Claims
- 1. A solid-state variable capacitor for use in an implantable medical device comprising a closed environment which contains a liquid-vapor phase material, the solid-state variable capacitor measuring the amount of liquid existing in the medical device, the solid-state variable capacitor comprising:a first capacitor plate located within the closed environment; a second capacitor plate fixed with respect to the first capacitor plate and located within the closed environment; and a dielectric material located within the closed environment and being formed of a material suitable for absorbing the liquid phase of the liquid-vapor phase material, the dielectric properties of the dielectric material varying with the absorption of the liquid phase to vary a capacitance according to the phase status of the liquid-vapor phase material.
- 2. The solid-state variable capacitor of claim 1, wherein the dielectric material is ring shaped.
- 3. The solid-state variable capacitor of claim 1, wherein the dielectric material is comprised of a material selected from the group consisting of polyvinyl alcohol, felt and cellulose.
- 4. The solid-state variable capacitor of claim 1, wherein at least one of the first and second capacitor plates is provided on a conductive flex circuit.
- 5. The solid-state variable capacitor of claim 1, wherein the dielectric material is disk shaped.
- 6. In an implantable medical device comprising a closed environment, the medical device containing a liquid-vapor phase material therein, a method of detecting the amount of liquid existing in the medical device, the method comprising:providing a solid-state variable capacitor within the closed environment and having an absorbent dielectric material, the dielectric material suitable to absorb the liquid phase of the liquid-vapor phase material, the dielectric properties of the dielectric material varying with the absorption of the liquid phase to vary a capacitance according to the phase status of the liquid-vapor phase material; measuring the capacitance of the capacitor; and determining the amount of liquid from the measured capacitance.
- 7. The method of claim 6, wherein the medical device is a drug delivery device.
- 8. The method of claim 6, wherein the medical device is an implantable pump.
Parent Case Info
This application is a divisional of application Ser. No. 09/070,176 filed on Apr. 30, 1998, now U.S. Pat. No. 6,210,368.
US Referenced Citations (16)