Thanks to the Defense Spectrum Office (DSO) for funding the work presented in this article.

NOTE: The ITS channel sounder system is shown in Figure 1 and Figure 2, and a benchtop evaluation setup is shown in Figure 3. Reference these figures while setting up the CW-channel sounder to ensure all components are properly configured. The following sections explain how to verify and validate a system prior to making measurements.
1. Measurement system setup
NOTE: This section describes how a system is set up for field measurements. First, system losses in both the transmitting and the receiving side of the system must be accounted for and measured separately before the full system is assembled. Then, the full system is assembled, and individual instruments are configured, calibrated, and synchronized to prepare for lab verification and validation.
<ol>
	<li>Measure the S-parameters, using a VNA2, for individual system components before assembling the system: cables, attenuators, power splitters, directional couplers, and low-pass filters. 
	NOTE: This will characterize losses and identify broken cables, or a device out of specification.</li>
	<li>Assemble the Type N cable at the output of the power amplifier, the directional coupler, the bandpass filter, and the Type N cable that will be connected to the antenna, and use the VNA to measure the component chain. 
	NOTE: This measurement will include internal reflections that are not seen by measuring individual components with a VNA.</li>
	<li>Record the S21 value, which will be a negative number, and will be used as the transmitting system losses. Use these values to correct the received signal level discussed in the representative results section.</li>
	<li>Transmitting system setup
	<ol>
		<li>Plug in all devices to a power source: either an uninterruptible power supply (UPS) or a surge-protected set of outlets. Make sure that all instruments are in a powered off state while hooking components together.</li>
		<li>Assemble the transmitting equipment (Figure 1).
		<ol>
			<li>Connect the 10 MHz output of the rubidium oscillator to the Ref IN port of the VSG using a Bayonet-Neill-Concelman (BNC) cable. Connect RF OUT port of the VSG to the input of the directional coupler IN port using a Type N cable. No power amplifier is inserted until Protocol Step 3.2.</li>
			<li>Connect the OUT port of the directional coupler to the input port appropriate bandpass filter (if needed) using a Type N female to female connector. 
			NOTE: A bandpass filter is used to minimize harmonic frequencies in other bands.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Assemble the Type N cable that will be connected to the receiving antenna, the filter, the cable between the filter and the power splitter, and the Type N cable that will be connected to the VSA; use the VNA to measure this system of components.</li>
	<li>Make the same measurement, but through the same components connected to the SA. Record the S21 values, which will be used as the receiving system losses on the VSA side of the power splitter and the SA side of the power splitter. Use these values to correct the received signal level discussed in the representative results section.</li>
	<li>Receiving system setup
	<ol>
		<li>Plug in all devices to a power source: either a UPS or a surge-protected set of outlets. Make sure all instruments are in a powered off state while hooking components together.</li>
		<li>Assemble the receiving equipment (Figure 2).
		<ol>
			<li>Connect a Type N cable to the input of the bandpass filter. Connect the output of the bandpass filter to the input of the power divider (port 1).</li>
			<li>Connect port 2 of the power divider to the RF IN port on the VSA. Connect port 3 of the power divider to the RF IN port on the SA.</li>
			<li>Using a BNC to banana plug cord, connect the Frequency Adj of the rubidium oscillator to the DC OUT of the direct-current (DC) power supply.</li>
			<li>Connect a 10 MHz output of the rubidium oscillator to the Ext Ref In port on the VSA using a BNC cable. Connect a 10 MHz output of the rubidium oscillator to the Ext Trig/Ref In port on the spectrum analyzer.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Power on the VSG and ensure that it is set to RF OFF. Power on the power meter. Turn all instruments on, and allow the instruments to warm up for an hour before making any measurements.</li>
	<li>Configure the VSA in VSA 89601B mode. While in VSA mode, set the center frequency to the CW frequency of interest. Finally, select the number of points taken with the desired length of the overall measurement in mind. 
	&#8203;NOTE: Although the system operates using a CW, the span must be set to capture any Doppler shifts and fading. The resolution bandwidth determines the filter used by the VSA to measure power as it sweeps across the frequency span, so selecting a low-resolution bandwidth allows a more precise measurement. As a tradeoff, a lower resolution bandwidth takes a greater time per point.</li>
	<li>Configure the VSA with the following settings: select VSA 89601B mode; center Frequency: Freq MHz (e.g., 1770 MHz); span: 3 kHz; TimeLen: 1 s; ResBW: 3.81938 Hz; NumPts: max (491026 pts, 409601 pts)-depends on VSA; Rng: -42 dBm; top graph upper scale value: -30 dBm.</li>
	<li>Ensure that the SA is controlled by instrument control software that uses programmable standard commands for programmable instruments (SCPI) commands, so that continuous sweeps can be collected and saved.
	<ol>
		<li>Set the SA such that the start and stop frequencies match the VSA center frequency. As the RBW similarly determines the filter size used by the SA, set the RBW to the same value as the span of the VSA measurement.</li>
		<li>Set the video bandwidth to the same value as the resolution bandwidth and the detection mode to sample to record unaveraged data. Leave attenuation off, making sure the SA will not be overloaded, and keep the preamp on.</li>
		<li>Configure the SA with the following for each sweep: StartFreq: Same center frequency as in the VSA setup (e.g., 1770 MHz); StopFreq: Same center frequency as in the VSA setup (e.g., 1770 MHz); RBW (MHz): 0.003; VBW (MHz): 0.003; detector: sample; sweep time: 500 ms; pts/trace: 461; preamp ON; attenuation: 0; auto attenuation: Off.</li>
		<li>On the SA, press Enter to access the menus. Enable External Reference by pressing the Shift button and selecting the System button on the spectrum analyzer. Then, select More | Port Settings | Ext Input | Ref using the softkeys near the screen.</li>
	</ol>
	</li>
	<li>Configure the VSG by selecting a CW output.
	<ol>
		<li>Set the frequency to 1770 MHz. Follow the procedure in section 4.22 to determine the linear range of the power amplifier.</li>
		<li>Set the VSG output amplitude to -4 dBm, the upper limit to the linear range of the power amplifier.</li>
	</ol>
	</li>
	<li>Calibrate the power meter.
	<ol>
		<li>Plug the power meter head into the reference port (channel A or B) and the other end of the power meter into a measurement port.</li>
		<li>Set the power meter frequency to 1770 MHz for the reference port used above. Zero and calibrate the power meter. Ensure the power meter reading remains within 0.2 dB of 0 dBm.</li>
		<li>Unplug the power meter head from the reference port, and connect the power meter head to the output of the attenuator shown in Figure 1.</li>
	</ol>
	</li>
	<li>Calibrate the VSA: Utilities | Calibration | Calibration. Turn RF ON the VSG. 
	&#8203;NOTE: Make sure there is a signal on the spectrum analyzer. If the signal level drops down to -120 dBm, the external reference is not on. If the signal is too strong, it will overload the receiving system and damage either the VSA or SA. Be aware of maximum input signal levels (usually shown on the front of the instrument), and stay at least 10 dB below this level.</li>
	<li>Synchronize the rubidium oscillators by setting the voltage, but do not exceed the maximum input voltage allowed on the rubidium synchronization port.
	<ol>
		<li>Change TimeLen on the top graph on the VSA screen to 100 ms. Set the y-axis on the bottom plot to I-Q.</li>
		<li>Press Current/Voltage on the front panel of the power supply. Change the voltage a little at a time and watch the dot on the VSA screen: if it rotates back and forth, do nothing, the frequencies are aligned. If it rotates in one direction consistently, change the power meter reading (voltage) until the dot on the I-Q plot starts to slow down, and it moves slowly back and forth (pendulum motion) (Figure 4).</li>
		<li>Set TimeLen on the top graph on the VSA screen back to 1 s, and set the y-axis back to Log Magnitude.</li>
	</ol>
	</li>
	<li>Take 10 records of acquisition on the SA to verify that all parameters have been set correctly, and that the signal level on the SA screen matches the signal level on the VSA lower screen.</li>
</ol>
2. Lab verification and validation
<ol>
	<li>Without attaching antennas, insert a variable attenuator between the transmitting side of the system and the receiving side of the system (Figure 5). Remove the power amplifier from the measurement setup for this verification.</li>
	<li>Set the stepped attenuator attenuation to 0 dB and the number of records on the VSA Input &#62; Recording to 120. 
	NOTE: One record is equal to the TimeLen set on the VSA.</li>
	<li>Set the number of sweeps on the SA to 120 records. Change the output amplitude of the VSG to 0 dBm, and press the RF ON button on the VSG.</li>
	<li>Set a peak marker to find the value of the signal strength, and verify a signal is seen on the VSA. Start the VSA by hitting the Record button at the top of the screen. Start an SA measurement using the instrument control software.</li>
	<li>Change the stepped attenuator to 10 dB, and repeat steps 4-10. Go through all settings of the stepped attenuator and record the values for each attenuation setting. 
	NOTE: As the attenuator approaches 90 to 110 dB, the signal will get noisier as it approaches the system noise floor of the instrument. Measurement values near the noise floor of the system will be highly variable.</li>
	<li>To verify the VSA received signal levels, calculate a 0.5 s windowed average to the 120 s VSA record, and average each sweep of the SA. Add the VSG output power level, the transmitting side and receiving side system losses, and the stepped attenuator setting. 
	NOTE: The value of the aforementioned sum in step 2.6 should equal the averaged received signal levels recorded by the VSA and the SA within 0.5 dB, for stepped attenuations less than 80 dB. If they do not, go back and remeasure system losses.</li>
</ol>
3. Field measurements
NOTE: Always test and verify the system before every measurement campaign.
<ol>
	<li>Complete steps 1.1-1.3 before each new measurement campaign, and set up the transmitting side of the system, as discussed in section 1.4. 
	&#8203;NOTE: This is typically housed in a cellular-on-wheels (COW), which remains fixed during measurements.</li>
	<li>Connect the power amplifier between the VSG and the directional coupler, as described in step 1.4.2.1.
	<ol>
		<li>Use a directional coupler that can handle the power levels generated by the power amplifier. Add a 50 dB attenuator to the directional coupler at the coupled port to stay within the specified input power levels of the power meter, and attach the power meter to this port. Connect the output Type N cable from the directional coupler to the transmitting antenna.</li>
		<li>Set up the receiving side of the system, as discussed in steps 1.5-1.6, inside a mobile vehicle. Connect the receiving antenna to the Type N cable connected to the filter.</li>
		<li>In addition to the SA setup steps 1.11.3-1.11.4, the GPS antenna needs to be set up in the SA.
		<ol>
			<li>Enable the GPS record: Meas Settings | Enable GPS Record | Standard GPS.</li>
			<li>Enable GPS on the spectrum analyzer by holding the Shift button and selecting the System button on the spectrum analyzer. Then, select More | GPS | GPS-ON &#38; GPS Info-ON using the softkeys near the screen.</li>
			<li>Place the GPS antenna on the roof of the receiver measurement vehicle. Ensure that the measurement software also reads in NMEA strings from the GPS for each sweep.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Continue the setup as discussed in steps 1.11-1.17, and set the number of records on the VSA Input | Recording based on estimated measurement time. Set the number of SA records to the number of VSA records plus about 300 records, noting that the SA sweeps slower than the VSA.</li>
	<li>Begin the measurement by first starting the VSA by pressing the Record button at the top of the screen. Initiate the spectrum analyzer measurement.</li>
	<li>After the measurement, save the VSA recording file | Save | Save Recording. Save Options | Save Headers with Data. When saving the file, append a _VSA to the end of the file. Change the name of the data file for the spectrum analyzer to match the filename of the VSA, but append _SA for the spectrum analyzer.</li>
</ol>

