The authors would like to thank Herman Liggesmeyer and Marvin Bende for their expert advice in electrotechnics and informatics.

1. Assembly of a basic volt-amperemeter for TEER measurement
<ol>
	<li>Prepare a standard USB charger as the 5 V D.C. power supply, a USB extension cord, a microcontroller that will be used as a programmable square wave generator, two standard multimeters that are able to measure alternating current and voltage as root mean square (True-RMS), four cables with banana plugs, a telephone extension cord with a RJ14 female connector including six pins with the inner four wired (6P4C), two short cables, a luster terminal, a 120 k&#937; pre-resistor, wire end ferrules, and soldering lugs. The tools required are an insulation stripper, a crimping tool, and a soldering iron.</li>
	<li>First, connect the USB extension to the microcontroller board.</li>
	<li>Strip the end insulation of two short cables. Solder one side per cable either directly to pins 0 and 2 of the microcontroller or to soldering lugs, which in turn are clipped on the respective pins. Crimp the other ends to the wire end ferrules and connect them to a luster terminal as depicted in Figure 1.</li>
	<li>Link the banana plugs to the multimeters. Strip and crimp the other end of each of the four cables.</li>
	<li>Cut the telephone extension cord in two pieces and dismantle and crimp the conductors of the side containing the female connector. Check for the continuity of the conductors and pins.</li>
	<li>The first multimeter will be used to measure current in &#181;A (note that the AC mode has to be set explicitly). Connect it in a series with a 120 k&#937; pre-resistor to pins five and six of the RJ14 connector, corresponding to the outer electrode pair of the chopstick electrode.</li>
	<li>Finally, link the second multimeter, which will be used to measure the transepithelial voltage drop in mV, via the luster terminal to pins three and four of the RJ14 connector, corresponding to the inner electrode pair of the chopstick electrode.</li>
	<li>If desired, mount the installation in a chassis.</li>
</ol>
2. Programming the microcontroller
<ol>
	<li>Modify the provided source code (supplemental coding file 1) as needed. In the given form, pins 0 and 2 will alternate between ground and +5 V with 40 ms half-time of oscillation. Thus, a square wave signal with an amplitude of 5 V and a frequency of approximately 12.5 Hz will be generated. The real values may differ due to the inaccuracy of the microcontroller&#39;s time emitter.</li>
	<li>Connect the microcontroller to a desktop computer via a USB port and upload the source code with matching software25.</li>
</ol>
3. Recording of voltage oscillograms (optional)
<ol>
	<li>Bypass pins five and six of the RJ14 connector with a 1 k&#937; test resistor and connect to an oscilloscope.</li>
	<li>Check for the frequency, peak voltage, and waveform. Digitize and export the data.</li>
	<li>If desired, record oscillograms from a reference device (EVOM) and the self-assembled voltammeter for comparison. 
	NOTE: In this case, the data was recorded with a Digital Storage Scope HM 208. Being a very basic digital oscilloscope, the image could be internally digitized (frozen) but had to be plotted using an analogue PM 8143 X-Y recorder. The image was subsequently scanned.</li>
</ol>
4. Cell cultivation and TEER measurement
<ol>
	<li>Seed Human Choroid Plexus Papilloma (HIBCPP) cells on cell culture filter inserts with a pore size of 3 &#181;m in DMEM/F12 (see Table of Materials) containing 10% fetal calf serum9. Grow the cells at 37 &#176;C in a water saturated atmosphere containing 5% CO2 as described by Dinner et al.9.</li>
	<li>When the filters reach an impedance of 70 &#937; &#8729; cm2, change to serum-free DMEM/F12 and define the timepoint as Day 0.</li>
	<li>Connect the electrode to the RJ14 port of the self-assembled voltammeter and plug in the USB power supply. Set the multimeters to AC voltage mode (mV) and AC current mode (&#181;A), respectively.
	<ol>
		<li>Alternatively, connect the electrode to a commercially available reference device and turn on according to the manufacturer&#39;s instructions.</li>
	</ol>
	</li>
	<li>Sterilize the electrode in 80% ethanol for 10 min and equilibrate in the appropriate medium for another 10 min.</li>
	<li>Put the electrode in both compartments of a cell culture filter insert system (the longer part of the electrode in the lower compartment and the shorter part in the upper compartment) containing a HIBCPP cell layer until the measurement values remain constant.</li>
	<li>For a reference device, note the impedance directly or calculate the impedance according to Ohm&#39;s law (R = U/I) for the self-assembled voltammeter. Be aware that electrode angle affects the measurements.</li>
	<li>Repeat the TEER measurement (steps 3&#8722;6) from Day 0 until Day 4.</li>
</ol>

