SENSOR

Abstract

A sensor measurement device includes: an impedance analyzer to determine an impedance of a sample; a first antenna configured to generate electromagnetic radiation having a first wavelength; an impedance-matching device, positioned in a radiation path between the first antenna and the sample, to receive the electromagnetic radiation from the first antenna and transmit electromagnetic radiation of the first wavelength into the sample, the impedance-matching device comprising a metasurface including: a substrate having a thickness no greater than the first wavelength of the electromagnetic radiation; and a plurality of elements supported by the substrate, wherein: the plurality of elements are spaced apart from one another across the substrate, each element has a first dimension no greater than the first wavelength of the electromagnetic radiation, and at least two elements of the plurality of elements differ in one or more of shape or size; and a second antenna configured to receive the electromagnetic radiation from the sample.

Claims

1. A sensor measurement device comprising: An impedance analyzer to determine an impedance of a sample; a first antenna configured to generate electromagnetic radiation having a first wavelength; an impedance-matching device, positioned in a radiation path between the first antenna and the sample, to receive the electromagnetic radiation from the first antenna and transmit electromagnetic radiation of the first wavelength into the sample, the impedance-matching device comprising a metasurface including: a substrate having a thickness no greater than the first wavelength of the electromagnetic radiation; and a plurality of elements supported by the substrate, wherein: the plurality of elements are spaced apart from one another across the substrate, each element has a first dimension no greater than the first wavelength of the electromagnetic radiation, and at least two elements of the plurality of elements differ in one or more of shape or size; and a second antenna configured to receive the electromagnetic radiation from the sample, wherein one or both of the first antenna and the impedance-matching device are tunable based on the impedance of the sample to reduce an impedance mismatch along the radiation path.

2. The sensor measurement device of claim 1, wherein the sample comprises a biological sample.

3. The sensor measurement device of claim 1, wherein the metasurface is configured to impose a specific phase and amplitude change along an incident wave of the electromagnetic radiation.

4. The sensor measurement device of claim 1, wherein, in the impedance-matching device, the first dimension is the direction for propagation of the electromagnetic radiation.

5. The sensor measurement device of claim 1, wherein, in the impedance-matching device, at least one of the plurality of elements has an irregular shape.

6. The sensor measurement device of claim 1, wherein the sample is bound by a container, and wherein the impedance-matching device is configured to transmit the electromagnetic radiation of the first wavelength into the sample from a position outside the container.

7. The sensor measurement device of claim 1, wherein, in the impedance-matching device, at least a subset of the plurality of elements are arranged in an irregular array.

8. The sensor measurement device of claim 1, wherein, in the impedance-matching device, the plurality of elements are arranged in an irregular array.

9. The sensor measurement device of claim 1, wherein, in the impedance-matching device, the substrate is a dielectric and the plurality of elements are conductive.

10. The sensor measurement device of claim 1, wherein, in the impedance-matching device, the substrate is conductive and the plurality of elements are a dielectric.

11. The sensor measurement device of claim 1, wherein, in the impedance-matching device, the plurality of elements are collectively arranged to resonate at the first wavelength of the electromagnetic radiation.

12. The sensor measurement device of claim 11, wherein the impedance-matching device further comprises an additional metasurface coupled to the metasurface, wherein the additional metasurface comprises: a substrate comprising a thickness no greater than a second wavelength of the electromagnetic radiation; and a plurality of elements supported by the substrate, wherein: each element has a first dimension no greater than a second wavelength of the electromagnetic radiation; at least two elements of the plurality of elements are non-identical; the additional metasurface is arranged, in cooperation with the metasurface, to resonate at a second wavelength of the electromagnetic radiation; and the first wavelength is different from the second wavelength.

13. The sensor measurement device of claim 12, wherein the additional metasurface shapes at least one of an amplitude or phase of the electromagnetic radiation.

14. The sensor measurement device of claim 1, further comprising an electronic calliper arranged to determine a distance between the first antenna and the second antenna.

15. The sensor measurement device of claim 1, wherein one or both of the first antenna and the impedance-matching device comprise a tunable component including one or more of a varactor or a variable resister.

16. The sensor measurement device of claim 1, wherein: the sample comprises blood; the sensor measurement device is arranged to measure a blood glucose level; and the sensor measurement device is wearable on at least one of a hand, a foot, an ear, or a lip.

17. The sensor measurement device of claim 1, wherein the first antenna, the impedance-matching device, and the second antenna are physically associated.

18. The sensor measurement device of claim 1, further comprising a second impedance-matching device arranged between the sample and the second antenna to transmit electromagnetic radiation of the first wavelength from the sample to the second antenna, the second impedance-matching device comprising a metasurface including: a substrate having a thickness no greater than the first wavelength; and a plurality of elements supported by the substrate, wherein: the plurality of elements are spaced apart from one another across the substrate; each element has a first dimension no greater than the first wavelength, and at least two elements of the plurality of elements differ in one or more of shape or size.

19. A method of coupling electromagnetic radiation into a sample using a sensor measurement device, the sensor measurement device comprising: an impedance analyzer to determine an impedance of a sample; a first antenna configured to generate electromagnetic radiation having a first wavelength; an impedance-matching device, positioned in a radiation path between the first antenna and the sample, to receive the electromagnetic radiation from the first antenna and transmit electromagnetic radiation of the first wavelength into the sample, the impedance-matching device comprising a metasurface including: a substrate having a thickness no greater than the first wavelength of the electromagnetic radiation; and a plurality of elements supported by the substrate, wherein: the plurality of elements are spaced apart from one another across the substrate, each element has a first dimension no greater than the first wavelength of the electromagnetic radiation, and at least two elements of the plurality of elements differ in one or more of shape or size; and a second antenna configured to receive electromagnetic radiation from the sample; the method comprising: positioning the sensor measurement device with respect to the sample such that the first antenna is disposed on a first side of the sample and the second antenna is disposed on a second side of the sample; determine an impedance of a sample; tuning one or both of the first antenna or the impedance-matching device based on the determined impedance to reduce an impedance mismatch along the radiation path; providing electromagnetic radiation having the first wavelength from the first antenna to the impedance-matching device; transmitting, by the impedance-matching device, electromagnetic radiation having the first wavelength from the first antenna into the sample; receiving, by the second antenna, electromagnetic radiation from the sample; and characterizing the sample based on the received electromagnetic radiation.

