WO2009136311A2

WO2009136311A2 - Contact pressure control for probe for material analysis

Info

Publication number: WO2009136311A2
Application number: PCT/IB2009/051708
Authority: WO
Inventors: Kiran K. Thumma; Bastiaan W. M. Moeskops; Yan Liu; Golo Von Basum
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2008-05-08
Filing date: 2009-04-27
Publication date: 2009-11-12
Also published as: WO2009136311A3

Abstract

A device for analyzing a material using illumination and optical sensing, has a probe (120) arranged to provide the illumination and for receiving light for the optical sensing, and having an optical grating (100) at a contact region of the probe for use in detecting contact pressure of the contact region on the material. A sensor senses light affected by the grating, and a controller (85) controls a contact pressure of the probe on the material, according to the determined contact pressure. By using a grating, there is little or no additional complexity in the construction of the probe, and little or no addition in the contact area of the probe. By determining contact pressure and adapting the probe position, interference effects in the analysis of the material caused by or made worse by contact pressure being too high or too low or fluctuating too much, can be reduced or avoided.

Description

Contact pressure control for probe for material analysis

FIELD OF THE INVENTION

This invention relates to devices for analysis of a material, and to corresponding systems and methods.

BACKGROUND OF THE INVENTION

Obtaining values for properties of materials of any kind, such as for example biological or physical quantities in a living body in a non-invasive way has been thoroughly studied over the last few years. Obtaining accurately reproducible results by using sophisticated sensing and actuating devices for medical purposes may become difficult when sensors have to be repeatedly removed and replaced.

Currently, many efforts have been put in developing instruments for noninvasive measurement of physiological parameters in a human or animal body, such as for example glucose measurements, based on optical methods. Although these methods have proven to have sufficient sensitivity for in-vitro and/or ex-vivo glucose quantification, devices based on such currently existing techniques have not been successfully brought to the market. The main reason for that is that the accuracy of recently developed devices is not sufficient to get an FDA (food and drug administration) approval.

Also instruments have been developed for minimally invasive measurement of physiological parameters in a human or animal body, such as for example glucose measurements, e.g. based on optical methods. These methods make use of a sensor implanted beneath the skin which is in contact with subcutaneous fluids. The sensor may include gels, particles, liquids which are biodegradable. Preferably, the biosensor that has to be implanted is small in size, and does not require a complicated or painful insertion below the skin.

Non-invasive measurement is the most desirable method for consumers. But the uncertainty and inaccuracy hampered the acceptance of non- invasive tests. There is a strong need in the non-invasive glucose-monitoring market to solve the inaccuracy or unreliability problems.

Many techniques have been investigated to non-invasively detect skin analyte(s) concentration by means of optical, electrical and/or optoelectronic methods, such as for example non-invasive glucose monitoring. Typically, in vivo measurements deal with a larger number of chemical, physical, and physiological interfering elements compared to in vitro measurements. These interfering elements induce ^reproducibility and inaccuracy of non- invasive measurements. Information on the presence of interfering elements, their effects, and variability range are often not known. Typically, data analysis of a system where a number of interfering elements is present is based on chemometric tools, e.g. multivariate analysis. However, for complex and variable systems such as e.g. human tissue, chemometric analysis becomes more complicated and may be prone to large errors.

The accuracy and reproducibility of these measurements are generally poor due to the many interfering elements and ^reproducibility comparing with in vitro case.

An example of an irreproducible factor is the placement of the measurement device on the skin. The morphology of the skin is different at different locations, which leads to variations in the optical properties from site to site. Another irreproducible factor is the relative position of the sensing device to an implanted minimally invasive biosensor. Non- invasive measurement is the most desirable method for consumers. But the uncertainty and inaccuracy hampers the acceptance of non- invasive tests. There is a strong need in the non-invasive glucose-monitoring market to solve the inaccuracy or unreliability problems.

It has been found that various interfering elements, such as e.g. humidity, temperature, perfusion rate etc., affect the results of such non- invasive measurements. Additionally, the skin- interface plays a big role during performance of the non- invasive measurements. Therefore, in known techniques the shape of probe may be adapted so as to ensure contact of the probed with the skin. For example, US 5,906,580 relates to a probe having a shape suitable for fitting different application sites. This document mentions that the size and shape of a probe of an ultrasound system may depend on its intended application. For example, when the probe is intended for use in non- invasive scanning of a surface of a body, the probe may have a flexible face that conforms to specific parts of the body as it is moved across such specific parts.

