Compact Wireless Research Articles

Optimization for Compact and High Output LED-Based Optical Wireless Power Transmission System

Optical wireless power transmission (OWPT) is a technology that supplies energy remotely. Due to the great advantages of long transmission distances, high directionality, no electromagnetic interference noise, and loose safety regulations, light emitting diode (LED) based OWPT systems become appropriate candidates for powering various applications, especially for the Internet of things (IoT). In this paper, improved LED-OWPT systems are proposed based on a collimation scheme for optimizing the system dimension and output. In a single LED configuration, the system dimension is compressed by 46% while the high transmission efficiency is maintained. As for the LED-array system, the dimension is compressed by 56%, and the output is enhanced by 40%. In the experiment, a high electricity output of 532 mW is achieved at 1 m transmission distance. In addition, the effect of misalignment between LED and lens and the potential of long-distance transmission are clarified in the LED-array OWPT system.

Miniaturized design of coupled bi‐element array antenna using sequential inductive and interdigital capacitive circuits

An electrically small array antenna (ESAA) is proposed including two tightly coupled half-monopole antennas (TCMAs) as a single radiation element with two excitation ports. By properly using two consecutive inductive-capacitive loadings in the conventional bi-element monopole, total electrical length of the resonant frequency is increased, significantly and then the frequency migrates from 4 to 0.5 GHz as a frequency sample (i.e., an 88% reduction). This combination consists of several stubs on each of the monopoles and an interdigital capacitor designed in the dead space between them so that only a compact overall size of 0.02 λ 0 × 0.035 λ 0 at 0.5 GHz is occupied. The studies on different subsections of the TCMA are done and additionally an extended circuit model and simplified one are presented which agrees well with simulation. Due to the fully symmetrical design and elimination of the cross currents, a stable omni-directional radiation pattern with high polarization purity and radiation efficiency over 20 dB and 78% is achieved, respectively. An implemented prototype exhibits an improved impedance matching and measured 10 dB S11 bandwidth of 34% which are in good agreement with simulation. The proposed TCMA can be a good candidate for compact wireless systems such as RFID sensors.

Compact, Reflectionless Band-Pass Filter: Based on GaAs IPD Process for Highly Reliable Communication

For highly reliable and compact communication of front-end modules, a miniaturized reflectionless band-pass filter, based on the GaAs integrated passive device (IPD) process, is proposed in this work. The stop-band signal absorption rate of the filter can reach more than 90% and greatly reduce the influence of electromagnetic interference for sensitive devices. First, a circuit topology of reflectionless filter is proposed. Then, the miniaturized reflectionless band-pass filter is designed and fabricated based on GaAs IPD process with a compact size of only 0.85 mm × 1.33 mm × 0.09 mm (0.011λ × 0.018λ × 0.001λ). The filter operates at frequency ranging from 3.3 GHz to 4.5 GHz for 5G communication, the insertion loss (S21) is less than 3 dB, the return loss in the passband (S11) is over 15 dB, the stopband return loss (S11) is over 10 dB, and the out-of-band suppression (S21) reached 19 dB. All the measured results are in good agreement with the simulated results. It shows great potential in the process of designing highly reliable and compact monolithic integrated wireless modules and wearable electronics.

Printed Closely Spaced Antennas Loaded by Linear Stubs in a MIMO Style for Portable Wireless Electronic Devices

An easy-to-manufacture and efficient four-port-printed Multiple Input Multiple Output (MIMO) antenna operating across an ultra-wideband (UWB) region (2.9–13.6 GHz) is proposed and investigated here. The phenomenon of the polarization diversity is used to improve the isolation between MIMO antenna elements by deploying four orthogonal antenna elements. The proposed printed antenna (40 × 40 × 1.524 mm3) is made compact by optimizing the circular-shaped radiating components via vertical stubs on top of the initial design to maximally reduce unwanted interaction while placing them together in proximity. The measurements of the prototype MIMO antennas corroborate the simulation performance. The findings are compared to the recent relevant works presented in the literature to show that the proposed antenna is suitable for UWB MIMO applications. The proposed printed UWB MIMO antenna could be a good fit for compact portable wireless electronic devices.

