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This paper proposes a radio frequency (RF) switch-based radar system for simultaneously detecting multitarget and multidirectional vital signs. Compared with traditional continuous wave (CW) radars that encounter mixed and distorted phases due to multiple reflections, frequency modulation CW (FMCW) radars have a suitable range resolution and relatively simple system architecture. Moreover, FMCW radars have the inherent capabilities of conducting multiple target monitoring and providing distance information. Based on our proposed algorithm, the vital signs of two targets at different distances from the antenna can be detected simultaneously even closely separated within the resolution bin limitation by simply using the proposed algorithm upon an FMCW radar to extract the vital signs separately. Moreover, instead of using multiple radar systems, a single transceiver can detect the vital signs from multiple directions and multiple targets by adding an RF switch as a multiplexer. This RF switch provides the mixing function. Therefore, a low intermediate frequency (IF) architecture was proposed by using the proposed RF switch-based radar system. This architecture simultaneously conducts multidirectional vital sign detection; thus, the signal-to-noise ratio (SNR) can be improved by appropriately selecting the IF value to reduce the flicker noise. The heart rate (HR) demodulation in a baseband is also challenging due to the low SNR and the respiratory rate (RR) harmonic for FMCW vital sign radars. Therefore, we applied an ensemble empirical mode decomposition algorithm to extract the intrinsic mode functions of RR and HR. Experimental results revealed that the proposed algorithm can significantly improve the SNR and accuracy. The vital sign errors of detecting multiple targets are less than 3% on average.

A dual-resonant mixed coupling structure is proposed to enable lateral and angular misalignment immunity in wireless power and data transfer systems. By considering the duality property of electrical coupling and magnetic coupling, mixed coupling coils make the efficiency of wireless power transfer nearly insensitive to axial and angular misalignment. A complete, sophisticated equivalent circuit is proposed and demonstrates the features of the dual-resonant characteristic and lateral and angular misalignment tolerance. Compared to traditional printed spiral coil systems, the proposed mixed coupling structure reduces decline rate of S21 by 26.4% and 78.1% at 35-mm axial misalignment and 90° angular misalignment at low resonant frequency, respectively. Moreover, at high resonant frequency, S21 only drops 16.5% with 60-mm lateral misalignment and is almost flat for 90° angular misalignment. Last but not least, data communication is also validated by transmitting a 200-kHz frequency shift keying signal, and the probability errors remain at acceptable level when misalignment occurs.

This paper presents a variational mode decomposition (VMD)-based heart rate extraction algorithm to extract heart rate of the target under intermittent interference of non-stationary clutters caused by another person. When nonstationary clutters exist around the interested target, the heart rate detection becomes difficult for FMCW radars. In regard to the situation, VMD is utilized to extract the heartbeat signal and suppress the effect of non-stationary clutters after applying filter preprocessing. This approach is compared to other methods based on ensemble empirical mode decomposition (EEMD) and traditional fast Fourier transform (FFT). As a result, the proposed algorithm can achieve low computational load and high accuracy of heart rate extraction with relative error of 1.7%. The heartbeat signal extracted by the proposed algorithm has signal-to-noise ratio (SNR) improvement of 2.4 dB compared with EEMD algorithm.

In this paper, a method for measuring weak vibration is presented by using microwave sensors. A set of complementary split ring resonators (CSRRs) is utilized to detect a pendulum with metallic patch above the CSRR when any external vibration occurs. The whole system response of the pendulum structure and the CSRRs is analyzed to evaluate the vibration force. Furthermore, the material of the pendulum string could be changed to achieve different sensitivities and natural frequencies, which can be applied for interference cancellation and measurement of different axial orientation. The proposed test system was fabricated and tested to detect the vibration amplitude less than 0.19 mm and the vibration frequency can be detectable as low as 0.5 Hz.

In this paper, a press-button-type piezoelectric energy harvester (PEH) is presented. The proposed device is composed of a piezoelectric bender, four magnets, a button, and a reverted spring. The proposed structure is triggered by an impact driven by magnetic force, so this novel trigger mechanism enhances its optimal power output. Based on the piezoelectricity, beam theory, and the vibration theory, a complete numerical model was developed to simulate and predict the output voltage. A prototype was fabricated for verification, and the characterization of the energy harvester was measured. The harvested power and energy by a single impact was recorded as ${\text{20 mW}}$ and ${\text{190}\,\mu \text{J}}$ , respectively, at an optimum resistive load of ${\text{30 k}\Omega }$ . The measured data agreed with the results of numerical model. Finally, the piezoelectric energy charger extractor (PECE) was used to store the harvested energy. The energy stored in a capacitor of ${\text{1}\,\mu \text{F}}$ was ${\text{42.1}}\,{\mu \text{J}}$ .