<ol>
	<li>Commerce Spectrum Management Advisory Commmittee. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> 1755-1850 MHz Airborne Operations: Air Combat Training System Sub-Working Group Final Report. , (2014).</li><li>Best practices for radio propagation measurements. NTIA Technical Memo TM-19-535. U.S. Dept. of Commerce Available from: <a target="_blank" href="https://www.its.bldrdoc.gov/publications/3211.aspx">https://www.its.bldrdoc.gov/publications/3211.aspx</a> (2018)</li><li>Hammerschmidt, C. A., Johnk, R. T., Tran, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Calibration+of+a+Vector+Network+Analyzer+for+Measurements+in+Radio+Frequency+Propagation+Channels.">Calibration of a Vector Network Analyzer for Measurements in Radio Frequency Propagation Channels.</a> Journal of Visualized Experiments. (160), e60874 (2020).</li><li>Channel sounder measurement verification: conducted tests. NTIA Joint Report JR-20-549. U.S. Department of Commerce Available from: <a target="_blank" href="https://www.its.bldrdoc.gov/publications/3241.aspx">https://www.its.bldrdoc.gov/publications/3241.aspx</a> (2020)</li><li>Molisch, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Wireless communications. 2nd edition. , (2010).</li><li>Anderson, C. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Design+and+implementation+of+an+ultrabroadband+millimeter-wavelength+vector+sliding+correlator+channel+sounder+and+in-building+multipath+measurements+at+2.5+&amp;+60+GHz.">Design and implementation of an ultrabroadband millimeter-wavelength vector sliding correlator channel sounder and in-building multipath measurements at 2.5 &amp; 60 GHz.</a> Virginia Polytechnic Institute and State University. , (2002).</li><li>Johnk, R., Hammerschmidt, C. A., Stange, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+high-performance+CW+mobile+channel+sounder.">A high-performance CW mobile channel sounder.</a> Proceedings of the 2017 IEEE International Symposium on Electromagnetic Compatibility &amp; Signal/Power Integrity (EMCSI. , (2017).</li><li>Johnk, R., Hammerschmidt, C. A., McFarland, M. A., Lemmon, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+fast-fading+mobile+channel+measurement+system.">A fast-fading mobile channel measurement system.</a> Proceedings of the 2012 IEEE International Symposium on Electromagnetic Compatibility (EMC). , 584-587 (2012).</li><li>Vector signal analysis basics. Keysight Technologies Available from: <a target="_blank" href="https://www.keysight.com/us/en/assets/7018-02891/application-notes/5990-7451.pdf?success=true">https://www.keysight.com/us/en/assets/7018-02891/application-notes/5990-7451.pdf?success=true</a> (2020)</li><li>Johnk, R. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+mobile+propagation+measurement+system.">A mobile propagation measurement system.</a> Proceedings of the 2009 IEEE International Symposium on Electromagnetic Compatibility (EMC. , (2009).</li><li>. 3.5 GHz Exclusion zone analysis and methodology. NTIA Technical Report 15-517 Available from: <a target="_blank" href="https://www.its.bldrdoc.gov/publications/2805.aspx">https://www.its.bldrdoc.gov/publications/2805.aspx</a> (2015)</li><li>The national map. United States Geological Survey Available from: <a target="_blank" href="https://viewer.nationalmap.gov/basic">https://viewer.nationalmap.gov/basic</a> (2017)</li><li>Radiocommunication Sector of International Telecommunication Union. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Propagation+by+diffraction.">Propagation by diffraction.</a> Propagation by diffraction. ITU-R Recommendation. , 526 (2019).</li><li>Yoza, N. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Narrowband+5+GHz+mobile+channel+characterization.">Narrowband 5 GHz mobile channel characterization.</a> Interdisciplinary Telecommunications Program, University of Colorado at Boulder. , (2015).</li></ol>

