size of the electrodes. In the existing art, also, as the second plate of the sensor has been made by Ag paste, it is not possible for the complete plate to sandwitch the dielectric material and therefore difficult to achieve the moisture sensitivity. Further, Due to second electrode of the sensor of Homayoonnai et al, the surface area of the electrodes may be decreased; the distance between the electrodes may be increased; dielectric constant of the sensing material may be decreased. These conditions are not suitable in order to increase the sensitivity of the sensor. In Homayoonnai et al, as the entire nanosensor assembly requires closed cabinet to execute the testing of various compounds at specific temperature and humidity, this sensor may not be worked in open atmosphere (regardless of the temperature). If this kind of sensor is placed in open atmosphere then air interference may create the noise in signal and thus affects the sensitivity. Also, in the existing art, the metal nanoparticles as used in this sensor needs ultrasonic generator which is the costlier step. Further, raw materials Cu and 1,3,5-benzenetricarboxylic acid for preparing the nanomaterial (sensing material) are the costlier products as compared to the raw materials of present invention. Further, the existing tecchnology uses the costly silver based material to fabricate the nanosensor. The earlier disclosures of the inventor [Application of semi-solvo thermally synthesized zinc oxide (ZnO) nanoparticles in food technology and their characterization International Journal of Nanotechnology and Applications, Volume 11, Number 1 (2017), pp. 75-80] teaches urea and ethylene glycol based zinc oxide nanoparticles. However, as the nanoparticles shows the nugget like morphology the same may not be effective in determing the moisture sensitivity. Patent Document 202021010152 (Earlier disclosure of the inventor) relates to a resistance based chemical nanosensor includes a nanocomposite comprises of a metal nanoparticles and agar. However, this prior art does not suggest capacitance based sensor. Also, as the entired printed circuit board (PCB) is coated with the sensing material in IN’152’ there is a chance to dislocate the sensing material from the functional area which might be due to the adhesion problem between the electrodes and the sensing materials which affects the moisture sensing. Futher limitation is corrosion of the electrode of this type of sensor which can occur after 5 times of it’s usage. Additional limitations of this prior art are i) continuous monitoring of moisture seepage may not be possible as moisture may not be uniformly distributed over the sensing material and also the sensor is mostly used for storage purpose so it is expected to deliver data for longer duration and hence, it is not used for continuous monitoring; ii) stability is upto one year only as the composite may be deformed by dehydration iii) reliability and linearity. Therefore, there is a need to overcome the aforesaid problems. OBJECT OF THE INVENTION It is an objective of the invention is to prepare low cost ZnO-NP deposited dielectric substrate which is highly sensitive towards moisture. It is another objective of the invention is to provide a capacitor includes ZnO-NP deposited dielectric substrate. It is another objective of the invention is to provide a ZnO-NP deposited dieletric substrate based sensor device for detecting moisture in packets of industrial products during transport and storage in particular tertiary packaging system. It is yet another objective of the invention is to provide a sensor by which a continuous monitoring of moisture seepage into a packaged products of the industry can be feasible where moisture imposed is a major issue in stability and safety of the products in particular food processing, printing, textile, cement or mining. It is yet another objective of the invention is to provide a sensor which requires less current, could provide an uniform result, is more sensitive and accurate. It is yet another objective of the invention is to provide a sensor which could solve the existing corrosion problem. It is yet another objective of the invention is to provide a sensor which could work in open atmosphere i.e. independent of the temperature. It is yet another objective of the invention is to provide a sensing material that can be stable for a longer duration. It is yet another objective of the invention is to provide a sensor having more reliability and linearity. It is further objective of the invention is to provide a method for measuring the moisture of a tertiary packaging system employing the aforesaid sensor. SUMMARY OF THE INVENTION According to one aspect of the invention, there is provided a method for depositing layer of zinc oxide nanoparticles over a substrate of hygroscopic material as dielectric substrate comprising the steps of i) seperately preparing two liquid mixture by dissolving 0.2M of zinc acetate in 50mL of water and 0.8M of urea in 50mL of aqueous ethylene glycol; ii) adding the said mixtures as obtained in step (i) and stirring the said mixtures to prepare a homogeneous solution; iii) subjecting the said