Development of wireless SHM sensor node for in-flight real-time monitoring using embedded CNT fiber sensors

Structural health monitoring (SHM) is essential for composite unmanned aerial vehicles (UAVs). Additionally, because UAVs are extremely sensitive to weight and volume, the minimal addition of weight and volume by the SHM system is crucial. Therefore, we proposed a compact and lightweight wireless SHM sensor node and an embedded carbon nanotube (CNT) fiber sensor for in-flight SHM of UAVs. The wireless SHM sensor node was composed of an analog sensing circuit, wireless microcontroller unit, and analog low pass filter. The small diameter CNT fiber sensor was developed to be easily embedded inside composite structures and to enhance their structural properties while performing as an SHM sensor. Glass composite skin with embedded CNT fiber sensors composed of ultra-high-molecular-weight polyethylene, polyurethane, CNT, and carbon black were installed in the aircraft. For comparison, a strain gauge attached at the center of a long CNT fiber sensor was also used during in-flight measurement. In-flight strain measurements from both the CNT fiber sensor and the strain gauge were continuously transmitted to the ground station and were compared with the flight data. Furthermore, an impact tester was installed inside the wing to simulate impact during flight, and in-flight impact measurements by the CNT fiber sensor were demonstrated.

Energy-Efficient Integrated Circuit Solutions Toward Miniaturized Closed-Loop Neural Interface Systems.

Miniaturized implantable devices play a crucial role in neural interfaces by monitoring and modulating neural activities on the peripheral and central nervous systems. Research efforts toward a compact wireless closed-loop system stimulating the nerve automatically according to the user's condition have been maintained. These systems have several advantages over open-loop stimulation systems such as reduction in both power consumption and side effects of continuous stimulation. Furthermore, a compact and wireless device consuming low energy alleviates foreign body reactions and risk of frequent surgical operations. Unfortunately, however, the miniaturized closed-loop neural interface system induces several hardware design challenges such as neural activity recording with severe stimulation artifact, real-time stimulation artifact removal, and energy-efficient wireless power delivery. Here, we will review recent approaches toward the miniaturized closed-loop neural interface system with integrated circuit (IC) techniques.

Compact Wireless Motor Drive Using Orthogonal Bipolar Coils for Coordinated Operation of Robotic Arms

This article proposes and implements a compact wireless motor drive using orthogonal bipolar coils for the coordinated operation of robotic arms. The key is to orthogonally integrate two bipolar coils to form a compact magnetic coupler (CMC), while each CMC serves as the transmitting coil and receiving coil, respectively. Instead of adopting the one-to-many coil structure and operating at multiple frequencies, in this article, two bipolar coils in the CMC are mutually decoupled and separately energized to drive two permanent magnet dc (PMDC) motors. As such, the wireless and selective motor drives can be achieved via the shared power-transfer channel at a single resonant frequency. All controls and switches are concentrated at the transmitter so that the receiver is entirely sealable. Accordingly, the coordinated operation of robotic arms can be realized with the high integration and no electrocution. Theoretical calculations and experimental results are given to validate the flexibility and feasibility of the proposed system.

Ultralow Power and Compact Backscatter Wireless Device and Its SDR-Based Reading System for Environment Monitoring in UHF Band

In this letter, we demonstrate the possibility to design a compact and ultralow power wireless node for environment sensing operating in the UHF band at 868 MHz. The wireless device is based on an ultralow power 8 b microcontroller associated with a digital temperature and relative humidity sensor. It communicates according to the backscattering principle to a software-defined radio (SDR) controlled by a graphical user interface developed in GNU Radio. The wireless node features a power consumption of 5 μA under 1.8 V, which is good enough for communicating data with a packet error rate of 10% at 110 b/s over a range of 30 m in an indoor environment for a transmitting power of 20 dBm. The design of the wireless node and its SDR-based detection system is validated with wireless measurements both in an anechoic chamber and in the indoor environment.

Split Ring Resonator-Based Bandstop Filter for Improving Isolation in Compact MIMO Antenna.

