Wearable devices are drawing increasing attention in both academia and industry in that they can offer unprecedented information related to human health in real-time and human–machine interactions, which is expected to enable a paradigm shift in the digital world. For this shift to occur, green and sustainable energy technology for powering flexible wearable devices is a roadblock. This paper is dedicated to reviewing cutting-edge wearable power generation methodologies, for which we discuss their pros and cons, underlying physics, and general design/evaluation criteria. Sensor types, materials, processing technology, power consumption, and methods of testing the stretchability and flexibility of wearable devices are also summarized. Based on application scenarios in healthcare, industrial inspection, structural monitoring, armed forces and consumer electronics, an integrated system architecture of wearable, flexible systems is presented. Finally, future perspectives of wearable technologies are outlined by covering the aspects of all-in-one printable wearable electronics, fiber and textile electronics, self-powered self-awareness wearable systems, hybrid-integrated Systems on a Chip (SoC) for flexible electronics, and Internet of Things (IoT)-enabled self-contained systems towards full life cycle monitoring.

Power generation for wearable systems

A power conversion device includes a power switching circuit that supplies AC voltages generated between switching elements operating as upper arms and switching elements operating as lower arms, and a control circuit that generates and supplies to the driver circuit signals for controlling the switching operation of the switching elements by a PWM method in a first operational region in which frequency of an AC power to be outputted is low, and that generates and supplies to the driver circuit signals for controlling the switching operation of the switching elements at timings based upon the phase of the AC power to be outputted in an operational region in which the frequency of the AC power to be outputted is higher than in the first operational region.

Power Conversion Device

A combined optical and electrical transmission assembly includes a combined optical, electrical and power cable having an optical fiber, electrical wiring and a power line combined therein or a combined optical and electrical cable having an optical fiber and electrical wiring combined therein, and a combined optical and electrical transmission module that includes an electrical-to-optical conversion unit having a laser for converting electrical signals to optical signals and a driving IC for driving the laser, and/or an optical-to-electrical conversion unit having a photodiode for converting optical signals to electrical signals and an amplification IC for amplifying electrical signals from the photodiode. The combined optical and electrical transmission module is connected to both ends of the combined optical, electrical and power cable or the combined optical and electrical cable. The combined optical and electrical transmission modules are each connected with an electrical cable for transmitting electrical signals with an external device and a power cable for transmitting power. The length of the power cable is shorter than that of the electrical cable.

Combined optical and electrical transmission assembly and module

An optoelectronic module for converting and coupling an information-containing electrical signal with an optical fiber including a housing having an electrical input for coupling with an external cable or information system device and for transmitting and receiving information-containing electrical signals over such input, and a fiber optic connector adapted for coupling with an external optical fiber for transmitting and receiving an optical signal; an electro-optic subassembly coupled to the information containing electrical signal and converting it to and/or from a modulated optical signal corresponding to the electrical signal; means disposed in the housing for determining the electrical and/or optical protocols or packet formats in use; and a processor for adapting the module to utilize the electrical and optical protocol or packet format.

Reconfiguration and Protocol Adaptation of Optoelectronic Modules and Network Components

A novel three-dimensional (3D) electret-based micro power generator with multiple vibration modes has been developed, which is capable of converting low-level ambient kinetic energy to electrical energy. The device is based on a rotational symmetrical resonator which consists of a movable disc-shaped seismic mass suspended by three sets of spiral springs. Experimental analysis shows that the proposed generator operates at an out-of-plane direction at mode I of 66 Hz and two in-plane directions at mode II of 75 Hz and mode III of 78.5 Hz with a phase difference of about 90°. A corona localized charging method is also proposed that employs a shadow mask and multiple discharge needles for the production of micro-sized electret array. From tests conducted at an acceleration of 0.05 g, the prototype can generate a maximum power of 4.8 nW, 0.67 nW and 1.2 nW at vibration modes of I, II and III, respectively. These values correspond to the normalized power densities of 16 µW cm−3 g−2, 2.2 µW cm−3 g−2 and 4 µW cm−3 g−2, respectively. The results show that the generator can potentially offer an intriguing alternative for scavenging low-level ambient energy from 3D vibration sources.

