A method for harvesting energy in a diaper and a diaper

Abstract

A method for harvesting energy in a diaper, wherein the diaper comprises electrodes and electronics connected to the electrodes, wherein the electrodes comprise at least one electrode pair for energy harvesting, the at least one electrode pair comprising an anode and a cathode; and wherein the method comprises: harvesting chemical energy using the at least one electrode pair and electrolyte solution for powering the electronics when the electrodes of the diaper are at least partly immersed in the electrolyte solution; and extracting information relating to the electrolyte solution when the electrodes of the diaper are at least partly immersed in the electrolyte solution by measuring electrical parameters relating to the electrolyte solution by using the electronics powered by the harvested energy and the electrodes used for the energy harvesting.

Description

[0001] A METHOD FOR HARVESTING ENERGY IN A DIAPER AND A DIAPER

[0002] TECHNICAL FIELD

[0003] The invention concerns energy harvesting using electrodes and electrolyte solution and extraction of information related to the electrolyte solution. Especially the invention concerns the invention claimed in the independent claims.

[0004] BACKGROUND

[0005] The proliferation of internet-of-things (loT) devices continues to grow exponentially, with billions of loT sensor nodes already in use, and this number is projected to surge into the hundreds of billions in the near future. Amid this rapid expansion, one of the most significant challenges is how to power these devices adopting sustainable and environment-friendly solutions. Conventional batteries are inadequate to meet the power demands of this vast loT ecosystem. Recent years have witnessed remarkable advancements in loT sensors, particularly in wearable biomedical devices. Innovative approaches have emerged to design energy-optimized electronic systems, opening the door to batteryless applications through energy harvesting techniques.

[0006] Energy harvesting from saltwater, for example, salt concentration gradient in seawater, has been a topic of interest since the 1970s. Despite its potential, it has historically received limited attention due to its comparative limitations against more promising energy sources. However, with advancements in integrated circuit technology, the development of power-efficient circuits and systems that operate at micro- and nano-watt scales has emerged. This technological progress has paved the way for energy harvesting from ambient surroundings on a microscale, enabling the powering of Internet of Things (loT)- based devices.

[0007] Dehydration is becoming a big problem in aged care. Dehydration can have a much more deadly impact on an older person and affects the brain's functioning ability. Measuring hydration status is challenging due to complex dynamics associated with fluid regulation. Water balance is a continuous process of water losses from kidneys, lungs, and skin and occasional uptake through oral intakes. Due to tightly controlled mechanisms to maintain fluid balance and the relatively small insensible water losses, urine excretion is roughly proportional to the amount of fluid consumed. In healthy subjects, diluted and concentrated urine is expected with increased and decreased water intakes, respectively.

[0008] Monitoring urine output remains important to the care of adult patients admitted to the hospital. In acute decompensated heart failure, ongoing assessment of urine output is required to adjust diuretic dosing in keeping with current recommendations for hospitalized patients. In patients with acute kidney injury, evaluation of urine output is essential for diagnosis and management.

[0009] Thus, there is a need to develop further solutions for batteryless devices in wearable and / or loT-based devices, such as biomedical devices or diapers.

[0010] SUMMARY

[0011] The following presents a simplified summary in order to provide basic understanding of some aspects of various invention embodiments. The summary is not an extensive overview of the invention. It is neither intended to identify key or critical elements of the invention nor to delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to a more detailed description of exemplifying embodiments of the invention.

[0012] An objective of the invention is to present an energy harvesting diaper and a method for an energy harvesting diaper. Another objective of the invention is to present a diaper and a method for extraction of information relating to an electrolyte solution deposit in the diaper.

[0013] The objectives of the invention are reached by an energy harvesting diaper and a method for an energy harvesting diaper as defined by the respective independent claims.

[0014] According to a first aspect, a method for harvesting energy in a diaper is provided, wherein the diaper comprises electrodes and electronics connected to the electrodes, wherein the electrodes comprise at least one electrode pair for energy harvesting, the at least one electrode pair comprising an anode and a cathode; and wherein the method comprises: harvesting chemical energy using the at least one electrode pair and electrolyte solution for powering the electronics when the electrodes of the diaper are at least partly immersed in the electrolyte solution; and extracting information relating to the electrolyte solution when the electrodes of the diaper are at least partly immersed in the electrolyte solution by measuring electrical parameters relating to the electrolyte solution by using the electronics powered by the harvested energy and the electrodes used for the energy harvesting.

[0015] In one embodiment of the invention, the diaper may comprise a diaper body and at least one absorption layer for absorbing liquids deposit in the diaper.

[0016] In one embodiment of the invention, the at least one electrode pair may be arranged in contact with the at least one absorption layer or in such vicinity to the at least one absorption layer that the at least one electrode pair is at least partly immersed in the electrolyte solution when the electrolyte solution is deposit in the diaper.

[0017] In one embodiment of the invention, the electrolyte solution may be a solution comprising at least sodium electrolytes and chloride electrolytes.

[0018] In one embodiment of the invention, the electrolyte solution may be urine.

[0019] In one embodiment of the invention, at least one of the electrodes may be flexible.

[0020] In one embodiment of the invention, at least one of the electrodes may be manufactured with printed electronics technology.

[0021] In one embodiment of the invention, the anode may comprise carbon and the cathode may comprise zinc.

[0022] In one embodiment of the invention, the electrolyte solution and the at least one electrode pair may form at least one galvanic cell.

