## 2 Sensor Selection and Layout  
In the driver-physiological-state-monitoring system, the selection and proper layout of sensors are crucial to the accuracy and stability of data collection. To achieve the efficient and precise acquisition of physiological signals, this paper adopts MEMS (Micro-Electro-Mechanical System) sensors and optical fiber sensors, integrated into a smart cushion [1; 21]. MEMS sensors, due to their miniaturization, low power consumption, and high sensitivity, are widely used in driver health monitoring, particularly for tracking, especially in tracking physiological signals, such as the heart rate and respiratory rate [22]. These sensors have the advantage of real-time heart rate and respiratory frequency data acquisition, maintaining stable performance during prolonged driving without interfering with the driver's normal activities [15]. Optical fiber sensors, known for their superior anti-interference capability and high signal-to-noise ratio, are particularly effective in complex driving environments [23]. In this study, optical fiber sensors are positioned in the pressure contact areas of the smart cushion to monitor the driver's posture and body pressure distribution in real time, providing additional data for analyzing the driver's physiological state [24]. These sensors can not only detect pressure changes but, when combined with heart rate and respiratory frequency signals, can more accurately assess the driver's fatigue level and stress response [17]. Electronic Vehicle Identification (EVI) plays a critical role in this system. EVI technology assigns each vehicle a unique electronic identifier, enabling the integration of the vehicle's operational status (such as speed, acceleration, etc.) to be associated with the driver's physiological monitoring data [25]. By incorporating EVI technology, the system can not only monitor the driver's physiological state in real time but also analyze the vehicle's operating conditions to provide a more comprehensive assessment of the driver's health status. For example, when the driver's heart rate suddenly increases, data from EVI on sudden braking or high-speed driving can help to assess whether there is a potential health risk [16]. The design of the smart cushion integrates these two types of sensors to form a multimodal sensing system. MEMS sensors are primarily responsible for monitoring the heart rate and respiratory frequency, while optical fiber sensors capture dynamic variations in seat pressure to enhance the overall stability and reliability of the signals. The sensor is optimized for the driver's working environment, ensuring effective physiological signal acquisition under diverse driving conditions. The smart cushion is shown in Figure 1.  
The experiment utilized a smart cushion developed by the research team, which integrates MEMS sensors and optical sensors. This custom-designed cushion was specifically chosen for its ability to monitor physiological parameters, such as the heart rate and breathing frequency, in real time during driving. It was not purchased as a commercially available product, but rather developed to meet the specific needs of this research. The smart cushion uses an array of MEMS sensors that are initially positioned relative to the center of the driver's seating position. After this initial placement, the system dynamically adjusts the sensor weights based on the driver's body position and posture to achieve optimal signal quality. The smart cushion monitors the physiological parameters of the driver, including the heart rate and breathing frequency. The accuracy of these measurements is primarily determined by the precision of the MEMS and optical sensors integrated into the cushion. However, measurement errors may arise from factors, such as sensor calibration, sensor  
Figure 1: Smart cushion. noise, and the variability in driver posture during use. The error in measuring the heart rate and breathing frequency is typically within \(\pm\)8%, as indicated by previous testing.