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Energy harvesting (EH) offers several benefits for integrating compact low-power wireless nodes into emerging microscale applications, such as the Internet of Things (IoT), wearable and implantable medical diagnosis, and so on. In this study, an optimum approach is developed to design an adaptive high-performance rectifier for EH wireless charging. The rectifier architecture is based on a simple voltage doubler configuration. The structure can be extended to achieve the desired output voltage level without altering the impedance matching network. The voltage doubler stage is duplicated symmetrically to increase the voltage to the desired levels. The matching circuit employs a simple L-network that consists of a series-inductive branch and a shunt LC branch. To verify the logical operation of this approach, two rectifier prototypes were developed, and the performance of each structure was separately evaluated and compared. The comparison shows good agreement between the simulation and measurement results of the two configurations. For example, the peak measured efficiency is 65% at an RF input power of 10 dBm, and the simulated value is 70% with a terminal load of 3.3 $\text{k}\Omega $ . The main objective of the proposed design is to enhance the output voltage without changing the matching network.

We developed a thermo-optic effect based silica optical phased array (OPA) chip and evaluated its tunability of phases of lightwaves. The THz waves, whose phases are controlled by the OPA chip, are generated from four arrayed uni-travelling-carrier photodiodes (UTC-PDs) based on heterodyne photomixng. Meanwhile, the UTC-PDs, which integrated with $4\times 4$ slot antennas, are fabricated on a monolithic InP substrate chip for 300-GHz wave beam combining and steering. Through the optoelectronic THz-wave phase control, the feasibility of 300-GHz beam continuous steering is successfully demonstrated in a range of 50°.

Tunable microwave devices have the benefits of added functionality, smaller form factor, lower cost, and lightweight, and are in great demand for future communications and radar applications as they can extend the operation over a wide dynamic range. Current tunable technologies include several schemes such as ferrites, semiconductors, microelectromechanical systems (MEMS), and ferroelectric thin films. While each technology has its own pros and cons, ferroelectric thin film-based technology has proved itself as the potential candidate for tunable devices due to its simple processes, low power consumption, high power handling, small size, and fast tuning. A tunable Composite Right Left-Handed Zeroth Order Resonator (CRLH ZOR) is introduced in this chapter and it relies mainly on the latest advancement in the ferroelectric materials. It is common that for achieving optimum performance for the resonant structure, this involves the incorporation of an additional tuning by either mechanical means (i.e. with tuning screws) or other coupling mechanisms. The integration between electronic tuning and High-Temperature Superconducting (HTS) components yields a high system performance without degradation of efficiency. This leads not only low-loss microwave components that could be fine-tuned for maximum efficiency but will provide a tunable device over a broadband frequency spectrum as well. The dielectric properties of the ferroelectric thin film, and the thickness of the ferroelectric film, play a fundamental role in the frequency or phase tunability and the overall insertion loss of the circuit. The key advantages of using ferroelectric are the potential for significant size-reduction of the microwave components and systems and the cabibility for integration with microelectronic circuits due to the utilization of thin and thick ferroelectric film technology. In this chapter, ZOR is discussed and the conceptual operation is introduced. The ZOR is designed and simulated by the full-wave analysis software. The response is studied using electromagnetic characteristics with the applied electric field, ferroelectric thickness, and the operating temperature.

We have proposed an optically controlled THz power tuning method based on THz wave interference. Through interfered THz waves at the T-junction transmission line, adjustment of the THz power is achieved, and tuning control is attained by varying the optical time delay of the beat-note lightwaves. To demonstrate and verify THz power tuning with an optical delay line, we have also fabricated a monolithic chip on an InP substrate, which integrates arrayed uni-traveling-carrier photodiodes and a planar slot antenna array for 300GHz wave generation. The experimental results reveal that the power transmission of this THz power tuner can be continuously adjusted with a wider tuning range than 7 dB at 300 GHz band. It should be a promising solution for the integration of compact THz wave planar photonic circuits.

