This paper presents measurements techniques of wearable antennas and RF medical systems in vicinity of human body. The antennas radiation characteristics on human body have been measured by using a phantom. The phantom electrical characteristics represent the human body electrical characteristics. The phantom has a cylindrical shape with a 40 cm diameter and a length of 1.5 m. The phantom electrical characteristics are similar to the human body electrical characteristics. The antenna under test was placed on the phantom during the measurements of the antennas radiation characteristics. The phantom was employed to compare the electrical performance of several new wearable antennas. The phantom was also employed to measure the electrical performance of several antenna belts in vicinity of human body. The results of antenna with thinner belt are better than the results of the same antenna array with thicker belt.
Wearable antennas and wearable systems were presented in books and journals; see [
The phantom is fiberglass cylinder with 1.5 m height and 0.4 m diameter as shown in
The electrical characteristics of several wearable antennas were measured by using the phantom. The position of the transmitting antennas along the z axis and x axis was varied as listed in tables, (Z = 0, Z = −15 cm and Z = 15 cm). The angular angle of the transmitting antenna was varied from 0˚ to 270˚. Signal reception levels and immunity to noise was measured for several types of wearable antenna. The antennas electrical performance was
compared and the best antenna was chosen according to the system electrical requirements.
Test procedure and process is described below.
1) Test procedure
The test checks two parameters of the antennas array:
Signal reception levels.
Immunity to noise.
2) Measured antennas
The test checks the following antenna arrays:
Four sensor antenna array in a belt, antenna in orientations of +45˚, +45˚, +45˚, −45˚.
Sensor belt with four loop antennas in orientations of +45˚, +45˚, +45˚, −45˚.
Sensor belt with four antenna in orientations of +45˚, −45˚, +45˚, −45˚.
Thin belt with four sensor Array in orientations of +45˚, −45˚, +45˚, −45˚.
Four loop antenna array in a sleeve.
3) Test process
Place the antenna array on the phantom as shown in the figure and connect to the recorder.
Signal reception levels.
Place the transmitter in the phantom in the following coordinates, 5 minutes per each location.
Z values: from −15 cm to +15 cm in 15 cm increments, 0 being the level of the antennas center.
X values: from −5 cm to −20 cm in 15 cm increments, 0 being the container’s wall where the antennas are attached.
q values: from 0˚ to 270˚ in 90˚ increments, 0˚ being perpendicular to the middle of the antennas set.
4) Immunity to noise
Place the transmitter outside the phantom in the following coordinates, 5 minutes per each location:
Z values: from −40 cm to +40 cm in 10 cm increments, 0 being the level of the antennas center.
X values: 100 cm from container’s wall q values: from 0˚ to 270˚ in 90˚ increments, 0˚ being perpendicular to the middle of the antennas set.
Measurements of five antenna array configuration was measured. For all the configurations the lower measured signal level was when the transmitting antenna is located at z = 15 cm and x = −5 cm. For all the configurations the higher measured signal level was when the transmitting antenna is located at z = 0 cm and x = −5 cm.
The measured antenna consists of four loop antennas with a tuning capacitor as shown in
Antenna1 (X cm, Z cm) | Angle q | |||
---|---|---|---|---|
Z = 0 cm | 0˚ | 90˚ | 180˚ | 270˚ |
Signal level (dB) X = −5, Z = 0 | −60 | −63 | −81 | −65 |
Signal level (dB) X = −20, Z = 0 | −78 | −70 | −65 | −74 |
Z = 15 cm | ||||
Signal level (dB) X = −5, Z = 15 | −81 | −89 | −83 | −82 |
Signal level (dB) X = −20, Z = 15 | −86 | −89 | −81 | −85 |
Z = −15 cm | ||||
Signal level (dB) X = −5, Z = −15 | −70 | −76 | −81 | −68 |
Signal level (dB) X = −20, Z = −15 | −79 | −64 | −74 | −81 |
Noise test | Angle q | |||
Z = 0 cm | 0˚ | 90˚ | 180˚ | 270˚ |
Signal level (dB) | −72 | −74 | −74 | −74 |
Noise level (dB) | −95 | −95 | −95 | −95 |
Z = 40 cm | ||||
Signal level (dB) | −72 | −74 | −74 | −74 |
Noise level (dB) | −88 | −88 | −88 | −88 |
Z = −40 cm | ||||
Signal level (dB) | −72 | −74 | −74 | −74 |
Noise level (dB) | −94 | −93 | −94 | −95 |
The measured antenna consists of four loop antennas without a tuning capacitor as shown in
