25-08-2017, 09:32 PM
UWB Radar in Medicine
[attachment=33974]
ABSTRACT
The wonders of science and technology in the medical field paved a way for the diagnosis of diseases. Diagnosis is possible only by continuous monitoring of human body.CT scan ,X ray etc are some of the ways. Eventhough they are helpful for complete diagnosis of human body ,these are having heavy electromagnetic radiations .Continuous use of this will lead to othert problems in human body .So UWB radar having less electromagnetic radiation could be used in medical field .My paper is a detailed study of UWB radar in medical field
Ultra-wideband radar holds great promise for a variety of medical applications. Ultra-wideband sensors can be used for detection of internal injuries, monitoring of respiratory and cardiac functions, and continuous non-contact imaging of the human body. Sensors are low-power, portable, and do not require physical contact with the patient. In the hospital, vital signs monitoring and imaging application could improve patient outcomes.
INTRODUCTION
Motion sensing and imaging ultra-wideband (UWB) radar systems have strong potential for use in the medical field. UWB radar is non-invasive, low power, and can be manufactured in a small, portable form factor. We have demonstrated the use of UWB radar in a variety of medical applications. A handheld UWB sensor has demonstrated the feasibility of detecting the presence of traumatic internal injuries including intracranial hematoma and pneumothorax. A UWB vital signs monitor tracks cardiac and respiratory motions remotely, without direct skin contact. UWB radar arrays can image the human body. This paper will explore key tradeoffs in the design of ultra-wideband systems for medical applications and provide several examples of research in this area.
ULTRA WIDE BAND
Unlike narrowband systems, which transmit continuous waveforms at a specific frequency, ultra-wideband systems transmit narrow impulse-like signals that span a broad frequency range [Figure 2.1]. The pulse width of a UWB system is typically within a range of 100’s of picoseconds to several nanoseconds, with rise times as fast as 50 picoseconds, corresponding to a frequency range that can span several gigahertz. Since the energy of the pulse is distributed across a many frequencies, the power spectral density is much lower in magnitude than a narrowband system. To a narrowband system, ultra-wideband signals appear below the noise floor, and are therefore very difficult to detect.UWB signals can be used in many applications, including imaging, vehicular radar, and communications. Examples of imaging applications are ground penetrating radar, through-wall imaging to detect the location or movements of objects, surveillance, search and rescue, and medical systems. Vehicular radar systems are commonly used for collision avoidance and roadside assistance. Ultra-wideband communication systems are useful for high data rate transmission in harsh propagation environments, such as indoor applications with dense multi-path channels, for consumer electronics, and for covert operations. The FCC defines ultra-wideband signals to be those with fractional bandwidth exceeding 20% of the center frequency, or those with greater than 500 MHz bandwidth1. Although development of ultra-wideband technologies began in 1960’s the technology is far from mature. Widespread commercial use has been limited, largely as a result of FCC restrictions. Due to concerns of interference with existing communication and navigation systems, the FCC limits UWB frequency bands and output power. Medical applications are limited to the 3.1 to 10.6 GHz range1. Through wall imaging applications may operate below 960 MHz, or in the 1.99 to 10.6 GHz range. Commercial devices are currently limited in power.
INNER WORKINGS
UWB uses a kind of pulse modulation. To transfer data, a UWB transmitter emits a single sine wave pulse (called a monocycle) at a time. This monocycle has no data in it. On the contrary, it is the timing between monocycles (the interval between pulses) that determines whether data transmitted is a 0 or a 1. A UWB pulse typically ranges between .2 and 1.5 nanoseconds. If a monocycle is sent early (by 100 pico seconds), it can denote a 0, while a monocycle sent late (by 100 pico seconds) can represent a 1.
Spacing between monocycles changes between 25 to 1000 nanoseconds on a pulse-to-pulse basis, based on a channel code. A channel code allows data to be detected only by the intended receiver. Since pulses are spaced and timing between pulses depends on the channel, it’s already in encrypted form and is more secure than conventional radio waves.
