Pulsed Radio Frequency Signals Research Articles

Comment on Redmayne, M.; Maisch, D.R. ICNIRP Guidelines' Exposure Assessment Method for 5G Millimetre Wave Radiation May Trigger Adverse Effects. Int. J. Environ. Res. Public Health 2023, 20, 5267.

This article discusses the contention in the commented-upon paper that Brillouin precursors generated by 5G New Radio (5G NR) and other cellular systems are a possible cause of tissue damage at deeper layers of tissue than the power penetration depth of the carrier frequency. The original theory for Brillouin precursors from pulsed radiofrequency signals (RF-EMF) and speculation about their possible health effects dates back to the 1990's and was based on studies of the propagation of very short (nanosecond) ultrawide-bandwidth RF pulses through water. This assumption is not correct for cellular telephone signals due to their narrow bandwidth. The commented-on paper provides no alternative rationale as to why Brillouin effects should cause tissue damage from RF-EMF radiation from cellular and other communications systems. Other inaccuracies in this paper concerning thermal responses of tissue to RF-EMF are also noted.

Carbon nanoparticles characteristics synthesized in pulsed radiofrequency discharge and their effect on surface hydrophobicity

AbstractCarbon nanoparticles were synthesized using a 13.56 MHz radiofrequency (RF) discharge of Ar/CH4 plasma in pulsed mode to control the nanoparticle size. Experimental observations have shown that the size of carbon nanoparticles increases with the frequency of the pulse signal. It was also found that by using a frequency modulated pulsed RF signal it is possible to control the size of carbon nanoparticles in the 40–70 nm range, where the plasma‐enhanced chemical vapour deposition method is the main mechanism for nanoparticle growth. Transmission electron microscopy image analysis showed two types of nanoparticles, some of which are an agglomerate of nanoparticles with an amorphous structure, while the others are nanometre‐sized with crystalline structures. Changes in the modulation frequency and synthesis time help to obtain different films with different values of the contact angle.

Phase Fluctuation Cancellation for Uplink Radar Arrays Based on Passive Frequency Mixing

Precise time-difference detections among different radars in uplink radar arrays require ultrastable phase transfer in bidirectional analog optical fiber links. We propose and demonstrate a scheme based on passive frequency mixing to satisfy this requirement in which two continue wave (CW) radio frequency (RF) signals after passing through double-path of the transport fiber are utilized for dynamic phase fluctuation cancellation in uplink and downlink, respectively. Our scheme has the capabilities on stable phase transfers for both CW and pulsed RF signals. Experimental results show that the phase stability improvements in uplink and downlink are greater than a factor of 30 and a factor of 20 for 2.4-GHz RF signals over a 2-h measurement period along 25-km single mode fiber.

Feasibility analysis of WDM links for radar applications

Abstract Active phased array antennas enhances the performance of modern radars by using multiple low power transmit/receive modules in place of a high power transmitter in conventional radars. Fully distributed phased array radars demand the distribution of various signals in radio frequency (RF) and digital domain for real time operation. This is normally achieved through complex and bulky coaxial distribution networks. In this work, we intend to tap the inherent advantages of fiber links with wavelength division multiplexed (WDM) technology and a feasibility study to adapt these links for radar applications is carried out. This is done by analysing various parameters like amplitude, delay, frequency and phase variation response of various radar waveforms over WDM links. This also includes performance evaluation of non-linear frequency modulation (NLFM) signals, known for better signal to noise ratio (SNR) to specific side lobe levels. NLFM waveforms are further analysed using pulse compression (PC) technique. Link evaluation is also carried out using a standard simulation environment and is then experimentally verified with other waveforms like RF continuous wave (CW), pulsed RF and digital signals. Synchronization signals are generated from this variable duty cycle digital signals during real time radar operation. During evaluation of digital signals, variable transient effects for different duty cycles are observed from an amplifier configuration. A suppression method is proposed to eliminate this transient effects. Further, the link delay response is investigated using different lengths of fiber spools. It can be inferred from the experimental results that WDM links are capable of handling various signals significant to radar applications.