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P., 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=Immortalized+human+cerebral+microvascular+endothelial+cells+maintain+the+properties+of+primary+cells+in+an+in+vitro+model+of+immune+migration+across+the+blood+brain+barrier.">Immortalized human cerebral microvascular endothelial cells maintain the properties of primary cells in an in vitro model of immune migration across the blood brain barrier.</a> Journal of Neuroscience Methods. 212, 173-179 (2013).</li><li>Weksler, B. B., 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=Blood-brain+barrier-specific+properties+of+a+human+adult+brain+endothelial+cell+line.">Blood-brain barrier-specific properties of a human adult brain endothelial cell line.</a> Federation of American Societies for Experimental Biology Journal. 19, 1872-1874 (2005).</li><li>Lippmann, E. S., Al-Ahmad, A., Azarin, S. M., Palecek, S. P., Shusta, E. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+retinoic+acid-enhanced,+multicellular+human+blood-brain+barrier+model+derived+from+stem+cell+sources.">A retinoic acid-enhanced, multicellular human blood-brain barrier model derived from stem cell sources.</a> Scientific Reports. 4, 4160 (2014).</li><li>Stins, M. 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T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+the+human+colon+carcinoma+cell+line+(Caco-2)+as+a+model+system+for+intestinal+epithelial+permeability.">Characterization of the human colon carcinoma cell line (Caco-2) as a model system for intestinal epithelial permeability.</a> Gastroenterology. 96, 736-749 (1989).</li><li>Yeste, J., 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=Geometric+correction+factor+for+transepithelial+electrical+resistance+measurements+in+Transwell+and+microfluidic+cell+cultures.">Geometric correction factor for transepithelial electrical resistance measurements in Transwell and microfluidic cell cultures.</a> Journal of Physics D Applied Physics. 49 (37), 3754 (2016).</li><li>Northrup, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=VI:+The+Measurement+of+Low+Resistance.">VI: The Measurement of Low Resistance.</a> Methods of Measuring Electrical Resistance. , 100-131 (1912).</li><li>Li, H., Sheppard, D. 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J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Impedance-based+cell+monitoring:+barrier+properties+and+beyond.">Impedance-based cell monitoring: barrier properties and beyond.</a> Fluids and Barriers of the CNS. 10, 5 (2013).</li><li>Hufnagl, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Time Resolved Transepithelial Impedance Spectroscopy Of Caco 2 Monolayers Relying on Lithographically Patterned Basolateral Electrode Cell Arrays. , (2010).</li><li>Guimer&#224;, A., Gabriel, G., Parramon, D., Calder&#243;n, E., Villa, R., D&#246;ssel, O., Schlegel, W. 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The authors have no competing financial interests or other conflicts of interest.

Before a self-made voltammeter can be used in a daily routine, it is essential to check the device for proper function. In our case, a half-time of oscillation of 40 ms (12.5 Hz) was programmed, but the effective oscillation time turned out to be 60 ms (16.7 Hz). This inaccuracy of the microcontroller&#39;s time emitter had no detectable impact on TEER measurements. It might be best to determine the actual frequency using the frequency setting of one of the multimeters. If any deviation is found, the source code can be a...

