Calorimetric radar absorptivity measurement using a microwave oven

Abstract

The measurement of the microwave absorptivity of materials typically requires expensive and arcane equipment and methods. I show that, for moderately absorbing materials (loss tangent δ 0.005 or higher), useful measurements can be easily made using a thermometer and a normal domestic microwave oven: the heat absorbed for suitably designed sample size and geometry relates directly to the absorptivity. This technique, although not supremely accurate, is quick and inexpensive and may be useful for rapid investigations, educational projects and situations in which samples are awkward to handle. I show that water ice spiked with even only 0.2% ammonia is about three orders of magnitude more absorbing than is pure ice at −80 • C.

Dielectric properties of Jovian satellite ice analogs for subsurface radar exploration: A review

“…The reported values confirmed the behavior observed at lower frequency by Lorenz [], with an increase from 3.13 to 4.38 in the real part and from 0.0013 to 0.0042 in the imaginary part as a function of the ammonia concentration. It is worth noting that Paillou et al [] also calculated the loss tangent of their ammonia‐rich ice samples, obtaining values lower than 10 −3 , which are much smaller than those previously estimated from calorimetric data acquired using a microwave oven [ Lorenz , ; Lorenz and Shandera , ].…”

“…The dielectric behavior of frozen, highly concentrated water‐ammonia solutions has been investigated at low frequency (near DC and at about 1 MHz) by Lorenz [] and in the microwave range by Lorenz [], Lorenz and Shandera [], and Paillou et al []. The measurements performed by Lorenz [] were conducted on several samples of water‐ammonia ices (from a few percent to 30% of ammonia) frozen with liquid nitrogen at a temperature of about 77 K (see details in Lorenz []).…”

Enhancement of Batch Waste Activated Sludge Digestion by Microwave Pretreatment

“…The container was covered with a plastic lid to prevent evaporation during the irradiation. Due to problems related to monitoring temperature profiles inside the MW oven, such as interaction with the MW field causing local heating within the sample ( Lorenz 1999 ; Loupy, 2002 ), temperature measurements were done outside the MW oven as soon as microwaving was terminated. After the container was removed, the sample was vigorously stirred and the maximum temperature was recorded within 10 s. Temperature readings were taken with fast response insulated thermo‐couple probes [Cole‐Parmer (P‐08506‐75), T‐type, fine‐gauge Teflon PTFE response time of 0.5 s, Labcor Technical Sales Inc., ON, Canada] connected to a module for analog‐to‐digital conversion and recorded by a laboratory computer system [LabVIEW Software Version 6, National Instruments Co., Austin, TX, USA].…”

Physical properties of ammonia‐rich ice: Application to Titan

“…It may be that our measurements are affected by temperature gradients in the sample. We made simple loss measurements using ices frozen in the parallel plate capacitor [Lorenz, 1999] with an LCR meter, figure 4, and find that the conductivity increases dramatically with temperature, even several 10s of K below the eutectic.…”

“…We measured the microwave absorptivity of NH3-doped ice calorimetrically, recording the temperature rise in a calibrated microwave oven with a ballast load, as described in [Lorenz, 1999]. The first set of results, using only weaklydoped ice at dry-ice temperatures is shown in Figure 3 …”