Modulation Methods
Several modulation techniques can be used to create UWB signals, some more efficiently than others. In its formative years, some of the most popular methods to create UWB pulse streams used mono-phase techniques such as pulse amplitude (PAM), pulse position (PPM), or on-off keying (OOK). In these techniques, a ‘1’ is differentiated from a ‘0’ either by the size of the signal or when it arrives in time – but all the pulses are the same shapes. A more efficient approach, bi-phase ultra-wideband, is also being deployed. Bi-phase differentiates a ‘1’ with a ‘right-side-up’ pulse and a ‘0’ with an ‘upside-down’ pulse and works by reading pulses both “backwards” and “forwards,” irrespective of time. Multi-phase UWB is not being deployed today as it is too cost-prohibitive for the consumer and enterprise markets.
SENSING WITH ULTRA-WIDEBAND
A family of ultra-wideband sensors known as micro-power impulse radar (MIR) was developed at Lawrence Livermore National Laboratory. MIR sensors emit extremely narrow electromagnetic pulses and analyze received reflection signals for characteristic indicators of material boundaries and movements. MIR sensors are safe for medical use, since UWB signals are non-ionizing and emitted power is very low. In a typical MIR sensor used for medical applications, peak transmit power is 60 milliwatts and average transmit power is 25 microwatts. The basic components of an MIR radar system include a transmitter, a reflective target, a receiver, and a signal processor [Figure 2]. The transmitter generates a series of short pulses. The shape of transmitted pulses is determined largely by the characteristics of the antenna. At dielectric interfaces, portions of the transmitted pulse reflect back toward the antenna. The receiver uses a range gate to sample the echo signals during a specific time interval corresponding to the round trip time of flight from the transmitter to the target, and back to the receiver9. A sensor with a fixed range gate can only detect echo signals from a single radial distance. By sweeping the range gate across a time span, or equivalent time sampling, targets can be detected within a specified distance range. Multiple pulses are integrated to achieve a sufficient signal-to-noise ratio. Signal processing of the received pulse echoes may be performed in analog circuitry, using an FPGA, or using software algorithms running on a computer.
Distance Measurement
One application of UWB radar is to measure the distance between the radar source and a reflective target. Ranging applications are based on measuring the round trip time of flight of a transmitted pulse. For example, if the time between sending a pulse and receiving its backscatter echo is 20 ns, we can infer that the signal was reflected at the target after 10 ns. If the target is in air, we can assume that the pulse velocity, v, is 3.0 x 108 m/s, the speed of light. Using the simple relationship, d =vt, we find the reflecting target was positioned 3 meters away from the radar. By sweeping the range gate across a time span of 15 ns to 25 ns, we can detect reflected pulses from targets within a distance range of 4.5 to 7.5 meters. Distance measurements become challenging when the nature of target mediums is unknown. Since propagation velocity is material dependent, assumptions are made about the electromagnetic properties and thickness of target materials. For example, at 2 GHz, the relative permittivity, εr, of muscle and fat are 5.5 and 4.5, respectively13.
UWB IN MEDICINE
UWB features for medical application
UWB pulse is generated in a very short time period (sub-nano second).So it has spectrum below the allowed noise level. This feature makes it possible to get Gbps speed by using 10GHZ spectrum. So UWB is suitable to be used for high-speed over short distances. Such “noise-like” feature relies on ultra-short waveforms and does not require IF processing because they can be operated at baseband. This UWB feature has long been appreciated as key advantages for medical engineering.
Penetrating through obstacles
In discussing this capability, we could compare UWB with ultrasound. Although UWB and ultrasound are in fact very similar and many of the signal processing techniques used in ultrasonic systems can be applied to UWB systems, it is different from ultrasound which has broad application in today’s world. The major difference is that ultrasound is basically a line of sight technology and it is very short range.
However, UWB is different because it does not use high frequency and has high gain, which means that UWB impulse of very bit is so many that it can get much higher gain than other popular conventional spread spectrum systems. That also explains why UWB can penetrate through walls. This makes UWB viable for wide area applications where obstacles are certain to be encountered, although ultrasound may also be in operable in these circumstances. The feature makes it easy to image organs of human body for medical application.
High precision ranging at the centimeter level
Another feature of UWB is the high precision ranging at centimeter level based on the ultra-short pulse characteristic. High precision of ranging also means strong multi-path resolving capability. The conventional wireless technique used continuous wave and the standing time is much longer than multi-path transmission time. The UWB pulse is much shorter, thus it has very strong temporal and space resolving capability (For 1 nano second pulse, the multi-path resolving power equals to 30cm), which is suitable for the localization and detection in the medical applications.
