Electromagnetic design for cooking

Designing and building high power, solid-state RF systems for RF cooking requires a good understanding of electromagnetics and its interaction with food.  Electromagnetic (EM) design considerations influence the RF module circuitry, the power feed into the cavity, and the actual cavity design.  These three parts are, in fact, inseparable and must be considered together.

When designing a high power RF circuit, the impact of EM fields on components must be considered.  This is especially true when dealing with oven cavities, which are essentially reflective loads, as opposed to what is usually the case with communications and radar systems in which the antennas are typically non-reflective.

The first step in generating high power RF signals using solid-state electronics is generating a low power RF signal that has the correct frequency and phase as required by the cooking algorithm.  This, in turn, is fed to a high power transistor which serves as an amplifier, creating a high power replica of the low power RF signal.

Once we generate the high power signal, the next step is to transmit it into the cavity efficiently.  Every interface creates losses and the goal is to minimize those as much as possible.  Respecting engineering and regulatory constraints, the RF feed must meet multiple requirements – including cost, of course.  Some of these requirements arise from external aspects such as space limitation or high working temperatures.

When it reaches the cavity, RF power must be dissipated uniformly and in a manner that optimizes the impact on the food load.  Cavities such as those in ovens must meet many other requirements, including air flow, probes, accessories, various internal mechanical fixtures and a door.

The entire design must also allow the RF module to pick up reflections from the cavity, in order to feed the algorithm with suitable data to calculate heating parameters and gain an understanding of the current state of the cooking process (either ended or modifications are needed).  Additionally, a reasonable manufacturing variance in each component, especially the cavity, must be taken into account to build a system which can accommodate these changes.  The cavity expands when it heats, adding another variability to take into account.  Finally, the food itself, which is viewed as an EM ‘load’, also changes in size, shape and material.

There are literally endless combinations of changes that could influence our systems.  To assist our development process, we leverage powerful computers, simulation software and proprietary tools developed in-house.  It is not rare to have computers running heavy simulation work overnight or over the weekend to give us the answers we’re after.  Nevertheless, we always validate simulations through experiments, maintaining a proper balance between the two.

To address these challenges, Goji has in-house experts in the fields of EM, RF, and system and electronics engineering, who have worked together to find optimal designs for RF cooking applications.  Our advanced team love and live this up-and-coming field, and are continuously thinking of the next product evolution.