Epithelial and endothelial cells function as cellular boundaries, separating the apical and basolateral sides of the body. If they are connected through tight junctions, passive substance diffusion through the paracellular spaces is restricted1, resulting in the formation of a selectively permeable barrier. Several artificial barrier systems have been developed2 using microvascular endothelial cells (HBMEC, blood-brain barrier3,4,5,6,7), choroid plexus epithelial cells (HIBCPP/PCPEC, blood-cerebrospinal fluid barrier8,9,10,11,12,13,14), colorectal adenocarcinoma cells (Caco-2, gastrointestinal models15), or airway/alveolar cell lines (pulmonary models16,17). These systems typically consist of cells grown in a monolayer on permeable membranes (i.e., filter insert systems) to allow access to the apical and basolateral sides. It is important that the integrity of the model system matches the in vivo conditions. Hence, several techniques have been developed to analyze barrier function by measuring paracellular diffusion of tracer compounds across the cell layer. These substances include radiolabeled sucrose, dye-labeled albumin, FITC-labeled inulin, or dye-labeled dextrans2. However, chemical dyes can make cells unusable for further experiments. To monitor barrier systems noninvasively, measurement of transepithelial/transendothelial electrical resistance (TEER) across a cellular monolayer can be used2,18,19. Because bipolar electrode systems are influenced by the electrode polarization impedance at the electrode-electrolyte interface, tetrapolar measurements are generally used to overcome this limitation20. The underlaying technique is a four-terminal sensing (4T) that was first described in 1861 by William Thomson (Lord Kelvin)21. In brief, the current is injected by a pair of current-carrying electrodes while a second pair of voltage-sensing electrodes is used to measure the voltage drop20. Nowadays, so-called chopstick electrodes consist of a pair of double electrodes, each containing a silver/silver-chloride pellet for measuring voltage and a silver electrode for passing current2. The electrical impedance is measured between the apical and the basolateral compartment with the cell layer in between (Figure 1). A square wave signal at a frequency of typically 12.5 Hz is applied at the outer electrodes and the resulting alternating current (AC) measured. Additionally, the potential drop across the cell layer is measured by the second (inner) electrode pair. Electrical impedance is then calculated according to Ohm&#39;s law. TEER values are normalized by multiplying impedance and cell layer surface area and are typically expressed as &#937; &#8729; cm2.
There are systems in which cells and electrodes are arranged in a more sophisticated way, but are also based on the 4T measuring principle and can be used with the same measurement devices. EndOhm systems, for example, in which the filter is inserted, contain a chamber and cap with a pair of concentric electrodes with the same structure as the chopstick electrode. The shape of the electrodes allows for a more uniform current density flow across the membrane, thereby reducing variation between readings. Even more complex (but also more accurate) is an Ussing chamber, where a cell layer separates two chambers filled with Ringer&#39;s solution22. The chamber itself can be gassed with oxygen, CO2, or N2, and stirred or supplemented with experimental substances. As ion transport across the cell layer occurs, a potential difference can be measured by two voltage-sensing electrodes near the tissue. This voltage is cancelled out by two current-carrying electrodes placed next to the cell layer. The measured current will then give the net ion transport and the transepithelial resistance, which reflects barrier integrity, can be determined22. TEER measurement can also be applied on body-on-a-chip systems that represent barrier-tissue models23,24. These systems mimic in vivo conditions of the cells and often consist of several types of cells, stacked on top of each other in layers.
The following protocol explains how to set up a cost-effective and reliable voltammeter with programmable output frequency that produces no statistically significant differences in TEER compared to commercially available measurement systems.