[attachment=33974]
ABSTRACT
The wonders of science and technology in the medical field paved a way for the diagnosis of diseases. Diagnosis is possible only by continuous monitoring of human body.CT scan ,X ray etc are some of the ways. Eventhough they are helpful for complete diagnosis of human body ,these are having heavy electromagnetic radiations .Continuous use of this will lead to othert problems in human body .So UWB radar having less electromagnetic radiation could be used in medical field .My paper is a detailed study of UWB radar in medical field
Ultra-wideband radar holds great promise for a variety of medical applications. Ultra-wideband sensors can be used for detection of internal injuries, monitoring of respiratory and cardiac functions, and continuous non-contact imaging of the human body. Sensors are low-power, portable, and do not require physical contact with the patient. In the hospital, vital signs monitoring and imaging application could improve patient outcomes.
INTRODUCTION
Motion sensing and imaging ultra-wideband (UWB) radar systems have strong potential for use in the medical field. UWB radar is non-invasive, low power, and can be manufactured in a small, portable form factor. We have demonstrated the use of UWB radar in a variety of medical applications. A handheld UWB sensor has demonstrated the feasibility of detecting the presence of traumatic internal injuries including intracranial hematoma and pneumothorax. A UWB vital signs monitor tracks cardiac and respiratory motions remotely, without direct skin contact. UWB radar arrays can image the human body. This paper will explore key tradeoffs in the design of ultra-wideband systems for medical applications and provide several examples of research in this area.
ULTRA WIDE BAND
Unlike narrowband systems, which transmit continuous waveforms at a specific frequency, ultra-wideband systems transmit narrow impulse-like signals that span a broad frequency range [Figure 2.1]. The pulse width of a UWB system is typically within a range of 100’s of picoseconds to several nanoseconds, with rise times as fast as 50 picoseconds, corresponding to a frequency range that can span several gigahertz. Since the energy of the pulse is distributed across a many frequencies, the power spectral density is much lower in magnitude than a narrowband system. To a narrowband system, ultra-wideband signals appear below the noise floor, and are therefore very difficult to detect.UWB signals can be used in many applications, including imaging, vehicular radar, and communications. Examples of imaging applications are ground penetrating radar, through-wall imaging to detect the location or movements of objects, surveillance, search and rescue, and medical systems. Vehicular radar systems are commonly used for collision avoidance and roadside assistance. Ultra-wideband communication systems are useful for high data rate transmission in harsh propagation environments, such as indoor applications with dense multi-path channels, for consumer electronics, and for covert operations. The FCC defines ultra-wideband signals to be those with fractional bandwidth exceeding 20% of the center frequency, or those with greater than 500 MHz bandwidth1. Although development of ultra-wideband technologies began in 1960’s the technology is far from mature. Widespread commercial use has been limited, largely as a result of FCC restrictions. Due to concerns of interference with existing communication and navigation systems, the FCC limits UWB frequency bands and output power. Medical applications are limited to the 3.1 to 10.6 GHz range1. Through wall imaging applications may operate below 960 MHz, or in the 1.99 to 10.6 GHz range. Commercial devices are currently limited in power.
INNER WORKINGS
UWB uses a kind of pulse modulation. To transfer data, a UWB transmitter emits a single sine wave pulse (called a monocycle) at a time. This monocycle has no data in it. On the contrary, it is the timing between monocycles (the interval between pulses) that determines whether data transmitted is a 0 or a 1. A UWB pulse typically ranges between .2 and 1.5 nanoseconds. If a monocycle is sent early (by 100 pico seconds), it can denote a 0, while a monocycle sent late (by 100 pico seconds) can represent a 1.
Spacing between monocycles changes between 25 to 1000 nanoseconds on a pulse-to-pulse basis, based on a channel code. A channel code allows data to be detected only by the intended receiver. Since pulses are spaced and timing between pulses depends on the channel, it’s already in encrypted form and is more secure than conventional radio waves.