[0023] In one embodiment of the invention, the electrical parameters of the electrolyte solution may comprise at least one of the following: voltage and current; resistivity; impedance; and dielectric properties.

[0024] In one embodiment of the invention, the extracted information related to the electrolyte solution may comprise at least one of the following for the electrolyte solution in the diaper: the electrical parameters; presence; amount; and composition. In one embodiment of the invention, the diaper may further comprise means for wireless transmission for transmitting the extracted information related to the electrolyte solution out of the diaper for monitoring the state of the diaper.

[0025] In one embodiment of the invention, the method may further comprise means for connecting external electronics to the electrodes and perform a capacitive measurement of the electrodes by using the external electronics to monitor the condition of the diaper before the electrodes of the diaper have been immersed in the electrolyte solution.

[0026] In one embodiment of the invention, the methods above may be performed by a diaper.

[0027] According to the second aspect, a diaper comprising electrodes and electronics connected to the electrodes is provided, wherein the electrodes comprise at least one electrode pair for energy harvesting, the at least one electrode pair comprising an anode and a cathode; and wherein the diaper is configured to: harvest chemical energy using the at least one electrode pair and electrolyte solution for powering the electronics when the electrodes of the diaper are at least partly immersed in the electrolyte solution; and extract information relating to the electrolyte solution when the electrodes of the diaper are at least partly immersed in the electrolyte solution by measuring electrical parameters relating to the electrolyte solution by using the electronics powered by the harvested energy and the electrodes used for the energy harvesting.

[0028] In one embodiment of the invention, the diaper may be further configured to perform the method according to any embodiment of the invention, e.g. the methods as described above.

[0029] Various exemplifying and non-limiting embodiments of the invention both as to constructions and to methods of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific exemplifying and non-limiting embodiments when read in connection with the accompanying drawings.

[0030] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of unrecited features. The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of “a” or “an”, i.e. a singular form, throughout this document does not exclude a plurality.

[0031] BRIEF DESCRIPTION OF FIGURES

[0032] The embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings.

[0033] Figure 1 illustrates schematically an example of an electrode pair cathode according to the invention and an example of an electrode pair anode over a cathode.

[0034] Figure 2 illustrates an example of manufactured harvesting electrodes.

[0035] Figures 3(a) and 3(b) illustrate exemplary measurement setups used for the measurements.

[0036] Figure 4 illustrates an example of the effect of surface area on the harvested energy and voltages.

[0037] Figure 5 illustrates an example of the effect of inter-electrode distance on the harvested energy and voltages.

[0038] Figure 6 illustrates an example of the output voltage and output current response of printed harvesting electrodes.

[0039] Figure 7 illustrates an example of the harvested energy and voltages of the printed electrode over a longer time in the electrolyte.

[0040] DESCRIPTION OF EXEMPLIFYING EMBODIMENTS

[0041] According to an embodiment of the invention energy from electrolyte solution is harvested with energy harvesting electrodes.

[0042] According to a further embodiment of the invention energy from electrolyte solution is harvested in a diaper, also referred to as a smart diaper, with energy harvesting electrodes.

[0043] Figure 1 illustrates an example of the electrodes according to one embodiment of the invention. The electrodes form at least one electrode pair that is used for energy harvesting. The electrode pair comprises at least two electrodes, wherein the at least two electrodes comprise an anode and a cathode.

[0044] According to an embodiment of the invention the materials of the harvesting electrodes comprise at least one of (but are not limited to) zinc, carbon, graphite aluminium, magnesium, silver, and copper. Generally, any suitable pair from galvanic series can be used as the at least one electrode pair used in the invention. Example pairs are zinc-carbon, zinc-manganese oxide, zinc-air, zincsilver, zinc-copper, zinc-iron, aluminium-copper, magnesium-copper, magnesium-silver and aluminium-nickel.

[0045] In one example embodiment of the invention the electrode pair comprises zinc and air. When using air as an electrode material in the electrode pair, carbon can be used as catalyst for collecting the current from the electrode material itself.

[0046] Carbon or other suitable material can also be used as catalyst and current collector with other electrode materials, especially with the electrode materials mentioned in this context.

[0047] According to an embodiment of the invention the anode is an oxidizing electrode. In the at least one electrode pair the anode is the less noble material.

[0048] According to an embodiment of the invention the cathode is a reducing electrode and in the at least one electrode pair is the more noble material.

[0049] At least one of the electrodes can be manufactured with printed electronics manufacturing. The printed electronics manufacturing enables more streamlined manufacturing where the at least one of the electrodes can be manufactured on to a layer used in a diaper. This layer can but is not limited to be absorbing layer or diaper back sheet. The layer can also be some other layer not currently known to be used in diapers.

[0050] Herein the printed electronics can mean for example that the depositing of the layers in the electrodes may be performed by printing, sputtering, or painting. According to an example embodiment of the invention at least one of the layers may be deposited with the mentioned methods and possible further layers can be deposited with the same method as the at least one of the layers or with other method, comprising the mentioned methods as well as methods not mentioned herein.

[0051] In one example embodiment of the invention, the layer used for depositing the electrode material, also called as substrate, is made of paper. The electrode material can be deposited by printing or sputtering a thin layer of the electrode material on to the substrate. It is also possible to deposit the electrode material on the substrate in a form of thin wires in a mesh like structure instead of a layer form.

[0052] In a further example embodiment of the invention, instead of paper as a substrate material, one may use cloth, plastic, or even a printed circuit board. The substrate material can also be made from several different materials, for example from some of the ones mentioned above.