Quantization Noise Reduction Techniques for Digital Pulsed RF Signal Generation Based on Quadrature Noise Shaped Encoding

The digital generation of pulsed radio frequency (RF) signals based on noise shaped encoding in complex baseband is a popular concept in digital RF transmitters. However, as the pulsed complex-baseband signals are up-converted to an RF frequency, a conjugate image overlaps with the signal band, which complicates the center frequency tuning for the transmitters in question. In this paper novel ways related to equalization techniques used for imbalanced digital complex valued systems are presented to mitigate conjugate image noise. Firstly, the distortion generation mechanism of the digital up-conversion is explained. Based on the analysis two cancelation techniques are derived. Secondly, novel quadrature encoder topologies implementing the given compensation techniques are developed. The analytical and the simulation based results show conjugate quantization noise suppression of more than 50 dB, which extends the potential center frequency tuning range considerably. Finally, a comparison with previously given encoders reveals nearly 10 dB improvement in dynamic range.

Pulsed electromagnetic fields potentiate neurite outgrowth in the dopaminergic MN9D cell line

Pulsed electromagnetic fields (PEMF) exert biological effects and are in clinical use to facilitate bone repair and wound healing. Research has demonstrated that PEMF can induce signaling molecules and growth factors, molecules that play important roles in neuronal differentiation. Here, we tested the effects of a low-amplitude, nonthermal, pulsed radiofrequency signal on morphological neuronal differentiation in MN9D, a dopaminergic cell line. Cells were plated in medium with 10% fetal calf serum. After 1 day, medium was replaced with serum-containing medium, serum-free medium, or medium supplemented with dibutyryl cyclic adenosine monophosphate (Bt2 cAMP), a cAMP analog known to induce neurite outgrowth. Cultures were divided into groups and treated with PEMF signals for either 30 min per day or continuously for 15 min every hour for 3 days. Both serum withdrawal and Bt2 cAMP significantly increased neurite length. PEMF treatment similarly increased neurite length under both serum-free and serum-supplemented conditions, although to a lesser degree in the presence of serum, when continuous treatments had greater effects. PEMF signals also increased cell body width, indicating neuronal maturation, and decreased protein content, suggesting that this treatment was antimitotic, an effect reversed by the inhibitor of cAMP formation dideoxyadenosine. Bt2 cAMP and PEMF effects were not additive, suggesting that neurite elongation was achieved through a common pathway. PEMF signals increased cAMP levels from 3 to 5 hr after treatment, supporting this mechanism of action. Although neuritogenesis is considered a developmental process, it may also represent the plasticity required to form and maintain synaptic connections throughout life.

Compressive sensing of sparse radio frequency signals using optical mixing

We demonstrate an optical mixing system for measuring properties of sparse radio frequency (RF) signals using compressive sensing (CS). Two types of sparse RF signals are investigated: (1) a signal that consists of a few 0.4 ns pulses in a 26.8 ns window and (2) a signal that consists of a few sinusoids at different frequencies. The RF is modulated onto the intensity of a repetitively pulsed, wavelength-chirped optical field, and time-wavelength-space mapping is used to map the optical field onto a 118-pixel, one-dimensional spatial light modulator (SLM). The SLM pixels are programmed with a pseudo-random bit sequence (PRBS) to form one row of the CS measurement matrix, and the optical throughput is integrated with a photodiode to obtain one value of the CS measurement vector. Then the PRBS is changed to form the second row of the mixing matrix and a second value of the measurement vector is obtained. This process is performed 118 times so that we can vary the dimensions of the CS measurement matrix from 1×118 to 118×118 (square). We use the penalized ℓ(1) norm method with stopping parameter λ (also called basis pursuit denoising) to recover pulsed or sinusoidal RF signals as a function of the small dimension of the measurement matrix and stopping parameter. For a square matrix, we also find that penalized ℓ(1) norm recovery performs better than conventional recovery using matrix inversion.