Modulation Methods
Several modulation techniques can be used to create UWB signals, some more efficiently than others. In its formative years, some of the most popular methods to create UWB pulse streams used mono-phase techniques such as pulse amplitude (PAM), pulse position (PPM), or on-off keying (OOK). In these techniques, a ‘1’ is differentiated from a ‘0’ either by the size of the signal or when it arrives in time – but all the pulses are the same shapes. A more efficient approach, bi-phase ultra-wideband, is also being deployed. Bi-phase differentiates a ‘1’ with a ‘right-side-up’ pulse and a ‘0’ with an ‘upside-down’ pulse and works by reading pulses both “backwards” and “forwards,” irrespective of time. Multi-phase UWB is not being deployed today as it is too cost-prohibitive for the consumer and enterprise markets.
SENSING WITH ULTRA-WIDEBAND
A family of ultra-wideband sensors known as micro-power impulse radar (MIR) was developed at Lawrence Livermore National Laboratory. MIR sensors emit extremely narrow electromagnetic pulses and analyze received reflection signals for characteristic indicators of material boundaries and movements. MIR sensors are safe for medical use, since UWB signals are non-ionizing and emitted power is very low. In a typical MIR sensor used for medical applications, peak transmit power is 60 milliwatts and average transmit power is 25 microwatts. The basic components of an MIR radar system include a transmitter, a reflective target, a receiver, and a signal processor [Figure 2]. The transmitter generates a series of short pulses. The shape of transmitted pulses is determined largely by the characteristics of the antenna. At dielectric interfaces, portions of the transmitted pulse reflect back toward the antenna. The receiver uses a range gate to sample the echo signals during a specific time interval corresponding to the round trip time of flight from the transmitter to the target, and back to the receiver9. A sensor with a fixed range gate can only detect echo signals from a single radial distance. By sweeping the range gate across a time span, or equivalent time sampling, targets can be detected within a specified distance range. Multiple pulses are integrated to achieve a sufficient signal-to-noise ratio. Signal processing of the received pulse echoes may be performed in analog circuitry, using an FPGA, or using software algorithms running on a computer.
Distance Measurement
One application of UWB radar is to measure the distance between the radar source and a reflective target. Ranging applications are based on measuring the round trip time of flight of a transmitted pulse. For example, if the time between sending a pulse and receiving its backscatter echo is 20 ns, we can infer that the signal was reflected at the target after 10 ns. If the target is in air, we can assume that the pulse velocity, v, is 3.0 x 108 m/s, the speed of light. Using the simple relationship, d =vt, we find the reflecting target was positioned 3 meters away from the radar. By sweeping the range gate across a time span of 15 ns to 25 ns, we can detect reflected pulses from targets within a distance range of 4.5 to 7.5 meters. Distance measurements become challenging when the nature of target mediums is unknown. Since propagation velocity is material dependent, assumptions are made about the electromagnetic properties and thickness of target materials. For example, at 2 GHz, the relative permittivity, εr, of muscle and fat are 5.5 and 4.5, respectively13.
UWB IN MEDICINE
UWB features for medical application
UWB pulse is generated in a very short time period (sub-nano second).So it has spectrum below the allowed noise level. This feature makes it possible to get Gbps speed by using 10GHZ spectrum. So UWB is suitable to be used for high-speed over short distances. Such “noise-like” feature relies on ultra-short waveforms and does not require IF processing because they can be operated at baseband. This UWB feature has long been appreciated as key advantages for medical engineering.
Penetrating through obstacles
In discussing this capability, we could compare UWB with ultrasound. Although UWB and ultrasound are in fact very similar and many of the signal processing techniques used in ultrasonic systems can be applied to UWB systems, it is different from ultrasound which has broad application in today’s world. The major difference is that ultrasound is basically a line of sight technology and it is very short range.
However, UWB is different because it does not use high frequency and has high gain, which means that UWB impulse of very bit is so many that it can get much higher gain than other popular conventional spread spectrum systems. That also explains why UWB can penetrate through walls. This makes UWB viable for wide area applications where obstacles are certain to be encountered, although ultrasound may also be in operable in these circumstances. The feature makes it easy to image organs of human body for medical application.
High precision ranging at the centimeter level
Another feature of UWB is the high precision ranging at centimeter level based on the ultra-short pulse characteristic. High precision of ranging also means strong multi-path resolving capability. The conventional wireless technique used continuous wave and the standing time is much longer than multi-path transmission time. The UWB pulse is much shorter, thus it has very strong temporal and space resolving capability (For 1 nano second pulse, the multi-path resolving power equals to 30cm), which is suitable for the localization and detection in the medical applications.