Microwave Cavity Characterization

Applications include a variety of materials, some specific areas include:

Measurements are performed by measuring the cavity resonance empty, and then measuring the resonance with the sample material placed at its center. The permittivity is calculated from the shift in resonance and the loss calculated from the broadening of the resonance with and without the sample.

In addition to characterization we also provide custom microwave cavity manufacture and sales. Our Model 9446C circular cavity for microwave heating and wireless Internet frequencies is shown below.  The cavity has a resonance frequency of 2450 MHz with a Q exceeding 7000.  Prices are available on request.

Example Measurements

1. 4500 MHz Teflon  An example measurement at 4500 MHz is shown below. The red peak is the cavity resonance empty and the blue the cavity containing Teflon, showing a shift from 4514.780 to 4438.980 MHz between the two measurements. Various parameters for the 2 resonance are listed on the side, such as resonant frequency, full-width at half-maximum, cavity Q, and sample volume. Dielectric values are calculated below, giving the expected value of 2.06 for Teflon with a loss tangent around 0.0009. 

2. 4500 MHz adhesive  A low-loss silicone adhesive is then compared with the empty cavity and teflon, as shown in the figure below. Here the frequency shift is larger and the resonance broadening more clear, with the dielectric values calculated to be 3.21 for the permittivity and 0.017 for the loss tangent.

3. 14400 MHz foam  Characterization at higher frequencies is available up to 18 GHz. The figure below shows a characterization of the Spray-On Insulating-Foam for the space shuttle external tank at 14400 MHz. Because of its low density, the foam permittivity is near unity at 1.05 with a loss tangent around .0011.

4. 850 MHz ceramic Characterization at lower frequencies is available down to 850 MHz. A 270 x 50 mm circular cavity provides characterization at 850 MHz cellular frequencies with a 1950 MHz second-harmonic available for PCS. The figure below shows an alumina ceramic along with the empty-cavity and Teflon resonance, showing a permittivity of 9.35 and a loss tangent of 0.00050.  

Cavity Frequencies

Other cavities and frequencies are available and we custom-engineer cavities at specific frequencies as requested. Our current available cavities are listed below, and these frequencies can be modified slightly by shimming or dielectric loading.

Broadband Measurement  The above frequencies can be measured individually or combined, to provide a broadband spectrum over the range in low-loss materials.  An example is the loss spectrum of an RTV silicone adhesive over the range 850 MHz to 9010 MHz, as shown below.

Technical References

Additional information on Microwave Cavity measurement can be in:

1. Anand Parkash, J.K. Vaid, and Abhai Mansingh,  "Measurement of Dielectric Parameters at Microwave Frequencies by Cavity Perturbation Technique", IEEE Trans. Microwave Theory and Techniques, Vol. 27, No. 9, 791 (1979). 
   

2. Olivier Klein, Steve Donovan, Martin Dressel, George Gruner, "Microwave Cavity Perturbation Technique: Principles/Applications", Intl. J. of Infrared and Millimeter Waves, Vol 14, No. 12, pages 2423-2517. (1993)
   

3. A.W. Kraszewski, S. O. Nelson,  J. Microwave Power and Electromagnetic Energy, Vol. 31, No. 3, p. 178 (1996).
   

4. Technique of Microwave Measurements, Carol G. Montgomery.