Name: fourier transform signals in time and frequency
Uploaded: 2024-09-26T13:17:03.000Z
Duration: 1 min 7 s
Channel: JoVE

من بين العناصر الرئيسية لتحويل فورييه ، تعتبر وظيفة sinc فريدة من نوعها من حيث أنها تساوي 1 عندما تكون حجتها صفرا وتظهر تناسقا متساويا.
في مجال التردد ، يتحول تحويل فورييه لنبضة مستطيلة إلى دالة sinc هذه ، والتي تظهر تناسقا مع ذروة في الأصل وفصوص أصغر تدريجيا على كلا الجانبين.
تمثل الإشارة الأسية ، وهي دالة ذات قيمة معقدة ، تذبذبا جيبيا عند تردد معين. عند تعرضه لتحويل فورييه ، يصبح محتوى التردد الخاص به نبضة واحدة تقع عند تردد معين. 
يشير هذا إلى أن الموجة المربعة المثالية تشتمل على عدد لا حصر له من الترددات التوافقية التي تمثلها فصوص دالة sinc.
دالة دلتا تساوي صفرا في كل مكان باستثناء الصفر، حيث تكون لانهائية. تحويل فورييه لدالة دلتا هو ثابت ، مما يدل على أن دالة دلتا تحتوي على جميع الترددات ذات الحجم المتساوي.

الإشارات الأساسية لتحويل فورييه

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تحويل فورييه هو أداة رياضية محورية في معالجة الإشارات، حيث تمكن من تحويل إشارات المجال الزمني إلى تمثيلات المجال الترددي الخاصة بها. ومن بين العناصر العديدة داخل هذا المجال، تتمتع بعض الدوال مثل دالة الجيب، ودالة دلتا، والإشارات الأسية بأهمية كبيرة بسبب خصائصها وتداعياتها الفريدة.

تتميز دالة الجيب، التي تعرف بأنها sinc(x) = sin(πx)/(πx)، بشكل خاص بتماثلها وسلوكها عند الصفر. فهي تحقق قيمة تساوي واحدًا عندما تكون حجتها صفرًا وتظهر تماثلًا متساويًا حول المحور y. تظهر هذه الدالة بشكل بارز في المجال الترددي باعتبارها تحويل فورييه لنبضة مستطيلة. تتحوَّل النبضة المستطيلة، التي تتميز بسعة ثابتة على فترة زمنية محددة، إلى دالة جيبية. تكون دالة الجيبية الناتجة متماثلة مع ذروة واضحة عند نقطة الأصل، وتقل سعة فصوصها عندما تبتعد عن المركز. يُظهِر هذا التحويل أن النبضة المستطيلة في مجال الزمن تتألف من سلسلة لا نهائية من الترددات التوافقية.

دالة دلتا، أو دالة ديراك دلتا، هي عنصر حاسم آخر في دراسة تحويلات فورييه. يتم تعريفها على أنها صفر في كل مكان باستثناء الصفر، حيث تكون كبيرة بشكل لا نهائي بحيث يكون تكاملها على الخط الحقيقي بالكامل مساويًا لواحد. ينتج تحويل فورييه لدالة دلتا قيمة ثابتة عبر جميع الترددات، مما يشير إلى أن دالة دلتا تشمل جميع الترددات بنفس المقدار. تجعل هذه الخاصية دالة دلتا أداة أساسية لتحليل الإشارات وتركيبها، حيث تعمل كأساس لبناء وظائف أخرى من خلال الالتفاف.

الإشارات الأسية، التي تمثلها الدوال ذات القيمة المركبة من الشكل 𝑒^𝑗𝜔𝑡، أساسية في وصف التذبذبات الجيبية عند ترددات معينة. عندما تخضع إشارة أسية لتحويل فورييه، تكون النتيجة نبضة واحدة عند التردد المقابل في مجال التردد. يسلط هذا التحويل الضوء على محتوى التردد النقي للإشارة الأسيّة، موضحًا أنها تتكون من مكون تردد واحد بدون أي توافقيات.

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من بين العناصر الرئيسية لتحويل فورييه ، تعتبر وظيفة sinc فريدة من نوعها من حيث أنها تساوي 1 عندما تكون حجتها صفرا وتظهر تناسقا متساويا.
في...

Education

JoVE Core

Electrical Engineering

الهندسة الكهربائية

Unit 1

الوحدة الأولى

The Fourier Transform

تحويل فورير

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الرئيسية

Basic signals of Fourier Transform

fourier transform signals in time and frequency

The Fourier Transform links time-domain signals to frequency-domain signals. It is a key tool in signal processing. It helps show how a waveform can be described by frequency parts instead of only by time changes.

The sinc function is one of the basic signals in this topic. It is written as sinc(x) = sin(πx)/(πx). It equals 1 when x is 0, and it has even symmetry about the y-axis. In the frequency domain, it appears as the Fourier transform of a rectangular pulse.

A rectangular pulse has a constant amplitude over a limited interval. When it is transformed, the result is a sinc function with a strong peak at the center. Its side lobes get smaller as they move away from the origin. This shows that a rectangular pulse in time is made of an infinite set of harmonic frequencies.

The delta function, also called the Dirac delta function, is another important signal. It is zero everywhere except at zero, where it is infinitely large in a way that makes its total area equal to one. Its Fourier transform is a constant across all frequencies. That means the delta function contains equal magnitude at every frequency and is useful for signal analysis and synthesis through convolution.

Exponential signals are also fundamental in Fourier analysis. They are complex-valued functions written in the form e^jωt and describe sinusoidal oscillations at a specific frequency. When an exponential signal is transformed, it becomes a single impulse at that same frequency in the frequency domain. This shows that the signal has one pure frequency component and no harmonics.