solution as obtained in step (ii) to autoclaving process at 200°C for 30 hours to obtain a precipitate product; iv) subjecting the said product as obtained in step (iii) to centrifugation process at 5000rpm for 15 minute twice with water and once with ethanol to romove the water soluble and water insoluble impurities respectively; v) subjecting the product as obtained in step (iv) to calcination process at 600°C for 8 hours to remove the volatile impurities; vi) preparing a suspension comprises of the product as obtained in step (v) and ethanol; vii) dipping a hygroscopic substrate in the suspension as prepared in step (vi) so as to obtain an uniform distribution of the said product onto the substrate. viii) drying the substrate as obtained in step (vii) at room temperature; wherein shape of the product as obtained in step (v) is flake having pores; and wherein diameter of the pores is 10-50nm. According to second aspect of the invention, there is provided a zinc oxide nanoparticles deposited dielectric substrate sandwitched between two conducting metal electrodes forming a capacitor configured for altering capacitance based on presence of moisture level, wherein the said deposition of the nanoparticles includes means for extracting zinc nanoparticles from a uniform mixture of solution of 0.2M of zinc acetate in 50mL of water and 0.8M of urea in 50mL of aqeous ethylene glycol; means for preparing a suspension of the extracted zinc oxide nanoparticles in ethyl alcohol with concentration 1mg/mL; and means for dipping the substrate of cellulose paper in the said nanoparticle solution for 5 minute for depositing the said nanoparticles over the said substrate. According to third aspect of the invention, there is provided a capacitor including a zinc oxide nanoparticles deposited dielectric substrate sandwitched between two metal electrodes configured for use with a sensor device configured for detecting moisture comprising of : a circuitry for sensing the change in the capacitance of the said capacitor due to the absorption of atmospheric moisture and output an amplified signal; a microcontroller for receiving the said amplified signal and displaying the corresponding real time moisture content values as complared from a look up table. In accordance with these and other objects which will become apparent hereinafter, the instant invention will now be described with particular reference to the accompanying drawing. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Figure 1 schematically illustrates the process steps for preparing ZnO-NP deposited cellulose paper as dielectric substrate in accordance with the present invention; Figure 2 illustrates the FESEM images of ZnO-NP in accordance with the present invention; Figure 3 illustrates the TEM images of ZnO-NP nanoparticles in accordance with the present invention; Figure 4 illustrates the sensor device in accordance with the present invention; Figure 5 illustretes the working of sensor device in accordance with the present invention; Figure 6 illustrates an arrangement of the capacitor plate electrodes and the sensing material in which Fig. 6a shows sandwitch arrangement of the sensing material between two electrode plates & Fig. 6b shows parallal arrangement of the electrodes in accordance with the present invention; Figure 7 illustrates sensitivity of the sensor with or without ZnO-NP towards moisture seepage in accordance with the present invention; & Figure 8 illustrates the application of sensor in accordance with the present invention; Figure 9 illustrates comparative moisture sensitivity studies with regard to length of the electrode in which Fig. 9a, 9b & & 9c shows the sensitivity graph of 1cm x 1cm, 3cm x 3cm, 5cm x 5cm respectively in accordance with the present invention. Other objects, features and advantages of the inventions will be apparent from the following detailed description in conjunction with the accompanying drawings of the inventions. DETAILED DESCRIPTION OF THE INVENTION Referring to Fig. 1, the present invention provides a method for depositing layer of zinc oxide nanoparticles over a substrate of hygroscopic material as a dielectric substrate for detection of moisture as hereinbelow: Method: Two liquid mixtures are prepared seperately by dissolving 0.2M zinc acetate in 50 mL and 0.8M urea in 50 mL solution of aqueous ethylene glycol (35 mL ethylene glycol and 15 mL deionized water) on a magnetic stirrer. Both the liquid mixture are added with continuous stirring to form a homogenous solutions. The homogeneous solution is then transferred to Teflon-lined stainless steel autoclaveing process at 200°C for 30 hours to obtain the precipitate. The resultant precipitate as obtained is subjected to a centrifugation process at 5000 rpm for 15 minute twice with DI water and once with absolute ethanol to remove water soluble and insoluble impurities respectively. The the product is subjected to calcination process at 600°C for 8 hours to remove volatile impurities. The following according to present invention is the chemical reaction when the homogeneous solution containing zinc acetate and urea mixture is subjected under the elevated temperature:

As shown in Fig. 2 and Fig. 3, the characterization of ZnO particles as above obtained are performed. FESEM examination (Fig. 2) is conducted for obtaining size and surface morphological information of ZnO particles whereas, topography and morphology of the nanoparticles is observed by TEM microscopy (Fig. 3). Figure 2 shows the formation of perforated flakes like particles wherein each flake is having thickness of 20-40 nm. The length of the nano flake is 500 nm to 1µm while width is 200-500 nm. Due to such perforated nano flake like structures, the specific surface area of said nanoparticle increases. TEM image (Fig. 3) also shows a representative flake having the pores wherein the diameter of the pores is 10-50nm which come into view that the said nanoparticles is a good mesoporous material indicating present ZnO-NP as advantageous over the existing ZnO-NP as the pores may hold more water and provide more number of active sites, which overall can enhance the dielectic behaviour of a sensing material and conduction. In preferred embodiment of the invention, the hygroscopic substrate is a cellulose material which would be an advantageous matrix over agar as it is observed by the present inventors that the dispersal of nanoparticles at higher loading percentage in agar matrix would lead to agglomeration of material which ultimately loses its strength, transparency and activity. In an embodiment of the invention, suitable method for depositing ZnO-NP onto the cellulose paper is either coating or spraying. In preferred embodiment, the method is coating. Briefly, the deposition method is that a suspension is prepared by adding ZnO-NP in absolute ethanol and the cellulose paper (0.8 mm Whatman Cellulose Blotting Paper, Grade GB005) is dipped in the suspension of ZnO- NP for 5 minute to obtain an uniform distribution of ZnO-NP onto the paper. In an embodiment of the invention, concentration of the nanoparticles is upto to 1mg/mL, beyond that it affects surface roughness and porosity of cellulose paper, which leads to desorption of water molecule subsequently affects the moisture sensitivity. Preferably, the concentration is 0.5- 1.0mg/mL. Most preferably, the concentration is 1.0mg/mL. In preferred embodiment of the invention, the moisture is an absolute moisture. As shown in Fig. 4 & 5, the present invention provides also a sensor (9) for detecting moisture in packets of industrial products during transport and storage comprising i) sensing material (6) ii) insulated plate electrodes (5); iii) plate holder (4); iv) microcontroller system (1); v) data cable (2); vi) single core wire (3); vii) serial port (7); & viii) a Display unit (8) In an embodiment, the present invention provides a capacitor (5) which comprises two parallel metal plates and ZnO-NP deposited dielectric substrate wherein the ZnO-NP deposited dielectric substrate is sandwitched between two conducting metal plates for altering capacitance based on presence of moisture level. Briefly, the design of sensor (9) according to present invention includes ZnO-NP deposited dielectric substrate (6) is placed between the two parallel aluminium plate electrodes (5) which is covered by an insulating plastic material to avoid the corrosion. The device also comprises a holder to hold the plates so as to close enough to avoid air interference and keep the sensing material at an appropriate place to achieve the desired capacitance. The device further comprises a microcontroller system (1) which provides the output signal in a digital form into the display unit (8) through the data cable (2) while moisture seepage is occured. In preferred embodiment, the sensing material consist of ZnO-NP deposited dielectric substrate. As shown in Figure 6(a) & (b), the capacitor plates according to present invention is parallelly arranged under which the sensenting material is placed for changing the capacitance while the moisture is present. In preferred embodiment, the plate is made up of aluminium. In preferred embodiment of the invention, the capacitor plates 3cm x 3cm in dimension cut in 2 pieces which further attached to single core wire (3). These plates are then placed vertically in an insulating plastic material in such a way that they are parallel to each other. In preferred embodiment, the space between the two electrodes is 0.5mm and the insulating plastic material is polyethylene (PE). In order to meeting the sentivity requirements such as i) increase the surface of the electrodes; ii) decreases the distance between the same & iii) increase the dielectric constant of the sensing material, 3cm x 3cm as the size of the plates is found as a surprising feature of the invention. It has also been found by the present inventors that the overall less current requirement, high sensitivity and good response time is observed using the plate size of 3cm x 3cm only which otherwise is not possible. In an embodiment of the invention, present device includes a plate holder. Capacitance measurement setup is not relatively simple as resistance measurement and it is more susceptible to the external environment as atmospheric air acts as dielectric between two electrodes. Therefore, in conventional capacitors the dielectric material and electrodes enclosed within metallic cylinder to achieve desired performance of capacitor. However, in the present invention such metallic cylinders are not feasible to use due to flat shape of the electrodes and the device requirement to absorb external moisture into the capacitor. Therefore, a holder is designed to hold the plate so as to close enough to avoid air interference and keeping sensing material at the proper place to achieve suitable capacitance. The plate holder according to present invention is made up of poly-lactic acid polymer. In an embodiment of the invention, the present invention includes a circuitry for sensing the change in the capacitance of the said capacitor due to the absorption of atmospheric moisture and output an amplified signal. The circuitry according to present invention is connected to the capacitor (5) through either in series or in parallel. In an embodiment of the invention, the present invention also includes a microcontroller (1) for receiving the said amplified signal and displaying the corresponding real time moisture content values as complared from a look up table (Table 1). The operating voltage and frequency of the microcontroller according to present invention are 5V DC and 16MHz respectively. In-built oscillator circuit & binary ripple counter of the system converts analog data collected by the sensing material into a digital data with resolution of 10 bits and the data transmitted to USB of computer at baudrate of 9600 bauds/sec. In the context of microcontroller system, which was programmed to execute measurements of the frequency signals at intervals of 10 ms. This testing enables to get quantitative analysis of change in capacitance with change in frequency. The in-built oscillator circuit has set frequency at 16 MHz. As the amount of moisture seeped inside the capacitor, the capacitance values are changed; this changed the frequency of output signal, which was analysed by microcontroller to sense the amount of moisture. After signal conditioning done by the microcontroller, the signal referred to the display unit by either USB cable or Wi-Fi module. The formula used to calculate the capacitance value is;