20. A method for designing an impedance-matching device for a sensor measurement device, the sensor measurement device comprising: a first antenna configured to generate electromagnetic radiation having a first wavelength; the impedance-matching device, positioned in a radiation path between the first antenna and a test sample, to receive the electromagnetic radiation from the first antenna and transmit the electromagnetic radiation into the test sample, the impedance-matching device comprising a metasurface including: a substrate having a thickness no greater than the first wavelength of the electromagnetic radiation; and a plurality of elements supported by the substrate, wherein: the plurality of elements are spaced apart from one another across the substrate, each element has a first dimension no greater than the first wavelength of the electromagnetic radiation, and at least two elements of the plurality of elements differ in one or more of shape or size; and a second antenna configured to receive electromagnetic radiation from the sample; the method comprising: positioning the first antenna on a first side of the test sample and the second antenna on a second side of the test sample; determining an impedance of the test sample; calculating a sheet impedance for the metasurface that will couple the electromagnetic radiation of the first wavelength into the sample with maximum transmission; and using analytical modelling to design the plurality of elements of the metasurface such that, when the plurality of elements are combined together in a pattern, cause the metasurface to have the calculated sheet impedance.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Embodiments of the present disclosure will now be described with reference to the accompanying drawings in which:

[0039] FIG. 1 is a metasurface having a periodic pattern;

[0040] FIG. 2 is a metasurface having a non-periodic pattern;

[0041] FIG. 3 shows multiple metasurface layers in a periodic configuration;

[0042] FIG. 4 shows multiple metasurface layers in a non-periodic configuration;

[0043] FIG. 5 shows real and imaginary sheet impedances to refract a normally incident electromagnetic wave to an angle of 45 degrees;

[0044] FIG. 6 shows reflection and transmission coefficients derived from the sheet impedances of FIG. 5;

[0045] FIG. 7 illustrates various views of the metasurface element of the design example;

[0046] FIG. 8 plots S-parameters obtained changing the length of the parallel copper bars of the top metasurface component of the design example;

[0047] FIG. 9 plots S-parameters obtained changing the gap of the metal ring of the bottom metasurface element;

[0048] FIG. 10 shows optimisation progress for the metamaterial element dimensions;

[0049] FIG. 11a shows the optimised geometry characteristics for the metasurface element at 60 GHz;

[0050] FIG. 11b is a metasurface structure in accordance with embodiments;

[0051] FIG. 11c, 11d and 11e are further views of a metasurface structure in accordance with embodiments;

[0052] FIGS. 11f, 11g and 11h show an example of a planar near-field focusing component;

[0053] FIG. 11i shows a simulation result of the power penetration in the case when the metasurface in accordance with the present disclosure is placed against human skin;

[0054] FIGS. 12a to 12m show some design configurations;

[0055] FIG. 13 is an overview of the system;

[0056] FIG. 14a shows system components of the sensor measurement device in accordance with embodiments;

[0057] FIG. 14b shows system components of another sensor measurement device in accordance with embodiments;

[0058] FIGS. 15a to 15d show some examples of single and dual sensors;

[0059] FIG. 16 shows a tuning antenna with an impedance analyser;

[0060] FIGS. 17a to 17c show the sensor in use;

[0061] FIGS. 18a and 18b are isometric views of a measurement system through a human hand;

[0062] FIGS. 19a and 19b are exploded views of a metasurface with antenna configuration in (a) period and (b) non-periodic patterns;

[0063] FIG. 20 is an exploded side view of antenna and three metasurface layers;

[0064] FIG. 21 plots an output signal as a function of glucose concentration in a sample containing water and glucose;

[0065] FIG. 22 plots an Output signal as a function of concentration in samples containing water and glucose, water & glucose & salt, and water & salt;

[0066] FIG. 23 plots an output signal as a function of glucose concentration in samples containing water and glucose in very small amounts;

[0067] FIG. 24 shows an output signal as a function of the concentration of palm kernel oil in a mixture of palm kernel and rapeseed oil; and

[0068] FIG. 25 shows relaxation frequencies of the Cole-Cole model for different oil species.

[0069] In the figures, like reference numerals refer to like parts.

DETAILED DESCRIPTION OF THE DRAWINGS

[0070] Embodiments refer to “biological material” which is a material that is typically either plant material, animal material, or some other substance that can be found in a life form. Some examples include human tissue (hand, skin, muscle, ear, etc.), animal tissue (e.g. from a mouse, cow, or pig), water, blood, milk, saliva, tears, urine, carbonated drinks, and fruit juice, wine, and oil. However, it may be understood that the present disclosure is equally applicable to any biological sample.

[0071] Embodiments refer to “irregular” shapes which include shapes having no axis of symmetry and shapes having only one axis of symmetry.

[0072] A metamaterial comprises a substrate component having a thickness no greater than a first wavelength of the electromagnetic radiation; and a plurality of elements supported by the substrate component, wherein each element has a first dimension no greater than a first wavelength of the electromagnetic radiation. Embodiments refer to a “metasurface” which may be considered a special type of metamaterial. Specifically, a metasurface is a metamaterial in which at least two of the elements of the plurality of elements are non-identical, or different, in any one or more of size, shape, orientation and composition. A metasurface is only two-dimensional.