(1) Background: This work presents a high-efficiency, high sensitivity, compact rectifier based on a dual-band impedance matching network that employs a simple and straightforward T-matching circuit, for sub-1 GHz license-free applications. The development of a low-cost RF energy harvester dedicated to the ISM bands is introduced. The proposed rectifier design is optimized to operate at the sub-GHz frequency bands (0.9 to 2.4 GHz), specifically those at the ISM 900 and 2400 MHz. The motivation for this band is due to the low attenuation, well-known fundamental electromagnetic theories and background, and several wireless communications are emitting at those bands, such as RFID (2). Methods: The rectifier design is based on a simple, balanced single-series diode connected with a T-matching circuit. The dual-band performance is achieved by deploying reactive elements in each branch. The full mathematical analysis and simulation results are discussed in the manuscript. (3) Results: The rectifier can achieve a 80 MHz bandwidth around 920 MHz frequency and 200 MHz around the higher band 2.4 GHz. The resultant conversion efficiency level is maintained above 45% at both bands with a peak efficiency reaches up to 70% at the higher band. The optimum terminal load attached to the circuit at which the peak efficiency is achieved, is given as 4.7 kΩ. (4) Conclusion: Due to the compactness and small footprint, simple design, and simple integration with microwave circuits, the proposed rectifier architecture might find several potential applications in wireless RF energy harvesting.

As fossil fuel levels are exhausted, building a more sustainable world is an issue that is coming to the fore as a crucial consideration in the development of new technology. The energy needs of the planet's population are immense, and an environmentally friendly source of energy is desperately needed. Energy harvesting from renewable sources is not a new concept - windmills have been around since the first century - but the desire to harness renewable energy has intensified. Energy harvesting technology is the term given to technology used for collecting unused energy from the surrounding environment and converting it into electrical power. Solar, wind and hydroelectric power are perhaps the best-known of these technologies. However, there are many other forms of energy that are under developed and hold much potential for powering the future. These include vibration, pressure, heat and temperature difference. While large-scale power generation cannot be realised using these sources due to their low levels, devices with low power demands may be able to harness such energy sources, potentially eliminating the need for an external power source. Dr Haruichi Kanaya at Kyushu University is leading a team investigating wireless technology.

A CPW-fed circular polarization reconfigurable antenna is proposed in this paper. The antenna consists of two symmetrically placed inverted L-shaped slots. By using a T-type bias device to change the bias states of two PIN diodes which connect the two slots with the feed port respectively, right-hand circular polarization (RHCP) and left-hand circular polarization (LHCP) can be realized accordingly. For both states, the measured −10 dB impedance bandwidth is 5.78–5.96 GHz, while the measured 3 dB axial ratio bandwidth is 5.64–5.91 GHz (4.7%), both the bandwidths can cover the 5.8 GHz ISM band. By using floating ground and reflector board to enhance the front to back ratio of the antenna, 6.84 dBi measured gain can be realized at 5.8 GHz.

On-chip distributed transmission line resonators in CMOS technology have become the interest of research subjects recently (Ono et al. 2001; Umeda et al., 1994; Kanaya et al., 2006; Wolf, 2006) because of their size which becomes more compact, as the frequency of application increases. Among the various transmission lines, coplanar waveguide (CPW) has more engineering applications (Toyoda, 1996; Civello, 2005) because it is easy to fabricate by LSI technology since the signal line and ground plane exist on the same plane so that no via holes are required for integrating active components such as transistors on Sisubstrate (Toyoda, 1996). The applications of the CPW were reported for many on-chip LSI components. The CPW was exploited as an inductor and used to design a conventional-type matching circuit for LNA (Ono et al., 2001) in microwave-band frequency, and they are most popular in monolithic microwave integrated circuit (MMIC) (Umeda et al., 1994). However, the application of CPW lines as an inductor takes larger space than the conventional spiral inductors (Umeda et al., 1994). Some of the present authors have also implemented the onchip CPW impedance-matching circuit for a 2.4 GHz RF front-end (Kanaya et al., 2006) and for 5GHz band power amplifier (Pokharel et al., 2008) using impedance inverters. In designing the matching circuits using impedance inverters and quarter wavelength resonators realized by on-chip CPW (Kanaya et al, 2006; Pokharel et al., 2008) the size of the matching circuits becomes compact thus reducing the chip area by about 30% than using spiral inductors for 2.4GHz-band applications and 40% for 5 GHz-band applications. However, the applications of on-chip CPW resonators in designing other components such as a voltage-controlled oscillator (VCO) have not been reported yet. A conventional VCO consists of a LC-resonator to produce an oscillation at the frequency band of interest, and this LC-resonator may be replaced by a CPW resonator. Such possibilities are investigated in this paper. In a conventional VCO, the performance such as phase noise of the VCO depends on the quality (Q) factor of the LC resonator. Usually, a spiral inductor is used in 17