This paper presents a resonator-based sensor for vital sign detection using a spherical dielectric resonator (SDR) operating at a frequency of approximately 26 GHz. The SDR at K-band can function as a highly-sensitive sensor due to reduced conduction loss, low radiation leakage, compact size, and enhanced signal-to-interference-plus-noise ratio (SINR) compared with traditional planar metallic resonators. Based on the proposed SDR sensor, the fingertip pulse signs can be detected merely by the sole sensoring resonator without external circuits. The SINR of the heartbeat signal detected at the fingertip is improved by more than 4.2 dB, compared to a metallic resonator-based sensor.

A new concept of transforming a non-planar MUT to a planar MUT with an effective air gap is proposed in this paper. The air gap existing between the MUT and sensor usually make large error in measurement, but by sensing with a multiring sensor, the effect of the air gap can be eliminated. However, in the case of a non-planar MUT, the curved surface of MUTs make the multiring of the sensor sensed different thickness of air gap. Thus, the approach of above cannot be use to eliminate the frequency shift cause by the air gap, and this will cause a undesired error in the experiment. Therefore, a triple-ring complementary split-ring resonator (CSRR) is used to estimate the effective air gap that make the smallest difference of the three resonance frequencies. Finally, with the transforming equation, a non-planar porcine fat with 10 mm thickness, 20 mm radius of curvature and 0 mm air gap are transformed into an effective planar MUT with 0.646 mm planar air gap. The result compare to simulation only with an error of 0.067 mm.

Inductive wireless power transfer (WPT) systems are achieved by novel parallel serpentine coils. By considering the uniform magnetic field distribution generated by parallel serpentine coil, high lateral misalignment tolerance can be achieved by little mutual inductance variance. Furthermore, a method to improve the efficiency of WPT using serpentine coils is also presented in this paper. The measured efficiency is 49% when two coils are aligned, and still maintains 39% when 35 mm lateral misalignment occurs. Comparing with the conventional spiral coil, efficiency decay rate (EDR) suffers 57% degradation at lateral misalignment of 35 mm. The proposed coil improves lateral misalignment tolerance for only 20% EDR at the same condition.

A neural network-based method for multi-layer permittivity measurement is proposed in this paper. This method uses the multiple-square concentric complementary split-ring resonator (CSRR) to take multiple non-identical resonance frequency measurement, and a scalable, iterative neural network approach is applied to estimate for dielectric property measurement. Instead of the tedious development and establishment of analytic formulas, neural network engine solver can simplify this step and still have acceptable accuracy. The dual-layer MUTs measurement had an average error of 8.78% for e1 and an average error of 8.9% for e2. It can be extended to the measurement of more than two layers substrate.

This paper proposed a wearable throat vibration system using a microwave sensor. Compared with millimeterwave measurement systems, a simple split-ring resonator can clearly detect and evaluate vocal fold vibration in the industrial, scientific and medical band. Higher harmonics can still be identified and quantified. A high-sensitivity microwave split-ring resonator has a sharp resonance response corresponding to the variation of the electrical fields timely in the near field to detect throat vibration. The use of amplitude modulation can be detected using an envelope detector at low cost and sensitively senses details of the vibration from vocal fold. Finally, the actual measurement results prove that the microwave sensor can measure approximately eleventh harmonics.

FMCW radar systems enable remote vital sign and range detection but suffer from proximity clutter issues. When a large clutter exists around the target of interest, capture effect occurs and the reflected waveform from clutter would dominate the phase of the baseband signal, destroying the vital sign detection. This paper presents a novel and clutter-resistant demodulation to extract slow-time signal under strong reflected interference signals of a stationary or non-stationary clutter at close range. By applying amplitude-based demodulation, signals of the stationary clutter can be distinguished and excluded. Therefore, vital sign can be clearly determined even under the condition of strong close reflected interferences. Furthermore, extracting heartbeat clearly from FMCW under interference of clutter is relatively difficult using traditional complex signal demodulation algorithms. This paper proposes a novel EEMD-PCA-Correlation algorithm to solve this problem. From the experiment results, the average error of heartbeat with a clutter within 1 cm is 0.537%

