A 24-GHz Front-End Integrated on a Multilayer Cellulose-Based Substrate for Doppler Radar Sensors †
"> Figure 1
<p>Block diagram of the radar sensor. The circuit uses a branch-line power divider to couple the voltage-controlled oscillator (VCO) to both the antenna and the mixer. If the target moves, a Doppler frequency shift <math display="inline"> <semantics> <msub> <mi>f</mi> <mi>δ</mi> </msub> </semantics> </math> is produced in the reflected wave and is detected by the mixer circuit. The resistance <math display="inline"> <semantics> <msub> <mi>R</mi> <mrow> <mi>I</mi> <mi>F</mi> </mrow> </msub> </semantics> </math> and the capacitor <math display="inline"> <semantics> <msub> <mi>C</mi> <mrow> <mi>I</mi> <mi>F</mi> </mrow> </msub> </semantics> </math> constitute a low-pass filter and terminate the mixer output port. LO: local oscillator; RF: radio frequency.</p> "> Figure 2
<p>Fabrication process. (<b>a</b>) Photo-resist deposited on the metal layer and patterned using a mask, UV and a developer. (<b>b</b>) Wet etching of the metal surface. (<b>c</b>) Adhesive laminate after the etching of the metal layer: the adhesive material underneath is exposed. (<b>d</b>) Application of the sacrificial layer and removal of the protection layer. (<b>e</b>) Circuit transferred to the host substrate. (<b>f</b>) Sacrificial layer removal; the last step also removes the adhesive material. M: metal, A: adhesive, P: protection, R: photo-resist, S: sacrificial layer, SUB: host substrate.</p> "> Figure 3
<p>Multilayer substrate. (<b>a</b>) Cross-section of the multilayer substrate structure adopted for the fabrication of the 24-GHz radar front-end. (<b>b</b>) Materials. Bulk copper with conductivity <math display="inline"> <semantics> <mrow> <msub> <mi>σ</mi> <mi>m</mi> </msub> <mo>=</mo> <mn>5</mn> <mo>.</mo> <mn>8</mn> <mo>×</mo> <msup> <mn>10</mn> <mn>7</mn> </msup> <mspace width="0.366667em"/> <mrow> <mi mathvariant="normal">S</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics> </math> is adopted to implement all the metal layers. The substrate parameters as follows: <math display="inline"> <semantics> <mrow> <mi>h</mi> <mo>=</mo> <mn>230</mn> <mspace width="0.366667em"/> <mrow> <mi mathvariant="sans-serif">μ</mi> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics> </math>, <math display="inline"> <semantics> <mrow> <msub> <mi>t</mi> <mi>a</mi> </msub> <mo>=</mo> <mn>30</mn> <mspace width="0.366667em"/> <mrow> <mi mathvariant="sans-serif">μ</mi> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics> </math>, <math display="inline"> <semantics> <mrow> <msub> <mi>t</mi> <mi>m</mi> </msub> <mo>=</mo> <mn>35</mn> <mspace width="0.366667em"/> <mrow> <mi mathvariant="sans-serif">μ</mi> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics> </math>. The photo-paper and the acrylic adhesive relative permittivity are: <math display="inline"> <semantics> <mrow> <msub> <mi>ε</mi> <mi>r</mi> </msub> <mo>=</mo> <mn>2</mn> <mo>.</mo> <mn>9</mn> </mrow> </semantics> </math> and <math display="inline"> <semantics> <mrow> <msub> <mi>ε</mi> <mrow> <mi>r</mi> <mo>,</mo> <mi>a</mi> </mrow> </msub> <mo>=</mo> <mn>1</mn> <mo>.</mo> <mn>3</mn> </mrow> </semantics> </math> respectively. The photo-paper loss tangent is: <math display="inline"> <semantics> <mrow> <mi>tan</mi> <mi>δ</mi> <mo>=</mo> <mn>0</mn> <mo>.</mo> <mn>08</mn> </mrow> </semantics> </math>.</p> "> Figure 4