[0053] The electrodes can be made flexible using the printed electronics manufacturing but also with other manufacturing methods. With flexible electrodes the need for other materials in the diaper can be reduced as there is no need for additional padding for comfort of the end user between the electrodes and the end user.

[0054] In one example embodiment of the invention, in case of more than one electrode pair in the diaper the physical dimensions of the electrodes may vary. For example, the second electrode pair may be longer or shorter than the first one. This extends also to further electrode pairs, meaning that the possible third electrode pair may be longer or shorter than the first and / or the second electrode pair. Having electrode pairs of different lengths enables one way to estimate the volume of the electrolyte solution deposit in the diaper.

[0055] In a further example embodiment of the invention, the more than one at least one electrode pair can be arranged in the diaper spatially related to the at least one absorbing layer of the diaper. In case of flexible electrode pairs of different physical dimensions, it is possible to bend electrodes in such way that the electrode can be arranged on different sides of the at least one absorbing layer.

[0056] In case where all the electrodes in the at least one electrode pair are manufactured with printed electronics manufacturing there may not be need for additional electrodes to be used in the diaper. This would highly increase the recyclability of the diaper when compared to e.g. solid, non-flexible sheet electrodes. In one example embodiment of the invention, it is also possible to include multiple electrodes and electrode pairs on one substrate layer. This kind of structure can be called as the electrode arrangement. The electrode arrangement can also include multiple layers of substrate that may each have at least one electrode. The fabrication and properties of the individual electrodes stated herein, can also be extended to the electrode arrangement.

[0057] According to an example embodiment of the invention, the cathode 110 is fabricated on top of a layer 112 that can be inserted during the manufacturing inside the diaper by depositing at least one layer of electrically conductive carbon 114 on the layer 112. The at least one carbon 114 layer may be cured after each layer deposited. A galvanic connection 118 to the cathode 110 is provided ensuring that short circuits are avoided. A specific structure can be used for avoiding an unintentional short circuit between the cathode 110 and other parts. Figure 1 (a) presents an example illustration of the described cathode.

[0058] According to a further embodiment of the invention, the anode 120 is fabricated on top of a layer 122 that can be inserted during the manufacturing inside the diaper by depositing at least one layer of electrically conductive carbon 124 on the layer. The at least one carbon layer 124 may be cured after each layer deposited. On top of the at least one carbon layer 124 is deposited at least one layer of electrically resistive zinc 126. The at least one layer of zinc 126 may be cured after each layer deposited. A galvanic connection 128 to the cathode 120 is provided by ensuring that short circuits are avoided. A specific structure can be used for avoiding an unintentional short circuit between the anode 120 and other parts. Figure 1 (b) presents an example illustration of the described anode.

[0059] According to another embodiment of the invention, the material of the at least one electrode can also be in a sheet form, that can be e.g. rolled, before the manufacture of the electrode pair. The sheet form of the electrode material is separate from the printed electronics. However, the sheet material and printed electronics material can be used with each other as well, e.g., the at least one electrode pair may comprise an anode made of material of sheet form and the cathode may be made with printed electronics, or vice versa. Other possible combinations of the materials are also possible according to embodiments of the invention. Figure 2 presents a cathode and an anode fabricated according to an example embodiment of the invention. The dimensions of the electrodes, width 110w, 120w and length 11 Oi, 120i, used in some embodiment in the invention are 7 cm each. This corresponds to a surface area of 49 cm2on both sides of the electrode. However, the invention is not limited to these dimensions.

[0060] In one embodiment of the invention, the at least one electrode pair for energy harvesting comprises more than one electrode pairs that are arranged in series or in parallel.

[0061] In one embodiment of the invention the electrodes may further comprise electrodes for measuring capacitively parameters related to the electrolyte solution using a separate sensor such as coplanar capacitive sensor or capacitive sensor of some other type.

[0062] Figure 3(a) presents an example embodiment of the invention.

[0063] The electrolyte solution 330 usable with the solution of the invention comprises preferably at least one of the following sodium, chloride, and potassium electrolytes.

[0064] In one example embodiment, the electrolyte solution 330 is urine. In laboratory conditions a solution resembling urine, referred to as pseudo-urine, can be used in place of urine to demonstrate the applicability of an energy harvesting diaper.

[0065] The urine comprises typically urea, uric acid, protein, glucose, sodium, potassium, chlorine, inorganic phosphorus, and calcium. Among the above components, at least uric acid, sodium, potassium, chlorine, inorganic phosphorus, and calcium are electrolytes that exist in the form of ions in the urine. The measurements and tests performed in this document with pseudourine are reproducible with urine or other similar electrolyte solution. Therefore, the word pseudo-urine is interchangeable with words urine or electrolyte solution in the context of this document.

[0066] In one example embodiment of the invention, the electrical parameters relating to the electrolyte solution is at least one of the following: voltage, current, resistivity, impedance, and dielectric properties.

[0067] When the electrode pair 310, 320 is at least partly immersed in an electrolyte solution 330, the electrode pair and the electrolyte solution form a galvanic cell 306, known also as a voltaic cell. According to the working principle of the galvanic cell, the electrodes of the galvanic cell have potential difference and current can be withdrawn from the galvanic cell 306. Therefore, the galvanic cell can be used as power or energy source, thus power can be withdrawn from the galvanic cell.

