The Army Research Laboratory (ARL) has developed a new method of measuring human physiological stress parameters. This consists of an acoustic sensor positioned inside a fluid-filled bladder in contact with the body. Packaging the sensor in this manner minimizes outside environmental interferences, and signals within the body are transmitted to the bladder with minimal losses. This fluid-coupling technology comfortably conforms to the human body, and enhances the signal-to-noise ratio (SNR) of human physiology to that of ambient noise. An acoustic sensor system can detect changes in a person's physiological status resulting from exertion or injuries such as trauma, penetrating wound, hypothermia, dehydration, heat stress and many other conditions or illnesses. A sensor contacting the torso, head, or throat region picks up the wearer's voice very well through the flesh, with fidelity sufficient to be used as a hands-free voice activation mechanism. Several different sensor configurations developed for evaluation include torso mount, neck attachment, and standard PASGT helmet headband mount.
Potential technology transfer applications in the civilian realm include clinical surveillance in convalescent and Veterans' Administration residences, medical transports, hospitals, and telemedicine. Fire, rescue, and police personnel may benefit from hands-free voice communications with embedded health and performance monitoring. Drivers of vehicles and aircraft could also be monitored.
The data in Figure 1 includes a spoken count from one to ten, and then mouth breathing for the remainder of the data set. Naturally, the heartbeat is present in the low-frequency region. Note, in both the time-waveform and the spectrogram of this figure, the high SNR of voice compared to the "physiological ambient noise" that includes heartbeats and breaths. This, combined with the sensor's inherent noise immunity, could make this sensor location ideal for monitoring voice for voice-stress analysis and communications, in addition to physiology.
The detection of physiology and voice is very important for medical evaluation during evacuation, vehicle/aircraft operator monitoring, or voice commands in a high-noise environment, such as a tactical operations center with multiple speakers. The ability of body-coupled sensors to detect physiology and reduce background noise was investigated, with preliminary results as seen here. An acoustic sensor embedded within aqueous-couplant gel was attached to one side of a speaker's neck. Positioned in front of the person's mouth was a boom-microphone configuration. Figures 2 and 3 show simultaneously collected breath and voice data before, during, and after a speaking subject is submerged in a C-weighted noise field of 105 dB (referenced to 20 micropascals, measured in front of the throat) inside an acoustic anechoic chamber (hearing protection was required). The person wearing the sensors repeatedly vocalized a one-to-ten count between the times of 14 and 19 seconds, 25 and 33 sec, 65 and 71 sec, and 71 and 77 sec, and vocalized "105 dB" between 47 and 50 sec.
The boom-microphone in Figure 2 did not detect any voice during the high-amplitude noise between 20 and 71 sec. In Figure 3, however, the counting is clearly visible throughout the loud noise with the body-coupled gel sensor. Playing the data collect through headsets, the listener could clearly hear and understand the spoken words from the gel sensor, but not the boom-microphone.
Acoustic sensors provide a low-cost, lightweight, noninvasive, and adaptable means to monitor many aspects of a soldier's health and activity. Unlike most medical sensor technologies that look at only one physiological variable, a single acoustic sensor can collect information related to the function of the heart, lungs, and digestive tract, or it can detect changes in voice or sleep patterns, other activities, and mobility. Software algorithms that evaluate data from acoustic sensors can be continuously modified to monitor new parameters, to monitor the correlation between different body functions, or even to understand the interrelations between the soldier's physiology, the task at hand, and the surrounding environment.