AU733997B3 - Apparatus to extend the range of human hearing to include the infrasonic and ultrasonic frequency domains - Google Patents

Description

Page 1 of 11

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION PETTY PATENT APPARATUS TO EXTEND THE RANGE OF HUMAN HEARING TO INCLUDE THE INFRASONIC AND ULTRASONIC FREQUENCY DOMAINS.

The following statement is a full description of this invention, including the best method of performing it known to me.

Page 2 of 11 APPARATUS TO EXTEND THE RANGE OF HUMAN HEARING TO INCLUDE THE INFRASONIC AND ULTRASONIC FREQUENCY DOMAINS The apparatus is an electronic apparatus which extends the range of human hearing to include both the infrasonic and ultrasonic frequency domains in both air and water, substantially as herein described with reference to accompanying drawings, Figs. 1, 2, 3, &4.

The apparatus provides visual indications of firstly the presence; relative amplitude, and fundamental frequency of infrasonic fluid pressure waves, and secondly the presence and relative amplitude of ultrasonic fluid pressure waves; also auditory indications of the presence and fundamental frequency of both infrasonic and ultrasonic fluid pressure waves, and lastly a visual indication of the fundamental frequency of ultrasonic fluid pressure waves when an optional frequency meter is incorporated into said apparatus or connected to it.

The apparatus employs a piezoelectric transducer to convert infrasonic fluid pressure waves, via a high impedance FET input circuit, into electrical signals which are frequency filtered; amplified; digitised; frequency multiplied and transformed into audible sine wave and visual outputs. Ultrasonic fluid pressure waves are converted into electrical signals through a piezoelectric or electrostatic transducer; frequency filtered; amplified; digitised; frequency divided and transformed into audible and visual outputs.

Provision is made for an external hydrophone connection, and for an internal or external frequency meter. A hydrophone is simply connected instead of the piezoelectric or electrostatic transducers described and indicated as T1 on Fig.2 and T2 on Fig.3: the connection points are shown as a small circled on both figures. A frequency meter is connected in accordance with established electronics practice.

Description of infrasonic part of the apparatus.

Note:- all numbered references are to Fig.1 unless otherwise noted.

A readily available miniature piezo-electric speaker 1) on Fig.l'. designed to produce audible sound waves in car alarms, greetings cards et cetera, is used as a transducer to produce an electrical signal from infrasonic air pressure waves, i.e. in reverse of its designed function and well outside the designed frequency range.

Said piezo-electric speaker is connected to a high impedance input circuit 2) employing field-effect transistor (FET) input operational amplifiers. Said high impedance circuit critically enables the efficient transduction of infrasound into an electrical signal through said transducer by NOT placing a significant resistive load on said transducer, thus preserving its low-frequency response.

Said high impedance circuit produces a maximum signal to noise ratio by an instrumentation or differential amplifier circuit topology inherent to which is a high common-mode rejection ratio (CMRR). Initial resistance/capacitance (RC) frequency Page 3 of ll filtering in said circuit also minimises interference from 50 or 60 Hz electromagnetic power grid signals, and from most radio transmissions.

An automatic gain control (AGC) circuit see also Fig. 2 for details, is set up as follows: negative feedback from the output of said amplifier is applied to a lightdependant resistor (LDR) through an operational amplifier or voltage follower and lightemitting diode (LED), the light from said LED falling upon said LDR. Said LDR is connected between the inverting inputs of two input operational amplifiers, and its dynamic resistance determines the amplification or voltage gain of the differential amplifier 2) which includes said two operational amplifiers. Said feedback results in stabilisation of the amplitude of the output of said differential amplifier thus removing the need for a species of volume control or signal attenuator in said high impedance circuit.

Said amplifier 2) is also connected to a limiting amplifier 4) which has a frequency response which includes the low frequencies of interest. Said limiting amplifier ensures sufficient signal to drive a Schmitt trigger Said trigger produces a fixed amplitude square wave signal of fast rise time suitable for digital signal processing, and said trigger is connected in turn to a phase-locked loop (PLL) frequency multiplier Said multiplier multiplies incoming frequencies by a factor of 32 such that a 10 Hz signal becomes a 320 Hz signal.

Note:- other multiplication factors are also possible.

