I. Introduction
In the last years various wearable electrical devices have been proposed especially in medical, fitness and military fields [1]. In portable devices, the electricity supply is a key challenge and a promising solution is the scavenging of energy by means of wearable harvesters for overcoming primary batteries drawbacks [2] –[4]. Great number of wearable harvesting systems have been proposed, which can be classified based on the transduction mechanisms [5] –[7] such as piezoelectric, thermoelectric, photovoltaic and electromagnetic ones. In this paper the attention is focused on backpack energy harvesters, with potential applications to excursionist and military a [8–9]. During human walking, a regenerative backpack oscillates up and down with the human body allowing the recovery of a part of the mechanical energy that would be wasted. By using piezoelectric or electromagnetic transducers, the recovered mechanical energy can be transformed into electrical energy.