Compact Solar Cell Ultra-Wideband Dipole Antenna

Transcription

1 Compact Solar Cell Ultra-Wideband Dipole Antenna Mina Danesh*, John R. Long High-Frequency Electronics Research Lab July 16, 2010 Delft University of Technology Challenge the future

2 Outline Motivation UWB transceiver specifications Dimes solar cell technology UWB antenna topology Solar antenna fabrication Solar cell DC characteristics Solar and copper-only antennas RF performances: RF input characteristics Antenna radiation patterns Antenna gain & efficiency Conclusions Compact Solar Cell Ultra-Wideband Dipole Antenna Mina Danesh 2 17

3 Motivation Solar energy harvesting for autonomous wireless transceivers Applications pp (outdoor & indoor environments) Wireless sensor networks Wireless body-area networks Space applications Active RFID Asset & people tracking Positioning System-in-Package Sensor* Radio transceiver Solar antenna Power management Energy storage storage* Higher integration: combined DC and RF energy source Size Si reduction d ti Overall cost reduction Smart System Integration Compact Solar Cell Ultra-Wideband Dipole Antenna Mina Danesh 3 17

4 UWB transceiver specifications UWB antenna requirements Transceiver specifications: Frequency band: GHz Low-power consumption: < 10 mw (peak power) Differential circuits directly integrated to antenna Compact package Outdoor applications For impulse-radio or FM UWB modulations Low duty-cycling (< 10%), average power in µw or nw Antenna requirements: Frequency bandwidth: GHz Efficiency > 50% Gain: ~ 0 dbi Radiation pattern: omnidirectional Compact Solar Cell Ultra-Wideband Dipole Antenna Mina Danesh 4 17

5 Dimes solar cell technology Thin-film amorphous silicon cells Amorphous hydrogenated silicon p-i-n junction Asahi glass with TCO (SnO 2 ) 10% efficiency attained Front view 2 cm 0.7 mm 1 µm 0.39 µm 300 µm <p> asi:h <i> asi:h <n> asi:h Ag/Al back contact Glass SnO Ag/Al back contact Ag/Al front contact + Cross-section 9 cm Back view 4 x 4 mm 2 Back contacts - - Front contacts Compact Solar Cell Ultra-Wideband Dipole Antenna Mina Danesh 5 17

6 UWB dipole antenna topology Broadband planar fat dipole antenna 1.5 mm FR-4 substrate 2cm 2cm~ λ /4 at 4 GHz (Integrated circuit) 3 mm 2 mm gap z θ φ x y Differential feed HFSS simulation model Compact Solar Cell Ultra-Wideband Dipole Antenna Mina Danesh 6 17

7 Solar dipole antenna fabrication Solar cell Rs Cb RF Glass SnO 2 <p> asi:h <i> asi:h <n> asi:h RF / DC- RF gnd Ag/Al back contact DC- L Cc FR-4 Cc Ag/Al front contact Silver epoxy DC+ DC+ L 2 cm Front view Back view 2 cm 2.7 cm 2 Back contact (DC- & RF) Front contact (DC+) V DC- RF decoupling V DC+ z θ y 3 mm overlap 2 cm Solar cell 1 Solar cell 2 φ x 4.8 cm Differential (2-port) feed DC+ DC- & RF 1. DC connections for RF decoupling on substrate backplane 2. Solar cells in series or parallel DC connection Compact Solar Cell Ultra-Wideband Dipole Antenna Mina Danesh 7 17

8 Solant dipole antenna (enhanced layout) mm FR-4 substrate 2. Symmetric layout Back view Front view RF front-end IC Compact Solar Cell Ultra-Wideband Dipole Antenna Mina Danesh 8 17

