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In this paper, a new 7-bit frequency discriminator for instantaneous frequency measurement applications is presented for the first time. The proposed discriminator is designed using microstrip band-stop spiral filters to achieve a compact size structure with high reject values between pass and reject bands. As these passive filters are fabricated on available ordinary substrates, the proposed structure is ultralow cost. Rectangular and circular spiral resonators are used to reject the specific frequency bands in each channel. The designed filters for each channel divide the frequency bandwidth into several pass/reject bands to produce the desired binary code. The proposed structure works in S-band with the maximum frequency error of 16 MHz. The proposed discriminator was simulated by a momentum simulator of an advanced design system (ADS) and fabricated on a 20-mil Rogers RO4003 substrate with tan($\delta$) and a conductor thickness about 0.002 and $18~\mu \text{m}$ , respectively. An excellent agreement was achieved between the simulation results obtained by ADS and those of measurements; the average frequency shift is less than 10 MHz. [ABSTRACT FROM AUTHOR]

This paper proposes an energy efficient instrumentation set-up for pulse-compression thermal-wave imaging with a low-power LED excitation source. The set-up consists of three different subsystems that are synchronised in time. The individual systems consist of a LED modulation circuitry, reference signal measurement circuitry, and an IR camera trigger signal generation circuitry for frame capture. A separate reference acquisition circuitry is useful in quantifying defect depth resolution. This paper also proposes a nonuniform frame capture technique to reduce the memory allocation space of the recorded video. The technique is based on varying the sampling rate with a change in instantaneous frequency and is specifically useful for frequency modulated excitation signal. The proposed technique is implemented on a carbon fiber reinforced polymer test-piece. The variation of pulse compression parameters with different defect dimension is studied, and the results are verified with an electro-thermal simulator. Further, an objective comparison of pulse compression experiment for different experiment duration is presented. [ABSTRACT FROM PUBLISHER]

The classical time-invariance assumption is often not (exactly) met in real-life applications. As a natural extension of the frequency response function (FRF), the time-variant FRF (TV-FRF) provides quick insight into the complex dynamics of time-variant systems. Recently, a procedure has been proposed to estimate nonparametrically the TV-FRF from known input, noisy output measurements of time-variant systems operating in open loop. However, in many applications, feedback is present either due to an explicit control action or due to the interaction between a nonideal actuator and the system under test. The extension of the open-loop approach to noisy input, noisy output measurements of time-variant systems operating in closed loop requires the deconvolution of the time-variant impulse response of the cascade of two time-variant systems. In this paper, this nontrivial problem is solved for a particular class of time-variant systems. The robustness of the approach with respect to the system assumption is demonstrated via simulations and measurements on an electronic circuit. [ABSTRACT FROM PUBLISHER]

We present a method for the suppression of frequency shifts in pulsed atomic clocks based on the Ramsey scheme, caused by unwanted interaction of the atoms with the resonant interrogation field during the free atomic evolution time (Ramsey time). The method relies upon a precise control of the field’s frequency detuning during the period of free evolution. The frequency detuning reduces the frequency shift caused by the interaction between the free precessing atoms and the interrogation field. We present measurements that allow us to limit the uncertainty contributions due to such an interaction at the atomic fountain clock PTB-CSF2 to 3.8\times 10^-17 . [ABSTRACT FROM PUBLISHER]