Many techniques have been investigated to non-invasively detect skin analyte(s) concentration by means of optical, electrical and/or optoelectronic methods, such as for example non-invasive glucose monitoring. Typically, in vivo measurements deal with a larger number of chemical, physical, and physiological interfering elements compared to in vitro measurements. These interfering elements induce ^reproducibility and inaccuracy of non- invasive measurements. Moreover, things like skin- interface, shape and angle of the probe applied to the measuring site, may influence the accuracy of the measurement.

Conventional probe heads have a flat surface, which requires a perpendicular orientation of the probe onto the skin to achieve a close contact with the skin. However, it may be difficult to precisely control the angle of the probe during non- invasive measurement, especially when hand- handling the probe. The angle CC may be varied from measurement to measurement, from person to person and from measurement site to measurement site. US 5,588,440 describes a probe for contacting a desired area of skin for assessing and locating soft tissue lesions manifested by pain in the tissue of human beings and animals. The probe has a rounded tip which has an opening through which there protrudes three sensors, one measuring moisture content, one for measuring sound produced during massage of the skin at that area and one for measuring applied force. However, problems with respect to the contact between the measurement part of the probe and the skin can arise with this probe when, for particular reasons, measurements have to be performed by placing the probe under an angle with respect to the skin.

SUMMARY OF THE INVENTION

An object of the present invention relates to providing devices for analysis of a material, and corresponding systems and methods. A first aspect of the invention provides:

A device for analyzing a material using illumination and optical sensing, the device having a probe arranged to provide the illumination and for receiving light for the optical sensing, and having an optical grating at a contact region of the probe for use in detecting contact pressure of the contact region on the material, and the device having a sensor for sensing light affected by the grating, and a controller arranged to make the analysis of the material, according to the determined contact pressure. The following analyses are included within the scope of the invention:

1. According to the determined contact pressure.

2. Multiple measurements are made and only the measurements which fall within pressure limits are considered.

3. Multiple measurements are made and use is made of a correcting algorithm to modify the measurement spectrum using tools such as PLS (Partial least squares), MVA(multivariate analysis) etc. By using a grating, there is little or no additional complexity in the construction of the probe, and little or no addition in the contact area of the probe. By making the analysis dependent on the determined contact pressure, interference effects in the analysis of the material caused by or made worse by contact pressure being too high or too low or fluctuating too much, can be reduced or avoided, and measurements can be made more accurate or reliable.

Another aspect of the invention provides a corresponding method of controlling a contact pressure of a probe for analyzing a material using illumination and optical sensing, the device having a probe arranged to provide the illumination and for receiving light for the optical sensing, and having an optical grating at a contact region of the probe, the method having the steps of sensing light affected by the grating to detect contact pressure of the contact region on the material, and making the analysis of the material according to the determined contact pressure.

Another aspect provides a computer program for carrying out a corresponding method of analyzing according to a determined contact pressure of a probe.

Embodiments of the invention can have any other features added, some such additional features are set out in dependent claims and described in more detail below.

Any of the additional features can be combined together and combined with any of the aspects. Other advantages will be apparent to those skilled in the art, especially over other prior art. Numerous variations and modifications can be made without departing from the claims of the present invention. Therefore, it should be clearly understood that the form of the present invention is illustrative only and is not intended to limit the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. IA shows the diffuse reflectance spectra at different contact states plotted against wavelength, z represents the Z position of the probe, and a negative value of z means that the probe does not contact the skin;

Fig. IB shows the relative variability of the diffuse reflectance spectra at different contact states plotted against wavelength. The negative signal means that the diffuse reflectance decreases with increasing Z position of the probe,

Fig. 2 shows a reflection spectra of the FBG with different forces, (a) -7.5 N. (b) 0 N. (c) 7.5 N, Fig. 3 shows a flow chart for the automatic control system according to an embodiment,

Fig. 4 shows a view of an embodiment,

Fig. 5 shows a plan view of the fiber arrangement in the probe according to the embodiment of Fig. 4,

Fig. 6 shows a view of another embodiment, and

Figs. 7 and 8 show examples of spectra of the source for illuminating the grating, and spectra of the reflection from the grating, for a broadband source and a narrowband source respectively.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. Any reference signs in the claims shall not be construed as limiting the scope. The drawings described are only schematic and are non- limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes.

