Food thermometer for microwave oven

Claim 2

Apparatus for monitoring the internal temperature of food being cooked in the cooking cavity of a microwave oven with microwaves of a predetermined frequecy having a predetermined wavelength λ, said apparatus comprising: a. a temperature-sensing probe adapted for insertion into the food to be cooked, said probe including an elongated conductive housing having a reference point to indicate optimum insertion depth into the food, the distal end of said housing being closed and shaped to facilitate insertion into the food, and said probe further including a thermally-responsive electrical element positioned internally of said housing near the distal end; b. circuitry responsive to thermally-induced changes in a characteristic of said electrical element to produce a control effect indicative of the food temperature; and c. a flexible shielded cable connecting said electrical element to said circuitry, said cable having first and second ends and generally extending between said probe and a wall of the cooking cavity, said first end of the cable shield being connected to said probe housing; and d. a choke for presenting a high impedance to microwave energy of wavelength λ, said choke being coupled to the cable shield at said second end of the cable shield to electrically isolate said second end of the cable shield from the cooking cavity wall at the predetermined microwave freqeuncy; the total effective electrical length of said cable measured along said cable, from said choke to the reference point on said housing, being approximately equal to n λ/2, where n is any integer, whereby in use the cable is non-resonant at said predetermined wavelength λ, said electrical element is completely shielded from microwave energy, and the cable shield is isolated from said cavity wall.

Claim 3

The apparatus of claim 1, wherein said choke comprises a cavity having an effective electrical length equal to n λ/4, where n is any odd integer, one end of said cavity being closed and the other being open, a high impedance to microwave energy of the predetermined frequency appearing across the open end of said cavity.

Claim 4

The apparatus of claim 1, wherein said second end of the cable shield is connected to the cooking cavity wall; said choke comprises a generally cup-shaped member having a cylindrical side wall surrounding the adjacent portion of said cable shield coaxially therewith and spaced therefrom, and an end wall closing said cylindrical side wall at the end thereof disposed away from said second end of the cable shield and connected to the cable shield, the other end of said cylindrical wall being open, and said cylindrical side wall having an effective electrical length equal to n λ/4 where n is any odd integer; and the length of said cable is measured along said cable from the open end of said cylindrical wall of said choke to the reference point on said housing.

Claim 5

The apparatus of claim 3, wherein said open end of said cylindrical side wall is spaced a distance of less than λ/8 from the cooking cavity wall.

Claim 6

The apparatus of claim 1, wherein the length of said probe housing measured from said insertion depth reference point to the distal end of said housing is approximately equal to λ14.

Claim 7

The apparatus of claim 1, wherein the predetermined frequency is 915 MHz and the predetermined wavelength λ is 12.9 inches.

Claim 8

The apparatus of claim 1, wherein said choke and said cable are surrounded by a continuous layer of dielectric material.

Claim 9

Apparatus for monitoring the internal temperature of food being cooked in the cooking cavity of microwave oven with microwaves of a predetermined frequency having predetermined wavelength λ, said apparatus comprising: a. a temperature-sensing probe adapted for insertion into the food to be cooked, said probe including an elongated conductive housing, the distal end of which is closed and shaped to facilitate insertion into the food, and said probe further including a thermally-responsive electrical element positioned internally of said housing near the distal end; b. circuitry responsive to thermally-induced changes in a characteristic of said electrical element to produce a control effect indicative of the food temperature; and c. a flexible shielded cable connecting said electrical element to said circuitry, said cable having first and second ends and generally extending between said probe and a wall of the cooking cavity; d. a first choke for presenting a high impedance to microwave energy of wavelength λ, said first choke being coupled to the cable shield at the first end thereof nearest said probe to electrically isolate said first end from said probe housing at the predetermined microwave frequency; e. a second choke for presenting a high impedance to microwave energy of wavelength λ, said second choke coupled to the cable shield at the second end thereof nearest the cavity wall to electrically isolate said second end from the cavity wall at the predetermined microwave frequency; the total effective electrical length of said cable, measured along the cable from said first choke to said second choke, being approximately equal to n λ/4, where n is any odd integer, whereby in use the cable is nonresonant at said predetermined wavelength λ, said electrical element is completely shielded from microwave energy, and the cable shield is isolated at both ends.