where, C = capacitance (F); A = overlap area of the two plates (m²); ε₀ = dielectric constant (ε₀ ≈ 8.854×10⁻¹² F⋅m⁻¹); ε_r = dielectric constant of the material between the plates; d = distance between the plates (m)

In the present invention, changing the capacitance is developed after seepage of deionised (DI) or tap water into the sensing layer (Table 2, Figure 7). Since ZnO nanomaterials have higher dielectric constant (2.7) than cellulose (2.3) use of such nanomaterials to develop chemical sensor would be a good choice for higher sensitivity and accuracy. Change in composition of dielectric medium between conducting plates changes the capacitance value. The dielectric constant of ZnONPs is 2.7 and that of water is 80. So, as the moisture seeped into the capacitor, the capacitance value is changed accordingly. Since, water molecules have high polarity the dielectric value of the sensing layer changes significantly with respect to water content seeped into the capacitor and subsequently the capacitance of the sensor. Additionally, zinc oxide retains semiconductor behaviour where it can show dielectric property at low temperature and conductor at high temperature. Therefore, water seepage into the ZnONPs-Cellulose sensor keeps the temperature low of the system and maintains its dielectric property rather; dielectric constant of the sensor increases with moisture level and so the capacitance. Consequently, capacitance is directly proportional to the moisture seeped into the sensor.

