## 3 A Taxonomy of Measuring Methods, Techniques, and Sensors in Physiological-Based DMSs
### Electrocardiography (ECG)
#### 3.1.2 Non-Contact ECG Sensors  
Unlike contact techniques for ECG signal monitoring, the non-contact acquisition does not rely on galvanic contact with the driver's body. The ECG signal pickup is achieved through capacitive connection (Figure 2d). Typically, capacitive electrodes are separated from the body by fabric or other textile layers, which is more comfortable for the driver, as they do not need to be in constant contact with the electrodes.  
In 2008, [PERSON] and [PERSON] [37] proposed capacitive ECG (cECG) acquisition with solid copper plate electrodes, coated with a protective acrylic paint, placed on the backrest of a car seat at a 45-degree angle to improve the signal-to-noise ratio (SNR) by simulating the typical axis of the heart. The reference electrode (\"right leg\") is also placed in the backrest around the other electrodes. This design can be considered as one of the precursors from which a wide variety of sensor seats evolved over the next years. They differ in the number of electrodes, size, shape, locations, and material. [PERSON] et al. [38] presented a concept for integrating textile capacitive electrodes into the driver's seat. In this specific design, the electrodes are placed horizontally and laterally. However, the lateral placement of the electrodes does not seem optimal because the driver's body may not completely cover the area above the electrodes. In 2011, [PERSON] et al. [39] published a design with six rectangular metal plate electrodes integrated into the backrest of the driver's seat. The large-sized reference electrode is placed on the seat. This arrangement allows the strongest signal to be selected, considering the different pairs of electrodes. This also allows adaptation to different cardiac axes and to the torso size of different drivers.  
The practical applicability of this design was tested on the Ford testing track in Lommel (Belgium). The presented results show that ECG recording during driving is possible 85% of the time with three layers of clothing, with an increase to 93% when the driver's clothing is two layers.  
In 2011, [PERSON] et al. [40] demonstrated pilot studies with textile, capacitive electrodes integrated into the backrest of a car seat. Two such electrodes were placed horizontally in the lumbar region, through which they recorded the ECG signal. In 2012, [PERSON] et al. [41] developed a system for measuring vital parameters in a car, including a sensitive textile seat cover. Their design includes two sensing textile electrodes, located horizontally in the lumbar region of the backrest, and a reference electrode placed above the two sensing electrodes. The authors validated the performance of this capacitive ECG measurement system in real-world driving tests. They reported a sensitivity of up to 95.5% and a precision of up to 92.6%, paying special attention to the strong influence of vehicle dynamics on the quality of the ECG signal. They concluded that information about driving dynamics can be used to improve the precision of future capacitive ECG measurements. In the same year, [PERSON] et al. [42] presented another capacitive ECG monitoring system with two sensing and one reference electrodes integrated into the driver's seat. The active measuring electrodes are flat copper plates, positioned horizontally relative to each other in the backrest, while the reference electrode is made of conductive textile and positioned on the seat.