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The purpose of this paper is to investigate experimentally the effect of natural frequency of the experimental set‐up on wear rate of glass fiber‐reinforced plastic (GFRP).

Experimental and dimensional analysis. A pin‐on‐disc apparatus having facility of vibrating the test samples at different directions, amplitudes and frequencies was designed and fabricated. The natural frequency of the set‐up was varied by adding dead loads of the set‐up from 0 to 50 kg. At each added load, the wear rate has been measured.

The presence of natural frequency of vibration indeed affects the wear rate considerably. The values of wear rate increase with the increase of natural frequency of vibration of the experimental set‐up. As the wear rate increases with increasing natural frequency of vibration, therefore, maintaining appropriate level of natural frequency vibration wear may be kept to some lower value to improve mechanical processes. The empirical formula of wear rate is derived from the dimensionless analysis. The wear rate obtained from the correlation shows better relationship with experimental results.

It is expected that the applications of these results will contribute to the improvement of different concerned mechanical systems and machines.

Considering the lack of correlation among wear rate, natural frequency of the experimental set‐up and other operating parameters, the present research was started to find out suitable correlation and a way of reducing wear rate by applying known natural frequency of vibration at a particular direction. Therefore, in this paper, an attempt is made to investigate the wear behavior of GFRP under natural frequency of the experimental set‐up. It is expected that the applications of these results will contribute to the improvement of different concerned mechanical systems.

The use of frequency output for measurement transmission remains common in the design of smart transmitters. Conventional methods of frequency generation, based on counting clock cycles, have a precision which is inversely proportional to the frequency to be generated. Consequently, frequency output precision could be much lower than the measurement precision. This paper describes a simple frequency generation technique which, when implemented in low‐cost hardware, provides a precision of 10⁻⁶ per cent for all frequencies. The method represents an intermediate non‐available frequency by dithering between two exact frequencies. Averaging over some reasonably short timescale provides the desired frequency to high precision.

This paper aims to discuss a comprehensive analysis of the effects of torque and flux hysteresis bands on the inverter average switching frequency considering an induction machine drive under the control of the Takahashi DTC strategy.

The analysis of the effects of torque and flux hysteresis bands on the inverter average switching frequency is carried out taking into account the speed range and the sampling period.

It has been found that the inverter average switching frequency could be more or less taken down according to the speed range and the sampling period by selecting suitable flux and torque hysteresis bands.

This work should be extended by an experimental validation of the established results.

The reduction of the inverter switching frequency is of great importance in direct torque controlled induction motor drive as far as it leads to a decrease of the torque ripple and an increase of the efficiency.

For given torque and flux hysteresis bands, the inverter average switching frequency presents nonlinear shape. Given the fact that the flux switching frequency is a linear function of the speed, one can conclude that the nonlinearity of the inverter average switching frequency is due to the torque switching frequency. This statement has been proven by the introduction of the so‐called focal speeds for the torque switching frequency turns to be null.

In wireless communication system, use of multiple antennas for different requirements of system will increase the system complexity. However, reconfigurable antenna is maximizing the connectivity to cover different wireless services that operate different frequency range. Pattern reconfigurable antenna can improve security, avoid noise and save energy. Due to their compactness and better performance at different applications, reconfigurable antennas are very popular among the researchers. The purpose of this work, is to propose a novel design of S-shaped antenna with frequency and pattern diversity. The pattern and frequency reconfiguration are controlled via ON/OFF states of the PIN diode.

The geometrical structure of the proposed antenna dimension is 18 × 18 × 0.787 mm³ with εr = 2.2 dielectric constant. Three S-shaped patches are connected to a ring patch through PIN diodes. The approximate circumference of ring patch is 18.84 mm and length of patch is 5 mm, so approximate length of radiating patch is 14.42 mm and effective dielectric constant is 1.93. Conductor backed coplanar waveguide (CPW) is used for feeding. The proposed antenna is designed and simulated on CST microwave studio and fabricated using photolithography process. Measurements have been done in anechoic chamber.

Antenna shows the dual band operation at 2.1 and 3.4 GHz frequency. The first band remains constant at 2.1 GHz resonant frequency and 200–400 MHz impedance bandwidth. Second band is switched at seven different resonant frequencies as 3.14, 3.45, 3.46, 3.68, 3.69, 3.83 and 3.86 GHz with switching of the diodes. The −10 dB bandwidth is more than 1.4 GHz.

