Beatrice Lang
Increasing the frequency of an electrical voltage source is a topic of interest in electrical engineering. One approach to achieving this is by manipulating the time period of one complete cycle, as frequency is defined as the number of cycles per second. Additionally, the type of waveform desired, such as pulse or sinusoidal, plays a role in determining the methods for increasing frequency. kHz-frequency electrical stimulation has been studied in the context of activating specific nerve fibers, particularly small, unmyelinated vagus afferents. These studies have revealed insights into the relationship between stimulus frequency, intensity, and the selectivity of fiber activation.
| Characteristics | Values |
|---|---|
| How to increase frequency | Change time or frequency |
| Frequency and voltage dependence | Frequency is not voltage dependent |
| Waveform | Pulse, Sinus |
| Myelinated fiber activation | At low frequencies (<1 kHz), myelinated fibers are not blocked |
| Myelinated fiber activation | At higher frequencies (>2 kHz), large myelinated fibers are blocked |
| Unmyelinated fiber activation | At low frequencies (<1 kHz), unmyelinated fibers are not blocked |
| Unmyelinated fiber activation | At higher frequencies (>2 kHz), unmyelinated fibers are progressively activated |
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What You'll Learn
Change time or frequency settings
To increase electrical frequency to kHz, you can change the time or frequency settings. Frequency is measured in cycles per second, so to increase the frequency, you need to decrease the time for each cycle.
For example, if you want to achieve a frequency of 2kHz, you need to ensure that the time period of one complete cycle (on time + off time) is 0.5ms. This can be done by adjusting the pulse cycle time.
It's important to note that changing the frequency may require different approaches depending on the waveform you're working with (e.g., pulse, sinus). Additionally, the relationship between voltage and frequency should be considered. In some cases, the voltage source may need to be adjusted to achieve the desired frequency.
When dealing with kHz-frequency electrical stimulation, it's important to consider the type of fibers being activated. Simulations suggest that both large, myelinated, and small, unmyelinated fibers can be activated or blocked, and the selectivity can be attained by adjusting the stimulus frequency and intensity. At low frequencies (<1kHz), neither fiber type is blocked, but as frequencies increase (>2kHz), large myelinated fibers are blocked while unmyelinated fibers are progressively activated at higher intensities.
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Pulse voltage output
Understanding Pulse Voltage Output
Techniques to Increase Frequency
To increase the frequency of pulse voltage output, adjustments can be made to either the time period or the frequency directly. One common approach is to minimise the pulse cycle time, reducing the duration of each cycle to achieve a higher frequency.
Applications and Parameters
Pulse Width Modulation
Pulse-width modulation (PWM) is a technique where the output voltage is measured, and a switch is turned on or off accordingly. This method creates useful timbral variations in synthesis instruments. PWM is commonly used in audio amplifiers and computer power supplies, with frequencies ranging from a few kHz to tens of kHz.
Flowmeter Pulse Output
Flowmeters are instruments that measure flow rate, and some are designed to provide a pulse output at a frequency proportional to the flow rate. These pulses can be counted to provide a totalised flow readout. The scaling of the output can be adjusted to represent specific volumes or masses of fluid.
Pulse Output Simulations
Pulse output simulations are used to understand the behaviour of electrical systems. For instance, a pulse output simulation with a fixed 1 ms positive pulse and a variable interval can be controlled using push buttons. This allows for experimentation with different pulse parameters.
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Modulating stimulus frequency
The ability to modulate stimulus frequency is particularly important in the context of high-frequency stimulation (HFS), which is used to control abnormal neuronal activity associated with movement disorders, seizures, and psychiatric disorders. HFS has been found to suppress somatic activity and generate excitation of axons, but the mechanisms behind its therapeutic action are not yet fully understood. Studies have shown that HFS can drive axons at the stimulus frequency, and its effects on axonal activity include disrupting HFS-evoked excitation and generating a complete conduction block of secondary evoked activity.
