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Diffusion magnetic resonance imaging (dMRI) allows for a non-invasive visualization and quantitative assessment of white matter architecture in the brain by characterizing restrictions on the random motion of water molecules. Ultra-high field MRI scanners, such as those operating at 7 Tesla (7T) or higher, can boost the signal-to-noise ratio (SNR) to improve dMRI compared with what is attainable at conventional field strengths such as 3T or 1.5T. However, wavelength effects at 7T cause reduced transmit magnetic field efficiency in the human brain, mainly in the posterior fossa, manifesting as signal dropouts in this region. Recently, we reported a simple approach of using a wireless radiofrequency (RF) surface array to improve transmit efficiency and signal sensitivity at 7T. In this study, we demonstrate the feasibility and effectiveness of the RF enhancer in improving in vivo dMRI at 7T. The electromagnetic simulation results demonstrated a 2.1-fold increase in transmit efficiency with the use of the RF enhancer. The experimental results similarly showed a 1.9-fold improvement in transmit efficiency and a 1.4-fold increase in normalized SNR. These improvements effectively mitigated signal dropouts in regions with inherently lower SNR, such as the cerebellum, resulting in a better depiction of principal fiber orientations and an enhanced visualization of extended tracts. [ABSTRACT FROM AUTHOR]

Diffusion magnetic resonance imaging (dMRI) allows for a non-invasive visualization and quantitative assessment of white matter architecture in the brain by characterizing restrictions on the random motion of water molecules. Ultra-high field MRI scanners, such as those operating at 7 Tesla (7T) or higher, can boost the signal-to-noise ratio (SNR) to improve dMRI compared with what is attainable at conventional field strengths such as 3T or 1.5T. However, wavelength effects at 7T cause reduced transmit magnetic field efficiency in the human brain, mainly in the posterior fossa, manifesting as signal dropouts in this region. Recently, we reported a simple approach of using a wireless radiofrequency (RF) surface array to improve transmit efficiency and signal sensitivity at 7T. In this study, we demonstrate the feasibility and effectiveness of the RF enhancer in improving in vivo dMRI at 7T. The electromagnetic simulation results demonstrated a 2.1-fold increase in transmit efficiency with the use of the RF enhancer. The experimental results similarly showed a 1.9-fold improvement in transmit efficiency and a 1.4-fold increase in normalized SNR. These improvements effectively mitigated signal dropouts in regions with inherently lower SNR, such as the cerebellum, resulting in a better depiction of principal fiber orientations and an enhanced visualization of extended tracts.

The alteration of the hydrostatic pressure gradient in the human body has been associated with changes in human physiology, including abnormal blood flow, syncope, and visual impairment. The focus of this study was to evaluate changes in the resonant frequency of a wearable electromagnetic resonant skin patch sensor during simulated physiological changes observed in aerospace applications. Simulated microgravity was induced in eight healthy human participants (n = 8), and the implementation of lower body negative pressure (LBNP) countermeasures was induced in four healthy human participants (n = 4). The average shift in resonant frequency was −13.76 ± 6.49 MHz for simulated microgravity with a shift in intracranial pressure (ICP) of 9.53 ± 1.32 mmHg, and a shift of 8.80 ± 5.2097 MHz for LBNP with a shift in ICP of approximately −5.83 ± 2.76 mmHg. The constructed regression model to explain the variance in shifts in ICP using the shifts in resonant frequency (R2 = 0.97) resulted in a root mean square error of 1.24. This work demonstrates a strong correlation between sensor signal response and shifts in ICP. Furthermore, this study establishes a foundation for future work integrating wearable sensors with alert systems and countermeasure recommendations for pilots and astronauts. [ABSTRACT FROM AUTHOR]