Pattern reconfigurability can be achieved using mechanical movement of antenna easily but it is not a reliable approach for planar antennas. Electronic switching method is used in proposed antenna. Antenna size is very small so fabrication is very crucial task. Measured results are deviated from simulation results due to fabrication error and effect of leads of diodes, connecting wires and battery.

The reconfiguration of the proposed antenna is controlled via ON/OFF states of the three PIN diodes. The lower band of 2.1 GHz is fixed, while second band is switched at five different resonant frequencies as 3.27, 3.41, 3.45, 3.55 and 3.88 GHz, with switching of the PIN diodes with all state of diodes and exhibit pattern reconfigurability at 2.1 GHz frequency. At second band center frequency is significantly changed with state of diodes and at 3.4 GHz pattern is also changed with state of diodes, hence antenna exhibits frequency and pattern reconfigurability.

A novel design of pattern and frequency reconfigurable antenna is proposed. Here, work is divided into two parts: first is frequency reconfiguration and second is radiation pattern reconfiguration. PIN diodes as switch are used to select the frequency band and reconfigure the radiation pattern. This proposed antenna design is novel dual band frequency and pattern reconfigurable antenna. It resonates at two distinct frequencies, i.e. 2.1 and 3.4 GHz, and has a pattern tilt from 0° to 355°. The conductor backed CPW feed technique is used for impedance matching.

The purpose of this paper is to present, a novel boost‐active clamp bridge single stage high‐frequency zero voltage soft‐switching‐pulse width modulation (ZVS‐PWM) inverter, which converts the utility frequency AC power into high‐frequency AC power with an embedded controller. This single stage high‐frequency inverter is composed of a single‐phase diode bridge rectifier, a non‐smoothing filter, a boost‐active clamp bridge type ZVS‐PWM high‐frequency inverter, and an induction‐heated load with planar type litz wire working coil assembly. Also, the paper discusses how to extend the soft‐switching operation ranges and improve power conversion efficiency.

The proposed converter is simulated and it is implemented using embedded controller.

It was found that the single stage high‐frequency induction heating (IH) inverter using boosted voltage function can eliminate the DC and low‐frequency components of the working coil current and reduce the power dissipation of the circuit components and switching devices.

The paper shows that the PWM HF inverter is preferred for IH, since it has reduced switching losses and switching stresses. The paper can be extended to PC‐based wireless control, which can be part of a distributed control system in major industrial heating systems.

A highly accurate method of current spectrum estimation of a nonlinear load is presented in this paper. Using the method makes it possible to evaluate the current injection frequency domain model of a nonlinear load from previously recorded time domain voltage and current waveforms. The paper aims to discuss these issues.

The method incorporates the idea of coherent resampling (resampling synchronously with the base frequency of the signal) followed by the discrete Fourier transform (DFT) to obtain the frequency spectrum. When DFT is applied to a synchronously resampled signal, the spectrum is free of negative DFT effects (the spectrum leakage, for example). However, to resample the signal correctly it is necessary to know its base frequency with high accuracy. To estimate the base frequency, the first-order Prony's frequency estimator was used.

It has been shown that the presented method may lead to superior results in comparison with window interpolated Fourier transform and time-domain quasi-synchronous sampling algorithms.

The method was designed for steady-state analysis in the frequency domain. The voltage and current waveforms across load terminals should be recorded simultaneously to allow correct voltage/current phase shift estimation.

The proposed method can be used in case when the frequency domain model of a nonlinear load is desired and the voltage and current waveforms recorded across load terminals are available. The method leads to correct results even when the voltage/current sampling frequency has not been synchronized with the base frequency of the signal. It can be used for off-line frequency model estimation as well as in real-time DSP systems to restore coherent sampling of the analysed signals.

The method proposed in the paper allows to estimate a nonlinear load frequency domain model from current and voltage waveforms with higher accuracy than other competitive methods, while at the same time its simplicity and computational efficiency is retained.

To provide detailed information about the novel universal frequency‐to‐digital converter UFDC‐1, which can help engineers and researchers to design new digital sensors and transducers, as well as smart sensors and sensor systems.

The high performance of the UFDC‐1 is achieved by using four novel measuring methods for frequency‐time parameters. All existing integrated frequency‐to‐digital converters and frequency (time) output sensors have been reviewed and current design requirements for the UFDC‐1 have been formulated.

