Graphene-based waveguide resonators for submillimeter-wave applications

Implantable intrabody communication (IBC) is a method that enables low-power, high-security communication between implanted in-body devices that could track biomedical signals and an on-body receiver by using the human body as a communication medium. As the human body consists of various tissues that each have different conductivity, this paper explores the effects of the conductivity of the communication medium on the channel gain over a wide frequency range from 10 MHz up to 300 MHz through the measurements and two models: an electrical circuit model and a FEM simulation model. Measurements are conducted using a liquid phantom with varying conductivity values from 0 S/m up to 1 S/m, covering most human tissues in the frequency range of interest. The circuit and FEM models are designed to mimic the measurement setup in order to verify the measurement results. Results show that the circuit model predicts the communication channel characteristics well at lower frequencies but cannot account for the influence of the measurement setup at higher frequencies. The influence of wire inductances, which can cause a resonant behavior when measuring at frequencies above 100 MHz, was observed using the FEM model. The results also show that the higher the conductivity of the tissue in which the device is implanted, the lower the gain of the signal, with the difference in gain being more prominent when capacitive termination with a high-impedance load is used instead of low-impedance termination. These findings provide valuable insight for selecting the appropriate interface (low-impedance vs. high-impedance termination) across specific frequency ranges for in-body to on-body (IB2OB) communication devices, while illustrating the effect of tissue conductivity on an IBC channel, thereby supporting the optimized design and implementation of reliable IB2OB communication systems.

Paper deals with the complex permittivity measurement of biological tissues. Application of a waveguide probe for this measurement is shown. A non-destructive and non-invasive method based on reflection coefficient measurement attaching the material under test is used. New types of the probes are under investigation - the section of waveguide with H cross-section, the section of waveguide with the rectangular cross-section and with shorted walls, the section of waveguide with inserted dielectric wedge and finally the section of waveguide filled by the liquid dielectric. Properties of these prototypes are studied in the frequency range from 300 kHz to 3 GHz. The method of finite difference in time domain is utilized for the numerical modeling and simulation of the reflection coefficient. The condition for the input reflection coefficient of the waveguide probe is the range from (0.7 - 0.3) in the broad frequency band. Although the waveguide is a narrowband microwave component, its modifications could have broadband frequency behavior of the reflection coefficient. Results indicate that the most interesting and suitable is the solution with removable dielectric. This liquid dielectric with the low value of permittivity has significant influence on the cut-off frequency of waveguide with dominant mode propagation.

A quasi-hermetic photodiode module featuring a WR-12 rectangular waveguide (RW) output has been developed for operation in the E-band. The module makes use of a grounded coplanar-waveguide-to-rectangular-waveguide transition implemented on a Rogers RT/duroid 5880 laminate that does not require any mechanical modifications of the RW. Simulations show that the transition has excellent radio frequency (RF) characteristics (return loss larger than 30 dB, insertion loss smaller than 2 dB, maximum group delay deviation smaller than 1 ps). Measurements confirm the simulated results and highlight the importance of via-holes to reduce the overall loss. The maximum output power delivered by the module, at a DC photocurrent of 10 mA, is -12.5dBm. At 73 GHz, the 1-dB compression point is found to be at a photocurrent of ~ 9mA, with an RF output power of ~ -13.5dBm . The measured output power has less than 1 dB ripple in the frequency range of interest.

System identification in frequency domain using wavelets: Conceptual remarks

In this paper the design of rectangular waveguide filters in Ka-band with constant bandwidth is discussed. Only the cavities are assumed to be tuned, while the couplings must be dimensioned in order to get constant the bandwidth in the tuning bands. The tuning elements are implemented by means of dielectric rods driven by a single stepper micro-motor. As a result, all the rods are assumed to have the same penetration in the cavities for each tuning band. The design of a filter with 500 MHz bandwidth tuned in the band 29-31 GHz is presented, together with the preliminary simulation results.

An improved structure of a high-power adapter is proposed for broadband matching of coaxial transmission lines and rectangular waveguides with a narrow side wall that are network used in space communication systems. Numerical simulation and optimization of such a microwave two-port are performed with the aid of the finite-element method in a frequency interval of 2.5–4.9 GHz. The sizes of a modified coaxial-to-waveguide adapter that provide the desired electrodynamic characteristics in the specified frequency interval are determined.