Where the term "comprising" is used in the present description and claims, it does not exclude other elements or steps. Where an indefinite or definite article is used when referring to a singular noun e.g. "a" or "an", "the", this includes a plural of that noun unless something else is specifically stated.

Furthermore, the terms first, second and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

Furthermore, some of the embodiments are described herein as a method or combination of elements of a method that can be implemented by a processor of a computer system or by other means of carrying out the function. Thus, a processor with the necessary instructions for carrying out such a method or element of a method forms a means for carrying out the method or element of a method. Furthermore, an element described herein of an apparatus embodiment is an example of a means for carrying out the function performed by the element for the purpose of carrying out the invention. References to a signal can encompass any kind of signal in any medium, and so can encompass an electrical or optical or wireless signal or other signal for example. References to analyzing can encompass processing a signal in any way to derive or enhance information about the material. References to a controller can encompass any means for controlling and so can encompass for example a personal computer, a microprocessor, analog circuitry, application specific integrated circuits, software for the same, and so on. References to material are intended to encompass any type of material, and can include tissue of any type, either in vitro or ex- vivo or in- vivo.

In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

By way of introduction to the embodiments, the problem of interference by contact pressure variation in optical sensing such as non invasive blood glucose monitoring will be discussed briefly. Non-invasive glucose monitoring is an important step towards a better control of glucose levels. Most of the non-invasive techniques rely on optical means of determining the analytes present in the blood. Near infrared spectroscopy is proved to be a promising method for determination of the glucose levels non-invasively. Minimally invasive glucose monitoring can also be used to control glucose levels. Minimally invasive techniques can rely on optical means for receiving signals from a subcutaneous microsensor in contact with subcutaneous body tissue and fluids. The analytes present in the blood can be determined by analyzing the light returned from the microsensor. Near infrared spectroscopy has also proved to be a promising method for determination of the glucose levels minimally invasively. The term "minimally invasive" as used for example in the phrase minimally invasive measurement of physiological parameters in a human or animal body, includes those methods where there is a minor level of invasion. An example is where the measurement itself is non- invasive but the determination of the analyte is done with the help of an implanted microsensor, e.g. a subcutaneous microsensor. The sensor is implanted beneath the skin which is in contact with subcutaneous fluids. The sensor may include gels, particles, liquids which are biodegradable. Preferably, the biosensor that has to be implanted is small in size, and does not require a complicated or painful insertion below the skin. The micro sensor comprises an assay such as for example for the determination of glucose, e.g. based on optical methods. The measurement of glucose through spectroscopy can be made by a change in the absorption of light according to the absorption and scattering properties of minimally invasive microsensors, or to the change in light emitted or reflected from such microsensors located below the skin. Such methods using microsensors may include, for example, observing fluorescence (e.g. fluorescence resonance energy transfer) of a competitive binding assay encapsulated in microcapsules, for example based on competitive binding between the protein Concanavalin A and various saccharide molecules, specifically a glycodendrimer and glucose, the microcapsules can be polyelectrolyte microcapsules, detecting glucose using boronic acid-substituted violegens in fluorescent hydrogels in which a fluorescent anionic dye and a viologen are appended to boronic acid, which serve as glucose receptors, and are immobilized into a hydrogel, the fluorescence of the dye being modulated by the quenching efficiency of the viologen based receptor which is dependent upon the glucose concentration, other methods, e.g. to monitor oxygen or pH or other "smart tattoo" methods. Electromagnetic radiation is delivered via fibers to the skin surface. These fibers are in contact with the skin to get maximum coupling efficiency. This radiation is absorbed by various analytes present in the blood or is incident upon a subcutaneous microsensor. Due to the variation of feree exerted on the skin, the optical properties of the analytes changes. It is known that variations in the force exerted by a probe on the skin cause errors in spectroscopic sensing techniques that probe the skin underneath. To increase accuracy the exerted force has to be reproducible and constant.