9 Isc = 35 ma 35 Current (ma) or Pow wer (mw) Solar cell DC characteristics 2 x 2 cm 2 solar cells W/m 2 light source Imp ~ 30 ma Pmp2 = 17.4 mw Pmp1 = 16.8 mw Current1 Power1 Current2 Power2 Back view Front contact (DC+) 2.7 cm 2 Back contact (DC- & RF) Current density = 13 ma / cm 2 Solar cell efficiency = 6.3% Real environment: variable current source 5 Fixed voltage supply needed use DC/DC converter or regulator Voltage (V) Vmp = 0.57 V Voc = 0.85 V Compact Solar Cell Ultra-Wideband Dipole Antenna Mina Danesh 9 17

10 Solar dipole DC power management unit Outdoors in direct sunlight 5pm Solar cells in parallel DC connection to maximize current 1. Supercapacitor charges with maximum available solar cells current 2. Once supercapacitor is fully charged, solar cells deliver minimum current to sustain DC-DC converter Solar Energy Harvesting Power Management Solution for Outdoor Applications Solar cell 1 Solar cell V to 0.8 V C 1 Vstart = 0.5 V, < 10 ma Boost DC-DC converter MPPT circuit 2 V to 4.5 V C 2 Supercapacitor Buck DC-DC converter 1.8V C 3 LDO_1 1.2V LDO_2 0.7 V EN Compact Solar Cell Ultra-Wideband Dipole Antenna Mina Danesh 10 17

11 Solar antenna RF performances RF input reflection coefficient tion coeffic cient (db) nput reflec ifferential i D Initial design of solant without DC connections 2. Copper-only version of solant Copper antenna was not optimized for input matching Input mismatch: 1. DC interconnects (~2-6 GHz) 2. Coax cable + SMA connector Solant (sim) -25 Solant (meas) Copper(meas) Solant (new) Frequency (GHz) Coax cable length de-embeddingembedding Compact Solar Cell Ultra-Wideband Dipole Antenna Mina Danesh 11 17

12 Solar antenna RF performances Input impedances Solant (sim) Solant (meas) Copper(meas) Solant (new) Solant (sim) Solant (meas) Copper(meas) Solant (new) Differential Re[Zin] (Ohms s) Differential Im m[zin] (Ohms s) Frequency (GHz) Frequency (GHz) Backside DC connections affect signal reflections at the input port Compact Solar Cell Ultra-Wideband Dipole Antenna Mina Danesh 12 17

13 Solar antenna RF performances Total Field Radiation Patterns 4 GHz 7.5 GHz 10 GHz Copper-only dipole Solar dipole (prototype 1) Solar dipole (prototype 2) Compact Solar Cell Ultra-Wideband Dipole Antenna Mina Danesh 13 17

14 Solar antenna RF performances Surface currents comparisons 4 GHz 7.5 GHz 10 GHz Copper-only dipole Solar dipole (prototype 1) Solar dipole (prototype 2) Compact Solar Cell Ultra-Wideband Dipole Antenna Mina Danesh 14 17

15 Solar antenna RF performances Antenna Maximum Gain & Efficiency B) Ma aximum ante enna gain (d Copper dipole -4 Solant dipole+dc Solant dipole Frequency (GHz) Ante nna radiatio on efficiency (%) Copper dipole 10 Solant dipole+dc Solant dipole Frequency (GHz) Compact Solar Cell Ultra-Wideband Dipole Antenna Mina Danesh 15 17

16 Conclusions Planar Dipole Solar Antenna Amorphous silicon solar cell as a dipole antenna DC source and RF radiator/receiver for low-power UWB transceiver applications Solar antenna (solant) directly integrated with other circuitry (power management and RF front-end) Solant behavior comparable to copper-only antenna Radiation patterns change and losses increase: 1. Solar cell stack-up (adjacent contacts) 2. Material characteristics 3. DC interconnections Further system integration design under way Overall RP measurements planned Compact Solar Cell Ultra-Wideband Dipole Antenna Mina Danesh 16 17

17 Acknowledgments: 1. Martijn Tijssen for fabricating the solar cells at Dimes 2. Loek van Schie for fabricating the prototype boards For more information on the project: Website: Small-area Solar Antenna for Low- Power UWB Transceivers (EuCap 2010) Compact Solar Cell Ultra-Wideband Dipole Antenna Mina Danesh 17 17