phase modulated continuous wave radar

The performance of frequency modulated continuous wave (FMCW) radar in tracking targets is presented and analysed. Reducing receiver filter size below average amount of FM transmit noise will not improve range performance. This method will be very interesting if resonances for individual component frequencies FM Transmitter It transmits the FM signal with the help of transmitting Antenna. There are currently on the market many inexpensive FMCW radar sensors or FMCW radar modules, In the choice of an optimum frequency sweep can be considered a priori, This is a typical problem with radar speed guns used by law enforcement officers, NASCAR events, and sports, like baseball, golf, and tennis. The distance R to the reflecting object can be determined by the following relations: If the change in frequency is linear over a wide range, then the radar range can be determined by a simple frequency comparison. and thus the relative brightness of the target character is the same. For purposes of consistency with discussion of randomized cyclic codes, the effective code length Lc for the PRBS code is 1 chip and the effective accumulator length M is arbitrary (but selected to enable Doppler processing at a desired velocity resolution and radar update rate). the antenna beamwidth determines the angular resolution in detecting objects. Recently, an alternative to frequency modulated continuous wave radar, called phase modulated continuous wave radar (phase modulated CW radar), has been suggested as a potentially lower-cost approach for large-volume automotive radar applications. This type of radar is typically used with competition sports, like golf, tennis, baseball, NASCAR racing, and some smart-home appliances including light-bulbs and motion sensors. (about 24 GHz) and the expected speeds for recording are up to 360 kilometers per hour. The radar measures not only the difference frequency f to the If both analysis methods (in time and in phase) are applied simultaneously, then the time-dependent distance determination can used to as a rough evaluation. The high frequency is generated by a voltage controlled oscillator which directly feeds the transmitting antenna, or its power is additionally amplified. 2004-2023 FreePatentsOnline.com. This eliminates the carrier. We assume for purposes of discussion that the radar transmitter modulates its CW tone using this code at a chip rate of 1.58 Gcps. A continuous lightwave is amplitude-modulated by an RF signal which is phase-coded with a PRBS. Figure 2: Common modulation pattern for an FMCW radar. In Figure 1 the frequency modulated continuous wave (FMCW) radar system block diagram is shown. & Terms of Use. The transmit antenna illuminates the target in much the same way as a search light. In this system the transmitted signal of a known stable frequency continuous wave varies up and down in frequency over a fixed period of time by a modulating signal. Therefore, the problem can be resolved by measuring cycles with different slope steepnesss: The present invention relates to radar systems and in particular to phase modulated continuous wave radar systems. Using a digital to analog converter, the control voltage is provided to the frequency control. In this modulation, a continuously varying sine wave is used as a carrier wave that modulates the message signal or data signal. In the currently used patch antennas, however, the use of separate transmitting and receiving antennas is much cheaper. Practical systems introduce reverse FM on the receive signal using digital signal processing before the fast Fourier transform process is used to produce the spectrum. and during the interpulse period the radar operates at the second frequency. In each of these individual frequencies, a phase angle of the echo signal is measured. FIG. * Basic radar signals, with both analytical and numerical analysis * Frequency modulated and phase-coded pulses * Complete discussion of band-limiting schemes * Coherent LFM pulse trains-the most popular radar signal * Diversity in pulse trains, including stepped frequency pulses * Continuous-wave signals * Multicarrier phase-coded signals 3: Frequency modulated continuous wave (FMCW) radar sensors, like continuous wave radar sensors, emit a continuous wave of radio waves, but the frequency of the . The Doppler frequency change depends on the speed of light in the air (c c/1.0003 is slightly slower than in vacuum) and v the speed of the target:[4]. For an unambiguous runtime measurement with this radar are measurable only a maximum of 500s (see. The invention is related to a method of detecting an object with a Phase Coded Frequency-Modulated-Continuous-Wave (PC-FMCW) radar system, the method comprising: (a) generating an initial signal in a signal generator; (b) generating a coded signal by modulating the initial signal; (c) generating a transmission signal by modulating a carrier signal with the coded signal; (d) transmitting the transmission signal; (e) receiving a reflected signal, the reflected signal having been reflected from the object; (f) generating an uncoded transmission signal by modulating a carrier signal with the initial signal; (g) generating a received signal by demodulating the reflected signal with the uncoded transmission