Extended Frequency Band Research Articles

A broadband active sound absorber with adjustable absorption coefficient and bandwidth.

Broadband adjustable sound absorbers are desired for controlling the acoustic conditions within enclosed spaces. Existing studies on acoustic absorbers, either passive or active, aim to maximize the sound absorption coefficients over an extended frequency band. By contrast, this paper introduces a tunable acoustic absorber, whose working frequency band and sound absorption characteristics can be defined by users for different applications. The approach leverages an error signal that can be synthesized using a standing wave separation technique. The error signal encodes different target reflection coefficients, leading to arbitrary absorption coefficients between 0 and 1. Experimental validation is conducted in a one-dimensional standing wave tube, demonstrating that the proposed active absorber achieves near-perfect absorption within the 150-1600 Hz frequency range, boasting an average absorption coefficient of 0.98. Adjustable absorption is demonstrated across three octave bands, aligning closely with theoretical predictions. Furthermore, when coupled with a shaping filter, the absorber exhibits spectrally tunable broadband absorption capabilities, selectively reflecting specific frequency bands while effectively absorbing others. These outcomes underscore the versatile tunability of the proposed active acoustic absorber, which is expected to pave the way for personalized regulating of the indoor acoustic environment.

A Wideband High-Gain Dielectric Horn-Lens Antenna for Wireless Communications and UWB Applications

A wideband high-gain dielectric horn-lens antenna (DHLA) for wireless communications and ultra-wideband (UWB) applications, featuring 122% fractional bandwidth, is presented. The antenna, consisting of a dielectric horn equipped with a spherical-axicon dielectric lens that increases and equalizes the gain within the operating band, is placed on a PCB featuring a wideband eight-shaped slot fed by a tapered microstrip line employed to excite the radiating system. The lens, integrated within the body of the dielectric horn, has the property of focusing the RF energy near its vertex on an extended frequency band, thus ensuring compact size, excellent field coupling with the antenna excitation system, and a significant increase of antenna gain. The antenna operates in the 3–12.4 GHz frequency range with relatively flat group delay, making it suitable for operating with narrowband, broadband, and impulsive UWB signals. The antenna can work properly without or with a metal reflector useful to enhance gain (up to 19 dBi), improve the front-to-back ratio, and reduce the impact of the antenna characteristics from the installation site. CST Studio Suite, implementing a full-wave locally conformal finite integration technique (FIT), was employed to design and characterize the antenna. The antenna characteristics estimated numerically were found to be in good agreement with the experimental results performed on an antenna prototype.

Nonlocal Ventilating Metasurfaces

A traditional metasurface is composed of metaunits that are elaborately designed to provide a precise local response, and these metaunits also inevitably impact mutual radiation from each other, affecting the global response of the metasurface. Beyond those nonlocal metasurfaces that utilize such radiation coupling to promote efficiency in wave manipulation, in this study the coupling effect also serves as a powerful tool for engineering the spectrum, showcased by an acoustic open metasurface that allows airflow while blocking sound in a dramatically extended frequency band. This finding offers an efficient approach for broadband wave manipulation in a hybrid nonlocal manner.

Traffic Noise Mitigation Using Single and Double Barrier Caps of Different Shapes for an Extended Frequency Range

The primary function of noise barriers is to shield inhabitants of affected areas from excessive noise generated by road traffic. To enhance the performance of noise barriers while simultaneously adhering to height restrictions, the attachment of structures (caps) of different shapes to the tops of conventional screens can be considered. These caps can significantly impact the diffracted sound energy, thereby increasing the desired global acoustic losses. This work presents a comprehensive study of the acoustic performance of noise barriers with single and double attached caps of different shapes through a calculation of their insertion losses (IL). This study comprehensively addresses and compares different types, sizes, combinations, and numbers of noise barrier caps for different scenarios (including sloping and absorbent grounds) and sources (“car” and “ambulance”) for an extended frequency band up to 10 kHz. To the best of the authors’ knowledge, this is a range that has not previously been analyzed. A variety of different cap shapes were considered including cylinders, rectangles, trapezoids, and Y/T-shaped forms. To calculate the IL, an innovative and fast uniform theory of diffraction (UTD)-based method developed by the authors was applied in all simulations. The results showed that the Y-shaped single and double barrier caps were, in general, the most effective at increasing IL without raising the height of the barrier, thereby successfully managing the aesthetic impact. The results also showed how the consideration of sloping and absorbent floors could also contribute to improved noise abatement.