Claim 10

Apparatus for monitoring the internal temperature of food being cooked in the cooking cavity of microwave oven with microwaves of a predetermined frequency having predetermined wavelength λ, said apparatus comprising: a. a temperature-sensing probe adapted for insertion into the food to be cooked, said probe including an elongated conductive housing, the distal end of which is closed and shaped to facilitate insertion into the food, and said probe further including a thermally-responsive electrical element positioned internally of said housing near the distal end; b. circuitry responsive to thermally-induced changes in a characteristic of said electrical element to produce a control effect indicative of the food temperature; and c. a flexible shielded cable connecting said electrical element to said circuitry, said cable having first and second ends and generally extending between said probe and a wall of the cooking cavity; d. a first choke for presenting a high impedance to microwave energy of wavelength λ, said first choke being coupled to the cable shield at the first end thereof nearest said probe to electrically isolate said first end from said probe housing at the predetermined microwave frequency; e. a second choke for presenting a high impedance to microwave energy of wavelength λ, said second choke coupled to the cable shield at the second end thereof nearest the cavity wall to electrically isolate said second end from the cavity wall at the predetermined microwave frequency; the total effective electrical length of said cable, measured along the cable from said first choke to said second choke, being approximately equal to n λ/4, where n is any odd integer, whereby in use the cable is nonresonant at said predetermined wavelength λ, said electrical element is completely shielded from microwave energy, and the cable shield is isolated at both ends.

Claim 11

The apparatus of claim 8, wherein said first end of the cable shield is connected to the probe housing and said second end of the cable shield is connected to the cooking cavity wall; said first choke comprises a first generally cup-shaped member having a first cylindrical side wall surrounding the adjacent portion of said cable shield coaxially therewith and spaced therefrom, and an end wall closing said first cylindrical side wall at the end thereof disposed away from said first end of the cable shield and connected to the cable shield, the other end of said first cylindrical wall being open, and said cylindrical side wall having an effective electrical length equal to n λ/4, where n is any odd integer; said second choke comprises a second generally cup-shaped member having a first cylindrical side wall surrounding the adjacent portion of said cable shield coaxially therewith and spaced therefrom, and an end wall closing said second cylindrical side wall at the end thereof disposed away from said second end of the cable shield and connected to the cable shield, the other end of the cylindrical side wall being open, and said cylindrical side wall having an effective electrical length equal to n λ/4, where n is any odd integer; and the length of said cable is measured along said cable from the open end of said first choke cylindrical side wall to the open end of said second choke cylindrical side wall.

Claim 12

The apparatus of claim 8, wherein said first and second chokes and said cable are surrounded by a continuous layer of dielectric material.

Claim 13

Apparatus for monitoring the internal temperature of food being cooked in the cooking cavity of a microwave oven with microwaves of a predetermined frequency having a predetermined wavelength λ, said apparatus comprising: a. a temperature-sensing probe adapted for insertion into the food to be cooked, said probe including an elongated conductive housing, the distal end of which is closed and shaped to facilitate insertion into the food, and said probe further including a thermally-responsive electrical element positioned internally of said housing near the distal end; b. circuitry responsive to thermally-induced changes in a characteristic of said electrical element to produce a control effect indicative of the food temperature; and c. a flexible shielded cable connecting said electrical element to said circuitry, said cable having first and second ends and generally extending between said probe and a wall of the cooking cavity; d. a choke for presenting a high impedance to microwave energy of wavelength λ, said choke being coupled to the cable shield at the first end thereof nearest said probe to electrically isolate said first end from said probe housing at the predetermined microwave frequency; the total effective electrical length of said cable, measured along the cable from the cooking cavity wall to the choke, being approximately equal to n λ/2, where n is any integer, whereby in use the cable is nonresonant at said predetermined wavelength λ, said electrical element is completely shielded from microwave energy, and the cable shield is isolated from said probe.