The measured antenna consists of four tuned loop antennas with a tuning capacitor as shown in
The measured antenna consists of four loop antennas with a tuning capacitor as shown in
The measured antenna consists of four loop antennas without a tuning capacitor inserted in a sleeve, as shown in
Measurements results of antenna number 5 are listed in
Antenna 1 (X cm, Z cm) | Angle q | |||
---|---|---|---|---|
Z = 0 cm | 0º | 90º | 180º | 270º |
Signal level (dB) X = −5, Z = 0 | −63 | −70 | −82 | −72 |
Signal level (dB) X = −20, Z = 0 | −84 | −66 | −66 | −79 |
Z = 15 cm | ||||
Signal level (dB) X = −5, Z = 15 | −82 | −93 | −90 | −84 |
Signal level (dB) X = −20, Z = 15 | −88 | −83 | −79 | −90 |
Z = −15 cm | ||||
Signal level (dB) X = −5, Z = −15 | −74 | −82 | −85 | −92 |
Signal level (dB) X = −20, Z = −15 | −86 | −70 | −77 | −81 |
Noise test | Angle q | |||
Z = 0 cm | 0º | 90º | 180º | 270º |
Signal level (dB) | −67 | −69 | −72 | −68 |
Noise level (dB) | −85 | −85 | −86 | −85 |
Z = 40 cm | ||||
Signal level (dB) | −66 | −69 | −72 | −68 |
Noise level (dB) | −80 | −83 | −86 | −85 |
Z = −40 cm | ||||
Signal level (dB) | −68 | −69 | −72 | −69 |
Noise level (dB) | −84 | −82 | −83 | −83 |
Antenna 1 (X cm, Z cm) | Angle q | |||
---|---|---|---|---|
Z = 0 cm | 0˚ | 90˚ | 180˚ | 270˚ |
Signal level (dB) X = −5, Z = 0 | −63 | −63 | −82 | −69 |
Signal level (dB) X = −20, Z = 0 | −83 | −70 | −68 | −76 |
Z = 15 cm | ||||
Signal level (dB) X = −5, Z = 15 | −85 | −86 | −85 | −86 |
Signal level (dB) X = −20, Z = 15 | −89 | −88 | −86 | −85 |
Z = −15 cm | ||||
Signal level (dB) X = −5, Z = −15 | −72 | −79 | −83 | −74 |
Signal level (dB) X = −20, Z = −15 | −85 | −69 | −77 | −82 |
Noise test | Angle q | |||
Z = 0 cm | 0˚ | 90˚ | 180˚ | 270˚ |
Signal level (dB) | −68 | −70 | −76 | −70 |
Noise level (dB) | −91 | −91 | −92 | −92 |
Z = 40 cm | ||||
Signal level (dB) | −68 | −70 | −76 | −70 |
Noise level (dB) | −90 | −88 | −90 | −88 |
Z = −40 cm | ||||
Signal level (dB) | −68 | −70 | −76 | −70 |
Noise level (dB) | −89 | −87 | −90 | −87 |
Antenna 1 (X cm, Z cm) | Angle q | |||
---|---|---|---|---|
Z = 0 cm | 0˚ | 90˚ | 180˚ | 270˚ |
Signal level (dB) X = −5, Z = 0 | −61 | −62 | −81 | −63 |
Signal level (dB) X = −20, Z = 0 | −79 | −69 | −67 | −73 |
Z = 15 cm | ||||
Signal level (dB) X = −5, Z = 15 | −86 | −88 | −88 | −83 |
Signal level (dB) X = −20, Z = 15 | −90 | −84 | −82 | −86 |
Z = −15 cm | ||||
Signal level (dB) X = −5, Z = −15 | −70 | −81 | −82 | −67 |
Signal level (dB) X = −20, Z = −15 | −80 | −67 | −74 | −81 |
Noise test | Angle q | |||
Z = 0 cm | 0˚ | 90˚ | 180˚ | 270˚ |
Signal level (dB) | −70 | −70 | −76 | −70 |
Noise level (dB) | −95 | −95 | −95 | −95 |
Z = 40 cm | ||||
Signal level (dB) | −70 | −70 | −76 | −70 |
Noise level (dB) | −92 | −92 | −91 | −92 |
Z = −40 cm | ||||
Signal level (dB) | −70 | −70 | −76 | −70 |
Noise level (dB) | −92 | −92 | −91 | −92 |
Antenna 1 (X cm, Z cm) | Angle q | |||
---|---|---|---|---|
Z = 0 cm | 0˚ | 90˚ | 180˚ | 270˚ |
Signal level (dB) X = −5, Z = 0 | −67 | −52 | −58 | −60 |
Signal level (dB) X = −20, Z = 0 | −68 | −70 | −77 | −78 |
Z = 15 cm | ||||
Signal level (dB) X = −5, Z = 15 | −90 | −86 | −92 | −90 |
Signal level (dB) X = −20, Z = 15 | −84 | −86 | −90 | −86 |
Z = −15 cm | ||||
Signal level (dB) X = −5, Z = −15 | −85 | −90 | −85 | −92 |
Signal level (dB) X = −20, Z = −15 | −90 | −85 | −75 | −78 |
Noise test | Angle q | |||
Z = 0 cm | 0˚ | 90˚ | 180˚ | 270˚ |
Signal level (dB) | −70 | 70 | −70 | −70 |
Noise level (dB) | −90 | −90 | −90 | −90 |
Z = 40 cm | ||||
Signal level (dB) | −72 | −72 | −72 | −72 |
Noise level (dB) | −90 | −90 | −90 | −90 |
Z = −40 cm | ||||
Signal level (dB) | −73 | −73 | −73 | −73 |
Noise level (dB) | −90 | −90 | −90 | −90 |
Best results are achieved with the first antenna with tuning capacitor antennas in orientations of +45˚, +45˚, +45˚, −45˚. The results of antenna number 4 with thinner belt are better than the results of the same antenna array with thicker belt. For all the configurations the higher measured signal level was when the transmitting antenna is located at z = 0 cm and x = −5 cm. For all the configurations the lower measured signal level was when the transmitting antenna is located at z = 15 cm and x = −5 cm. The effect of the antenna location on the human body should be considered in the antenna design process.
Albert Sabban, (2016) Wearable Antenna Measurements in Vicinity of Human Body. Wireless Engineering and Technology,07,97-104. doi: 10.4236/wet.2016.73010