It is very important to test a system as described in this protocol before attempting to make measurements in an outdoor environment. In this way, any bad components or instabilities can be traced and identified in the measurement system and can be resolved. The critical steps in this protocol are to 1) test the individual components first, and verify that they are operating within their specification, 2) assemble transmitting and receiving sides separately and test the chain of components, 3) assemble the transmitting and receiving side by inserting a stepped attenuator and measuring the signal levels as the attenuation is changed to make sure the received signal levels in the VSA and SA are as calculated. Further troubleshooting can be performed by using a VSG, such as the one shown in the Table of Materials, that has an option to generate fading simulations, which can be used to test the system using simulated waveforms in various fading environments encountered in real-world propagation environments. Once the measurement system is operating correctly, measurements can be made in an outdoor environment with the confidence that measurements will be accurate.
Another important step is to monitor the transmitting power throughout the measurement to verify that the system is operating correctly. The power amplifier is characterized and tested separately to understand its linearity and out-of-band emissions spectra. The power amplifier may be validated on the benchtop with the rest of the setup, but care must be taken to reduce the signal power below the maximum rated power input to the VSA using appropriately rated attenuators. Neither the GPS antenna nor its settings should be used for lab verification and validation. As the VSA&#39;s screen is not capable of providing real-time monitoring of the environment, the addition of an SA as a real-time monitor helps determine the current state of the system. There are several types of channel-sounding measurement systems to capture channel characteristics for radio systems: CW, direct pulse, frequency domain using a VNA, correlation-based, swept-time delay cross-correlator.
One limitation of this system is that a CW signal probing the local environment does not contain time-domain information such as time-delay profiles. A time-delay profile gives information about the timing of source reflections of the signal in the local environment. However, an advantage of using a CW signal is that it is easier to obtain permission to transmit on one frequency in various bands using the narrowband CW signal rather than trying to transmit a wide-band signal. CW systems can have a larger dynamic range than other systems, and the signal can usually propagate further in the environment. A CW signal also has audio sampling rates that result in smaller file sizes than other types of channel-sounding systems. With this system, data collections are continuous and can last for several hours. The CW-channel sounder measurement system discussed in this article can be used at different frequencies, depending on the range of the various assembled components. The system can be used in an outdoor propagation environment or an indoor propagation environment15.

