Ultra-thin flexible rectenna integrated with power management unit for wireless power harvester/charging of smartwatch/wristband.

This paper proposes a circularly polarized ultra-thin flexible antenna with a flexible rectifier and power management unit (PMU) for smartwatch/wristband applications. The flexible antenna is compact (0.17λ0 × 0.20λ0 × 0.0004λ0) and has a stepped ground plane. A parasitic element is used at the substrate bottom to reduce the specific absorption rate (SAR) and enhance the gain up to 3.2 dBi, at the resonating frequency of WLAN/Wi-Fi (2.45 GHz). The SAR of the proposed design is also analysed at the resonating frequency, and it satisfies the guidelines of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and IEEE C95.1-2019 human safety standards. An impedance matching circuit is used between the antenna and the RF energy harvester to improve conversion efficiency. Polarization mismatch is avoided with the help of circular polarization, achieved by tuning stubs of size 0.02λ0 × 0.044λ0. The integration of the antenna and rectenna results in a good conversion efficiency of 78.2% at - 5 dBm of input power with a load resistance of 2 KΩ. The availability of RF signals allows the user to charge the smartwatch/wristband by connecting the PMU circuit with the RF energy harvester.

Circularly polarized differential intra-oral antenna design validation and characterization for tongue drive system.

Assistive devices are becoming increasingly popular for physically disabled persons suffering tetraplegia and spinal cord injuries. Intraoral tongue drive system (iTDS) is one of the most feasible and non-invasive assistive technology (AT), which utilises the transferring and inferring of user intentions through different tongue gestures. Wireless transferring is of prime importance and requires a suitable design of the intra-oral antenna. In this paper, a compact circularly polarized differential intra-oral antenna is designed, and its performance is analysed within heterogeneous multilayer mouth and head models. It works at 2.4 GHz in the Industrial, Scientific, and Medical (ISM) band. The footprint of the differential antenna prototype is 0.271 λg [Formula: see text] 0.271 λg [Formula: see text] 0.015 λg. It is achieved using two pairs of spiral segments loaded in diagonal form near the edges of the central rotated square slot and a high dielectric constant substrate. Its spiral-slotted geometry further provides the desired swirling and miniaturization at the desired frequency band for both mouth scenarios. Additionally, corner triangular slits on the radiating patch assist in tuning the axial ratio (< 3 dB) in the desired ISM band. To validate the performance of the proposed in-mouth antenna, the measurement was carried out using the minced pork and the saline solution for closed and opened mouth cases, respectively. The measured - 10 dB impedance bandwidth and peak gain values in the minced pork are from 2.28 to 2.53 GHz (10.39%) and - 18.17 dBi, respectively, and in the saline solution, are from 2.3 to 2.54 GHz (9.92%) and - 15.47 dBi, respectively. Further, the specific absorption rate (SAR) is estimated, and the data communication link is computed with and without a balun loss. This confirms that the proposed differential intraoral antenna can establish direct interfacing at the RF front end of the intraoral tongue drive system.

Low-loss MIMO antenna wireless communication system for 5G cardiac pacemakers.

Cardiovascular diseases (CVDs) are one of the leading causes of death globally. The Internet of things (IoT) enabled with industrial, scientific, and medical (ISM) bands (2.45 and 5.8 GHz) facilitates pacemakers to remotely share heart health data to medical professionals. For the first time, communication between a compact dual-band two-port multiple-input-multiple-output (MIMO) antenna (integrated inside the leadless pacemaker) and an outside-body dual-band two-port MIMO antenna in the ISM 2.45 and 5.8 GHz frequency bands is demonstrated in this work. The proposed communication system offers an attractive solution for cardiac pacemakers as it can operate on a 5G IoT platform while also being compatible with existing 4G standards. The experimental verification of the proposed MIMO antenna low-loss communication capability is also presented by comparing it to the existing single-input-single-output communication between the leadless pacemaker and outside body monitoring device.

High-current space-charge-limited pulses using ultrashort laser pulses.

The maximum current that can be delivered by a 1-D vacuum diode is limited due to the space-charge reduction of the accelerating field. For a steady-state operation, this is given by the Child-Langmuir space-charge limit. However, for pulsed diode sources, the instantaneous current can be much higher than this limit, as long as the pulse length is much less than the transit time across the diode gap. This enables the generation of high current pulses with pulse durations of the order of tens of picoseconds using photocathodes driven by ultrashort laser pulses. The generation of such short and powerful electromagnetic pulses is important for numerous applications such as ultrawideband radar or as photocathode sources for accelerators. In this work, the limiting current pulse is investigated in the case of a very short, square-top initial pulse and it is found that these pulses propagate in a self-similar manner, remaining as a square-top charge cloud in space throughout their acceleration and propagation. The resultant current and pulse duration turn out to be dependent on only three parameters, which are the applied voltage, the vacuum transit time, and the fraction of the saturation charge density in the initial charge cloud. The resultant scaling of the resultant peak current and pulse duration are calculated numerically as a function of starting sheet-charge density, allowing the calculation of the resultant pulses for any ultrashort, pulse-driven vacuum photodiode design.