<p>Fabricated 24-GHz front-end on a multi-layer cellulose-based substrate. (<b>a</b>) Antenna side. (<b>b</b>) Active circuit side. (<b>c</b>) Demonstrator including external VCO, intermediate frequency (IF) amplification and triggering stages. The used substrate area is <math display="inline"> <semantics> <mrow> <mn>20</mn> <mo>×</mo> <mn>27</mn> <mspace width="0.266667em"/> <msup> <mrow> <mi>mm</mi> </mrow> <mn>2</mn> </msup> </mrow> </semantics> </math>. The realized cellulose circuit has the size of a postage stamp.</p> "> Figure 5
<p>People detection results. (<b>a</b>) Experimental setup. (<b>b</b>) Analog output corresponding to a person at an 8-m distance with a relative speed of 1.7 m/s. (<b>c</b>) Analog and digital outputs associated to a person at a 3-m distance that slowly moves. In the last case the relative speed is of only 0.4 m/s. These signals are measured after the amplification and, possibly, after the triggering stages of the demonstrator (see <a href="#sensors-17-02090-f004" class="html-fig">Figure 4</a>).</p> "> Figure 6
<p>People detection results. (<b>a</b>) Time domain output signal corresponding to a person at a 6-m distance with a relative speed of about 1.5 m/s. (<b>b</b>) Frequency domain output signal obtained performing the FFT of panel (<b>a</b>). The main peak corresponds to a Doppler frequency of <math display="inline"> <semantics> <mrow> <mn>244</mn> <mspace width="0.266667em"/> <mrow> <mi>Hz</mi> </mrow> </mrow> </semantics> </math>.</p> "> Figure 7
<p>Via-through connection in a multilayer cellulose circuit: structure (<b>a</b>) and simulated scattering parameters (<b>b</b>). The main geometrical parameters are the hole diameter <math display="inline"> <semantics> <mrow> <msub> <mi>D</mi> <mi>h</mi> </msub> <mo>=</mo> <mn>1</mn> <mo>.</mo> <mn>05</mn> <mspace width="0.266667em"/> <mrow> <mi>mm</mi> </mrow> </mrow> </semantics> </math>, and via diameter of <math display="inline"> <semantics> <mrow> <mn>0</mn> <mo>.</mo> <mn>2</mn> <mspace width="0.266667em"/> <mrow> <mi>mm</mi> </mrow> </mrow> </semantics> </math>.</p> "> Figure 8
<p>Branch-line coupler and patch antenna array. Branch-line: manufactured prototype (<b>a</b>) and experimental results (<b>b</b>). The coupler diameter is about <math display="inline"> <semantics> <mrow> <mn>4</mn> <mo>.</mo> <mn>4</mn> <mspace width="0.266667em"/> <mrow> <mi>mm</mi> </mrow> </mrow> </semantics> </math>. After Reference [<a href="#B39-sensors-17-02090" class="html-bibr">39</a>]. Antenna array:manufactured prototype (<b>c</b>) and experimental results (<b>d</b>). The antenna dimensions are <math display="inline"> <semantics> <mrow> <mn>20</mn> <mo>×</mo> <mn>20</mn> <mspace width="0.266667em"/> <msup> <mrow> <mi>mm</mi> </mrow> <mn>2</mn> </msup> </mrow> </semantics> </math>. After Reference [<a href="#B40-sensors-17-02090" class="html-bibr">40</a>].</p> "> Figure 9
<p>Manufactured layout (<b>a</b>) and experimental results (<b>b</b>) of the Schottky diode mixer. No components are soldered to the printed circuit board (PCB) shown in (<b>a</b>). The active area of the structure is about <math display="inline"> <semantics> <mrow> <mn>4</mn> <mo>.