Nonlinear contact between tip and sample in tapping mode atomic force microscopy (AFM) systems induces higher harmonics, which may be useful for extraction of some characteristics of the sample. In this paper, a new efficient method for implementing multichannel digital lock-in technique is presented, which is able to measure the amplitude and phase of multiple modulated frequency signals. In order to solve the two most important problems in AFM systems, which are resolution and cost, previous multichannel lock-in amplifier methods are investigated and an improved algorithm for amplitude and phase extraction using fast Fourier transform is developed. In addition, we propose a novel multichannel digital lock-in algorithm including an $N$ -slow digital filter and a multichannel direct digital synthesis block for generating reference signals. We achieve optimal noise reduction using the appropriate decimation filters prior to harmonic extraction. This modification results in a significant hardware reduction in implementation compared with classical designs. Since the precision of the design is sensitive to the sampling frequency, we perform the suitable sampling rate conversion using fractional delay and decimation filters, which enhance the accuracy and noise resiliency of the designed architectures. Experimental results prove the efficiency of the proposed method in multiple modulated frequencies extraction. Also, FPGA implementation results show that the proposed architecture is superior to previous structures, especially in the aspect of area. [ABSTRACT FROM PUBLISHER]

The prediction of the clock offset plays an important role in the generation of a time scale, clock steering, and time offset prediction of the onboard clocks. The mathematical model method based on the stochastic differential equations has been dealt with the clock prediction problem. In this paper, we examine the method from a theoretical point of view. We derive the analytic expressions of the theoretical prediction uncertainties when the clocks are modeled by the sum of a white frequency modulation noise, a random walk frequency modulation noise in both the linear model case and the quadratic polynomial model case. Simulations and an experiment for predicting the time deviations of International Atomic Time-TA(National Time Service Center) are used to validate the theoretical analyses. The simulations and the experiment show that the prediction performances agree with the theoretical evaluations; therefore, we consider that the research is useful in applications. Furthermore, we illustrate that the prediction uncertainty can be minimized only by choosing an optimal observation interval. From simulations, for a typical cesium clock, the method is effective for short-term prediction, whereas for a typical hydrogen maser, for all prediction times the uncertainties of the deterministic part are predominant, and we thus consider that the method in the quadratic polynomial model case deserves further investigation. [ABSTRACT FROM PUBLISHER]

We present a novel method for demodulating multiple frequency components of an ac magnetic field for use in electromagnetic tracking systems. Our undersampling method allows for a low sampling rate to acquire signals of interest in a range of 20–30 kHz without significant loss of precision. Lower sample rates give additional computation time between each sample, allowing for real-time demodulation without expensive high speed data acquisition and processing hardware. This also allows the use of low speed high precision analog-to-digital converters (ADCs) for sampling high frequency signals. The presented system demodulates 16 frequency components from two signals using an Arduino Due microcontroller and a two channel 16-bit ADC. The demodulated signals are then used to accurately determine the position of a magnetic sensor to within 1 mm in a volume 25 cm \times 25~cm \times 25 cm. The system accuracy compares well with both commercial and research systems in terms of accuracy, but at a dramatically lower cost. [ABSTRACT FROM PUBLISHER]

This paper describes a novel instrument based on a self-mixing optical interferometer, able to reconstruct the target speed and direction, without heterodyne detection. The real-time elaboration employs the signal nonlinearity to recover the speed sign in the frequency domain. The target speed is measured by the signal frequency, while the speed sign is evaluated by the phase of the harmonics in the frequency domain. The high-sensitivity of the elaboration allows the measurement over diffusive target with distances up to 10 m. The measurements results have been successfully compared with a very-high resolution commercial calibrated instrument. [ABSTRACT FROM PUBLISHER]

We compare the sensitivity performance of two optically pumped atomic magnetometers based on the Mx and frequency-modulated Bell-Bloom configurations. The Cs magnetometers are implemented using a millimeter-scale microfabricated vapor cell. It is found that the Bell-Bloom magnetometer yields sensitivities similar to those of the Mx magnetometer when operated under equally optimized conditions. The Bell-Bloom approach offers several attractive features over the Mx approach for chip-scale magnetometer instrumentation. [ABSTRACT FROM AUTHOR]

