Microwave SusceptorsMicrowave Susceptors60 years of Microwave Heating60 years of Microwave Heating40 years after the Amana Radar Range40 years after the Amana Radar Range

Wolfgang DeckerWolfgang DeckerVAST FILMS, Ltd.VAST FILMS, Ltd.

Darlington, PADarlington, PA

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Fall Meeting 2007Fall Meeting 2007Scottsdale, AZScottsdale, AZ

OutlineOutline

uu A Short History of the Microwave OvenA Short History of the Microwave Oven

•• Legends and FactsLegends and Facts

uu The Microwave SusceptorThe Microwave Susceptor

•• The Early IdeasThe Early Ideas

•• The Current FormatThe Current Format

uu ApplicationsApplications

•• PackagingPackaging

•• PatterningPatterning

•• DevelopmentsDevelopments

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The History of the Microwave OvenThe History of the Microwave Ovenuu Raytheon “Radar Range”Raytheon “Radar Range”

•• Most cited Legend: “Percy Spencer walked by a Most cited Legend: “Percy Spencer walked by a running magnetron and a Hershey Bar melted running magnetron and a Hershey Bar melted in his pocket”in his pocket”

•• Truth much more benign:Truth much more benign:uu In 1945 Laurence Marshal, owner of Raytheon, In 1945 Laurence Marshal, owner of Raytheon,

ordered his engineers to create ideas for products to ordered his engineers to create ideas for products to ensure survival after war’s endensure survival after war’s end

uu Percy Spencer, chief developer for vacuum tube and Percy Spencer, chief developer for vacuum tube and magnetron applications, suggested to develop MW magnetron applications, suggested to develop MW range for heating applicationsrange for heating applications

uu The effect of MW heating was known at the time The effect of MW heating was known at the time already! If the “Hershey Bar Incident” indeed already! If the “Hershey Bar Incident” indeed happened it may have only reinforced idea of food happened it may have only reinforced idea of food heating.heating.

uu Building and Marketing of Equipment to the General Building and Marketing of Equipment to the General Public a new concept for Raytheon.Public a new concept for Raytheon.

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The History of the Microwave OvenThe History of the Microwave Oven•• Main difficulty: Finding the right FrequencyMain difficulty: Finding the right Frequency

uu Penetration Depth into Food Stuff depending on Penetration Depth into Food Stuff depending on FrequencyFrequency

uu Frequency determines size of CavityFrequency determines size of Cavity

uu Decision was made by FCC and ITU: Use either 950 MHz Decision was made by FCC and ITU: Use either 950 MHz or 2.45 GHz. or 2.45 GHz.

•• First commercial MW Oven was presented in First commercial MW Oven was presented in 1947:1947:uu Weight: ~ 300 kgWeight: ~ 300 kg

uu Height: 1.6 mHeight: 1.6 m

uu Power: 220 VPower: 220 V

uu Water Cooled MagnetronWater Cooled Magnetron

uu Cost: USCost: US--$ 2,000 (in 1947)$ 2,000 (in 1947)

•• Equals ~ USEquals ~ US--$ 20,000 today!!!$ 20,000 today!!!

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The Amana Radar RangeThe Amana Radar Rangeuu 1965: Raytheon bought Refrigerator Company AMANA1965: Raytheon bought Refrigerator Company AMANA

•• Goal: Develop a small MW oven, as a small appliance, Goal: Develop a small MW oven, as a small appliance, priced at USpriced at US--$ 500 $ 500 uu Raytheon’s Magnetron Cost: USRaytheon’s Magnetron Cost: US--$ 300!!$ 300!!uu Solution: New Japan Radio Co. (NJRC) Magnetron for USSolution: New Japan Radio Co. (NJRC) Magnetron for US--$ $

2525uu No mass production of components availableNo mass production of components available

•• Diodes and High Voltage Capacitors not available!!Diodes and High Voltage Capacitors not available!!

uu 1967 the Amana Radar Range was 1967 the Amana Radar Range was introduced. introduced.

uu Massive Sales Campaigns (mimicking Massive Sales Campaigns (mimicking Harry Truman’s Wistle Stop Train!!)Harry Truman’s Wistle Stop Train!!)

uu 1975 MW Oven Sales surpassed Gas 1975 MW Oven Sales surpassed Gas Oven SalesOven Sales

uu Today more than 95% of American Today more than 95% of American Households have Microwave OvensHouseholds have Microwave Ovens

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The Microwave “Susceptor”The Microwave “Susceptor”uu From the Entries of the Raytheon From the Entries of the Raytheon

Development Team:Development Team:•• “Refreshing corn popped, takes 20 seconds (!). “Refreshing corn popped, takes 20 seconds (!).