The UFDC‐1 enables the transition from traditional analog (voltage and current) sensors output to frequency‐time output. This yields a lot of benefits due to the properties of frequency as informative parameter. No output standardization is necessary, as opposed to the case of analog output sensors. Users can now work with the UFDC‐1, the same as with traditional ADCs. Sensor manufacturers can simply integrate the UFDC‐1 in microsystems and digital output sensors in order to produce serial output or bus capability.

The UFDC‐1 has many applications: obtaining a digital output from any frequency, period, duty‐cycle, time interval, phase‐shift, pulse number output sensors, up to one chip digital sensors design and smart (self‐adaptive) sensors, thanks to its programmable relative error and non‐redundant conversion time. The UFDC‐1 can work with any existing frequency‐time domain sensor to produce a digital output or create multiparametric smart sensors and systems.

This paper fulfils an identified information need and offers practical help to engineers and researchers in designing new digital sensors and transducers, as well as smart sensors and systems using a minimum of hardware.

Extends the evolutionary structural optimization method to the solution for the natural frequency optimization of a two‐dimensional structure with additional non‐structural lumped masses. Owing to the significant difference between a static optimization problem and a structural natural frequency optimization problem, five basic criteria for the evolutionary natural frequency optimization have been established. The inclusion of these criteria into the evolutionary structural optimization method makes it possible to solve structural natural frequency optimization problems for two‐dimensional structures with additional non‐structural lumped masses. Gives two examples to demonstrate the feasibility of the extended evolutionary structural optimization method when it is used to solve structural natural frequency optimization problems.

The experiments of this study investigated the effect of the subgrade degree of saturation on the value of the stresses generated on the surface and the middle (vertical and lateral stresses). The objectives of this study can be identified by studying the effect of subgrade layer degree of saturation variation, load amplitude and load frequency on the transmitted stresses through the ballast layer to the subgrade layer and the stress distribution inside it and investigating the excess pore water pressure development in the clay layer in the case of a fully saturated subgrade layer and the change in matric suction in the case of an unsaturated subgrade layer.

Thirty-six laboratory experiments were conducted using approximately half-scale replicas of real railways, with an iron box measuring 1.5 x 1.0 × 1.0 m. Inside the box, a 0.5 m thick layer of clay soil representing the base layer was built. Above it is a 0.2 m thick ballast layer made of crushed stone, and on top of that is a 0.8 m long rail line supported by three 0.9 m (0.1 × 0.1 m) slipper beams. The subgrade layer has been built at the following various saturation levels: 100, 80, 70 and 60%. Experiments were conducted with various frequencies of 1, 2 and 4 Hz with load amplitudes of 15, 25 and 35 kN.

The results of the study demonstrated that as the subgrade degree of saturation decreased from 100 to 60%, the ratio of stress in the lateral direction to stress in the vertical direction generated in the middle of the subgrade layer decreased as well. On average, this ratio changed from approximately 0.75 to approximately 0.65.

The study discovered that as the test proceeded and the number of cycles increased, the value of negative water pressure (matric suction) in the case of unsaturated subgrade soils declined. The frequency of loads had no bearing on the ratio of decline in matric suction values, which was greater under a larger load amplitude than a lower one. As the test progressed (as the number of cycles increased), the matric suction dropped. For larger load amplitudes, there is a greater shift in matric suction. The change in matric suction is greater at higher saturation levels than it is at lower saturation levels. Furthermore, it is seen that the load frequency value has no bearing on how the matric suction changes. For all load frequencies and subgrade layer saturation levels, the track panel settlement rises with the load amplitude. Higher load frequency and saturation levels have a greater impact.

This study aims to propose a method for monitoring bearing health in the time–frequency domain, termed the Lock-in spectrum, to track the evolution of bearing faults over time and frequency.

The Lock-in spectrum uses vibration signals captured by vibration sensors and uses a lock-in process to analyze specified frequency bands. It calculates the distribution of signal amplitudes around fault characteristic frequencies over short time intervals.

Experimental results demonstrate that the Lock-in spectrum effectively captures the degradation process of bearings from fault inception to complete failure. It provides time-varying information on fault frequencies and amplitudes, enabling early detection of fault growth, even in the initial stages when fault signals are weak. Compared to the benchmark short-time Fourier transform method, the Lock-in spectrum exhibits superior expressive ability, allowing for higher-resolution, long-term monitoring of bearing condition.

The proposed Lock-in spectrum offers a novel approach to bearing health monitoring by capturing the dynamic evolution of fault frequencies over time. It surpasses traditional methods by providing enhanced frequency resolution and early fault detection capabilities.