[0073] Device for Coupling Electromagnetic Radiation

[0074] In overview, the present disclosure describes use of certain types of metamaterials to enhance radio wave penetration through the skin and, therefore, solve the mismatch problem. This is achieved by harnessing the novel and special electromagnetic properties of a subset of metamaterials.

[0075] Conventionally, metamaterials comprise unit cells arranged in periodic patterns. However, the inventors have recognised that a specific type of metamaterial, sometimes called a “metasurface”, is particularly advantageous for coupling electromagnetic radiation into biological samples particularly biological samples in a container.

[0076] Metasurfaces are easy to fabricate and offer the opportunity to build low-loss structures. The properties of the metasurface are determined from the periodicity and the design of their constituent elements. Note that, unlike other metamaterials, which are periodic arrangements of the same element, a metasurface usually comprises of different elements. Likewise, the elements of a metasurface are not necessarily periodically arranged. The present disclosure relates to a metamaterial in which at least two of the sub-wavelength elements of the plurality of elements are different in shape and/or size and/or composition and/or orientation.

[0077] FIG. 1 shows a metasurface 100, in accordance with the present disclosure, comprising a substrate component 101 and a plurality of elements 103. As shown in FIG. 1, elements 103 differ in size and shape. However, in this embodiment, elements 103 are arranged in a substantially regular array. That is, the spacing between the centres of adjacent elements is substantially constant in two orthogonal directions.

[0078] There is therefore provided a device arranged to couple electromagnetic radiation, the device comprising a first metamaterial comprising: a substrate component having a thickness no greater than a first wavelength of the electromagnetic radiation; and a plurality of elements supported by the substrate component, wherein each element has a first dimension no greater than a first wavelength of the electromagnetic radiation and at least two of the elements of the plurality of elements are non-identical.

[0079] Advantageously, the inventors have found that using a metasurface significantly reduces the losses associated with resonances occurring in conventional metamaterials. In fact, it is found that a nearly loss-less system can be produced using a metamaterial wherein at least two of the elements of the plurality of elements are non-identical. Further advantageously, this type of metamaterial is very thin and easy to fabricate. This makes it even more preferable as a sensor for biological materials particularly biological materials in a container. In particular, it makes the device particularly suitable as an antireflective component such as an antireflection coating. These advantageous are achieved because impedance matching and/or shaping of the electromagnetic radiation can be achieved when differing size and/or shape elements are used.

[0080] In an embodiment, the first dimension is the direction for propagation of the electromagnetic radiation. In embodiments, the first dimension is the thickness of each element. Accordingly, the elements are not designed to provide substantial energy storage which requires greater volume. In embodiments, all dimensions of each element are less than the wavelength of the electromagnetic radiation. In embodiments, the first wavelength comprises a bandwidth of wavelengths including the first wavelength.

[0081] Some of the elements 103 shown in FIG. 1 may be considered irregular and/or asymmetric. That is, in an embodiment, at least one of the elements of the plurality of elements has an irregular shape. In an embodiment, all the elements of the plurality of elements have an irregular shape. Advantageously, this allows for finer tuning of the characteristics of metasurface because more degrees of freedom are available in the tuning of its performance.

[0082] In an embodiment, the biological material is bound by a container. In embodiments, the biological material is enclosed by the container. In an embodiment wherein the biological material is blood, the container includes skin. In an embodiment wherein the biological material is food stuff, the container is a plastic bottle. Further examples are given below.

[0083] FIG. 2 shows an embodiment in which the elements are arranged in a non-periodic pattern. FIG. 2 shows a metasurface 200 comprises a substrate component 201 and a plurality of irregularly positioned elements 203. The elements 203 are also irregular in size and shape. It is not essential that all elements in the array of elements are irregularly arranged. In an embodiment, at least a subset of the elements is arranged in an irregular array. In a further embodiment, all the elements are arranged in an irregular array. Advantageously, irregularity in the positioning of the elements allows for finer tuning of the characteristics of metasurface.

[0084] The metasurfaces shown in FIGS. 2 and 3 are substantially planar. That is, in an embodiment, the substrate component is planar. The metasurface is designed for electromagnetic radiation to pass through in a direction perpendicular to the plane of the metasurface. In other embodiments, the metasurface is non-planar or curved such as spherical or cylindrical. In embodiments, the substrate is flexible. Losses associated with transmission through the metasurface are reduced because the electromagnetic radiation passes through a smaller volume of metamaterial.

[0085] In an embodiment, the substrate component is a dielectric, and the elements are conducting. In an embodiment, the elements are formed from any conducting material including homogeneous materials such as metals as well as composites and nanocomposites including Bragg reflectors. The elements may be formed, for example, from silver, gold, copper and/or aluminium, or any other metal that supports reflections at the wavelength of interest.

[0086] The skilled person will understand that any suitable technique for producing the conducting component on a dielectric support structure may be appropriate. In embodiments, etching, photoresist etching, e-printing or lithographic techniques are used. In other embodiments, a self-assembly chemical process is used.

[0087] In an alternative embodiment, the substrate component is conducting, and the elements are a dielectric.

[0088] The thickness of the elements may be few micrometres to a few centimetres. At least one dimension of the elements is sub-wavelength.

[0089] The “sub-wavelength” periodic arrangement of metallic and dielectric elements allows the periodic conducing component to resonate at a resonant frequency (or wavelength). The skilled person will understand that there may be a narrow band of frequencies centred on the resonant frequency at which at least partial resonance will occur. At the resonant frequency, radiation will be at least partially “captured” by the metamaterial and amplification may occur by constructive interference, for example. The metamaterial forms a type of waveguide in which the fields inside the “waveguide” are bound and contained, permitting amplification. Accordingly, there is provided a device arranged to increase the penetration of radiation into a target.