[0068] A galvanic cell 306 is formed in the diaper 300 between the electrodes of the at least one electrode pair 310, 320 when an electrolyte solution 330 forms a bridge between the electrodes of the at least one electrode pair 310, 320 for the ions to be transported in the electrolyte solution 330 between the electrodes of the at least one electrode pair 310, 320.

[0069] According to an embodiment of the invention, the at least one electrode pair 310, 320 is arranged in contact with the at least one absorption layer 302 or in such vicinity to the at least one absorption layer 302 that the at least one electrode pair is at least partly immersed in the electrolyte solution 330 when the electrolyte solution 330 is deposit in the diaper 300.

[0070] According to an example embodiment of the invention, the electrodes of the at least one electrode pair 310, 320 are arranged with respect to the at least one absorption layer 302 so that when the electrolyte solution 330 is deposit in the diaper 300 a galvanic cell 306, that comprises the at least one electrode pair 310, 320 and deposit electrolyte solution 330, is formed in the diaper 300. Therein the at least one absorption layer 302 is at least partly immersed in the electrolyte solution 330 as well as the electrodes of the at least one electrode pair 310, 320, and the galvanic cell 306 is therefore formed.

[0071] The voltage difference between the electrodes 310, 320 and the amount of energy that can be withdrawn from the galvanic cell 306 depend on the materials used as the electrodes 310, 320 and the electrolyte solution 330.

[0072] According to an example embodiment of the invention it may be beneficial to impregnate some area of the electrode substrate with a chemical compound to improve the generation of electrical power via the at least one electrode pair. Such chemical compound may comprise carbon and zinc. Specifically zinc chloride may be used.

[0073] According to an exemplary embodiment of the invention, the diaper 300 comprises a diaper body and electrodes. At least two of the electrodes 310, 320 are arranged between the layers of the diaper 300 in such way that when the diaper is at least partly immersed in an electrolyte solution 330, such as urine or pseudo-urine, the electrolyte solution 330 and the at least two of the electrodes 310, 320 form a galvanic cell 306.

[0074] The electrolyte solution 306 is deposit in the diaper 300 for at least partly immersing the energy harvesting electrodes 310, 320 in the electrolyte solution 330 for forming a galvanic cell 306.

[0075] In an example embodiment of the invention, the absorbing layer 302 of the diaper 300 is made of a superabsorbent polymer. The absorbing layer 302 may be arranged next to a distribution layer that distributes the deposit electrolytic solution 330 more uniformly over the absorbing layer 302.

[0076] In a further example embodiment, different electrodes 310, 320 may be arranged on the same side of the at least one absorbing layer 302 but as well on different sides of the absorbing layer 302. In other words, the electrodes 310, 320 are not needed to be arranged on only one side of the at least one absorbing layer 302. In case of more than one absorbing layer in the diaper, first piece of the electrodes can be arranged with respect to first at least one absorbing layer and further pieces of the electrodes with respect to a further at least one absorbing layer.

[0077] In an embodiment of the invention, the measurement electronics 340 used for measuring electrical parameters relating to the electrolyte solution 330 is arranged in the diaper 300. The measurement electronics 340 may be powered by the energy harvested by the galvanic cell 306 in the diaper 300.

[0078] According to an example embodiment of the invention, the measurement electronics 340 may be fabricated with printed electronics technology or on printed circuit board.

[0079] In one example embodiment of the invention, the diaper 300 comprise means for transmission 350, e.g. a transmitter, for transmitting the extracted information related to the electrolyte solution 330 out of the diaper 300. In such application, e.g. loT application, the monitoring of the state of the diaper, e.g. whether the diaper has any electrolyte solution 330 in it, the amount of the electrolyte solution 330, the composition of the electrolyte solution 330, or the electrical parameters of the electrolyte solution 330 measured using the electrodes, can be performed wirelessly.

[0080] The maximum distance between the transmitter 350 and the equipment receiving the transmitted information, the monitor, can be related to the transmission protocol. Such protocols include but are not limited to Bluetooth, Bluetooth LE, ZigBee, Z-Wave, a proprietary RF protocol.

[0081] According to an example embodiment of the invention, any low power transmission protocol that can be powered with the amount of energy harvested with the electrodes can be used. The harvested power in this embodiment can be used for powering both the measurement electronics as well as the electronics used for transmitting the information.

[0082] In one example embodiment of the invention, it is also possible that the power for information transmission is obtained from the receiver wirelessly during information transmission. Some of the power received wirelessly during information transmission can also be used for powering the measurement electronics. Also, the transmission electronics can in addition to the power received from the information transmission use power harvested in the diaper.

[0083] In one example embodiment of the invention a proprietary RF protocol is used for the information transmission. Due to the limited power resources available, a slower data transfer and narrower bandwidth than, for example, in Bluetooth or Bluetooth LE protocols can be an advantage. The transmission band of the proprietary protocol could be in the range of 0.5 MHz to 20 Mhz.

[0084] According to an exemplary embodiment, the electronics 340, 350 can be set to deep sleep state for conserving the harvested energy for longer periods. In the context of this application deep sleep state could also include sequential measurements at predefined time intervals, measuring information when a trigger for electrical parameters related to the electrolyte solution 330 or other electrolyte solution 330 parameters is triggered, or some other way for power saving in addition to powering at least partly the electronics off.