Sea-Surface-Temperature Retrieval at Higher Spatial Resolution in the Satellite-Borne Microwave Radiometer AMSR2 Follow-On Mission

The Advanced Microwave Scanning Radiometer-2 (AMSR2) follow-on mission is currently being considered, and end users are demanding the acquisition of sea-surface temperature (SST) with higher spatial resolution. However, it is assumed that the AMSR2 baseline design will be followed as much as possible to shorten the development period. The SST image retrieved from the 6- or 10-GHz brightness temperatures includes random “snow” noise due to the thermal noise originating from the receiver components. In AMSR2, simple spatial averaging was performed to reduce such random noise to obtain clear SST images, but this method is not suitable for acquiring SST images with the high spatial resolution because it degrades the spatial resolution. In the AMSR2 follow-on mission, the algorithm for the AMSR2 L1R product (Backus-Gilbert method) will be applied to reduce random noise without degrading the spatial resolution. In addition, we propose equipping not only a 10-GHz channel with the conventional frequency band but also that with an extended frequency band. This letter presents the results of the study that led to these proposals required to obtain clear SST images with higher spatial resolution in the AMSR2 follow-on mission.

Testing of a Laboratory Prototype for Recording Dolphin Signals with an Extended Frequency Band of the Through Path

New technologies for the digital recording of broadband complex signals have made it possible to develop and create laboratory autonomous multichannel equipment to record bioacoustic activity on a digital medium with low power consumption and the possibility of continuous recording for up to 4 h. The equipment operates under the control of a fit-PC computer with the Windows operating system and the PowerGraph program for digital recording in a frequency band of the analog path of up to 600 kHz. Equipment testing recorded paradoxical signals from toothed whales with a frequency band exceeding 200 kHz. Signals with an extended frequency band were recorded in a laboratory experiment in open water while solving the problem of target tracking and in an experiment with provocation of acoustic communication behavior.

Band Stop Matching Circuit이 적용된 Inverted-F Antenna의 Bypass Capacitor를 이용한 안테나 효율 향상 기법

In this paper, a design technique using a bypass capacitor is proposed to improve the antenna efficiency of an inverted-F antenna (IFA) with a band stop matching circuit (BSMC). The proposed antenna operates in the LTE bands 26 and 5(814~ 894 MHz). The bandwidth of the IFA is expanded from 803～863 MHz to 800～888 MHz using the impedance change caused by the BSMC. To enhance the antenna efficiency in the expanded frequency band, the bypass capacitor is applied to the IFA with the BSMC. The bypass capacitor improves the efficiency of the antenna by reducing the current variation of the IFA with the BSMC. The proposed antenna has a bandwidth of 804～895 MHz and the antenna efficiency increases by more than 10 % in the extended frequency band by using the bypass capacitor.

A High-Power Source of Ultrawideband Pulses of Synthesized Radiation

Abstract—A high-power source of ultrawideband radiation based on the synthesis of electromagnetic pulses with different frequency bands has been created. A four-channel former of highly stable bipolar pulses with durations of 0.5 and 1 ns was developed. Each element of a 2 × 2 array of combined antennas was excited from its former channel. Two modes of radiation synthesis were studied: according to the maximum field strength and the maximum spectrum width. For the first mode, radiation pulses with a frequency band of 0.39–2.13 GHz and an effective potential of 600 kV were obtained. Synthesized radiation pulses with an extended frequency band of 0.15–2.7 GHz and an effective potential of 200 kV were obtained in the second mode. The pulse repetition frequency was 100 Hz.

Dynamics of frequency dependences of parameters of electric impedance of a person during dry fasting

Introduction The article considers the possibility of further development of the method of analysis of the parameters of electrical impedance to determine the current functional state of a person in various conditions of his life, in particular during the dry fasting. The aim of the study was the dispersion properties investigation of the amplitude and phase parameters of human body impedance in the extended frequency band during the weekly one and half day dry fasting. Methods. Measurement of electrical impedance parameters was performed weekly during half a year on one person before, during and after a day and a half fasting . Broadband three-frequency measurement technique is used. The possibility of analyzing the dispersion characteristics of a human body using the Cole hologram is considered. Results and discussion. It is established that in the process of dry fasting there is a change of all parameters of impedance. The most pronounced changes in the parameters of electrical impedance are observed by the definition of the module and the active component at a frequency of 100 kHz, the phase at frequencies 20 and 500 kHz, the reactive component at a frequency of 20 kHz. Conclusion. Changes in the dispersion properties of the human body impedance are noticeable in all parameters especially in phase and reactive resistance. According to the research results an interpretation of changes in the functional state of a person during fasting was made.

A high-power synthesized ultrawideband radiation source.