The impact of HFS on axonal conduction has been observed in both in-vitro and in-vivo settings. Fiber tracts were found to be unable to follow extracellular pulse trains above 50 Hz in-vitro and 125 Hz in-vivo. The number of cycles required for failure was dependent on the frequency, and reversible conduction block occurred at higher stimulus amplitudes. These findings highlight the importance of modulating stimulus frequency in HFS applications, as it can affect the ability of axons to propagate signals effectively.
Furthermore, the concept of modulating stimulus frequency extends beyond the realm of neuroscience and into the field of auditory perception. Imaging studies have revealed that sounds that vary in frequency and amplitude over time activate the non-primary auditory cortex, particularly in the posterolateral region. This activation is observed when comparing modulated stimuli with their unmodulated counterparts. By sinusoidally modulating either the frequency or amplitude of a sound, researchers can create controlled stimuli where the temporal characteristics are determined by the modulating waveform. This approach has been utilized in functional magnetic resonance imaging (fMRI) studies to investigate brain responses to acoustical signals.
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Compound action potentials
CAPs are often evoked by 2- to 16-kHz tone bursts at several sound levels. For example, in one study, a solution was slowly injected into the cochlear apex of anesthetized guinea pigs. As the solution flowed from apex to base, it sequentially reduced CAP responses from low to high-frequency cochlear regions.
CAPs can also be evoked by a single-cycle 1 kHz haversine stimulus, which has been studied in anesthetized cats. The haversine CAP waveform consisted of two or three short latency peaks with peak-to-peak intervals of about 1.0 ms. Latencies of the CAP peaks decreased with increased stimulus intensity and were strongly dependent on stimulus polarity.
In another study, CAPs evoked by high-level low-frequency (including 2 kHz) tone bursts showed little CAP contribution from CF regions ≤ 2 kHz. This suggests that CAP origins may be identified by a spatially specific technique.
To increase electrical frequency to kHz, one can make changes in either time or frequency. For example, if the time period of one complete cycle is 0.5 ms, the frequency would be 2 kHz.
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Asynchronous activity in A-, B- and C-fibers
Increasing the frequency of a voltage source can be achieved by making changes in either time or frequency. For example, if you have a time period of 0.5ms for one complete cycle (on time + off time), your frequency will be 2kHz.
Now, onto the topic of asynchronous activity in A-, B-, and C-fibers. These fibers are nerve fibers that transmit information about touch and pain to the spinal cord and brain. They are classified into different groups based on their size and conduction velocity, with A-fibers being the fastest and C-fibers being the slowest. A-fibers are further divided into A-alpha, A-beta, and A-delta subtypes, all of which are insulated with myelin. C-fibers, on the other hand, are unmyelinated, which contributes to their slower conduction velocity.
A-fibers are activated at relatively low intensities, even at low frequencies (<1kHz). At higher frequencies (>2kHz), large myelinated fibers like A-fibers are blocked at low intensities. C-fibers, being unmyelinated, are progressively activated at higher intensities and frequencies. This is why C-fibers are associated with a slower, lasting, and spread-out type of pain. They respond to various stimuli, including thermal, mechanical, and chemical changes, and can detect physiological changes in the body, such as hypoxia, hypoglycemia, and the presence of certain metabolites.
Changes in laryngeal EMG, HR, and BI during VNS are driven by asynchronous activity in A-, B-, and C-fibers. Optogenetic stimulation of cholinergic B-fibers causes bradycardia, while stimulation of glutamatergic sensory afferents, which include C-fibers, slows down breathing in a dose-dependent manner. These responses provide insight into the changes in asynchronous fiber activity elicited by VNS.
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Frequently asked questions
You can increase the frequency by making changes in either time or frequency. Ensure that you have changed the time period of one complete cycle (on time + off time).
You can change the frequency in SPICE by using a command-line option for the voltage source.
Try to increase the frequency by minimizing the pulse cycle time.
Frequency is calculated by the number of cycles per second.
