SYSTEM, APPARATUS AND METHOD FOR BIOMEDICAL WIRELESS PRESSURE SENSING

• US 20090299216A1
• Filed: 05/29/2009
• Published: 12/03/2009
• Est. Priority Date: 06/02/2008
• Status: Active Grant

• Current Assignee: California Institute of Technology
• Original Assignee: California Institute of Technology
• Inventors: TAI, Yu-Chong, CHEN, Po-jui
• Granted Patent: US 8,926,524 B2
• Time in Patent Office: Days
• US Class Current: 600/561
• CPC Class Codes: A61B 2560/063 Devices specially adapted for delivering implantable medical measuring apparatus
• CPC Class Codes: A61B 2562/0247 Pressure sensors
• CPC Class Codes: A61B 2562/028 Microscale sensors, e.g. electromechanical sensors [MEMS]
• CPC Class Codes: A61B 3/16 for measuring intraocular pressure, e.g. tonometers
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/02014 Determining aneurysm
• CPC Class Codes: A61B 5/031 Intracranial pressure

Abstract

An implantable polymer-based pressure sensor featuring an electrical LC-tank resonant circuit for passive wireless sensing without power consumption on the implanted site. The sensor is microfabricated with parylene to create a flexible coil substrate that can be folded for smaller physical form factor during implantation, and can be stretched back without damage for enhanced inductive sensor-reader coil coupling. Data received from the sensor can be enhanced to provide improved pressure measurements at increased distances.

Claims

1. A biomedical pressure sensor comprising:

a flexible substrate;

a flexible planar inductor mounted on the flexible substrate;

a flexible diaphragm chamber mounted on the flexible substrate;

one or more upper capacitor plates in or on an upper portion of the diaphragm chamber, wherein the one or more upper capacitor plates are electrically connected to the flexible planar inductor;

one or more lower capacitor plates in or on a lower portion of the diaphragm chamber, wherein the one or more lower capacitor plates are electrically connected to the flexible planar inductor; and

a pressure reference chamber in fluidic communication with the flexible diaphragm chamber.

2. The biomedical pressure sensor according to claim 1, wherein the planar inductor comprises one or more conductive structures arranged as coils on the flexible substrate.

3. The biomedical pressure sensor according to claim 1, wherein the flexible diaphragm chamber is deformable and the deformation in the flexible diaphragm is proportional to an external pressure exerted on the flexible diaphragm and wherein a variation in the deformation causes a gap between the one or more capacitor plates and the one or more lower capacitor plates to vary.

4. The biomedical pressure sensor according to claim 1, wherein the flexible structure has a discoid shape and the planar inductor comprises a spiral planer inductor.

5. The biomedical pressure according to claim 1 wherein the flexible substrate comprises a polymer, or the flexible diaphragm chamber comprises a polymer, or the flexible substrate and the flexible diaphragm chamber comprise a polymer.

6. The biomedical pressure sensor according to claim 5, wherein the polymer comprises biocompatible material.

7. The biomedical pressure sensor according to claim 5, wherein the polymer comprises parylene.

8. The biomedical pressure sensor according to claim 1, wherein dimensions and materials of the biomedical pressure sensor are chosen to facilitate surgical implantation of the sensor.

9. The biomedical pressure sensor according to claim 1, wherein the pressure reference chamber comprises an upper structure disposed adjacent the flexible substrate, a lower structure attached to the upper structure, and an access hole providing fluidic communication between the pressure reference chamber and the flexible diaphragm chamber.

10. The biomedical pressure sensor according to claim 9, wherein materials for the upper structure and the lower structure are chosen for good biocompatibility and the chosen materials comprise at least one of the following materials:

silicon, glass, metal, dielectrics, or polymers.

11. The biomedical pressure sensor according to claim 1, wherein materials and dimensions for the biomedical pressure sensor are chosen for use in physiological pressure monitoring applications comprising intraocular, intracranial, cerebrospinal fluid, cardiovascular, or blood pressure sensing.

