DESIGN OF MEDICAL RADIOMETER FRONT-END FOR IMPROVED PERFORMANCE.
DESIGN OF MEDICAL RADIOMETER FRONT-END FOR IMPROVED PERFORMANCE.
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DOI：
10.2528/pierb10101204
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
Stauffer PR
中科院分区：
文献类型：
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作者：
Klemetsen O;Birkelund Y;Jacobsen SK;Maccarini PF;Stauffer PR
我们研究了建立一种价格便宜、体积小、稳定、高灵敏度、由现成的微波元件组成的单频段Dicke辐射计的可能性。选择的频段是3.25-3.75 GHz，这为有损组织的辐射测量应用提供了空间分辨率(天线尺寸)和传感深度之间的合理折衷。该仪器的预期应用是乳腺癌检测的非侵入性温度监测和加热期间的温度监测。我们已经发现了足够小(<；5 mm×5 mm)且具有令人满意的总体灵敏度的现成微波组件。实现了两种不同的Dicke辐射计：一种是在前端使用Dicke开关来选择天线或噪声参考通道进行放大的传统设计。第二种设计在Dicke开关前面放置一对匹配的低噪声放大器，以降低系统噪声系数。在构建辐射计的原型印刷电路板前端布局之前，进行了数值模拟以验证设计思想。这两种设计在以3.5 GHz为中心的500 MHz带宽上提供了大约50分贝的总功率增益。尽管使用三级级联放大器配置来增强热信号，但没有观察到稳定性问题。原型在两个不同的水浴中进行了校准后的灵敏度测试。实验表明，与前面有Dicke开关的其他设计相比，在Dicke开关之前(靠近天线)实现低噪声放大器时，灵敏度更高(高36%)。在交替加热和辐射读数的多层体模中也测试了辐射计的性能。实验结果表明，首先采用Dicke开关的结构，在微波加热时必须将开关锁定在参考位置，以避免损坏有源元件(放大器和功率表)。对于前置低噪声放大器的配置，如果在微波加热天线存在的情况下使用，将会损坏辐射计的有源组件。然而，这种设计显著提高了测量温度的灵敏度，值得进一步研究，以确定保护放大器第一前端辐射计的方法。
We have investigated the possibility of building a singleband Dicke radiometer that is inexpensive, small-sized, stable, highly sensitive, and which consists of readily available microwave components. The selected frequency band is at 3.25–3.75 GHz which provides a reasonable compromise between spatial resolution (antenna size) and sensing depth for radiometry applications in lossy tissue. Foreseen applications of the instrument are non-invasive temperature monitoring for breast cancer detection and temperature monitoring during heating. We have found off-the-shelf microwave components that are sufficiently small (< 5 mm × 5 mm) and which offer satisfactory overall sensitivity. Two different Dicke radiometers have been realized: one is a conventional design with the Dicke switch at the front-end to select either the antenna or noise reference channels for amplification. The second design places a matched pair of low noise amplifiers in front of the Dicke switch to reduce system noise figure. Numerical simulations were performed to test the design concepts before building prototype PCB front-end layouts of the radiometer. Both designs provide an overall power gain of approximately 50 dB over a 500 MHz bandwidth centered at 3.5 GHz. No stability problems were observed despite using triple-cascaded amplifier configurations to boost the thermal signals. The prototypes were tested for sensitivity after calibration in two different water baths. Experiments showed superior sensitivity (36% higher) when implementing the low noise amplifier before the Dicke switch (close to the antenna) compared to the other design with the Dicke switch in front. Radiometer performance was also tested in a multilayered phantom during alternating heating and radiometric reading. Empirical tests showed that for the configuration with Dicke switch first, the switch had to be locked in the reference position during application of microwave heating to avoid damage to the active components (amplifiers and power meter). For the configuration with a low noise amplifier up front, damage would occur to the active components of the radiometer if used in presence of the microwave heating antenna. Nevertheless, this design showed significantly improved sensitivity of measured temperatures and merits further investigation to determine methods of protecting the radiometer for amplifier first front ends.