We describe a new method for high-frequency precision sensing. The method combines synchronous detection with chopping in a fully differential architecture that includes an instrumentation amplifier. An integrated circuit implementation of the proposed synchronous chopping demodulator front end was designed and fabricated in a 0.35-μm CMOS process technology and tested with high-frequency inductive position sensors. The measured results show that the new technique offers considerable advantages in terms of offset reduction compared to traditional techniques for these sensors, which rely on a microcontroller to measure the offset before each position measurement is taken. The measured average input-referred offset for the 20 fabricated chip samples is 87 μV at a chopping frequency of 500 kHz when the resonant target is off and synchronous demodulation and transmitter excitation are both applied at 1 MHz. The technique, in addition to improving system resolution and immunity to common-mode interference, allows these high-frequency position sensors to work with multiple targets, thus increasing speed and functionality. [ABSTRACT FROM AUTHOR]

A method for the accurate spectral analysis of signals containing components that do not require synchronism either with each other or with the sampling clock is presented. The method employs an algorithm based on the quadrature amplitude demodulation which is applied in a number of stages to achieve an accurate decomposition of a given time domain signal into frequency components. Using the simulated signal examples, the suitability of the method for the analysis of noisy quantized nonrepetitive signals is considered. When compared to the discrete Fourier transform, the benefits of using the method for the accurate detection of nonsynchronous tones in a signal are demonstrated. [ABSTRACT FROM AUTHOR]

A setup has been developed for determining the axial position of the active magnetic sensor element inside its case with respect to a reference face at the outside of the sensor case. For an axial Hall-sensor providing a sensitivity of 1 mV/μT, an uncertainty in the order of ±6 μm is achieved, i.e., the uncertainty of the distance between reference point and Hall element, as specified by the producer, can be reduced by a factor of about 50. For a fluxgate sensor having two rods of 5 mm in length, it is possible to localize its axial magnetic center within nearly the same uncertainty. [ABSTRACT FROM AUTHOR]

In this paper, a method for precise rms measurement of periodic signals based on signal reconstruction is presented. Reconstruction is performed in two steps. In the first step, the Fourier coefficients are estimated from integrative samples, and in the second step, using the method of least squares and precision measurement of rectified-signal average, the estimators are corrected. It is shown that this approach considerably increases accuracy of the rms measurements of low-frequency signals. [ABSTRACT FROM AUTHOR]

We obtained fline = (351 721 960 559 ± 39) kHz, k = 1, as the absolute frequency of F = 4 → F′ = 5 transition of cesium D2 line by measuring the frequency of an external cavity diode laser (ECDL) locked to the center of the line with frequency modulation transfer technique. The frequency of ECDL was measured by an optical frequency synthesizer based on a 1-GHz femtosecond laser system linked to the hydrogen maser. To increase the S/N ratio of the beat note signal, a distributed Bragg reflector laser was injection locked to one of the optical comb components. [ABSTRACT FROM AUTHOR]

Presents an efficient method for evaluating the carrier frequency error in Gaussian minimum shift-keying (GMSK) communication systems. Frequency error measurement; GMSK neural network based demodulator; Method validation; Conclusion.

Presents the design of a fully-integrated angular speed sensor system based on a capacitive carrier frequency measurement principle. Requirements imposed on sensors in the automotive area; Consequences for the general system design; Alternatives to extract the baseband signal from the carrier.

Proposes a technique to address the problem of constructing a robust feature space for automatic classification of signals from narrow-band-in-air ultrasonic sensors. Description of the algorithms; Estimation of the Laguerre coefficients; Evaluation of Laguerre feature space quality.

Discusses a study which described the frequency stabilization of frequency-double Nd: YAG lasers against the hyperfine structure (HFS) components of iodine by means of the sub-Doppler frequency modulation technique. Experimental setup of the study; Frequency differences between the HFS components of the iodine transition; Conclusions.

Presents information on a study which demonstrated a real-time and full polarimetric FM-CW radar system. Design of real-time polarimetric FM-CW radar system; Decomposition of scattering matrix; Real-time classification experiment; Conclusions.