The Institute for Telecommunication Sciences (ITS) is the research laboratory of the National Telecommunications and Information Administration (NTIA), an agency of the U.S. Department of Commerce. ITS has a long history of conducting accurate, well-regarded radio frequency (RF) propagation measurements. The increase in spectrum-sharing has been accompanied by the need for accurate, reproducible measurements that provide a better understanding of the radio environment that multiple services will have to share. For the past few years, the military services have been developing spectrum-sharing arrangements with commercial wireless carriers in the Advanced Wireless Services (AWS)-3 band (1755-1780 MHz)1. This will allow commercial wireless carriers to use the AWS-3 band prior to phasing military services out of the band. The use of the band will be coordinated by both isolating systems geographically and by modeling frequency interference scenarios. To share this band of spectrum, propagation measurements are necessary to develop and improve propagation models for the evaluation of RF interference between the military and commercial wireless systems within the band.
The Defense Spectrum Organization (DSO) is responsible for the management of the AWS-3 transition and has tasked ITS and others with performing a series of channel-sounding measurements. These measurements will be used to build new models for the calculation of the impact of foliage and man-made structures in the environment (collectively known as clutter). Improved propagation modeling that accounts for clutter could lead to fewer restrictions on commercial transmitters in the vicinity of military systems. The CW-channel-sounder system discussed in this article has been used for the past five years to collect radio propagation measurement data and calculate the clutter attenuation. This measurement system produces accurate, repeatable, and unbiased results, and DSO encouraged ITS to share its institutional knowledge-including best measurement practices for the measurement and processing of RF propagation data-with the wider technical community.
Best measurement practices require understanding a system from the component level to the assembled-system level. These best measurement practices have been documented in the recently published NTIA Technical Memorandum TM-19-5352 that describes a set of best practices for the preparation and verification of radio propagation measurement systems. ITS recently completed a JoVE article on calibrating a VNA used to measure component losses and identify bad components for this measurement system3. This article is a continuation in documenting these best measurement practices for the wider community. Although best practices are discussed in this article for a CW-channel sounder, these same techniques can be used to verify other channel sounder systems: VNA systems; CW systems; full-bandwidth, correlation-based systems; direct pulse systems; and sliding correlator-based systems4,5,6.
This article describes in detail how to setup a CW-channel sounder measurement system using a vector signal analyzer (VSA), a spectrum analyzer (SA), two rubidium oscillators, a power meter, a vector signal generator (VSG), and various filters and power dividers for measurements in an outdoor measurement environment7,8. The transmitting side of the system consists of the VSG, which generates a CW signal that is boosted by a power amplifier. This is then split by a directional couple to divert some of the signal to the power meter, which allows the user to monitor the system output. The rest of the signal is sent to the receiving side of the system via the propagation channel. The receiving side consists of a low-pass filter to reduce interference and harmonics produced by the power amplifier. The filtered signal is split in a power divider and fed into the SA for monitoring during the measurement along with a time stamp and Global Positioning System (GPS) location. The other half of the signal is sent to the VSA to be downconverted into in-phase quadrature (I-Q) data in the range of 1-5 kHz. The sampling rate is determined by the instrument span9 and is guided by the expected Doppler spectrum shifts, which are a function of the speed of the vehicle. The resulting time series is then transferred to a computer for postprocessing and data analysis.
Rubidium clocks are used at both the transmitter and receiver to provide highly accurate measurements and highly stable frequencies. The rubidium clock at the receiving end has a fine frequency adjustment for the precise alignment of the transmitting and receiving frequencies. Typically, the frequencies are adjusted to be within 0.1 Hz of each other for testing. Rubidium clocks are essential for high-accuracy CW propagation measurements. They ensure precise time base accuracy over the course of the measurements and prevent frequency drift of the transmitter and receiver. This article also details how to validate and verify that a system is making accurate measurements in a laboratory setting, both with and without an antenna, prior to making measurements in an outdoor environment. The system has been used for an extensive series of outdoor and indoor tests at frequencies ranging from 430 MHz to 5.5 GHz and for many different transmitting powers7,8,10.

<table><tbody><tr><td>Cabling</td><td>Micro-Coax</td><td></td><td>Various lengths</td></tr><tr><td>Directional Coupler</td><td>Anatech Electronics, Inc.</td><td></td><td>AM1650DC833</td></tr><tr><td>Filter 1</td><td>K&amp;amp;L Microwave, Inc.</td><td></td><td>8FV50-1802-T95-O/O</td></tr><tr><td>GPS Antenna</td><td>Trimble</td><td></td><td>SMA connection to SA</td></tr><tr><td>Instrument Control &amp;amp; Processing Software</td><td>MATLAB</td><td></td><td>Used to store and process measurement data</td></tr><tr><td>Power Amplifier</td><td>Ophir RF</td><td></td><td>5263-003</td></tr><tr><td>Power Divider</td><td>Mini-Circuits</td><td></td><td>ZAPD-20+</td></tr><tr><td>Power Meter and Power Sensor</td><td>Keysight</td><td></td><td>E4417A/E4412A</td></tr><tr><td>Receiving Antenna</td><td>Cobham</td><td></td><td>OA2-0.3-10.0V/1505</td></tr><tr><td>Rubidium Frequency Standard</td><td>Stanford Research Systems</td><td></td><td>FS725</td></tr><tr><td>SA</td><td>Agilent</td><td></td><td>N9344C</td></tr><tr><td>Transmitting Antenna</td><td>COMTELCO</td><td></td><td>BS1710XL6</td></tr><tr><td>Vector Signal Generator</td><td>Rohde &amp;amp; Schwarz</td><td></td><td>SMIQ</td></tr><tr><td>VSA</td><td>Keysight Technologies</td><td></td><td>N9030A</td></tr></tbody></table>

continuous-wave propagation channel-sounding measurement system - testing, verification, and measurements

Channel sounders are used to measure channel characteristics for radio systems. There are several types of channel sounders used today: continuous-wave (CW), direct pulse, frequency domain using a vector network analyzer (VNA), correlation-based, and swept-time delay cross-correlator. Each of these has unique advantages and disadvantages. CW systems have a larger dynamic range than other systems with a signal that can propagate further into the environment. As the audio sampling rates allow smaller file sizes than other systems, data collection can be continuous and last for several hours. This article discusses a CW-channel sounder system, which has been used to make numerous propagation loss measurements in various cities in the United States of America. Such propagation measurements should be accurate, reproducible, and free of artifacts or biases. This article shows how to set up the measurement, how to validate and verify that the system is making reliable measurements, and finally, it shows results from some of the measurement campaigns such as repeatability measurements, clutter loss measurements (where clutter loss is defined as the excess loss from free-space transmission loss), and reciprocity measurements.