[0085] In one example embodiment of the invention the diaper 300 comprise means for connecting 360, i.e. at least one connector, for connecting external electronics to the diaper 300. The external electronics can power the electronics 340, 350 comprised in the diaper 300 via the at least one connector 360. The connection 360 for the external electronics can be galvanic, capacitive, inductive, or other suitable connection type for delivering power to the electronics 340, 350 in the diaper 300.

[0086] When the diaper 300 is powered with the external electronics, a capacitive measurement can be performed using the electrodes 310, 320 in the diaper. The performed capacitive measurement of the electrodes, preferably the electrodes 310, 320 for harvesting the energy, can be used to monitor the condition of the diaper 300 before the electrodes have been at least partly immersed in the electrolyte solution 330. With the capacitive measurement it is possible to monitor that the electrodes 310, 320 are operational and are not damaged. The damage of the electrodes could occur during the manufacturing process, storing, transporting, or when putting on the diaper to the user.

[0087] During the manufacturing process the diaper can also be powered on between or during different manufacturing steps one or multiple times for ensuring the operation of the electrodes.

[0088] In an example embodiment of the invention, the conductivity of the urine can be used to determine different kidney functions. Human urine has an electrical conductivity typically ranging from 0.1 to 3.4 S / m. When the kidney function is normal, the filtration rate of glomeruli in the kidneys is higher. As a result, the quantity of these electrolytes being filtered to enter the urine is larger. Thus, the urine has a higher conductivity. Conversely, when the kidney functions are abnormal, the filtration rate of the glomeruli in the kidneys is lower. As a result, the quantity of these electrolytes in the urine is smaller, thus causing the urine to have a lower conductivity. Therefore, by correlating the urine conductivity measured by the processing unit with conductivity data associated with different kidney functions, a kidney function status associated with the urine can be determined.

[0089] One benefit of the solution of the invention is that no separate battery component is needed. The electronics powered with the harvested energy in the diaper start to operate when the electrodes are at least partly immersed in the electrolyte solution. Therefore, no aging battery components is needed.

[0090] According to one example embodiment of the invention the materials and methods used in the experimental tests leading to some embodiments of the invention are presented. The materials and methods used during the experimental tests, including the materials and fabrication methods for the electrodes used, the concentration of the electrolyte solution used, and the measurement setup and methods used are presented in the following paragraphs. The invention is not limited to the example embodiment presented.

[0091] The zinc and carbon materials as rolled sheets and printable inks are used to develop the harvesting electrodes to harness chemical energy from indigenously developed pseudo-urine. The design and development of the harvesting electrodes, chemical formulation of pseudo-urine, and the measurement setup to evaluate the effect of the surface area of the electrodes and inter-electrode distance on harvested energy and level of voltages are discussed in detail under the following subsections.

[0092] Off-the-shelf flexible rolled sheets of carbon material and zinc metal are used initially to develop the harvesting electrodes for the preliminary measurements to assess the proof-of-concept. A sheet of pure conductive carbon holding a thickness of 0.1 mm (Fly Fiber, 2022) is used to develop the harvesting electrodes as the cathode having a size of 7x7 cm. The harvesting electrodes as the anode of the same size are developed with an off-the-shelf flexible rolled sheet of 99.99% pure zinc metal (Tools Store, 2022). Both the cathode and anode electrodes have a surface area of 98 cm2 each with 49 cm2 on either side of the electrode. The electrical connections for the carbon cathode are implemented using a small path of copper tape with conductive adhesive (3M, StPaul, Minnesota, USA) and for the zinc anode by directly soldering the copper wire to the sheet surface. The connections are secured with water-resistant tape to avoid short circuits.

[0093] The printed harvesting electrodes of 7x7 cm size are developed using zinc and carbon inks on the inner side of the diaper back sheet. The Figure 1 (a) depicts the cross-section of the cathode electrode design with printable carbon ink on the single side of the diaper back sheet whereas (b) shows the cross-section of the anode design with printable zinc ink on top of the carbon-based current collector layer on the single side of diaper back sheet.

[0094] An example embodiment of the fabrication method of the cathode and the anode used in the experimental tests is discussed in the following paragraphs. The invention is not limited to this example embodiment and other fabrication or manufacturing methods for the electrodes may be used as well. The cathode (reducing electrode) with the same geometry as described in the Figure 1 is fabricated by deposition and curing of electrically conductive carbon ink (Saral Carbon 700A, by Saralon GmbH). Consecutive two layers of carbon ink with a sheet resistance of 30 Q / n / 25 pm are deposited sequentially and each layer is thermally dried in a 95 °C preheated oven (ProtoFlow E, by LPKF Laser & Electronics) at 100 °C for 10 minutes. The electrical connections are implemented using a small patch of copper tape with conductive adhesive (3M, StPaul, Minnesota, USA) on the dried carbon ink layer. The connections are secured with water-resistive tape to avoid short circuits.

[0095] The fabrication of the anode (oxidizing electrode) is conducted by depositing and curing the electrically resistive zinc ink (Saral Zinc 700, by Saralon GmbH). Consecutive two layers of Zinc ink with a thickness of 100 microns are deposited sequentially and each layer is thermally dried in a 95 °C preheated oven (ProtoFlow E, by LPKF Laser & Electronics) at 100 °C for 10 minutes. Two consecutive layers of carbon ink are printed as a current collector under the zinc anode as shown in Figure 1 (b) because of the low conductive properties of zinc ink. The finished version of the printed cathode and anode are shown in Figure 2.

