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Interview: Innovating Impedance Measurement

Tim400pixelZurich Instruments is a test and measurement company based in Zurich, Switzerland, which develops and produces lock-in amplifiers, phase-locked loops, impedance analyzers, arbitrary waveform generators and boxcar averagers. We talked to Dr Tim Ashworth, Applications Manager at Zurich Instruments, about the latest innovations in impedance analysis and the Mid-Frequency Impedance Analyzer and Precision LCR (MFIA) Meter launched last year.

 How do impedance analyzers work and what are the challenges?

Impedance measurements are generally carried out as a function of frequency. This is a well-known method of characterising electrical components and materials such as dielectrics, biological matter and ceramics. However, today’s impedance analyzers lack innovation, so many instruments have frustrating user-interfaces, and they suffer from a lower frequency limit which misses the interesting frequency ranges.

Furthermore, since impedance may change by many orders of magnitude as the frequency is swept, the instrument must capable of handling a wide impedance range to get the best data. Other challenges arise due to the connection between the instrument and the sample. This is typically done by using a dedicated cable or clamp, known as a fixture. This fixture can introduce parasitic capacitance and inductance which may reduce the accuracy of the measured impedance.

What innovations does the MFIA bring to answer these challenges?

Zurich Instruments has taken an innovative approach to impedance analysis when it developed the MFIA impedance analyzer. The hardware of the MFIA delivers unsurpassed accuracy for measurements over a large impedance range. It also directly measures the voltage across and current through the device under test, eliminating the need for a feedback loop required by auto-balanced bridge which is common in many instruments. Removing this feedback loop allows lower measurement frequencies; right down to Millihertz and below.

However, the true innovation is thanks to our powerful software. It offers many easy-to-use software tools, such as the parametric sweeper which allows the user to sweep many different parameters and measure and display impedance parameters in a dynamic graphical window. This allows seamless impedance data from 1 mHz to 5 MHz with unrestricted data-point density. The data is displayed in real time, and the resulting multi-trace graph can be adjusted as desired in a matter of seconds and exported in vector graphics, ready for publication.

How does the MFIA compare with other models on the market? 

The MFIA features a modern, industry-leading software interface with many easy-to-use tools which greatly speed up the process of getting impedance data from the workbench to the final publication.

It is very important that the data is reliable and accurate, so the MFIA includes unique data-verification called the confidence-indicator, which flags up data points which are based on unreliable fundamentals. This means the user gets data that’s not just reliable, but also accurate thanks to the unbeaten basic accuracy of 0.05% over a wide frequency range of 1 mHz to 500 kHz. Furthermore, our comprehensive accuracy chart allows users to quickly see the accuracy for a given parameter set. 

The impedance analyzer is based on a lock-in amplifer; what does this means for users?

The MFIA uniquely features the full functionality of our MFLI lock-in amplifier, all in the same box! Launched in 2015, the MFLI has thousands of happy users worldwide. The MFLI is a powerful lock-in amplifier which allows the user to measure small periodic signals in noisey background thanks to its dynamic range of 120 dB. It is also fast when taking measurements, with time constants down to 1 us. This is very useful when measuring capacitive transients.

How can the MFIA help users new to the field of impedance analysis?

The confidence-indicators mentioned earlier are a key feature when taking impedance data. They ensure trust in the measured data for both new and experienced users. In addition, we also include another innovative feature called the compensation-advisor. This guides the user through the process of compensating parasitics due to the fixtures that connect the sample to the instrument. This gives certainty to any user when using those all-important fixtures.

What are the market segments for the MFIA?

The MFIA addresses a wide range of applications where low to mid frequency impedance needs to be measured accurately, including applications requiring high impedance measurements. There has been a lot of interest from materials researchers in dielectrics (polymers and ceramic), users characterising electronic components (supercapacitors and high-Q capacitors) and bio-impedance.

How is the outlook for impedance measurement?

Zurich Instruments is a young dynamic company, always innovating and improving. Innovation leadership is our goal, so we integrate an ever-increasing amount of functionality into our class-leading hardware, making sure it remains easy to use. This means our customers benefit from efficient work flows and reduced setup complexity; helping them to save time on instrumentation, and focus on their ultimate goals.

Thanks to the MFIA, a breath of innovation has arrived to a key research area long neglected by instrument builders. Users can now take accurate data with confidence.

Thank you very much for the interview!

www.zhinst.com/



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