80% of kernels popped”80% of kernels popped”•• “… potatoes flavor was good but potato was “… potatoes flavor was good but potato was

not crisp”not crisp”•• “Mashed frozen potatoes, the taste was good, “Mashed frozen potatoes, the taste was good,

but they did not brown. Time required: 1 but they did not brown. Time required: 1 Minute (!)”Minute (!)”

•• “… steak doesn’t brown.”“… steak doesn’t brown.”

uu Two conclusions:Two conclusions:•• Raytheon used massive power in their systemsRaytheon used massive power in their systems•• Microwave by itself does not provide browning Microwave by itself does not provide browning

and crisping!and crisping!

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The Microwave “Susceptor”The Microwave “Susceptor”

uu Unlike Infrared Radiation MW heats Unlike Infrared Radiation MW heats by deep penetrationby deep penetration

uu Not enough heat on the outside of Not enough heat on the outside of foodstuff to “dry the skin”foodstuff to “dry the skin”

uu Microwave Susceptors create a hot Microwave Susceptors create a hot surface through absorption of MW surface through absorption of MW EnergyEnergy

uu Surface hot enough to crisp and Surface hot enough to crisp and brown the food.brown the food.

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MW SusceptorMW Susceptoruu US Patent 3,783,220 to Tanizaki, filed June 1971, US Patent 3,783,220 to Tanizaki, filed June 1971,

describes a plate with a thin conductive absorber describes a plate with a thin conductive absorber on a plate or dish to provide a heating surface for on a plate or dish to provide a heating surface for crisping of browning in the MW.crisping of browning in the MW.•• Proposes TinProposes Tin--Oxide, Silicon Carbide or other conductive Oxide, Silicon Carbide or other conductive

materials on Glass or Ceramic Platesmaterials on Glass or Ceramic Plates•• “In operation, an electronic vortex current is generated “In operation, an electronic vortex current is generated

in the film by the action of the electromagnetic waves in the film by the action of the electromagnetic waves causing the thin film to heat and become an infrared causing the thin film to heat and become an infrared source.”source.”

•• Patent even describes the required composition of the Patent even describes the required composition of the plate to prevent cracking or crazing!plate to prevent cracking or crazing!

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The Microwave SusceptorThe Microwave Susceptoruu USUS--Patent 4,230,924 to Brastad, filed October 1978, Patent 4,230,924 to Brastad, filed October 1978,

describes the use of thin film aluminum on PET.describes the use of thin film aluminum on PET.

Source: /4/

Absorption of MW in Thin Aluminum Coatings on PET

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The Microwave SusceptorThe Microwave Susceptor

uu Most common susceptor construction Most common susceptor construction today:today:•• PET film metallized with AlPET film metallized with Al

uu Optical Density 0.20 to 0.30, depending on applicationOptical Density 0.20 to 0.30, depending on application

uu Resistivity Range from 10 to 100 Resistivity Range from 10 to 100 OO//ƒƒ

•• Lamination to SupportLamination to Supportuu Required to prevent susceptor film from meltingRequired to prevent susceptor film from melting

uu Typically paper of various caliperTypically paper of various caliper

uu Occasionally also Cellophane is usedOccasionally also Cellophane is used

PET FILM

Aluminum Adhesive

Support Paper / Cellophane

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Patterned SusceptorsPatterned Susceptorsuu Goal of Patterned SusceptorGoal of Patterned Susceptor

•• Additional FunctionalityAdditional Functionality

uu e.g. differential cookinge.g. differential cooking

uu US Patent 3,302,632 to Fichtner describes a “Microwave US Patent 3,302,632 to Fichtner describes a “Microwave Utensil” using Metal Mesh with different mesh sizes to Utensil” using Metal Mesh with different mesh sizes to absorb different amounts of MW energy for different food absorb different amounts of MW energy for different food typestypes

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Patterned SusceptorsPatterned Susceptors

uu Patterned Susceptors used to control MW Energy Patterned Susceptors used to control MW Energy absorbed by food and susceptorabsorbed by food and susceptor•• e.g. Marie Calendar’s Pot Pie e.g. Marie Calendar’s Pot Pie

High absorption on the wall to ensure crispy side

Reduced absorption in the bottom to balance crisping and bulk heating

No absorption on the rim to prevent charring

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Patterned SusceptorPatterned Susceptoruu Used as a Safety DeviceUsed as a Safety Device

