Increased energy harvesting from backpack to serve as self-sustainable power source via a tube-like harvester

•We developed a tube-like energy harvester to generate electricity during walking.•It is embedded into a backpack to provide continuous power to electronics.•The energy harvester structure is very compact and occupies very little space.•A prototype was built to test the proposed backpack-based energy harvester design.•Experiments showed that the harvester can provide several watts of electrical power. In recent years, there has been increasing demand for portable power sources because of the rapid development of portable and wearable electronic devices. This paper describes the development of a backpack-based energy harvester to harness the biomechanical energy of the human body during walking. The energy harvester was embedded into a backpack and used a spring-mass-damping system to transfer the energetic motion of the human body into rotary generators to produce electricity. In the oscillation system, the weight of the harvester itself and the load contained in the backpack serve together as the seismic mass; when excited by human trunk motion, the seismic mass drives a gear train to accelerate the harvested energetic motion, which is then delivered to a generator. A prototype device was built to investigate its performance, which has a maximum diameter of 50mm, a minimum diameter of 28mm, a length of 250mm, and a weight of 380g. Experiments showed that the proposed backpack-based harvester, when operating with a 5kg load, could produce approximately 7W of electrical power at a walking velocity of 5.5km/h. The normalized power density of the harvester is 0.145kg/cm3, which is 7.6 times as much as that of Rome’s backpack harvester [26]. Based on the results of metabolic cost experiments, the average conversion efficiency from human metabolic power to electrical power is approximately 36%.