## 3 System Concept and Hardware
### Sensors  
As stated by [PERSON]'s law, all objects emit radiation in a wide range of wavelengths [9]. The maximum of this radiation depends on the body's temperature, as visualized in Figure 3. For bodies colder than 3000 K, most of the emitted radiation lies in the infrared spectrum. Therefore, to measure the temperature of most bodies, it is necessary to use sensors sensible for wavelengths above 1 \(\upmu\)m.  
DIN 5031 and the International Commission on Illumination define areas IR-A, IR-B, and IR-C, while ISO 20473 gives the designations and classifications in the near-infrared (NIR), middle-infrared (MIR) and far-infrared (FIR) ranges. The term LWIR is not officially defined by a norm but is commonly used and encompasses the area of 8-15 \(\upmu\)m, therefore  
Figure 1: (**a**) Schematic mounting concept of sensor showing alignment and field of view, (**b**) close up of mounted sensor system consisting of (1) an NM500 evaluation USB stick, (2) an 80 \(\times\) 64 sensor, (3) a 160 \(\times\) 120 sensor, (4) a Raspberry Pi4, and (5) a battery pack. (**c**) Full view of mounted sensor system.  
Figure 2: Rendering of the extended prototype, showing (1) radar, (2) 80 \(\times\) 64 pixel LWIR sensor, (3) 160 \(\times\) 120 pixel LWIR sensor, (4) Raspberry Pi 4, and (5) power supply and Radar-MCU.  
lying in the range of MIR and IR-C. Translated to emitting temperatures, long-wave infrared (LWIR) radiation is emitted by objects of a temperature between 193 K and 362 K. For this reason, LWIR sensors are well suited to monitoring everyday objects.  
The two most common types of sensors for detecting LWIR radiation are photon detectors and bolometers. Photon detectors consist of semiconductor chips which detect incoming light, similiar to digital cameras, by utilizing the inner photoelectric effect [11]. It is necessary to cool these detectors to low temperatures because the necessary bandgaps only become available at low temperatures. This additional cooling is the reason why most of these cameras are quite large and require a high amount of power. The other kind of sensor is bolometers. Bolometers work through the absorption of incoming light and detecting the resulting rise in temperature. Modern advances in micro-manufacturing techniques allow for the construction of arrays of bolometers with a pixel pitch below 12 \(\upmu\)m. Such bolometers are often referred to as microbolometers, offering the advantages of a lower size and lower cost and power consumption, but they typically have more noise and lower sensetivity when compared with photon detectors.  
Due to power and cost constraints, we decided to use bolometer sensors for our project. In preceding projects, we compared different bolometer sensors with different resolutions, technologies, and fields of view (FoVs). For our proof-of-concept system, we settled on a sensor with a resolution of 160 \(\times\) 120 pixels and a FoV of 57\({}^{\circ}\). In our previous work, we showed that sensors with lower resolutions are also suitable [2]. The decision was based on a lower noise-equivalent temperature difference (NETD) and a more suitable FoV of the 160 \(\times\) 120 pixel sensor.