•• e.g. Graphic Packaging Safety Susceptore.g. Graphic Packaging Safety Susceptor

uu USUS--Patent 5,412,187 “Fused MW Structure”Patent 5,412,187 “Fused MW Structure”

uu Areas between crosses work like fuses and deactivate zones Areas between crosses work like fuses and deactivate zones that absorb too much MW energythat absorb too much MW energy

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Patterned SusceptorPatterned Susceptoruu Patterned Susceptor to achieve “Grill Effect”Patterned Susceptor to achieve “Grill Effect”

•• e.g. Stouffer’s Bistro Sandwiche.g. Stouffer’s Bistro Sandwichuu Die Cut Susceptor laminated to fluted boardDie Cut Susceptor laminated to fluted board

uu Same effect can be achieved with striped susceptor Same effect can be achieved with striped susceptor laminated to C1S ovenable paperlaminated to C1S ovenable paper

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Patterned and Formed SusceptorPatterned and Formed Susceptor

uu 33--D shaping of Susceptor to better adapt to specific D shaping of Susceptor to better adapt to specific food itemfood item•• e.g. DiGiorno’s Microwave Crust Pizzae.g. DiGiorno’s Microwave Crust Pizza

Press Shape rises Pizza to allow better ventilation and release of moisture => better crisping

Additional Susceptor Ring place on top of Pizza Edge to allow better crisping

No susceptor on outside wall to allow MW to penetrate underneath the food item

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MW Susceptors MW Susceptors –– The FutureThe Future

uu Most important: Adding ConvenienceMost important: Adding Convenience

•• Finding ways to reduce consumer actionFinding ways to reduce consumer actionuu Certain Foods still require stirringCertain Foods still require stirring

•• Further Reduce Cooking TimesFurther Reduce Cooking Timesuu Large Food Items (Lasagna Family Pack)Large Food Items (Lasagna Family Pack)

•• Adapt to other Food ItemsAdapt to other Food Itemsuu A full menu in the MicrowaveA full menu in the Microwave

1.1. The Appetizer being warm enough to eat immediatelyThe Appetizer being warm enough to eat immediately

2.2. The Entrée nicely cooked and hotThe Entrée nicely cooked and hot

3.3. The Dessert is icecream, still frozenThe Dessert is icecream, still frozen

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ReferencesReferences

uu /1/ W. Hammack: ”The greatest Invention since Fire”, on AmericanHeritage.com, /1/ W. Hammack: ”The greatest Invention since Fire”, on AmericanHeritage.com, www.americanheritage.com/articles/magazine/it/2005/4/2005_4_48.htmlwww.americanheritage.com/articles/magazine/it/2005/4/2005_4_48.html

uu /2/ H. Tanizaki: “Method and Apparatus for Browning Exterior Surfaces of Foodstuff /2/ H. Tanizaki: “Method and Apparatus for Browning Exterior Surfaces of Foodstuff in an Electronic Range”, US Patent 3,783,220, filed June 30, 1971, issued January 1in an Electronic Range”, US Patent 3,783,220, filed June 30, 1971, issued January 1,,

19741974

uu /3/ W. Brastad: “Package Food Item and Method for Achieving Microwave Browning /3/ W. Brastad: “Package Food Item and Method for Achieving Microwave Browning Thereof”, US Patent 4,230,924, filed October 10, 1978, issued May 12, 1981Thereof”, US Patent 4,230,924, filed October 10, 1978, issued May 12, 1981

uu /4/ J. Cesnak et al.:” Properties of Thin Metallic Films for Microwave Susceptors”, /4/ J. Cesnak et al.:” Properties of Thin Metallic Films for Microwave Susceptors”, Czech J. Food Science, Vol. 21, No. 1:34Czech J. Food Science, Vol. 21, No. 1:34--40 (2003)40 (2003)

uu /5/ E. C. Fichtner: “Microwave Cooking Utensil”, US Patent 3,302,632, filed /5/ E. C. Fichtner: “Microwave Cooking Utensil”, US Patent 3,302,632, filed December 6, 1963, issued February 7, 1967December 6, 1963, issued February 7, 1967

uu /6/ G. Walters: “Fused Microwave Conductive Structure”, US Patent 5,412,187, filed /6/ G. Walters: “Fused Microwave Conductive Structure”, US Patent 5,412,187, filed January 5, 1994, issued May 2, 1995January 5, 1994, issued May 2, 1995

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