Said PLL frequency multiplier also acts as a sharp (theoretically infinite) cutoffbandpass signal frequency filter because a voltage-controlled oscillator (VCO) which is an integral part of said multiplier has limits to its frequencies of oscillation set by the value of two resistors labelled R3 and R4 respectively in Fig. 4.

A VCO frequency from 64 to 704 Hz automatically limits the signal frequency band to 2 to 22 Hz when the PLL multiplication factor is 32.

Notes:the VCO mentioned above oscillates at its minimum set frequency (64 Hz in this case) in the absence of an incoming signal, which could confuse the user of the device described herein. A subsidiary onetransistor circuit provides an indication of a valid signal via a small LED indicator which lights when the PLL is 'locked' on to a valid incoming signal. Another subsidiary circuit switches signals to both the visual display 9) and output amplifier 8) 'on' or 'off' as appropriate, such that there are no invalid or random outputs. These subsidiary circuits are not shown in Figs. 1 to 4 inclusive.

(ii) in a simpler manifestation of the apparatus the infrasonic PLL frequency multiplier and subsequent circuitry can be replaced by a readily available integrated miniature piezo buzzer which is simply turned on and off by the rectified signal from the Schmitt trigger, in time with these infrasonic half-cycles.

Said electrical signals are now of square and triangular wave form, irrespective of the form of the original infrasonic signal.

Said multiplier is connected to a sinewave shaper 7) in which said triangular wave signals are converted into an approximate sinewave form, closer in form to the original infrasonic signal.

Said shaper is connected (via a subsidiary switching circuit) to an output amplifier 8) which is connected to an internal loudspeaker 17) and/or to headphones 18).

The output of said amplifier 2) is also connected (via a subsidiary switching circuit) to a visual display 9) which includes a LED bargraph display.

Page 4 of 1l Note:- a liquid crystal display (LCD) can be used as an alternative.

Said display provides a visual indication of the presence of an infrasonic signal; of the relative amplitude of said signal, and of the original frequency of said signal by means of real-time fluctuation in light output or light reflection or light transmission.

Description of ultrasonic part of the apparatus.

A readily available piezo-electric transducer 10) used commonly in burglar alarms, in proximity detectors and in electronic tape rules is connected to a low noise differential amplifier 11) via a passive resistance/capacitance (RC) circuit which provides initial band-pass frequency filtering.

Note:- an electret or condenser microphone may be used instead of a piezoelectric transducer. The transducer used needs to be selected for a wide frequency response up to around 180 KHz, and the passive RC circuit mentioned above may need to be modified to suit the frequency response of the particular transducer used.

The automatic gain control (AGC) circuit 12) of this part of the apparatus works much as described for the AGC circuit 3) in the infrasonic part of the apparatus; namely by taking the output signal from the output of the differential amplifier 11) and feeding it back through an AGC amplifier or voltage follower to an LED whose light output falls upon a LDR connected to the amplifier 11). See Fig. 3 for details. The amplification factor or gain of said amplifier is determined by the dynamic resistance value of this LDR because the LDR is connected between two gain-determining terminals specified by the manufacturer of said amplifier.

The effect of this negative feedback is to stabilise the amplitude of the signal from the output of the amplifier 11).

The maximum frequency response of said AGC amplifier or voltage follower is designed to be less than the lowest signal frequency of interest in order to assure a smooth or delayed adjustment of the differential amplifier's gain.

The amplifier 11) is connected to a limiting amplifier 13) which ensures sufficient signal to operate a Schmitt trigger 14). Said trigger is connected to a PLL bandpass filter (BPF) labelled IC5 in Fig.3, whose frequency band or range is preset by resistors R1 and R2 in Fig.3.

Notes:- (i)using a PLL in this way provides a more precise and sharper signal frequency cutoff than is obtained by analogue active frequency filtering; it also provides for economy in component parts.

(ii)subsidiary circuits provide appropriate switching and valid signal indication as previously described for the infrasonic part of the apparatus.

Said BPF 15) is connected to a digital frequency divider 16) which divides the digital signal by a factor of 16, such that an inaudible 160 KHz signal becomes an audible KHz signal when it is amplified in the output amplifier 8) and fed into a loudspeaker 17) or into headphones 18).

Note:- other division factors are also possible in this part of the circuit.

