A low noise stable radiometer front-end for passive microwave tissue thermometry

ABSTRACT

A low noise, high gain, stable radiometer front-end is presented for non-invasive tissue thermometry using custom designed narrow band low noise amplifiers (LNAs) and band pass filter (BPF) with 1.3 GHz centre frequency and − 20 dB pass band of 332 MHz. The fabricated LNAs have >15 dB gain, unconditional gain stability and noise figure (NF) < 1.45 dB in the pass band. The maximum insertion loss of the BPF is <1 dB over 1.2–1.4 GHz with 50 dB suppression in the surrounding communication bands. The cascaded radiometer front-end has measured gain of 45–50 dB, NF < 1.75 dB in the pass band and > 30 dB suppression in the adjacent personal communication bands. The Allan deviation of the total power radiometer indicates long term system stability and presence of Gaussian thermal noise for integration time, $\tau <12.8\mathrm{s}$. Radiometer measurements of a matched load at room temperature for $\tau =3\mathrm{s}$ indicate acceptably low influence of external electromagnetic interference (EMI) and system noise equivalent temperature of 145 K. The brightness temperature measured by the total power radiometer using a resonant slot antenna demonstrates the ability to detect a 0.3°C change in the test load temperature with better than 0.1°C accuracy.

KEYWORDS:

• Allan deviation
• band pass filter
• LNA
• microwave
• radiometer
• tissue thermometry

Acknowledgements

This research is funded by the Science and Engineering Research Board, Government of India, grant number SB/S3/EECE/015/2015.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by Science and Engineering Research Board, Government of India [grant number SB/S3/EECE/015/2015].

Notes on contributors

Vidyalakshmi M. Ravi

Vidyalakshmi M. Ravi received her Bachelor’s degree in Electronics and Communications Engineering from Anna University, India (2005–2009), and Master of Science degree in Electronics and Communication Engineering from National Institute of Technology Tiruchirappalli, India (2009–2011). She is currently a doctoral student in the Department of Engineering Design, Indian Institute of Technology (IIT) Madras, India. Her research interests are in antennas, microwave circuits, medical microwave radiometers, EM compliance testing of devices, telecommunications.

Kavitha Arunachalam

Kavitha Arunachalam received her Bachelor’s degree in Electronics and Communications Engineering from College of Engineering Guindy, Anna University, India (1994–1998), and Doctoral degree in Electrical Engineering from Michigan State University, East Lansing, USA (2002–2007). In 2007, she joined the Department of radiation oncology, Duke University Medical Center, USA as a post doctoral research associate, where she contributed towards electromagnetic (EM) medical device design and development, and preclinical/clinical testing of thermal therapy applicators. She is with the Department of Engineering Design, IIT Madras, India since June 2010. Her research interests are antennas, medical microwave radiometry, bio-electromagnetism, hyperthermia physics, EM sensors for material characterization and testing.