The increasing demand for embedding a tire pressure measurement system (TPMS) in wheels as a car safety device has drawn considerable research attention. A TPMS is an electronic safety system designed for monitoring the air pressure inside pneumatic tires on automobiles and other vehicles. However, the power supply of the pressure sensor of a TPMS still relies on batteries, which exhibit several drawbacks such as low durability, difficulty of replacement, and most notably, inferior sustainability in terms of environmental impact. An alternative approach for replacing the battery in a TPMS involves harvesting vibration energy from the environment [1
]. Energy harvesters are devices that transform ambient energy, such as kinetic, heat, light, and acoustic energy, into electric energy. Kinetic energy harvesters are ideal power sources for TPMSs because the wheels of cars roll on roads.
Kinetic energy harvesting is often conducted using electromagnetic [5
] and piezoelectric harvesting devices [8
], and micro-scale energy harvesters composed of different materials have been presented by researchers [14
]. The number of studies on harvesting energy from the environment for TPMSs has increased in recent years. The rotating speed of a wheel varies with the speed of the car, determined by the driver. This means that the efficiencies of energy harvesters for TPMSs should be considered at different wheel speeds. Common linear kinetic (mass-spring-damper) systems, which have a narrow frequency range, are poorly suited for energy harvesters in TPMSs. This is because the output power of a linear harvester drops dramatically under off-resonance conditions [16
]. This problem can be overcome by using nonlinear mechanisms, such as nonlinear springs [17
], nonlinear oscillators [20
], frequency tunable mechanisms [21
], and multi-frequency harvesters [25
]. The number of studies conducted on nonlinear energy harvesters as power sources for the pressure sensors in TPMSs has increased in recent years. An electromagnetic energy harvester [27
] mounted on the inner tire generated sufficient power to transmit tire sensor data multiple times per minute. Xuan et al.
] proposed a seesaw-structured energy harvester for TPMSs; the proposed harvester can effectively overcome the effect of high centrifugal forces and was tested using an average power of 5.625 μW at 750 rpm. In [29
], a piezofiber energy harvester was developed and mounted inside the tire to provide 34.5 μJ for one wheel cycle. Wang et al.
] developed pendulum-based energy harvesters for harvesting the kinetic energy from a rotating wheel. The generated power ranged from 300 to 400 μW at wheel speeds between 300 and 500 rpm. A high centrifugal force was exerted on the device mounted on the wheel, especially at high wheel rotation speeds. When the kinematic pair of the energy harvester mounted on the wheel functions as the rotary union, friction force, which is caused by the high centrifugal force and results in kinetic energy loss, cannot be avoided [33
This study proposes a novel nonlinear suspended energy harvester (NSEH), which is embedded in a rotating wheel, for a TPMS. The device comprises a permanent magnet as a mass, two suspended springs, and two coil sets for converting kinetic energy to electric energy. The NSEH demonstrates nonlinear kinetic behaviors because of the centrifugal and gravitational force as well as the stiffness of the two suspended springs. The rest of this paper is organized as follows. The “Overall design of the NSEH” section focuses on the design concept of the NSEH and derivation of its kinetic equations. The dynamic behaviors of the NSEH, including the transient response observed using analytical models and finite element software, as well as a spectrum analysis are described. The magnetic field strength analysis used for calculating the electromotive force (EMF) is presented in the “Output voltage and electromagnetic damping” section. In the “Experimental results” section, the prototype of the NSEH, experimental setups, and power generation results are presented. Finally, the conclusions are provided in the “Conclusions” section.