</mo> <mn>6</mn> <mspace width="0.266667em"/> <mrow> <mi>mm</mi> </mrow> </mrow> </semantics> </math> in diameter. Measured and simulated conversion loss are compared in the plot; these results are obtained by sweeping the LO power between <math display="inline"> <semantics> <mrow> <mo>−</mo> <mn>10</mn> <mspace width="0.266667em"/> <mrow> <mi>dBm</mi> </mrow> </mrow> </semantics> </math> and <math display="inline"> <semantics> <mrow> <mn>5</mn> <mspace width="0.266667em"/> <mrow> <mi>dBm</mi> </mrow> </mrow> </semantics> </math> with <math display="inline"> <semantics> <mrow> <msub> <mi>f</mi> <mrow> <mi>R</mi> <mi>F</mi> </mrow> </msub> <mo>=</mo> <mn>24</mn> <mspace width="0.266667em"/> <mrow> <mi>GHz</mi> </mrow> </mrow> </semantics> </math>, <math display="inline"> <semantics> <mrow> <msub> <mi>f</mi> <mrow> <mi>L</mi> <mi>O</mi> </mrow> </msub> <mo>=</mo> <mn>23</mn> <mo>.</mo> <mn>95</mn> <mspace width="0.266667em"/> <mrow> <mi>GHz</mi> </mrow> </mrow> </semantics> </math>, <math display="inline"> <semantics> <mrow> <msub> <mi>f</mi> <mrow> <mi>I</mi> <mi>F</mi> </mrow> </msub> <mo>=</mo> <mn>50</mn> <mspace width="0.266667em"/> <mrow> <mi>MHz</mi> </mrow> </mrow> </semantics> </math>, and <math display="inline"> <semantics> <mrow> <msub> <mi>P</mi> <mrow> <mi>R</mi> <mi>F</mi> </mrow> </msub> <mo>=</mo> <mo>−</mo> <mn>30</mn> <mspace width="0.266667em"/> <mrow> <mi>d</mi> <mi>B</mi> <mi>m</mi> </mrow> </mrow> </semantics> </math>. After Reference [<a href="#B46-sensors-17-02090" class="html-bibr">46</a>].</p> ">
Abstract
:1. Introduction
2. Basic Theory and Front-End Sensitivity
3. Materials and Methods
3.1. Adhesive Copper-Laminate Process
3.2. Fabrication of The Multilayer Cellulose-Based Front-End
3.3. Building-Block Design and Characterization
4. Results
4.1. People Detection
5. Discussion
Acknowledgments
Author Contributions
Conflicts of Interest
Appendix A.
Appendix A.1. Via-Through Optimization
Appendix A.2. Branch-Line Coupler
Appendix A.3. Patch Array Antenna
Appendix A.4. Single-Balanced Diode Mixer
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(m) | (Hz) | v (m/s) | (V) | |
---|---|---|---|---|
Measurements | Model | |||
4 | 195 | 1.2 | 52.6 | 59.7 |
6 | 244 | 1.5 | 25.8 | 26.5 |
195 | 1.2 | 25.1 | ||
8 | 273 | 1.7 | 16.9 | 14.9 |
Ref. | Technology | (GHz) | Antenna Gain (dBi) | (dBm) | Range (m) | (mm/s) | Size (mm) |
---|---|---|---|---|---|---|---|
[10] | 0.25-μm CMOS | 2.4 | 8 | 10 | 0.5 | n.a. | n.a. |
[25] | RO3003 and FR4 | 24 | 7 | 15 | 2 | 0.5 | |
[27] | LTCC and FR4 | 24 | n.a. | n.a. | n.a. | 0.8 | |
[29] | LTCC | 24 | n.a. | 20 (*) | 70 | n.a. | |
[30] | LTCC | 24 | 8.6 | 15 (*) | 30 | n.a. | |
[44] | discrete comp. | 24 | 18 | 6 | 300 | n.a. | |
[32] | cellulose single-layer | 24 | 7 | 3 | n.a. | n.a. | |
this work | cellulose multilayer | 24 | 7.4 | 7 | 10 | 50 |
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Alimenti, F.; Palazzi, V.; Mariotti, C.; Virili, M.; Orecchini, G.; Bonafoni, S.; Roselli, L.; Mezzanotte, P. A 24-GHz Front-End Integrated on a Multilayer Cellulose-Based Substrate for Doppler Radar Sensors. Sensors 2017, 17, 2090. https://doi.org/10.3390/s17092090
Alimenti F, Palazzi V, Mariotti C, Virili M, Orecchini G, Bonafoni S, Roselli L, Mezzanotte P. A 24-GHz Front-End Integrated on a Multilayer Cellulose-Based Substrate for Doppler Radar Sensors. Sensors. 2017; 17(9):2090. https://doi.org/10.3390/s17092090
Chicago/Turabian StyleAlimenti, Federico, Valentina Palazzi, Chiara Mariotti, Marco Virili, Giulia Orecchini, Stefania Bonafoni, Luca Roselli, and Paolo Mezzanotte. 2017. "A 24-GHz Front-End Integrated on a Multilayer Cellulose-Based Substrate for Doppler Radar Sensors" Sensors 17, no. 9: 2090. https://doi.org/10.3390/s17092090