Device and method for measuring a property of living tissue
A device for measuring the glucose level in living tissue has electrodes ( 5, 6 ) for being brought into contact with the specimen and a voltage-controlled oscillator ( 31 ) as a signal source for generating an AC voltage in a given frequency range. The AC voltage is applied to the electrodes ( 5, 6 ). A voltage over the electrodes is fed to a processing circuitry ( 37, 38 ), which converts it to the glucose level using calibration data. The voltage-controlled oscillator ( 31 ) has a symmetric design with adjustable gain for generating signals in a large frequency range with low distortions at a low supply voltage. The processing circuit comprises a simple rectifier network with software-based correction. The electrodes ( 5, 6 ) are of asymmetric design and optimized for biological compatibility.
1. A device for measuring a property of living tissue, in particular a glucose level of the tissue, said device comprising
an electrode arrangement for application to the tissue,
a signal source for generating an AC voltage at a series of frequencies in a given frequency range to be applied to said electrode arrangement, and
processing circuitry comprising
measuring means for measuring a series of measurement values at the series of frequencies, each measurement value depending on dielectric properties of the tissue at one frequency,
fitting means for fitting a function M(f, b 0 , . . . , b K ) with parameters b 0 to b K to the measurement values at their given frequencies, or to values derived from the measurement values at their given frequencies, and determining the parameters b 0 to b K thereby, and
means for using at least part of the parameters b 0 to b K for determining said property,
wherein said processing circuitry comprises a measuring circuit having a first input for an input value dependent on said property and on said AC voltage and a second input for an input value dependent on said AC voltage but substantially independent of said property, wherein said measurement values are derived from a ratio between said first and said second input value.
2. A device for measuring a property of living tissue, in particular a glucose level of the tissue, said device comprising
an electrode arrangement for application to the tissue,
a signal source for generating an AC voltage at a series of frequencies in a given frequency range to be applied to said electrode arrangement, and
processing circuitry comprising
measuring means for measuring a series of measurement values at the series of frequencies, each measurement value depending on dielectric properties of the tissue at one frequency,
fitting means for fitting a function M(f, b 0 , . . . , b K ) with parameters b 0 to b K to the measurement values at their given frequencies, or to values derived from the measurement values at their given frequencies, and determining the parameters b 0 to b K thereby, and
means for using at least part of the parameters b 0 to b K for determining said property,
wherein said function M(f, b 0 , . . . , b K ) is of the form
M ( f, b 0 , . . . , b K )= b 0 +b 1 ·f+ . . . +b 3 ·f R ,
in particular with R=3.
3. A device for measuring a property of living tissue, in particular a glucose level of the tissue, said device comprising
an electrode arrangement for application to the tissue,
a signal source for generating an AC voltage at a series of frequencies in a given frequency range to be applied to said electrode arrangement, and
processing circuitry comprising
measuring means for measuring a series of measurement values at the series of frequencies, each measurement value depending on dielectric properties of the tissue at one frequency,
fitting means for fitting a function M(f, b 0 , . . . , b K ) with parameters b 0 to b K to the measurement values at their given frequencies, or to values derived from the measurement values at their given frequencies, and determining the parameters b 0 to b K thereby, and
means for using at least part of the parameters b 0 to b K for determining said property,
wherein said function M(f, b 0 , . . . , b K ) is of the form
M
(
f
,
b
0
,
…
b
K
)
=
∑
k
=
0
K
b
k
·
χ
k
(
f
)
and wherein said fitting means is adapted to store a precalculated matrix A and/or data derived from said precalculated matrix A for fitting a plurality of series of measurement values, wherein matrix A=A ij is defined by
A ij =χ j ( f i ).
4. The device of claim 3 , wherein said fitting means is adapted to store the matrix (A T ·A) −1 ·A T .
5. The device of claim 1 ,
wherein said electrode arrangement comprises a strip electrode for being placed against said body,
an outer electrode for being placed against said body, wherein said outer electrode comprises two lateral sections extending substantially parallel to and on opposite sides of said strip electrode, wherein a first of said sections is wider than a second of said sections.