Modern wearable devices show promising results in terms of detecting vital bodily signs from the wrist. However, there remains a considerable need for a device that can conform to the human body's variable geometry to accurately detect those vital signs and to understand health better. Flexible radio frequency (RF) resonators are well poised to address this need by providing conformable bio-interfaces suitable for different anatomical locations. In this work, we develop a compact wearable RF biosensor that detects multisite hemodynamic events due to pulsatile blood flow through noninvasive tissue–electromagnetic (EM) field interaction. The sensor consists of a skin patch spiral resonator and a wearable transceiver. During resonance, the resonator establishes a strong capacitive coupling with layered dielectric tissues due to impedance matching. Therefore, any variation in the dielectric properties within the near-field of the coupled system will result in field perturbation. This perturbation also results in RF carrier modulation, transduced via a demodulator in the transceiver unit. The main elements of the transceiver consist of a direct digital synthesizer for RF carrier generation and a demodulator unit comprised of a resistive bridge coupled with an envelope detector, a filter, and an amplifier. In this work, we build and study the sensor at the radial artery, thorax, carotid artery, and supraorbital locations of a healthy human subject, which hold clinical significance in evaluating cardiovascular health. The carrier frequency is tuned at the resonance of the spiral resonator, which is 34.5 ± 1.5 MHz. The resulting transient waveforms from the demodulator indicate the presence of hemodynamic events, i.e., systolic upstroke, systolic peak, dicrotic notch, and diastolic downstroke. The preliminary results also confirm the sensor's ability to detect multisite blood flow events noninvasively on a single wearable platform. [ABSTRACT FROM AUTHOR]

The alteration of the hydrostatic pressure gradient in the human body has been associated with changes in human physiology, including abnormal blood flow, syncope, and visual impairment. The focus of this study was to evaluate changes in the resonant frequency of a wearable electromagnetic resonant skin patch sensor during simulated physiological changes observed in aerospace applications. Simulated microgravity was induced in eight healthy human participants (n = 8), and the implementation of lower body negative pressure (LBNP) countermeasures was induced in four healthy human participants (n = 4). The average shift in resonant frequency was −13.76 ± 6.49 MHz for simulated microgravity with a shift in intracranial pressure (ICP) of 9.53 ± 1.32 mmHg, and a shift of 8.80 ± 5.2097 MHz for LBNP with a shift in ICP of approximately −5.83 ± 2.76 mmHg. The constructed regression model to explain the variance in shifts in ICP using the shifts in resonant frequency (R2 = 0.97) resulted in a root mean square error of 1.24. This work demonstrates a strong correlation between sensor signal response and shifts in ICP. Furthermore, this study establishes a foundation for future work integrating wearable sensors with alert systems and countermeasure recommendations for pilots and astronauts.

Modern wearable devices show promising results in terms of detecting vital bodily signs from the wrist. However, there remains a considerable need for a device that can conform to the human body’s variable geometry to accurately detect those vital signs and to understand health better. Flexible radio frequency (RF) resonators are well poised to address this need by providing conformable bio-interfaces suitable for different anatomical locations. In this work, we develop a compact wearable RF biosensor that detects multisite hemodynamic events due to pulsatile blood flow through noninvasive tissue–electromagnetic (EM) field interaction. The sensor consists of a skin patch spiral resonator and a wearable transceiver. During resonance, the resonator establishes a strong capacitive coupling with layered dielectric tissues due to impedance matching. Therefore, any variation in the dielectric properties within the near-field of the coupled system will result in field perturbation. This perturbation also results in RF carrier modulation, transduced via a demodulator in the transceiver unit. The main elements of the transceiver consist of a direct digital synthesizer for RF carrier generation and a demodulator unit comprised of a resistive bridge coupled with an envelope detector, a filter, and an amplifier. In this work, we build and study the sensor at the radial artery, thorax, carotid artery, and supraorbital locations of a healthy human subject, which hold clinical significance in evaluating cardiovascular health. The carrier frequency is tuned at the resonance of the spiral resonator, which is 34.5 ± 1.5 MHz. The resulting transient waveforms from the demodulator indicate the presence of hemodynamic events, i.e., systolic upstroke, systolic peak, dicrotic notch, and diastolic downstroke. The preliminary results also confirm the sensor’s ability to detect multisite blood flow events noninvasively on a single wearable platform.

