Patent Application: US-201514840852-A

Abstract:
system for monitoring the hydration status of a living being by exploiting the modulation of backscattered rf electromagnetic waves from a wearable patched placed on the skin , said system comprising : a rf - tag adapted to be directly or indirectly fixed to the skin and containing at least one passive integrated circuit coupled to an antenna ; an electromagnetic rf power source for supplying different signal frequencies to said rf - tag ; a reader adapted to receive and to process the backscattered electromagnetic waves generated by said electromagnetic power source .

Description:
the invention will be better understood below with some examples . it should be understood that they are presented to exemplify certain forms of the invention which are not intended to limit the scope of the invention . fig1 represents the concept of the invention for determining hydration with a single - site backscattering measurement , multi - parameter extraction and wireless communication to a smart hub ( called here mobile device ) exploiting : an rf tag placed on the skin , an electromagnetic rf source such as the ones available in mobile phones , an rf reader to detect and evaluate the backscattered signals . fig2 shows an equivalent circuit of the sensing meta - material composed of a tag flexible substrate , antenna and the skin . the variable impedance of the skin modulates the backscattered wave characteristics which thus carry information on the skin hydration level . fig3 depicts the rf reader that includes both the transmitter for the electromagnetic rf sources and the receiver , based on a conventional architecture but with ability to vary the frequency of the electromagnetic wave that is backscattered , according to the method described in this invention . in one example of the invention , the passive monitoring tag is powered by an incident wave emitted by a smart hub and comprises a thin flexible substrate ( e . g . polyethylene naphthalate , polyethylene terephthalate , polyurethane , polytetrafluoroethylene , paper , polyimide , silicone , etc .) and protective insulating material , one or more antennas to sense signals , in a way adapted to contact human body ( skin ), and integrated circuit to send backscattered signals to the same mobile hub , and two temperature sensors for sensing both the core - body temperature and the environment temperature . the system is primarily intended to monitor body hydration level but may encompass many other uses . in the example illustrated on fig1 an external smart hub is configured to emit electromagnetic waves at a plurality of frequencies in the low ghz range ( implemented in smartphones ) at the passive tag in contact with an individual &# 39 ; s skin . the backscattered waves are wirelessly sent back to a data acquisition module of the same smart hub . this mobile hub is equipped with dedicated signal processing algorithms to treat the signals , extract physiological parameters such as the water fraction of the tissue , the cardiac output , the red blood cell content and determine the hydration level . the extraction of the physiological parameters is made possible by the fact that the backscattered waves sent back by the tag antenna are modulated by the varying electrical properties ( e . g . impedance , permittivity ) of the skin tissue in contact with the tag . that is to say , the meta - material composed of the tag flexible substrate , antenna and the skin exhibits an equivalent impedance which varies as function of the skin properties that are particularly dependent on its level of hydration ( fig2 ). the loss between the incident and backscattered waves are mainly dominated by the properties of the tissue and they modify the apparent impedance of the passive tag antenna . permittivity changes , due to the skin tissue dehydration for instance , generate variation of the phase velocity and wavelength of the backscattered radiations . these alterations enable to extract the red blood cell content as well as the cardiac output by doppler flowmetry for instance . similarly , at ghz frequencies , the polarization of water molecules in the skin tissue dominates the losses by adsorption of the waves and enables to determine the tissue water content . a significant part of the invention concerns the use of different signal frequencies that enables to probe at different depth of the skin tissue . such method scanning different frequencies in the investigation , not only provides access to different tissue layers related losses with a good control of the analyzed depth but also permits to discriminate the most relevant signals from perturbations and noise . the system according to the invention exploits a backscattering high frequency ( mhz , ghz or higher ) wave measurement which mirrors the impedance characteristics of a combined flexible patched antenna and of a biological tissue , depending on its hydration level . externally supplied electromagnetic waves with different signal frequencies in the mhz to ghz range are used and their backscattering characteristics detected and measured . different modulation schemes available for state - of - the - art tag - to - reader wireless communication can be used . from this measurement , multiple parameters reflecting both hypernatremia and hypovolemia , are extracted therefore levels of any type of body ( de ) hydration can be quantified . such a system can be directly applied on the skin of a person and / or inside some types of garments . the system is non - invasive and preferably includes a remote rf - tag temperature sensing for accurate calibration on the same substrate . the system can be made in disposable ( such as based on organic electronic or dissolvable materials ) and non - disposable ( using established and industrially available rf technologies ) embodiments . the integration of the antenna can be made on a bio - compatible thin flexible material ( such as polyimide ) substrate on which metal lines using any type of thin metal layers define the antennas ( the use of highly conductive metals or of noble metals such as platinum and gold is preferred for best performance ). the rf - tag is autonomous and does not require any integrated power source . it is powered by the energy coming from the rf waves . the rf - tag is designed to wirelessly communicate ( backscatter radiation from ), preferably with a rf reader integrated in a personal portable hub serving as display interface and offering full local analog - to - digital conversion and digital signal processing capability ( running specific algorithms ) to extract the information for hydration level but also for other complementary biological parameters characterizing body fluids and skin features . first responders in general and firefighters in particular , are highly exposed to dehydration : the high temperature around them , the physical effort , and the heavy clothing they wear , make them prone to high sweat rates . studies have shown that dehydration leads to a loss of alertness , concentration and increased fatigue . this is particularly damaging for professionals who need to react swiftly and remain highly focused . studies have shown that as the level of dehydration increases during exercise , various physiological functions are progressively impacted : heart rate and core temperature continually increase over time , while blood volume , stroke volume , cardiac output , and skin blood flow all decrease . for athletes , dehydration is the consequence of the thermal regulation of the body through sweating , which is a mix of water and minerals . in the most intensive effort , the quantity of water lost by the human body can overpass 3 . 5 litres . in case this loss of water and minerals is not compensated , dehydration can lead to hypovolemia ( drop in blood pressure ), hypokalemia ( paralysis of limbs ) and hyponatremia ( breathing disorder , disorientation ). these cases are extreme , but what is sure to be a consequence of dehydration is underperforming . glucose is the gas of the body and glycogen is made of three molecules of water . thus , without water , an athlete will not be able to use its reserves of glucose . it is estimated that a water loss of 1 % to 2 % leads to a drop in performance of 10 %. fragile segments of the population , like the elderly and infants , are also at risk of dehydration , particularly during extreme heat . the summer 2003 heat wave in france for example caused 14 ′ 802 heat - 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