[0096] An exemplary electrolyte solution is presented below. The electrolyte solution, also referred to as the urine or the pseudo-urine, concentration used in the experimental tests is discussed in the following paragraph. The invention is not limited to the used concentration, but the presented concentration can be used to replicate the measurement and validate the embodiments of the invention.

[0097] Typical human urine contains sodium, chloride, and potassium electrolytes along with more than 150 different constituents. The specific conductivity of sodium chloride solution (1 .3 kUcm2 / mol) is close to the specific conductivity of ammonium chloride solution (1.5 kUcm2 / mol) of same concentration at room temperature.

[0098] The reference concentration of sodium electrolytes in urine exhibits a range of 80 to 240 mmol / l and the concentration of chloride electrolytes has a range of 85 to 260 mmol / l for adults. In this study, the chemical composition of pseudourine suitable for chemical energy harvesting from zinc-carbon electrodes is formulated at Aalto University labs using sodium chloride (NaCI) at an electrolyte concentration of 220 mmol / l. This concentration falls within the established range of reference concentrations for sodium and chloride in the urine. It is noteworthy that a one-mole solution of NaCI consists of a molar mass of 23 g / mol for sodium and 35.5 g / mol for chloride. The pseudo-urine is used as an electrolyte for the zinc-carbon harvesting electrodes to replace the hazardous electrolyte ammonium chloride (NH4CI) used in commercial zinc-carbon dry batteries.

[0099] An example embodiment of the measurement setup is discussed below. The measurement setup used in the experimental tests used for validating the invention is presented in the following paragraphs. The invention is not limited to use only the presented measurement setup. In addition, the setup is presented for possibility to replicate the measurements by the reader.

[0100] A galvanic cell, also called a voltaic cell, is developed using pseudo urine and printed harvesting electrodes. The positive electrode and negative electrode inside the electrolyte behave as half-cells which are combined together using a salt bridge of electrolyte to make galvanic cells. The salt bridge of pseudo-urine, also called the ion bridge of NaCI electrolyte, connects the oxidation and reduction reactions of the half cells. The oxidation-reduction reaction generates the electric current and the salt bridge prevents the charge accumulation around the anode and cathode electrodes of half cells and facilitates the continuous production of electricity.

[0101] The multimeter (73 III, Fluke) with an accuracy of 0.3% and resolution of 0.1 mV is used to measure the open circuit voltages (OCV) of the galvanic cell having zinc-carbon harvesting electrodes immersed in pseudo-urine. A direct current (DC) energy analyzer and power profiler instrument Otii Arc Pro (Qoitech, Sweden) is employed together with Otii Battery Toolbox to load and characterize the zinc-carbon flexible harvesting electrodes inside pseudo-urine as electrolyte. The galvanic cell is established as a vertical container, holding the pseudo-urine of one liter. In the galvanic cell of the measurement setup, the harvesting electrodes are deployed on the inner side of the container in a parallel position. Figure 3(b) depicts the established measurement setup to evaluate the harvested energy. Various measurement scenarios are established to analyze the harvested voltage level and amount of energy from pseudo-urine where a fixed power amount is withdrawn with a lower voltage threshold of 500 mV. In the first measurement scenario, the rolled sheet-based zinc-carbon harvesting electrodes with a surface area of 98 cm2 are deployed in the galvanic cell with an inter-electrode distance of 7 cm. The pseudo-urine-based electrolyte is poured inside the cell with an increasing submerge depth of 1 cm for electrodes in each measurement hence increasing the submerged electrode area of 14 cm2 for each step to analyze the effect of the variations in the electrode area on harvested energy when partially submerged. The voltage level and the amount of harvested energy are analyzed for cases when the electrodes are only partially submerged in urination events of a small quantity. The second measurement scenario uses the same zinc-carbon electrodes fully immersed in one liter pseudo-urine electrolyte of the galvanic cell where the distance between anode and cathode is varied from 5 mm to 30 mm with a step increment of 5 mm.

[0102] In the third measurement scenario, the printed zinc-carbon flexible electrodes are fully immersed in one liter of pseudo-urine electrolyte of the galvanic cell in face-to-face orientation at a distance of 7 cm to evaluate the change in voltages and current flow when a fixed power amount of 800 uW is continuously withdrawn over time. The last scenario evaluates the intermittent energy harvesting events every 30 minutes where the same printed zinc-carbon electrodes are fully immersed in the pseudo-urine electrolyte of a galvanic cell for a longer time of 11 hours to understand the possibility of powering the loT sensor node performing measurements for multiple urination events inside the same diaper.

[0103] The results of the experimental measurements acquired using the example embodiment of the measurement setup and discussion of the results are presented in the following paragraphs. The invention is not limited to the results or the discussion presented herein. In addition, the results are presented for the reader for validating their measurement results of their replicated measurements.

[0104] The evaluation measurements of the zinc-carbon harvesting electrodes inside pseudo-urine electrolyte are conducted using measurement setup as shown in Figure 3(b). The OCV level of 1032 mV is measured for the developed zinccarbon harvesting single galvanic cell and 2060 mV when the two galvanic cells are connected in series. The harvested voltage level of the single galvanic cell, with fully immersed electrodes in the electrolyte, drops to 875 mV when loaded with a power draw of 100 uW and further drops to 831 mV when loaded with a power draw of 800 uW. The effect of variation in the submerged surface area out of the total area of 98 cm2 of harvesting electrodes on the amount of harvested energy from the first measurement scenario is depicted in Figure 4. It is observed that the amount of harvested energy is linearly proportional to the submerged surface area of the harvesting electrode with a variation of 4.3 uWh / cm2 to 1 .9 uWh / cm2 when the percentage of the submerged surface area of the single electrode increases from 14% to 100%. Another interesting observation is made that the voltage level gets as high as 1068 mV when the percentage of the submerged surface area is reduced to 14% and the galvanic cell is loaded with 100 uW power draw.