The measurement of glucose through near- infrared spectroscopy is based on a change in the concentration of glucose being indicated by a change in the absorption of light according to the absorption and scattering properties of glucose and/or the effect of glucose changes upon the anatomy and physiology of the sampled site. However, in addition to the effect of glucose on the near- infrared light probing signal that is delivered to the skin, the probing signal is also reflected, diffusely reflected, transmitted, scattered, and absorbed in a complex manner related to the structure and composition of the tissue. When near- infrared light is delivered to the skin, a proportion of reflected light, or specular reflectance, is typically between 4-7% of the delivered light over the entire spectrum. Absorption by the various skin constituents accounts for the spectral extinction of the light within each layer. Scattering is the main process by which the beam may be returned to contribute to the diffuse reflectance of the skin. Scattering also has a strong influence on the light that is diffusely transmitted through a portion of the skin. The scattering of light in tissues is in part due to discontinuities in the refractive indices on the microscopic level, such as the aqueous-lipid membrane interfaces between each tissue compartment or the collagen fibrils within the extracellular matrix. The spectral characteristics of diffuse remittance from tissue result from a complex interplay of the intrinsic absorption and scattering properties of the tissue, the distribution of the heterogeneous scattering components, and the geometry of the point(s) of irradiation relative to the point(s) of light detection. At least some of these factors are affected by changes in contact pressure of the probe as will be described below.

The near- infrared absorption of light in tissue is primarily due to overtone and combination absorbances of C-H, N-H, and O-H functional groups. As skin is primarily composed of water, protein, and fat; these functional groups dominate the near-IR absorption in tissue. As the main constituent, water dominates the near- infrared absorbance above 1100 nm and is observed through pronounced absorbance bands at 1450, 1900, and 2600 nm. Protein in its various forms, in particular, collagen is a strong absorber of light that irradiates the dermis. Near-infrared light that penetrates to subcutaneous tissue is absorbed primarily by fat. In the absence of scattering, the absorbance of near- infrared light due to a particular analyte, A, can be approximated by Beer's Law. An approximation of the overall absorbance at a particular wavelength is the sum of the individual absorbance of each particular analyte given by Beer's Law. The concentration of a particular analyte, such as glucose, can be determined through a multivariate analysis of the absorbance over a multiplicity of wavelengths because it is unique for each analyte. However, in tissue compartments expected to contain glucose, the concentration of glucose is at least three orders of magnitude less than that of water. Given the known extinction coefficients of water and glucose, the signal targeted for detection by reported approaches to near-infrared measurement of glucose, i.e. the absorbance due to glucose in the tissue, is expected to be, at most, three orders of magnitude less than other interfering tissue constituents. Therefore, the near-infrared measurement of glucose requires a high level of sensitivity over a broad wavelength range. Multivariate analysis is often utilized to enhance sensitivity.

In addition, the diverse scattering characteristics of the skin, e.g. multiple layers and heterogeneity, cause the light returning from an irradiated sample to vary in a highly nonlinear manner with respect to tissue analytes, in particular, glucose. Simple linear models, such as Beer's Law have been reported to be invalid for the dermis.

Dynamic properties of the skin also add to the difficulties. Variations in the physiological state and fluid distribution of tissue profoundly affect the optical properties of tissue layers and compartments over a relatively short period of time. For all these reasons therefore, the optical properties of the tissue sample are modified in a highly nonlinear and profound manner that introduces significant interference into noninvasive tissue measurements.

In the home environment, self monitoring of blood glucose is a vital element in diabetes management. Current monitoring techniques rely on inconvenient and painful nature of drawing blood through the skin prior to analysis. Therefore, new methods for self monitoring of blood glucose levels are required to improve the prospects for more rigorous control of blood glucose in diabetic patients. Numerous approaches have been explored for measuring blood glucose levels by various companies, on non invasive or minimally invasive technologies that rely on spectroscopy. None of the companies have shown reliable glucose measurements due to various constraints. To date, no non invasive technology for self monitoring of blood glucose has been given an FDA approval.

Near infrared spectroscopy of skin is a promising approach to the non- invasive or minimally invasive prediction of a person's blood glucose level. Near infrared spectroscopy involves the illumination of a spot on the body with electromagnetic radiation (light in wavelength region 750-2500nm). The light is partially absorbed and scattered, according to its interaction with the tissue analytes prior to being reflected back to a detector. The glucose information is extracted from the spectral measurement from the detected signal. The illumination to the tissue is done via a fiber probe which is in contact with the skin for maximizing the light coupling to the skin.