The ever-growing expectation for high data rates has led to the introduction of multiple-input multiple-output (MIMO) technologies to wireless connectivity. Such a system requires an MIMO antenna with high isolation. At the same time, the MIMO dimension should not be compromised for achieving high isolation. Thus, isolation techniques that do not allow an increase in dimension need to be fostered for MIMO antenna design. In this paper, a novel low-profile, miniaturized MIMO antenna with high isolation was developed considering a split ring resonator (SRR)-based bandstop filter as a decoupling network. The bandstop filter was designed with a unit cell split ring resonator structure and was deployed between two closely spaced monopole MIMO antenna elements to obtain isolation as high as 39.25 dB at 2.61 GHz. Two open-circuit stub lines were attached with the MIMO feeding network to achieve good impedance matching at resonance frequency. The proposed antenna exhibited a peak gain of 3.8 dBi and radiation efficiency of 84%. It had a low envelop correlation coefficient (ECC < 0.12), high diversity gain (DG > 9.95 dB), low mean effective gain ratio (MEG 1/MEG 2 < 0.05 dB), and low channel capacity loss (CCL < 0.042 bits/s/Hz) at resonance frequency. The overall antenna dimension was restricted to for its easy integration in compact wireless devices.

Design of Dual Frequency Coupled Resonators Using DGS and Microstrip Resonators for Dual Band WPT Applications

This paper introduces a new design for a highly efficient and more compact size dual frequency wireless power transfer (WPT) system, which can operate at both 0.65 GHz and 1.56 GHz bands. The idea of the structure depends on designing a symmetrical system containing Tx and Rx. Each Tx and Rx has a feed line on the top layer with two stubs; each stub has different dimensions than the other one. The bottom layer contains two C-shaped defected ground structures (DGS). By changing the dimensions of one stub, the frequency resonance corresponds to this stub is changed without any change on the other resonance. The system has a size of 20 × 20 mm2. Further, the system achieves efficiencies of 72 % and 89 % at 0.65 GHz and 1.56 GHz, respectively with a transmission distance of 8 mm. The proposed dual frequency WPT is implemented and verified. Good concurrences among electromagnetic (EM) simulations and the measurements have been attained. The system is suitable for recharging shortrange applications.

Isolation Improvement between Closely-Spaced Antennas Using EBG

Isolation improvement between two closely spaced antennas using a single column EBG is proposed for compact wireless devices. The proposed design developed for the 2.4 GHz WLAN band achieves more than 17 dB isolation improvement between two planar inverted-F antennas (PIFAs) compared to the no-EBG case. As a result, improved MIMO capacity is also achieved. The proposed design can be scaled up or down in frequency and may be implemented for small devices such as, smart watches, Wi-Fi routers, internet of things (IoT) devices etc.

Antenna coupled bolometer simulation for terahertz radiation detection diffracted by a small metal object

Terahertz (THz) wave technologies are becoming near future wireless technologies because of its advantages of considerable bandwidth and still unlicensed spectrum. Its small bandwidth offers a more compact wireless device on a scale of micrometers. Detection is a challenge for applying these potential technologies. An antenna coupled with a bolometer device is a candidate to capture emitted THz wave radiation. Another consideration can be any possible obstacles. This paper presents a simulation of Terahertz wave radiation detected with a dipole antenna connected to a bolometer. This research uses a 3D simulation software of CST Microwave Studio to simulate linearly THz plane waves radiation passing through a small metal object. Some dipole antennas coupled bolometer detect the power of the plane wave radiation in location after the emitted plane waves hit the object. The result shows that the highest detected power can be detected. Even the detector is located at the center of the area blocked by the metal object. This condition indicates that diffraction is high enough, affected by the comparable size, the metal, wavelength, and observation distances. More studies to characterize this diffraction effect are becoming useful, especially for THz imaging applications, such as metal detection for an airport security system.

Personalized Human Activity Recognition Based on Integrated Wearable Sensor and Transfer Learning.