12. A method for pressure sensing comprising:

deploying a flexible diaphragm chamber comprising a variable capacitor within an environment within which pressure is to be measured;

electrically coupling the variable capacitor to a first inductor to form a resonant circuit;

positioning a second inductor to electromagnetically couple with the first inductor;

applying signals at various frequencies from the second inductor to the first inductor;

measuring signal responses from the second inductor;

performing measurement averaging on the measured signal responses to create a time averaged difference vector;

determining a resonant frequency of the resonant circuit based on data within the time averaged difference vector; and

calculating a pressure present at the flexible diaphragm chamber based on the determined resonant frequency.

13. The method according to claim 12, wherein performing measurement averaging comprises:

measuring baseline signal responses from the second inductor without any electromagnetic coupling between the second inductor and the first inductor to create a plurality of baseline data vectors, wherein each baseline data vector comprises each measured baseline signal response in relation to a frequency at which it was measured;

measuring sensor signal responses from the second inductor with electromagnetic coupling between the second inductor and the first inductor to create a plurality of signal data vectors, wherein each signal data vector comprises each measured senor signal response in relation to a frequency at which it was measured;

subtracting each baseline data vector from a corresponding signal data vector to form a plurality of difference vectors; and

averaging the values at each frequency in each difference vector to create the time averaged difference vector.

14. The method according to claim 12, wherein performing measurement averaging comprises:

measuring baseline signal responses from the second inductor without any electromagnetic coupling between the second inductor and the first inductor to create a plurality of baseline data vectors, wherein each baseline data vector comprises each measured baseline signal response in relation to a frequency at which it was measured;

measuring sensor signal responses from the second inductor with electromagnetic coupling between the second inductor and the first inductor to create a plurality of signal data vectors, wherein each signal data vector comprises each measured senor signal response in relation to a frequency at which it was measured;

averaging the values at each frequency in each baseline data vector to create a time averaged baseline data vector;

averaging the values at each frequency in each signal data vector to create a time averaged signal data vector; and

,

subtracting the time averaged baseline data vector from the time averaged signal data vector to form the time averaged difference vector.

15. The method according to claim 12, wherein determining a resonant frequency comprises finding an extremum within the data of the time averaged difference vector and, wherein the resonant frequency comprises a frequency value at the extremum.

16. The method according to claim 12, wherein determining a resonant frequency comprises:

calculating averages of a plurality of values within the time averaged difference vector to create a frequency averaged vector, and

finding an extremum within the data of the frequency averaged vector,

and wherein the resonant frequency comprises a frequency value at the extremum.

17. The method according to claim 16, wherein calculating averages of a plurality of values within the time averaged difference vector comprises calculating a moving average of the values within the time averaged difference vector.

18. The method according to claim 12, wherein the method comprises physiological pressure onitoring for intraocular, intracranial, cerebrospinal fluid (CSF), cardiovascular, or blood pressure sensing.

19. A system for biomedical pressure sensing comprising:

an internal pressure sensor comprising;

a flexible substrate;

a flexible planar inductor mounted on the flexible substrate;

a flexible diaphragm chamber mounted on the flexible substrate;

one or more upper capacitor plates in or on an upper portion of the diaphragm chamber, wherein the one or more upper capacitor plates are electrically connected to the flexible planar inductor;

one or more lower capacitor plates in or on a lower portion of the diaphragm chamber, wherein the one or more lower capacitor plates are electrically connected to the flexible planar inductor; and

a pressure reference chamber in fluidic communication with the flexible diaphragm chamber;

an external reader coil adapted for electromagnetically coupling to the flexible planar inductor; and

a reader apparatus coupled to the external reader coil.

20. The system according to claim 19, wherein the reader apparatus comprises frequency-dependent impedance measurement electronics.

21. The system according to claim 20, wherein the frequency-dependent impedance measurement electronics performs multiple frequency scans of the internal pressure sensor to provide measured impedance data and wherein pressure measurements are based upon time averages of the measured impedance data subtracted from background data.

22. The system according to claim 21, wherein frequency averaging is performed on the time averaged data.

23. The system according to claim 19, wherein the internal pressure sensor is adapted for folding to a form factor suitable for surgical procedures before insertion into an environment from which measurements are to be made.

24. The system according to claim 19 wherein the flexible substrate comprises polymer or the flexible diaphragm chamber comprises polymer, or the flexible substrate and the flexible diaphragm chamber comprise polymer.

25. The system according to claim 19 wherein the system measures intraocular pressure and the external reader coil and the reader apparatus are adapted for mounting on a structure worn on a user'"'"'s head.