An isotropic, elastic solid permits the propagation of one straight-crested, nondispersive surface wave, called a Rayleigh wave. If a thin film of a different material is deposited on the substrate, an infinite number of straight-crested surface waves are possible, all of which are dispersive, including the one corresponding to the Rayleigh wave. Since the solution of the three-dimensional equations of elasticity is extremely unwieldy and the films may be considered thin in the frequency range of interest, the approximate equations of low-frequency extension and flexure of thin plates are employed in the solution to account for the motion of the platings. These approximate equations enable the entire effect of the plating to be treated as a boundary condition at the surface of the substrate. The accuracy of the approximation is shown to be excellent in the frequency range of interest. It is shown that platings which load the substrate reduce the velocity of straight-crested surface waves, while platings which stiffen the substrate increase the velocity. A condition is derived which tells whether a given combination of materials will lower or raise the surface-wave velocity. The solution for straight-crested waves in isotropic solids is extended to include waves with trigonometric and hyperbolic crests. An approximation technique is introduced, which enables the use of the dispersion curves for straight-crested waves in connection with the extended solution for waves with variable crests, in order to obtain approximate solutions for surface waves guided by thin films of finite width. The results of the calculation are shown to compare favorably with experiment. The analysis shows that strips of finite width may be used to guide surface waves only when the film loads the substrate and that slots of finite width in the film must be used when the film stiffens the substrate. It is also shown that while the strip configuration has a highly dispersive surface-wave velocity, the slot configuration has a large frequency range around which the surface wave velocity is essentially nondispersive. A formula for the coupling length between two weakly coupled, adjacent strips (or slots) is obtained by means of a perturbation technique, and shows that the coupling length increases rapidly with decreasing wavelength.

Early predator detection is a key component of the predator-prey arms race and has driven the evolution of multiple animal hearing systems. Katydids (Insecta) have sophisticated ears, each consisting of paired tympana on each foreleg that receive sound both externally, through the air, and internally via a narrowing ear canal running through the leg from an acoustic spiracle on the thorax. These ears are pressure-time difference receivers capable of sensitive and accurate directional hearing across a wide frequency range. Many katydid species have cuticular pinnae which form cavities around the outer tympanal surfaces, but their function is unknown. We investigated pinnal function in the katydid Copiphora gorgonensis by combining experimental biophysics and numerical modelling using 3D ear geometries. We found that the pinnae in C. gorgonensis do not assist in directional hearing for conspecific call frequencies, but instead act as ultrasound detectors. Pinnae induced large sound pressure gains (20–30 dB) that enhanced sound detection at high ultrasonic frequencies (>60 kHz), matching the echolocation range of co-occurring insectivorous gleaning bats. These findings were supported by behavioural and neural audiograms and pinnal cavity resonances from live specimens, and comparisons with the pinnal mechanics of sympatric katydid species, which together suggest that katydid pinnae primarily evolved for the enhanced detection of predatory bats.

In this work, we report on in-substrate passive components using a high performance glass interposer and through glass via (TGV) technology and a multi-layer superlattice conductor architecture. Minimal RF loss is achieved using low dielectric loss glass substrates and superlattice conductors featuring skin effect suppression. Half mode substrate integrated waveguide (HMSIW) resonators and two-pole bandpass filters, embedded inside a glass interposer substrate, are used as test vehicles for the demonstration of insertion loss improvement in K-band. The utilized conductor is made of 20 layers of Cu/NiFe with each pair of 360 nm/30 nm, respectively, where NiFe layers with negative permeability in frequency range of interest are used for eddy current cancelling and improving the conductor loss. Control devices using the same glass substrate and conductor made of pure copper are fabricated for comparison purposes. The glass interposer substrate (SGW3, Corning Incorporated) has a thickness of 0.13 mm and the TGV's with a diameter of 0.08 mm. Up to 0.3 dB reduction in the insertion loss is achieved by using the proposed superlattice approach on glass substrates.

We propose a low-speed photonic sampling for independent high-frequency characterization of a Mach–Zehnder modulator (MZM) and a photodetector (PD) in an optical link. A low-speed mode-locked laser diode (MLLD) provides an ultra-wideband optical stimulus with scalable frequency range, working as the photonic sampling source of the link. The uneven spectrum lines of the MLLD are firstly characterized with symmetric modulation within the interesting frequency range. Then, the electro-optic modulated signals are down-converted to the first Nyquist frequency range, yielding the self-referenced extraction of modulation depth and half-wave voltage of the MZM without correcting the responsivity fluctuation of the PD in the link. Finally, the frequency responsivity of the PD is self-referenced measured under null modulation of the MZM. As frequency responses of the MZM and the PD can be independently obtained, our method allows self-referenced high-frequency measurement for a high-speed optical link. In the proof-of-concept experiment, a 96.9 MS/s MLLD is used for measuring a MZM and a PD within the frequency range up to 50 GHz. The consistency between our method and the conventional method verifies that the ultra-wideband and self-referenced high-frequency characterization of high-speed MZMs and PDs.