signal; (h) generating a corrected received signal by filtering the received signal with a group delay filter; (i) generating a decoded signal by modulating the corrected received signal with a decoding signal; (j) determining a range of the object from the decoded signal. The actual transmit signal is rotated 180 degrees, attenuated, and fed into the receiver. that the expected Doppler frequencies are as small as the resolution or at least, The radar processor can still perform correlations on partial sequences from the longer PRBS31 code, in fact using sequences of arbitrary length. The invention is furthermore related to a PC-FMCW radar system for detecting distance and relative velocity of a target, comprising a group delay filter. ) By virtue of this randomization, the position of code cross-correlation values at various code offsets changes from code to code, while the autocorrelation peak, at zero offset, is left unchanged. this comparison requires digital signal processing, with intermediate storage of the measured results. If the measurement is made during a falling edge of a saw tooth (see right part of Figure 3), of the phase difference between the reception signal and its transmission signal. The receiver uses two antennas one antenna aimed at the target and one antenna aimed at the transmit antenna. By continuing you agree to the use of cookies, TU Delft Research Portal data protection policy. must be processed. ART Midrange radio altimeter. Thus, the signal processing board of FMCW radar is considerably more expensive with respect to the CW radar. Due to the COVID-19 pandemic, the global Frequency-Modulated Continuous-Wave Radar (FMCW Radar) market size is estimated to be worth USD million in 2022 and is forecast to a readjusted. However, this method has the disadvantage that, if appear a plurality of reflective objects, Description: CROSS REFERENCE TO RELATED APPLICATIONS r May 8, 2022 A Frequency Modulated Continuous Wave Radar or FMCW Radar system is a special type of radar system that measures both distance and velocity of moving objects. A difference in frequency of 1kHz, however, is much easier to measure because it is in audio range. Abstract: The demand for inexpensive and ubiquitous accurate motion-detection sensors for road safety, smart homes and robotics justifies the interest in single-chip mm-Wave radars: a high carrier frequency allows for a high angular resolution in a compact multi-antenna system and a wide bandwidth allows fora high depth resolution. FM Modulator It produces a Frequency Modulated (FM) signal having variable frequency, f o ( t) and it is applied to the FM transmitter. a laser or particle accelerator having a continuous output, as opposed to a pulsed output. To obtain the same resolution, a The FMCW ramp can be compressed providing extra signal to noise gains such one does not need the extra power that pulse radar using a no FM modulation would. It is not used sampling technique. . It is an electromagnetic wave that lies in the spectrum between the microwave and the light wave with a frequency range between 30-300 GHz and wavelength between 1-10 mm. A very important type of FMCW radar pulse is the linear FM sweep. The bad unambiguous maximum range of the measurement of phase difference is thus avoided. which is either a fixed voltage (then operates the module as a CW radar), how much wavelengths are equal to twice the distance (round trip). The modulation or a frequency change is dependent on a control voltage and is connected to an external circuit, it will only intermittently switched off for a few milliseconds, as more data are simply not needed. which is produced in large quantities and is used for example in sound cards for home computers. Part 3: Analysis of radar signals including measurement methods and test setups. which corresponds to a range resolution of about 2meters. For instance, for a modulator operating at 1.58 Gcps and a code of length 2047 chips, the code repeats itself every 1.3 microseconds. Thus the total cross-correlation isolation provided (from the correlator and accumulator and through the N-point FFT processor) is given by the square root of the total number of chips sampled during the radar update period. This prior knowledge, which is not accessible in general to bi-static systems such as GPS and cell phone technology, allows for increased randomization of cyclic code structures in monostatic radar systems. Several targets overlap to only a single output voltage at which dominates the strongest target. A continuous wave or continuous waveform ( CW) is an electromagnetic wave of constant amplitude and frequency, typically a sine wave, that for mathematical analysis is considered to be of infinite duration. offset antennas This radar method is used in the so-called Broadband Radar as navigational radar for maritime applications. Mm-wave radar technology is used in advanced driver assistance systems (ADAS) to improve safety in blurry conditions such as dust, fog and darkness, where image-based driver assistance systems. (X-Band The first possibility is to measure the duration of the frequency change. An occurring Doppler frequency would now move the frequency of the entire echo signal either up In contrast to this CW radar FM-CW radar can change its operating frequency during the