Method and device for measurement of electrical bioimpedance

• US 20060100539A1
• Filed: 11/28/2003
• Published: 05/11/2006
• Est. Priority Date: 12/06/2002
• Status: Active Grant

• Current Assignee: Tallinn Technical University
• Original Assignee: Tallinn Technical University
• Inventors: Kink, Andres, Parve, Toomas, Land, Raul, Min, Mart
• Granted Patent: US 7,706,872 B2
• Time in Patent Office: Days
• US Class Current: 600/547
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body

Abstract

A method of measuring of an electrical bio-impedance, the method being characterized in that a symmetrical bipolar pulse-form periodical excitation signal (electrical current or voltage) is applied to the input (11) of the bio-object (1), a corresponding reaction of the bio-object to the mentioned excitation signal is measured from the output (12), which is connected to the input (201) of the synchronous detector (200). A symmetrical bipolar pulse-form periodical signal is also applied to the reference input (202) of the synchronous detector (200), whereby both pulse-form signals are shortened by the predetermined time interval in each half period of the signal, said time intervals being different for the excitation and reference signals. The proposed method ensures an increased accuracy of the impedance analysis by decreasing the influence of the higher harmonics in the spectra of the excitation and reference signals of the synchronous detectors to the measurement result. The use of the rectangular signals ensures that the device for implementing of the proposed method has a simple design and low power consumption.

Claims

1-9. -9. (canceled)

10. A method for measuring of an electrical impedance of an object using periodic non sine wave signals, the method comprising:

applying an excitation signal to the object; and

measuring a response to the excitation signal using synchronous demodulation, whereas both the excitation signal and a reference signal driving a synchronous detector are generated from a rectangular waves, and both signals having constant value sections, and wherein said excitation signal or said reference signal is modified so that constant value sections of the modified signal are shortened by a predetermined first time interval, during which the modified signal has different value from the constant value sections of that signal.

11. The method according to claim 10, wherein said predetermined first time interval is selected so that the 3rd harmonic of said modified signal is suppressed.

12. The method according to claim 11, wherein said predetermined first time interval equals to about approximately π

/6.

13. The method according to claim 10, wherein the other signal is also modified so that constant value sections of that signal are shortened by a predetermined second time interval during which the signal has different value from the constant value sections of that signal.

14. The method according to claim 13, wherein said other signal has value of zero during said predetermined first time interval.

15. The method according to claim 13, wherein said predetermined second time interval is selected so that the 5th harmonic of the other signal is suppressed.

16. The method according to claim 15, wherein said predetermined first time interval equals to about approximately π

/10.

17. The method according to claim 10, wherein the first signal has a value of zero during said predetermined first time interval.

18. A device for measuring of an electrical impedance of an object, comprising:

first generator for generating an excitation signal, wherein the excitation signal is a modified rectangular wave signal, wherein the excitation signal has constant value sections, that are shortened by a first time interval during each half period of the excitation signal to suppress higher harmonics of the excitation signal;

second generator for generating a reference signal, wherein the reference signal is modified rectangular wave signal, wherein the reference signal has constant value sections, that are shortened by a second time interval during each half period of the reference signal to suppress higher harmonics of the reference signal; and

a synchronous detector, having a first input, and a reference input, wherein the excitation signal is applied to an input of the object, a response signal is received from an output of the object through the first input of the synchronous detector, and the reference signal is applied to the reference input.

19. The device according to claim 18, wherein a phase shift between the excitation signal and the reference signal is 90°

.

20. A device for measuring of an electrical impedance, of an object, comprising:

an in-phase and a quadrature measurement channels;

a generator of driving signals;

a circuit of an excitation signal, the output of which is connected to an input of the object, wherein first and second outputs of the generator of driving signals are connected to inputs and of reference circuits of synchronous detectors , wherein the generator of driving signals comprises a generator of quadrature signals and two formers of the bipolar rectangular signals;

the circuit of the excitation signal comprises a device for generating a shortened pulse, the control input of which is connected to the output of the auxiliary signal of the generator of quadrature signals, the input is connected to the output of the former of the bipolar rectangular signal, and the output is connected to the input of the object;

the reference voltage circuit of the synchronous detector of the in-phase measurement channel comprises a device for generating of shortened pulse is introduced, the control input of which is connected to the output of the auxiliary signal of the generator of quadrature signals, the input is connected to the output of the former of the bipolar rectangular signal, and the output is connected to the reference input of the synchronous detector;

the reference circuit of the synchronous detector of the quadrature measurement channel comprises a device for generating of shortened pulse, the control input of which is connected to the output of the auxiliary signal of the generator of quadrature signals, the input is connected to the output of the former of the bipolar rectangular signal, and the output is connected to the reference input of the synchronous detector.

21. The device according to claim 20, wherein the generator of quadrature signals comprises a shift register of predetermined bit length and the quadrature triggers.

22. The device according to claim 20, wherein the synchronous detectors are implemented on the basis of a switching multiplier.

23. The device according to claim 22, wherein the switching multiplier in the synchronous detectors is implemented on the basis of digital techniques.

24. The device according to in claim 20, wherein the synchronous detectors are implemented on the basis of an analog multiplier.

25. The device according to claim 23, wherein the switching multiplier in the synchronous detectors is implemented on the basis of mixed signal analogue/digital techniques.