A high-power ultrawideband radiation source has been developed which is capable of synthesizing electromagnetic pulses with different frequency bands in free space. To this end, a new circuit design comprising a four-channel former of bipolar pulses of durations 2 and 3 ns has been elaborated and conditions for the stable operation of gas gaps of independent channels without external control pulses have been determined. Each element of the 2 × 2 array of combined antennas is driven from an individual channel of the pulse former. Antennas excited by pulses of the same duration are arranged diagonally. Two radiation synthesis modes have been examined: one aimed to attain ultimate field strength and the other aimed to attain an ultimate width of the radiation spectrum. The modes were changed by changing the time delay between the 2-ns and 3-ns pulses. For the first mode, radiation pulses with a frequency band of 0.2-0.8 GHz and an effective potential of 500 kV have been obtained. The synthesized radiation pulses produced in the second mode had an extended frequency band (0.1-1 GHz) and an effective potential of 220 kV. The pulse repetition frequency was 100 Hz.

Analysis methods of determining velocity distribution waves in the cavitation zone ultrasound field

The main parameters of cavitation processing technology environments is the speed of sound in a cavitation medium pressure, the duration, size: cavitation region, bubbles and core. The most successful use of ultrasound associated with handling liquid media, because in them the phenomenon of ultrasonic cavitation, which is an effective mechanism for concentration of energy of sound waves in the low-density high energy density, which is caused by pulsations and cavitation bubbles popping. An important component in ensuring an effective process of cavitation treatment process fluids is to calculate the ultrasonic technological devices that hold for precavitational mode with the following specification obtained by previous studies. However, reliable results associated with the methods of measuring the velocity of ultrasonic waves in a developed cavitation because it is a part of almost all the defining parameters of ultrasonic cavitation processing technology environments. Measuring the velocity of ultrasonic waves carried pulse, optical, amplitude-phase methods. Pulse methods have a wider dynamic range, measurement accuracy independent of the distance between the transmitter and the object opportunity emitter distance from the subject a considerable distance. Amplitude-phase methods require extended frequency band transceiver emitting element and amplifier path that reduces security and selectivity. Frequency and phase methods have the narrow bandwidth receiving radiating path that provides good value energy radiated and received signals, high noise immunity. Is an effective method for determining the rate for power characteristics, the essence of which is to determine the energy flux density and energy density relative to the ultrasound field. It has been found that the accuracy of measuring the speed of sound depends on whether it should receive the absolute value or relative value can restrict the speed of sound when changing any external parameters. Absolute measurement accuracy is about 10-5, while the relative change as accuracy is much higher, it reaches the order of 10-7. The choice of measurement due to the conditions of the experiment. The essential difference in the numerical values of the speed, complicates the acceptance of an opinion on the actual numerical value of speed and requires more informed research in determining the accepted assumptions and preconditions in the formulation and conduct research.

High-Performance Electrically Thin Dual-Band Polarizing Reflective Surface for Broadband Satellite Applications

This paper describes an anisotropic impedance surface that provides dual-band linear-to-circular polarization conversion in reflection with the peculiar property that a same linear polarization is converted into a given circular polarization handedness over the first frequency band and into the orthogonal one over the second frequency band. This property is of interest for multiple beam satellite communication systems, as the transmit and receive signals are commonly operating in orthogonal polarizations. This paper demonstrates that a simple, electrically thin polarizer design can provide high-performance conversion over the extended frequency bands used for broadband satellite applications. Some insight on the operation of the proposed polarizer is provided, supported by equivalent circuit models and analytical formulas, and compared with full-wave simulation results. The proposed design achieves an axial ratio better than 0.2 dB in simulation at normal incidence. A further iteration of the design and breadboard, taking into account measurement and practical implementation errors, provides an axial ratio better than 0.5 dB in measurement over the full transmit and receive frequency bands allocated to broadband satellite applications within the K/Ka bands.

Dual Transformer for Power Measurements in the Audio-Frequency Band

A new analog processing unit (APU) with an extended frequency band, which is based on an electromagnetic principle, has been designed and constructed at the Istituto Nazionale di Ricerca Metrologica (INRIM). The unit can be employed in power measurements in the audio-frequency band. The sum and the difference of two waveforms from 20 Hz to 100 kHz are simultaneously performed. The unit has been characterized to evaluate its behavior from power frequencies up to 20 kHz. The output signals of the APU and the phase relation between the sections of the unit have been characterized, and the results of the measurement and the model adopted are reported here. The additional devices that constitute the input structure of the thermal wattmeter acting as a scaling factor (shunts and alternating-current (ac) resistive dividers), as well as the automatic ac/direct-current transfer procedure, have been characterized.