Table 2 and Figure 7 shows that the sensor containing flaked shaped ZnONP deposited cellulose paper is more sensitive towards moisture seepage as compared to plain cellulose paper in tap water. Also, greater capacitance is observed for concentration 1mg/mL compared to 0.5mg/mL (in tap water). In preferred embodiment of the invention, packets of industrial products includes a tertiary packaging system. In preferred embodiment of the invention, the tertiary packaging system is paperboard cartons of moisture sensitive goods. In an embodiment of the invention, the moisture sensitive good is selected from a group consisting of food processing, printing, textile, cement or mining goods. In an embodiment of the invention, the food processing good is selected from a group consisting of wheat flour, milk powder, biscuits, grains or sugar. In preferred embodiment of the invention, the food processing good is milk- powder. The invention is now illustrated by non-limiting examples: Example 1 (inventive example): Application of the sensor device onto a paperboard cartons of milk powder: As shown in Fig. 2 & Fig. 3, a ZnO-NP deposited dielectric cellulose paper (6) sandwitched between two conducting aluminium electrodes (5) was used with a sensor device (1) for detecting moisture, wherein the deposition of method is hereinbelow: Method: Two liquid mixtures were prepared seperately by dissolving 0.2M zinc acetate in 50 mL and 0.8M urea in 50 mL solution of aqueous ethylene glycol (35 mL ethylene glycol and 15 mL deionized water) on a magnetic stirrer. Both the liquid mixture were added with continuous stirring to form a homogenous solutions. The homogeneous solution was then transferred to Teflon-lined stainless steel autoclaveing process at 200°C for 30 hours to obtain the precipitate. The resultant precipitate as obtained was subjected to a centrifugation process at 5000 rpm for 15 minute twice with DI water and once with absolute ethanol to remove water soluble and insoluble impurities respectively. The the product was subjected to calcination process at 600°C for 8 hours to remove volatile impurities (Fig. 1). As shown in Fig. 8, the sensor device was applied to a paperboard cartons (10) of milk powder to detect moisture seepage during transport. The perishable or semi-perishable foodstuffs were initially packaged in primary packet (direct interaction with food) then all primary packages into one secondary packet and finally enclosed all secondary packages in one big tertiary packet made of paperboard cartons. The present device (9) was placed on two vertical sides of the tertiary packets with the hygroscopic sensing assembly (6) between the capacitive plates (5) to absorb the moisture and monitored by microcontroller system (1) wherein the size of the plates is 3cm x 3cm. The operating voltage and frequency of the microcontroller system (1) were 5V DC and 16MHz respectively. In-built oscillator circuit & binary ripple counter of the system converts the analog data collected by the sensing assembly (6) into a digital data with resolution of 10 bits and the data transmitted to USB of computer at baudrate of 9600 bauds/sec. In this trail, the microcontroller was programmed to execute measurements of the frequency signals at intervals of 10 ms which enables to get quantitative analysis of change in capacitance with change in frequency. As the amount of moisture seeped inside the capacitor, the capacitance values are changed; this changed the frequency of output signal, which was analysed by microcontroller to sense the amount of moisture. After signal conditioning done by the microcontroller, the signal referred to the display unit by either USB cable or Wi-Fi module. Example 2 (Comparative example): The same application method was followed onto a paperboard cartons of milk powder as in Example 1 except the size of the plates which herein was 1cm x 1cm. Example 3 (Comparative example): The same application method was followed onto a paperboard cartons of milk powder as in Example 1 except the size of the plates which herein was 5cm x 5cm.

*Moisture seepage with respect to sensitive amount of moisture taken was 100 µL It is observed by the present inventors that flooded result (Figure 9a) in view of the moisture seepage was found while the electrode size is 1cm x 1cm. It was also found that as the small size electrode plates only managed the moisture seepage upto 100µL, more water seepage can not give quantitative results as sensing material is saturated with moisture and also damage the capacitor by short circuit. For large size electrode (5cm x 5cm), moisture seepage was not found as uniform (Figure 9c) which may be due to the large surface area and less signal to noise ratio for the electrode. Surprisingly, uniform moisture seepage and more sensitivity with good response time was found in 3cm x 3cm as size of the electrodes (Figure 9b). It is also found by the present inventors that the size of the electrode greatly affects the current input required by the circuit. Table 3 shows that the plate having size of 5cm X 5cm needs more current than 3cm X 3cm, consequently, the overall power consumption would be increased, which greatly reduces the battery life of the device. Comparative stability studies: The stability of both the sensing material viz. ZnONP-agar and ZnONP- celulose paper were studied at room temperature for 12 months in open atmosphere. During the study both the materials was analysed for their polymeric degradation and fragmentation. It is observed that the ZnONP- agar composite was fragmented and damaged due to moisture loss over a period of 12 months whereas ZnONP-celulose paper was found to be intact even after 30 months (Table 4). Table 4: Stability study

Although the foregoing description of the present invention has been shown and described with reference to particular embodiments and applications thereof, it has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the particular embodiments and applications disclosed. It will be apparent to those having ordinary skill in the art that a number of changes, modifications, variations, or alterations to the invention as described herein may be made, none of which depart from the spirit or scope of the present invention. The particular embodiments and applications were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such changes, modifications, variations, and alterations should therefore be seen as being within the scope of the present invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.