This paper demonstrates a closed-loop wireless power transfer (WPT) system for deep brain stimulation-implanted biomedical applications. A novel two-layer PCB FR4 coil design is proposed as a second coil for enlarging the WPT efficiency. High-efficiency implantable WPT technology was achieved by applying an inner dual-layer printed spiral coil (PSC) and outer helical coil and this coordinated with a T-type impedance-matching network. To reduce the loading effect, which lowers Q factor in implanted devices, four-coil WPT systems are recommended compared with two- or three-coil WPT systems. A practical four-coil system was implemented for verification, for which a dual-layer printed circuit board composed of a PSC, with a load loop on the other side of FR4, was designed and implemented around the system on a chip. PSCs for biomedical implants can be optimized by designing the geometric parameters. The implant coil occupies an area measuring $5 \times 5$ mm, and is implemented on both an FR4 board and an implantable flexible substrate with the optimized geometric parameters. Finally, the transmission efficiencies of using FR4 and flexible printed circuit boards, at a distance of 10 mm, were 19.1% and 14.8% through the air and 11.7% and 7.7% through the tissue, respectively, thus enabling the supply of milliwatts of power to the stimulation circuits, and successfully demonstrating the stimulation tissue model with a V/I output current of up to 180 $\mu \text{A}$ .

To realize a portable, capillary-driven, and parallelized microfluidic chip, how to evenly distribute a liquid plug from the inlet to multiple daughter microchannels is a challenging task. Two approaches were adopted to generate sufficient capillary pressure to allow a liquid plug spontaneously flowing through bifurcation features, including enlarging the contact perimeter between the liquid plug and microchannel walls and applying hydrophilic coating to the microchannel walls. A 1-to-2 bifurcation microfluidic chip and a 1-to-4 bifurcation microfluidic chip were designed and fabricated on PMMA substrates for experiments. Initially red food dye was used to demonstrate the effectiveness of the chips, and experiment results revealed that the 1-to-2 microfluidic chip is capable of 100% liquid splitting efficiency with a CV of 5.7% whereas the 1-to-4 microfluidic chip is capable of 83% liquid splitting efficiency with a CV of 6.7%. After successfully conducting experiments with red food dye, human whole blood and blood plasma were introduced into the 1-to-2 microfluidic chips and splitting efficiency was investigated. The experiment results showed a 33% and 67% splitting efficiency for human whole blood and blood plasma, respectively. And the lower splitting efficiency can be attributed to the complex and Non-Newtonian fluidic property of the blood.

In the present study, we use a training design in two experiments to examine whether bilingual language switching facilitates two components of cognitive control, namely monitoring and inhibitory control. The results of Experiment 1 showed that training in language switching reduced mixing costs and the anti-saccade effect among bilinguals. In Experiment 2, the findings revealed a greater decrease of mixing costs and a smaller decrease of the anti-saccade effect from pre- to post-training for the language switching training group compared to the L2 training group. Overall, the results suggest that extensive exercise in monitoring and inhibitory control among languages in an experimental setting may enhance the corresponding components of cognitive control. We discuss these findings in the context of the relationship between bilingual language control and executive control.

A novel cuffless blood pressure (BP) measurement technology is proposed in this paper. Systolic BP (SBP) and diastolic BP (DBP) can be estimated by measuring pulse transit time (PTT) between radial and carotid artery. The pulse signals of artery are measured by split-ring resonator microwave sensors with high sensitivity in a non-contact manner. Instead of measuring resonance frequency deviation, the measurements can be performed by detecting amplitude variation for not only simplified circuits but also increasing sampling rate and sensitivity. In addition, cascading a notch filter can steepen the transition response of sensor to further improves 135 times sensitivity compared to traditional frequency-based method. From experiment results, PTT and BP show the significant negative correlation, and the correlation coefficient is more than -0.79. Based on the relational function of PTT and BP, SBP and DBP can be estimated accurately, and the average error is lower than 8.4%.

This paper presents a novel approach to simultaneously monitor multi-target vital-signs using a frequency modulation continuous wave (FMCW) radar within the resolution limitation. For a traditional system architecture on multi-target vital-signs monitoring, complicated systems are required such as phased array radar or continuous wave (CW) radar with beamforming technology. In contrast, this architecture has the advantage of enhanced resolution capability, relatively simple circuit, and low cost. By using advanced signal processing such as adaptive boundary, we can detect multi-target vital signs even though the difference of the distances to the two targets is less than the range resolution of FMCW radar. In terms of demodulation, heart rate (HR) is susceptible to the harmonic of respiratory rate (RR) using complex signal demodulation (CSD). Therefore, this paper uses an ensemble empirical mode decomposition (EEMD) algorithm to extract the intrinsic mode functions of RR and HR. Experiments show that, we can improve signal-to-noise ratio (SNR) and accuracy significantly using this algorithm. And the vital sign errors of the two targets separated at 70 cm and 50 cm are averagely 2.35% and 4.44%, respectively.