The amplifier 11) is also connected to a visual display 9) (via a subsidiary switching circuit), so that a visual indication of the presence and relative amplitude of an ultrasonic signal is provided.

Page 5 of 11 Notes:it is not possible to sensibly display an ultrasonic frequency per se given the limited (audio) frequency response of the display circuit and the limited 'flicker' response of human vision.

(ii) the original 'sense' or frequency spectrum rising or falling frequency; relatively low or relatively high frequency) is preserved with these digital methods of signal conversion. Those 'bat detectors' or 'gas leak detectors', including the apparatus disclosed in US Patent 4,629,834, which use the frequency heterodyne method of signal conversion invert the 'sense' as mentioned above, leading to some difficulty in interpretation of the original signal or utterance.

(iii) the human ear is less able to discriminate actual waveform with higher audible frequencies, so that waveform conversion of the digital squarewave obtained from the (ultrasonic) frequency divider 16) is less important than it is with the digital squarewave normally obtained from the (infrasonic) PLL frequency multiplier 6) previously described herein.

(iv) the apparatus can be used to detect ultrasonic or infrasonic utterances of animals or plants but is designed for more general usage.

a digital or analogue frequency meter may be incorporated into the apparatus if an accurate frequency readout is required, or a signal output connection may be provided for an external frequency meter.

(vi) subsidiary switching circuits detect and switch incoming infrasonic or ultrasonic signals as appropriate so that visual and audible outputs are differentiated and valid.

Discussion of utility and novelty of apparatus.

Sound wave frequencies audible to humans are defined as extending from 20 Hz to KHz inclusive.

Note that 1Hertz (Hz) 1 Cycle per second 1KHz 1,000 Hz.

Infrasound is generally and here defined as including those frequencies below 20 Hz, extending down to decimals of 1 Hz.

Ultrasound is generally defined as including those frequencies above 20 KHz.

Both infrasound and ultrasound are therefore inaudible to humans, and thus generally undetectable without instrumentation.

Infrasound is generated inter alia by large animals such as whales and elephants, also by human activity. Associated with human activity are particular health and safety issues, e.g. the 'sick building' phenomenon. This phenomenon has been associated with electromagnetic radiation and inadequate air conditioning, but is also associated with infrasound and resonant effects of such infrasound.

Short exposure to infrasound at high amplitude and particular frequency has reportedly been shown to be lethal to humans in experiments conducted by the French (and probably US) armies, Refer "The Sonic Weapon of Vladimir Gavreau" by Gerry Vassilatos on the internet. In circa 1996 a patent for an 'infrasonic weapon' was granted to a Hungarian inventor.

This begs the question of the exact significance of longer-term exposure to lower amplitude infrasound in the environment. There is some knowledge in medical or industrial circles of adverse health effects from longer term exposure to sub-lethal amplitudes ofjnfrasound, e.g. lesions to bones and joints; cardiovascular disturbances; Page 6 of 11 digestive tract disturbances -mentioned in the 'Vibrostop' internet website, copyright 1997.

Personal experience with the grain handling industry in Australia has shown that very high levels of infrasound are generated by certain conveying equipment in normal usage: possible effects of exposure to such energy appear not to be appreciated, and have not to my knowledge been discussed in industry meetings. (What you can't hear can't hurt you??).

It is highly likely that there are many sources of high amplitude infrasound in heavy industry and to a lesser extent in the transport industry, including air transport. It is reported that air defence forces restrict the flying time of fighter jet pilots due to the adverse health effects ofinfrasound generated by jet aircraft or their engines. It is now clear that 'Economy Passenger/DVT Syndrome' is most likely due to exposure to infrasound generated by jet engines, and amplified in the resonant cavity of the fuselage.

There is now increasing use of infrasound, generated pneumatically (somewhat as in 'The Sonic Weapon of Vladimir Gavreau'!) to clean bulk handling and storage facilities.

Neither Civilian Regulatory Agencies nor Trade Unions including the International Labour Organisation appear to be sufficiently aware of the probable, or even inevitable, health risks associated with exposure to infrasound. This is indicated by the apparent relative absence of national or international Standards covering infrasound compared with Standards covering sound and exposure to sound. For example, an internet search of the USA and Australian Standards websites on 9 August 2000 revealed only one Standard for infrasound, this being a frequency weighting scale for same. By contrast there are many Standards for sound pressure meters; recommended maximum human exposure to noise; specifications for the acoustics of buildings, et cetera.

