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A wireless liquid sensing system includes a beverage container and a table top for holding the container. Embedded in the walls and bottom of the container are two electrically conductive plates coupled to a transponder wire coil. A reader radiates an RF signal at a predetermined frequency through a

A wireless liquid sensing system includes a beverage container and a table top for holding the container. Embedded in the walls and bottom of the container are two electrically conductive plates coupled to a transponder wire coil. A reader radiates an RF signal at a predetermined frequency through a reader antenna. A microprocessor, also coupled to the transponder coil and the two plates, is powered by a rectifier circuit that gains power from then radiated RF signal. The microprocessor amplitude modulates the RF signal in accordance with the amount of liquid in the container. The reader can then detect this modulation with a peak detector to sense the amount of the substance in the container when the transponder antenna is inductively coupled to the reader antenna at the predetermined frequency.

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1. A system for sensing an amount of a substance, comprising: a container; two plates mounted thereon, the plates being electrically conductive; a transponder antenna coupled to the two plates; and a reader having a reader antenna resonating at a predetermined frequency, the reader sensing an

1. A system for sensing an amount of a substance, comprising: a container; two plates mounted thereon, the plates being electrically conductive; a transponder antenna coupled to the two plates; and a reader having a reader antenna resonating at a predetermined frequency, the reader sensing an amount of a substance in the container when the transponder antenna is inductively coupled to the reader antenna at the predetermined frequency depending on the amount of the substance in the container. 2. The system of claim 1 wherein the container is a beverage container and the substance is a consumable liquid, and further comprising: a table top configured to mount the reader antenna along a periphery of a surface of the tabletop. 3. The system of claim 1 wherein a first plate is mounted in walls of the container, and a second plate mounted in a bottom of the container. 4. The system of claim 1 wherein the transponder and reader antennas are in the form of wire coils. 5. The system of claim 1 wherein the reader antenna has a substantially larger cross-sectional area than the transponder antenna. 6. The system of claim 1 wherein the amount of substance in the container is directly controlled in response to the sensing. 7. The system of claim 1 further comprising: a tuned, resonant circuit for generating a drive signal at the predetermined frequency. 8. The system of claim 1 wherein the predetermined frequency is selected from a range of frequencies, and the predetermined frequency maximizes the inductive coupling. 9. The system of claim 1 including a plurality of containers, each container including the two plates and the transponder coil, and further comprising: a capacitor coupled to each transponder coil, each capacitor having a capacity unique for each container to offset the predetermined frequencies. 10. The system of claim 1 further comprising: a microprocessor coupled to the two plates and the transponder coil; a rectifier circuit coupled to the microprocessor, the rectifier circuit configured to gain power for the microprocessor from the inductive coupling between the transponder and reader antennas. 11. The system of claim 10 further comprising: means for loading the transponder antenna to modulate the predetermined frequency according to the amount of the substance in the container. 12. The system of claim 11 wherein the modulation is by amplitude. 13. The system of claim 12 wherein the amplitude is measured by a peak detector. 14. The system of claim 10 including a plurality of containers, each container including the two plates, the transponder coil, the microprocessor and the rectifier circuit, and wherein each microprocessor stores a unique identification number for a particular container. 15. The system of claim 10 wherein the microprocessor stores a date and a substance identification. 16. A method for sensing an amount of a substance, comprising: resonating a reader antenna at a predetermined frequency; and modulating the predetermined frequency in a transponder antenna coupled to two electrically conductive plates mounted in a container according to an amount of substance in the container; and sensing the modulated predetermined frequency in a reader coupled to the reader antenna to determine the amount of substance in the container when the reader and transponder antennas are inductively coupled. 17. A system for sensing an amount of a substance in a container, comprising: two capacitive plates mounted on the container; a first coil having ends directly coupled to the two plates; and a reader having a second coil resonating at a predetermined frequency, the reader sensing an amount of a substance in the container when the first coil is inductively coupled to the second coil by capacitively coupling of the two plates at the predetermined frequency depending on the amount of the substance in the container.