A millimeter-wave Dicke-type radiometer is developed for non-destructive measurement of biological samples. We have studied the effect of background noise on the receiving power as well as the relationship between the sugar content and the receiving power, and found that the raise of the difference between the thermal noise of the target and the background noise is the most important to measure the slight change of the radiation power due to the concentration change (i.e. the change of the emissivity). Furthermore, We understood that contact measurement was necessary to keep the background noise constant and to lower it.
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