Claims

CLAIMS:

1. A method for depositing layer of zinc oxide nanoparticles over a substrate of hygroscopic material as dielectric substrate, comprising the steps of i) preparing two liquid mixture by dissolving 0.2M of zinc acetate in 50mL of water and 0.8M of urea in 50mL of aqueous ethylene glycol separately; ii) adding the said mixtures as obtained in step (i) and stirring the said mixtures to prepare a homogeneous solution; iii) subjecting the said solution as obtained in step (ii) to autoclaving process at 200°C for 30 hours to obtain a precipitate product; iv) subjecting the said product as obtained in step (iii) to centrifugation process at 5000rpm for 15 minute twice with water and once with ethanol to romove the water soluble and water insoluble impurities respectively; v) subjecting the product as obtained in step (iv) to calcination process at 600°C for 8 hours to remove the volatile impurities; vi) preparing a suspension comprises of the product as obtained in step (v) and ethanol; vii) dipping a hygroscopic substrate in the suspension as prepared in step (vi) so as to obtain an uniform distribution of the said product onto the substrate. viii) drying the substrate as obtained in step (vii) at room temperature; wherein shape of the product as obtained in step (v) is flake having pores; and wherein diameter of the pores is 10-50nm.

2. The method as claimed in claim 1, wherein the hygroscopic material is a cellulose paper.

3. The method as claimed in claim 1, wherein concentration of the suspension in step (vi) is 0.5- 1.0 mg/mL.

4. The method as claimed in claim 1, wherein the dipping step in step (viii) is carried out for 5 minutes.

5. The method as claimed in claim 1, wherein length of the flake is 500nm-

1μm.

6. The method as claimed in claim 1, wherein width of th

500nm.

7. A zinc oxide nanoparticles deposited dielectric substrate (6) sandwitched between two conducting metal electrodes (5) forming a capacitor configured for altering capacitance based on presence of moisture level, wherein the said deposition of the nanoparticles includes means for extracting zinc oxide nanoparticles from a uniform mixture of solution of 0.2M of zinc acetate in 50mL of water and 0.8M of urea in 50mL of aqeous ethylene glycol; means for preparing a suspension of the extracted zinc oxide nanoparticles in ethyl alcohol with concentration lmg/mL; and means for dipping the substrate of cellulose paper in the said nanoparticle solution for 5 minute for depositing the said nanoparticles over the said substrate.

8. A zinc oxide nanoparticles deposited dielectric substrate (6) sandwitched between two conducting metal electrodes (5) forming a capacitor as claimed in claim 7, wherein the means for extracting zinc oxide nanoparticles further includes means for dissolving 0.2M of zinc acetate in 50mL of water and 0.8M of urea in 50mL of ethylene glycol in order to obtain two liquid mixtures; means for mixing the liquid mixtures obtained in step (i) in order to prepare a homogeneous solution; means for autoclaving at 200°C upto 30 hours the said solution as obtained in step (ii) in order to obtain a precipitate product; means for centrifugation process at 5000rpm for 15 minute subjecting the said product obtained in step (iii) twice with water and once with ethanol in order to romove the water soluble and water insoluble impurities respectively from the said product; means for calcination at 600 °C for 8 hours subjecting the product as obtained in step (v) in order to obtain zinc oxide nanoparticles; and wherein shape of the nanoparticles is flake having pores; and wherein diameter of the pores is 10-50nm.

9 A zinc oxide nanoparticles deposited dielectric substra between two conducting metal electrodes forming a capacitor as claimed in claim 8, wherein length of the flake is 500nm-1μm.

10. A zinc oxide nanoparticles deposited dielectric substrate sandwitched between two conducting metal electrodes forming a capacitor as claimed in claim 8, wherein the width of the flake is 200-500nm.

11. A capacitor including a zinc oxide nanoparticles deposited dielectric substrate sandwitched between two metal electrodes (5) as claimed in claim 7 configured for use with a sensor device (9) configured for detecting moisture comprising of : a circuit^ for sensing the change in the capacitance of the said capacitor due to the absorption of atmospheric moisture and output an amplified signal; a microcontroller (1) for receiving the said amplified signal and displaying the corresponding real time moisture content values as complared from a look up table.

12. The capacitor including a zinc, oxide nanoparticles deposited dielectric substrate sandwitched between two metal electrodes as claimed in claim 1 1, wherein the size of the electrode is 3cm x 3cm.

13. The capacitor including a zinc oxide nanoparticles deposited dielectric substrate sandwitched between two metal electrodes as claimed in claim 11, wherein the electrode is made up of aluminium.

14. The sensor device as claimed in claim 11, wherein the circuitry includes a plurality of said capacitors (5) connected in series or in parallel.

15. The sensor device as claimed in claim 11, wherein the said sensor is configured for detecting the absolute moisture of a tertiary packaging system.