# InoT Sensor Network for Wild-Animal Detection near Roads
## 3 Design of DSN Hardware  
### PIR Sensors  
Various sensors can be used for the potential detection of animals in the roadside area: light-beam interruption or reflection; radar; thermal radiation sensors; optical and/or thermal imaging; etc. Since it is required to cover relatively long stretches of road (hundreds of meters or more), the designed DSNs should be relatively cheap and with an autonomous power supply. For these reasons (cost and energy consumption), the use of video/thermal imaging sensors and radars has been abandoned. Since it was decided that DSNs will be installed on roadside-marker posts, which are placed on roadsides every 50 m or 100 m (on straight stretches of roadsides, the distance between the roadside-marker posts can technically and economically be increased to 100 m [40]), therefore, the distance of detection of the animal detection sensors should be at least 50 m. Pyroelectric (PIR) sensors that detect thermal infrared (IR) radiation (wavelength 8-14 \(\upmu\)m) are the most energy efficient. PIR sensors have two or more thermal IR radiation passive pyroelectric sensitive elements. Pyroelectric sensors generate an electric charge only when the intensity of IR radiation changes, making them very suitable for detecting warm moving objects. These are among the least energy-consuming motion sensors. The current used by modern PIR sensors, together with the amplifier and the detection scheme (Figure 5), can be less than 30 \(\upmu\)A [43; 44]. To increase the detection distance (aperture) of the sensors, IR lenses are used for wavelengths from a few to tens of micrometers. To reduce cost and weight, plastic Fresnel multisegmented or simple lenses (sometimes mirrors or a combination of lenses and mirrors) are usually used. Using PIR sensors with sector view multisegment lenses, and for potentially higher sensitivity (detection distance of moving warm objects), there is a high probability of false positives on a windy day when sun-heated tree or bush branches (tall grass) move near the sensors. Foggy nights, rainfall, and snowstorms can decrease the detection distance of the sensors. For this reason, it is more logical to concentrate on the directionality and detection distance of the sensors along the roadside. In practice, PIR sensors with four different IR lenses were tested: one multisegment and three single-zone lenses from different manufacturers. The tests were carried out in the forest, when the air temperature was 20 \({}^{\circ}\)C (April 2021), and the objects--a person--were detected (see results in Table 2). Experiments were repeated with three different persons with weights of -40 kg (object 1), -60 kg (object 2), -80 kg (object 3) and heights of 130 cm, 170 cm, and 190 cm. Each person walked on the forest path (average speed 5-6 km/h) from a distance of 60 m towards the PIR sensor. Then sensor-triggered measurements were taken. An average of 10 measurements with each object and each Fresnel lens is presented in Table 2. Here LENS 1 is a multisegmented Fresnel lens (Fresnel Factory Inc., San Jose, CA, USA, PF305-8324), LENS 2 (Fresnel Factory Inc. PF03-3025), LENS 3 (Fresnel Factory Inc. PF20-06015), and LENS 4 (Fresnel Factory Inc. PF28) are single-segment Fresnel lenses. The purpose of the tests is to determine, under equal conditions, which optical system will  
Figure 5: Internal structure of the PIR sensor [43]. ensure the maximum detection distance. As expected, the maximum distance (nearly 40 m) was recorded by sensors with a single zone and the largest dimensions (LENS 3: d = 3 cm) Fresnel lens.