Human activity recognition (HAR) based on the wearable device has attracted more attention from researchers with sensor technology development in recent years. However, personalized HAR requires high accuracy of recognition, while maintaining the model’s generalization capability is a major challenge in this field. This paper designed a compact wireless wearable sensor node, which combines an air pressure sensor and inertial measurement unit (IMU) to provide multi-modal information for HAR model training. To solve personalized recognition of user activities, we propose a new transfer learning algorithm, which is a joint probability domain adaptive method with improved pseudo-labels (IPL-JPDA). This method adds the improved pseudo-label strategy to the JPDA algorithm to avoid cumulative errors due to inaccurate initial pseudo-labels. In order to verify our equipment and method, we use the newly designed sensor node to collect seven daily activities of 7 subjects. Nine different HAR models are trained by traditional machine learning and transfer learning methods. The experimental results show that the multi-modal data improve the accuracy of the HAR system. The IPL-JPDA algorithm proposed in this paper has the best performance among five HAR models, and the average recognition accuracy of different subjects is 93.2%.

Defining Optimal Exercises for Efficient Detection of Parkinson’s Disease Using Machine Learning and Wearable Sensors

Our society exhibits a worldwide trait of a quickly growing cohort of patients with neurodegenerative diseases, such as Parkinson's disease (PD). According to the analysts, there is a plausible “PD pandemic” to occur within the next two decades. Nowadays, the research in the area focuses on how to detect, predict, or classify PD and similar diseases without addressing the point of what activities or exercises a subject should do to improve the performance of these tasks. In this article, we propose a method based on machine learning (ML) and wearable sensors to identify the optimal exercises for the efficient detection of PD in patients. We first define 15 common tasks that are typically used to diagnose PD in modern clinical practice. However, these exercises still carry a high risk of misdiagnosis and, moreover, not all of them work well in the scope of existing ML solutions to support the diagnosis. Herein, we collect the data in a real clinical setting using a compact wearable wireless sensor node entailing a board gyroscope, accelerometer, and magnetometer. Application of ML methods to the collected data reveals three “most efficient” exercises to assist diagnosticians with the highest discriminating power (0.9 ROC AUC in each task). The proposed solution can be implemented as a medical decision support system for real-time PD diagnostics.

Reconfigurable Multistage RF Rectifier Topology for 900 MHz ISM Energy-Harvesting Applications

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.

Low-Profile Ultrawideband Circularly Polarized Metasurface Antenna Array

A compact low-profile ultrawideband circularly polarized (CP) metasurface antenna (MSA) array is presented in this letter. The array consists of 2 × 2 sequentially rotated symmetric MSA elements and a wideband four-way feeding network providing stable phases of 0°, 90°, 180°, and 270°. By using the constructed feeding network and MSA element, the CP array can achieve an ultrawideband CP performance with a low profile of 0.05λ L . The measured results show that the proposed MSA array achieves the 10 dB impedance bandwidth of 97.2%, 3 dB axial ratio bandwidth of 83.2%, and 3 dB gain variation bandwidth of 73.8%. Compared with the other designs in published literatures, the proposed CP MSA array owns the advantages of low profile with a simple structure and good CP performance without any air gap, thus indicating a promising candidate in compact wideband wireless systems.

GHz AlN-based multiple mode SAW temperature sensor fabricated on PEN substrate

Polymeric based surface acoustic wave (SAW) devices represent one of the most interesting platform for the development of wireless passive sensors for IoT and smart packaging applications. An important feature to be addressed in order to develop a compact and conformable wireless SAW sensor is the increase of the working frequency which allows an easy antenna integration and miniaturization.In this work, we present a disposable polymeric SAW temperature sensor device working in the GHz range, based on aluminum nitride (AlN) and built on a 125 μm thick film of polyethylene naphthalate. The flexible device has been compared to the same SAW device fabricated onto silicon substrates. The polymeric based SAW device shows three operating wave modes corresponding to the Rayleigh, Love, and Lamb, highlighting that the Lamb mode exhibits a resonance frequency as high as 1.325 GHz, corresponding to a phase wave velocity of 10,600 m/s, an electromechanical coupling of 2.91 % and Q factor of 109. Temperature coefficient of frequency (TCF) values of 149, 109, 53 ppm/°C have been calculated for the Rayleigh, Love and Lamb waves, respectively.The different behavior of the three SAW modes let us envision the development of a multiple sensing platforms based on different modes in the same device (e.g. temperature, microbiological contamination, light exposure).