During the probe contact with the skin, the probe exerts force on the point of contact. Due to the variation of the amount of feree exerted the optical properties at the contact location changes. These changes in optical properties have a large effect on the absorption spectrum and results in an incorrect determination of glucose levels as shown in Figure 1. For an accurate determination of glucose levels, the force exerted on the skin should be kept constant. At least some embodiments described are concerned with the problem of exerting constant contact force on the skin.

This can lead to obtaining more reproducible non invasive or minimally invasive measurements of glucose levels by keeping the contact force constant. As will be described, embodiments have a device that controls the force exerted on the skin, within a closed loop system. A force sensor made of fiber Bragg grating (FBG) can be embedded in an optomechanical skin interface and be used to measure force applied on the skin. This sensor is advantageous as no additional components are required and it can measure localized forces at the point of measurement. The FBG force sensor can be connected to an actuator which is used as a feed back loop to apply the desired force during the measurement. This facilitates obtaining reproducible measurements and increased reliability of non invasive or minimally invasive measurements of blood or skin analytes in vivo. Additional features: The making of the analysis can be made according to the determined pressure by controlling a location of the probe to control the contact pressure according to the determined pressure. Alternatively or as well, optical sensing measurements of the material made while the contact pressure is outside given limits can be discarded, or be corrected according to the determined contact pressure. This can for example use an algorithm to modify the spectrum obtained by the sensing, using tools such as PLS(Partial least squares), MVA(multivariate analysis) etc. The probe can comprise an optical fiber for the illumination, the optical grating being incorporated in the optical fiber. The device can have a first optical source coupled to the optical fiber for the illumination and a second optical source coupled to the optical fiber for providing light affected by the optical grating. The first optical source can comprise a broadband laser source for near infra red spectroscopy.

The probe can comprise one or more fibers for the illumination and one or more fibers for the receiving. The controller can be arranged to control a mechanical actuator to maintain the contact pressure between predetermined limits. The device can have one or more further optical gratings at different parts of the contact region, for use in detecting contact pressure, the controller being arranged to control the orientation according to the sensed contact pressure at the different parts.

The device can have a mechanism for scanning the probe to generate an image of the material. The method can involve for non invasive or minimally invasive monitoring of blood in a human or animal body, having the step of optical sensing to determine the concentration of given constituents of the blood. The method can have the step of using near infra red spectroscopy for analyzing the material. Fiber Bragg Gratings It is known that Bragg Gratings impressed in optical fibers may be used to detect a perturbation such as force or temperature at the location of the gratings described in US. Pat Nos. 4806012 and 4761073. In such a sensor the core of the optical fiber is written with periodic grating patterns effective for reflecting a narrow wavelength band of light launched into the core depending on the force at the grating location. Spectral shifts in the transmitted and reflected light indicate the intensity of force or temperature variations at positions of the grating. The spectral shift resulting due to application of different forces is shown in Figure 2, see US5394488, US5401956, and S.K.Yao et al Vol. 21 Applied Optics 1982. 3059-3060.

Further information is available in US 5401956 which shows a Fiber Bragg Grating (FBG) used as a strain measuring sensor. The output from the fiber grating is converted to an electrical signal by a detector and monitored by a signal processor which detects drops in transmitted power level and provides output signals indicative of the perturbation for each sensor. The above mentioned literature gives more details of how the FBG can be used as a force sensor. FBG sensor includes a laser diode that provides a broadband source light to a coupler which provides a source light to a fiber Bragg grating which reflects a first reflection wavelength of light. The reflected wavelength from the grating changes the wavelength according to the force applied at the tip of the fiber.

By controlling the force applied on the skin, the unwanted changes in optical properties can be minimized, and better measurements made.

There are various ways to determine the force exerted on the skin. One of the methods is to incorporate a force sensor in the probe which gives an online reading of the exerted force. But this involves an additional force sensing component or sub assembly which needs to be incorporated into the probe thereby increasing the complexity. It is preferable to determine the force without any additional components to the probe for determining the force. The embodiments described can enable the fibers which are used in the near infrared spectroscopy to be used also as a force sensor which monitors the force exerted on the skin. Even if separate fibers are used for the pressure sensing, these are relatively easy to incorporate without adding complexity. By providing a feedback loop to the force actuator, a constant force can be applied to the probe. This, in turn, will improve accuracy and reproducibility of non- invasive or minimally invasive measurements. Mounting system The probe can be incorporated into a mounting device. The mounting device can comprise a mechanical actuator to exert a controlled amount of force on the skin.