[0105] The effect of variations in the inter-electrode distance on the amount of harvested energy from zinc-carbon electrodes is analyzed in the second measurement scenario. The galvanic cell with fully immersed zinc-carbon electrodes in the pseudo-urine electrolyte is loaded with 100 uW for the initial 10 seconds. The load is increased to 500 uW power afterward and the harvested energy is recorded until the voltage level drops to the threshold level of 500 mV. The measurement is repeated by increasing the inter-electrode distance by 5 mm for each measurement using the same electrodes and electrolyte. The results of harvested energy and starting voltage levels with inter-electrode distance variations are presented in Figure 5. It is observed that the amount of harvested energy reduces linearly with an increase in the inter-electrode distance and drops 25% when the distance is doubled. The starting voltage level of the galvanic cell has also seen a loss of 130 mV because the redox process deteriorates the surface of the harvesting electrodes over the harvesting time period. This phenomenon is discussed further in the fourth measurement scenario.

[0106] The printed zinc-carbon electrodes on the inner side of the diaper back sheet having 50% surface area (49 cm2) are used in the third measurement scenario. The printed electrodes are fully immersed in the one-liter pseudo-urine electrolyte and the galvanic cell is loaded with 800 uW power draw. The trend of voltage level and current flow is observed over time until the voltage level drops to the threshold of 500 mV. The voltage and current response of the printed zinccarbon electrodes is depicted in Figure 6. It is observed that the single cell of single-side printed zinc-carbon electrodes is capable of supporting output current flow up to 1 .6 mA. The same setup of printed zinc-carbon electrodes from the previous measurement scenario is further used to evaluate the performance of harvesting electrodes when fully immersed in the same electrolyte for a longer period of time. A fixed power amount of 800 uW is withdrawn in each measurement session until the voltage level reduces to the threshold of 500mV and the session is repeated every 30 minutes up to 11 hours. The results of the harvested energy and the starting voltage level of the single galvanic cell for each measurement session are plotted over time as shown in Figure 7. It is observed that the amount of the harvested energy from the same electrodes in the same electrolyte drops linearly over time. It is evident that even after 11 hours the printed zinc-carbon electrodes are still capable of providing 25% of the first harvested energy. The starting voltage level also dropped linearly for each following harvest session and after 11 hours there was only a 110 mV drop in single cell voltage level from the first harvest. The proposed novel chemical energy harvesting solution using printed zinc-carbon electrodes in a pseudourine electrolyte has yielded promising results. The printed zinc-carbon harvesting electrodes may be adopted with a power-optimized on-chip system for smart diapers interfaced with printed coplanar capacitive sensors to detect wet diapers and quantify voided volumes in a diaper. The harvested energy from the proposed printed harvesting electrodes is sufficient to power on-chip circuits fundamental for most of the front-end sensor interface electronics such as 0.39- 3.56 juW wide dynamic range universal multi-sensor interface circuit and 462 nW 2-axis gesture sensor interface based on capacitively controlled ring oscillators. It can also power energy-optimized wireless communication blocks of the loT sensor nodes such as a low-power wireless transceiver with a 67 nW differential pulse-position modulation (DPPM) transmitter. The on-chip sensor-end electronics might be combined with the low-power DPPM transmitter to develop a self-powered loT sensor node for smart diapers running on harvested energy from urine with sustainable and economical printed harvesting electrodes.

[0107] The discussion and conclusions relating to the experimental tests are presented in the following paragraphs. The discussion and conclusions relate to the experimental tests performed leading to some embodiments of the invention and the results acquired using the example embodiment of the measurement setup and does not limit the invention only to the presented discussion and conclusions. Zinc-carbon-based dry batteries with manganese dioxide and ammonium chloride electrolytes have been available commercially for more than 150 years. There is a market growth trend for zinc carbon batteries because these are more sustainable and environment friendly as compared to their competitors. However, the wide use of ammonium chloride as an electrolyte in dry batteries still poses challenges of being hazardous for humans and harmful to aquatic life.

[0108] The presence of the discussed electrolytes in urine makes it suitable to be used as an electrolyte for zinc-carbon harvesting electrodes to harness chemical energy from urine. In this study, a novel energy-harvesting approach is proposed involving the design and development of zinc-carbon-based flexible electrodes using printed electronics technology to harvest chemical energy from urine in diapers. The electrodes are printed directly onto the diaper back-sheets, aiming to offer a sustainable, environmentally friendly, and cost-effective disposable solution. This innovation intends to eliminate the need for batteries, which are not only hazardous but also challenging to recycle. The primary objective is to harvest the chemical energy to supply power to the energy-optimized circuits of loT sensor nodes and integrate the printed harvesting electrode seamlessly into smart diapers.

[0109] The materials used to develop the printed harvesting electrodes, the preparation of pseudo urine, the experimental setup, and the various measurement scenarios are discussed in this application. Also, this application includes a discussion of the measurement results with the help of graphs and charts and concludes the work by discussing the findings and limitations along with the potential future prospects of the research.