<table><tbody><tr><td>120 kOhm resistor</td><td></td><td></td><td>General (generic) equipment</td></tr><tr><td>Banana plug cables</td><td></td><td></td><td>General (generic) equipment</td></tr><tr><td>Cables</td><td></td><td></td><td>General (generic) equipment</td></tr><tr><td>Chopstick electrode</td><td>Merck Millicell</td><td>MERSSTX01</td><td></td></tr><tr><td>Chopstick electrode (alternative)</td><td>WPI World Precision Instruments</td><td>STX2</td><td></td></tr><tr><td>Crimping tool</td><td></td><td></td><td>General tool</td></tr><tr><td>Digispark / ATtiny85</td><td>AZ-Delivery Vertriebs GmbH</td><td>Digispark Rev.3 Kickstarter</td><td></td></tr><tr><td>DMEM:F12</td><td>Gibco (Thermo Fisher)</td><td>31330038</td><td></td></tr><tr><td>Fetal calf serum (FCS)/Fetal Bovine Serum (FBS)</td><td>Life Technologies</td><td>10270106</td><td></td></tr><tr><td>Filter inserts 3&amp;micro;m translucent</td><td>Greiner Bioone</td><td>662631</td><td></td></tr><tr><td>HIBCPP</td><td></td><td></td><td>Hiroshi Ishikawa / Horst Schroten</td></tr><tr><td>Insulation stripper</td><td></td><td></td><td>General tool</td></tr><tr><td>Luster terminal</td><td></td><td></td><td>General (generic) equipment</td></tr><tr><td>Oscilloscope</td><td>HAMEG</td><td>Digital Storage Scope HM 208</td><td></td></tr><tr><td>Plotter</td><td>PHILIPS</td><td>PM 8143 X-Y recorder</td><td></td></tr><tr><td>Software Arduino</td><td>https://www.arduino.cc</td><td>Arduino 1.8.9</td><td></td></tr><tr><td>Soldering iron</td><td></td><td></td><td>General tool</td></tr><tr><td>Soldering lugs</td><td></td><td></td><td>General (generic) equipment</td></tr><tr><td>Telephone cable with RJ14 (6P4C) connector</td><td></td><td></td><td>General (generic) equipment</td></tr><tr><td>Test resistor</td><td>Merck Millicell</td><td>MERSSTX04</td><td></td></tr><tr><td>True-RMS multimeters</td><td>VOLTCRAFT</td><td>VC185</td><td></td></tr><tr><td>USB charger</td><td></td><td></td><td>General (generic) equipment</td></tr><tr><td>USB extension cord</td><td></td><td></td><td>General (generic) equipment</td></tr><tr><td>Voltohmmeter for TEER measurement</td><td>WPI World Precision Instruments</td><td>EVOM</td><td></td></tr><tr><td>Voltohmmeter for TEER measurement (alternative)</td><td>Merck Millicell</td><td>ERS</td><td></td></tr><tr><td>Wire end ferrules</td><td></td><td></td><td>General (generic) equipment</td></tr></tbody></table>

a simple approach to perform teer measurements using a self-made volt-amperemeter with programmable output frequency

Transepithelial/endothelial electrical resistance (TEER) has been used since the 1980s to determine confluency and permeability of in vitro barrier model systems. In most cases, chopstick electrodes are used to determine the electric impedance between the upper and lower compartment of a cell culture filter insert system containing cellular monolayers. The filter membrane allows the cells to adhere, polarize, and interact by building tight junctions. This technique has been described with a variety of different cell lines (e.g., cells of the blood-brain barrier, blood-cerebrospinal fluid barrier, or gastrointestinal and pulmonary tract). TEER measurement devices can be readily obtained from different laboratory equipment suppliers. However, there are more cost-effective and customizable solutions imaginable if an appropriate voltammeter is self-assembled. The overall aim of this publication is to set up a reliable device with programmable output frequency that can be used with commercially available chopstick electrodes for TEER measurement.

To compare the operation of a self-assembled voltammeter with its commercially available counterpart, a voltage oscillogram of both devices was recorded.
As shown in Figure 2A, the reference instrument generated a square wave signal with an amplitude of 80 mV and an oscillation time of 80 ms, which corresponds to a frequency of 12.5 Hz, when operating on-load with a 1 k&#937; test resistor.
...