The pressure actuator and sensor can use piezo-electric elements to sense and exert pressure. The force sensors can be, amongst others, a load-cell, strain-gauge, or piezo- based device. The control unit contains electronics and logic in the form of an algorithm or hardware-based servo loop. Examples of actuators are DC motors, steppermotors, voice coils or other actuators. The same or a different mechanism can be used for scanning the probe parallel with a surface of the material to build up a line or an image. Figures 3,4, 5 embodiment of a device

Figure 3 shows an example of closed loop control system (algorithm) that regulates the exerted force using feedback from the FBG, to keep a constant force. A force is applied at step 10. The contact pressure is sensed and the controller determines if it is within an allowable range at step 20. If not, the force is adjusted, either up or down to try to get within the desired range. Once in range, an optical sensing measurement is taken at step 30. Figure 4 shows some of the principal components of a device according to an embodiment. Many other arrangements can be conceived. There is an optomechanical skin probe 120 having illumination fibers 110 to deliver the electromagnetic radiation to a contact region against the skin. An FBG 100 is shown on one of the illumination fibers, near the contact region. Some fibers 70 are used for collecting light for making the measurements. The FBG reflects one predetermined wavelength according to the Bragg condition. In the probe, an additional fiber can be incorporated which determines the force or the same fiber can be used which is also used for illumination for the near infrared spectroscopy. A broadband laser source 60 for the NIR spectroscopy is shown. Also in Figure 4 is shown a sensor in the form of photodiode PD 90, and a controller (85). The controller can be used for processing the optical sensing measurements, and for controlling the probe by means of an actuator 80. There is a separate light source 40 for use with the FBG, using an He Ne laser in this case. A coupler 50 is shown for tapping off some light to the PD, and a mirrored surface is used for combining the light from the different sources into the same fiber. The controller can have interfaces for input and output to and from an operator, and network interfaces as desired. In principle the device can be implemented as a portable hand held analyzer powered by batteries for example.

In Figure 5 there is shown a plan view of an optomechanical probe in which the middle fiber is the illumination fiber with the FBG and the surrounding fibers are the collection fibers. Figure 6 shows a side view of an alternative embodiment having a single sensing fiber. The light path for measurements of the material is shown. In principle the sensing photodiode could be built into the probe without the need for the sensing fiber.

An advantage of the FBG is that it reflects only one particular wavelength while transmitting all the other wavelengths. In NIR spectroscopy which generally ranges from 750 nm - 2500 nm, the FGB can be designed for a reflecting wavelength say for e.g. 630nm, the fiber with FBG reflects only 630 nm while allowing all the NIR wavelengths. Two types of illumination of the FBG will be described, though others are conceivable. A first type involves a broadband source, and a spectrum is shown in Figure 7. The x axis represents wavelength and the y axis represents intensity or power as usual. The reflection spectrum of the FBG is produced by the multiplication of the source spectrum and the FBG reflection spectrum. As the force on the fiber changes, it causes a shift in the FBG reflection spectrum. This results in a signal that is nearly constant in intensity over the measured force range, but with a shift in the wavelength which can be detected by a spectrometer, or a photodiode with suitable optical components to convert the wavelength shift to a change in intensity, using filters for example.

A second example uses a narrowband source, and a spectrum is shown in Figure 8. Again the x-axis represents wavelength and the y-axis represents intensity or power. The narrowband source has a peak wavelength which coincides with an edge of the FBG reflection spectrum. The intensity of the multiplication/convolution of the source and FBG spectrum quickly decreases as the FBG reflection shifts. The narrowband nature of the source light allows little change in wavelength, so that force changes show up mainly as intensity changes, which can be detected directly by the photodiode. In some embodiments one or more of the fibers which is used for near infrared spectroscopy, is imprinted with an FBG. The light propagates along the fiber to a FBG which reflects a predetermined narrow wavelength band of light beam. The fiber and the FBG is embedded in a probe which is part of an optomechanical structure which is being monitored for the contact force it applies to the material being analyzed. The light exits from the grating and propagates along the fiber to an optical detector. The optical detector provides an electrical detection signal indicative of the force applied. The signal processing circuits process the electrical signal and indicates the force applied on the structure. When the system is under force, the signal processing circuit determines the force by determining a reduction in wavelength by comparing the unstrained case and knowing the relationship between a change in force and a change in wavelength.