The following results were obtained during a field verification of the presented system. The transmitter was located on the Kohler Mesa behind the Department of Commerce Boulder Laboratories in Boulder, Colorado. The receiver was driven through Boulder, Colorado, in a specially designed measurement vehicle (see Figure 6), and continuous measurements were taken. The SA stores the swept data as log magnitude format in an event data structure, while the GPS data are stored in a separate event data structure within in the same file. An example of data for one sweep is shown in Figure 7. The stored data are converted to linear power in Watts; a mean is computed for all points in that sweep and then converted back to log magnitude. The GPS information is assigned to this mean value for the sweep shown by the red X at a value of &#8722;71.5 dBm. This process is done for every sweep in the file.
Next, the baseband I-Q data from the VSA are processed as shown in equation 1. The power in dBm is calculated for every I-Q sample. The VSA collects peak data, which must be converted to dBm, during this step.
<img alt="Equation 1" src="/files/ftp_upload/62124/62124eq01.jpg" />(1)
During the measurement, the baseband I-Q data are stored in a temporary file. No GPS information is acquired by the VSA. The length of the file is chosen such that the number of records requested is equal to the number of seconds of drive time. Once the measurement has finished, the data are written to a file whose structure is preprogrammed by the VSA software developers. Data saved into this file include the time difference between measurement samples, the frequency, and the complex data samples. The processing step involves the smoothing of the magnitude of the baseband I-Q data over a 500 ms window for the entire data set to approximate a 40-wavelength driving distance. Figure 8 shows how the smoothed mean power compares to the raw data for a larger portion of a drive test. The raw data are shown by the blue trace, and the smoothed mean power is shown by the red trace.
The VSA and SA data sets are aligned using a circular convolution. The VSA data point at each second is aligned with the SA samples generated at each second to transfer the GPS coordinates from the SA to the VSA data points. A linear regression model aligns the data by minimizing the residuals between the measured power levels of the two data sets. The aligned data are presented by plotting the SA power in dBm on the x-axis and the VSA power in dBm on the y-axis (Figure 9). As the SA system noise floor is higher than the VSA system noise floor, the graph will show a downward curvature at points below approximately -115 dBm for data sets close to the noise floor. Figure 9 and Figure 10 show&#160;the alignment of the VSA power and the SA power vs. the elapsed time in seconds. The GPS time stamp from the SA mean power is then attached to the first data point of the VSA average-smoothed power data series. The vertical offset between the two data sets is eliminated by correcting for cable loss from the power divider to the SA; however, as only the time-stamped VSA data are used, this extra step is unnecessary. These data are then saved and used in the Longley-Rice/Irregular Terrain Model (ITM)11,12 to predict terrain losses. The VSA data are corrected by adding system losses and removing system gains to obtain the measured basic transmission loss (BTL) or basic transmission gain (BTG) along the drive route as shown in Figure 11 and Figure 12 and given by equation 2.
<img alt="Equation 2" src="/files/ftp_upload/62124/62124eq02.jpg" />(2)
where, BTL is the basic transmission loss, Pt and Pr are the transmitting and receiving powers in dBm, Gt and Gr are the gains of the transmitting and receiving antennas in dBi, respectively, and Lt and Lr are the system losses for the transmitting system and receiving system in dB, respectively.
In Figure 11, the purple star is the transmitting location. The yellow and purple dots represent the highest and lowest received signal levels, respectively. A plot of the measured BTG (black x&#39;s), the ITM-modelled BTG (blue +&#39;s), free-space transmission gain (FSTG) (red circles), and the system noise floor (pink dots) is shown in Figure 12. When the ITM BTG equals the FSTG, there are no terrain interactions, and all losses (difference between FSTG and MBTG)&#160; can be assumed to come from buildings, foliage, or other interactions with the surrounding environment. This is shown in Figure 13, where the black line is the terrain pulled from the USGS terrain database13, the red, dashed line is the line-of-sight (LOS) line between the transmitting antenna and the receiving antenna, and the blue, dotted and dashed lines are the upper and lower first Fresnel zones14 where most of the energy is localized.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/62124/62124fig01.jpg" /> 
Figure 1:&#160;Diagram of transmitting components and connections. Transmitting side of continuous-wave (CW)-channel sounder. Abbreviations: RF = radio frequency; Ref = reference. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62124/62124fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/62124/62124fig02.jpg" /> 
Figure 2:&#160;Diagram of receiving components and connections. Receiving side of continuous-wave (CW) channel sounder. Abbreviations: GPS = Global Positioning System; RF = radio frequency; Ext Ref = external reference; GPS Ant = GPS antenna; Ext Trig/Ref = external Trigger/Reference; TCP/IP = transmission control protocol/internet protocol; Freq Adj = Frequency-adjusted; DC = direct current. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62124/62124fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/62124/62124fig03.jpg" /> 
Figure 3: CW channel sounder system in laboratory. A benchtop deployment of the Institute for Telecommunication Sciences (ITS) channel sounder for system validation and accuracy testing showing the main components. Abbreviations: VSA = vector signal analyzer; VSG = vector signal generator. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62124/62124fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/62124/62124fig04.jpg" /> 
Figure 4:&#160;I-Q display. Frequency adjustment using in-phase and quadrature (I-Q) plot. Abbreviations: CW = continuous-wave; TimeLen = time length; I-axis = in-phase axis; Q-axis = quadrature axis. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62124/62124fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/62124/62124fig05.jpg" /> 
Figure 5:&#160;Verification and validation system setup. System setup for verification and validation measurements. Abbreviations: I-Q = in-phase quadrature; RF = radio frequency; Ref = reference; GPS = Global Positioning System; Ext Trig/Ref = external trigger/Reference; TCP/IP = transmission control protocol/internet protocol; Freq Adj = frequency adjusted; DC = direct current. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62124/62124fig05large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/62124/62124fig06.jpg" /> 
Figure 6:&#160;Cellular-on-wheels (COW) and measurement van. Photo showing green van used for receiving system and cellular-on-wheels (COW) used to house transmitting system. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62124/62124fig06large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/62124/62124fig07.jpg" /> 
Figure 7:&#160;Spectrum analyzer sweep and sweep average. Single sweep for spectrum analyzer data capture consisting of 461 points over a 0.5 s sweep time. Abbreviation: SA = spectrum analyzer. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62124/62124fig07large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/62124/62124fig08.jpg" /> 
Figure 8:&#160;Vector signal analyzer received power and moving average. In-phase and quadrature (I-Q) magnitude data (blue trace) for a small slice of a larger run compared to the mean power (red trace) calculated over a 0.5 s window. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62124/62124fig08large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 9" class="xfigimg" src="/files/ftp_upload/62124/62124fig09.jpg" /> 
Figure 9:&#160;VSA and SA signal alignment. Alignment of vector signal analyzer power and spectrum analyzer power. Abbreviations: VSA = vector signal analyzer; SA = spectrum analyzer. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62124/62124fig09large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 10" class="xfigimg" src="/files/ftp_upload/62124/62124fig10.jpg" /> 
Figure 10:&#160;VSA and SA received power after signal alignment. Aligned vector signal analyzer power and spectrum analyzer power vs elapsed time in seconds. Abbreviations: VSA = vector signal analyzer; SA = spectrum analyzer. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62124/62124fig10large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 11" class="xfigimg" src="/files/ftp_upload/62124/62124fig11.jpg" /> 
Figure 11:&#160;Geolocation of measured basic transmission gain. Measured basic transmission gain along the drive route. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62124/62124fig11large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 12" class="xfigimg" src="/files/ftp_upload/62124/62124fig12.jpg" /> 
Figure 12:&#160;Measured and modelled basic transmission gain.&#160;Measured basic transmission gain (blue x&#39;s), Irregular-Terrain Model (ITM) basic transmission gain (BTG) (black +&#39;s), free-space transmission gain (red circles), and system noise floor (pink dots) vs. elapsed time along the drive route. Abbreviations: MBTG = Measured basic transmission gain; ITM = Irregular-Terrain Model. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62124/62124fig12large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 13" class="xfigimg" src="/files/ftp_upload/62124/62124fig13.jpg" /> 
Figure 13:&#160;Terrain profile and first Fresnel zone. United States Geological Survey terrain profile (black line) for elapsed time 1636.2 s. The upper (first) Fresnel zone (blue, dotted line) and lower (first) Fresnel zone (blue, dashed line) are also plotted along with the line-of-sight line (red, dashed line) between the transmitting antenna and receiving antenna. Abbreviations: USGS = United States Geological Survey; NED = national elevation database. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62124/62124fig13large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Continuous-Wave Propagation Channel-Sounding Measurement System - Testing, Verification, and Measurements at JoVE.com

