Development of online closed-loop frequency shifting strategies to improve heating performance of foods in a solid-state microwave system.

The solid-state microwave generator is promising to replace magnetron as a power source in domestic ovens for its precise and flexible control over a wide range of operational parameters and its potential to improve heating performance. Shifting frequency during microwave heating, either orderly or using complementary heating patterns, has yielded better heating performance than traditional single-frequency heating. This study developed three online frequency shifting strategies (orderly, pre-determined complementary, and dynamic complementary) that simultaneously collected heating performances and provided closed-loop feedback through customized algorithms to control the frequency shifting during the microwave heating processes. Each algorithm was implemented and tested on two model foods with different dielectric properties (gellan gel and mashed potato). The three frequency shifting algorithms had similar frequency sweeping processes but considerably different frequency shifting procedures for different replications and food products. The dynamic complementary frequency shifting strategy simultaneously evaluated the heating performance and determined the next-step complementary frequency. The method had shown better heating uniformity than the orderly and pre-determined complementary frequency shifting strategies. The dynamic complementary frequency shifting strategy could accommodate different food products and can be incorporated into future smart microwave ovens.