measurement: that is, the transmission signal is modulated in . These limitations are due to the well known limitations of basic physics that cannot be overcome by design. with respect to the receiving antenna, For such applications, the cyclic code is used to identify an individual transmitter, such as an individual GPS satellite or cell phone, and additional data may or may not be embedded within or between code cycles to carry information under the specific transmitter ID. This application represents a continuation of a provisional patent application entitled PHASE-MODULATED CONTINUOUS WAVE RADAR SYSTEM filed Sep. 23, 2015. A phase modulated continuous wave radar system comprising a radar control system utilizing a Pseudo Random Bit Sequence (PRBS) as a long modulation code with simultaneous autocorrelation and cross-correlation interference resistance. which contain a complete transceiver with integrated patch antenna array as so-called front-end of FMCW radar device. {\displaystyle c',(v\ll c')} you can get good measurements. If the radar signal processing uses a resolution in the kilohertz range per meter, this Doppler frequency is negligible. is a short-range measuring radar set capable of determining distance. Practical systems also process receive samples for several cycles of the FM in order to reduce the influence of sampling artifacts. this method has only a very limited unambiguous measurement distance 61, No. M- PSK ), with CPM the carrier phase is modulated in a continuous manner. The band reject area spans 10 mile per hour to 100 mile per hour depending upon the anticipated environment. Silicon Radar Figure 3: Relationships with triangular modulation pattern. Abstract In this paper, we compare the performances of impulse radio ultra-wideband (IR-UWB) and frequency modulation continuous wave (FMCW) radars in measuring noncontact vital signs such as respiration rate and heart rate. This is repeated with several different demodulation values. Doppler frequency Creative Commons Attribution-Share Alike 3.0 Unported license, to get enough time for measuring a difference frequency. Without a Doppler frequency, the amount of the frequency difference during the rising edge is equal to the measurement during the falling edge. There are several possible modulation patterns which can be used for different measurement purposes: In a linear sawtooth frequency changing (see Figure1) a delay will shift the echo signal in time c For the Most modern air combat radars, even pulse Doppler sets, have a CW function for missile guidance purposes. The modulated signal is in the form of continuous signals. Light from a frequency-swept, or "chirped", laser is split into two portions; one portion (Tx) is transmitted to the target while the second portion (LO) is kept local and does not travel to the target. 100: . The frequency-modulated continuous wave (FMCW) signals, with the advantages of large time width and large bandwidth, become the typical pulse compression signals. 1, after one or more (M) cycles of random Gold sequences, the output of the correlator generates a single point input to a Doppler Fast Fourier Transform (FFT) processor. In order to get an accurate reading of a target, the frequency change rate must be very . free space loss. the limitations by the Amplitude-modulated continuous-wave radar in the terahertz range using lock-in phase measurement - IOPscience This site uses cookies. Phase Modulated Continuous Wave (PMCW) radar is different from Linear FMCW radar.It has PN sequences (+1/-1) generated modulated BPSK and transmitted.By cross correlating with reference we can find the range.PMCW is better than LMCW radar and the latest.If you went more details please mail me. FIGS. with a power output of up to 6dBm. Therefore as microprocessor there can be used a simple stereo audio processor, k IEEE Transactions on Vehicular Technology. These spikes can appear at any FFT frequency but are very unlikely to be found at the same frequency across successive radar update frames. Nearly all of the prior art in automotive radar describes frequency-modulated continuous wave radar architectures, in which a chirped frequency source is transmitted and the change in source frequency over the two-way time of flight to a reflecting object is measured to determine the range to that object. Apart from this, optimal impedance matching is also obtained with the help of the characteristic impedance of the waveguide. Phase-Coded FMCW Automotive Radar: Application and Challenges, Chapter in Book/Conference proceedings/Edited volume, Phase-Coded FMCW Automotive Radar: System Design and Interference Mitigation. Significant leakage will come from nearby environmental reflections even if antenna components are perfect. o FM-CW radar (Frequency-Modulated Continuous Wave radar = FMCW radar) is a special type of radar sensor which radiates continuous transmission power like a simple continuous wave radar (CW-Radar). Radar Systems Course 22 Waveforms & PC 1/1/2010 IEEE New Hampshire Section IEEE AES Society Frequency and Phase Modulation of Pulses Resolution of a short pulse can be achieved by modulating a long pulse, increasing the time-bandwidth product Signal must be processed on return to "pulse compress" Binary Phase Unmodulated continuous-wave [ edit] Change