Continuous-Wave Propagation Channel-Sounding Measurement System - Testing, Verification, and Measurements

This report describes the setup, validation and verification, and results from propagation measurements using a continuous-wave, radio frequency channel-sounding measurement system.

Channel sounders are used to measure channel characteristics for radio systems. There are several types of channel sounders used today: continuous-wave ...

continuous-wave-propagation-channel-sounding-measurement-system

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3.0K Views.  Institute for Telecommunication Sciences. Propagatiemetingen vormen de basis voor modellen en beleid. Het verifiëren en valideren van een meetsysteem voordat dit soort belangrijke metingen worden gedaan, is van cruciaal belang. We hebben deze techniek gebruikt om andere meetsystemen te valideren, zodat de metingen consistent zijn.Dit systeem is eenvoudig te monteren en te gebruiken. Het gebruik van dit protocol zorgt ervoor dat u uw systeem begrijpt voordat u metingen uitvoert in een complexere omgeving. Dit protocol behandel...

Video: Continuous-Wave Propagation Channel-Sounding Measurement System - Testing, Verification, and Measurements

Fabrication, Operation and Flow Visualization in Surface-acoustic-wave-driven Acoustic-counterflow Microfluidics

Surface acoustic waves (SAWs) can be used to drive liquids in portable microfluidic chips via the acoustic counterflow phenomenon. In this video we present the fabrication protocol for a multilayered SAW acoustic counterflow device. The device is fabricated starting from a lithium niobate (LN) substrate onto which two interdigital transducers (IDTs) and appropriate markers are patterned. A polydimethylsiloxane (PDMS) channel cast on an SU8 master mold is finally bonded on the patterned substrate. Following the fabrication procedure, we show the techniques that allow the characterization and operation of the acoustic counterflow device in order to pump fluids through the PDMS channel grid. We finally present the procedure to visualize liquid flow in the channels. The protocol is used to show on-chip fluid pumping under different flow regimes such as laminar flow and more complicated dynamics characterized by vortices and particle accumulation domains.

In this video we first describe fabrication and operation procedures of a surface acoustic wave (SAW) acoustic counterflow device. We then demonstrate an experimental setup that allows for both qualitative flow visualization and quantitative analysis of complex flows within the SAW pumping device.

Surface acoustic waves (SAWs) can be used to drive liquids in portable microfluidic chips via the acoustic counterflow phenomenon. In this video we ...

Using Microwave and Macroscopic Samples of Dielectric Solids to Study the Photonic Properties of Disordered Photonic Bandgap Materials

Recently, disordered photonic materials have been suggested as an alternative to periodic crystals for the formation of a complete photonic bandgap (PBG). In this article we will describe the methods for constructing and characterizing macroscopic disordered photonic structures using microwaves. The microwave regime offers the most convenient experimental sample size to build and test PBG media. Easily manipulated dielectric lattice components extend flexibility in building various 2D structures on top of pre-printed plastic templates. Once built, the structures could be quickly modified with point and line defects to make freeform waveguides and filters. Testing is done using a widely available Vector Network Analyzer and pairs of microwave horn antennas. Due to the scale invariance property of electromagnetic fields, the results we obtained in the microwave region can be directly applied to infrared and optical regions. Our approach is simple but delivers exciting new insight into the nature of light and disordered matter interaction.