Claim 14

Apparatus for monitoring the internal temperature of food being cooked in the cooking cavity of a microwave oven with microwaves of a predetermined frequency having a predetermined wavelength λ, said apparatus comprising: a. a temperature-sensing probe adapted for insertion into the food to be cooked, said probe including an elongated conductive housing, the distal end of which is closed and shaped to facilitate insertion into the food, and said probe further including a thermally-responsive electrical element positioned internally of said housing near the distal end; b. circuitry responsive to thermally-induced changes in a characteristic of said electrical element to produce a control effect indicative of the food temperature; and c. a flexible shielded cable connecting said electrical element to said circuitry, said cable having first and second ends and generally extending between said probe and a wall of the cooking cavity; d. a choke for presenting a high impedance to microwave energy of wavelength λ, said choke being coupled to the cable shield at the first end thereof nearest said probe to electrically isolate said first end from said probe housing at the predetermined microwave frequency; the total effective electrical length of said cable, measured along the cable from the cooking cavity wall to the choke, being approximately equal to n λ/2, where n is any integer, whereby in use the cable is nonresonant at said predetermined wavelength λ, said electrical element is completely shielded from microwave energy, and the cable shield is isolated from said probe.

Claim 15

The apparatus of claim 11, wherein said first end of the cable is connected to the probe housing and said second end of the cable shield is connected to the cooking cavity wall; said choke comprises a generally cup-shaped member having a cylindrical side wall surrounding the adjacent portion of said cable shield coaxially therewith and spaced therefrom, and an end wall closing said cylindrical side wall at the end thereof disposed away from said first end of the cable shield and connected to the cable shield, the other end of said cylindrical wall being open, and said cylindrical side wall having an effective electrical length equal to n λ/4, where n is any odd integer; and the length of said cable is measured along said cable from the cavity wall to the open end of said choke cylindrical side wall.

Claim 16

Apparatus for monitoring the internal temperature of low impedance food being cooked in a microwave oven with microwaves of a predetermined wavelength, said apparatus comprisng a coaxial transmission line having an outer conductor grounded at one end thereof to the associated oven and an inner conductor, temperature-sensing means connected between the inner and outer conductors of said coaxial transmission line at the other end thereof, a conductive housing connected to said outer conductor of said transmission line adjacent to said other end thereof for cooperation therewith to surround said temperature-sensing means and shield it from microwave energy, said housing being adapted for insertion into the food being cooked to a predetermined reference point on said housing, indicator means coupled to said coaxial transmission line at said one end thereof and responsive to said temperature-sensing means for producing a signal indicative of the interior temperature of the associated food, filter structure coupled to the outer conductor of said transmission line adjacent to said one end thereof and defining an annular cavity having an effective electrical length equal to λ/4 where λ is said predetermined wavelength for presenting a high impedance to microwave energy of wavelength λ, the effective electrical distance from the end of said cavity nearest said one end of said transmission line to said reference point on said housing being approximately equal to n λ/2 where n is any integer, whereby in use said temperature sensing means is completely shielded from microwave energy and said indicator means and said transmission line are effectively isolated from microwave energy at said predetermined wavelength.