Shoulder injury is one of the most common phenomena that occurs for astronauts when they are training for space flight. During training, astronauts are required to wear a full space suit, known as the extravehicular mobility unit (EMU). The major component of the EMU that attributes to shoulder injury is the hard upper torso (HUT). This component is primarily comprised of a rigid fiberglass shell with metal scye bearing joints. Placement of the scye bearing joints for the shoulders does not allow for enough range of motion, which can lead to rotator cuff tears. Additionally, shoulder injury also occurs when donning the suit and training in the Neutral Buoyancy Laboratory (NBL). The EMU currently does not contain any provision to account for this biomechanical interference to adjust for optimum range of motion. The objective of this paper is to propose a novel detection scheme using a wearable electromagnetic resonant spiral sensor that could allow for a quantitative value of proximity between the shoulder and the metallic scye bearing joint of the HUT. The presence of the liquid cooling and ventilation garment (LCVG) is also investigated in the environment to validate that accuracy of proximity detection is still achieved. Optimal location for the wearable proximity sensor would be on top the LCVG around the shoulder joint where the scye bearing joints are more likely to meet the shoulder. The first study investigated the ability of the wearable proximity sensor to detect the distance from an aluminum sheet (representing the scye bearing joint) with no LCVG present, while the second study incorporated the wearable proximity sensor on top of the LCVG for a simulated suit environment. Four scenarios were performed with two wearable proximity sensors, resonating at different frequencies, placed in an environment with and without the LCVG. Ten repeated tests were used to train and an additional ten tests to validate a regression learning algorithm to predict the distance for each scenario. Experimental results indicated that the wearable proximity sensors in both the open air and with the LCVG have enough accuracy to provide a root mean square error (RMSE) of approximately 1 mm or less. This accuracy is sufficient for use in the space suit to provide quantitative information for suit fit. The use of this proximity detection scheme incorporated into the suit will offer previously unknown information regarding suit fit, while also influencing optimum fit for future suit generations. • Measuring proximity to metal components in the suit will alleviate astronaut injury. • An electromagnetic spiral proximity sensor will provide quantitative measurements. • Proximity measurements can be trained and predict with millimeter accuracy. • Sensor design alterations can improve accuracy and resolution of proximity detect. [ABSTRACT FROM AUTHOR]

Non-intrusive monitoring of blood flow parameters is vital for obtaining physiological and pathophysiological information pertaining to dynamic cardiovascular events and is feasible to achieve via non-invasive, conformal, wearable technologies. Here, we present a proof-of-concept of a fully integrated, high frequency (bandwidth 40 MHz), electromagnetic sensing device for monitoring limb hemodynamics and morphology associated with blood flow. The sensing architecture integrates a novel radio frequency (RF) skin patch resonator embedded with a coplanar outer loop antenna and a scalable, standalone wireless readout hardware based on standing wave ratio (SWR) bridge. The resonator itself is a copper-based open circuit planar Archimedean spiral with a rectangular cross-sectional area, chemically etched on a flexible polyimide substrate. The readout hardware is developed exploiting off-the-shelf components, fabricated on the top of a rigid FR4 substrate. The proposed readout circuit can measure resonant frequency of an RLC network. When energized by the external oscillating RF field via loop antenna, the resonator produces an electromagnetic field response which can be perturbed by dielectric variation inside its field boundary. Through leveraging this principle, the in-vitro experimental results from the benchtop models suggest that the resonator's RF attributes such as resonant frequency shift and magnitude variation of reflection coefficient due to fluid volume displacement can be successfully detected through the proposed hardware architecture. Hence, the system could be an alternative to the conventional, multimodal, non-invasive wearable sensing with an unprecedented capability of ubiquitous fluid phenomena detection from multiple sites of the human body. [ABSTRACT FROM AUTHOR]