Our representative results include the first experimental demonstration of the existence of a complete and isotropic PBG in a two-dimensional (2D) hyperuniform disordered dielectric structure. Additionally we demonstrate experimentally the ability of this novel photonic structure to guide electromagnetic waves (EM) through freeform waveguides of arbitrary shape.

Disordered structures offer new mechanisms for forming photonic bandgaps and unprecedented freedom in functional-defect designs. To circumvent the computational challenges of disordered systems, we construct modular macroscopic samples of the new class of PBG materials and use microwaves to characterize their scale-invariant photonic properties, in an easy and inexpensive manner.

Recently, disordered photonic materials have been suggested as an alternative to periodic crystals for the formation of a complete photonic bandgap (PBG). ...

The Measurement of Unsteady Surface Pressure Using a Remote Microphone Probe

Microphones are widely applied to measure pressure fluctuations at the walls of solid bodies immersed in turbulent flows. Turbulent motions with various characteristic length scales can result in pressure fluctuations over a wide frequency range. This property of turbulence requires sensing devices to have sufficient sensitivity over a wide range of frequencies. Furthermore, the small characteristic length scales of turbulent structures require small sensing areas and the ability to place the sensors in very close proximity to each other. The complex geometries of the solid bodies, often including large surface curvatures or discontinuities, require the probe to have the ability to be set up in very limited spaces. The development of a remote microphone probe, which is inexpensive, consistent, and repeatable, is described in the present communication. It allows for the measurement of pressure fluctuations with high spatial resolution and dynamic response over a wide range of frequencies. The probe is small enough to be placed within the interior of typical wind tunnel models. The remote microphone probe includes a small, rigid, and hollow tube that penetrates the model surface to form the sensing area. This tube is connected to a standard microphone, at some distance away from the surface, using a "T" junction. An experimental method is introduced to determine the dynamic response of the remote microphone probe. In addition, an analytical method for determining the dynamic response is described. The analytical method can be applied in the design stage to determine the dimensions and properties of the RMP components.

Here, we present a protocol to measure, with high spatial resolution, the unsteady surface pressure in turbulent flows. This method demonstrates the construction of a remote microphone probe (RMP) and the determination of its frequency-dependent, complex transfer function. An analytical determination of the dynamic response is presented and validated.

Microphones are widely applied to measure pressure fluctuations at the walls of solid bodies immersed in turbulent flows. Turbulent motions with various ...

Characterization of Anisotropic Leaky Mode Modulators for Holovideo

Holovideo displays are based on light-bending spatial light modulators. One such spatial light modulator is the anisotropic leaky mode modulator. This modulator is particularly well suited for holographic video experimentation as it is relatively simple and inexpensive to fabricate1-3. Some additional advantages of leaky mode devices include: large aggregate bandwidth, polarization separation of signal light from noise, large angular deflection and frequency control of color1. In order to realize these advantages, it is necessary to be able to adequately characterize these devices as their operation is strongly dependent on waveguide and transducer parameters4. To characterize the modulators, the authors use a commercial prism coupler as well as a custom characterization apparatus to identify guided modes, calculate waveguide thickness and finally to map the device's frequency input and angular output of leaky mode modulators. This work gives a detailed description of the measurement and characterization of leaky mode modulators suitable for full-color holographic video.

This work describes fabrication and characterization of anisotropic leaky mode modulators for holographic video.

Holovideo displays are based on light-bending spatial light modulators.  One such spatial light modulator is the anisotropic leaky mode modulator.  This ...

Fabrication and Testing of Photonic Thermometers

In recent years, a push for developing novel silicon photonic devices for telecommunications has generated a vast knowledge base that is now being leveraged for developing sophisticated photonic sensors. Silicon photonic sensors seek to exploit the strong confinement of light in nano-waveguides to transduce changes in physical state to changes in resonance frequency. In the case of thermometry, the thermo-optic coefficient, i.e., changes in refractive index due to temperature, causes the resonant frequency of the photonic device such as a Bragg grating to drift with temperature. We are developing a suite of photonic devices that leverage recent advances in telecom compatible light sources to fabricate cost-effective photonic temperature sensors, which can be deployed in a wide variety of settings ranging from controlled laboratory conditions, to the noisy environment of a factory floor or a residence. In this manuscript, we detail our protocol for the fabrication and testing of photonic thermometers.

We describe the process of fabrication and testing of photonic thermometers.

In recent years, a push for developing novel silicon photonic devices for telecommunications has generated a vast knowledge base that is now being ...

Chemistry

High-speed Continuous-wave Stimulated Brillouin Scattering Spectrometer for Material Analysis

Recent years have witnessed a significant increase in the use of spontaneous Brillouin spectrometers for non-contact analysis of soft matter, such as aqueous solutions and biomaterials, with fast acquisition times. Here, we discuss the assembly and operation of a Brillouin spectrometer that uses stimulated Brillouin scattering (SBS) to measure stimulated Brillouin gain (SBG) spectra of water and lipid emulsion-based tissue-like samples in transmission mode with &lt;10 MHz spectral-resolution and &lt;35 MHz Brillouin-shift measurement precision at &lt;100 ms. The spectrometer consists of two nearly counter-propagating continuous-wave (CW) narrow-linewidth lasers at 780 nm whose frequency detuning is scanned through the material Brillouin shift. By using an ultra-narrowband hot rubidium-85 vapor notch filter and a phase-sensitive detector, the signal-to-noise-ratio of the SBG signal is significantly enhanced compared to that obtained with existing CW-SBS spectrometers. This improvement enables measurement of SBG spectra with up to 100-fold faster acquisition times, thereby facilitating high spectral-resolution and high-precision Brillouin analysis of soft materials at high speed.

We describe the construction of a rapid continuous-wave-stimulated-Brillouin-scattering (CW-SBS) spectrometer. The spectrometer employs single-frequency diode-lasers and an atomic vapor notch-filter to acquire transmission spectra of turbid/non-turbid samples with high spectral-resolution at speeds up to 100-fold faster than those of existing CW-SBS spectrometers. This improvement enables high-speed Brillouin material analysis.

