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Microwave Drying - Fiber Optic Temperature Solutions

posted by Rugged Monitoring on 2020-07-06

Lately, microwave drying technique is a sure way of getting best quality of low or no moisture content foods. We base this on the fact that microwave drying procedure is faster, power efficient and uniform when compared to the conventional methods like hot air drying, spray drying and drum drying.  Temperature Controlled Microwave drying have immensely contributed to the production of top-quality dehydrated foods. Fiber optic temperature sensing technology is the most suitable and accurate technique in measuring temperature of samples inside microwave. 

What is Microwave drying?

Microwaves are electromagnetic waves that possess varying wavelength from 1millimeter to 1 meter and frequency that ranges between 300 MHz and 300 GHz. Microwaves are widely being used for faster heating in many industries and at home. The similar microwave heating is also being used in drying the food, vegetables, fruits, and fodder.

Conventional methods of food drying had many issues. Several properties of food materials may considerably change during the drying process, such as, moisture content, temperature, mass, color, surface texture, etc. The dielectric properties of food materials are most affected. In the final stage of drying, conventional methods tend to shrink the food materials.

Microwave drying, unlike conventional drying, is faster and can boost up the drying rate from the initial stage till the last stage of drying. This helps in preserving the quality, color, texture, and taste of the dried food. Microwave drying also avoids the food shrinkage during the drying process.

The endgame for industrial microwave drying processes is to turn out greater quality of food products in a fast, efficient, affordable and low cost manner as compared to other conventional drying methods.

Why Fiber Optic Temperature Monitoring?

Temperature monitoring is very crucial in keeping the highest quality control in microwave food drying. Microwave power and duration influences the drying temperature and final product quality. Prolonged microwave heating at high power can lead to the burnt food and poor color, flavor, texture, and quality. Therefore, cyclic microwave heating is being implemented instead of continuous microwave heating. Real-time temperature monitoring and control is crucial in cyclic microwave heating.

Traditional temperature sensors like thermocouples, RTDs cannot be used in microwave drying because they produce sparks inside microwaves. Infrared thermal imaging sensors are being used in microwave heating applications as they are contact less sensors. Infrared sensors have the following imitation in temperature monitoring in microwave drying: 

  • The sensors are not accurate as it depends on the correct emissivity constant of the food material.
  • The sensors cannot be used in a long conveyor type microwave.
  • The sensors require regular calibration and maintenance i.e. cleaning / changing lenses.

 is by far the best technology in temperature monitoring of samples during microwave drying. The Fiber optic sensors can work effectively in a harsh microwave environment of 300MHz to 300GHz and radiofrequency of 100 kHz to 100 MHz.  In specific, Gallium Arsenide technology based fiber optic temperature sensor are very robust, accurate and safe for microwave assisted food drying applications. These sensors have the following advantages in microwave drying applications:

  1. Safe sensors, no risk of sparks / arching inside microwave
  2. Robust sensors with longer lifespan
  3. Bio-safe and no risk of food contamination
  4. Ideal for long conveyor belt type microwaves
  5. Highly accurate (±0.8 ⁰ C) over a wide temperature range (-100 ⁰ C to + 300 ⁰ C)
  6. Maintenance free sensors and monitors
  7. No need for calibration and temperature compensation.

Applications of Microwave drying

Microwave drying application to food materials is a significant breakthrough in the food service and packaging industry. It has salvaged the major drawbacks of conventional drying. The application of microwave drying spans across the following areas but not limited to;

1. Crop Fodder Drying

Microwave drying ovens are used to remove moisture from lots of forage and hay. It dries the fodder in a fast and efficient way; however, monitoring the temperature of the oven is critical to avoiding total or partial damage of the fodder. This is where the Gallium Arsenide based fiber optic temperature sensor comes in to help regulate, monitor, and report real time temperature changes so as to increase quality and cut down losses on animal feed. 

2. Crisp Drying

Crisp drying is a food (mostly fruits) preservative technique used to reduce moisture content, delay microbial growth, and extend food shelf life while helping to cut down other significant cost (transportation and storage). As earlier mentioned, our fiber optic technology plays a vital role in securing the freshness and quality of food products during the drying process.

3. Food Grains, Vegetables and Flower Drying

Microwave vacuum drying is very popular in dry conservation of food grains, vegetables and flowers. For example, carrot and onions are dried to preserve for longer time, grains are put under microwave and RF ovens for pasteurization etc.  GaAs based fiber optic sensors are widely used in temperature monitoring of microwave drying process.  This technology also helps in reducing the production loss during the drying process.


Microwave drying has proved to be the faster and energy efficient drying technology compared to the conventional drying. Use of microwave in freeze-drying could save about 95% - 98% of drying time compared to convention methods. More importantly the microwave drying produces higher quality output with better rehydration characteristics. However, real-time temperature monitoring and control is necessary for uniformity of microwave heating and higher quality output. Fiber optic temperature sensing technology is the best available in the market for efficient temperature control in microwave drying. 

There are many other applications in the industry that use microwave heating i.e. pasteurization / Sterilization, Extraction, Synthesis, Digestion etc. Use of microwave in heating and related applications is increasing worldwide. Need for fiber optic temperature sensors is also growing into all RF/microwave heating applications.

We provide high quality, robust and accurate fiber optic sensing technology to meet industry standard at an affordable price in the market. 

For more inquiries, visit www.ruggedmonitoring.com.