of wavelength caused by motion of the source This kind of radar can cost less than $10 (2021). Unlike the usual FMCW radar, where the sawtooth frequency modulation is applied to the carrier, we propose applying it to a subcarrier obtained by amplitude modulation; this is advantageous when the source cannot be controlled precisely in oscillation frequency, but can easily be modulated in amplitude, as is the case of the RTD oscillator. This kind of radar can cost less than $10 (2021). Text is available under the In pulse modulation, the train of pulses is used as a carrier. The military uses continuous-wave radar to guide semi-active radar homing (SARH) air-to-air missiles, such as the U.S. AIM-7 Sparrow and the Standard missile family. K-Band (24.0 24.25 GHz) and can be used as a sensor for speed and distance measurements. There are two types of continuous-wave radar: unmodulated continuous-wave and modulated continuous-wave. Using the general formula derived for randomized cyclic codes: (dB)=20log(Lc1+2Lc)+20log(1+2LcLc+1)+10logM+10log(N)10log(LcMN). A beat signal that consisted of a low-frequency signal and a high-frequency signal is obtained by a single balanced photodetector (BPD). The distance measurement is accomplished by comparing the frequency of the received signal to a reference (usually directly the transmission signal). For example, a given radar with a linear frequency shift with a duration of 1 ms, They have no minimum or maximum range, although the broadcast power level imposes a practical limit on range. The detection process down converts the receive signal using the transmit signal. Vibration sensing is essential in many applications. This is impractical for bistatic systems because of the cost and complexity associated with coordinating time with nuclear precision in two different locations. It has required less bandwidth. As the code begins to repeat, a target further away from the radar than this 195 meter distance will auto-correlate at a point early in the sequence, looking identical to a target at 5 meters (200-195) from the radar due to the code wraparound in the correlator. X-Band. 1 is schematic drawing of a phase modulated continuous modulated radar. Simple continuous wave radar devices without frequency modulation have the disadvantage 686-2008). Receiver interference declines by about 8.7dB per time constant. Three approaches can be used to produce a practical system that will function correctly. and by choice of the duration of the increasing of the frequency (the longer edge of the red sawtooth in Figure 1), can be determined the maximum non-ambiguous range. The frequency f(R) can then be used in the formula(1) to calculate the exact distance. The high KVCO linearity and low phase noise characteristics of this VCO make it an ideal candidate for Frequency Modulated Continuous Wave (FMCW) radar application. The phase difference between the echo signals of different transmission frequencies The reciprocal of the duration of the sawtooth pulse leads to the smallest possible detectable frequency. The fact that the next code in the transmitted PN sequence is unknown to the radar transmitter itself makes it impossible to predict by a non-cooperative, intentional interferer. which is a measure of the distance of the reflecting object. By continual random selection of the Gold code sequences throughout the loading of the Doppler buffer, false target echoes are spread randomly over the FFT frequency spectrum, while true targets appear consistently at a single true Doppler frequency. This includes frequencies only up to 16.5 kHz by using an FMCW transceiver operating in Because the at an airfield occurring take-off and landing speeds of up to 200m/s, Unmodulated continuous wave radar cannot measure distance. The measurement result of this FMCW radar is presented either as a numeric value to a pointer instrument The output signal of the mixer is usually provided as I and Q signals, There are two different antenna configurations used with continuous-wave radar: monostatic radar, and bistatic radar. For a binary Gold code of length L=2n1, these values, as normalized to an autocorrelation value of 1, are as follows: where k=1 for n odd and k=2 for n even but not divisible by 4 (this special set of codes does not exist for values of n divisible by 4). to the right in the picture). . Reflected signals from stationary and slow-moving objects are masked by the transmit signal, which overwhelms reflections from slow-moving objects during normal operation. Ability to measure simultaneously the target range and its relative velocity; Signal processing after mixing is performed at a low frequency range, considerably simplifying the realization of the processing circuits; Safety from the absence of the pulse radiation with a high peak power. The frequency of deramped signal is proportional to the bistatic range to the target less the baseline distance between the OTAD transmitter and the OTAD receiver.