[0090] In embodiments, the device is tuned to the source and target medium. It is found that an incident wave travels along the path of least resistance of the conducting component of the metamaterial. For example, if source provides a plane wave of radiation, symmetric conducting elements may be preferred. The shape and configuration of the conducting may also be chosen to match the polarisation of the incident radiation. For example, conducting elements having horizontal and vertical features may be preferred for horizontally and vertically polarised radiation.

[0091] The conducting elements may comprise features having a length optimised for a wavelength of interest. In embodiments, the length of a primary feature is approximately half the wavelength of the incident radiation. For example, a conducting component having a long element, such as a spiral or a regular meander, will have a relatively long resonant wavelength. For example, the number of turns in the spiral of regular meander may be increased to increase the resonant wavelength. The conducting elements may comprise a sense of rotation such as a left-handed or right-handed spiral optimised for circularly or elliptically polarised radiation, for example. The shape and dimension of the elements may be optimised experimentally or numerically.

[0092] In embodiments, optimization of the shape of the elements is achieved via numerical simulation such that the device enhances the penetration of waves at a particular wavelength. The shape of the elements can also be optimised to modify the amplitude and phase of the incident wave in a way that the output wave has particular properties, such as maximized transmission, or a phase front result in a focusing wave, or a wave with a specific polarisation (e.g. linear or right-hand circular). In one embodiment, there is designed a model of the system in an electromagnetic simulator. The model includes all the components of the system: the source medium, the device component or components, the target medium, and any other features embedded in the target medium that needs to be imaged. Then the electromagnetic properties as a function of frequency of each component are specified, such as the electric permittivity, permeability, conductivity, or loss. Then the S-parameters (reflection and transmission) of the system are evaluated as a function of frequency. The frequency range where the transmission is maximized may indicate the optimal operational range of the system. In other embodiments, the aim is not to maximise transmission but to form a transmitted wave having a particular phase and amplitude at each location behind each metasurface element. For example, the phase may be changed linearly along the metasurface elements to form an output wave which propagates at an angle compared to the incident one. When the geometry of the elements is modified, the transmission peak will be varied accordingly. Thus, one can modify the shapes (or their period) to tune the operational frequency to the frequency or frequencies of interest (e.g., the radiation frequencies of the antenna system that generates the incident waves).

[0093] An operational principle of the metamaterial is that it is highly resonant around specific frequencies. For those frequencies, the wave transmission through the array is enhanced multiple times and thus increased wave penetration through the target occurs. That is, the plurality of elements are collectively arranged to resonate at a first wavelength of the electromagnetic radiation. The resonance condition is determined by the geometry of the array elements and is optimized for transmission when it is placed on top of a particular target. That is, the components of the device are tailored to the target.

[0094] Each element of the plurality of elements may be individually tuned to the source, container. and biological material. To design a metasurface in accordance with the present disclosure, it may be modelled as a transmission line element. For example, the metasurface can act as a matching stub between the two media, and its impedance can be designed such that the desired transmission from one medium to another is optimized. The transmission coefficients are related to the sheet impedances using analytical modelling. Then, the impedance of the metasurface will determine the custom design of the unit element (e.g., tested with simulation software), which, when combined in a pattern will create the metasurface with the necessary response at the frequency of interest to allow the high transmission of incident radiation with minor reflections.

[0095] In embodiments, metasurfaces are designed and used specifically to interact with human tissue on the transmitted side. The metasurface is specifically designed to 1) maximize the transmission through the tissue or biological sample, and/or 2) focus the incident energy on a particular spot inside the receiving sample. This can be achieved by optimizing the shape of the metasurface elements based on the desired phase that should be imparted on the incident wave.

[0096] The transmission line theory implies that the metasurface can act as a matching stub between the air and the skin tissue. By knowing the characteristics of air and skin, the transmission and reflection coefficients can be derived and related to the sheet impedance of the metasurface. These impedance characteristics will determine the custom design of the subwavelength unit element, which microscopically will “manipulate” the incident wave and provide the necessary reactance for the impedance matching. This custom design is obtained performing some numerical calculations using a numerical computing environment. After this modelling, the calculated structures are evaluated and optimized using electromagnetic evaluation software.

[0097] The substrate serves as a support structure for the shaped elements. In embodiments, the shaped elements are coated on the surface of the substrate. In other embodiments, the shaped elements are embedded within the substrate. The skilled person will understand that the array of shaped elements may be supported on the substrate in a variety of ways. In embodiments, the substrate is flexible. In embodiments, the device is a multilayer device comprising a plurality metallic-comprising layers and/or dielectric-comprising layers.

[0098] Metasurface Design Example

[0099] The following is an example of how to design a metasurface array.

[0100] The purpose of the metasurface is to impose a specific phase and amplitude change along an incident wave. The properties of the metasurface are extracted by the ratio of the desired electric and magnetic field before and after the metasurface.

[0101] The first step to design the metasurface is to determine the necessary sheet impedances at the operating frequency.

[00001]$\begin{array}{cc}{Y}_{\mathrm{es}}=\frac{2\left(H_1^z-H_2^z\right)}{E_1^y-E_2^y}=\frac{2-2^{5/4}{e}^{-\mathrm{jkysin}\left(\varphi \right)}}{\eta +2^{1/4}{e}^{-\mathrm{jkysin}\left(\varphi \right)}}& \left(1.1\right)\end{array}$$\begin{array}{cc}{Z}_{\mathrm{ms}}=\frac{2\left(E_1^y-E_2^y\right)}{H_1^z-H_2^z}=\frac{2\eta -2^{5/4}\eta \cos \left(\varphi \right)e^{-\mathrm{jkysin}\left(\varphi \right)}}{1+2^{1/4}{e}^{-\mathrm{jkysin}\left(\varphi \right)}}& \left(1.2\right)\end{array}$

[0102] Here Y.sub.es and Z.sub.ms are the sheet admittances and impedances of the metasurface (which are a function of frequency and position). H and E are the electric and magnetic fields around the metasurface: the superscripts (y or z) indicate the vector field components, while the subscripts indicate the position before (index=1) or after (index=2) the metasurface. In this example the wave propagates along the x-direction, and the metasurface is located in the y-z plane.