Recent years have witnessed a significant increase in the use of spontaneous Brillouin spectrometers for non-contact analysis of soft matter, such as ...

Measurements of Waves in a Wind-wave Tank Under Steady and Time-varying Wind Forcing

This manuscript describes an experimental procedure that allows obtaining diverse quantitative information on temporal and spatial evolution of water waves excited by time-dependent and steady wind forcing. Capacitance-type wave gauge and Laser Slope Gauge (LSG) are used to measure instantaneous water surface elevation and two components of the instantaneous surface slope at a number of locations along the test section of a wind-wave facility. The computer-controlled blower provides airflow over the water in the tank whose rate can vary in time. In the present experiments, the wind speed in the test section initially increases quickly from rest to the set value. It is then kept constant for the prescribed duration; finally, the airflow is shut down. At the beginning of each experimental run, the water surface is calm and there is no wind. Operation of the blower is initiated simultaneously with the acquisition of data provided by all sensors by a computer; data acquisition continues until the waves in the tank fully decay. Multiple independent runs performed under identical forcing conditions allow determining statistically reliable ensemble-averaged characteristic parameters that quantitatively describe wind-waves&#39; variation in time for the initial development stage as a function of fetch. The procedure also allows characterizing the spatial evolution of the wave field under steady wind forcing, as well as decay of waves in time, once the wind is shut down, as a function of fetch.

This manuscript describes a fully computer-controlled procedure that allows obtaining reliable statistical parameters from experiments of water waves excited by steady and unsteady wind forcing in a small-scale facility.

This manuscript describes an experimental procedure that allows obtaining diverse quantitative information on temporal and spatial evolution of water ...

Calibration of Vector Network Analyzer for Measurements in Radio Frequency Propagation Channels

In situ measurements of radio frequency (RF) spectrum activity provide insight into the physics of radio frequency wave propagation and validate existing and new spectrum propagation models. Both of these parameters are essential to supporting and preserving interference-free spectrum sharing, as spectrum use continues to increase. It is vital that such propagation measurements are accurate, reproducible, and free of artifacts and bias. Characterizing the gains and losses of components used in these measurements is vital to their accuracy. A vector network analyzer (VNA) is a well-established, highly accurate, and versatile piece of equipment that measures both magnitude and phase of signals, if properly calibrated. This article details the best practices for calibrating a VNA. Once calibrated, it can be used to accurately measure components of a correctly configured propagation measurement (or channel sounding) system or can be used as a measurement system itself.

This protocol describes best practices for calibrating a vector network analyzer prior to use as an accurate instrument, intended to measure components of a radio frequency propagation measurement test system.

In situ measurements of radio frequency (RF) spectrum activity provide insight into the physics of radio frequency wave propagation and validate existing ...

Assembly and Characterization of an External Driver for the Generation of Sub-Kilohertz Oscillatory Flow in Microchannels

Microfluidic technology has become a standard tool in chemical and biological laboratories for both analysis and synthesis. The injection of liquid samples, such as chemical reagents and cell cultures, is predominantly accomplished through steady flows that are typically driven by syringe pumps, gravity, or capillary forces. The use of complementary oscillatory flows is seldom considered in applications despite its numerous advantages as recently demonstrated in the literature. The significant technical barrier to the implementation of oscillatory flows in microchannels is likely responsible for the lack of its widespread adoption. Advanced commercial syringe pumps that can produce oscillatory flow, are often more expensive and only work for frequencies less than 1 Hz. Here, the assembly and operation of a low-cost, plug-and-play type speaker-based apparatus that generates oscillatory flow in microchannels is demonstrated. High-fidelity harmonic oscillatory flows with frequencies ranging from 10-1000 Hz can be achieved along with independent amplitude control. Amplitudes ranging from 10-600 &#181;m can be achieved throughout the entire range of operation, including amplitudes &#62; 1 mm at the resonant frequency, in a typical microchannel. Although the oscillation frequency is determined by the speaker, we illustrate that the oscillation amplitude is sensitive to fluid properties and channel geometry. Specifically, the oscillation amplitude decreases with increasing channel circuit length and liquid viscosity, and in contrast, the amplitude increases with increasing speaker tube thickness and length. Additionally, the apparatus requires no prior features to be designed on the microchannel and is easily detachable. It can be used simultaneously with a steady flow created by a syringe pump to generate pulsatile flows.

The protocol demonstrates a convenient method to produce harmonic oscillatory flow from 10-1000 Hz in microchannels. This is performed by interfacing a computer-controlled speaker diaphragm to the microchannel in a modular manner.

Microfluidic technology has become a standard tool in chemical and biological laboratories for both analysis and synthesis. The injection of liquid ...

Studying Cavitation Enhanced Therapy

Interest in the therapeutic applications of ultrasound is significant and growing, with potential clinical targets ranging from cancer to Alzheimer&#8217;s disease. Cavitation - the formation and subsequent motion of bubbles within an ultrasound field - represents a key phenomenon underpinning many of these treatments. There remains, however, considerable uncertainty regarding the detailed mechanisms of action by which cavitation promotes therapeutic effects and there is a need to develop reliable monitoring techniques that can be implemented clinically. In particular, there is significant variation between studies in the exposure parameters reported as successfully delivering therapeutic effects and the corresponding acoustic emissions. The aim of this paper is to provide design guidelines and an experimental protocol using widely available components for performing studies of cavitation-mediated bioeffects, and&#160;include real-time acoustic monitoring. It is hoped that the protocol will enable more widespread incorporation of acoustic monitoring into therapeutic ultrasound experiments and facilitate easier comparison across studies of exposure conditions and their correlation to relevant bio-effects.

The presented experimental protocol can be used to perform real time measurements of cavitation activity in a cell culture device with the aim of enabling investigation of the conditions required for successful drug delivery and/or other bioeffects.

Continuous-Wave Propagation Channel-Sounding Measurement System - Testing, Verification, and Measurements

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