## 1 Introduction  
It is widely known that vibrations are always present in running vehicles. Vibration is a mechanical motion phenomenon where a mass point oscillates around the equilibrium point. It is the source that causes discomfort, which is extremely harmful to vehicle operators and passengers. Pathology studies have shown that vehicle driver exposure under low-frequency vibrations generates whole-body-vibration (WBV), which always results in various health concerns and consequences, such as tiredness, fatigue, motion sickness, and vertebrae diseases [1], an increased risk of certain cancers, digestive issues, and vision damage [2], lower back pain [3], impairment of balance [4], and reduction in the human body reaction time and effectiveness [5]. Various types of vehicles, including motorcycles, cars, trucks, and buses, are very often subjected to road surface unevenness-induced vibrations. Research shows that a vehicle driver usually experiences vibrations in a wide frequency range, particularly in the frequency range from 0 to 20 Hz [6]. In order to improve ride comfort, a good seating suspension isolation system is essential. The seating suspension isolation system is a set of complex structures designed to isolate vibration from the vehicle floor to the human body. The main objective of the system is to reduce the vibration transmissibility between the source of vibrations and the seated human beings. The seating suspension isolation system reduces the effects of vibrations on the vehicle driver and passenger. Over the decades, automotive engineers have been working hard to design a vehicle suspension system to reduce vibration transmitted to seated occupants and improve ride comfort. Although a variety of vibration control techniques have been developed to tackle vibration problems related to the seat structure design, which has achieved considerable progress [7], designing a good vehicle suspension system is still a challenging task for automotive engineers. For example, a lightweight structure is most commonly adopted in the seating suspension system design, because the lightweight structure contributes to reduced fuel consumptions and emissions. However, the lightweight structure design will naturally result in side effects of the degraded noise and vibration performance of the seating suspension system. Current design trends involve applying lightweight materials or structures in a more environmentally friendly design of the seating suspension system to achieve efficient vibration isolation effects and improve vehicle ride comfort. To be more specific, most frequently under constraints imposed on the frequency-dependent vibration attenuation efficiency, load capacity, installation and operation costs, and energy consumption all need to be considered in [8]. The vibration control system includes three types: Passive [9; 10], semi-active [11], and active systems [12]. For an active vibration control system, unwanted vibrations are cancelled by an equal-in-amplitude but opposite-in-phase force that is generated by actuators and control algorithms [13] using sensors for vibration measurement. The active vibration control system usually has a better vibration reduction performance, but it needs external energy to power up the control system [14; 15]. Figure 1 shows a prototype of an active vibration control system [16]. The semi-active vibration control system has worse vibration reduction performance than the active vibration control system [17]. However, the semi-active vibration control system would consume much less energy or power. Control units of the semi-active vibration control system would increase the weight and design complexity compared to the passive vibration control system [18]. A passive vibration control system has worse vibration reduction performance than the active and semi-active vibration control systems. However, the cost of the passive vibration control system is generally lower than that of the active and semi-active vibration control systems.