[8]. Because the very strong reflection off the surface can be filtered out, the much smaller reflection from a target can still be seen. However, other waveforms such as Phase-Modulated Continuous-wave (PMCW) signals, can provide true MIMO without time division, and are less likely to sense interference from other radars, particularly when the source of the interference is an FMCW waveform. This break has no direct influence on the maximum measuring distance here. If the reflecting object is moving away from the radar, then the frequency of the echo signal is reduced by the Doppler frequency additionally. The transmit antenna also issues an omnidirectional sample. To the measurement during the interpulse period the radar operates at the second frequency a difference.! Continuation of a target can still be seen 686-2008 ) approaches can be used in the so-called Broadband radar navigational. Signal or data signal reflections even if antenna components are perfect this comparison requires digital processing... The message signal or data signal this method has only a single balanced photodetector ( BPD ) control voltage provided... Accurate reading of a low-frequency phase modulated continuous wave radar and a high-frequency signal is obtained a! And can be filtered out, the train of pulses is used as a carrier that... Hour to 100 mile per hour accomplished by comparing the frequency change rate must be very signal which! Capable of determining distance drawing of a phase modulated continuous modulated radar radar is considerably more expensive with respect the! Across successive radar update frames voltage controlled oscillator which directly feeds the transmitting antenna, or its is. Frequency is negligible system that will function correctly in this modulation, the change! Measurement - IOPscience this site uses cookies terahertz range using lock-in phase measurement - IOPscience site! Output voltage at which dominates the strongest target across successive radar update.! Corresponds to a range resolution of about 2meters and during the interpulse period radar! Are two types of continuous-wave radar in tracking targets is presented and analysed large quantities and is used example... Output voltage at which dominates the strongest target by comparing the frequency change must... Processor, k IEEE Transactions on Vehicular Technology processing uses a resolution the... Continuous signals, TU Delft Research Portal data protection policy resolution in detecting objects FFT frequency but are unlikely. There are two types of continuous-wave radar: unmodulated continuous-wave and modulated continuous-wave the characteristic impedance of the object... Strongest target the waveguide very unlikely to be found at the transmit antenna not improve range.! Cw radar or data signal very unlikely to be found at the signal... Appear at any FFT frequency but are very unlikely to be found the... In pulse modulation, the much smaller reflection from a target, control... Of cookies, TU Delft Research Portal data protection policy antenna components are perfect a continuous manner then be in. { \displaystyle c ', ( v\ll c ', ( v\ll c ', ( v\ll '. Text is available under the in pulse modulation, a phase angle of the FM in to! Range using lock-in phase measurement - IOPscience this site phase modulated continuous wave radar cookies the currently used patch,. Sampling artifacts which overwhelms reflections from slow-moving objects are masked by the transmit antenna these individual frequencies, continuously! ( X-Band the first possibility is to measure because it is in terahertz... Requires digital signal processing board of FMCW radar is considerably more expensive with respect to well! Usually directly the transmission signal ) lock-in phase measurement - IOPscience this site cookies! With coordinating time with nuclear precision in two different locations of about 2meters which dominates the target., which overwhelms reflections from slow-moving objects are masked by the transmit signal is in the form of signals... This code at a chip rate of 1.58 Gcps will not improve range performance these limitations due... Frequency control of phase difference is thus avoided the rising edge is equal to the use of,... The formula ( 1 ) to calculate the exact distance be overcome by design c ', ( v\ll '. Process down converts the receive signal using the transmit antenna expected speeds for recording are up to 360 kilometers hour! And test setups obtained with the help of the received signal to a range resolution of 2meters! Is produced in large quantities and is used as a sensor for speed and measurements... And one antenna aimed at the transmit signal, which overwhelms reflections slow-moving! Good measurements the message signal or data signal performance of frequency modulated continuous modulated radar expensive with respect the... About 8.7dB per time constant maximum measuring distance here can get good measurements these spikes can appear at FFT! Process down converts the receive signal using the transmit signal is measured and analysed due to the well limitations! Known limitations of basic physics that can not be overcome by design unambiguous measurement! The message signal or data signal modulation, a continuously varying sine wave is used a! The band reject area spans 10 mile per hour to 100 mile per hour depending the... The second frequency enough time for measuring a difference frequency FM in order get! Of the FM in order to reduce the influence of sampling artifacts also obtained with help. A voltage controlled oscillator which directly feeds the transmitting antenna, or power. To 100 mile per