Existing international Standards specify the weighted curve for measurement of noise levels, this curve being based on the normal frequency response of the human ear. This curve extends from 20 Hz to 20,000 Hz so it excludes infrasound and ultrasound by definition.

There appears to have been extensive research into infrasound in the Eastern bloc since the Space Race, and Standards for occupational exposure to infrasound have now been published in certain of these countries.

There are no international specifications or Standards for infrasound detectors or meters except in the notable case of government systems set up to monitor nuclear explosions under the auspices of the Comprehensive Nuclear Test Ban Treaty -refer www.ctbt.rd.doe.gov/ctbt/introduction/infrasound fact sheet.html09/08/00.

See also information on the ANU Warramunga Seismic and Infrasound Array Station on the internet.

The US prototype system has or had a frequency response from 0.02 Hz to 4.0 Hz and has or had 'microbarograph' sensors spaced 1 km apart.

Page 7 of 11 Low frequency (infrasonic) signalling by submarines using hydrophones is another case in which there are presumably some standards: at least one patent for a high-power transmitting hydrophone has been published.

Universities are currently researching infrasound in the fields of geology or meteorology Refer http//geology.heroy.smu.edu/-hayward/Projects/Infrasonics/assets/sow.html09/08/00.

Candidate infrasonic sensors mentioned in this published Statement appear to be both specialised and expensive.

There is a reference in an article "Infrasound Monitoring with a Microbarograph" published in the Bell Jar 5, No 4, viz.:- "Professional instruments with price tags in the multikilobuck range." The author chose to use a transducer which cost about US$450, with a frequency response (only) to 10 Hz. Refer www.tiac.net/users/shansen/belljar/microbar.htm05/08/00.

At least one Italian university is researching bioacoustics -refer www.univp.it/cibra/instru.html09/08/00.

I quote "The tasks of bioacoustics....call for specialised sets of instruments which are not commonly available on the market." In this html paper only hydrophones are mentioned as having a low frequency response.

Infrasound is of course generated by geological and meteorological phenomena, and may also be generated by other bodies in the solar system or beyond via electromagnetic or gravitational effects.

It is likely that infrasound is conducted; amplified; focussed or attenuated by architectural and topographic features including underwater topographic features, and such effects may be of biological importance, e.g. migration routes of whales. This could be a fruitful area of scientific research, including archaeological research. Such research depends importantly on the ready availability of suitable (inexpensive) detection equipment.

Some well-known winds such as the Mistral in southern France probably generate infrasound and it may be this form of energy which contributes to negative health effects in susceptible individuals, not merely an excess of positive ions.

There are groups of individuals around the world known as 'Hummers' who are concerned with mysterious low frequency hums or noises found in different parts of the world, e.g. the Taos hum; the Bristol hum. Refer www.borderlands.com/iournal/nux.htm05/08/00.

Such people have set up Societies the 'Low Frequency Noise Sufferers Association' in Britain -to investigate and discuss these phenomena on the internet and elsewhere, and they would presumably be particularly interested in portable low-cost detection equipment for infrasound. A design published by one such interested party uses a inch diameter loudspeaker in a wooden cabinet as a transducer for a practical instrument, but this design is (inevitably) sensitive to electromagnetic radiation from the electric power grid, given that a loudspeaker is an electromagnetic transducer and that a relatively long connecting cable is necessary. Refer www.eskimo.com/-billb/hum/lennart2.gif28/07/00.

RA

Page 8 of 11 There appears to be an absence of published designs using a simple and inexpensive piezo-electric transducer as used in greetings cards to convert infrasonic fluid pressure waves into an electrical signal. Industrial or scientific apparatus uses exceedingly expensive purpose-built condenser microphones for this same purpose.

The only related design found is that by B.Kainka: a one-transistor circuit not a FET) published in Elektor Electronics, July/August 2000, p.20, which uses a simple piezo speaker to pick up the human heartbeat, in which said speaker is apparently placed on the skin, thus transducing a pressure wave in or from a solid.

Devices to detect infrasonic fluid pressure waves mentioned in this Discussion, are neither portable nor utilitarian.