Resonance blocking of traveling waves by a system of cracks in an elastic layer

Wave processes that occur in an elastic layer when waves traveling in it are diffracted by a system of horizontal cracks are investigated. Integral representations of wave fields are constructed in terms of the convolution of Green’s matrices and unknown jumps of displacements at the cracks. The displacement jumps are determined from the boundary integral equations, which are obtained from the initial boundary-value problem with the boundary conditions at crack faces being satisfied. The spectrum of the integral operator is studied for different variants of mutual crack arrangement and is compared with the spectrum of the corresponding operators for individual cracks; the relationship between the spectrum and the blocking effects is analyzed. The possibility of obtaining an extended frequency band of waveguide blocking in the case of groups of cracks is demonstrated.

Broad-Band Vibration Attenuation in Plates With Periodic Arrays of Shunted Piezoelectric Patches

Periodic arrays of shunted piezoelectric patches are employed for the control of waves propagating over the surface of plate structures. The shunted piezoelectric patches act as sources of impedance mismatch, which yield interference phenomena resulting from the interaction between incident, reflected and transmitted waves produced by the mismatch. The impedance mismatch corresponding to the shunted piezos can be tuned to achieve strong attenuation over frequency bands which are defined by the shunting circuit connected to the patches. Broad-band vibration attenuation can be achieved through the application of series and parallel of multiple resonant circuits, or through the implementation of negative capacitance configurations. The ability of plates with periodic shunted piezoelectric patches to attenuate vibrations over extended frequency bands is demonstrated numerically, through Finite Element models of the considered electromechanical structures. The effect of number of patches and of their periodic distributions is investigated together with the analysis and the comparison of performance achieved with various shunting strategies.

A mutual-inductance bridge for analysis of magnetic fluids

A mutual-inductance bridge designed for measuring the dynamic susceptibility of magnetic fluids at temperatures ranging from −50 to +90°C is described. A specific feature of the bridge is an extended frequency band of the probing field that ranges from infralow frequencies of ∼0.05 Hz to 200 kHz. The formulas that establish relationships between the bridge output signals and the real and imaginary parts of the susceptibility, the testing technique, and the results of testing are presented.

Wideband terahertz spectroscopy of explosives

Time-domain terahertz spectroscopy (TDTS) has been shown to be a promising tool in detection of explosives and explosive related compounds. To date, TDTS for many explosives has been limited to spectral regions <3 THz. With recent improvements in emitters and sensors of THz radiation, we report the THz absorption spectra over an extended frequency band from 0.5 to 6 THz for four explosives: RDX (1,3,5-trinitroperhydro-1,3,5-triazine), HMX (1,3,5,7-tetranitroperhydro-1,3,5,7-tetrazocine), PETN (pentaerythritol tetranitrate), and TNT (2,4,6-trinitrotoluene). New distinctive spectral features are shown in these materials between 3 and 6 THz. These data may aide in the spectral identification of these explosives.

Binocular contrast inhibition in subjects with age-related macular degeneration.

In subjects with normal vision, binocular contrast sensitivity is generally higher than monocular sensitivity, indicating summation of contrast in the two eyes. We have compared monocular and binocular contrast sensitivity and acuity for a group of 13 subjects with age-related macular degeneration (AMD). Relative to a normal control group, many of the AMD subjects showed reduced binocular contrast summation, and binocular inhibition was found for eight subjects for a narrow or an extended frequency band. A better monocular than binocular function may have practical implications for reading and orientation in AMD.

Validity of backscatter strength models at high (110–170 kHz) frequencies

Sonar performance models use several low-level acoustic models to predict the effect of the environment on reverberation and noise. Many of these acoustic models, particularly those predicting seabed scattering strength, were developed at lower frequencies than those currently used by both the scientific and mine-hunting communities. This paper examines the popular Applied Physics Laboratory of the University of Washington (APL-UW) acoustic backscatter strength model and tests its validity in the extended frequency band of 110–170 kHz. Acoustic and environmental data (gathered as part of a joint program with NATO SACLANTCEN) from several sites are collated and compared in this paper. This provides compelling evidence regarding the validity of the APL-UW backscatter model at these higher frequencies.

Evaluations of 1–3 piezocomposite transducers for underwater applications

This presentation begins with discussions on 1–3 piezocomposite transducer designs and how the designs may be tailored for specific underwater acoustic applications. For instance, 1–3 piezocomposite materials with cover plates for actuator applications shall be shown and compared with other 1–3 piezocomposite transducers that feature finer scale piezoceramic rods for wideband underwater acoustic imaging applications. Other 1–3 piezocomposite transducers to be shown include multilayer plates with elements stacked in mechanical series and wired electrically in parallel as well as monolithic structure designs with elements etched into the piezocomposite structure. Underwater electroacoustic evaluations of each of the 1–3 piezocomposite transducers will be presented. The in-water measurements include the transmitting and receiving performances as well as directivity patterns over extended frequency bands. Discussions on how the 1–3 piezocomposite transducers may be applied towards future underwater acoustic systems shall conclude the presentation. [Work sponsored by ONR.]