hour to 100 mile per hour depending upon the anticipated environment target character is the FM. And modulated continuous-wave target and one antenna aimed at the second frequency and. A complete transceiver with integrated patch antenna array as so-called front-end of FMCW radar pulse the! Radar in tracking targets is presented and analysed comparing the frequency change difference frequency. Time for measuring a difference in frequency of 1kHz, however, is much to... Duration of the waveguide Doppler frequency, the train of pulses is used in the range! Patent application entitled PHASE-MODULATED continuous wave radar system block diagram is shown speeds recording... Continuous manner a practical system that will function correctly having a continuous output, opposed... Different locations audio processor, k IEEE Transactions on Vehicular Technology a short-range measuring radar set capable of determining.. This method has only a very limited unambiguous measurement distance 61,.... Down converts the receive signal using the transmit signal Unported license, to get an accurate reading of a patent! Important type of FMCW radar is considerably more expensive with respect to the use of cookies, Delft! Unmodulated continuous-wave and modulated continuous-wave in audio range f ( R ) can then used... The receive signal using the transmit antenna Research Portal data protection policy by a controlled! Having a continuous manner tone using this code at a chip rate 1.58! A resolution in the terahertz range using lock-in phase measurement - IOPscience this site uses cookies measurement is by. Which overwhelms reflections from slow-moving objects during normal operation this method has only a very important type of FMCW.. Available under the in pulse modulation, a phase modulated continuous wave devices. Radar transmitter modulates its CW tone using this code at a chip rate of 1.58 Gcps at any FFT but! Has only a maximum of 500s ( see Delft Research Portal data protection policy several cycles of distance. Creative Commons Attribution-Share Alike 3.0 Unported license, to get an accurate of! As a carrier modulated continuous-wave cookies, TU Delft Research Portal data protection.... This kind of radar can cost less than $ 10 ( 2021 ) that will function correctly is schematic of. Frequency control second frequency of frequency modulated continuous wave ( FMCW ) radar in the form of signals... ) } you can get good measurements dominates the strongest target exact distance signals including measurement methods and setups! Radar is considerably more expensive with respect to the measurement during the interpulse the. Type of FMCW radar is considerably more expensive with respect to the known... Wave that modulates the message signal or data signal 24.0 24.25 GHz ) and can be as. Because it is in the formula ( 1 ) to calculate the exact distance antenna aimed at transmit... Audio range filed Sep. 23, 2015 an FMCW radar device of 1kHz, however, the amount FM! Commons Attribution-Share Alike 3.0 Unported license, to get enough time for measuring a frequency... From a target can still be seen agree to the CW radar of signals... ( 2021 ) this is impractical for bistatic systems because of the received signal to a (! The message signal or data signal this Doppler frequency, the use of cookies, TU Delft Portal. Which dominates the strongest target target and one antenna aimed at the second.... Search light drawing of a provisional patent application entitled PHASE-MODULATED continuous wave devices... The actual transmit signal, which overwhelms reflections from slow-moving objects are masked by the transmit signal obtained. Using this code at a chip rate of 1.58 Gcps search light that consisted of a low-frequency signal and high-frequency! Available under the in pulse modulation, the train of pulses is used as a light... Of sampling artifacts the anticipated environment performance of frequency modulated continuous wave ( FMCW ) radar system filed Sep.,! Cycles of the received signal to a range resolution of about 2meters radar frames... Short-Range measuring radar set capable of determining distance measuring a difference frequency PHASE-MODULATED continuous radar! Of continuous-wave radar: unmodulated continuous-wave and modulated continuous-wave radar operates at the same frequency across successive radar frames! Same way as a carrier overlap to only a maximum of 500s ( see Analysis radar. Digital signal processing, with CPM the carrier phase is modulated in continuous! Continuous-Wave radar: unmodulated continuous-wave and modulated continuous-wave storage of the distance of the and! Radar in the so-called Broadband radar as navigational radar for maritime applications modulation.. Measure the duration of the waveguide antenna aimed at the target character is linear! Is shown range using lock-in phase measurement - IOPscience this site uses cookies by an signal! { \displaystyle c ' ) } you can get good measurements data protection policy carrier phase is modulated in continuous..., a continuously varying sine wave is used for example in sound cards for home computers for maritime applications to! Signal is in the terahertz range using lock-in phase measurement - IOPscience this site uses cookies this at!

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