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A Simple Approach to Perform TEER Measurements Using a Self-Made Volt-Amperemeter with Programmable Output Frequency

Here, we demonstrate how to set up an inexpensive volt-amperemeter with programmable output frequency that can be used with commercially available chopstick electrodes for transepithelial/endothelial electrical resistance measurements.

Transepithelial/endothelial electrical resistance (TEER) has been used since the 1980s to determine confluency and permeability of in vitro barrier model ...

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21.5K Views.  University of Tübingen. Here, we demonstrate how to set up an inexpensive volt-amperemeter with programmable output frequency that can be used with commercially available chopstick electrodes for transepithelial/endothelial electrical resistance measurements.

Video: A Simple Approach to Perform TEER Measurements Using a Self-Made Volt-Amperemeter with Programmable Output Frequency

Measurement of Bioelectric Current with a Vibrating Probe

Electric fields, generated by active transport of ions, are present in many biological systems and often serve important functions in tissues and organs. For example, they play an important role in directing cell migration during wound healing. Here we describe the manufacture and use of ultrasensitive vibrating probes for measuring extracellular electric currents. The probe is an insulated, sharpened metal wire with a small platinum-black tip (30-35 &mu;m), which can detect ionic currents in the &mu;A/cm2 range in physiological saline. The probe is vibrated at about 200 Hz by a piezoelectric bender. In the presence of an ionic current, the probe detects a voltage difference between the extremes of its movement. A lock-in amplifier filters out extraneous noise by locking on to the probe's frequency of vibration. Data are recorded onto computer. The probe is calibrated at the start and end of experiments in appropriate saline, using a chamber which applies a current of exactly 1.5 &mu;A/cm2. We describe how to make the probes, set up the system and calibrate. We also demonstrate the technique of cornea measurement, and show some representative results from different specimens (cornea, skin, brain).

The manufacture, calibration and use of non-invasive vibrating probes to measure bioelectric current in various biological systems is described.

Electric fields, generated by active transport of ions, are present in many biological systems and often serve important functions in tissues and organs. ...

Bioengineering

Electrochemical Impedance Spectroscopy as a Tool for Electrochemical Rate Constant Estimation

Electrochemical impedance spectroscopy (EIS) was used for advanced characterization of organic electroactive compounds along with cyclic voltammetry (CV). In the case of fast reversible electrochemical processes, current is predominantly affected by the rate of diffusion, which is the slowest and limiting stage. EIS is a powerful technique that allows separate analysis of stages of charge transfer that have different AC frequency response. The capability of the method was used to extract the value of charge transfer resistance, which characterizes the rate of charge exchange on the electrode-solution interface. The application of this technique is broad, from biochemistry up to organic electronics. In this work, we are presenting the method of analysis of organic compounds for optoelectronic applications.

Electrochemical impedance spectroscopy (EIS) of species that undergo reversible oxidation or reduction in solution was used for determination of rate constants of oxidation or reduction.

Electrochemical impedance spectroscopy (EIS) was used for advanced characterization of organic electroactive compounds along with cyclic voltammetry (CV). ...

Chemistry

Design and Characterization Methodology for Efficient Wide Range Tunable MEMS Filters

Here, we demonstrate the advantages of the laser Doppler vibrometer (LDV) over conventional techniques (the network analyzer), as well as the techniques to create an application-based microelectromechanical systems (MEMS) filter and how to use it efficiently (i.e., tuning the tuning-capability and avoiding both failure and stiction). LDV enables crucial measurements that are impossible with the network analyzer, such as higher mode detection (highly sensitive biosensor application) and resonance measurement for very small devices (fast prototyping). Accordingly, LDV was used to characterize the frequency tuning range and resonance frequency at different modes of the MEMS filters built for this study. This wide range frequency tuning mechanism is based simply on Joule heating from the embedded heaters and relatively high thermal stress with respect to the temperature of a fixed-fixed beam. However, we demonstrate that another limitation of this method is the resulting high thermal stress, which can burn the devices. Further improvement was achieved and shown for the first time in this study, such that the tuning capability was increased by 32% through an increase in the applied DC bias voltage (25 V to 35 V) between the two adjacent beams. This important finding eliminates the need for the extra Joule heating at the wider frequency tuning range. Another possible failure is through stiction and requirement of structure optimization: We propose a simple and easy technique of low frequency square wave signal application that can successfully separate the beams and eliminates the need for the more sophisticated and complicated methods given in the literature. The above findings necessitate a design methodology, and so we also provide an application-based design.