A coplanar‐waveguide‐fed planar integrated cavity backed slotted antenna array using TE 33 mode

This short communication presents a substrate integrated waveguide planar cavity slotted antenna array. The proposed antenna array, excited in its TE33 higher mode, incorporates a grounded coplanar-waveguide (CPW) CPW-feeding excitation mechanism. The electromagnetic energy is coupled to the air through 3 × 3 slot array etched on top metallic layer. The proposed antenna operates in the X-band for the frequency range around the 10 to 11 GHz with resonances at 10.4 and 10.8 GHz frequencies. The proposed antenna array was fabricated and tested. Experimental results show good impedance matching with enhanced radiation characteristics, in terms of peak gain, cross-polarization level, and low back-radiation. The proposed antenna has the advantages of low-footprints, lightweight, high gain, low-cost, and ease of integration with other electronic circuits. With these characteristics, the proposed antenna array can find its applications in compact wireless digital transceivers.

Investigation of path loss and modeling for digital terrestrial television over Nigeria

Accurate prediction of path losses is a key factor in Digital Terrestrial Television (DTTV) to ensure Quality of Service (QoS). This study investigates the path losses of three Digital Terrestrial Television Base Stations (DTTBS) in Lagos, Kaduna and Katsina cities of Nigeria. The Received Signal Strength (RSS) of the DTTBS was measured at intervals along selected routes around the stations using a digital signal strength meter. So also, the transmitter-receiver distances of data points with their corresponding geographic coordinates and heights were measured using a hand held GPS receiver. Also measured concurrently were some of the location's - based surface meteorological parameters such as temperature, atmospheric pressure and humidity, using a compact wireless weather station. In addition, the corresponding surface radio refractivity values along the routes were computed using the meteorological parameters recorded. Data were collected during dry and wet season months' covering a period of three years. Path losses were calculated using Okumura-Hata model. Results for all the routes and seasons revealed that path loss increases with increase in trans-receiver distances, however path losses were higher during wet compared to dry season's month. Path losses estimated were highest in Kaduna followed by Ikorodu-Lagos and least in Katsina. Average high positive correlation coefficients of 0.76, 0.75 and 0.74 were obtained between path losses and line of sight for Lagos (Coastal zone), Kaduna (Sudan Savannah) and Katsina (Sahel Savannah) respectively. In the same order, negative correlation coefficients of -0.72, -0.79 and -0.63 were obtained between path losses and RSS. In addition, Modified Okumura Hata Model(s) (MOHPL) that incorporates the effect of the specified tropospheric parameters were proposed. Results also revealed that path losses obtained by Okumura-Hata model increase with increase in LOS separation distance from the base station following a consistent exponential rise while the Modified Okumura-Hata Model (MOHPL) followed similar trend with few exceptions of crests and troughs depicting the influence of the incorporated location's-based tropospheric parameters. Another finding is that Okumura Hata model under estimated the path losses associated with digital terrestrial television channel over the study locations. In order to ensure high reliability of power budgets and link's design, the proposed models are recommended for use over the study locations. The overall findings of this work will be useful for the accurate prediction of path losses and the design of power budgets and links over digital terrestrial television and similar wireless channels on the UHF band.

Design of high gain dual T-shaped stub antenna for satellite communication

The ultra wide band (UWB) antennas play a vital role in supporting different wireless standards and are suitable for wide variety of applications. This paper is aimed to present a novel UWB dual notch microstrip antenna with modified ground plane. The antenna is designed to operate in UWB ranging from 2 GHz to 12 GHz with multi band operation. This will help in operating the antenna for different operations independently. The proposed structure will operate in two notch bands 3.3-4 GHz (Wi-MAX), 5.05-5.9 GHz (WLAN) and the structure is suitable for long distance communications because of its increased directivity. The structure can also be used for X-Band applications for various applications of traffic control, weather forecasting and vehicle speed detection systems. It is observed that, the proposed structure is offering a gain of 5.2 dBi with improved directivity with a beam width of 42.230. This makes the antenna structure suitable for long distance satellite communications. The antenna is supporting the circular polarization at higher the frequencies and can be useful for the upcoming 5G mobile applications. Moreover, the proposed structure offers the less interference at the receiver. The structure is found to be smaller in dimensions, easily fabricated at low costs and can be integrated into any compact wireless devices. The structure is simulated using a commercially available software Ansys-HFSS and is analyzed.