Fourier Transform Signals in Time and Frequency

fourier-transform-signals-in-time-and-frequency

continuous -time fourier transform

From Fourier Series to Fourier Transform

The Fourier transform extends Fourier series ideas to nonperiodic functions. A Fourier series breaks a periodic signal into a sum of sines and cosines. When the period becomes infinite, that discrete sum changes into a continuous integral. A pulse-train waveform shows this change clearly. With a finite period, the repeating rectangular pulses can be represented by a Fourier series. As the period grows without bound, the waveform becomes a single isolated pulse, and the description shifts to...

basic signals of fourier transform

The Fourier Transform links time-domain signals to frequency-domain signals. It is a key tool in signal processing. It helps show how a waveform can be described by frequency parts instead of only by time changes. The sinc function is one of the basic signals in this topic. It is written as sinc(x) = sin(πx)/(πx). It equals 1 when x is 0, and it has even symmetry about the y-axis. In the frequency domain, it appears as the Fourier transform of a rectangular pulse. A rectangular pulse has a...

properties of fourier transform i

Fourier Transform in Radio Broadcasting

Fourier Transform properties help radio broadcasting manage signals in the time and frequency domains. These properties are useful for sending multiple audio channels at once, changing clip speed, adding broadcast delays, adjusting audio frequencies, and demodulating signals. They make it easier to transmit and receive audio clearly. When broadcasters combine several audio signals, the Fourier Transform simplifies the process. If f(t) and g(t) have Fourier Transforms F(ω) and G(ω), then the...

properties of fourier transform ii

Fourier Transform Rules in Signal Analysis

The Fourier Transform helps analyze signals by linking the time domain and the frequency domain. Its properties show how a signal changes when it is shifted, differentiated, or combined with another signal. These rules are important in signal processing, radio broadcasting, and audio work. The frequency shifting property shows that moving a signal in frequency causes a phase change in time. If x(t) has a Fourier Transform X(f), then multiplying x(t) by e^j2πf0t gives a transform of X(f−f0).

parseval's theorem for fourier transform

Signal Energy in Time and Frequency

Parseval's theorem links signal energy in the time domain and the frequency domain. In signal processing, it shows that the same energy can be calculated in either view. This makes it an important idea for comparing time-based and frequency-based analysis. To find signal energy, the standard approach uses a resistor value of 1 ohm. In that case, power equals the square of the signal's voltage or current. This gives a simple way to relate power to energy before moving into Fourier analysis. <br...

discrete-time fourier transform

DTFT and Frequency Analysis of Digital Signals

The Discrete-Time Fourier Transform (DTFT) shows how a discrete-time signal can be analyzed in the frequency domain. It takes a signal from the time domain and reveals its frequency components and spectral features. In the DTFT, the integral used for continuous-time signals is replaced by a summation to match the discrete form of the signal. The DTFT spectrum X(Ω) is periodic with a period of 2π. This periodicity means that X(Ω) can be written as a Fourier series, which helps with analysis and...

properties of dtft i

DTFT Signal Properties and Frequency Effects

Discrete-Time Fourier Transforms (DTFTs) help describe discrete-time signals in the frequency domain. The main DTFT properties include linearity, time shifting, frequency shifting, time reversal, conjugation, and time scaling. These rules make it easier to analyze and change signals in signal processing. Linearity is the most basic property. If two discrete-time signals are multiplied by constants a and b and then added together, the DTFT of the result is the weighted sum of the two individual...

properties of dtft ii

DTFT Rules for Differentiation and Energy

The DTFT has useful rules for frequency differentiation, convolution, accumulation, and energy checks. These rules help students see how a discrete-time signal changes in the frequency domain. For frequency differentiation, start with a DTFT pair and differentiate both sides with respect to ω. After multiplying by j, the result gives the DTFT of n x[n]. This property is useful for studying how the slope of a spectrum relates to the signal in time. Convolution brings out another key DTFT rule.

discrete fourier transform

DFT for Finding Signal Frequencies

The Discrete Fourier Transform (DFT) turns a finite set of time-domain samples into frequency components. It is a key tool in signal processing because it evaluates a discrete signal at evenly spaced frequency intervals. The result shows the magnitude and phase of each complex sinusoid in the signal. The DFT also follows several important properties. It is linear, so the DFT of a sum of sequences equals the sum of their individual DFTs. When a sequence shifts in time, its DFT changes by a...

fast fourier transform

Fast Fourier Transform for Signal Analysis

The Fast Fourier Transform (FFT) is a computational algorithm that makes the Discrete Fourier Transform (DFT) faster to calculate. It works by splitting the calculation into smaller parts. This reduces the amount of work needed to move data between the time domain and the frequency domain. A direct N-point DFT needs N² complex multiplications. The FFT lowers that cost to about (N/2)log₂N multiplications. That difference becomes more important as N gets larger, because the FFT cuts the number...

key terms and concepts

Learn how the Fourier Transform connects time and frequency through sinc, delta, and exponential signals. Built for grades 9–12 science students.

Fourier Transform Signals in Time and Frequency | JoVE K12

JoVE Core Electrical Engineering offers easy-to-understand animated videos that cover fundamental concepts of electric circuits along with circuit analysis techniques. It incorporates first-order and second-order circuits using operational amplifiers and circuit transformation concepts. The inclusion of practical design examples and real-world applications through scientist-in-action videos adds significant educational value, making complex concepts accessible.

electrical engineering

Fourier Transform Signals in Time and Frequency

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