A protocol for a fixed-fixed beam design using a laser Doppler vibrometer (LDV), including the measurement of frequency tuning, modification of tuning capability, and avoidance of device failure and stiction, is presented. The superiority of the LDV method over the network analyzer is demonstrated due to its higher mode capability.

Here, we demonstrate the advantages of the laser Doppler vibrometer (LDV) over conventional techniques (the network analyzer), as well as the techniques ...

Engineering

Fabrication Procedures and Birefringence Measurements for Designing Magnetically Responsive Lanthanide Ion Chelating Phospholipid Assemblies

Bicelles are tunable disk-like polymolecular assemblies formed from a large variety of lipid mixtures. Applications range from membrane protein structural studies by nuclear magnetic resonance (NMR) to nanotechnological developments including the formation of optically active and magnetically switchable gels. Such technologies require high control of the assembly size, magnetic response and thermal resistance. Mixtures of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and its lanthanide ion (Ln3+) chelating phospholipid conjugate, 1,2-dimyristoyl-sn-glycero-3-phospho-ethanolamine-diethylene triaminepentaacetate (DMPE-DTPA), assemble into highly magnetically responsive assemblies such as DMPC/DMPE-DTPA/Ln3+ (molar ratio 4:1:1) bicelles. Introduction of cholesterol (Chol-OH) and steroid derivatives in the bilayer results in another set of assemblies offering unique physico-chemical properties. For a given lipid composition, the magnetic alignability is proportional to the bicelle size. The complexation of Ln3+ results in unprecedented magnetic responses in terms of both magnitude and alignment direction. The thermo-reversible collapse of the disk-like structures into vesicles upon heating allows tailoring of the assemblies&#39; dimensions by extrusion through membrane filters with defined pore sizes. The magnetically alignable bicelles are regenerated by cooling to 5 &#176;C, resulting in assembly dimensions defined by the vesicle precursors. Herein, this fabrication procedure is explained and the magnetic alignability of the assemblies is quantified by birefringence measurements under a 5.5 T magnetic field. The birefringence signal, originating from the phospholipid bilayer, further enables monitoring of polymolecular changes occurring in the bilayer. This simple technique is complementary to NMR experiments that are commonly employed to characterize bicelles.

Fabrication procedures for highly magnetically responsive lanthanide ion chelating polymolecular assemblies are presented. The magnetic response is dictated by the assembly size, which is tailored by extrusion through nanopore membranes. The assemblies&#39; magnetic alignability and temperature-induced structural changes are monitored by birefringence measurements, a complimentary technique to nuclear magnetic resonance and small angle neutron scattering.

Bicelles are tunable disk-like polymolecular assemblies formed from a large variety of lipid mixtures. Applications range from membrane protein structural ...

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.

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 ...

Fabrication and Validation of an Organ-on-chip System with Integrated Electrodes to Directly Quantify Transendothelial Electrical Resistance

Organs-on-chips, in vitro models involving the culture of (human) tissues inside microfluidic devices, are rapidly emerging and promise to provide useful research tools for studying human health and disease. To characterize the barrier function of cell layers cultured inside organ-on-chip devices, often transendothelial or transepithelial electrical resistance (TEER) is measured. To this end, electrodes are usually integrated into the chip by micromachining methods to provide more stable measurements than is achieved with manual insertion of electrodes into the inlets of the chip. However, these electrodes frequently hamper visual inspection of the studied cell layer or require expensive cleanroom processes for fabrication. To overcome these limitations, the device described here contains four easily integrated electrodes that are placed and fixed outside of the culture area, making visual inspection possible. Using these four electrodes the resistance of six measurement paths can be quantified, from which the TEER can be directly isolated, independent of the resistance of culture medium-filled microchannels. The blood-brain barrier was replicated in this device and its TEER was monitored to show the device applicability. This chip, the integrated electrodes and the TEER determination method are generally applicable in organs-on-chips, both to mimic other organs or to be incorporated into existing organ-on-chip systems.