Electrically Small Circularly Polarized UWB Intraocular Antenna System for Retinal Prosthesis.

OBJECTIVE: This paper presents the design of an electrically small circularly polarized (CP) 3 × 3 mm2 antenna system as an intraocular unit for retinal prosthesis application. METHODS: The system is operating in ISM and ultra-wideband (UWB) bands to target high programmability of retina stimulation and recording, respectively. The electrical dimensions, including the ground plane, are λ0/41 × λ0/41 × λ0/191. Physical limitations of the antenna are discussed based on Hansen and Collin's limitations. The proposed wire patch antenna exhibits wideband characteristics by combining multiple modes of the patch antenna in the presence of an interface PCB circuit. RESULTS: By loading polyimide encapsulated patch with stubs, dominant TM010 mode is combined with the higher order modes TM020-TM070 to exhibit wide -10 dB impedance bandwidth of 2-11 GHz. Annular rings and shorting pins in the ground plane provide CP radiation at 2.45, 5.8, and 8 GHz with 3-dB axial-ratio bandwidth of 0.3, 0.16, and 1.2 GHz, and far-field left hand circularly polarized (LHCP) gain of -18.4, -7.6, and -4.7 dBic, respectively, in broadside direction. A biocompatible antenna system is designed using Ansys HFSS in the presence of a detailed multilayer canonical eye model. Additionally, it is examined in an anatomical HFSS head model. Near and far-field electric field distribution is studied along with peak 1-g average specific absorption rate (SAR) calculations. CONCLUSION: The proposed antenna is fabricated, and the performance, including coupled power from an external antenna, is measured in a custom made eye model including head phantom. A reasonable agreement is obtained between simulated and measured results. SIGNIFICANCE: To generate an artificial vision, image perception capability could be improved with implantable UWB communication systems that feature particularly high data-rate and small size.

Ultra-Miniature Circularly Polarized CPW-Fed Implantable Antenna Design and its Validation for Biotelemetry Applications.

The paper presents a coplanar waveguide (CPW)-fed ultra-miniaturized patch antenna operating in Industrial, Scientific and Medical (ISM) band (2.4-2.5 GHz) for biotelemetry applications. The proposed antenna structure is circular in shape and its ground plane is loaded with a pair of slots for obtaining circular polarization. In the proposed design, asymmetric square slots generate phase condition for right-hand circularly polarized (RHCP) radiation. And, by merely changing the position of the slots, either RHCP or left-hand circularly polarized (LHCP) radiation can be excited. In the proposed design, a meandered central strip is used for miniaturization. The simulations of the proposed antenna are carried out using Ansys HFSS software with a single-layer and multilayer human tissue models. The antenna shows good performance for different tissue properties owing to its wide axial ratio bandwidth and impedance bandwidth. The antenna is fabricated and measurements are carried out in skin mimicking phantom and pork. Simulated and measured performances of the antenna are in close agreement. The power link budget is also calculated using an exterior circularly polarized (CP) receiving antenna.

Microwave Imaging of Breast Tumor Using Time-Domain UWB Circular-SAR Technique.

This paper explores the competency of the time domain ultra-wideband (UWB)-circular synthetic aperture radar (CSAR) to image the breast and detect tumors. The image reconstruction is performed using a time domain global back projection technique adapted to the circular trajectory data acquisition. This paper also proposes a sectional image reconstruction method to compensate for the group velocity changes in different layers of a multilayer medium. Experiments on an advanced breast phantom examines the suitability of this technique for breast tumor imaging. The advanced breast phantom is designed based on a MRI of a real patient, fabricated using 3D printing technology, and filled with liquids that emulate normal and cancerous tissues. The measurement results, compared with MRI imaging of the phantom, demonstrate the suitability of the UWB-CSAR method for breast tumor imaging. This method can be a tool for early diagnosis as well as for treatment monitoring during chemotherapy or radiotherapy.

Breast tumor detection using UWB circular-SAR tomographic microwave imaging.

This paper describes the possibility of detecting tumors in human breast using ultra-wideband (UWB) circular synthetic aperture radar (CSAR). CSAR is a subset of SAR which is a radar imaging technique using a circular data acquisition pattern. Tomographic image reconstruction is done using a time domain global back projection technique adapted to CSAR. Experiments are conducted on a breast phantoms made of pork fat emulating normal and cancerous conditions. Preliminary experimental results show that microwave imaging of a breast phantom using UWB-CSAR is a simple and low-cost method, efficiently capable of detecting the presence of tumors.