This paper presents a general sub-structuring approach to predict the acoustic performance of ducted ventilation systems. The modeling principle is to determine the subsystem characteristics by calculating the transfer functions at their coupling interfaces, and the assembly is enabled by using a patch-based interface matching technique. For a particular example of a bended ventilation duct connecting an inlet and an outlet acoustic domain, a numerical model is developed to predict its sound attenuation performance. The prediction accuracy is thoroughly validated against finite element models. Through numerical examples, the rigid-walled duct is shown to provide relatively weak transmission loss (TL) across the frequency range of interest, and exhibit only the reactive behavior for sound reflection. By integrating sound absorbing treatment such as micro-perforated absorbers into the system, the TL can be significantly improved, and the system is seen to exhibit hybrid mechanisms for sound attenuation. The dissipative effect dominates at frequencies where the absorber is designed to be effective, and the reactive effect provides compensations at the absorption valleys attributed to the resonant behavior of the absorber. This ultimately maintains the system TL at a relatively high level across the entire frequency of interest. The TL of the system can be tuned or optimized in a very efficient way using the proposed approach due to its modular nature. It is shown that a balance of the hybrid mechanism is important to achieve an overall broadband attenuation performance in the design frequency range.

The presence of laser phase noise (or frequency jitter) limits the resolution of a variety of interferometric sensors ranging from fiber optic acoustic sensors to gravitational wave detectors. At low frequencies, 0 to 100 kHz, the laser phase noise in semiconductor and diode pumped solid-state lasers is dominated by 1/f noise, the source of which is not well understood. We report on phase noise measurements for external cavity semiconductor lasers (ECSLs) utilizing a fiber Bragg grating in a compact butterfly package design produced by K2 Optronics. The results show that the phase noise is dominated by 1/f noise for low frequencies (10 to 100 kHz) transitioning to a white noise due to spontaneous emission for f > 100 kHz. We observed a factor of 40 improvement in the magnitude of the 1/f phase noise as compared to previously published results for a Hitachi HLP 1400 830 nm diode laser. The magnitude of the low frequency phase noise ranges from 100 to 10 microradians per meter per root Hz for frequencies ranging from 10 Hz to 2 kHz. These results are within a factor of 10 for phase noise measurements of the more expensive Lightwave Electronics Nd:YAG laser and a variety of Er-doped fiber lasers in this frequency range. For nominally similar ECSLs, experimental results indicate that the phase noise increases for lasers with larger leakage currents. Linewidth measurement results showed a Schawlow-Townes inverse power dependence for output powers up to 33 mWatts with the observed onset of a linewidth floor of 30 kHz. The RIN of the ECSLs varied from -120 to -155 dB Vrms per root Hz for frequencies ranging from 10 to 500 kHz. These RIN results are roughly equal to those observed for the Nd:YAG laser for frequencies less that 100 kHz. In summary, such low phase noise and RIN results make such ECSLs suitable for all but the most sensitive fiber optic sensing applications where the frequency range of interest is below 1 MHz.

In-plane thermal diffusivity determination using beam-offset frequency-domain thermoreflectance with a one-dimensional optical heat source

The objective of this research is to develop a methodology and means for testing and identifying the optimal non-invasive electrodes for clinical impedance spectroscopic measurements from human subjects in a frequency range from 10 Hz to 1 MHz. Many electrodes are available on the market for clinical applications, ranging from ECG to TENS electrodes. These electrodes must function only within specific, relatively narrow frequency ranges. When used for wide-band impedance spectroscopic measurements, they significantly reduce the usable bandwidth of the system. Unfortunately, most manufacturers do not test their electrodes to determine their performances over a wide range of frequencies such as would be required for impedance spectroscopy. Due to the lack of data about electrode performance, we had to develop a testing protocol to determine the characteristics of various non-invasive electrodes throughout the frequency range of interest. The most important measurement characteristics is the recording accuracy of the electrodes. The instrument that we used to conduct the research is a custom-made impedance spectrometer that interfaces to a laptop computer. The main hypotheses of the project are that a testing protocol can be developed and optimal non-invasive electrodes can be identified for use in clinical measurements of tissue impedance throughout a range of frequencies, while maintaining good signal-to-noise ratio. Preliminary results support the principal hypotheses.

This paper presents an approximate method for general fractional order dynamic systems. Firstly, a novel piecewise approximate method is proposed for fractional order integrator based on its frequency distributed mode. Based on the above method, an integer order approximation system is constructed to approximate a fractional order system. Theoretical analysis results show that the proposed method can achieve much better performance than the existing schemes for a given order in an interested frequency range. The advantage of the proposed method lies in that the resulting system are standard integer order system, which facilitates systematic stability analysis and controller synthesis in view of the well-developed linear or nonlinear system theory. Numerical simulations are presented to illustrate the effectiveness of the proposed approach in the end.