**4. Measurements**

For the multivariate analysis applied later it is necessary to measure a large number of objects varying in their dielectric and geometric properties. Here, two series of measurements are presented.

The first series comprised objects of moist clay granules. Five irregularly shaped moulds were manufactured from polystyrol foam3. They were then filled with clay granules having different amounts of moisture. One of the moulds is shown in Figure 7. The moisture content was varied in a range from about 4.5% to 24%4 and reference measurements were carried out with a gravimetric method5. Furthermore, three rotation angles of 0◦, 22.5◦ and 45◦ were applied to the test objects when putting them on the movable table in order to have more variation in the received signals. Overall 90 different objects were measured. The measurements were carried out in random order to avoid correlations with environmental effects, e.g. temperature variations.

Since there are eight receiving antennas and the movable table is moved to four positions, 32 pulses are received for every object under test when using a switch. With the Wilkison divider and delay lines, the pulses of the eight antennas are received instantaneously as a series of pulses. Two of the received series of pulses for two different objects having moisture contents of 4.88% and 20.93% are shown as examples in Figure 8. Although the variation in moisture content is high, the variation in the pulse shape is rather low.

The second series comprised plastic bottles filled with ethanol-water mixtures6. The water content was varied in a range from 2% to 20% in steps around 2%; reference measurements were carried out using a precision balance7. Ten bottles were filled with a total of around 190g

<sup>3</sup> In the following: *test series 1*

<sup>4</sup> All given moisture contents are on a wet basis.

<sup>5</sup> A Sartorius MA100 is used, accuracy of the weighing function: 0.1% for samples > 1g and 0.02% for samples > 5g. The weight of the samples was about 4 <sup>−</sup> 8g. <sup>6</sup> In the following: *test series 2*

<sup>7</sup> The gravimetric water content was determined using a Kern EW 4200-2NM. The repeatability is 0.01g.

330 Ultra-Wideband Radio Technologies for Communications, Localization and Sensor Applications ISOPerm: Non-Contacting Measurement of Dielectric Properties of Irregular Shaped Objects <sup>9</sup> ISOPerm: Non-Contacting Measurement of Dielectric Properties of Irregular Shaped Objects 331

(a) One of the moulds manufactured from Styrofoam. (b) Mould filled with moist clay granules. (c) A bottle filled with an ethanol-water

mixture.

8 Will-be-set-by-IN-TECH

later, that the received signals of each antenna placed at its unique position are sampled separately. Therefore, the antennas are switched sequentially onto the input of the TDT and are sampled there, after being amplified by a low noise amplifier (LNA). The MOSFET switch used requires relatively high hard- and software effort and it has to be synchronised with the other components included in the system. Furthermore, these switches have a latency of some

A simpler solution is to use a broadband combiner. The signals received by the individual antennas are combined using a broadband eight-way Wilkinson divider. Prior to combining there is a delay of *τ* = 2ns between two adjacent inputs. It is possible to separate the individual pulses in time. Compared to using a receiver having more channels, or using a switch, the hardware effort is greatly reduced and the instantaneous sampling of all pulses is possible in about 20ns. One of the disadvantages that has to be considered is that there is an increased insertion loss of ideally 9dB; at 1GHz and 5GHz the measured insertion losses are 9.3dB and 10.7dB, respectively. There are also losses and temperature dependencies due to

For the multivariate analysis applied later it is necessary to measure a large number of objects varying in their dielectric and geometric properties. Here, two series of measurements are

The first series comprised objects of moist clay granules. Five irregularly shaped moulds were manufactured from polystyrol foam3. They were then filled with clay granules having different amounts of moisture. One of the moulds is shown in Figure 7. The moisture content was varied in a range from about 4.5% to 24%4 and reference measurements were carried out with a gravimetric method5. Furthermore, three rotation angles of 0◦, 22.5◦ and 45◦ were applied to the test objects when putting them on the movable table in order to have more variation in the received signals. Overall 90 different objects were measured. The measurements were carried out in random order to avoid correlations with environmental

Since there are eight receiving antennas and the movable table is moved to four positions, 32 pulses are received for every object under test when using a switch. With the Wilkison divider and delay lines, the pulses of the eight antennas are received instantaneously as a series of pulses. Two of the received series of pulses for two different objects having moisture contents of 4.88% and 20.93% are shown as examples in Figure 8. Although the variation in

The second series comprised plastic bottles filled with ethanol-water mixtures6. The water content was varied in a range from 2% to 20% in steps around 2%; reference measurements were carried out using a precision balance7. Ten bottles were filled with a total of around 190g

<sup>5</sup> A Sartorius MA100 is used, accuracy of the weighing function: 0.1% for samples > 1g and 0.02% for samples > 5g.

<sup>7</sup> The gravimetric water content was determined using a Kern EW 4200-2NM. The repeatability is 0.01g.

moisture content is high, the variation in the pulse shape is rather low.

nanoseconds. The switch has an insertion loss of 4dB at 2GHz and 8.6dB at 8GHz.

the delay lines, which have to be taken into account.

**4. Measurements**

effects, e.g. temperature variations.

<sup>3</sup> In the following: *test series 1*

<sup>4</sup> All given moisture contents are on a wet basis.

The weight of the samples was about 4 <sup>−</sup> 8g. <sup>6</sup> In the following: *test series 2*

presented.

(a) Instantaneous sampled pulses received by the eight antennas using a broadband Wilkinson divider and delay lines.

**Figure 8.** Examples of received pulses from two objects having different moisture content.

of liquid, and another ten with about 140g. Therefore, overall 20 objects were measured. A photograph of one of the measured objects containing 113.15g ethanol and 27.94g of water is shown in Figure 7.

The time domain signals are gated in order to extract the time interval of interest: about 10 to 30 equidistant amplitude values per pulse are empirically chosen and subjected to the multivariate calibration methods which will be explained in the next section 5.