Effect of Time-Averaging of Pulsed Radio-Frequency Signals on Specific Absorption Rate Measurements

The effect of the time-averaging of pulsed radio-frequency (RF) signals on the specific absorption rate (SAR) measurements is studied. Probes employed for SAR measurements are usually calibrated using continuous wave (CW) signals. The response of such probes is different when measuring pulsed RF waveforms. The CW probe calibration data are applicable to the average power of the pulsed RF signal. The time-domain response of a commercially available off-the-shelf SAR probe to a global system for mobile communication signal is investigated. The error induced by the time-averaging process is evaluated. The ensemble average procedure is compared to the alternative peak detection method valid for signals with known duty cycle. The analysis can be extended to other pulsed RF waveforms with specifications that satisfy the time-domain characteristics of the probe.

Thirty‐five years in bioelectromagnetics research

For 35 years, I have been involved in various bioelectromagnetics research projects including acute and long-term radiofrequency (RF) bioeffects studies, dosimetry, exposure systems, MRI safety, cancer studies involving hyperthermia and electrochemical treatment, development of RF exposure and measurement standards, and product compliance. My first study demonstrated that effects on isolated nerve and muscle preparations were due to thermal effects of RF exposure. The recording of cochlear microphonics in animals shows the mechanical nature of the microwave auditory effect. In 1992, we published the results of a large-scale lifetime study in which 100 rats were sham-exposed and 100 rats were exposed for 21 h/day for 25 months to a pulsed RF signal. In dosimetry studies, human models were employed as well as many animal species including mice, rats, rabbits, monkeys, and birds of many sizes. Cancer hyperthermia studies demonstrated that knowledge of temperature distribution was crucial for successful treatment. Research on electrochemical treatment of tumors with direct current involved cellular, animal, and clinical studies. Over the past few decades, there has been rather extensive investigation of the public health impact of RF exposure. In my opinion, future research in bioelectromagnetics should place greater emphasis on medical applications.

The Effects of Pulsed 860 MHz Radiofrequency Radiation on the Promotion of Neurogenic Tumors in Rats

In a previous study, this laboratory reported a statistically nonsignificant trend for shortened latency of ethylnitrosourea (ENU)-induced brain tumors in Sprague-Dawley rats exposed to an 860 MHz pulsed radiofrequency (RF) signal. The present study was designed to investigate further any promoting effect of the pulsed RF signal on latency and other characteristics of neurogenic tumors in the progeny of pregnant rats treated with 6.25 or 10 mg/kg ENU. The resulting 1080 offspring were randomized equally by number, sex and ENU dose into pulsed RF, sham and cage control groups. The rats were exposed to the pulsed RF signal 6 h per day 5 days per week; the sham-exposed group was similarly confined for the same periods, and the cage controls were housed in standard cages. An essentially equal number of rats from each group were killed humanely every 30 days between the ages of 171 and 325 days; 32 rats died and 225 rats were killed when they were moribund. Postmortem examinations on the 1080 rats revealed 38 spinal cord tumors, 191 spinal nerve tumors, 232 cranial nerve tumors, and 823 brain tumors. A methodical study of the tumor characteristics disclosed no evidence that exposure to the pulsed RF signal affected the incidence, malignancy, volume, multiplicity, latency or fatality associated with any kind of neurogenic tumor.

A controllable phase coherent pulsed RF signal generator for microwave network analyzer measurements

In this paper, a method is proposed to build a phase coherent modulated radio-frequency (RF) signal with high depth, which can be used as an excitation signal for nonlinear pulsed-RF network analyzer measurements. The source consist of an RF carrier modulated by an arbitrary waveform generator whose sampling clock is phase coherent to the carrier. A software feedback technique is used to eliminate spurious harmonics and to correct the amplitude and phase distortions in the IF signal path. This technique allows to create a modulated excitation signal with a known spectrum (in amplitude and phase). Such a modulation signal is required to fully characterize a device-under-test under noncontinuous wave (modulated or pulsed) test conditions with a sampling downconvertor. The measurement of a controlled pulsed-RF spectrum shows the obtained performance (the bandwidth is limited to 4 MHz at this moment).

Objective measurement of receiver sensitivity

The sensitivity of radar receivers is checked with a pulsed radio frequency signal which is adjusted until the observed magnitude is distinguishable from the background noise level as displayed on an oscilloscope. Because of the noisy nature of the display the results are highly subjective, but by eliminating the idiosyncratic element, a calibration instrument has been designed to give a rapid and accurate presentation to the operator.