## 5 Sample Preparation and Loss Measurement
### AC Loss Measurements  
Both test samples are placed inside an E-shape core with the exact same design. The AC losses are then measured at different frequency levels (up to 2 kHz), using the test setup in Figure 12. A DC source is used for the DC losses measurements. Additionally, a 12 kVA amplifier is used as an AC variable voltage variable frequency input source for the AC loss measurements. Additionally, voltage and current probes are used to measure the voltage and the current of the test sample. Moreover, a dSpace MicroLabBox 1202 is used as a real time interface and for data acquisition (DAQ). There is also a power analyzer (PA4000) used to measure the AC and DC losses. A 4-channel scope is used to monitor the waveforms. The test sample is connected in series with a water-cooled power resistor. This zero-inductance resistance is useful to maintain sinusoidal current waveforms at high frequencies. Finally, a specially designed cooling jacket is also used with a water chiller to maintain the temperature at a constant level (see Appendix A). The main purpose of this devise is to perform the AC loss measurements at a defined temperature value.  
Figure 11: 3D printed semi-stranded coil with transposed strand location made using SLM of ASIi10 Mg aluminum alloy.  
Figure 12: Test setup for the AC losses of the coil samples.  
The results are compared with those from the AM solid copper coil, as shown in Figure 13. As expected, the total AC losses of the semi stranded aluminum coil start to reduce significantly at frequencies above 300 Hz. Additionally, the total power losses are decomposed into three main components; core losses, DC losses, and AC losses.  
The core loss in the E-shape core is calculated from its components; hysteresis loss, classical eddy current loss and excess loss, as indicated in the following equation:  
\[P_{core}=K_{h}\ f\ B_{m}^{a}+K_{cl}f^{2}B_{m}^{2}+K_{exc}f^{1.5}B_{m}^{1.5} \tag{1}\]  
where \(K_{h}\) and \(\alpha\) are the hysteresis coefficient and exponent. \(K_{cl}\) and \(K_{exc}\) are the classical eddy current loss and excess loss coefficients. All these coefficients are estimated from curve fitting of the measured iron losses of the laminated silicon steel at different magnetic flux densities (\(B_{m}\)) and frequencies (\(f\)). The core losses are equal for both coils. The main differences are in the DC and AC losses.  
In the DC losses, it is clear that the copper coil has lower DC losses compared to the aluminum one. However, as the frequency increases, the AC losses of the copper coil starts to increase to extremely high levels. This is not the case for the semi stranded aluminum coil in which the AC losses increase slowly with the frequency. As a result, it has an overall better performance.  
To sum up, it is clear that the semi stranded aluminum coil can effectively limit the AC loss component especially at high frequencies. That is the main reason behind its superiority over the 3D printed copper coil at high frequency domain with only 30% weight. Accordingly, these proposed coils have the potential for improving power density and efficiency in different weight sensitive applications, including electric traction, and automotive applications. Furthermore, additive manufacturing technology will certainly help in developing the process of electrical machines manufacturing especially with the emergence of new tools such as multi material printing which allows for simultaneous printing of conducting and non-conducting material. This will be very beneficial for the printing of electrical windings along with the electrical insulation.  
Figure 13: The measured losses at different frequency levels for the solid copper coil and the semi-stranded aluminum coil.