https://iopscience.iop.org/article/10.1088/0960-1317/24/6/065022/pdf

A three-dimensional electret-based micro power generator for low-level ambient vibrational energy harvesting

We developed a compact vibration-driven electret generator that excelled at a power output. It succeeded in the operation of wireless sensor modules only on electricity from electret generators. This electret generator can supply enough power to operate a wireless sensor module without an external power source. It was necessary for enabling this operation to enhance the power output of the electret generator. We enhanced the power output by decreasing the parasitic capacitance. To decrease the parasitic capacitance, we fabricated a collector substrate using concave electrodes. We decreased it from 25 to 17 pF. As a result, the power output from our generator was enhanced from 40 to 100 µW considerably at an acceleration of 0.15 g (1.47 m s−2) and a resonance frequency of 30 Hz.

https://iopscience.iop.org/article/10.1088/0960-1317/21/10/104004/pdf

Power output enhancement of a vibration-driven electret generator for wireless sensor applications

A light transmission module includes a light transmission path for transmitting light, an optical element including a light emitting and receiving surface for optically coupling with the light transmitted by the light transmission path, and being formed with a light emitting and receiving point having a function of photoelectric conversion and an electrode pad on the light emitting and receiving surface. The light transmission module further includes a substrate mounted with the optical element and an electrical wiring and an electrical connecting member for electrically connecting the electrode pad and the electrical wiring. The substrate includes a wiring exposed surface where the electrical wiring is exposed. The electrical connecting member is made of solidified object of a liquid conductive material arranged to contact the electrical wiring, which is exposed at the wiring exposed surface, and the electrode pad.

Optical transmission module, electronic device and method for manufacturing optical transmission module

A detection device for detecting a state of electric power has a first current transformer that measures a first current on a first power line side of a connecting point between a first power line derived from a commercial power supply and a second power line derived from a power generation device which supplies electric power equal in frequency to the commercial power supply, a second current transformer that measures a second current on a second power line side of the connecting point, a first calculation unit that calculates a decision value based on a product of a measured value of the first current and a measured value of the second current, and a detection unit that detects a power flow direction of electric power of the first power line based on the decision value.

Detection device and method, and program

A voltage converting circuit includes a plurality of first capacitors that are charged by a power source, a second capacitor, connected in parallel to the plurality of first capacitors, which is able to be charged to a voltage that is supplied to a load circuit, and a plurality of switching circuits, provided in such a way as to correspond to the plurality of first capacitors, each of which switches states of connection between its corresponding first capacitor and the second capacitor. The first capacitors are sequentially connected to the second capacitor through the corresponding switching circuits as charging voltages of the first capacitors reach a predetermined connection voltage that is higher than a charging voltage of the second capacitor so that the first capacitors are not short-circuited with each other.

Voltage conversion circuit and electronic equipment

A connection member electrically connects an optical element configured to convert an electric signal to an optical signal or to convert an optical signal to an electric signal, a first substrate including an incident/releasing port of an optical transmission path for an optical signal at least one end portion thereof, and a second substrate to each other. The optical transmission path is optically coupled with the optical element to transmit the optical the connection. The connection member includes a connection unit connected to the second substrate and a holding unit having elasticity and holding the first substrate. The holding unit is provided with an electrode at a connecting position to the first substrate, and the holding unit holds the first substrate by connecting the first substrate to the electrode.

Hiroshi Sameshima

Papers

Power output enhancement of a vibration-driven electret generator for wireless sensor applications

Optical transmission module, electronic device and method for manufacturing optical transmission module

Detection device and method, and program

Voltage conversion circuit and electronic equipment

Optical transmission module, connecting part, and electronic device having optical transmission module