6. The device of claim 5 , further comprising an insulating layer covering said strip electrode and at least part of said first section of said outer electrode.
7. The device of claim 5 , wherein said outer electrode is annular.
8. The device of claim 1 ,
wherein said electrode arrangement comprises
at least one electrode placed on an outer side of an electrically insulating substrate,
at least one through-contact extending through said substrate and connecting said at least one electrode,
wherein an outer side of each through-contact is covered by a physiologically inert material.
9. The device of claim 8 , wherein the outer side of each through-contact is covered by a material selected from the group of glass, ceramics, plastics and a noble metals.
10. The device of claim 8 , wherein said electrode arrangement comprises at least a first electrode for being brought into direct contact with said body and wherein a surface of said first electrode consists of noble metal.
11. The device of claim 10 , wherein the surface of said first electrode consists of gold.
12. The device of claim 8 , wherein said electrode arrangement is part of a resonant circuit, and in particular wherein a resonance frequency of the resonant circuit lies in the given frequency range.
13. The device of claim 12 , wherein said electrode arrangement forms a capacitor and is arranged in series to or parallel to an inductance, wherein said capacitor and said inductance form said resonant circuit.
14. The device of claim 8 , wherein said electrode arrangement is arranged on a flat substrate.
15. A method for measuring a property of living tissue, in particular a glucose level of the tissue, said method comprising the steps of
applying an electrode arrangement to the tissue,
generating an AC voltage at a series of frequencies in a given frequency range and applying the AC voltage to said electrode arrangement,
measuring a series of measurement values at the frequencies, each measurement value depending on dielectric properties of the tissue at one frequency,
fitting a function M(f, b 0 , . . . , b K ) with parameters b 0 to b K to the measurement values at their frequencies, or through values derived from the measurement values at their frequencies, and determining the parameters b 0 to b K thereby, and
determining said property by using at least part of the parameters b 0 to b K ,
measuring a first input value dependent on said property and on said AC voltage,
measuring a second input value dependent on said AC voltage but substantially independent of said property, and
deriving said measurement values from a ratio between said first and said second input value.
16. A method for measuring a property of living tissue, in particular a glucose level of the tissue, said method comprising the steps of
applying an electrode arrangement to the tissue,
generating an AC voltage at a series of frequencies in a given frequency range and applying the AC voltage to said electrode arrangement,
measuring a series of measurement values at the frequencies, each measurement value depending on dielectric properties of the tissue at one frequency,
fitting a function M(f, b 0 , . . . , b K ) with parameters b 0 to b K to the measurement values at their frequencies, or through values derived from the measurement values at their frequencies, and determining the parameters b 0 to b K thereby, and
determining said property by using at least part of the parameters b 0 to b K ,
wherein said function M(f, b 0 , . . . , b K ) is of the form
M ( f, b 0 , . . . , b K )= b 0 +b 1 ·f+ . . . +b 3 ·f R ,
in particular with R=3.
17. A method for measuring a property of living tissue, in particular a glucose level of the tissue, said method comprising the steps of
applying an electrode arrangement to the tissue,
generating an AC voltage at a series of frequencies in a given frequency range and applying the AC voltage to said electrode arrangement,
measuring a series of measurement values at the frequencies, each measurement value depending on dielectric properties of the tissue at one frequency,
fitting a function M(f, b 0 , . . . , b K ) with parameters b 0 to b K to the measurement values at their frequencies, or through values derived from the measurement values at their frequencies, and determining the parameters b 0 to b K thereby, and
determining said property by using at least part of the parameters b 0 to b K ,
wherein said function M(f, b 0 , . . . , b K ) is of the form
M
(
f
,
b
0
,
…
b
K
)
=
∑
k
=
0
K
b
k
·
χ
k
(
f
)
said method further comprising the steps of
storing a precalculated matrix A and/or data derived from said precalculated matrix A, wherein matrix A=A ij is defined by A ij =χ j (f i ),
using said precalculated matrix A and/or said data derived from said precalculated matrix A for fitting a plurality of series of measurement values.
18. The method of claim 17 , comprising the step of storing the matrix (A T ·A) −1 ·A T .