[0103] This example relates to the design of a metasurface to refract an incident plane wave originating from air into a 45-degree angle at a 60 GHz frequency. It can alternatively be designed to focus the wave at a particular spot inside the target medium (e.g. biological material) on the transmission side, or exactly match the impedance (maximize transmission). The important factor is the ratio of the desired electric and magnetic fields exactly before and immediately after the metasurface elements.

[0104] The results obtained after calculating the fields along the metasurface length (perpendicular to the direction of propagation) are shown in FIG. 5.

[0105] In FIG. 5, periodicity is shown. This periodicity will lead to a periodic metasurface, which will be subdivided in individual unit cells. A typical number is between 5-20 elements for each period along the y axis, although more (smaller) elements can be used to increase the resolution.

[0106] Once the sheet impedances are known, it is possible to extract the values of the reflection and transmission coefficients using equations 1.3 and 1.4.

[00002]$\begin{array}{cc}T=\frac{\eta \left(4-Y_{\mathrm{es}}{Z}_{\mathrm{ms}}\right)}{\left(2+\eta Y_{\mathrm{es}}\right)\left(2\eta +Z_{\mathrm{ms}}\right)}& \left(1.3\right)\end{array}$$\begin{array}{cc}R=\frac{2}{2+\eta Y_{\mathrm{es}}}-\frac{2}{2\eta +Z_{\mathrm{ms}}}& \left(1.4\right)\end{array}$

[0107] Here η is the wave impedance of the background medium. FIG. 6 shows the reflection and transmission coefficients derived from the sheet impedances of FIG. 5.

[0108] The metasurface in accordance with the present disclosure is made of different unit cells, the study will focus on designing one of them. In an embodiment, to start the design, one of the unit cells is deliberately “tuned out”. In this example each metasurface element consists of two sub-elements on either side of a dielectric substrate (e.g. Teflon).

[0109] FIG. 7 shows various views of a metasurface element in accordance with this example.

[0110] The goal is to obtain S-parameters in accordance with equation 1.5 in order to achieve the correct performance for this block.

S.sub.11=−0.1327+0.1107i S.sub.21=−0.3290−0.9360i  (1.5)

[0111] FIG. 8 shows the obtained simulated S-parameters of the metasurface element as the length of the rods in the top element and the gap in the ring in the bottom element is varied.

[0112] FIG. 9 shows the S-parameters obtained changing the gap of the metal ring of the bottom metasurface element.

[0113] From this, it is possible to make a first approximation to the solution. However, to obtain the most accurate values, it is necessary to do an optimization. This optimization may be performed, for example, in simulation software.

[0114] FIG. 10 shows optimisation progress for the metasurface elements dimensions.

[0115] After optimization, the resulting S-parameters are:

S.sub.11=−0.1327+0.03968i S.sub.21=−0.3245−0.9261i  (1.6)

[0116] The optimized metasurface element is shown in FIG. 11a. The optimised S-parameters are indicated with vertical lines in FIGS. 8 and 9. In embodiments, each metasurface element is generally or substantially cross-shaped.

[0117] Each metasurface element can be designed in a similar fashion.

[0118] In an embodiment, there is provided a metasurface which comprises a combination of metallic crosses and so-called Jerusalem crosses separated by a dielectric substrate. In embodiments, the dielectric substrate is a liquid crystal polymer. FIG. 11b shows an exploded view of an embodiment comprising two metallic patterned layers separated by a dielectric and sandwiched between two dielectric layers (5 layers total). FIG. 11c is a schematic of the bare metasurface structure (two metallic patterns on either side of a dielectric). In embodiments, the metallic parts are embedded into the dielectric. In other embodiments, the metallic parts protrude the dielectric. FIGS. 11d and 11e show top and bottom views of the metallic layers.

[0119] In embodiments, the metasurface elements are optimised to induce convergence of the near-field. These “near-field focusing structures” can lead to focusing details of size well below the diffraction limit. Accordingly, the metasurface may be designed to provide focusing inside a sample—for example, a biological sample in a container. In conventional materials, focusing is usually achieved by properly shaping a homogenous material (e.g. glass), producing lens-type structures. With metasurfaces in accordance with the present disclosure, the shape of the structure can remain flat, but it is no longer homogenous, as it consists of different metallic and dielectric elements.

[0120] Additional Layers

[0121] The device may comprise a plurality of metasurfaces wherein each metasurface is tuned differently. For example, each metasurface may be arranged to resonate at a different wavelength. In embodiments, by at least partially overlapping the resonant wavelengths of a plurality of metasurfaces, a pseudo-broadband device is formed. For a pseudo-broadband device, the resonant frequency of adjacent layers may differ by an integer multiple of a half wavelength, for example.

[0122] In an embodiment, the device further comprising a second metamaterial coupled to the first metamaterial, wherein the second metamaterial comprises: a substrate component having a thickness no greater than a second wavelength of the electromagnetic radiation; and a plurality of elements supported by the substrate component, wherein each element has a first dimension no greater than a second wavelength of the electromagnetic radiation and at least two of the elements of the plurality of elements are non-identical.

