Rapid advancements in the Internet of Things (IoT) have revolutionized the world by creating a proliferation of low-power wireless devices and sensor nodes. The issue of powering these devices remains a challenge as they require regulated direct current (DC) supply for their operation. Mechanical energy scavenging mechanisms are viewed and promoted as renewable powering solutions for low-power electronics. However, such energy harvesting mechanisms generate alternating current (AC). Converting AC to DC is a critical issue as it involves using a rectifier, which is not a preferred option considering additional circuitry, power requirements along with the significant threshold voltage of even the most state-of-the-art diodes. DC Triboelectric Nanogenerators (DC-TENG) have emerged as a direct powering solution based on the triboelectric effect, similar to the conventional AC-TENG devices. Such devices incorporate specific strategies like electrostatic breakdown, mechanical switching, and dynamic Schottky junction to generate a unidirectional current. Based on these strategies, different topologies for DC-TENG devices have been developed by researchers over time. Since its inception in 2014, the study on DC-TENG has rapidly emerged and expanded. This article reviews the progress made in association with DC-TENG mechanisms and topologies, theoretical analysis, comparative study, and applications. This article also examines the challenges, recent advancements, and future research prospects in this domain.

The vast proliferation of wearables and smart sensing devices in the last decade has created an immense demand for new and efficient powering solutions. The research focus has shifted towards developing simple, cost-effective, flexible device topologies capable of capturing kinetic energy associated with the human body. Piezoelectric and Triboelectric mechanisms are widely employed to convert biomechanical energy to electrical power due to their inherent merits in terms of affordable designs and high energy conversion efficiencies. In this work, we propose a flexible hybrid generator topology incorporating both piezoelectric and triboelectric mechanisms to achieve high electrical output from human motion. To enhance the efficiency and obtain a symmetric output, dual triboelectric generators are employed, which generate time-multiplexed output across the same set of electrodes. The device displays a characteristic ability to distinguish between different body movements as its output depends on the contact area as well as the pressure generated by the motion. This creates numerous avenues for employing the device in self-powered tactile sensing applications. The unique single substrate design makes the device robust and increases its longevity. The V-shaped prototype having an active area of 3.5 cm × 2 cm, is tested under a wide range of biomechanical stimuli, including touching, tapping, and pressing motions. The practical applications of the proposed device as an add-on patch on fabrics, as an in-sole device, and for powering commercial electronics are demonstrated. Apart from this, the reported generator can also fuel low-power devices from various other day-to-day human activities.

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In this work, we present a highly effective and scalable design strategy of a triboelectric-piezoelectric hybrid array of three cantilever beams stacked over each other (wideband operation regime), which can also be rotated around their mean position to vibrate freely without impacting any other layer (narrowband operation regime). Contrary to a unique frequency response exhibited by conventional devices, the proposed device can switch between narrowband and wideband frequency responses around different central frequencies. This work elaborately discusses the frequency response of mechanical stopper-based PEG and TEGs at varying gap lengths, excitations, and resonant frequencies, and the design of the hybrid array is optimized based on it. The performance of this device is characterized using simulation analysis and experimental validation. Experimentally, the device generates net power greater than 0.3 µW (Piezoelectric) and 0.4 µW (Triboelectric) continually between the frequencies of 30 to 60 Hz in the wideband operation regime and output power of 0.81 µW, 0.65 µW, and 0.62 µW at 18, 27, and 36 Hz in the narrowband operation regime under mechanical excitation of 0.75g. The remarkable performance of the device at different frequency ranges demonstrates its potential in various harvesting and sensing applications.

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