Highlights • Although FBAR has already been used in industry product, study on RF performance on designs/process variations is still missing. • In this report various FBARs were designed, fabricated and analyzed to study wafer-level site-to-site RF variation on design and fabrication process. • Wafer-level and wafer-to-wafer variation of the device frequency response are fairly homogenous with the resonance frequency of the FBAR devices target ranging from 1.8 to 2.1 Ghz. • Simulation verified that this frequency variation correlates to the piezoelectric film variation of 1.6–1.9 μm variation. Abstract Thin film bulk acoustic resonator (FBAR) plays a very important role in radio frequency (RF) filters used in cell phone and other wireless systems. Although FBAR is commercialized, the design/process interactions on the frequency response variation in FBAR device are still lacking. Design and fabrication are two crucial aspects affecting FBAR device performance. In this report, various solidly mounted resonators (SMR) were designed, fabricated and analyzed to study wafer-level site-to-site RF variation on design and fabrication process. As a key process step for SMR FBAR, the optimization process of Mg-doped ZnO piezoelectric thin film deposition was studied by varying thin film sputtering conditions using various sputtering targets and by post annealing treatment after the deposition. The quality of this crucial layer was verified by XRD on its (0 0 2) crystallization and wafer-level FBAR RF characterization. FBAR devices with high quality were fabricated with an excellent resonant behavior near 2 GHz and a maximum return loss of −15 to 25 dB. Quality factor Q ranges from 400 to 800, with a coupling coefficient keff2 of 1.5–3%. Wafer-level and wafer-to-wafer variation of central frequency are within 1.8–2.1 GHz. Computer simulation verified that this frequency variation correlates to the piezoelectric film variation of 1.6–1.9 μm. Process control on this piezoelectric thin film is essential to maintaining the resonator frequency-controlled value when building duplexer RF circuits. The dependency of RF performance on FBAR size, density and orientation is not obvious, compared to that of the wafer-level FBAR device variation on fabrication process. Regarding to the Mg-doping effect in MgxZn1-xO piezoelectric film, the amount of Mg in MgxZn1-xO film during the sputtering process must be properly controlled within 30% to keep the piezoelectric quality. The average acoustic speed of the Mg-doped ZnO film is 6870 m/s with the estimated range of 5760–7980 m/s, which is better than that of pure ZnO film (6330 m/s). [ABSTRACT FROM AUTHOR]

Highlights • In this paper, surface acoustic wave (SAW) devices with various designs were fabricated on two types of piezoelectric substrates of LiNbO 3 bulk material and thin piezoelectric ZnO film on silicon. • Different sizes, orientation and types of SAW devices were laid out on the same mask to compare their RF performance with a same fabrication. • Devices were fabricated using lift-off technology with a double photoresist technique to achieve a steeper and narrower SAW pattern with a depth-to-width ratio of 1.27 and a steep resist angle of 85°. • The devices were then characterized using RF probe station together with vector network analyzer. • RF performance was also verified by 2D computer simulation implementing both electrical and piezoelectric physics models using the same device dimensions in the mask layout. • RF response of 128°Y LiNbO 3 from experiments agrees with simulation fairly well while the devices on ZnO/Si have larger frequency distribution due to process variation of the ZnO thin film on silicon wafer. • Quality factor of 34,000 was obtained from the SAW device fabricated in LiNO3 substrate and this Q value has a strong dependency on the numbers electrodes of IDT fingers and reflectors. • Temperature dependency was also measured for future wireless sensor application. • The temperature coefficient of frequency of 16 μm wavelength devices of LiNbO 3 substrate was −87.5 ppm/°C and was −72.41 ppm/°C for 12 μm wavelength devices. Abstract In this paper, surface acoustic wave (SAW) devices with various designs were fabricated on two types of piezoelectric substrates of LiNbO 3 bulk material and thin piezoelectric ZnO film on silicon. Different sizes, orientation and types of SAW devices were laid out on the same mask to compare their RF performance with a same fabrication. Devices were fabricated using lift-off technology with a double photoresist technique to achieve a steeper and narrower SAW pattern with a depth-to-width ratio of 1.27 and a steep resist angle of 85°. The devices were then characterized using RF probe station together with vector network analyzer. RF performance was also verified by 2D computer simulation implementing both electrical and piezoelectric physics models using the same device dimensions in the mask layout. RF response of 128°Y LiNbO 3 from experiments agrees with simulation fairly well while the devices on ZnO/Si have larger frequency distribution due to process variation of the ZnO thin film on silicon wafer. Quality factor of 34,000 was obtained from the SAW device fabricated in LiNO3 substrate and this Q value has a strong dependency on the numbers electrodes of IDT fingers and reflectors. Temperature dependency was also measured for future wireless sensor application. The temperature coefficient of frequency of 16 μm wavelength devices of LiNbO 3 substrate was −87.5 ppm/°C and was −72.41 ppm/°C for 12 μm wavelength devices. [ABSTRACT FROM AUTHOR]