[0123] In an embodiment, the second metamaterial is arranged, in cooperation with the first metamaterial, to resonate at a second wavelength of the electromagnetic radiation.

[0124] In an embodiment, the first wavelength is different to the second wavelength. In embodiments, the second wavelength also comprises a bandwidth of wavelengths including the second wavelength.

[0125] In embodiments, there is provided an additional near-field focusing component which is dedicated to providing the near-field focusing described above. In embodiments, the near-field focusing component is placed immediately adjacent the device for coupling EM radiation in accordance with the present disclosure. In an embodiment, the near-field focusing component is a 22 mm by 22 mm by 0.368 mm structure, made up of smaller square unit cells with a period of 2 mm. The unit cell comprises three layers of metallic elements separated by dielectric layers. Unit cells with a large range of transmission (S21) phases are required for the lens. Numerical simulation may be used to find suitable designs by varying parameters to affect the S21 phase and magnitude. The inventors found that single elements did not provide larger phase ranges and so, in embodiments, the near-field focusing component comprises multiple layers of elements. In embodiments using a three-layer design, the inventors found that it was possible to keep the total transmission high: all unit cells chosen had a S21 magnitude greater than 0.8. Unit cells with three layers of elements, produced a 360° S21 phase range. In embodiments, the outer two elements are rectangular bars, and the inner elements are split ring commutators. The target focal length was 18 mm.

[0126] An example near-field focusing component is shown in FIG. 11f (perspective view), 11g (front view) and 11h (back view).

[0127] In embodiments, there is provided an additional layer between the antenna and the device for coupling EM radiation which shapes the electromagnetic waves emitted by the antenna. This additional layer may be considered a beam-shaping layer. The beam-shaping layer shapes the amplitude and/or phase of the radiation pattern. In embodiments, the beam-shaping layer optimises the shape of the radiation pattern for the device for coupling EM radiation in accordance with the present disclosure. In embodiments, this layer is an appropriately shaped dielectric or non-metallic material. In other embodiments, this layer is itself a metamaterial or metasurface such as a periodic combination of metal parts on a dielectric substrate. In embodiments, the beam-shaping layer comprises Teflon, liquid crystal polymer, Rogers 3000 or Rogers 400 series materials, or other dielectric materials that adds phase to the impinging waves. In embodiments, the beam shaping layer also comprises copper, alumina, or other highly conductive material.

[0128] In embodiments, there is provided a disposable biocompatible layer arranged to couple the device to a target. In embodiments, the disposable biocompatible layer may be provided for reasons of hygiene. In other embodiments, the disposable biocompatible layer may comprise a dielectric component, optionally, supporting a planar array of conducting elements. The disposable biocompatible layer may therefore be “tuned” to the rest of the device. The disposable biocompatible layer may be deformable and/or may have a morphology arranged to attach to a part of the human body. The disposable biocompatible layer may be formed from a polymer-based material.

[0129] It may therefore be understood that, in embodiments, the device is a multilayer device comprising a plurality of metallic-comprising and/or dielectric-comprising layers. Advantageously, a multilayer structure may be arranged to cover a suitably large phase range whilst maintaining high transmission. In embodiments, the structure comprises at least three metasurface layers. In embodiments, each layer has a thickness of □/200 to □/3, optionally, □/150 to □/50, further optionally, □/120 to □/80. Advantageously, the inventors have found that this restriction on the thickness of each layer ensures that waves of interest are not overly attenuated due to propagation (expanding beams) before reaching the target (or fully transmitting through the device). This restriction on the thickness of each layer also helps minimise the device size.

[0130] Sensor for Biological Material

[0131] In an embodiment, there is provided a wearable device that clips onto the earlobe, hand, or other body part rich in blood and non-invasively monitors changes to blood glucose levels in real time, either instantaneously or continuously. The radio wave sensors transmit and receive thousands of individual low power radio wave signals tissue that are then combined to obtain accurate blood glucose readings using algorithms. Optionally, the glucose readings are displayed within seconds on the device, or they can be transmitted via Bluetooth to a mobile app, where the patient can manage the data and receive alerts. Further optionally, the data are then securely uploaded to an encrypted cloud-based historical record system, available to the patient or a doctor.

[0132] In an embodiment, there is provided non-invasive glucose measurements via the transmission and reflection of non-ionizing millimetre electromagnetic waves through the human blood. The devices in accordance with the present disclosure are applicable in the range 10 to 300 GHz. However, in an embodiment, the frequency of the waves is around the 40-100 GHz band, which is an available part of the spectrum open to medical and communication applications. Historically, this frequency band has not been adequately explored for glucose measurements.

[0133] There are two main methodologies for non-invasive glucose monitoring using electromagnetic waves. The first utilizes low-frequency radio waves, typically in the MHz or a few (up to 5) GHz region. The second utilizes much higher frequencies at the optical part of the spectrum. The fundamental limitation of both methods has always been the problem of bypassing the skin layer, causing sampling only at the interstitial fluid layer thus limiting their effective accuracy and speed. It has been reported that at the interstitial fluid layer glucose sensitivity is delayed by up to 30 minutes compared to intra-venous sampling. The interstitial fluid lies right beneath the skin and outside the blood arteries and capillaries.

[0134] Measurements in this band offer two distinct advantages that are superior to other non-invasive methods. First, the wavelength of the waves (around 5 mm in air) is large enough to allow penetration through human tissue such as the earlobe, yet simultaneously small enough to provide enough resolution of the blood regions inside it. Second, the small wavelength requires an equally small antenna to generate them. Thus, a mobile miniaturized wireless sensor that can be continuously worn on the human body, e.g. ear, is feasible, incorporating all the necessary electronics and processing power to perform the glucose measurements.