Today’s commercial forced exercise platforms had been validated not as a well-designed rehabilitation environment for rats with a stroke, for the reason that rat with a stroke cannot take exercise at a constant intensity for a long period of time. In light of this, this work presented an adaptive, fall-free ischemic stroke rehabilitation mechanism in an animal model, which was implemented in an infrared-sensing adaptive feedback control running wheel (IAFCRW) platform. Consequently, rats with a stroke can be safely rehabilitated all the time, and particularly at full capacity for approximately one third of a training duration, in a completely fall-free environment according to individual physical differences by repeated use of an acceleration/deceleration mechanism. The performance of this platform was assessed using an animal ischemic stroke model. The IAFCRW therapy regimen was validated to outperform a treadmill and a conventional running wheel counterpart with respect to the reduction in the neurobehavioral deficits caused by middle cerebral artery occlusion (MCAo). IAFCRW is the first adaptive forced exercise training platform short of electrical stimulation-assistance in the literature, and ischemic stroke rats benefit more in terms of the behavioral tests run at the end of a 3-week rehabilitation program after a stroke thereby.

This letter proposes an implantable wideband low-specific-absorption-rate (SAR) antenna on a flexible substrate. The proposed antenna structure was printed on a thin flexible substrate, which is suitable for implantable human body applications. A sigma-shaped monopole radiator and the C-shaped design excited fundamental and coupled modes that dominated the near E-field distribution evenly to achieve a low SAR. The proposed antenna was fabricated and measured on a flexible substrate. The smallest size (80 $~\hbox{mm}^{3}$ ) was achieved with low-profile flexible substrate compared to a state-of-the-art implantable antenna over 400 MHz, and 68% fractional bandwidth was achieved. The maximum peak value of the average SAR was approximately 230 W/kg when the input power was 1 W. The maximum input power of the proposed antenna was approximately 10 mW.

This paper presents a novel noncontact measurement technique that entails using a single-compound triple complementary split-ring resonator (SC-TCSRR) to determine the complex permittivity and thickness of a material under test (MUT). The proposed technique overcomes the problem engendered by the existence of air gaps between the sensor ground plane and the MUT. In the proposed approach, a derived governing equation of the resonance frequencies is used to estimate the thickness and complex permittivity of the MUT by calculating the resonant frequency $(f_{{ r}})$ and magnitude response in a single-step noncontact measurement process. This study theoretically analyzed and experimentally verified a simple and low-cost SC-TCSRR measurement method for assessing materials in a noncontact method. For a 0.2-mm air gap, the experiments yielded average measurement errors of 4.32% and 5.05% for the thickness and permittivity, respectively. The proposed SC-TCSRR technique provides excellent solutions for reducing the effect of air-gap conditions on permittivity, thickness, and loss tangent in noncontact measurements.

Fused helical and spiral (FHS) coils are proposed to improve the efficiency of wireless power transfer by using both neural network and generic algorithms. FHS coils take advantages of balancing the coupling coefficient and the quality factor. Moreover, neural network and generic algorithm are applied to optimize the structure and parameters of the FHS coils with variable pitches. From simulation, the proposed 3.25-mm FHS coil structure consists of three layers of 15 turns. The pitches of three layers are 0.075, 0.225, 0.3 mm, respectively. Due to more condensed magnetic field distribution, the power transmission efficiency is improved to 24% compared with traditional signal turn coil at distance of 20 mm.

This paper presents a novel active split ring resonator (SRR) for detecting the wrist and fingertip pulse signals. Though fingertip signal is extremely tiny in general, the proposed intermodulation multiplication technology can improve the sensitivity by more than 400%. The frequency shift of sensing can be multiplied to highly sensitive by measuring the 3rd, 5th, 7th and 9th intermodulation (IM) components. The pulse signal can be measured from the frequency deviations of SRR by interfering the coupling path on the surface of the sensor. In this work, the highest component can be achieved to 9th IM. The frequency shift of measuring the wrist pulse signal is increased from 3.5 MHz to 16 MHz. The fingertip signal is first measured by a microwave sensor and can achieve high accuracy of less than 0.75% error.