This publication describes the fabrication of an organ-on-chip device with integrated electrodes for direct quantification of transendothelial electrical resistance (TEER). For validation, the blood-brain barrier was mimicked inside this microfluidic device and its barrier function was monitored. The presented methods for electrode integration and direct TEER quantification are generally applicable.

Organs-on-chips, in vitro models involving the culture of (human) tissues inside microfluidic devices, are rapidly emerging and promise to provide useful ...

Electrical Safety Precautions and Basic Equipment

Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.
Electric machines and power electronics experiments involve electrical currents, voltages, power, and energy quantities that should be handled with extreme diligence and care. These may include three-phase AC voltage (208 V, 230 V, or 480 V), up to 250 V DC voltages, and currents that can reach 10 A. Electrocution occurs when an electrical path is established through the body with very low currents that can damage vital organs, such as a person&#8217;s heart, and may cause immediate death. All experiments must be performed in the presence of personnel trained to handle electricity at these voltage and current levels. In case of emergency, evacuate the lab through any of the exits and dial 911.

Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.
Electric machines and power electronics experiments ...

JoVE Science Education

DC/DC Boost Converter

Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.
Boost converters provide a versatile solution to stepping up DC voltages in many applications where a DC voltage needs to be increased without the need to convert it to AC, using a transformer, and then rectifying the transformer output. Boost converters are step-up converters that use an inductor as an energy storage device that supports the output with additional energy in addition to the DC input source. This causes the output voltage to boost.
The objective of this experiment is to study different characteristics of a boost converter. The step-up capability of the converter will be observed under continuous conduction mode (CCM) where the inductor current is non-zero. Open-loop operation with a manually-set duty ratio will be used. An approximation of the input-output relationship will be observed.

DC Boost Converters; Testing with Variable Input and Duty Ratio

Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.
Boost converters provide a versatile solution to stepping ...

Single Phase Rectifiers

Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.
A DC power supply is generally considered to be a device that supplies DC, or unidirectional, voltage and current. Batteries are one such power supply, however, they are limited in terms of lifetime and expense. An alternative method to providing unidirectional power is to transform AC line power to DC power using a rectifier.
A rectifier is a device that passes current in one direction, and blocks it in the other direction, enabling the transformation of AC to DC. Rectifiers are important in electronic circuits as they only allow current in a certain direction after a certain threshold forward voltage across them is overcome. A rectifier can be a diode, a silicon controller rectifier, or other types of silicon P-N junctions. Diodes have two terminals, the anode and the cathode, where current flows from anode to cathode. Rectifier circuits use one or more diodes that change AC voltages and currents, which are bipolar, to unipolar voltages and currents that can be easily filtered to achieve DC voltages and currents.

Single Phase Rectifiers; Full Wave and Half Wave Rectifier Tests

Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.
A DC power supply is generally considered to be a device ...

Thyristor Rectifier

Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.
Similar to diodes, thyristors, also called silicon controlled rectifiers (SCRs), pass current in one direction from the anode to cathode, and block current flow in the other direction. However, current passage can be controlled through a &#34;gate&#34; terminal, which requires a small current pulse to turn on the thyristor so it can start conducting.
Thyristors are four-layer devices, composed of alternating layers of n-type and p-type material, thereby forming PNPN structures with three junctions. The thyristor has three terminals; with the anode connected to the p-type material of the PNPN structure, the cathode connected to the n-type layer, and the gate connected to the p-type layer nearest the cathode.
The objective of this experiment is to study a controlled thyristor-based half-wave rectifier at different conditions, and understand how different timings of the gate pulse affect the DC output voltage.