[0135] Compared to optical methods, where the wavelength is much smaller (in the few micron range) the 40-100 GHz band is further advantageous because it generates waves with wavelength that are long enough to penetrate well into a biological sample. Water-based samples and tissue samples typically have very high loss and produce significant impedance mismatch, and thus a wave with shorter wavelength will perceive an electrically longer structure to penetrate through, attenuating significantly along the way. The inventors have identified 1000 GHz as the maximum frequency beyond which the wavelength is too short to penetrate deep enough through a biological sample without attenuating too much.

[0136] Compared to other methods of dielectric spectroscopy that utilize microwaves or radio waves, they typically operate at much lower frequencies (longer wavelengths), up to 10 GHz where the wavelength is 3 cm. These waves are long enough to perceive an electrically small sample without much attenuation. However, with some samples, they may not small enough to resolve details inside a sample, providing only averaged macroscopic information. In addition, if the sample is thin, e.g. 3 mm or less (such is the case for the earlobe), then a wave that is at least 10 times longer will be unable to sense any high-accuracy information from that sample. Thus, in an embodiment, 40 GHz is the lowest frequency below which the wavelength is too long to sense small details and ingredients in a sample with high, reproducible accuracy.

[0137] As a result, the inventors have found that 10-300 GHz, optionally 40-100 GHz, is the optimum band to produce accurate sensing measurements without attenuating the waves. More specifically, the inventors have found that two bandwidths, 59-64 and 68-72 GHz, are particularly suitable for a range of biological samples. In embodiments, the inventors have found that better results are achieved when the bandwidth is 4-6 GHz.

[0138] Many attempts have been made in the past to estimate glucose levels using resonating methods. These methods are extremely accurate, and they are commonly used for many years in characterizing materials. There is no question that they could be used to measure glucose accurately if all other factors remained constant. However their greatest strength is also their greatest weakness: if you try it on a different person, or for any physiological skin changes (e.g. aging, during pregnancies, sweating/wet or dry skin etc.), then the measurement will provide spurious readings. The skin has pores which our body uses to maintain a constant temperature. Something as simple as moving to a hotter room will trigger the production of sweat in the glands which will throw the measurement accuracy off. The structure in accordance with the present disclosure mitigates the effects of the skin and/or allows electromagnetic radiation to substantially penetrate the skin where it would otherwise be reflected.

[0139] In embodiments, the device in accordance with the present disclosure is arranged to minimise the reflection off skin and other certain biological tissue. In embodiments, the biological material of interest is blood, and the device is arranged to minimise the reflection off skin. In embodiments, there is therefore provided an antireflection coating for skin. In these embodiments, the skin may be considered a container for the biological material of interest.

[0140] FIG. 11i shows a simulation result of the power penetration using a metasurface, in accordance with the present disclosure, against human skin. Specifically, FIG. 11i shows the power reflected in, power transmitted, and power dissipated against frequency for the structure in contact with a layer of skin 0.58 mm thick. Solid lines correspond to the setup consisting of the metasurface and the skin and dashed lines correspond to a setup consisting of the skin only without metasurface.

[0141] The total thickness of the metasurface structure is 150 □m. The addition of the metasurface produces a decrease from 39% to 0.16% in the reflected power and an increase from 56% to 94% in the dissipated power at 60 GHz. The transmitted power increases from 4.5% to 6.3%. The main reason that a perfect transmission is not achieved is the presence of loss in the structure.

[0142] Sensor Configurations

[0143] Schematic representations of the sensor are shown in FIGS. 12a to 12m. The sensor can be placed in body areas that are rich in blood and without many other obstructions (such as bones). In the embodiments, the locations are the earlobe, the hand (between the thumb and the index finger), between toes, on the lips, although other locations could be used. The sensor can be held in place temporarily by hand or attached continuously.

[0144] Sensor for Food Stuff

[0145] In other embodiments, the device in accordance with the present disclosure is used to probe the properties of food stuff. That is, in embodiments, the biological material is food stuff. In other embodiments, the biological material is packaged food stuff and the device in accordance with the present disclosure is arranged and/or used to minimise reflection off the packaging. In embodiments, there is therefore provided an antireflection coating for packaging of food stuff. In embodiments, the food stuff is oil such as olive oil or composite oils containing olive oil.

[0146] System Overview

[0147] In an embodiment, there is provided a sensor system comprising a sensor 1303 that measures transmission through a sample under test (SUT), a software application (mobile, tablet, computer, etc.) that wirelessly receives the data in real time or whenever the connection becomes available, an online storage 1301 and database, and a client application/interface that displays the data to a user or third party. This is shown in FIG. 13.

[0148] The sensor comprises a transmitter and a receiver. In embodiments, the transmitter comprises of one, two, or more antennas for generating the radiation, and the metamaterial (typically placed between the antenna and the sample) to enhance the penetration through the sample.

[0149] There is therefore provided a sensor comprising: a transmitter comprising a first antenna and a first device (for coupling electromagnetic radiation, as described above) arranged to couple electromagnetic radiation emitted by the first antenna to a biological material; and a receiver comprising a second antenna and a second device (for coupling electromagnetic radiation, as described above) arrange to couple electromagnetic radiation transmitted by the biological material to the second antenna.

[0150] A block diagram of the components in a sensor in accordance with embodiments is shown in FIG. 14a. Some or all of the following components may be included: a battery 1407 for providing power; a screen 1408 to display the data; and LEDs 1409 to provide visual feedback; a vibration system 1411 to also provide feedback to the user; an electronic calliper component 1410 that can measure the distances between antennas; a printed circuit board 1401 that hosts the electronics; a Bluetooth or other communications component 1402 to transmit information to a receiver; an impedance analyzer 1403 to directly estimate the impedance of the sample under test; an accelerometer 1404 to sense motion; an antenna system 1405 to generate the radio wave signals; and the metamaterial component 1406 that enhances the penetration of the radiation inside the sample under test. FIG. 14b shows the components of a sensor in accordance with other embodiments including an additional beam shaping element 1450. In embodiments disclosed herein, the beam shaping element is a phase corrector by way of example only.