The development of a robust and independent wireless sensor node becomes a demand for modern wireless communication. The current study proposes wireless power transfer over a long distance to feed a ZigBee wireless module, which is connected to various environmental sensors. The rectenna design is based on a compact Vivaldi antenna integrated with a multilevel RF -DC rectifier. The antenna provides end-fire radiation with a realized gain of 1–2 dBi at 920 MHz. The RF -DC rectifier is stacked to boost output voltage to higher levels sufficient for supplying the ZigBee module. The demonstration was conducted at a long distance of 9–10 m; the received output power is enough to start-up the communication and keep sustainable data transmission. The data is taken and processed at a remote PC. The measurements were visualized and introduced to illustrate the proposed real application clearly.

Microcomputers mounted on communication modules in IoT devices have low impedance and poor efficiency when the power supply voltage is low. In a weak power supply by energy harvesting, power consumption increases due to deterioration of efficiency at low voltage. Therefore, the DC voltage required to operate the ZigBee module, etc., cannot be obtained, causing a severe problem that startup cannot be performed. To solve the problem, we realized a startup management circuit to cut off the power supply to the ZigBee module until the DC voltage reaches the microcomputer's operating voltage. The proposed system starts at around 2.3 V by using the rectenna operating at 920 MHz band RF signal.

Cultivated strawberries are a popular fruit in the world. It is essential to understand the water management to improve the strawberry yield in the greenhouse. This work aims to build a cost-effective battery less sensor platform to clarify the relationship between root growth and water management by monitoring the soil moisture content of strawberry seedlings in pots in real-time.

In Japan, the construction of extensive infrastructure such as roads, railways, airports, energy plants, and so on, became popular from the 1960s when the period of high economic growth began, and high-level investments continued for about 40 years. Recently, infrastructure serious accidents have occurred, which is caused by aging or lack of inspection are of significant social concern. Therefore, as the population declines in the future, infrastructure monitoring using wireless sensor networks (IoT, Internet of things) is an urgent issue. On the other hand, the power supply is indispensable for driving the sensor device and transferring data. In this research, focusing on microwaves (electromagnetic waves) radiated from broadcasting and/or telecommunication that have been rarely reused, a battery-less infrastructure monitoring sensor platform that uses electromagnetic waves as a power source is realized. The proposed system is composed of a circularly polarized wideband planar antenna, rectifier circuit with impedance matching circuit, sensor module and Bluetooth low energy (BLE) module. For the feasibility study, the temperature and humidity sensors are attached on the surface of a concrete block, which is the model of the infrastructure. The 920 MHz RF signal is injected into the receiving antenna as a power source. The data of the temperature and humidity are transmitted to the smartphone or laptop computer at every 2-s interval. We can obtain the battery-less infrastructure monitoring sensor platform.

Landslides have been occurring frequently because of rainfall, which leads to serious consequences, often plugging rivers, disrupting transportation, communication, and other lifeline projects and posing a serious threat to people's life and property. Therefore, effective early warning system for rainfall-induced landslide is particularly important. This research presented the development of early warning system that includes soil moisture sensor, temperature sensor, and data transmission system. Some tests were carried out to evaluate the feasibility of the developed system under different water contents. Test with different sample depths under the same water content was also used to verify the accuracy of this system. The results show that, the sensitivity of the sensor is affected by the initial state, and it takes about 10–20 min to reach the stable measurement state. With the increase of water content in soil samples, the resistance value obtained by the system decreases accordingly, which is consistent with theoretical results. The tests of early warning system also worked well under different depths of the same soil sample. The development of the current warning system is the basis for predicting landslides in the future, and lower development costs and accurate test results make it possible to be widely adopted to both the developed and developing nations.