This paper presents novel fabric substrate and manufacturing technique for microwave sensors. Fabric-substrate complementary split-ring resonator (FSCSRR) sensors can be applied to wearable devices for vital sign measurement. By attaching the microwave sensor, a soft wearable sensor based on FSCSRR in clothes can be realized. The respiratory and heartbeat signals can be high sensitively extracted by the frequency and amplitude deviations of FSCSRR where the sensor is placed inside a clothes, facing to the chest. The property of the fabric substrate is measured, and the impacts of the low-conductivity on sensitivity of the sensor is analyzed. Although the quality factor of sensor decreases, the proposed FSCSRR sensor is verified sufficiently sensitive while measuring of cardiorespiratory signals, and the errors of the heartbeat rate is less than 0.39%.

This paper presents a noise tolerable method for FMCW radar systems to detect vital sign under strong reflected interference signals of stationary clutter. By using phase accumulated demodulation, vital sign detection can be demodulated clearly even under existence of strong clutters influence, and noise can be decreased so that the delay-line can be reduced for the compact system implementation. From the measurement results, the measured absolute range has 4.69% error from 0.5 m to 3.05 m in average. Moreover, the vital sign is 2.25% and 1.49% error with stationary clutter interferer 0.75 m and 1.3 m behind the human target respectively.

Psycholinguistic studies of focus processing have yielded varying results regarding how focus affects language processing. We report the results of an event-related potential (ERP) experiment that used question-answer pairs in a discourse to manipulate whether a target word was contextually focused, contrastively focused, contextually defocused, or contextually neutral. We found a negative-going waveform that was sustained in the time-course (250–800 ms after the target word onset) with a maximum over frontal-central scalp sites. As the structure of the discourse made the target word more focused, the negative-going deflection was systematically reduced. We also observed a frontal positive-going waveform that was larger for the focus-marked words relative to the neutral target word in an earlier time window (150–250 ms, P200), which may reflect increased attention allocated to the focused items. We propose that the reduced negative ERPs for the focused words reflects facilitation of meaning integration when focus functions to establish reference in the discourse representation. This can be attributed to extra attention paid to the focus-marked items that in turn promotes the prominence of focus-marked referent and prompts the contextual priming mechanism that facilitates the access of propositionally relevant items in text memory during reading.

A urine testing chip based on the complementary split-ring resonator (CSRR) coupling with a microstrip and the microfluidic channel was developed and demonstrated for determining the water content of the urine. The CSRR is a resonant type of electromagnetic detector, which is sensitivity to the complex permittivity of materials. In addition, the complex permittivity of the tested urine sample is varied with the change of urine composition. Results show that the resonant frequency increased as the urine color became darker due to the decreased water content. Therefore, this microwave technique of the CSRR is proper to distinguish the urine for monitoring the hydration state.

Studies of bilingual proficiency have largely focused on word and sentence processing, whereas the text level has received relatively little attention. We examined on-line second language (L2) text comprehension in relation to L2 proficiency with ERPs recorded on critical words separated across a sentence boundary from their co-referential antecedents. The integration processes on the critical words were designed to reflect different levels of text representation: word-form, word-meaning, and situational levels (Kintsch, 1998). Across proficiency level, bilinguals showed biphasic N400/late positive component (LPC) effects related to word meaning integration (N400) and mental model updating (LPC) processes. More proficient bilinguals, compared with less proficient bilinguals, showed reduced amplitudes in both N400 and LPC when the integration depended on semantic and conceptual meanings. When the integration was based on word repetitions and inferences, both groups showed reduced N400 negativity while elevated LPC positivity. These effects reflect how memory mechanisms (processes and resources) support the tight coupling among word meaning, readers’ memory of the text meaning and the referentially-specified meaning of the text. They further demonstrate the importance of L2 semantic and conceptual processing in modulating the L2 proficiency effect on L2 text integration processes. These results align with the assumption that word meaning processes are causal components in variations of comprehension ability for both monolinguals and bilinguals.

This study numerically and experimentally investigates a photonic approach for microwave time delay, which takes advantage of the redshift of the laser cavity resonance induced by external optical injection in a semiconductor laser. The strong enhancement around the redshifted cavity resonance not only amplifies the power, but also shifts the phase of the microwave signals carried by the optical injection. Such a microwave phase shift is approximately linear over a few gigahertz, leading to a constant microwave time delay over the frequency range. A different time delay can be achieved by simply adjusting the injection power or frequency. For the microwave frequencies up to 40 GHz investigated in this Letter, a continuously tunable range of more than 80 ps in time delay is achieved over an instantaneous bandwidth of approximately 7 GHz. The quality of the data carried by the microwave signals is mostly preserved after time delay. Thus, a bit-error ratio down to 10−9 at 2.5 Gb/s is achieved with a possible detection sensitivity improvement of 5 dB.