[0151] In an embodiment, the transmitter further comprises a detector arranged to detect electromagnetic radiation reflected by the biological material. Advantageously, this allows for more accurate measurements of the biological material to be made.

[0152] In a further embodiment, the sensor is further arranged to determine the distance between the transmitter and receiver. In another embodiment, the sensor is further arranged to determine the impedance of the biological material. Advantageously, this allows the device to work with different biological materials such as with different people. In an embodiment, the sensor further comprises an accelerometer.

[0153] The antenna, the metamaterial, or both, could be active, tunable component so as to adjust their operation depending on the electromagnetic properties (permittivity, permeability, impedance) of the sample under test. For example, when a different sample is tested that has a slightly different impedance than the sample before it, the impedance analyser will sense that, and the antenna & metamaterial will be accordingly tuned to maximize the penetration through the sample. This can be achieved by integrating tunable electrical components such as variable capacitors (varactors), inductors, or resistors.

[0154] That is, in an embodiment, the sensor further comprises variable resistors and/or capacitors coupled to an antenna and/or metamaterial to provide tunability.

[0155] The sample under test may or may not be placed inside an enclosure or container. The skin can be considered as a container for animal or human tissue. In an embodiment, the biological material is human or animal tissue. In an embodiment, the sensor is wearable. In a further embodiment, the sensor is arranged to be worn on a hand, a foot, an ear, or a lip or wherein the sensor is handheld.

[0156] In an embodiment, the biological material is food stuff. In an embodiment, the food stuff comprises at least one selected from the group comprising oil, milk, wine, coffee, and fruit juice and/or the food stuff is bound by a container, optionally, a bottle or carton. In an embodiment, the container comprises glass and/or plastic.

[0157] There is also provided a system comprising the sensor and further comprising: a wireless receiver arranged to receive data related to the biological material from the sensor; a software application operating on a device remote to the sensor, the software application arranged to process the data; and an interface arranged to display the data and/or information related to the data. Advantageously, it may therefore be possible to remotely monitor a sample. For example, a medical professional may be able to remotely measure the blood sugar level of a patient.

[0158] FIGS. 15a to 15d show some examples of samples under test 1501, 1504, 1505, 1506 with single and dual antenna 1503 and metamaterial 1502 arrangements. FIG. 16 shows a tuning antenna 1602 including an impedance analyser 1603, metasurface 1601 for probing a sample under test 1604.

[0159] FIGS. 17a to 17c and 18 illustrate an example device in operation.

[0160] FIG. 18a shows a sensor comprising two antenna 180 and two metasurfaces 1802 arranged to improve coupling of electromagnetic radiation into and out of a human hand 1803. FIG. 18b shows the sensor with additional phase corrector components 1805.

[0161] FIG. 19 shows exploded views of metasurface with antenna configuration in periodic pattern (Top) and non-periodic pattern (Bottom).

[0162] FIG. 20 shows a layered device in accordance with embodiments comprising three metasurface layers 2001-2003 and an antenna layer 2004.

[0163] Advantageously, the device in accordance with embodiments of the present disclosure is passive. That is, it does not require a power supply. The device may therefore increase the overall energy efficiency.

[0164] There is provided an antireflective medium for a glucose sensor, the antireflective medium comprising a metasurface. There is also provided an antireflective coating for a food stuff container, the antireflective coating comprising a metasurface.

[0165] Although aspects and embodiments have been described above, variations can be made without departing from the inventive concepts disclosed herein.

EXAMPLE EXPERIMENTAL RESULTS

[0166] The two examples presented are glucose sensing in calibrated water-based samples, and oil sensing in oil mixtures. The measurements were performed in the 50-75 GHz band. The quantities presented are retrieved from the raw transmission and reflection recorded signals after applying noise filtering and other signal processing algorithmic operations.

Example 1: Glucose Sensing

[0167] FIG. 21 shows the correlation between the glucose concentration and the processed signal, repeated in two independently prepared sample solutions around 60 GHz. The results indicate the repeatability of the method and the algorithm utilized.

[0168] FIG. 22 compares the measurements obtained for three different types of sample: samples consisting of water and varying amounts of glucose, sample consisting of water, salt (NaCl) and varying amounts of glucose and samples consisting of water, varying amounts of salt and glucose. The results demonstrate that the three different solutions and their corresponding concentrations can be completely distinguished from each other. The purpose of using salt is that is a more realistic representation of human blood.

[0169] FIG. 23 presents the processed signal as a function of glucose concentration for very low concentrations (the normal range for adults is between 4 and 8 mMol/L) at a frequency of 68 GHz. It demonstrates that very low glucose concentrations can be quantified.

Example 2: Oil Sensing

[0170] In this example the unknown concentration of palm kernel oil in a mixture of palm kernel oil and rapeseed oil was determined for two different experimental runs. The processed data are fitted with a linear equation, which can be used to exactly determine the concentration of each oil species in the mixture.

[0171] FIG. 24 shows output signal as a function of the concentration of palm kernel oil in a mixture of palm kernel and rapeseed oil.

[0172] FIG. 25 shows the processed signals from the radio wave reflection measurements are fitted with an analytic Cole-Cole model, estimating the relaxation frequency of the model. Each oil species exhibits a characteristic relaxation frequency, which can be used to identify an unknown oil species in a sample. In this case a single sensor is used against the sample.

[0173] The sensor in accordance with embodiments is therefore highly effective at determining the concentration of oils in a mixture of oils.