[0110] A novel energy harvesting solution is proposed by designing and developing sustainable harvesting electrodes, leveraging the capabilities of printed electronics technology. These electrodes are engineered to harvest energy from pseudo urine, a readily available resource, with the ultimate goal of powering energy-efficient wearable loT sensor nodes for smart diapers. The study encompasses a comprehensive characterization of these sustainable harvesting electrodes, involving experiments conducted within a controlled laboratory environment, both inside a container and within a diaper setting. The results demonstrate great promise in the context of powering loT sensor nodes, particularly in the case of smart diapers. This research proclaims a significant stride towards addressing the power challenges with batteryless operations for the ever-expanding loT ecosystem.

[0111] The development of printed harvesting electrodes utilizing environment-friendly materials to harvest energy from pseudo urine is presented as a promising avenue to address the power challenges faced by the ever-expanding ecosystem of loT sensor nodes, particularly in the context of smart diapers. The successful demonstration of energy harvesting from urine to power loT sensor nodes, as outlined in the results, highlights the significant development towards sustainable and environmentally friendly solutions in the field of wearable biomedical devices. The printing of harvesting electrodes using zinc and carbon inks on the diaper back sheet can be seamlessly incorporated into the roll-to-roll process of the diaper production line. This study involves meticulous experimentation to evaluate the viability of zinc-carbon printed electrodes for chemical energy harvesting from urine. It offers a pathway towards implementing energy-efficient wearable loT sensor nodes with battery-less operations.

[0112] In the future, an on-chip power management unit might be incorporated with the single cell of proposed flexible printed harvesting electrodes to harness energy from urine and to ensure the continuous supply of regulated voltage to the on- chip front-end sensor interface circuits, control systems, and communication interfaces of an loT sensor node developed for smart diapers. The printed harvesting electrodes might also be further studied to provide an additional parameter together with measurement data from the printed coplanar capacitive sensors for reliable and precise quantification of the voided volume inside the diaper which is otherwise affected by body weight on wet diaper.

[0113] The invention has been explained above with reference to the aforementioned embodiments, and several advantages of the invention have been demonstrated. It is clear that the invention is not only restricted to these embodiments but comprises all possible embodiments within the spirit and scope of inventive thought and the following patent claims.

[0114] The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated.

Claims

CLAIMS1 . A method for harvesting energy in a diaper, wherein the diaper comprises electrodes and electronics connected to the electrodes, wherein the electrodes comprise at least one electrode pair for energy harvesting, the at least one electrode pair comprising an anode and a cathode; and wherein the method comprises: harvesting chemical energy using the at least one electrode pair and electrolyte solution for powering the electronics when the electrodes of the diaper are at least partly immersed in the electrolyte solution; and extracting information relating to the electrolyte solution when the electrodes of the diaper are at least partly immersed in the electrolyte solution by measuring electrical parameters relating to the electrolyte solution by using the electronics powered by the harvested energy and the electrodes used for the energy harvesting.

2. The method according to claim 1 , wherein the diaper comprises a diaper body and at least one absorption layer for absorbing liquids deposit in the diaper.

3. The method according to claim 2, wherein the at least one electrode pair is arranged in contact with the at least one absorption layer or in such vicinity to the at least one absorption layer that the at least one electrode pair is at least partly immersed in the electrolyte solution when the electrolyte solution is deposit in the diaper.

4. The method according to any of the preceding claims, wherein the electrolyte solution is a solution comprising at least sodium electrolytes and chloride electrolytes.

5. The method according to any of the preceding claims, wherein the electrolyte solution is urine.

6. The method according to any of the preceding claims, wherein at least one of the electrodes are flexible.

7. The method according to any of the preceding claims, wherein at least one of the electrodes is manufactured with printed electronics technology.

8. The method according to any of the preceding claims, wherein the anode comprises carbon and the cathode comprises zinc.

9. The method according to any of the preceding claims, wherein the electrolyte solution and the at least one electrode pair form at least one galvanic cell.

10. The method according to any of the preceding claims, wherein the electrical parameters of the electrolyte solution comprise at least one of the following:- voltage;- current;- resistivity;- impedance; and- dielectric properties.

11. The method according to any of the preceding claims, wherein the extracted information related to the electrolyte solution comprise at least one of the following for the electrolyte solution in the diaper:- the electrical parameters;- presence;- amount; and- composition.

12. The method according to any of the preceding claims, wherein the diaper further comprises means for wireless transmission for transmitting the extracted information related to the electrolyte solution out of the diaper for monitoring the state of the diaper.

13. The method according to any of the preceding claims further comprising means for connecting external electronics to the electrodes and performing a capacitive measurement of the electrodes by using the external electronics tomonitor the condition of the diaper before the electrodes of the diaper have been immersed in the electrolyte solution.

14. A diaper comprising: electrodes and electronics connected to the electrodes, wherein the electrodes comprise at least one electrode pair for energy harvesting, the at least one electrode pair comprising an anode and a cathode; and wherein the diaper is configured to: harvest chemical energy using the at least one electrode pair and electrolyte solution for powering the electronics when the electrodes of the diaper are at least partly immersed in the electrolyte solution; and extract information relating to the electrolyte solution when the electrodes of the diaper are at least partly immersed in the electrolyte solution by measuring electrical parameters relating to the electrolyte solution by using the electronics powered by the harvested energy and the electrodes used for the energy harvesting.

15. The diaper according to claim 14, wherein the diaper is further configured to perform the method of any of the claims 2 to 13.

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