This article presents a new application field of a giant magneto-impedance (GMI) sensor. It shows valuable findings for the GMI sensor on the possibility of a new receiving element in magnetic field communication. The proposed GMI sensors serve as antennas and mixers in receiver systems. They have the advantage of being easily implemented and in terms of mass production and manufacturing processes due to the manufacture base on a printed circuit board (PCB). Their smaller size, lower cost, and higher sensitivity have more advantages than conventional magnetic sensors, such as the magneto-inductive, anisotropic magneto-resistive, and giant magneto-resistive sensors. Two types of PCB-based GMI sensors are proposed. The first type of GMI sensor is directly wound around the solenoid-shaped pickup coil onto an alumina insulation tube inserted with an amorphous microwire. The second type of GMI sensor has a patterned pickup coil that does not require the winding of the coil, similar to the patterned pickup coil of a micro electro-mechanical system-based GMI sensor. This GMI sensor provides a new geometry that can be easily manufactured with two PCB substrates. The proposed GMI sensors achieve the equivalent magnetic noise spectral density to the high-sensitivity characteristics of the pT/ $\surd $ Hz level. The equivalent magnetic noise spectral density of 1.5 pT/ $\surd $ Hz at 20.03 MHz is obtained for the first type of GMI sensor, and 3 pT/ $\surd $ Hz at 3.03 MHz is achieved the second type. The analyzed results of the bandwidth and the channel capacity for the two types of GMI sensors are acceptable. This first analysis confirms the possibility of the implementation of GMI sensors in magnetic field communication. The results of this experiment confirm the high performance of the proposed GMI sensors and their applicability in magnetic field communication. The detailed experimental results of the proposed GMI sensors are presented and discussed.

In this paper, we present the results of a preliminary study on the self-powered autonomous wireless sensor node by using thermoelectric energy generator based on Silicon (Si) thermoelectric legs, energy management integrated circuit (EMIC), Radio Frequency (RF) module with a temperature and humidity sensor, etc. A novel thermoelectric module structure is designed as an energy generator module, which consists of 127 pairs of Silicon legs and this module is fabricated and tested to demonstrate the feasibility of generating electrical power under the temperature gradient of 70K. EMIC has three key features besides high efficiency, which are maximum power point tracking (MPPT), cold start, and complete self-power operation. EMIC achieved a cold start voltage of 200 mV, peak efficiency of 78.7%, MPPT efficiency 99.4%, and an output power of 34 mW through only the Thermoelectric Generator (TEG) source. To assess the capability of the device as a small scale power source for internet of things (IoT) service, we also tested energy conversion and storage experiments. Finally, the proposed sensor node system which can transmit and monitor the information from the temperature and humidity sensor through the RF module in real time demonstrates the feasibility for variable applications.

Radio reception relies on the medium which determines the propagation characteristics of the electromagnetic fields carrying the information. The permittivity varies greatly depending on the medium, but it remains nearly constant, except when magnetic materials are used. For this reason, magnetic fields, typically affected by permeability, can be utilized in microwave challenging environments. In this paper, a new approach based on the giant magnetoimpedance (GMI) effect is presented. The proposed GMI-based receiver has an effective double-superheterodyne topology, where “effective” means that the receiver actually has a single mixer but appears to have added a virtual mixer due to the GMI effect. The magnetic field-to-voltage conversion ratio (MVCR), the spurious free dynamic range (SFDR) and the receiver sensitivity are characterized, and from these results the optimal operating conditions of the fabricated receiver are obtained. Additionally, wireless digital communication using on-off keying (OOK) is demonstrated and transmitted and received waveforms are compared, with the final demodulation result of the receiver showing that the transmitted digital data are precisely extracted.

A capacitive‐type MEMS acoustic sensor with a planarised TiN/plasma‐enhanced chemical vapour deposition ‐Si ₃ N ₄ /TiN diaphragm based on a polyimide sacrificial layer is presented. The multi‐layer diaphragm has the effective residual stress of +31.5 MPa. Furthermore, this sensor features a 21% lower parasitic capacitance and a 56% lower air‐gap resistance in comparison with those of a sensor fabricated without planarisation. Five photomasks were used. In addition, to evaluate the frequency response, both an effective capacitance model and an equivalent circuit model equipped with a voltage‐controlled voltage source are newly proposed and compared with conventional models. The open‐circuit sensitivity is modelled to −45.4 dBV/Pa at 1 kHz with 9.6 V, indicating a difference of 0.9 dB in comparison with the open‐circuit sensitivity of the conventional model.

This paper presents a practical low-power, low-frequency magnetic induction (MI) transceiver based on symmetrical gaped two-loop antennas with an empirical circuit model for wireless underground communication. Because of the quasi-two-dimensional loop antennas for the transmitter (Tx) and the receiver (Rx), the tailored hardware platform is not only simple, but can be readily extended to a mutually orthogonal 3-D scheme. Through a mixed model of actual measurement data and theoretical parameters, we developed the two-loop antenna with the space of the antenna radius optimized for energy efficiency. The Tx power almost doubles that of the single Tx one, which provides channel expansion as well as system stability in terms of the Tx current level. Accordingly, the Rx signal is considerably increased by 9.5 dB in contrast with a typical single-Tx single-Rx configuration. Moreover, we used empirical-based modeling for a reliable electrical model. The empirical mutual inductance, which was modeled in a 25 m corridor, resulted in a channel correction factor of 0.86, showing that the signal intensity was reduced by 14% in the underground corridor compared to the free space. A maximum range of 68 m under a SNR of 9.5 dB and a path loss of 100.7 dB on a load of 50 Ω at 34.5 dBm were predicted from the model. In addition, this study confirmed the system feasibility by a SNR of 8.7 dB in a practical lossy environment between two floors, where its value was converted into a MI channel at a distance of 70 m in the underground corridor.

In this paper, we present a concave-patterned TiN/PECVD-Si ₃ N ₄ /TiN diaphragm micro-electro-mechanical system (MEMS) acoustic sensor based on a polyimide sacrificial layer. The use of the spin-coated polyimide eliminates the additional Al pad process of conventional device fabrication due to simple O ₂ ashing to release the sacrificial layer, simplifying the photolithography process. Also, to adjust the acoustic sensor for a bottom-ported package, its diaphragm was implemented to be placed over the back-plate. The TiN/PECVD-Si ₃ N ₄ /TiN multi-layer diaphragm was formed with the stress controllability of PECVD-Si ₃ N ₄ from −162 MPa to +109 MPa. Furthermore, a parallel-plate capacitance model on the basis of an approximately linearized electric field method (ALEM) is proposed to evaluate the capacitance of two plates. The modelled capacitance showed less than 3.7% error in FEM simulation, demonstrating the validity of the proposed model. At a zero-bias voltage, the effective intrinsic and parasitic capacitances in the active area were 1.656 pF and 0.388 pF, respectively. Moreover, with a pull-in analytical model by using ALEM, the effective tensile stress for the diaphragm was extracted to +31.5 MPa, where the pull-in voltage was 10.7 V. In succession, the dynamic response for the open-circuit sensitivity was modelled with an equivalent circuit model based on lumped parameters. The measured open-circuit sensitivity of −45.1 dBV Pa ⁻¹ at 1 kHz with a bias of 9.6 V was only slightly different from the modelled sensitivity of −45.0 dBV Pa ⁻¹ . Thus, these results demonstrate that the proposed sensor is suitable for a front-end voice capture module.