This paper presents the development of a non-contact, nonintrusive wrist pulse sensor based on the near-field variation of an array resonator. A compact resonator and its array were designed and fabricated on flexible substrate. The reflection coefficient of the resonator can vary as a function of the distance between the resonator and the walls of the major arteries, and the corresponding variation is utilized to obtain heart rate information at the wrist. To detect very weak pulse signals from the main arteries, a sensitivity enhancement technique was devised using a radio frequency (RF) array resonator. The sensor system was implemented with an RF switch to combine or select appropriate signals from the resonator element and was tested using the 2.4 GHz ISM band. The results demonstrated the sensor system’s excellent performance in both sequential and simultaneous detection schemes. The measurement results showed that a heartbeat pulse can be detected from both radial and ulnar arteries via the array resonators. Considering the high sensitivity and characteristics, the proposed detection system can be utilized as a wearable, long-term health monitoring device. [ABSTRACT FROM PUBLISHER]

Highlights: [•] High frequency resonators developed for frequency source applications. [•] Resonators manufactured using Electron Beam Lithography on ZnO/Diamond substrate (nucleation side). [•] Single and double port resonators built in the 3–6GHz frequency range. [•] Double port resonators found compatible with the oscillator application. [•] Oscillator demonstration at 3GHz : −90dBcHz−1 at 1kHz and a floor noise of −165dBcHz−1. [ABSTRACT FROM AUTHOR]

A 2.4 GHz TX in 65 nm CMOS defines three channels using three high-Q FBARs and supports OOK, BPSK and MSK. The oscillators have -132 dBc/Hz phase noise at 1 MHz offset, and are multiplexed to an efficient resonant buffer. Optimized for low output power \approx -10 dBm, a fully-integrated PA implements 7.5 dB dynamic output power range using a dynamic impedance transformation network, and is used for amplitude pulse-shaping. Peak PA efficiency is 44.4% and peak TX efficiency is 33%. The entire TX consumes 440 pJ/bit at 1 Mb/s. [ABSTRACT FROM PUBLISHER]

Abstract: Based on rigorous analysis of finite element method (FEM), moment method (MoM), and curves fitting techniques, a set of closed-form formulas for the characteristic impedance and the primary (L and C) parameters of the shielded split ring line, are presented. The general expressions give a good accuracy for a wide-range of discontinuity angles and are suitable for all shielded split ring lines which have an outer–inner conductors radius ratio between 2 and 10. These expressions can be easily implemented in CAD simulation tools, to design many components as RF resonators, filters, transmission lines, for wireless communication and probes for material characterization. The results of the design of an RF resonator using the shielded split ring line are presented. [Copyright &y& Elsevier]