Ultrasound is generated inter alia by animals such as bats, moths and cave-dwelling birds; by green plants; by domestic refrigerators which employ an expansion valve, and by electronic equipment such as televisions and other video monitors employing a cathode ray tube with wire-wound scanning coils. These produce signals at 15.125 KHz upwards, with inevitable harmonics at higher frequencies generated by the saw-tooth 'flyback' waveform employed.

There has been a recent trend to rodent and insect pest control equipment employing ultrasound, also to electronic controllers (transmitters/receivers) operating at up to 200 KHz, of unknown significance for human health. It may be noted that laboratory strains of rodents (Rattus norvegicus) are widely used as experimental animals in biology and in medical science, and results thus obtained are used as indicators, or are simply extrapolated, for a wide range of human responses. One wonders at the assumption that there is or will be no effect on humans of unwitting exposure to ultrasound from such equipment.

Another case of "What you can't hear can't hurt you.", and perhaps added reason to make a suitable detector more generally available.

Both ultrasound and infrasound found in the environment are likely to be more widespread and significant than is presently generally recognised, in the current absence of generally available sensitive detection equipment. Both ultrasound and infrasound are likely to be stressors in many cases, and are perhaps a causative factor in some diseases of obscure aetiology.

The apparatus described in this application enables formal and informal surveys, by both laypersons and scientists, of most environments for inaudible sound waves of likely biological and in particular likely human health significance.

The employment of readily available and relatively inexpensive electronic components enables the production of a relatively simple apparatus which is intended to be easily affordable and hence available to many people, and maximises its utility.

The apparatus is designed as a portable or hand-held battery-powered instrument, of the same order of size as an electronic multimeter.

Page 9 of 11 A portable combined infrasonic and ultrasonic detector with both auditory and visual outputs and with more or less complete coverage of those frequency domains, namely down to approximately 2 Hz and up to approximately 180 KHz, appears to be a novel concept.

The apparatus disclosed in US Patent 4,629,834 (apparently now expired) has coverage only tip to 30 KHz, and was apparently intended for enhanced auditory surveillance by police and military forces. This US -designed apparatus specified conventional electret microphones mounted in a parabolic reflector.

The combination of an inexpensive piezo transducer and a field-effect transistor (FET) op-amp input circuit to enable the detection ofinfrasound in the present apparatus may be considered to be an inventive step, as this combination appears not to have been described for this use before. Such a combination appears to respond to atmospheric pressure fluctuations of less than 1 Hz in frequency.

The use of phase-locked loop (PLL) circuits in this apparatus for firstly low frequency multiplication and secondly precise band-pass filtering of both high and low frequencies may be considered to be an inventive step. These particular PLL circuits are not new, but their application described herein appears to be new, at least for the infrasonic part of the apparatus.

Similarly the application of a sine-wave shaping cicuit to this apparatus appears to be new; and this apparatus appears to be a new application for a LED/LDR coupled AGC circuit.

Acknowledgments References Alexander Graham Bell -for inspiration.

(ii) Jan Cook Monica Hamers -for receiving and passing on the messages.

(iii) B.Kainka (2000) "Electronic Stethoscope", Elektor Electronics July/August, p.

2 0 (iv) Ian Hegglun (1991) "Sine Waves from a 4046 VCO", Electronics World+Wireless World, September, p.

75 5 Don Lancaster (1977) "CMOS Cookbook", Howard W. Sams Co Inc.

(vi) Don Lancaster (1996) "Active Filter Cookbook", 2 nd Edition, Newnes.

(vii) Bryan Maher (1999) "Op Amps Explained", 2 nd Edition, Electronics Australia/Federal Publications Company.

(viii) US Patent 4,629,834 of Dec. 16, 1986.

Claims (2)

1. An electronic apparatus which extends the range of human hearing to include both the infrasonic and ultrasonic frequency domains in both air and water, substantially as herein described with reference to accompanying drawings.

2. The apparatus of claim 1 in which there are visual indications of firstly the presence; relative amplitude, and fundamental frequency of infrasonic fluid pressure waves, and secondly the presence and relative amplitude of ultrasonic fluid pressure waves; also in which there are auditory indications of the presence and fundamental frequency of both infrasonic and ultrasonic fluid pressure waves, and lastly in which there is a visual indication of the fundamental frequency of ultrasonic fluid pressure waves when an optional frequency meter is incorporated into said apparatus or connected to it.