Microwave moisture sensors

Microwave moisture sensor Dielectric substance Attenuation of microwave transmitting along the dielectric substrate by moisture in sample 0.3-70% r.h. 0-35 °C few seconds Detection of moisture in grain, wood and paper... 

In our discussion of electromagnetic techniques, we omitted a few available technologies that provide some unique capabilities and, with further development, can attain practical application. One such technique involves the use of a microwave resonance sensor (Kobyashi and Miyahara, 1984) that uses a microwave cavity to measure solids concentration and velocity by monitoring the resonance frequency shift. However, this technique suffers from some shortcomings the frequency shift may be positive or negative, depending on the dielectric properties of the solids, and the cavity is extremely sensitive to changes in moisture content and temperature. 

In general, it is difficult to make online measurement of product quality it is often an inferred entity based on experience. The moisture content can be a measured variable if a suitable moisture sensor is used in the process. Analyzers are available for moisture analysis, which can be adapted for automatic, closed-loop dryer control. The most successful of these units rely on infrared, microwave, or capacitance detection [1]. Care must be exercised in the selection to allow for changes in bulk density or for void spaces, which will... 

Moisture sensors/methods standard gravimetric method (SGM) microwave phase shift (MPS) microwave attenuation (MA) near-infrared (NIR) capacitance and conductivity (CC) radiofrequency transmission (RFT) neutron moderation activation (NMA) low resolution (LR) direct physical measurement (DPM) based on the drag force principle. 

KDC Technology has developed a cost-effective microwave sensor technique for monitoring constituents and moisture in a wide variety of products including foods (KDC 1993). The KDC sensor is adaptable to measurement of process parameters of products contained in tubes, chutes, bins, vessels as well as moving on conveyer lines. 

Prohling or imaging of a physical variable, e.g., monitoring of moisture diffusion process through an organic material is readily accomplished with low frequency dielectric sensors. Alternatively, a microwave probe can be used, but the sample penetration depth of the microwave probe would be limited, in many cases, to a few microns, whereas the penetration depth of low frequency dielectric measurements can be controlled by changing the separation between the sensor head electrodes. 

Because of its precision application and enduring features, PPX films have been used in various applications, including hydrophobic coatings (moisture barriers, e.g., for biomedical hoses), barrier layers (e.g., for filter, diaphragms, valves), microwave electronics, implanted medical devices, sensors in hostile environments (automotive fuel/air sensors), electronics for aerospace and military, corrosion protection for metallic surfaces, reinforcement of microstructures, friction reduction (e.g., for guiding catheters, acupuncture needles and microelectromechanical systems) and protection of plastics and rubbers from harmful environmental conditions. 

---