Claim 17

Apparatus for monitoring the internal temperature of low impedance food being cooked in a microwave oven with microwaves of a predetermined wavelength, said apparatus comprisng a coaxial transmission line having an outer conductor grounded at one end thereof to the associated oven and an inner conductor, temperature-sensing means connected between the inner and outer conductors of said coaxial transmission line at the other end thereof, a conductive housing connected to said outer conductor of said transmission line adjacent to said other end thereof for cooperation therewith to surround said temperature-sensing means and shield it from microwave energy, said housing being adapted for insertion into the food being cooked to a predetermined reference point on said housing, indicator means coupled to said coaxial transmission line at said one end thereof and responsive to said temperature-sensing means for producing a signal indicative of the interior temperature of the associated food, filter structure coupled to the outer conductor of said transmission line adjacent to said one end thereof and defining an annular cavity having an effective electrical length equal to λ/4 where λ is said predetermined wavelength for presenting a high impedance to microwave energy of wavelength λ, the effective electrical distance from the end of said cavity nearest said one end of said transmission line to said reference point on said housing being approximately equal to n λ/2 where n is any integer, whereby in use said temperature sensing means is completely shielded from microwave energy and said indicator means and said transmission line are effectively isolated from microwave energy at said predetermined wavelength.

Claim 18

Apparatus for monitoring the internal temperature of low impedance food being cooked in a microwave oven with microwaves of a predetermined wavelength, said apparatus comprising a coaxial transmission line having an outer conductor grounded at one end thereof to the associated oven and an inner conductor, temperature-sensing means connected between the inner and outer conductors of said coaxial transmission line at the other end thereof, a conductive housing connected to said outer conductor of said transmission line adjacent to said other end thereof for cooperation therewith to surround said temperature-sensing means and shield it from microwave energy, said housing being adapted for insertion into the food being cooked to a predetermined reference point on said housing, indicator means coupled to said coaxial transmission line at said one end thereof and responsive to said temperature-sensing means for producing a signal indicative of the interior temperature of the associated food, first filter structure coupled to the outer conductor of said transmission line adjacent to said one end thereof and defining a first annular cavity having an effective electrical length equal to λ/4 where λ is said predetermined wavelength for presenting a high impedance to microwave energy of wavelength λ, and second filter structure coupled to the outer conductor of said transmission line adjacent to said housing and defining a second annular cavity having an effective electrical length equal to λ/4 for presenting a high impedance to microwave energy of wavelength λ, the effective electrical distance from the end of said first cavity nearest said one end of said transmission line to the end of said second cavity nearest said other end of said transmission line being approximately equal to n λ/4 where n is any odd integer, whereby in use said temperature-sensing means is completely shielded from microwave energy and said indicator means and said transmission line are effectively isolated from microwave energy at said predetermined wavelength.

Claim 19

Apparatus for monitoring the internal temperature of low impedance food being cooked in a microwave oven with microwaves of a predetermined wavelength, said apparatus comprising a coaxial transmission line having an outer conductor grounded at one end thereof to the associated oven and an inner conductor, temperature-sensing means connected between the inner and outer conductors of said coaxial transmission line at the other end thereof, a conductive housing connected to said outer conductor of said transmission line adjacent to said other end thereof for cooperation therewith to surround said temperature-sensing means and shield it from microwave energy, said housing being adapted for insertion into the food being cooked to a predetermined reference point on said housing, indicator means coupled to said coaxial transmission line at said one end thereof and responsive to said temperature-sensing means for producing a signal indicative of the interior temperature of the associated food, first filter structure coupled to the outer conductor of said transmission line adjacent to said one end thereof and defining a first annular cavity having an effective electrical length equal to λ/4 where λ is said predetermined wavelength for presenting a high impedance to microwave energy of wavelength λ, and second filter structure coupled to the outer conductor of said transmission line adjacent to said housing and defining a second annular cavity having an effective electrical length equal to λ/4 for presenting a high impedance to microwave energy of wavelength λ, the effective electrical distance from the end of said first cavity nearest said one end of said transmission line to the end of said second cavity nearest said other end of said transmission line being approximately equal to n λ/4 where n is any odd integer, whereby in use said temperature-sensing means is completely shielded from microwave energy and said indicator means and said transmission line are effectively isolated from microwave energy at said predetermined wavelength.