Though only one FBG is shown here, more such sensors can be used at different locations of the optomechanical device for point force measurements at different points on the contact region. This can be used to enable orientation of the probe to be controlled, to ensure even pressure over the contact region. As described, the control system, uses a force monitor, in the form of a sensing device (FBG and PD), as an input for force control, or as an input to the processing of the optical sensing measurements. This force control can keep the contact force constant using a suitable feedback control algorithm. This can use established control techniques such as proportional control, proportional-integral-differential control and so on. A suitable algorithm for processing the optical sensing can be as follows.

Detect reflection intensity from the FBG. Convert to a value for contact pressure. Compare to predetermined thresholds. If within thresholds, mark the optical sensing value (or spectrum) obtained at the same time as an acceptable measurement. Repeat all these steps to obtain many acceptable values and determine an average of the acceptable values. An alternative algorithm would additionally have a step of correcting the optical sensing value (or spectrum) according to the determined contact pressure value. As mentioned above, this could involve using tools such as PLS (Partial least squares), MVA(multivariate analysis) etc. Many applications of the embodiments can be envisaged. For the non invasive or minimally invasive monitoring of glucose accurately, an opto-mechanical probe skin interface, as proposed here, is needed by most techniques. The embodiments described can provide a solution where the problems related to the force can be removed thereby increasing the reproducibility and sensitivity of the measurements. This can also contribute in determining other skin properties (e.g. skin cancer, skin aging, etc.) by means of light.

Other variations can be envisaged within the scope of the claims.

Claims

CLAIMS:

1. A device for analyzing a material using illumination and optical sensing, the device having a probe (120) arranged to provide the illumination and for receiving light for the optical sensing, and having an optical grating (100) at a contact region of the probe for use in detecting contact pressure of the contact region on the material, and the device having a sensor (90, 110) for sensing light affected by the grating, and a controller (85) arranged to make the analysis of the material, according to the determined contact pressure.

2. The device of claim 1, the making of the analysis according to the determined pressure involving controlling a contact pressure according to the determined pressure.

3. The device of claim 1 or 2, the making of the analysis according to the determined pressure involving making more than one optical sensing measurement of the material and selecting from these measurements according to the respective determined contact pressures for each of the measurements.

4. The device of any of claims 1, 2 or 3, the making of the analysis according to the determined pressure involving making more than one optical sensing measurement of the material and selecting from these measurements according to the respective determined contact pressures for each of the measurements.

5. The device of any preceding claim, the probe comprising an optical fiber (110) for the illumination, the optical grating being incorporated in the optical fiber.

6. The device of claim 5 having a first optical source (40) coupled to the optical fiber for the illumination and a second optical source (60) coupled to the optical fiber for providing light to be affected by the optical grating.

7. The device of claim 6, the first optical source comprising a broadband laser source for near infra red spectroscopy.

8. The device of any preceding claim, the controller being arranged to control a mechanical actuator (80) to maintain the contact pressure between predetermined limits.

9. The device of any preceding claim and having one or more further optical gratings at different parts of the contact region, for use in detecting contact pressure, the controller being arranged to control the orientation according to the sensed contact pressure at the different parts.

10. The device of any preceding claim and having a mechanism for scanning the probe to generate an image of the material.

11. A method of making an analysis of a material using illumination and optical sensing, the device having a probe (120) arranged to provide the illumination and for receiving light for the optical sensing, and having an optical grating (100) at a contact region of the probe, the method having the steps of sensing light affected by the grating to detect contact pressure of the contact region on the material, and making the analysis of the material, according to the determined contact pressure.

12. The method of claim 11, having the step of using a first optical source coupled to an optical fiber for the illumination and using a second optical source coupled to the optical fiber for providing light to the optical grating for detecting the contact pressure.

13. The method of claim 11 or 12 for non invasive or minimally invasive monitoring of blood in a human or animal body, having the step of optical sensing to determine the concentration of given constituents of the blood.

14. The method of any of claims 11 to 13, having the step of using near infra red spectroscopy for analyzing the material.

15. A computer program product for performing, when executed on a computing means, a method of making an analysis according to the method of any of claims 11 to 14.